Synthetic resins are materials with a property ofinterest that is similar to natural plant resins: they are viscous liquids thatare capable of hardening permanently. Otherwise, chemically they are very differentfrom the various resinous compounds secreted by plants. Synthetic resinscomprise a large class of synthetic products that have some of the physicalproperties of natural resins but are different chemically. Synthetic resins arenot clearly differentiated from plastics.
In modern industry natural resins have been almostentirely replaced by synthetic resins, which are divided into two classes,thermoplastic resins, which remain plastic after heat treatment, andthermosetting resins, which become insoluble and infusible on heating. Thermoplasticresin softens repeatedly by heating. Thermosetting resin, on the other hand,hardens only once when heated. Thermoplastics produced by the local industryinclude Polystyrene (PS), Polyvinyl Chloride (PVC), Alkyds and Polyester Fiber,while those of thermosetting resins include Phthalic Anhydride, Aluminum PasteResin, Adhesive Resin, Acrylic Resin Urea- and Phenol-Formaldehyde, and ColoredPellets.