What Is Compostable Masterbatch?
Masterbatch is a concentrated mix of pigment or additive dispersed in a carrier resin, made as small pellets that a converter blends into a base resin at a low dosage during extrusion or moulding. Compostable masterbatch uses a compostable carrier resin (commonly PBAT, PLA or PBS) instead of ordinary polyethylene, so the carrier itself does not interfere with composting.
The idea is simple: instead of dosing raw pigment powder into a machine, which is messy and hard to control, the pigment is pre-dispersed into pellets. The converter then adds a small, measured percentage of masterbatch to the main compostable resin to get consistent colour or performance across a production run.
How Is Compostable Masterbatch Different From Ordinary Masterbatch?
Compostable masterbatch differs from ordinary masterbatch mainly in its carrier resin and pigment selection: the carrier itself must be compostable, and the pigments or additives must not leave heavy metals or persistent residues behind. Ordinary masterbatch is usually built around a polyethylene or polypropylene carrier with no such constraint.
A masterbatch built for polyethylene will not disperse well in a PBAT or PLA resin, and can drag in carriers or fillers that fail IS/ISO 17088's test requirements: disintegration within a set time, biodegradation, and heavy metal limits. So 'compostable' has to be a property of the whole formulated masterbatch, not an assumption based on the base resin alone.
What Goes Into a Compostable Masterbatch?
A compostable masterbatch typically combines three things: a compostable carrier resin, the active ingredient (a pigment, a UV stabiliser, a slip or anti-block additive, or a filler), and a dispersing agent that helps the active ingredient blend evenly through the carrier. Carrier resin usually makes up roughly half to two-thirds of the masterbatch by weight, with the rest split between the active ingredient and dispersant.
PBAT is a common carrier choice because its lower melting point lets pigments disperse well at temperatures below where PLA-based systems start to degrade. Pigment selection matters too: inorganic pigments containing heavy metals such as cadmium or lead are excluded, since even trace amounts can push a batch of coloured finished product over CPCB's compostability testing limits.
How Much Masterbatch Goes Into a Production Run?
Compostable colour masterbatch is usually dosed at a low percentage, commonly in the range of roughly 1 to 5 percent of the total resin weight (the 'letdown ratio'), depending on how deep the required colour is and whether the part is opaque or translucent. Additive masterbatches for functions like slip or anti-static run at similar or slightly different dosages depending on the effect needed.
Because the dosage is small, a converter's dosing accuracy matters as much as the masterbatch quality itself. Uneven dosing shows up as colour streaking or inconsistent performance across a roll or batch, so it is worth checking a supplier's letdown recommendation and running a trial before committing to a full production run.
Why Can the Wrong Masterbatch Void a Compostability Claim?
A finished compostable product is certified as a whole, not resin by resin, so every component added at the extruder, including masterbatch, has to pass the same IS/ISO 17088 tests: disintegration, biodegradation, ecotoxicity (plant growth), and heavy metal content. A masterbatch carrier that is not itself compostable, or a pigment carrying restricted heavy metals, can fail the finished article even when the base resin alone would have passed.
This is why buyers should ask for test data on the actual coloured or additised product, not just the natural, uncoloured resin. A supplier's IS 17088 certificate for its base granule does not automatically cover what happens once masterbatch is added on your line.
How Should Buyers Evaluate a Compostable Masterbatch Supplier?
Ask for three things before buying: the carrier resin used in the masterbatch, confirmation that it is designed for compostable base resins rather than adapted from a conventional plastics line, and test data (or a commitment to test) on the finished coloured or additised product against IS/ISO 17088. A supplier that cannot answer these clearly is a certification risk, not just a quality one.
Anjaneya Bio Products manufactures compostable masterbatch alongside its compostable granules, films and bags, so colour and additive formulations are developed and tested to hold up under the same IS/ISO 17088 and CPCB requirements as the base resin.
Key takeaway
Compostable masterbatch must be compostable in its own right, carrier resin, pigment and additive included, because the finished coloured or additised product is what gets tested against IS/ISO 17088, not the base resin alone. Buyers should ask for test data on the actual finished article before committing to a masterbatch and a production run.