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The Complete Book on Rubber Processing and Compounding Technology (with Machinery Details) 2nd Revised Edition ( ) ( Best Seller ) ( ) ( ) ( )
Author NIIR Board of Consultants and Engineers ISBN 9788178331621
Code ENI174 Format Paperback
Price: Rs 1875   1875 US$ 150   150
Pages: 680 Published 2016
Publisher Select
Usually Ships within 5 Days

The production of rubber and rubber products is a large and diverse industry. The rubber product manufacturing industry is basically divided into two major sectors: tyre and non-tyre. The tyre sector produces all types of automotive and nonautomotive tyres whereas the non-tyre sector produces high technology and sophisticated products like conveyor belts , rubber seals etc. The wide range of rubber products manufactured by the rubber industry comprises all types of heavy duty earth moving tyres, auto tyres, tubes, automobile parts, footwear, beltings etc.

 

The rubber industry has been growing tremendously over the years. The future of the rubber industry is tied to the global economy. Rapidly growing automotive sector in developing economies and increased demand for high-performance tyres are expected to contribute to the growth of the global industrial rubber market. The current scenario reveals that there is a tremendous scope for the development of rubber processing industries. The global market for industrial rubber products is projected to increase 5.8 % per year. Investment in rubber industry is expected to offer significant opportunities in the near future and realizing returns to investors willing to explore this sector.

 

This book deals with all aspects of rubber processing; mixing, milling, extrusion and molding, reclaiming and manufacturing process of rubber products. The major contents of the book are rubbers materials and processing, mixing technology of rubber, techniques of vulcanization, rubber vulcanization, rubber compounding, rubber reclaiming, manufacture of rubber products, latex and foam rubber, silicone rubber, polybutadiene and polyisoprene, styrene butadiene rubber, rubber natural etc. The book contains addresses of plant & machinery suppliers with their Photographs. 

 

It will be a standard reference book for professionals, entrepreneurs, those studying and researching in this important area and others interested in the field of rubber processing technology. 

1 RUBBERS: MATERIALS AND PROCESSING TECHNOLOGY

Natural Rubber Plantation

Tapping of Rubber Latex

Preservation and Coagulation of Latex

Chemical Nature of Natural Rubber Hydrobcarbon

Hydrogenated Rubber

Cyclized Rubber

Chlorinated Rubber

Rubbers from Stereo-regular Polymerization of Isoprene and Butadiene

Styrene-Butadiene Rubber (SBR)

Polychloroprene Rubber (CR)

Nitrile Rubber (NBR)

Butyl Rubber (IIR)

Ethylene-Propylene-Diene Terpolymer (EPDM)

Polysulphide Rubber (PSR)

Polyacrylic Rubber or Acrylate Rubber (ACR)

Fluorocarbon Rubber (FKM)

Introduction

Mastication and Mixing

Open Mill

Internal Mixers

Reclaimed Rubber

Fillers

Antidegradants

Accelerators

Retarders

Activators

Tyres

Belting and Hoses

Cellular Rubber Products

Miscellaneous Applications of Rubber

Passenger Tyre

Tube Compound for Car tyres

Conveyor Belts

Insulation Compound for Cables

Shoe Soles

2 MIXING TECHNOLOGY OF RUBBER

Two-roll Mills

Internal Batch Mixers

Continuous Mixers

Advantages of continuous mixing

Disadvantages of continuous mixing

Development of the Banbury Mixer

Operating Variables

Ram Pressure

Rotor Speed

Batch Size

Coolant Temperature

Unit Operations in Mixing

Single-Pass Versus Multiple-Pass Mixing

Types of Mix Cycle

Late Oil Addition

Upside-down Mixing

Sandwich Mixes

Analysis of Changes to the Mix Procedure

Acceleration of First-pass Compound

Mill Mixing of Speciality Compounds

Acceleration in Line with Internal Mixing

Testing of Raw Materials

Elastomers as Raw Materials

Fillers

Plasticisers and Process Oils

Small Ingredients

Control of Composition

Tracking the Mix Cycle

Compound Testing

Basic SPC Charting

Rheometer Data and its Meaning

Mixing Control Software

Peptisers in Natural Rubber

Effects of Temperature

Effects of Time

Effects of Use Level

Effects of Other Additives

Peptisers in SBR

Peptisers in Sulphur-containing Polymers

Additives to Increase Viscosity

Preventing Unwanted Chemical Reactions

Filler Treatments

Bin Storage Problems

Inspection of Banbury Mixers

Inspection at the Mezzanine Level

Side Cooling

Rotor Cooling

Rotors and Bearings

Rotor Bearing Lubrication

Dust Stops

Drop Door and Latch

Hydraulic System

Grease System

Dust Stop Lubrication

Drive Gears

Couplings

Inspection of the Banbury Platform

Ram and Cylinder

Heating Weight

Piston Rod

Weight Pin Assembly

Hopper Door

Air Line Filter

Hopper Operation

Mixer Maintenance and Lubrication

Each time the mixer is started

Once per shift

Once per day

Once per week

Once per month

Every six months

Anticipating Required Service

Dust Stop Maintenance

SSA Dust Stops

Assembly

Lapping

Running

Banbury Mixer — Hydraulic Dust Stops

Assembly

Run-in

Lapping

Production

Flushing

EPDM Expansion Joint Cover

Expansion Joint Intermediate Layer

Traffic Counter Treadle Cover

SBR/IR Belt Cover

EPDM Low Voltage Electrical Connector

Peroxide-cured Black-filled EPDM Compounds

EPDM Concrete Pipe Gasket

Injection-moulded NBR Gasket

CR/SBR Blend

Low Durometer CR/SBR Blend

Non-black CR for Injection Moulding

Hard Rubber Industrial Wheel

High Durometer NBR Masterbatch

NBR/PVC Cable Jacket

NBR/PVC/SBR Blend

Butyl Masterbatch

Butyl Masterbatch, Heat Interacted

Chlorobutyl/NR Blend

CSM CORD Jacket

Non-black Millable Urethane

Some Major Changes

Tempered Water

Power-controlled Mixing

Energy Conservation

Composition of EPDM Elastomers

Variables in EPM and EPDM Elastomers

Average Molecular Weight

Molecular Weight Distribution

Ethylene/Propylene Ratio

Type of Diene

Diene Level

How Processing Relates to Structure and Rheology

Practical Guidelines for Mixing EP Elastomers

Using Internal Mixers

Polymer Composition and Form

Filler/Oil Levels and Types

Cure Systems

Processing Aids

Mixing Process

Mixing Instructions

Fill Factor

Mixing Temperature

Machine Parameters

Ram Pressure

Coolant Temperature

Automation

Machine Condition

Downstream Processing Equipment

Using Two-roll Mills

Summary

Rework

Phase Mixing

Natural Rubber Viscosity Reduction

Measurement of Mixing Efficiency

Special Considerations

Raw Materials

Typical Formulations

Internal Mixing

Mill Mixing

Summary

Accounting Methods

Farrel Continuous Mixer

Operating Principles of the FCM

Commercial Applications for the FCM

Farrel Mixing Venting Extruder (MVX)

Designing the Rotor

Analysis of Dispersive Mixing

3 TECHNIQUES OF VULCANIZATION

Pressureless Vulcanization

Rubber Moulding

Factors of Mouding

Mouldin

Compression Moulding

Transfer Moulding

Injection Moulding

Helicure

Buffed Tread Crumb

Incineration and Pyrolysis of Tyres

Reclaimed Rubber

4 RUBBER VULCANIZATION

Physical Property Tests

Free Sulphur Determination

Solvent-swell Method

Mooney-Rivlin Equilibrium Modulus

Differential Scanning Calorimetry

Determination of Spring Constant

Sulphur Vulcanization

Peroxide Crosslinking

Resin Vulcanization

Electron Beam Vulcanization

Nitroso Compounds

Metal Oxides

5 RUBBER COMPOUNDING

General Compounding Principles

Tensile Strength

Tear Resistance

The Crescent Tear Test

The Hardness of Rubber

Set

Abrasion Resistance

Flex Cracking Resistance

Resilience

Heat Build-up

Temperature Resistance

Tyres

Retreading Materials

Conveyor Belting, Transmission Belting and Hose

Footwear

Rubber Roller

Medical Applications

‘O’ rings and Seals

Rubber Blends

Master Batches

Choice of Rubber

Fillers

Vulcanizing Agents

Peptizers

Accelerators

Activators

Anti-oxidants

Retarders

Softeners and Plasticizers

Rubber Crumb

Factice

Processing Aids

Special Purpose Additives

Unvulcanized compound properties

Vulcanized compound properties

6 RUBBER RECLAIMING

7 MANUFACTURE OF RUBBER PRODUCTS

Classification

Components

Tyre Building

Parts of a Conveyor Belt

Cover rubber

Manufacturing Process

Finished belt testing

PVC Belting

Steel Cord Belting

Design of Hoses

Hose Manufacture

Braided/spiralled hoses

Testing of Hose

Constructions

V-Belt Manufacture

Main Types of Power Transmission Belts

Preparation of Ingredients

Stability of Latex Compounds

Manufacture of Latex Products

Foaming and Gelling

Vulcanization

Classification and Terminology

Fabric Lined Water-proof Shoes

Canvas Shoes

Micro-cellular Soling

Manufacturing procedure

Types of Mountings

8 LATEX AND FOAM RUBBER

Selection of Raw Materials

Preparation of Raw Materials

Compounding and Design

Maturation

Processing and shaping

Dipped Goods

Latex Thread

Vulcanisation

Hot Air Cure

Hot Water Vulcanisation

Autoclave Vulcanisation

Radiation Vulcanisation

Ultrasonic Wave Curing

Testing of Rubber Products

Packing and Marketing

Conclusions and Recommendations

 

Manufacture of Latex Foam

Dunlop Process

Mechanism of Gelling

Compounding

Foaming and Gelling

Construction of Moulds

Curing

Washing

Drying

Finishing

Common Defects in Foam Making

Shrinkage

Foam Collapse

Setting

Complete Distortion of the Foam

Protein estimation protocol

Conlusion

9 SILICONE RUBBER

Electronics and Electrical Industries

Silicone Rubbers to Mimic Flesh

Silicone Polymers

Silicone Rubber Elastomers

Reinforcing Fillers

Semireinforcing or Extending Fillers

Additives

Curing Agents

Mixing

Freshening

Moulding

Extrusion

Calendering

Dispersion Coating of Fabric

Heavy-duty Hose

Bonding

Bonding Unvulcanised Silicone Rubber

Bonding Vulcanised Silicone Rubber

Post-baking

Condensation Cure—One-component

Condensation Cure—Two-component

Addition Cure

10 POLYBUTADIENE AND POLYISOPRENE

Polyisoprene

Cyclopolyisoprene

Gel and Branching

Polybutadiene

Isoprene

Butadiene

11 STYRENE BUTADIENE RUBBER (SBR)

Raw Materials

Production of Hydrocarbon Rubber

Manufacture of Emulsion SBR

Vinyl Content and Blockiness

Molecular Weight and Branching

Manufacture of Solution SBR

Property Control

Branching

Blending

Properties

Tg   Measurement

Molecular-weight Measurement

Dynamic Mechanical Measurements

Applications of SBR  

12 RECLAIMED RUBBER

Whole Tyre Reclaim

 

Drab and Coloured Reclaims

Butyl Reclaim

Scrap-rubber Preparation

Reclaimed Rubber

Digester Process

Reclaimator Process

Pan Process

Engelke Process

Testing and Evaluations of Reclaimed Rubber

Millroom Operations

Special Strengths Through Reclaiming

Further Advantages of Reclaiming - Applications

Major Uses of Reclaimed Rubber

Automobile floor mat

Semi-pneumatic tyre

Butyl inner tube

Innerliner

Carcass

Applications

Process

Characterisation of Reclaimed Waste Latex Rubber (WLR)

13 NITRILE AND POLYACRYLIC RUBBER

Uses of Nitrile Rubber

Mixing and Processing

Latest Developments

Composition

Raw Polymer Characteristics

Physical Characteristics

Heat, Fluid, Low-temperature Resistance

Applications

Cure Systems

Reinforcing Agents

Plasticiscrs

Process Aids

Antioxidants

Mixing

Extrusion/Calendering

Compound Storage Stability

Vulcanisation

Bonding Characteristics

Solution Characteristics

Blends

Future Developments

14 RUBBER NATURAL

Agriculture

Exploitation

Latex Composition

Types and Grades

Production

Latex Concentrate

Processing

Chemistry

Physical Properties

Economic Aspects

Applications

15. Addresses of Plant & Machinery Suppliers

16. Plant & Machinery Photographs 

 Rubbers: Materials and Processing Technology

RUBBERS MATERIALS: INTERDUCTION

The technology of rubber began with the natural product known as natural

rubber (NR). Historically, rubber (NR) as a material was known to

and used by man as early as the sixth century, as excavations subsequent

to the discovery of America have revealed. The early reported uses of

NR were limited to such items as playing balls and waterproof fabrics or

garments, People of Europe became familiar with this natural product

and its properties by the end of the eighteenth century. From its popular

application as eraser of pencil and ink marks developed in Europe in the

middle of the eighteenth century, the name “rubber” was coined to it.

