Phenolic molding scrap

Phenolic molding scrap is accepted back by some producers for re-use as filler in new compounds. Similarly, amino plastics (urea and melamine) present no problems in disposal or re-use when ground up. Molders have reused as much as 20 AVt% ground scrap with virgin molding compounds in injection molding and those who have adopted the technique have foimd it an effective method for recycling in-house scrap, but for sub-surface parts only. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

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