Plastic Materials: PP, PE, PVC, ABS & Engineering Resins

What Buyers Compare in Plastic Materials

Two quotes for the same "PP" can differ by a factor of three in price and behave nothing alike in production. The difference is almost never the resin family — it is the grade: its melt flow, its filler loading, its impact modification and the certificates that ship with it. Buyers sourcing from Chinese compounders and distributors usually narrow the field on four things: the processing method the part needs, the service temperature, the surface and colour requirement, and the compliance regime the finished product falls under.

Family	Typical use	What to specify first
PP (homopolymer / copolymer)	Containers, caps, automotive trim, housewares	Melt flow rate, impact grade, food-contact status
HDPE / LDPE / LLDPE	Bottles, film, pipe, crates	Density, MFI, film gauge or wall thickness
PVC (rigid / flexible)	Profiles, pipe, cable, sheet	Plasticiser type and phr, stabiliser system
ABS / PS / SAN	Housings, appliances, toys	Impact strength, gloss level, flame class
PET / rPET	Bottles, sheet, fibre	Intrinsic viscosity, food-grade certification
PA, POM, PBT, PC	Gears, housings, connectors, lenses	Glass or mineral loading, moisture conditioning
PPS, PEEK, PEI, PSU	Under-hood, electrical, medical	Continuous service temperature, UL yellow card
PLA, PBAT, PHA, starch blends	Single-use packaging, film	Certified compostability standard, shelf life

Specify the Grade, Not Just the Resin Name

A purchase order that says "PP, white" leaves the supplier free to ship whatever is in stock. State the parameters that drive your process and your part:

Melt flow rate or MVR — with the test condition (for example 230 °C / 2.16 kg), because a number without a condition is meaningless.
Density and filler content — 20% or 30% glass fibre, talc, calcium carbonate or flame-retardant package, stated as a percentage with tolerance.
Mechanical targets — tensile strength, flexural modulus, notched Izod impact, elongation at break.
Thermal limits — HDT at a stated load, Vicat softening point, continuous service temperature.
Flammability — the UL 94 class you need (HB, V-2, V-0, 5VA) and the wall thickness at which it was tested.
Colour control — a Pantone or RAL reference plus the acceptable ΔE, and whether the colour is pre-compounded or let down from a masterbatch at your plant.

Documents to Request Before You Approve a Resin

Compliance paperwork is where cheap offers fall apart. Ask for these with the quotation, not after the deposit:

COA per production lot — so incoming inspection has something to measure against.
Technical data sheet — the properties you are contracting on, with test methods.
Safety data sheet — required for transport and for your own EHS review.
REACH SVHC declaration — current candidate list version, not a three-year-old letter.
RoHS statement — for electrical and electronic applications.
Food-contact evidence — EU 10/2011 declaration of compliance or US FDA 21 CFR 177 status, depending on your market.
UL yellow card — if the part needs a recognised flame rating rather than a self-declaration.

Three Mistakes That Cost Buyers Money

Buying on price per kilogram alone. A 6% cheaper compound with a higher filler load can raise scrap rates and cycle time enough to wipe out the saving.
Accepting a grade substitution without a trial. "Equivalent" resins differ in shrinkage, and shrinkage is what decides whether your mould produces a part or a reject.
Ignoring regrind policy. Agree in writing how much regrind may be blended, from which parts, and whether it applies to food-contact or load-bearing components at all.

Frequently Asked Questions

What is the minimum order for plastic raw materials from China?

It depends on whether you buy compound or resin. Compounders often quote from one 25 kg bag for a sample and from one pallet or one tonne for a production run, while polymer producers and authorised distributors typically sell full 25 kg bags by the pallet or the 20-foot container. Always confirm whether the quoted price is FOB, CIF or EXW, and whether the MOQ applies per grade or per order.

How do I verify a supplier's resin is genuine and not reprocessed?

Ask for the lot number, the COA that matches it, and the original packaging in photographs before shipment. Request a third-party test — MFI, density, ash content and DSC are enough to separate virgin from heavily reprocessed material — and make acceptance conditional on that result.

Can I get food-contact certified material?

Yes, but the certificate must cover the specific grade, not the resin family. Ask for a declaration of compliance that names the grade, states the migration test conditions, and is issued for your destination market. Keep in mind that food-contact status can be lost in processing if you add non-compliant masterbatch or regrind.

What does "glass-filled 30%" actually mean in a quote?

It means the compound contains roughly 30% glass fibre by weight, but the properties still depend on fibre length retention, coupling agent and the base resin. Two 30% GF nylons can differ by 30% in tensile strength, so ask for the data sheet rather than assuming equivalence.