Earlier, the natural product was known by the term “Caoutchouc” which,

however, is now reserved in the English language to denote the pure rubber

hydrocarbon.

The process technology of making waterproof objects based on rubber-

coated fabrics passed into an advanced phase with the discovery of

coal tar naphtha as a good solvent for rubber by Charles Macintosh. This

led to the development of the “sandwich” process for the so-called double

texture fabric, imparting much improvements in the life and performance

of the waterproof garments. But the inherent drawback in the susceptibility

of rubber to changes of temperature (becoming soft and sticky

in warm wheather, and hard and stiff in cold weather) still remained unsolved,

thus limiting expansion and diversification of its use. The difficulty

was finally overcome through the discovery of vulcanization of

rubber using sulphur by Charles Goodyear in 1839 in USA. The process

was also developed in London by Thomas Hancock at about the same

time who applied for the first patent on vulcanization or curing of rubber

in 1843. The discovery of vulcanization, which in effect is a cross-linking

process, literally infused a revolution in the rubber industry and a

whole range of consumer and industrial rubber products soon became

available in the market.

NATURAL RUBBER (NR)

Natural Rubber Plantation

There was a time till the middle of the nineteenth century when raw

rubbers (NR) came almost entirely from the equatorial forest in the Amazon

valley in South America. Rubber randomly tapped and collected from

natural forests is variable in quality and is commonly known as wild rubber.

Under economic, technical and other compulsions, and for a regular,

uninterrupted supply of rubber, comprehensives plans for cultivation of

rubber trees from seeds of Hevea brasiliensis in the equatorial climatic

zones of South and South-East Asia began in the later part of the nineteenth

century. Present day NR or the Hevea rubber is almost entirely

obtained from the plantation industries.

Tapping of Rubber Latex

The rubber plant produces a milk-white latex that contains the natural

rubber hydrocarbon in a fine emulsion form in an aqueous serum.

After a thin shaving of bark of the Hevea tree has been cut, the latex that

comes out is allowed to flow into a cup through a spout that is stuck into

the bark below the bottom end of the cut. A little of sodium sulphite

solution put into the empty cup before tapping helps prevent some darkening

or discolouration of the latex which may otherwise develop as a

 consequence of an enzymatic reaction in the latex involving its phenolic

constituents producing the dark coloured pigment melanin.

Chlorinated Rubber

Natural rubber can be readily halogenated. Only chlorination has

been commercially developed. Direct chlorination with chlorine results

in both addition and substitution reactions and HC1 is evolved as a

byproduct. For only additive chlorination, maximum attainable chlorine

content would be about 51%, while for commercial products of good

stability, the range of chlorine content is 60-68%, and they are resinous

in character. It is generally believed that good degree of cyclization also

takes place on chlorination. Rubber, cut into small pieces is dissolved in

carbon tetra-chloride in presence of a small amount of benzoyl peroxide

which acts as a depolymerizing agent and lowers the solution viscosity.

A relatively uniform chlorinalion is achieved by spraying the solution at

the top of a chlorinating tower in which a stream of chlorine, let in at the

bottom, is allowed to ascend. The droplets of the chlorinated product

collect at the bottom. The collected solution from the bottom is degassed

to remove excess chlorine and then sprayed into a steam chamber where

the admitted steam causes rapid volatilization of CCl4. CCl4 is then recovered

and reused; the chlorinated rubber collected as a wet mass from

the bottom is washed, dried, milled if necessary and stored. Chlorinated

rubber is resistant to many chemicals. It even resists concentrated nitric

acid. It is, however, soluble in a wide range of solvents and it is used in

the formulation of many paints, lacquors, adhesives and printing inks.

Because of high chlorine content, chlorinated rubber has prominent flame

retardant characteristics.

Rubber can also be modified into a resinous product by

hydrochlorination. The rubber hydrochloride may be prepared directly

from stabilized latex using hydrochloric acid gas. It is, however, better

obtained by hydrochlorination with gaseous HCl using rubber in benzene

solution. Films made from the solution of the hydrochloride to which

plasticizers and stabilizers have been added are used for making laminates

with paper or films of other plastics such as cellulose acetate, etc.,

for use as heat sealable packages for dry food, cosmetics, shampoo, etc.

The hydrochloride also finds use in the formulation of adhesives and

bonding agents.

Polyacrylic Rubber or Acrylate Rubber (ACR)

Poly(ethyl acrylate) is soft and rubbery in nature. Copolymers of

ethyl acrylate (95%) and 2-chloroethyl acrylate or 2-chloroethyl vinyl

ether (cure site monomer) have been commercially developed and the

products are known as polyacrylic rubber or acrylate rubber. These rubbers

are suitably cured using aliphatic linear diamines and polyamines.

Cross-linking apparently occurs by HC1 elimination and intermolecular

link up through the diamines or via ester hydrolysis and establishment of

intermolecular amide linkages. Small amount of sulphur is used as an

anti-aging additive. The cured rubber is particularly useful as hoses, seals

and gaskets. Reinforcing carbon blacks are used as fillers. For pale shades,

siliceous fillers are used. The rubber has good resistance to oils and to

ozone and it may be used over a wide temperature zone (—40 to nearly +

200°C). The uncured polyacrylic rubbers are soluble in ketones, esters

and alcohol-ester mixtures. The cured polyacrylic rubbers are better than

nitrile rubbers in heat and oil resistance. Their resistance to ozone attack

and to sunlight and weathering are good. A terpolymer (AEM) of methyl

acrylate, ethylene and a cure site monomer, known in the trade by the

name Vamac, is of more recent development.

Fluorocarbon Rubber (FKM)

Fluorocarbon rubbers or elastomers are copolymers of vinylidene

fluoride and chlorotrifluoroethylene (50 : 50 or 30 : 70 ratio). Better products

are obtained by copolymerization of vinylidene fluoride and

bexafluoropropylene (“Viton” elastomers from Du Pont). They are usually

cured with amine type curatives in presence of a metallic oxide (litharge

or calcined magnesia). Curing is apparently effected by the elimination

of hydrogen fluoride.

The fluorocarbon (copolymer) elastomers are prepared by batch or

continuous process following the emulsion polymerization technique. The

latex-obtained is coagulated by hydrochloric acid and the polymer is

washed and dried. The Vitons are normally soluble in lower ketones and

the doughs formed are suitable for spreading over glass cloth to produce

coated fabrics useful as oil seals and gaskets with a long service life at

high temperatures ( 100 h at nearly 400°C, > 5000 h at 200°C).

The fluorocarbon rubbers exhibit excellent resistance to oils, lubricants,

hydrocarbon solvents, mineral acids and chemicals and to heat; in

these respects, they are superior to almost all other commercial rubbers.

The fluorocarbon rubbers can be suitably compounded to give vulcanizates

of tensile strength of about 200 kg/cm2 and elongation at break in the

range of 200-300%. They are flame resistant and they exhibit outstanding

resistance to oxygen and ozone attack. Their good low temperature

flexibility makes them advantageously useful at low temperatures up to

— 30°C. The application of fluorocarbon rubbers is limited to only special

or unusual service conditions where other rubbers are altogether unsuitable

and where their high cost is not a hindrance. The applications

include seals, gaskets and diaphragms, fire-resistant and protective clothing

from coated fabrics, and wire and cable insulation.

THERMOPLASTIC ELASTOMERS (TPE)

Development of thermoplastic elastomers (TPE) has narrowed the

basic difference between the processing of thermoplastics and elastomers

or rubbers for many non-tyre products. The TPEs make useful products

for which the tensile and set properties are not much critical, such as in

many automotive parts, footwear, cables, sealants and adhesives, hoses,

coated fabrics, tubings and sheetings. Their light weight, flexibility, impact

resistance and weathering resistance make them useful in many of

these applications.

The thermoplastic elastomers are processed like reusable and

reprocessable thermoplastics and under service conditions, they behave

like vulcanized rubbers. The useful mechanical and elastic properties of

conventional vulcanized rubbers are attributed to the chemical cross-links

established between the rubber chain molecules during vulcanization to

produce a space network structure. In the TPEs, the network is basically

formed through thermally labile physical cohesive forces between specific

segments of different polymer chains but not really through intermolecular

chemical linkages. At elevated and processing temperatures,

the thermolabile physical bonds weaken and finally break up, permitting

flow under shear and thus enabling them to be moulded or formed like a

conventional thermoplastic material. At and around ambient temperatures,

the TPEs exist in two phases; the soft rubbery phase forms the

continuous matrix in which the hard resinous phase remains dispersed in

discrete domains. The volume fraction of the rubbery matrix is usually

higher than that of the hard thermoplastic domains which materially act

as cross-links and as stiffening fillers or points of reinforcements.

RUBBER COMPOUNDING AND PROCESSING TECHNOLOGY

Introduction

No rubber is considered technically useful if its molecules are not

cross-linked by a process known as curing or vulcanization. The process

of vulcanization is usually associated with two chemical processes taking

place simultaneously, cross-linking and chain degradation, though at

widely different rates. For natural rubber and many synthetic rubbers,

particularly the diene rubbers, the curing agent most commonly used is

sulphur. But sulphur curing takes place at technically viable rates only at

a high temperature (> 140°C), and heating with sulphur alone leads to

optimum curing after nearly 8 h at 140°C using a fairly high dose of

sulphur (8-10 phr). Use of metal oxides, such as those of zinc, calcium,

magnesium, lead, etc., brings about some advantages with respect to time

of curing and improvements in physical properties without much reduction

in the sulphur dose. Aniline is considered as the first organic accelerator

tried in an attempt to quicken the curing process. Some of the more

efficient and less toxic modern organic accelerators of rubber vulcanization

are aniline derivatives. Sulphur dose has been substantially lowered

with the advent of organic accelerators.

Extensive studies and experimentation have revealed that neither

sulphur nor application of heat is indispensable for effecting cross-linking

and associated changes in physical properties of rubbers. Peroxides,

metal oxides, amines, amine derivatives and oximes have been found to

bring about curing of selected rubbers quite effectively. High-energy

radiations can bring about effective curing; but high-energy radiation

curing has not been developed into a commercial process of even limited

acceptability. Selenium and tellurium can substitute sulphur either totally

or partly to effect satisfactory curing of diene rubbers. Sulphur

monochloride can bring about room temperature or cold curing of diene

rubbers.

Improvements in physical and mechanical properties that can be

achieved through vulcanization using sulphur/accelerator systems only

are rather limited. The needs of imparting colour, stability, resistance to

tearing and abrasion, flexibility etc., and of improving processibility and

mechanical properties necessitate incorporation of a host of additives or

compounding ingredients in the rubber by what is commonly known as

the mixing or compounding process.

Rubber Vulcanization

VULCANIZATION AND ITS EFFECTS

Chemical crosslinks between macromolecules may occur in polymerization

or in fabricating articles, resulting in polymers with network structures.

The reaction which occurs during fabrication is known as “vulcanization”

in the rubber industry, and “curing” or “hardening” in the

plastics industry. Crosslinks in rubber are formed by the reaction with a

suitable “vulcanizing agent”, usually sulphur.

A typical crosslinking reaction is the formation of short chains of

sulphur atoms linking linear molecules in rubbers during vulcanization.

