Resins, plastic, definition thermosets

Plastics are subidivided into two types thermoplastic and thermosetting. The thermoplastics can be softened by heat and hardened again by subsequent cooling. This process is reversible and can be repeated many times. By contrast, the thermosetting resins are first softened and melted and, at subsequent heating to a definite temperature, they are irreversibly hardened, becoming insoluble [53]. 

Alkyd resins have been the workhorse for the coatings industry over the last half century. The term alkyd was coined to define the reaction product of polyhydric alcohols and polybasic acids, in other words, polyesters. However, its definition has been narrowed to include only those polyesters containing monobasic acids, usually long-chain fatty acids. Thus thermoplastic polyesters typified by polyethylene terephthalate (PET) used in synthetic fibers, films, and plastics and unsaturated polyesters typified by the condensation product of glycols and unsaturated dibasic acids (which are widely used in conjunction with vinylic monomers in making sheet molding compounds or other thermosetting molded plastics) are not considered as part of the alkyd family and are beyond the scope of the present discussion. 

Synonyms Condensation prods., epoxy Epoxides, polymers, epoxy resins Epoxy compds. Ethers, cyclic, epoxides, polymers Plastics, epoxy Polyethers, epoxy resins Classification Polymer Definition A thermosetting resin based on the reactivity of the epoxide group Toxicology LD50 (oral, rat) 2200 mg/kg strong skin irritant in uncured state poison by inhalation moderately toxic by ingestion little or no toxicity in cured state Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of Cr... 

Classification Thermosetting resin Definition Plastic derived from furfuryl alcohol or from furfural or reaction prods, of furfural and a ketone cured resins char, by heat/fire/chem. resist. 

Premix ( gunk ) n. A term originally apphed to mixtures of polyester resin with sisal or glass-fiber reinforcement and fillers, usually prepared by molders shortly before use. The ASTM definition (D 883) specifies that the premix should not be in web or filamentous form. The term premix is now often used by molding compounds of any thermosetting resin mixed with fillers, reinforcements, and catalysts. Strong AB (2000) Plastics materials and processing. Prentice-Hall, Columbus, OH. 

---