Colour Sorting and Consistency in Recycled Plastic: A Guide

Colour is one of the first things a buyer notices about recycled plastic and one of the most common reasons for complaints. A manufacturer who approves a light grey sample and then receives a darker, greenish lot has a real problem, even if every other property is the same. For suppliers, colour control is often what separates a one-time sale from a regular customer.

This guide explains the usual colour grades, why colour drifts, and what suppliers and buyers can do to keep it consistent.

The usual colour grades

Grade	Typical sources	Typical use
Natural or transparent	Unprinted film, natural containers, clean post-industrial scrap	Any colour, including light colours
White	White containers, white film, white parts	White and light coloured products
Single colour	Sorted coloured crates, parts or film	Same or darker colours
Mixed colour	Unsorted coloured scrap	Dark colours, grey or black
Black	Black scrap or mixed colours made black	Black products only

The lighter the grade, the more applications it can serve, because a dark colour can always be added but cannot be taken out. That is why sorting by colour early matters so much. See black recycled granules for more on the darkest grade.

Why colour drifts between lots

• Changing feed: post-consumer scrap varies from week to week, so the mix of colours changes.
• Printing and labels: ink on film and residues of labels add colour when melted.
• Heat history: overheating during grinding, agglomeration or pelletising can yellow or darken the plastic.
• Contamination: small amounts of another coloured polymer can tint a whole batch.
• Fillers: talc, calcium carbonate and other fillers change shade and opacity.

What suppliers can do

Sort by colour before size reduction and keep each colour grade in its own lot. Keep pelletising temperatures within a sensible range to avoid yellowing. Most importantly, keep a retained sample from every lot and compare new lots against an approved reference under the same light. Daylight or a consistent lamp is better than mixed workshop lighting.

When describing colour, be specific: light grey, dark grey, off-white, natural with slight yellow tint. A photo of granules next to a white sheet of paper helps buyers judge shade.

Blending lots for consistency

Large recyclers often blend several production lots in a mixing silo or by mixing bags in a fixed ratio. This averages out small differences so that each delivered lot is closer to the reference. Blending only works within a grade: mixing a white lot with a dark lot will simply produce a new grey. Record which lots went into each blend so problems can be traced.

Using masterbatch

Masterbatch is a concentrate of pigment in a carrier polymer. Suppliers sometimes add it during pelletising to bring every lot to the same target shade, for example a standard grey or black. Buyers often add their own masterbatch at the machine. A few points to keep in mind:

• the masterbatch carrier should be compatible with the base polymer;
• a lighter, consistent base needs less masterbatch to reach a given colour;
• darker or variable bases can make bright colours impossible to hit;
• black masterbatch can hide colour variation but limits the product to black.

Judging colour fairly

Colour should be judged the same way by both sides. Compare granules or moulded plaques rather than loose regrind, since particle size and surface texture change how colour looks. Use the same light source each time and place the new sample beside the reference, not from memory. If the buyer uses masterbatch, compare finished parts made with the usual dosage, because that is what their own customer will see.

What buyers should specify

Buyers can avoid most colour disputes by stating, in the requirement, the colour grade, whether slight variation is acceptable, whether they will add masterbatch, and how colour will be judged on arrival. Ask for a sample, keep it as the reference, and compare each delivery against it. See how to write a plastic RFQ and sampling and lot acceptance.

Colour matters across polymers, from recycled PP granules and recycled HDPE granules to recycled ABS.

On PlasticSetu

Buyers can get quotes by stating the colour grade they need, and the sourcing desk will arrange samples from matching suppliers. Suppliers can list your materials with a clear colour description and photos for each grade.