Lightly-vulcanized rubber shows good elastic properties, whereas vulcanization

to the maximum extent possible will lead to a full network

structure, and a hard and rigid material. Thermosetting resins may be

crosslinked by the addition of a curing agent, such as hexamethylene

tetramine and/or heat. Typical examples are epoxy resins, polyester resin

and poly-urethane foams. Owing to the greater restriction on the mobility

of the macro-molecular chains as a result of crosslinking, the modulus

and glass transition temperature increases in both hardened resins and

sulphur crosslinked rubber.

Charles Goodyear discovered sulphur vulcanization of rubber in 1839

and developed many new applications for rubber in industry.

Crosslinking of rubber occurs by a chemical process which is initiated

at favourable reaction sites by means of some form of energy input.

Double bonds in diene polymers or reaction sites left by abstraction of

hydrogen or halogen atoms are favourable reaction sites. These are coupled

by carbon-carbon crosslinks or by bridges formed with curatives

such as sulphur, acrylates, phenolics or triazines. Crosslinking through

sulphur atoms is quite common in biological molecules, e.g. disulphide

(cystine) bridges in polypeptides.

There are four principal changes which are brought about by vulcanization.

1. Rubber is converted from essentially a plastic substance of

very low strength to an elastic material of considerable strength

and resilience.

2. The physical properties, such as tensile strength and other

properties shown in Fig. 1 undergo a profound change as

vulcanization progresses.

3. The physical properties of vulcanizates are maintained over a

much wider temperature range than in the case of unvulcanized

rubber.

4. The crosslinked polymer (vulcanizate) only swells in liquids

which normally dissolve the uncrosslinked polymer.

Rubber Reclaiming

In the mid-1800s Charles Goodyear developed a technique for vulcanizing

rubber. He blended natural rubber with sulfur and placed it on his

wood stove, where the rubber cured into a water-impermeable sheet.

Because of the shortage of natural rubber at that time, a rubber-reclaiming

process, based on steam pressure to devulcanize used rubber, was

developed in 1858. The cured ground rubber was subjected to steam pressure

for 48 hours. Today, high cost silicone rubber polymers are reclaimed

in much the same way, although most synthetic polymers require more

complicated techniques. Rubber recycling has been extended to the recovery

of rubber in asphalt, scrap rubber as fuel, rubber pyrolysis, tire

splitting, and others. However, the discovery of plastics and oil-extended

rubbers and the drop in crude oil prices have led to a reduction in rubber

recycling except for expensive polymers, such as silicones (qv) and

fluorocarbons. Pyrolysis of scrap rubber is expensive and markets are

limited. It is more expensive to prepare and burn scrap rubber for fuel

than to burn natural gas, fuel oil, or coal. High fuel costs and petroleum

scarcity in Europe and other parts of the eastern hemisphere have resulted

in the use of recycled rubber as fuel and made it more economical

than in the United States. However, with today’s technological advances,

recycled rubber will be used more and more in the United States, but with

regulations for handling and disposing of worn tires. Crude oil costs have

dropped from about $189/m3 ($30/bbl) to $88/m3 ($14/bbl) over the last

few years, making it seemingly unprofitable to recycle rubber, especially

tires. However, tires discarded in landfills tend to float on top; mosquito

breeding and illegal tire disposal are causing problems which could be

alleviated by recycling. Approximately 70% of the scrap rubber, primarily

as tires, is discarded in landfills. Private landfills may charge up to S3

per tire, and disposal costs at municipal landfills are ca $0.30-0.60 per

tire. These costs encourage illegal disposal of tires. As the tire piles grow,

rubber recovery should become more economical. Companies entering

into multimillion dollar energy recovery projects will be encouraged by

an adequate supply of old tires.

Some states have restricted the disposal of tires in landfills, e.g., Washington,

Minnesota, and Oregon. Other states are studying legislation and

New Jersey is considering a surcharge. Iowa, Massachusetts, and Michigan

are studying tire-disposal problems, and Minnesota and Washington

have imposed a surcharge. Some communities refuse old tires while others

require tire splitting or shredding to prevent floating problems in

landfills. Fires resulting from the storage of tires have led to regulations

governing stockpiles. Mosquito infestation caused by illegal disposal of

tires has prompted Saginaw, Mich., to purchase a shredder for landfill

disposal.

Advances in the technology of shredding tires, reclaiming rubber,

retread equipment, energy-related projects, and pyrolysis are helping to

solve the disposal problem. Technical and marketing professionals associated

with the recycling and disposal industries are paying more attention

to tire-recycling and energy-generating projects.

SCRAP RUBBER AS FUEL SOURCE

The use of scrap rubber for fuel offers the best alternative for reusing

rubber, as fuel costs increase and tire disposal problems become more

serious. Tires in the form of 2.50-cm chips are most economical because

shredding is not expensive. Tires contain more than 90% organic materials

and have a heat value of ca 32.6 MJ/kg (ca 14,000 Btu/lb), compared

with coal values of 18.6-27.9 MJ/kg (ca 8,000-12,000 Btu lb). A cyclonic,

rotary-hearth boiler fired with whole tires was operated by the

Goodyear Tire and Rubber Co. from 1975 to 1977. It was designed to

burn 1400 kg/h and generated 11,300 kg of steam per hour.

In the Lucas tire-burning furnace, tires are conveyed into an airtight

chamber and then onto the outer rim of a rotating hearth. The chamber

prevents flashback fires and limits air leaks. An air-velocity head of 5.1

cm provides the turbulence necessary for combustion. Residues from the

burning tires form a char that increases combustion heat loss and tends to

clog furnace grates, but the carbon black content reduces slagging problems.

Improper combustion at the ash-removal area of the furnace may

prevent the burning of the carbon black. The Lucas-Goodyear furnace

was shut down because of mechanical problems and failure to comply

with Michigan’s air pollution emission standards.

Shredded tire chips have been burned in stoker-fired boilers. Uniroyal

fired a 15% mixture of tire chips with coal and both General Motors and

B. F. Goodrich have burned a 10% tire-chip mixture with coal. Tiregrinding

size-reduction problems and delivery costs have stymied projects

based on combined tire and coal fuel. The Lucas furnace was developed

to burn tires without size reduction. Transportation of tire scrap can cost

$0.05/kg, exclusive of grinding costs. Thus tire-fired boilers are limited

to areas with ample scrap-tire supplies, e.g., large cities or tire manufacturers.

The cost of burning one metric ton of tires per hour in an incinerator

was ca $0.20—0.40 per tire in 1974, which increased to $0.35-0.70

per tire in 1987.

The Oxford Energy Company uses a technology developed by

Gummi-Mayer Company (FRG) to incinerate tires and produce electricity.

The technology will be used in the Modesto Project near Westley,

Calif. The facility generates 14.4 MW of electricity and cost $38 × 106.

Construction began in December 1985 and was completed in August 1987.

The project is designed to generate electricity by incinerating whole waste

tires on reciprocating stoker grates located beneath two water wall boilers.

The boilers produce 55,000 kg of steam per hour and power a single

General Electric turbine generator. The facility is being constructed next

to the Filbin Tire Collection Agency, Inc., which administers one of the

largest stockpiles of waste tires in the United States (ca 300 × 103 t); the

stockpile increases annually by 27 t. Oxford Energy is also involved in

the construction of a New Hampshire tire incineration project, generating

15 MW of electricity; facility is expected to be completed in late

1988 at a cost of $35 × 106. The company has received air quality and

waste management permits from the State of New Hampshire. The firm

also plans to build a 22-MW electricity-generating facility in northeastern

Connecticut; construction is expected to be completed in 1989 at a

cost of $50 × 106. The company has projects to incorporate waste produced

from manufacturing facilities along with waste tires, thus providing

energy to manufacturing facilities as well as local utilities. Approximately

20 × 106 tires are stockpiled at two sites in New England.

These sites, together with the Filbin stockpile, contain at least 480 × 103

t of tires (53 × 106 tires).

CRYOGENIC PULVERIZING AND MECHANICAL TIRE

SHREDDING

Tires must be pulverized or shredded before they can be reclaimed

by devulcanization or used in asphalt and other recycling processes. The

tires are mechanically ground, sometimes using cryogenic freezing or

solvent-swelling techniques to enhance grinding efficiency. In one process,

a polar solvent is used to swell the rubber, followed by shearing to

reduce particle size. Ground tire-crumb rubber is commonly referred to

as rubber reclaim, even though the rubber has not been devulcanized.

Cryogenics in conjunction with mechanical action has been used to

make crumb rubber. Nitrogen cools the rubber below the glass-transition

temperature, and the brittle rubber is pulverized in a grinding mill. A

small cryogenic system can be installed at the site to integrate the scraprubber

crumb into the compound mixing process. Cryogenic-grinding

costs are $0.20-0.40/kg, depending on the desired particle size and the

type of rubber; harder rubber is easier to grind. Ground-rubber scrap can

be devulcanized, pyrolyzed, or recycled directly into the rubber compound.

Ground rubber is also added to plastics.

Air Products and Chemicals, Inc., Allentown, Pa., developed a cryogenic

process for grinding scrap tires in the mid-1960s. Liquid nitrogen

freezes the rubber to facilitate shredding. Midwest Elastomers installed a

cryogenic system in 1980 to powder tire peels in its Wapakoneta, Ohio,

plant. The equipment and materials for cryogenic processing are expensive

and have slowed expansion. Cryogenic grinding requires recycling

close to an air-processing facility to make the use of liquid nitrogen economical.

Air Products has a marketing and development relationship with

Brown & Ferris Industries to develop waste-to-energy and alternative

fuel projects.

The tires are mechanically ground with a two-roll, grooved-rubber

mill. The two-mill rolls turn at a ratio of ca 1:3, providing the shearing

action necessary to rip the tire apart. The rubber chunks are screened and

the larger material is recycled until the desired size is reached. Bead wire

is removed by hand or with magnets. For most applications, e.g.,

devulcanization or pyrolysis, crumb-rubber particles smaller than 1.19

mm (16 mesh) are desired, and several milling steps are required. Tire

fiber is removed in intermediate operations with hammer mills, reel beaters,

and air tables that blow a steady stream of air across the rubber

Latex and Foam Rubber

INTRODUCTION

Rubber latex is a term used to cover a range of colloids having macro

molecular substances as the dispersed phase and water as the dispersion

medium. Most important latex used in the rubber industry is natural rubber

(NR) latex. This is an aqueous dispersion of cis 1,4 polyisoprene in

water containing dissolved serum substances. NR latex is harvested from

Hevea brasilienesis trees by inflicting controlled wounds on the bark of

the trunk of the tree.

Under inorganic salts seven different types of ions are identified.

Similarly, under each of the organic ingredients a number of compounds

belonging to that group are characterised. In synthetic lattices also, a

number of ingredients other than the polymer and water are present.

PRODUCTS FROM LATEX

There are eight important steps in the manufacture of products from

latex –

1. Selection and quality control of raw materials

2. Preparation of raw materials

3. Compounding and design of the mix

4. Maturation

5. Processing/shaping

6. Vulcanisation

7. Testing for grading

8. Packing and marketing.

There are different types of products manufactured from latex. Some

of the steps are common in all products but differences exist in others.

The similarities and differences in the various steps for different types of

products are discussed below briefly:

Selection of Raw Materials

Following are the raw materials used in the latex industry —

Latex containing the polymer

Stabilisers and viscosity modifiers

Activator

Accelerator

Curing agent

Antioxidant

Special additives, if any

Gelling/coagulation system.

 

The raw material selected for product manufacture must be of good

quality and conforming to specifications prescribed for this by reputed

institutions like the BIS (ISI). In the case of natural rubber latex, there are

few processors who can supply high ammonia-preserved concentrated

natural rubber latex conforming to IS 5430. It may be noted that the specifications

for this HA latex have been formulated by the combined effort

of experts from rubber plantations and the goods manufacturing industry.

It is desirable for the industry to insist that the suppliers should deliver

of HA latices conforming to IS 5430.

In foam rubber there are two important processes in vogue commercially.

One is called the Dunlop process and the other called Tulalay process.

In India, most factories use the Dunlop process. In Dunlop process,

foaming is carried out in two stages. In the first stage latex is whipped up

with foam promoters and stabilisers till the desired expansion is obtained.

