How to Grade and Sort Plastic Scrap: A Supplier's Practical Guide

Most of the value in a load of plastic scrap is decided before it leaves your yard. Two suppliers can collect the same material, yet the one who sorts and grades it carefully will find buyers faster, face fewer rejections and build repeat business. Buyers pay for predictability: they want to know that every bag in a lot behaves the same way in their machine.

This guide explains a practical way to grade and sort plastic scrap, from separating polymers to keeping lots apart in storage and on paper.

Start with the polymer

The first and most important split is by polymer. Different plastics melt at different temperatures and most do not mix well, so a small amount of the wrong material can spoil a whole lot. Keep separate stockpiles for at least PP, HDPE, LDPE and LLDPE film, PET, PVC and engineering plastics such as ABS.

Some combinations are especially troublesome. PVC in a PET stream causes problems in processing, and PP mixed into HDPE changes how the material flows and how finished parts perform. If you handle both, give them separate areas, separate bags and separate labels.

Identify material you are not sure about

Resin identification codes on products help, but they are often missing, worn or wrong. Use simple checks before you guess:

• Look at the product type: raffia bags and woven sacks are usually PP; milk crates and many drums are HDPE; carry bags and liners are LDPE or LLDPE film.
• Float test in water: PP (about 0.90-0.91 g/cm3) and PE (LDPE about 0.91-0.94, HDPE about 0.94-0.97) float, while PET (about 1.38), PVC and most engineering plastics sink.
• Feel and flexibility: film that stretches and is soft is likely LDPE or LLDPE; stiff, crinkly film may be PP or HDPE.
• Lab tests: for regular streams, an MFI and density test gives you numbers you can quote to buyers.

For more methods, see how to identify plastic types and the knowledge page on resin identification codes.

Grade by form and source

Within one polymer, separate material by what it is and where it came from. These affect how buyers will use it.

Split by	Typical categories	Why it matters
Form	Lumps, purgings, film, rigid parts, regrind, flakes	Each needs different processing and goes to different buyers
Source	Post-industrial or post-consumer	Post-industrial material is usually cleaner and more consistent
Process	Injection, blow moulding, extrusion, film	Hints at the flow grade, and so the MFI range
Condition	Washed, unwashed, printed, unprinted	Decides how much cleaning the buyer must do

Post-industrial scrap from a single factory and a single process is the easiest material to grade, because its properties stay close from one lot to the next. Post-consumer material needs more checking and is usually sold with wider tolerances.

Sort by colour

Colour is a separate grade in its own right. A common sequence is natural or transparent, white, light single colours, dark single colours, mixed colours and black. Natural and white lots can be used for almost any colour of finished product, so they have the widest buyer base. Mixed colours usually end up black or dark grey. Once colours are mixed, they cannot be separated again, so sort early.

Keep lots separate, physically and on paper

A lot is a quantity of material that you are willing to describe with one set of specifications. To keep it meaningful:

1. Give each lot a simple reference, such as the polymer, form and date.
2. Store each lot in its own marked area, with bags facing out so labels can be read.
3. Do not top up an old lot with new material from a different source.
4. Record the source, quantity, colour and any test values against the lot reference.
5. Keep a retained sample from each lot until the buyer has accepted delivery.

When a buyer approves a sample and later receives material that does not match, the lot record and retained sample are what let you work out what went wrong. Our recycled plastic quality checklist lists the points buyers usually check on arrival.

Describe grades honestly

Write down what you have actually sorted, not what you hope it is. If a lot is mostly PP with some PE, say so. If there is label paper or sand, mention it. An accurate description lets the right buyer say yes; an optimistic one leads to a rejected load and freight costs on the return trip.

Listing graded material

Once your material is sorted into clear lots with specifications, it is ready to offer. PlasticSetu runs a sourcing desk that matches buyer requirements to supplier listings, which stay private to you and the desk. See how selling works, then list your materials with polymer, form, colour, source and quantity for each lot.