Plastics fall into two classes: thermoplastic and thermosetting. Thermoplastics soften or melt reversibly on heating; they include celluloid and other cellulose plastics, lucite, nylon, polythene, styrene polymers, vinyl polymers, polyformaldehyde, and polycarbonates. Thermosetting plastics, although moldable when produced as simple polymers, are converted by heat and pressure, and sometimes by an admixed hardener, to a cross-linked, infusible form. These include Bakelite and other phenol resins, epoxy resins, polyesters, silicones, urea-formaldehyde, and melanine-formaldehyde resins, and some polyurethanes.
Most plastics are mixed with stabilizers, fillers, dyes, or pigments and plasticizers if needed. There are several fabrication processes: making films by calendering (squeezing between rollers), casting or extrusion, and making objects by compression molding, injection molding (melting and forcing into a cooled mold) and casting.
The plastics industry began in 1872 with the manufacture of celluloid by the US inventor John W. Hyatt.
Related categories INDUSTRIAL CHEMISTRY
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