Thereafter the whipping rate is reduced and the foam is clarified or refined.

Gelling agents are added at the end of the foam clarifying stage.

The density of foam rubber produced depends on froth height. The level

in which latex is whipped should be calibrated properly for specific gravity

for various froath heights.

The materials selected for mould construction for foam production

must be light, cheap, should have high thermal capacity and good thermal

conductivity: A mould designed from copper free cast aluminum

meets these requirements. It is generally reported that in the cost of production

of foam rubber around 5% of the cost is on account of contribution

from mould cost. The tensile and cure properties of the hot wet gel

are appreciably lower than those of the dry finished products. So if care is

not exercised in stripping the foam from mould, it may as well be damaged.

For enabling easy and quick stripping, the mould surface should be

kept clean and polished. Mould release agent has to be applied on surface

of mould after each operation. Examples of mould release agents are

aqueous or alcoholic solutions of polyethylene glycol of fairly high molecular

weight such as carbo wax-4000, carboxymethyl cellulose or silicone

fluids.

In Tullalay process, the expansion of latex compound is achieved by

liberation of gases like oxygen liberated by catalytic decomposition of

hydrogen peroxide.

Latex Thread

In the production of latex rubber thread the matured latex has to be

carefully processed to avoid defects. The compounded matured latex is

de-aerated and filtered before it is allowed to pass through capillaries for

injection into an acid bath. The nozzle of the capillary is immersed in

coagulant. The nozzle depth in coagulant bath has direct relation to the

thread diameter. The rate of extrusion is 30-40 feet per minute. The orifice

of the nozzle is usually round and the size of the bore varies from 0.5

to 1 mm. Coagulant normally used is 15-40% acetic acid. Generally,

weaker solutions of acid are used for large diameter thread and strong

solutions for higher count threads. For the production of high count thread

alcohol is the most suitable coagulant. Between extruding nozzle and

winding, the thread is usually subjected to some degree of stretching which

may be upto 200%. Stretching is necessary to facilitate washing, to reduce

permanent set and to increase modulus of the thread.

Vulcanisation

Latex products are generally vulcanised at low temperatures and pressure

when compared to dry rubber products. It is desirable to wash, leach

and dry the latex products before subjecting them to vulcanisation temperature.

Vulcanisation of some products is carried out in hot air. Some

others are vulcanised in open steam in autoclaves.

Construction of Moulds

The moulds for foam rubber are usually made from cast aluminium

because of the lightness, durability and good heat conductivity of the

metal. When cushions and mattresses are made, cylindrical cores are attached

to the lids which give the characteristic cavity structure of the

back side of the foam. These cavities help to minimise the actual thickness

of the product to about 1 inch to ensure uniform curing throughout

the mass of the product. The cavities also assist in great saving of the

latex compound (of the order of 40%) without affecting the comfort. In

designing moulds, allowance should be given to shrinkage of the product

which amounts to roughly 8-10% linear.

Mould lubricants like polyethylene glycol and alkyl sulphate solutions

are applied to the mould surface to facilitate easy stripping of the

product after vulcanisation.

Curing

Mould foam products are normally cured by open steam (at 100°C)

which is more efficient and quicker than hot air curing. Thin sections of

foam, e.g., as used in carpet underlays, can be suitably cured by

hot air.

 

Polybutadiene and Polyisoprene

INTRODUCTION

Polyisoprene is a major component of manufacture rubber. It is also made

synthetically and forms are stereospecific cis 1-4, and trans-1-4-

polyisoprene. Both can be produced synthetically by the effect of heat

and pressure on isoprene in the presence of stereospecific catalyst. Natural

rubber is cis-1-4. Synthetic cis-1-4 is sometimes called synthetic natural

rubber. Trans-l, 4-polyisoprene resembles gutta percha. Polyisoprene

is the thermoplastic until mixed with sulphur and vulcanised. It supports

combustion and is non toxic

Polybutadiene is a synthetic thermoplastic polymer made by polymerising

1,3 butadiene with a stereospecific organometallic catalyst (butyl

lithium) though other catalysts such as titanium tetrachloride and aluminium

iodide may be used. The cis-isomer, which is similar to natural

rubber, is used in the tread due to its abrasion and crack resistance and

low heat built up. Large quantities are also used as blend in SBR rubber.

The trans-isomer resembles gutta percha and has limited utility, liquid

polybutadiene, which is sodium catalysed has speciality uses as a coating

resin. It is cured with organic peroxides. Combustible liquid form is probably

toxic by ingestion and inhalation, as well as skin irritant. The different

polymer structures of polybutadiene are given in Fig. 6.

POLYMER STRUCTURE

Polyisoprene

The polymerisation of isoprene and butadiene are examples of addition

polymerisation in which the repeating structural unit within the poly

mer backbone has the same molecular weight as the entering monomer

unit.

With isoprene, the building of this polymer backbone can occur in

several ways, depending upon where the addition occurs. The polymerisation

addition process can be a reaction involving the 1, 2-, 3, 4- or 1, 4-

positions of isoprene to give the structures shown in Figure 1.

In case of 1,2- and 3, 4- addition, an asymmetric carbon is formed

that can have either an R or an S (“d” or “1”) configuration. In general,

equal numbers of R and S configurations are produced during an addition

polymerisation, which results in no net optical activity for the polymer.

The disposition of the R and S configurations along the polymer

backbone, however, results in diastereomeric isomerism. Although many

combinations of sequences are possible, only three arrangements are commonly

considered in polymers. These diastereomeric isomers are referred

to as isotactic, syndiotactic, and atactic.

Gel and Branching

The structure and behaviour of polyisoprene is further complicated

by the possibility of branching and gel. The degree of gel and branching

is dependent upon the source of the cis-1, 4-polyisoprene. For Al-Ti catalysed

cis, 4-polyisoprene, the gel content is 5-25% most of which is termed

“loose” gel since it breaks down readily upon mastication. The gel content

in natural rubber is usually greater than that in the Al-Ti catalysed

polymer. This gel is also a “loose” gel. Lithium polymerised cis-l, 4-

polyisoprene usually contains no gel. Both natural rubber and Al-Ti-catalysed

cis-1,4-polyisoprene also contain large quantities of microgel.

The determination of the nature and degree of branching in natural

rubber and Al-Ti catalysed cis-1, 4-polyisoprene are complicated by the

presence of the gel and microgel. Removal of the gel/microgel fraction

from the soluble portion can have a marked effect on the resulting physical

properties such as viscosity, molecular weight, and branching.

Polybutadiene

The configurations of polybutadiene are cIS-, trans-, and vinyl. Since

either or both of the double bonds in butadiene can be involved in the

polymerisation mechanism, the resulting polymer may have a variety of

configurations. These result from the fact that the spatial arrangement of

the methylene groups in the polybutadiene backbone allow for geometric

isomerism to occur along the polymer chain. The different polymer structures

of polybutadiene are given in Figure 6.

Participation of both double bonds in the polymerisation process gives

rise to a 1, 4-addition, which can be either cis-1,4- or trans-l,4-, depending

upon the disposition of groups about the polymer double bond. Participation

of only one double bond results in a vinyl, or 1,2-addition, that

can have three possible structures just as 1,2- and 3,4- polyisoprene have

isotactic, syndiotactic, and atactic.

Reclaimed Rubber

INTRODUCTION

Reclaimed rubber is the product resulting when waste vulcanised scrap

rubber is treated to produce a plastic material which can be easily processed,

compounded and vulcanised with or without the addition of either

natural or synthetic rubbers. It is recognised that the vulcanisation process

is not truly reversible; however, an accepted definition for

devulcanisation is that it is a change in vulcanised rubber which results in

a decreased resistance to deformation at ordinary temperatures.

Reclaimed rubber is manufactured by suitable treatment to old and

worn out tyres, tubes and other used rubber articles with certain chemical

agents. A substantial devulcanisation or regeneration is effected to the

rubber compound in this process whereby its original plasticity is regained.

In short it may be stated that reclaiming is essentially a

depolymerisation process where the combined sulphur is not removed.

The reclaimed rubber is used in the manufacture of rubber goods, with or

without admixture of natural or synthetic rubber.

Recycled rubber can be more generally described as any sort of rubber

waste that has been converted into an economically useful form such

as reclaimed rubber, ground rubber, reprocessed synthetic rubber, and

die-cut punched parts.

One method of recycling some scrap rubber is to grind it as fine as

possible and work it into new rubber as an elastomeric filler. This was the

first method of reclaiming and is suitable only for compounding carriage

springs, which were fairly large barrel-shaped molded articles but not

suitable for footwear products.

In order to make a high-quality reclaim, the fibre must be removed

from the rubber scrap by soaking the rubber in water, and then taking a

small knife and starting the rubber from the cloth and stripping it off. But

this was not an effective way to produce large quantities of products.

TYPES OF RECLAIM

A variety of grades of reclaimed rubber is offered today, but mention

is made here of only the important ones.

Whole Tyre Reclaim

Whole tyre reclaim is the one produced in the largest quantity. Firstquality

reclaim made from whole tyres contains about 45% rubber hydrocarbon

by weight. The remaining 55% consists of valuable carbon

black, a little mineral filler, and softeners, all of which are substantially

unchanged by the reclaim manufacturing operation, and may be considered

to function as virgin materials. The manufacturing Minimum Staining Reclaim

Minimum staining reclaim can replace the conventional whole tyre

material when occasion demands. As implied, it has a much lower tendency

to stain, by either migration or contact, than conventional reclaim.

The reduction in staining characteristics is achieved by the use of activated-

carbon non-staining oils and by selecting tyres containing a higher

proportion of natural to synthetic rubber.

Drab and Coloured Reclaims

As the names imply, drab and coloured reclaims are made from nonblack

scrap. The digester process is usually employed and, when fabric is

present, a small addition of caustic is made in order to destroy it. The

period of heat treatment is usually several hours at 195°C.

Butyl Reclaim

Whereas reclaimed rubbers have been successfully produced from

scrap CR, NBR,SI, and other speciality rubbers, the only one of substantial

commercial importance is butyl reclaim. The starting material for this

is butyl inner tubes. A modified digester process is adopted, every precaution

being taken to avoid contamination by NR or SBR, because of

their adverse effect on the curing characteristics of the butyl. Extensive

control tests are necessary to ensure that the curing properties are satisfactory.

The nerve of butyl reclaim is much reduced compared with that

of the original polymer. Because of this, compounds containing butyl

reclaim will mix, calender, and extrude faster and more smoothly than

similar compounds based on virgin rubber.

Reclaimed Rubber

By the application of heat and chemical agents to ground vulcanised

waste rubber, a substantial regeneration of the rubber compound to its

original plastic state is effected, yielding a product known as ‘reclaim’ or

reclaimed rubber, capable of being processed, compounded, and

revulcanised. The process is essentially one of depolymerisation. Reclaimed

rubber has become widely accepted as a raw material which possesses

processing and economic characteristics that are of great value in

the compounding of natural and synthetic rubber stocks.

There are four principal reclaiming processes in use today, of which

the digester and reclaimator processes are important.

The raw material for reclaiming is scrap rubber in a wide variety of

forms, but tyres, as is to be expected, form the major quantity.

The first stage, in all processes, are the cracking and grinding of the

scrap rubber to reduce it to a crumb passing through a 20 to 30 mesh

screen.

Digester Process

At one time, most reclaim was made using the digester process. A

digester is essentially a steam-jacketed, agitator-equipped autoclave,

mounted either horizontally or vertically. This is a wet process in which

the coarsely ground scrap is submerged in a solution of water and reclaiming

agents. These agents may include many types of light and/or

heavy oils, naval stores, pine tar and coal tar pitches, and chemical

peptisers.

Until the advent of synthetic rubber, the digesting solution also included

caustic soda to remove free sulphur and to act as a defibring agent.

In fact, the process was generally referred to as the alkali digester

method.

The ground waste is loaded into a digester along with water, reclaiming

oils, and other additives, such as activated black (for minimum stain

ing grades). The digester is a cylindrical jacketed pressure vessel fitted

with a horizontal agitator, and steam can be supplied to both interior and

jacket, thus enabling a uniform temperature to be maintained throughout

the mass. The contents of the digester are then heated to about 190°C and

maintained at this temperature for some 4-10 hours with continuous agitation.

