Plastic Compounding & Coloring Chemicals

Thermal stability (often 260–320°C for engineering plastics), lightfastness, and chemical resistance to processing conditions are the key criteria. Inorganic pigments (TiO2, iron oxides, mixed metal oxides) provide the best heat stability and lightfastness. Organic pigments must be heat-stable grades engineered for plastics — DPP reds, quinacridone, and phthalocyanine grades with good dispersibility and migration resistance.

A masterbatch is a concentrated blend of pigments (and/or additives) dispersed in a carrier resin, produced by twin-screw compounding. It allows accurate dosing of small quantities of colorant into bulk resin without the hazards of handling fine pigment powders. Typical pigment loading is 20–60%. Carrier resin compatibility with the target polymer is critical — PP carrier for PP coloring, LDPE carrier for PE, etc.

Antioxidants (hindered phenols, phosphite types) prevent thermo-oxidative degradation during processing. UV stabilizers (HALS, benzotriazoles) extend outdoor service life. Impact modifiers (rubber-toughened acrylics, SBS, SEBS, core-shell impact modifiers) improve low-temperature toughness. Flame retardants (halogenated, ATH, red phosphorus) are compounded for electrical and building applications.

Dispersion quality is measured by extruding the masterbatch (or a let-down sample) into thin film and counting undispersed particles >10 µm by optical analysis. ASTM D2663 and DIN 53775 define dispersion ratings. Filter pressure value (FPV) — pressure rise across a fine screen during extrusion — is an alternative quick test. Good dispersion ensures consistent color and physical properties in the final molded part.

Food-contact plastics must comply with FDA 21 CFR 177 (USA), EU Regulation 10/2011 (EU), and GB 4806 (China). Pigments, additives, and modifiers must appear in positive lists for the specific polymer family. Migration testing in food simulants validates compliance. Recycled plastics must meet purity and traceability requirements (FDA Letter of No Objection or EFSA opinion).

PLA, PBAT, and other biopolymers are compounded with natural fibers (kenaf, flax, wood flour) in twin-screw extruders. Compatibilizers (maleic anhydride-grafted polymer) improve fiber-matrix bonding. Processing temperature must be controlled to avoid fiber thermal degradation (<200°C). Coupling agents and thermal stabilizers are added for better mechanical performance. Bio-based composites are increasingly specified for automotive interior trim and consumer packaging.