masterbatch (colour masterbatch)

Masterbatch is a solid additive system in which one or more active ingredients (pigments, dyes, or functional additives) are dispersed at high concentration (20–80% by weight) in a thermoplastic carrier resin, then granulated into pellets. When added to natural or recycled plastic at 1–5% loading during extrusion or injection moulding, the masterbatch disperses uniformly to impart the desired property. The carrier resin is typically matched or compatible with the base polymer being processed — LDPE carrier for PP or HDPE applications, PS carrier for ABS, PET carrier for PET. India has a well-developed masterbatch manufacturing industry, with major producers including Plastiblends India, Cabot India, and PolyOne (Avient India), as well as thousands of small compounders supplying regional converters.

Types of masterbatch relevant to recycled plastic processing: (1) Colour masterbatch — contains inorganic pigments (TiO₂ for white, carbon black for black, iron oxide or organic pigments for other colours); white masterbatch at 4–6% loading provides opacity and brightening in recycled polyolefins that tend to be grey or beige; cost Rs 80–200/kg; (2) UV stabiliser masterbatch — contains HALS (Hindered Amine Light Stabilisers) and/or UV absorbers; critical for rPP or rHDPE used in outdoor applications (pipes, crates, construction products) where virgin material's UV stabiliser has been consumed in the previous product life; cost Rs 150–400/kg; (3) Compatibiliser masterbatch — contains maleic anhydride-grafted polyolefins (MAH-g-PE, MAH-g-PP) that improve adhesion at phase boundaries in mixed-polymer recyclate (e.g. PP+PE blends from unsorted polyolefin streams); (4) Anti-oxidant masterbatch — provides thermal stabilisation during reprocessing, reducing chain scission and yellowing; essential for rPET and rPA (recycled nylon); (5) Flame retardant masterbatch — used in recycled engineering plastics (e-waste ABS, HIPS housing) where flame retardancy must be maintained or restored in the recycled product.

For recyclers producing recycled pellets for commercial sale, masterbatch is a quality-enabling investment. A white TiO₂ masterbatch at 4% loading on rHDPE transforms a grey, unattractive pellet (Rs 55/kg) into a white pellet that can substitute for virgin in packaging or construction applications (Rs 75–90/kg) — a Rs 20–35/kg value uplift for a masterbatch cost of Rs 3–8/kg (at 4% loading of Rs 80–200/kg masterbatch). However, masterbatch loading in food-contact recycled plastic must comply with FSSAI and EU 10/2011 migration limits — not all pigments approved for virgin use are necessarily safe in recycled material at equivalent loadings due to potential synergistic migration effects.

For e-waste recyclers recovering plastic housings (ABS, HIPS), re-compounding with appropriate flame retardant and UV masterbatch is the pathway to creating marketable engineering plastic recyclate rather than generic mixed-colour regrind. This requires a twin-screw compounding extruder (Rs 15–40 lakh) and flame retardant testing at a UL94-certified lab (Rs 8,000–20,000 per test). The investment is justified if the recycler can access a volume of homogeneous e-waste housing plastic (≥200 TPM) from a single equipment OEM or refurbisher — consistency of input determines consistency of output.