The digester is then ‘blown down’, and the contents deposited on

to a conveyor. Any necessary adjustments to the specific gravity and plasticity

by addition of plasticiser, carbon black, or fillers are carried out in

a ribbon blender, and the stock is then automatically conveyed to extruders

for straining, refining, and leafing on to a drum from which it is removed

in slabs.

Reclaimator Process

The reclaimator process is the only commercially successful continuous

technique for devulcanising tire scrap; all the others are batch

processes. Tyres are ground, the metal and fibre are mechanically separated,

then the rubber is further ground to a fine particle size. This fineground

rubber and the various reclaiming agents are all metered into a

blending system and conveyed to the reclaimator.

The reclaimator is a special type of screw-extrusion machine. It is

jacketed to provide for several zones of controlled temperature using either

hot oil or cooling water; in addition, the clearances between the screw

and the chamber wall are close and adjustable. The object is to subject

the rubber to a controlled amount of high heat and pressure in a continuously

moving environment. The residence time of the rubber in the machine

is less than 5 minutes. During this period, the rubber undergoes

devulcanisation. After the softened rubber is discharged from the head of

the machine, it is cooled and further processed in refining mills just as is

done in other reclaiming methods.

It can be shown that ground vulcanised rubber heated in a temperature

range of 120-200°C undergoes a rapid initial increase in plasticity,

and, on continued heating, passes through an inversion point and rehardens

unit, after prolonged heating, a further but slower increase in plasticity is

attained. It follows, therefore, that three points of equal plasticity occur

in this cycle. 

Rubbers: Materials and Processing Technology

RUBBERS MATERIALS: INTERDUCTION

The technology of rubber began with the natural product known as natural

rubber (NR). Historically, rubber (NR) as a material was known to

and used by man as early as the sixth century, as excavations subsequent

to the discovery of America have revealed. The early reported uses of

NR were limited to such items as playing balls and waterproof fabrics or

garments, People of Europe became familiar with this natural product

and its properties by the end of the eighteenth century. From its popular

application as eraser of pencil and ink marks developed in Europe in the

middle of the eighteenth century, the name “rubber” was coined to it.

Earlier, the natural product was known by the term “Caoutchouc” which,

however, is now reserved in the English language to denote the pure rubber

hydrocarbon.

The process technology of making waterproof objects based on rubber-

coated fabrics passed into an advanced phase with the discovery of

coal tar naphtha as a good solvent for rubber by Charles Macintosh. This

led to the development of the “sandwich” process for the so-called double

texture fabric, imparting much improvements in the life and performance

of the waterproof garments. But the inherent drawback in the susceptibility

of rubber to changes of temperature (becoming soft and sticky

in warm wheather, and hard and stiff in cold weather) still remained unsolved,

thus limiting expansion and diversification of its use. The difficulty

was finally overcome through the discovery of vulcanization of

rubber using sulphur by Charles Goodyear in 1839 in USA. The process

was also developed in London by Thomas Hancock at about the same

time who applied for the first patent on vulcanization or curing of rubber

in 1843. The discovery of vulcanization, which in effect is a cross-linking

process, literally infused a revolution in the rubber industry and a

whole range of consumer and industrial rubber products soon became

available in the market.

NATURAL RUBBER (NR)

Natural Rubber Plantation

There was a time till the middle of the nineteenth century when raw

rubbers (NR) came almost entirely from the equatorial forest in the Amazon

valley in South America. Rubber randomly tapped and collected from

natural forests is variable in quality and is commonly known as wild rubber.

Under economic, technical and other compulsions, and for a regular,

uninterrupted supply of rubber, comprehensives plans for cultivation of

rubber trees from seeds of Hevea brasiliensis in the equatorial climatic

zones of South and South-East Asia began in the later part of the nineteenth

century. Present day NR or the Hevea rubber is almost entirely

obtained from the plantation industries.

Tapping of Rubber Latex

The rubber plant produces a milk-white latex that contains the natural

rubber hydrocarbon in a fine emulsion form in an aqueous serum.

After a thin shaving of bark of the Hevea tree has been cut, the latex that

comes out is allowed to flow into a cup through a spout that is stuck into

the bark below the bottom end of the cut. A little of sodium sulphite

solution put into the empty cup before tapping helps prevent some darkening

or discolouration of the latex which may otherwise develop as a

 consequence of an enzymatic reaction in the latex involving its phenolic

constituents producing the dark coloured pigment melanin.

Chlorinated Rubber

Natural rubber can be readily halogenated. Only chlorination has

been commercially developed. Direct chlorination with chlorine results

in both addition and substitution reactions and HC1 is evolved as a

byproduct. For only additive chlorination, maximum attainable chlorine

content would be about 51%, while for commercial products of good

stability, the range of chlorine content is 60-68%, and they are resinous

in character. It is generally believed that good degree of cyclization also

takes place on chlorination. Rubber, cut into small pieces is dissolved in

carbon tetra-chloride in presence of a small amount of benzoyl peroxide

which acts as a depolymerizing agent and lowers the solution viscosity.

A relatively uniform chlorinalion is achieved by spraying the solution at

the top of a chlorinating tower in which a stream of chlorine, let in at the

bottom, is allowed to ascend. The droplets of the chlorinated product

collect at the bottom. The collected solution from the bottom is degassed

to remove excess chlorine and then sprayed into a steam chamber where

the admitted steam causes rapid volatilization of CCl4. CCl4 is then recovered

and reused; the chlorinated rubber collected as a wet mass from

the bottom is washed, dried, milled if necessary and stored. Chlorinated

rubber is resistant to many chemicals. It even resists concentrated nitric

acid. It is, however, soluble in a wide range of solvents and it is used in

the formulation of many paints, lacquors, adhesives and printing inks.

Because of high chlorine content, chlorinated rubber has prominent flame

retardant characteristics.

Rubber can also be modified into a resinous product by

hydrochlorination. The rubber hydrochloride may be prepared directly

from stabilized latex using hydrochloric acid gas. It is, however, better

obtained by hydrochlorination with gaseous HCl using rubber in benzene

solution. Films made from the solution of the hydrochloride to which

plasticizers and stabilizers have been added are used for making laminates

with paper or films of other plastics such as cellulose acetate, etc.,

for use as heat sealable packages for dry food, cosmetics, shampoo, etc.

The hydrochloride also finds use in the formulation of adhesives and

bonding agents.

Polyacrylic Rubber or Acrylate Rubber (ACR)

Poly(ethyl acrylate) is soft and rubbery in nature. Copolymers of

ethyl acrylate (95%) and 2-chloroethyl acrylate or 2-chloroethyl vinyl

ether (cure site monomer) have been commercially developed and the

products are known as polyacrylic rubber or acrylate rubber. These rubbers

are suitably cured using aliphatic linear diamines and polyamines.

Cross-linking apparently occurs by HC1 elimination and intermolecular

link up through the diamines or via ester hydrolysis and establishment of

intermolecular amide linkages. Small amount of sulphur is used as an

anti-aging additive. The cured rubber is particularly useful as hoses, seals

and gaskets. Reinforcing carbon blacks are used as fillers. For pale shades,

siliceous fillers are used. The rubber has good resistance to oils and to

ozone and it may be used over a wide temperature zone (—40 to nearly +

200°C). The uncured polyacrylic rubbers are soluble in ketones, esters

and alcohol-ester mixtures. The cured polyacrylic rubbers are better than

nitrile rubbers in heat and oil resistance. Their resistance to ozone attack

and to sunlight and weathering are good. A terpolymer (AEM) of methyl

acrylate, ethylene and a cure site monomer, known in the trade by the

name Vamac, is of more recent development.

Fluorocarbon Rubber (FKM)

Fluorocarbon rubbers or elastomers are copolymers of vinylidene

fluoride and chlorotrifluoroethylene (50 : 50 or 30 : 70 ratio). Better products

are obtained by copolymerization of vinylidene fluoride and

bexafluoropropylene (“Viton” elastomers from Du Pont). They are usually

cured with amine type curatives in presence of a metallic oxide (litharge

or calcined magnesia). Curing is apparently effected by the elimination

of hydrogen fluoride.

The fluorocarbon (copolymer) elastomers are prepared by batch or

continuous process following the emulsion polymerization technique. The

latex-obtained is coagulated by hydrochloric acid and the polymer is

washed and dried. The Vitons are normally soluble in lower ketones and

the doughs formed are suitable for spreading over glass cloth to produce

coated fabrics useful as oil seals and gaskets with a long service life at

high temperatures ( 100 h at nearly 400°C, > 5000 h at 200°C).

The fluorocarbon rubbers exhibit excellent resistance to oils, lubricants,

hydrocarbon solvents, mineral acids and chemicals and to heat; in

these respects, they are superior to almost all other commercial rubbers.

The fluorocarbon rubbers can be suitably compounded to give vulcanizates

of tensile strength of about 200 kg/cm2 and elongation at break in the

range of 200-300%. They are flame resistant and they exhibit outstanding

resistance to oxygen and ozone attack. Their good low temperature

flexibility makes them advantageously useful at low temperatures up to

— 30°C. The application of fluorocarbon rubbers is limited to only special

or unusual service conditions where other rubbers are altogether unsuitable

and where their high cost is not a hindrance. The applications

include seals, gaskets and diaphragms, fire-resistant and protective clothing

from coated fabrics, and wire and cable insulation.

THERMOPLASTIC ELASTOMERS (TPE)

Development of thermoplastic elastomers (TPE) has narrowed the

basic difference between the processing of thermoplastics and elastomers

or rubbers for many non-tyre products. The TPEs make useful products

for which the tensile and set properties are not much critical, such as in

many automotive parts, footwear, cables, sealants and adhesives, hoses,

coated fabrics, tubings and sheetings. Their light weight, flexibility, impact

resistance and weathering resistance make them useful in many of

these applications.

The thermoplastic elastomers are processed like reusable and

reprocessable thermoplastics and under service conditions, they behave

like vulcanized rubbers. The useful mechanical and elastic properties of

conventional vulcanized rubbers are attributed to the chemical cross-links

established between the rubber chain molecules during vulcanization to

produce a space network structure. In the TPEs, the network is basically

formed through thermally labile physical cohesive forces between specific

segments of different polymer chains but not really through intermolecular

chemical linkages. At elevated and processing temperatures,

the thermolabile physical bonds weaken and finally break up, permitting

flow under shear and thus enabling them to be moulded or formed like a

conventional thermoplastic material. At and around ambient temperatures,

the TPEs exist in two phases; the soft rubbery phase forms the

continuous matrix in which the hard resinous phase remains dispersed in

discrete domains. The volume fraction of the rubbery matrix is usually

higher than that of the hard thermoplastic domains which materially act

as cross-links and as stiffening fillers or points of reinforcements.

RUBBER COMPOUNDING AND PROCESSING TECHNOLOGY

Introduction

No rubber is considered technically useful if its molecules are not

cross-linked by a process known as curing or vulcanization. The process

of vulcanization is usually associated with two chemical processes taking

place simultaneously, cross-linking and chain degradation, though at

widely different rates. For natural rubber and many synthetic rubbers,

particularly the diene rubbers, the curing agent most commonly used is

sulphur. But sulphur curing takes place at technically viable rates only at

a high temperature (> 140°C), and heating with sulphur alone leads to

optimum curing after nearly 8 h at 140°C using a fairly high dose of

sulphur (8-10 phr). Use of metal oxides, such as those of zinc, calcium,

magnesium, lead, etc., brings about some advantages with respect to time

of curing and improvements in physical properties without much reduction

in the sulphur dose. Aniline is considered as the first organic accelerator

tried in an attempt to quicken the curing process. Some of the more

efficient and less toxic modern organic accelerators of rubber vulcanization

are aniline derivatives. Sulphur dose has been substantially lowered

with the advent of organic accelerators.

Extensive studies and experimentation have revealed that neither

sulphur nor application of heat is indispensable for effecting cross-linking

and associated changes in physical properties of rubbers. Peroxides,

metal oxides, amines, amine derivatives and oximes have been found to

bring about curing of selected rubbers quite effectively. High-energy

radiations can bring about effective curing; but high-energy radiation

curing has not been developed into a commercial process of even limited

acceptability. Selenium and tellurium can substitute sulphur either totally

or partly to effect satisfactory curing of diene rubbers. Sulphur

monochloride can bring about room temperature or cold curing of diene

rubbers.

