Sampling and Lot Acceptance for Recycled Plastic: A Buyer's Guide

Recycled plastic varies more than virgin resin. Two lots from the same supplier can differ in MFI, moisture, colour and contamination, and even bags within one lot can differ. A clear sampling and acceptance routine protects your production line and gives both you and your supplier a fair basis for decisions.

This guide covers how to take representative samples, what to keep, how to set acceptance criteria and how to handle disputes without losing a good supplier.

Approve a pre-shipment sample first

Before you order in bulk, test a sample of the actual lot you will receive, not a general "type sample". Ask the supplier to draw it from the lot and label it with the lot reference. Run your lab checks and, ideally, a short trial on your machine.

Once approved, split the sample. Keep part of it sealed and labelled as the reference, and tell the supplier you have done so. The bulk delivery is then judged against this reference.

How to sample a delivered lot

A single scoop from the top bag tells you very little. To get a representative picture:

1. Sample several bags: select bags from different parts of the truck or stack, not just the easiest ones to reach.
2. Sample within each bag: take material from the top, middle and bottom. A sampling spear or probe helps with jumbo bags.
3. Combine and reduce: mix the increments thoroughly, then divide into smaller portions by quartering or a sample divider.
4. Label everything: lot number, date, invoice reference, truck number and which bags were sampled.
5. Record visual checks: photograph bag condition, labels, any wet or damaged bags and visible contamination before unloading fully.

The number of bags to sample depends on lot size and how much variation you have seen before. Agree a method with your supplier in advance so neither side can question it later.

What to test on arrival

Keep the arrival checks quick and focused on what affects your process:

• MFI, per ASTM D1238 or ISO 1133 at the standard condition for the polymer;
• moisture content, especially for washed material and hygroscopic polymers such as PET, ABS, PC and nylon;
• ash content to detect filler or dirt;
• density or a simple float test to catch mixed polymers;
• colour against the retained sample, under the same light;
• visible contamination, gels or specks in a pressed sheet or trial part.

Our recycled plastic quality checklist lists these in one place.

Set acceptance criteria in writing

Acceptance criteria should be agreed before the order, not after a problem. For each important property, write a target and a tolerance, and say what happens if a lot falls outside it:

• accept as is;
• accept with a price adjustment agreed in advance;
• use it only in a lower-grade product;
• reject and return, with clarity on who pays freight.

Also agree the time window for raising a complaint after delivery. Suppliers reasonably expect issues to be raised promptly, before the material is mixed into production.

Retained samples

Keep a retained sample from every approved lot and from every delivery, sealed and labelled, for an agreed period. Store them dry and out of sunlight. Retained samples let you:

• compare a problem lot against the approved reference;
• show the supplier exactly what changed;
• trace a field complaint back to a specific lot.

Third-party labs and dispute handling

Most disagreements are settled by sharing test results and photos. When they are not, an independent lab is the fair referee. Agree in advance which lab, which test methods, and who pays; a common rule is that the side whose figure proves wrong bears the cost.

When a dispute arises:

1. Stop using the lot and isolate it.
2. Share photos, test results and the sampling record with the supplier.
3. Offer a joint sample, sealed in front of both parties or their representatives.
4. Send it to the agreed lab if needed, and settle according to the terms you agreed.

For more on choosing suppliers who handle this well, see our supplier checklist and negotiating recycled plastic quotes.

Samples and dispatch tracking through PlasticSetu

PlasticSetu's sourcing desk collects quotations from verified suppliers against your written requirement, arranges samples before you order, and tracks dispatch and delivery. Including your acceptance criteria in the requirement helps suppliers quote accurately. Get quotes to begin.