Improvements in physical and mechanical properties that can be

achieved through vulcanization using sulphur/accelerator systems only

are rather limited. The needs of imparting colour, stability, resistance to

tearing and abrasion, flexibility etc., and of improving processibility and

mechanical properties necessitate incorporation of a host of additives or

compounding ingredients in the rubber by what is commonly known as

the mixing or compounding process.

Rubber Vulcanization

VULCANIZATION AND ITS EFFECTS

Chemical crosslinks between macromolecules may occur in polymerization

or in fabricating articles, resulting in polymers with network structures.

The reaction which occurs during fabrication is known as “vulcanization”

in the rubber industry, and “curing” or “hardening” in the

plastics industry. Crosslinks in rubber are formed by the reaction with a

suitable “vulcanizing agent”, usually sulphur.

A typical crosslinking reaction is the formation of short chains of

sulphur atoms linking linear molecules in rubbers during vulcanization.

Lightly-vulcanized rubber shows good elastic properties, whereas vulcanization

to the maximum extent possible will lead to a full network

structure, and a hard and rigid material. Thermosetting resins may be

crosslinked by the addition of a curing agent, such as hexamethylene

tetramine and/or heat. Typical examples are epoxy resins, polyester resin

and poly-urethane foams. Owing to the greater restriction on the mobility

of the macro-molecular chains as a result of crosslinking, the modulus

and glass transition temperature increases in both hardened resins and

sulphur crosslinked rubber.

Charles Goodyear discovered sulphur vulcanization of rubber in 1839

and developed many new applications for rubber in industry.

Crosslinking of rubber occurs by a chemical process which is initiated

at favourable reaction sites by means of some form of energy input.

Double bonds in diene polymers or reaction sites left by abstraction of

hydrogen or halogen atoms are favourable reaction sites. These are coupled

by carbon-carbon crosslinks or by bridges formed with curatives

such as sulphur, acrylates, phenolics or triazines. Crosslinking through

sulphur atoms is quite common in biological molecules, e.g. disulphide

(cystine) bridges in polypeptides.

There are four principal changes which are brought about by vulcanization.

1. Rubber is converted from essentially a plastic substance of

very low strength to an elastic material of considerable strength

and resilience.

2. The physical properties, such as tensile strength and other

properties shown in Fig. 1 undergo a profound change as

vulcanization progresses.

3. The physical properties of vulcanizates are maintained over a

much wider temperature range than in the case of unvulcanized

rubber.

4. The crosslinked polymer (vulcanizate) only swells in liquids

which normally dissolve the uncrosslinked polymer.

Rubber Reclaiming

In the mid-1800s Charles Goodyear developed a technique for vulcanizing

rubber. He blended natural rubber with sulfur and placed it on his

wood stove, where the rubber cured into a water-impermeable sheet.

Because of the shortage of natural rubber at that time, a rubber-reclaiming

process, based on steam pressure to devulcanize used rubber, was

developed in 1858. The cured ground rubber was subjected to steam pressure

for 48 hours. Today, high cost silicone rubber polymers are reclaimed

in much the same way, although most synthetic polymers require more

complicated techniques. Rubber recycling has been extended to the recovery

of rubber in asphalt, scrap rubber as fuel, rubber pyrolysis, tire

splitting, and others. However, the discovery of plastics and oil-extended

rubbers and the drop in crude oil prices have led to a reduction in rubber

recycling except for expensive polymers, such as silicones (qv) and

fluorocarbons. Pyrolysis of scrap rubber is expensive and markets are

limited. It is more expensive to prepare and burn scrap rubber for fuel

than to burn natural gas, fuel oil, or coal. High fuel costs and petroleum

scarcity in Europe and other parts of the eastern hemisphere have resulted

in the use of recycled rubber as fuel and made it more economical

than in the United States. However, with today’s technological advances,

recycled rubber will be used more and more in the United States, but with

regulations for handling and disposing of worn tires. Crude oil costs have

dropped from about $189/m3 ($30/bbl) to $88/m3 ($14/bbl) over the last

few years, making it seemingly unprofitable to recycle rubber, especially

tires. However, tires discarded in landfills tend to float on top; mosquito

breeding and illegal tire disposal are causing problems which could be

alleviated by recycling. Approximately 70% of the scrap rubber, primarily

as tires, is discarded in landfills. Private landfills may charge up to S3

per tire, and disposal costs at municipal landfills are ca $0.30-0.60 per

tire. These costs encourage illegal disposal of tires. As the tire piles grow,

rubber recovery should become more economical. Companies entering

into multimillion dollar energy recovery projects will be encouraged by

an adequate supply of old tires.

Some states have restricted the disposal of tires in landfills, e.g., Washington,

Minnesota, and Oregon. Other states are studying legislation and

New Jersey is considering a surcharge. Iowa, Massachusetts, and Michigan

are studying tire-disposal problems, and Minnesota and Washington

have imposed a surcharge. Some communities refuse old tires while others

require tire splitting or shredding to prevent floating problems in

landfills. Fires resulting from the storage of tires have led to regulations

governing stockpiles. Mosquito infestation caused by illegal disposal of

tires has prompted Saginaw, Mich., to purchase a shredder for landfill

disposal.

Advances in the technology of shredding tires, reclaiming rubber,

retread equipment, energy-related projects, and pyrolysis are helping to

solve the disposal problem. Technical and marketing professionals associated

with the recycling and disposal industries are paying more attention

to tire-recycling and energy-generating projects.

SCRAP RUBBER AS FUEL SOURCE

The use of scrap rubber for fuel offers the best alternative for reusing

rubber, as fuel costs increase and tire disposal problems become more

serious. Tires in the form of 2.50-cm chips are most economical because

shredding is not expensive. Tires contain more than 90% organic materials

and have a heat value of ca 32.6 MJ/kg (ca 14,000 Btu/lb), compared

with coal values of 18.6-27.9 MJ/kg (ca 8,000-12,000 Btu lb). A cyclonic,

rotary-hearth boiler fired with whole tires was operated by the

Goodyear Tire and Rubber Co. from 1975 to 1977. It was designed to

burn 1400 kg/h and generated 11,300 kg of steam per hour.

In the Lucas tire-burning furnace, tires are conveyed into an airtight

chamber and then onto the outer rim of a rotating hearth. The chamber

prevents flashback fires and limits air leaks. An air-velocity head of 5.1

cm provides the turbulence necessary for combustion. Residues from the

burning tires form a char that increases combustion heat loss and tends to

clog furnace grates, but the carbon black content reduces slagging problems.

Improper combustion at the ash-removal area of the furnace may

prevent the burning of the carbon black. The Lucas-Goodyear furnace

was shut down because of mechanical problems and failure to comply

with Michigan’s air pollution emission standards.

Shredded tire chips have been burned in stoker-fired boilers. Uniroyal

fired a 15% mixture of tire chips with coal and both General Motors and

B. F. Goodrich have burned a 10% tire-chip mixture with coal. Tiregrinding

size-reduction problems and delivery costs have stymied projects

based on combined tire and coal fuel. The Lucas furnace was developed

to burn tires without size reduction. Transportation of tire scrap can cost

$0.05/kg, exclusive of grinding costs. Thus tire-fired boilers are limited

to areas with ample scrap-tire supplies, e.g., large cities or tire manufacturers.

The cost of burning one metric ton of tires per hour in an incinerator

was ca $0.20—0.40 per tire in 1974, which increased to $0.35-0.70

per tire in 1987.

The Oxford Energy Company uses a technology developed by

Gummi-Mayer Company (FRG) to incinerate tires and produce electricity.

The technology will be used in the Modesto Project near Westley,

Calif. The facility generates 14.4 MW of electricity and cost $38 × 106.

Construction began in December 1985 and was completed in August 1987.

The project is designed to generate electricity by incinerating whole waste

tires on reciprocating stoker grates located beneath two water wall boilers.

The boilers produce 55,000 kg of steam per hour and power a single

General Electric turbine generator. The facility is being constructed next

to the Filbin Tire Collection Agency, Inc., which administers one of the

largest stockpiles of waste tires in the United States (ca 300 × 103 t); the

stockpile increases annually by 27 t. Oxford Energy is also involved in

the construction of a New Hampshire tire incineration project, generating

15 MW of electricity; facility is expected to be completed in late

1988 at a cost of $35 × 106. The company has received air quality and

waste management permits from the State of New Hampshire. The firm

also plans to build a 22-MW electricity-generating facility in northeastern

Connecticut; construction is expected to be completed in 1989 at a

cost of $50 × 106. The company has projects to incorporate waste produced

from manufacturing facilities along with waste tires, thus providing

energy to manufacturing facilities as well as local utilities. Approximately

20 × 106 tires are stockpiled at two sites in New England.

These sites, together with the Filbin stockpile, contain at least 480 × 103

t of tires (53 × 106 tires).

CRYOGENIC PULVERIZING AND MECHANICAL TIRE

SHREDDING

Tires must be pulverized or shredded before they can be reclaimed

by devulcanization or used in asphalt and other recycling processes. The

tires are mechanically ground, sometimes using cryogenic freezing or

solvent-swelling techniques to enhance grinding efficiency. In one process,

a polar solvent is used to swell the rubber, followed by shearing to

reduce particle size. Ground tire-crumb rubber is commonly referred to

as rubber reclaim, even though the rubber has not been devulcanized.

Cryogenics in conjunction with mechanical action has been used to

make crumb rubber. Nitrogen cools the rubber below the glass-transition

temperature, and the brittle rubber is pulverized in a grinding mill. A

small cryogenic system can be installed at the site to integrate the scraprubber

crumb into the compound mixing process. Cryogenic-grinding

costs are $0.20-0.40/kg, depending on the desired particle size and the

type of rubber; harder rubber is easier to grind. Ground-rubber scrap can

be devulcanized, pyrolyzed, or recycled directly into the rubber compound.

Ground rubber is also added to plastics.

Air Products and Chemicals, Inc., Allentown, Pa., developed a cryogenic

process for grinding scrap tires in the mid-1960s. Liquid nitrogen

freezes the rubber to facilitate shredding. Midwest Elastomers installed a

cryogenic system in 1980 to powder tire peels in its Wapakoneta, Ohio,

plant. The equipment and materials for cryogenic processing are expensive

and have slowed expansion. Cryogenic grinding requires recycling

close to an air-processing facility to make the use of liquid nitrogen economical.

Air Products has a marketing and development relationship with

Brown & Ferris Industries to develop waste-to-energy and alternative

fuel projects.

The tires are mechanically ground with a two-roll, grooved-rubber

mill. The two-mill rolls turn at a ratio of ca 1:3, providing the shearing

action necessary to rip the tire apart. The rubber chunks are screened and

the larger material is recycled until the desired size is reached. Bead wire

is removed by hand or with magnets. For most applications, e.g.,

devulcanization or pyrolysis, crumb-rubber particles smaller than 1.19

mm (16 mesh) are desired, and several milling steps are required. Tire

fiber is removed in intermediate operations with hammer mills, reel beaters,

and air tables that blow a steady stream of air across the rubber

Latex and Foam Rubber

INTRODUCTION

Rubber latex is a term used to cover a range of colloids having macro

molecular substances as the dispersed phase and water as the dispersion

medium. Most important latex used in the rubber industry is natural rubber

(NR) latex. This is an aqueous dispersion of cis 1,4 polyisoprene in

water containing dissolved serum substances. NR latex is harvested from

Hevea brasilienesis trees by inflicting controlled wounds on the bark of

the trunk of the tree.

Under inorganic salts seven different types of ions are identified.

Similarly, under each of the organic ingredients a number of compounds

belonging to that group are characterised. In synthetic lattices also, a

number of ingredients other than the polymer and water are present.

PRODUCTS FROM LATEX

There are eight important steps in the manufacture of products from

latex –

1. Selection and quality control of raw materials

2. Preparation of raw materials

3. Compounding and design of the mix

4. Maturation

5. Processing/shaping

6. Vulcanisation

7. Testing for grading

8. Packing and marketing.

There are different types of products manufactured from latex. Some

of the steps are common in all products but differences exist in others.

The similarities and differences in the various steps for different types of

products are discussed below briefly:

Selection of Raw Materials

Following are the raw materials used in the latex industry —

Latex containing the polymer

Stabilisers and viscosity modifiers

Activator

Accelerator

Curing agent

Antioxidant

Special additives, if any

Gelling/coagulation system.

 

The raw material selected for product manufacture must be of good

quality and conforming to specifications prescribed for this by reputed

institutions like the BIS (ISI). In the case of natural rubber latex, there are

few processors who can supply high ammonia-preserved concentrated

natural rubber latex conforming to IS 5430. It may be noted that the specifications

for this HA latex have been formulated by the combined effort

of experts from rubber plantations and the goods manufacturing industry.

It is desirable for the industry to insist that the suppliers should deliver

of HA latices conforming to IS 5430.

In foam rubber there are two important processes in vogue commercially.

One is called the Dunlop process and the other called Tulalay process.

In India, most factories use the Dunlop process. In Dunlop process,

foaming is carried out in two stages. In the first stage latex is whipped up

with foam promoters and stabilisers till the desired expansion is obtained.

Thereafter the whipping rate is reduced and the foam is clarified or refined.

Gelling agents are added at the end of the foam clarifying stage.

The density of foam rubber produced depends on froth height. The level

in which latex is whipped should be calibrated properly for specific gravity

for various froath heights.

The materials selected for mould construction for foam production

must be light, cheap, should have high thermal capacity and good thermal

conductivity: A mould designed from copper free cast aluminum

meets these requirements. It is generally reported that in the cost of production

of foam rubber around 5% of the cost is on account of contribution

from mould cost. The tensile and cure properties of the hot wet gel

are appreciably lower than those of the dry finished products. So if care is

not exercised in stripping the foam from mould, it may as well be damaged.

For enabling easy and quick stripping, the mould surface should be

kept clean and polished. Mould release agent has to be applied on surface

of mould after each operation. Examples of mould release agents are

aqueous or alcoholic solutions of polyethylene glycol of fairly high molecular

weight such as carbo wax-4000, carboxymethyl cellulose or silicone

fluids.

In Tullalay process, the expansion of latex compound is achieved by

liberation of gases like oxygen liberated by catalytic decomposition of

hydrogen peroxide.

Latex Thread

In the production of latex rubber thread the matured latex has to be

carefully processed to avoid defects. The compounded matured latex is

de-aerated and filtered before it is allowed to pass through capillaries for

injection into an acid bath. The nozzle of the capillary is immersed in

coagulant. The nozzle depth in coagulant bath has direct relation to the

thread diameter. The rate of extrusion is 30-40 feet per minute. The orifice

of the nozzle is usually round and the size of the bore varies from 0.5

to 1 mm. Coagulant normally used is 15-40% acetic acid. Generally,

weaker solutions of acid are used for large diameter thread and strong

solutions for higher count threads. For the production of high count thread

alcohol is the most suitable coagulant. Between extruding nozzle and

winding, the thread is usually subjected to some degree of stretching which

may be upto 200%. Stretching is necessary to facilitate washing, to reduce

permanent set and to increase modulus of the thread.

Vulcanisation

Latex products are generally vulcanised at low temperatures and pressure

when compared to dry rubber products. It is desirable to wash, leach

and dry the latex products before subjecting them to vulcanisation temperature.

Vulcanisation of some products is carried out in hot air. Some

others are vulcanised in open steam in autoclaves.

Construction of Moulds

The moulds for foam rubber are usually made from cast aluminium

because of the lightness, durability and good heat conductivity of the

metal. When cushions and mattresses are made, cylindrical cores are attached

to the lids which give the characteristic cavity structure of the

back side of the foam. These cavities help to minimise the actual thickness

of the product to about 1 inch to ensure uniform curing throughout

the mass of the product. The cavities also assist in great saving of the

latex compound (of the order of 40%) without affecting the comfort. In

designing moulds, allowance should be given to shrinkage of the product

which amounts to roughly 8-10% linear.

Mould lubricants like polyethylene glycol and alkyl sulphate solutions

are applied to the mould surface to facilitate easy stripping of the

product after vulcanisation.

Curing

Mould foam products are normally cured by open steam (at 100°C)

which is more efficient and quicker than hot air curing. Thin sections of

foam, e.g., as used in carpet underlays, can be suitably cured by

hot air.

 

Polybutadiene and Polyisoprene

INTRODUCTION

Polyisoprene is a major component of manufacture rubber. It is also made

synthetically and forms are stereospecific cis 1-4, and trans-1-4-

polyisoprene. Both can be produced synthetically by the effect of heat

and pressure on isoprene in the presence of stereospecific catalyst. Natural

rubber is cis-1-4. Synthetic cis-1-4 is sometimes called synthetic natural

rubber. Trans-l, 4-polyisoprene resembles gutta percha. Polyisoprene

is the thermoplastic until mixed with sulphur and vulcanised. It supports

combustion and is non toxic

Polybutadiene is a synthetic thermoplastic polymer made by polymerising

1,3 butadiene with a stereospecific organometallic catalyst (butyl

lithium) though other catalysts such as titanium tetrachloride and aluminium

iodide may be used. The cis-isomer, which is similar to natural

rubber, is used in the tread due to its abrasion and crack resistance and

low heat built up. Large quantities are also used as blend in SBR rubber.

The trans-isomer resembles gutta percha and has limited utility, liquid

polybutadiene, which is sodium catalysed has speciality uses as a coating

resin. It is cured with organic peroxides. Combustible liquid form is probably

toxic by ingestion and inhalation, as well as skin irritant. The different

polymer structures of polybutadiene are given in Fig. 6.

POLYMER STRUCTURE

Polyisoprene

The polymerisation of isoprene and butadiene are examples of addition

polymerisation in which the repeating structural unit within the poly

mer backbone has the same molecular weight as the entering monomer

unit.

With isoprene, the building of this polymer backbone can occur in

several ways, depending upon where the addition occurs. The polymerisation

addition process can be a reaction involving the 1, 2-, 3, 4- or 1, 4-

positions of isoprene to give the structures shown in Figure 1.

In case of 1,2- and 3, 4- addition, an asymmetric carbon is formed

that can have either an R or an S (“d” or “1”) configuration. In general,

equal numbers of R and S configurations are produced during an addition

polymerisation, which results in no net optical activity for the polymer.

The disposition of the R and S configurations along the polymer

backbone, however, results in diastereomeric isomerism. Although many

combinations of sequences are possible, only three arrangements are commonly

considered in polymers. These diastereomeric isomers are referred

to as isotactic, syndiotactic, and atactic.

Gel and Branching

The structure and behaviour of polyisoprene is further complicated

by the possibility of branching and gel. The degree of gel and branching

is dependent upon the source of the cis-1, 4-polyisoprene. For Al-Ti catalysed

cis, 4-polyisoprene, the gel content is 5-25% most of which is termed

“loose” gel since it breaks down readily upon mastication. The gel content

in natural rubber is usually greater than that in the Al-Ti catalysed

polymer. This gel is also a “loose” gel. Lithium polymerised cis-l, 4-

polyisoprene usually contains no gel. Both natural rubber and Al-Ti-catalysed

cis-1,4-polyisoprene also contain large quantities of microgel.

The determination of the nature and degree of branching in natural

rubber and Al-Ti catalysed cis-1, 4-polyisoprene are complicated by the

presence of the gel and microgel. Removal of the gel/microgel fraction

from the soluble portion can have a marked effect on the resulting physical

properties such as viscosity, molecular weight, and branching.

Polybutadiene

The configurations of polybutadiene are cIS-, trans-, and vinyl. Since

either or both of the double bonds in butadiene can be involved in the

polymerisation mechanism, the resulting polymer may have a variety of

configurations. These result from the fact that the spatial arrangement of

the methylene groups in the polybutadiene backbone allow for geometric

isomerism to occur along the polymer chain. The different polymer structures

of polybutadiene are given in Figure 6.

Participation of both double bonds in the polymerisation process gives

rise to a 1, 4-addition, which can be either cis-1,4- or trans-l,4-, depending

upon the disposition of groups about the polymer double bond. Participation

of only one double bond results in a vinyl, or 1,2-addition, that

can have three possible structures just as 1,2- and 3,4- polyisoprene have

isotactic, syndiotactic, and atactic.

Reclaimed Rubber

INTRODUCTION

Reclaimed rubber is the product resulting when waste vulcanised scrap

rubber is treated to produce a plastic material which can be easily processed,

compounded and vulcanised with or without the addition of either

natural or synthetic rubbers. It is recognised that the vulcanisation process

is not truly reversible; however, an accepted definition for

devulcanisation is that it is a change in vulcanised rubber which results in

a decreased resistance to deformation at ordinary temperatures.

Reclaimed rubber is manufactured by suitable treatment to old and

worn out tyres, tubes and other used rubber articles with certain chemical

agents. A substantial devulcanisation or regeneration is effected to the

rubber compound in this process whereby its original plasticity is regained.

In short it may be stated that reclaiming is essentially a

depolymerisation process where the combined sulphur is not removed.

The reclaimed rubber is used in the manufacture of rubber goods, with or

without admixture of natural or synthetic rubber.

Recycled rubber can be more generally described as any sort of rubber

waste that has been converted into an economically useful form such

as reclaimed rubber, ground rubber, reprocessed synthetic rubber, and

die-cut punched parts.

One method of recycling some scrap rubber is to grind it as fine as

possible and work it into new rubber as an elastomeric filler. This was the

first method of reclaiming and is suitable only for compounding carriage

springs, which were fairly large barrel-shaped molded articles but not

suitable for footwear products.

In order to make a high-quality reclaim, the fibre must be removed

from the rubber scrap by soaking the rubber in water, and then taking a

small knife and starting the rubber from the cloth and stripping it off. But

this was not an effective way to produce large quantities of products.

TYPES OF RECLAIM

A variety of grades of reclaimed rubber is offered today, but mention

is made here of only the important ones.

Whole Tyre Reclaim

Whole tyre reclaim is the one produced in the largest quantity. Firstquality

reclaim made from whole tyres contains about 45% rubber hydrocarbon

by weight. The remaining 55% consists of valuable carbon

black, a little mineral filler, and softeners, all of which are substantially

unchanged by the reclaim manufacturing operation, and may be considered

to function as virgin materials. The manufacturing Minimum Staining Reclaim

Minimum staining reclaim can replace the conventional whole tyre

material when occasion demands. As implied, it has a much lower tendency

to stain, by either migration or contact, than conventional reclaim.

The reduction in staining characteristics is achieved by the use of activated-

carbon non-staining oils and by selecting tyres containing a higher

proportion of natural to synthetic rubber.

Drab and Coloured Reclaims

As the names imply, drab and coloured reclaims are made from nonblack

scrap. The digester process is usually employed and, when fabric is

present, a small addition of caustic is made in order to destroy it. The

period of heat treatment is usually several hours at 195°C.

Butyl Reclaim

Whereas reclaimed rubbers have been successfully produced from

scrap CR, NBR,SI, and other speciality rubbers, the only one of substantial

commercial importance is butyl reclaim. The starting material for this

is butyl inner tubes. A modified digester process is adopted, every precaution

being taken to avoid contamination by NR or SBR, because of

their adverse effect on the curing characteristics of the butyl. Extensive

control tests are necessary to ensure that the curing properties are satisfactory.

The nerve of butyl reclaim is much reduced compared with that

of the original polymer. Because of this, compounds containing butyl

reclaim will mix, calender, and extrude faster and more smoothly than

similar compounds based on virgin rubber.

Reclaimed Rubber

By the application of heat and chemical agents to ground vulcanised

waste rubber, a substantial regeneration of the rubber compound to its

original plastic state is effected, yielding a product known as ‘reclaim’ or

reclaimed rubber, capable of being processed, compounded, and

revulcanised. The process is essentially one of depolymerisation. Reclaimed

rubber has become widely accepted as a raw material which possesses

processing and economic characteristics that are of great value in

the compounding of natural and synthetic rubber stocks.

There are four principal reclaiming processes in use today, of which

the digester and reclaimator processes are important.

The raw material for reclaiming is scrap rubber in a wide variety of

forms, but tyres, as is to be expected, form the major quantity.

The first stage, in all processes, are the cracking and grinding of the

scrap rubber to reduce it to a crumb passing through a 20 to 30 mesh

screen.

Digester Process

At one time, most reclaim was made using the digester process. A

digester is essentially a steam-jacketed, agitator-equipped autoclave,

mounted either horizontally or vertically. This is a wet process in which

the coarsely ground scrap is submerged in a solution of water and reclaiming

agents. These agents may include many types of light and/or

heavy oils, naval stores, pine tar and coal tar pitches, and chemical

peptisers.

Until the advent of synthetic rubber, the digesting solution also included

caustic soda to remove free sulphur and to act as a defibring agent.

In fact, the process was generally referred to as the alkali digester

method.

The ground waste is loaded into a digester along with water, reclaiming

oils, and other additives, such as activated black (for minimum stain

ing grades). The digester is a cylindrical jacketed pressure vessel fitted

with a horizontal agitator, and steam can be supplied to both interior and

jacket, thus enabling a uniform temperature to be maintained throughout

the mass. The contents of the digester are then heated to about 190°C and

maintained at this temperature for some 4-10 hours with continuous agitation.

The digester is then ‘blown down’, and the contents deposited on

to a conveyor. Any necessary adjustments to the specific gravity and plasticity

by addition of plasticiser, carbon black, or fillers are carried out in

a ribbon blender, and the stock is then automatically conveyed to extruders

for straining, refining, and leafing on to a drum from which it is removed

in slabs.

Reclaimator Process

The reclaimator process is the only commercially successful continuous

technique for devulcanising tire scrap; all the others are batch

processes. Tyres are ground, the metal and fibre are mechanically separated,

then the rubber is further ground to a fine particle size. This fineground

rubber and the various reclaiming agents are all metered into a

blending system and conveyed to the reclaimator.

The reclaimator is a special type of screw-extrusion machine. It is

jacketed to provide for several zones of controlled temperature using either

hot oil or cooling water; in addition, the clearances between the screw

and the chamber wall are close and adjustable. The object is to subject

the rubber to a controlled amount of high heat and pressure in a continuously

moving environment. The residence time of the rubber in the machine

is less than 5 minutes. During this period, the rubber undergoes

devulcanisation. After the softened rubber is discharged from the head of

the machine, it is cooled and further processed in refining mills just as is

done in other reclaiming methods.

It can be shown that ground vulcanised rubber heated in a temperature

range of 120-200°C undergoes a rapid initial increase in plasticity,

and, on continued heating, passes through an inversion point and rehardens

unit, after prolonged heating, a further but slower increase in plasticity is

attained. It follows, therefore, that three points of equal plasticity occur

in this cycle. 

ABOUT NPCS

 

NIIR PROJECT CONSULTANCY SERVICES (NPCS) is a reliable name in the industrial world for offering integrated technical consultancy services. NPCS is manned by engineers, planners, specialists, financial experts, economic analysts and design specialists with extensive experience in the related industries.

Our various services are: Detailed Project Report,  Business Plan for Manufacturing Plant, Start-up Ideas, Business Ideas for Entrepreneurs, Start up Business Opportunities, entrepreneurship projects, Successful Business Plan, Industry Trends, Market Research, Manufacturing Process, Machinery, Raw Materials, project report, Cost and Revenue, Pre-feasibility study for Profitable Manufacturing Business, Project Identification, Project Feasibility and Market Study, Identification of Profitable Industrial Project Opportunities, Business Opportunities, Investment Opportunities for Most Profitable Business in India, Manufacturing Business Ideas, Preparation of Project Profile, Pre-Investment and Pre-Feasibility Study, Market Research Study, Preparation of Techno-Economic Feasibility Report, Identification and Section of Plant, Process, Equipment, General Guidance, Startup Help, Technical and Commercial Counseling for setting up new industrial project and Most Profitable Small Scale Business.

NPCS also publishes varies process technology, technical, reference, self employment and startup books, directory, business and industry database, bankable detailed project report, market research report on various industries, small scale industry and profit making business. Besides being used by manufacturers, industrialists and entrepreneurs, our publications are also used by professionals including project engineers, information services bureau, consultants and project consultancy firms as one of the input in their research.

Our Detailed Project report aims at providing all the critical data required by any entrepreneur vying to venture into Project. While expanding a current business or while venturing into new business, entrepreneurs are often faced with the dilemma of zeroing in on a suitable product/line.

 


And before diversifying/venturing into any product, wish to study the following aspects of the identified product:


• Good Present/Future Demand
• Export-Import Market Potential
• Raw Material & Manpower Availability
• Project Costs and Payback Period


We at NPCS, through our reliable expertise in the project consultancy and market research field, Provides exhaustive information about the project, which satisfies all the above mentioned requirements and has high growth potential in the markets. And through our report we aim to help you make sound and informed business decision.

 

The report contains all the data which will help an entrepreneur find answers to questions like:

• Why I should invest in this project?
• What will drive the growth of the product?
• What are the costs involved?
• What will be the market potential?


The report first focuses on enhancing the basic knowledge of the entrepreneur about the main product, by elucidating details like product definition, its uses and applications, industry segmentation as well as an overall overview of the industry sector in India. The report then helps an entrepreneur identify the target customer group of its product. It further helps in making sound investment decision by listing and then elaborating on factors that will contribute to the growth of product consumption in India and also talks about the foreign trade of the product along with the list of top importing and top exporting countries. Report includes graphical representation and forecasts of key data discussed in the above mentioned segment. It further explicates the growth potential of the product.

The report includes other market data like key players in the Industry segment along with their contact information and recent developments. It includes crucial information like raw material requirements, list of machinery and manufacturing process for the plant. Core project financials like plant capacity, costs involved in setting up of project, working capital requirements, projected revenue and profit are further listed in the report.


Reasons for buying the report:

• This report helps you to identify a profitable project for investing or diversifying into by throwing light to crucial areas like industry size, demand of the product and reasons for investing in the product.

• This report provides vital information on the product like its definition, characteristics and segmentation.

• This report helps you market and place the product correctly by identifying the target customer group of the product.

• This report helps you understand the viability of the project by disclosing details like raw materials required, manufacturing process, project costs and snapshot of other project financials.

• The report provides forecasts of key parameters which helps to anticipate the industry performance and make sound business decision.

 

Our Approach:


• Our research reports broadly cover Indian markets, present analysis, outlook and forecast.

• The market forecasts are developed on the basis of secondary research and are cross-validated through interactions with the industry players. 

• We use reliable sources of information and databases.  And information from such sources is processed by us and included in the report.

 

Our Market Survey cum Detailed Techno Economic Feasibility Report Contains following information:

 

 

Ø  Introduction

·         Project Introduction

·         Project Objective and Strategy

·         Concise History of the Product

·         Properties

·         BIS (Bureau of Indian Standards) Provision & Specification

·         Uses & Applications

 

Ø  Market Study and Assessment

·         Current Indian Market Scenario

·         Present Market Demand and Supply

·         Estimated Future Market Demand and Forecast

·         Statistics of Import & Export

·         Names & Addresses of Existing Units (Present Players)

·         Market Opportunity

 

Ø  Raw Material

·         List of Raw Materials

·         Properties of Raw Materials

·         Prescribed Quality of Raw Materials

·         List of Suppliers and Manufacturers

 

Ø  Personnel (Manpower) Requirements

·         Requirement of Staff & Labor (Skilled and Unskilled) Managerial, Technical, Office Staff and Marketing Personnel

 

Ø  Plant and Machinery

·         List of Plant & Machinery

·         Miscellaneous Items

·         Appliances & Equipments

·         Laboratory Equipments & Accessories

·         Electrification

·         Electric Load & Water

·         Maintenance Cost

·         Sources of Plant & Machinery (Suppliers and Manufacturers)

 

Ø  Manufacturing Process and Formulations

·         Detailed Process of Manufacture with Formulation

·         Packaging Required

·         Process Flow Sheet Diagram

 

Ø  Infrastructure and Utilities

·         Project Location

·         Requirement of Land Area

·         Rates of the Land

·         Built Up Area

·         Construction Schedule

·         Plant Layout and Requirement of Utilities

 

Project at a Glance

Along with financial details as under:

 

  •     Assumptions for Profitability workings

  •    Plant Economics

  •    Production Schedule

  •    Land & Building

            Factory Land & Building

            Site Development Expenses

  •    Plant & Machinery

             Indigenous Machineries

            Other Machineries (Miscellaneous, Laboratory etc.)

  •    Other Fixed Assets

            Furniture & Fixtures

            Pre-operative and Preliminary Expenses

            Technical Knowhow

            Provision of Contingencies

  •   Working Capital Requirement Per Month

             Raw Material

            Packing Material

            Lab & ETP Chemical Cost

           Consumable Store

  •   Overheads Required Per Month And Per Annum

         Utilities & Overheads (Power, Water and Fuel Expenses etc.)

             Royalty and Other Charges

            Selling and Distribution Expenses

  •    Salary and Wages

  •    Turnover Per Annum

  •   Share Capital

            Equity Capital

            Preference Share Capital

 

  •    Annexure 1:: Cost of Project and Means of Finance

  •    Annexure 2::  Profitability and Net Cash Accruals

                Revenue/Income/Realisation

                Expenses/Cost of Products/Services/Items

                Gross Profit

                Financial Charges     

                Total Cost of Sales

                Net Profit After Taxes

                Net Cash Accruals

  •   Annexure 3 :: Assessment of Working Capital requirements

                Current Assets

                Gross Working. Capital

                Current Liabilities

                Net Working Capital

                Working Note for Calculation of Work-in-process

  •    Annexure 4 :: Sources and Disposition of Funds

  •    Annexure 5 :: Projected Balance Sheets

                ROI (Average of Fixed Assets)

                RONW (Average of Share Capital)

                ROI (Average of Total Assets)

  •    Annexure 6 :: Profitability ratios

                D.S.C.R

                Earnings Per Share (EPS)

               

             Debt Equity Ratio

        Annexure 7   :: Break-Even Analysis

                Variable Cost & Expenses

                Semi-Var./Semi-Fixed Exp.

                Profit Volume Ratio (PVR)

                Fixed Expenses / Cost 

                B.E.P

  •   Annexure 8 to 11:: Sensitivity Analysis-Price/Volume

            Resultant N.P.B.T

            Resultant D.S.C.R

   Resultant PV Ratio

   Resultant DER

  Resultant ROI

          Resultant BEP

  •    Annexure 12 :: Shareholding Pattern and Stake Status

        Equity Capital

        Preference Share Capital

  •   Annexure 13 :: Quantitative Details-Output/Sales/Stocks

        Determined Capacity P.A of Products/Services

        Achievable Efficiency/Yield % of Products/Services/Items 

        Net Usable Load/Capacity of Products/Services/Items   

       Expected Sales/ Revenue/ Income of Products/ Services/ Items   

  •    Annexure 14 :: Product wise domestic Sales Realisation

  •    Annexure 15 :: Total Raw Material Cost

  •    Annexure 16 :: Raw Material Cost per unit

  •    Annexure 17 :: Total Lab & ETP Chemical Cost

  •    Annexure 18  :: Consumables, Store etc.,

  •    Annexure 19  :: Packing Material Cost

  •    Annexure 20  :: Packing Material Cost Per Unit

  •    Annexure 21 :: Employees Expenses

  •    Annexure 22 :: Fuel Expenses

  •    Annexure 23 :: Power/Electricity Expenses

  •    Annexure 24 :: Royalty & Other Charges

  •    Annexure 25 :: Repairs & Maintenance Exp.

  •    Annexure 26 :: Other Mfg. Expenses

  •    Annexure 27 :: Administration Expenses

  •    Annexure 28 :: Selling Expenses

  •    Annexure 29 :: Depreciation Charges – as per Books (Total)

  •   Annexure 30   :: Depreciation Charges – as per Books (P & M)

  •   Annexure 31   :: Depreciation Charges - As per IT Act WDV (Total)

  •   Annexure 32   :: Depreciation Charges - As per IT Act WDV (P & M)

  •   Annexure 33   :: Interest and Repayment - Term Loans

  •   Annexure 34   :: Tax on Profits

  •   Annexure 35   ::Projected Pay-Back Period And IRR