The short answer
At the dock, match the PO, packing list and COA to the labels on every package, check that boxes and liners are dry and sealed, and keep a labeled retain from each lot. Then run quick checks: moisture, melt flow against the COA, a visual check for color and contamination, and density or ash on filled grades. To qualify a new source, review documents first, test a sample, run a trial in the production mold with dimensional and functional checks, get customer approval or PPAP where required, and record lot traceability.
Many resin problems can be caught before the material reaches a hopper. This is a procedure you can hand to receiving and quality. For why you want a second source, see why you need a second source; for matching a different grade, see how to find an equivalent grade.
Before the truck arrives
Ask the supplier to email the COA when the order ships, so you can review it before the material lands. Give receiving the PO, grade, color, number of packages and expected weight. If the lot numbers are on the COA ahead of time, the dock check takes minutes.
At the dock
- Paperwork. The bill of lading, packing list and PO agree on grade, color and quantity. Every lot number on the packing list has a COA. See what a COA shows.
- Count and condition. Count the packages. Look for crushed or wet gaylords, torn or open liners, punctured bags and loose wrap. Write any damage on the bill of lading before you sign, and photograph it. A clean signature makes a freight claim much harder.
- Labels. Each gaylord or bag shows the grade, color and lot, and the lot matches a COA. One lot per package is normal. Covered, handwritten or replaced labels deserve a question; see resin supplier scams for the warning signs.
- Temperature. In cold weather, leave sealed packages to warm up before opening, or condensation will wet the pellets. More in storing resin and moisture pickup.
Keep a retain from every lot
Take a sample of about 1–2 lb (0.5–1 kg) from each lot, from a freshly opened package. Seal it in a moisture-barrier bag or jar and label it with grade, color, lot, PO and date received. Keep it for as long as your quality system or customer requires. If parts fail in the field a year later, the retain is the only way to retest what you actually ran. Retains of hygroscopic resins pick up moisture over time, so dry them before any melt flow test. Resin shelf life covers how long stock keeps.
Quick tests and what to do when one fails
| Check | How | Acceptance guidance | If it fails |
|---|---|---|---|
| Paperwork | PO, packing list, bill of lading and COA against what arrived | Grade, color, quantity and every lot number agree | Hold the lot; ask the supplier for the missing or corrected document before use |
| Packaging | Look at every package at the dock | Boxes dry and square; liners sealed; bags not punctured; pallets wrapped | Note it on the bill of lading before signing, photograph, quarantine, file a freight claim |
| Labels | Each package against the COA | Grade, color and lot on every label; each lot has a COA | Hold; relabeled or unlabeled packages need an explanation from the supplier |
| Moisture | Loss-in-weight analyzer or Karl Fischer, as received and after drying | After drying, within the data sheet target (for example 0.02% or less for PC) | Check the dryer and dry longer; tell the supplier if as-received moisture is unusually high |
| Melt flow (MFR/MVR) | ASTM D1238 or ISO 1133 at the COA's temperature and load, on dried resin | Within the producer's spec; many molders flag about 10–20% off the COA value | Retest, test the retain; if confirmed, hold and send data to the supplier |
| Color and contamination | Spread pellets on a white tray; compare with the retain or color standard; mold a plaque | No foreign pellets, specks, fines or odd colors; color matches the standard | Quarantine and photograph; check whether it is one package or the whole lot |
| Density | ASTM D792 or ISO 1183 | Usually within about 0.01–0.02 g/cm³ of the data sheet or COA | Suspect the wrong grade or filler level; run an ash test |
| Ash (filled grades) | ASTM D5630 or ISO 3451, muffle furnace | Within the producer's range, often about ±2 points of nominal (28–32% for a GF30) | Hold; wrong filler content changes shrinkage, stiffness and the part |
Typical guidance only. The producer's specification and your customer's requirements set the real limits, and values vary by grade. Agree on test methods with your supplier before a dispute, not during one.
Melt flow is the check most worth doing in-house. Test at the same temperature and load the COA uses, for example 230°C / 446°F and 2.16 kg for polypropylene or 300°C / 572°F and 1.2 kg for polycarbonate. Wet PC, PET or nylon can read far higher than the COA because water breaks the chains in the barrel, so dry the sample first. See melt flow index explained and the resin drying guide.
Qualifying a new source
- Documents first. Get the data sheet, a recent COA (several lots if possible), the SDS and the compliance documents your customers need; see resin compliance documents. For the same grade from a new distributor, confirm it ships in the producer's original packaging with the producer's lot numbers.
- Test the sample. Run moisture, melt flow, density or ash and color on the sample, and compare against its COA and against a retain of your current material.
- Trial run. Use the production mold, starting from your current process. Record every setting you change. Run long enough for the process to settle; many shops run at least a full shift or a few hundred parts.
- Dimensional checks. Measure after parts have cooled and stabilized, often 24 hours or more, and longer for nylon, which keeps changing as it absorbs moisture. Compare with the drawing and with parts from the current material, including capability on critical dimensions if your customer requires it.
- Functional checks. Assembly, snap fits, torque, drop or impact, heat or chemical exposure, color and gloss: whatever the part sees in service.
- Approval. For production automotive parts, a change of material or material source normally requires customer notification and, unless the customer waives it, a new PPAP submission before shipping. Medical and other regulated parts go through the customer's change control. If the drawing names a grade, any change needs the customer's sign-off.
- Records. Add the source to your approved supplier list and file the trial report, test data and retains together.
Lot traceability
Record which resin lot went into which work order, press and shipment. Keep the COA, the retain and the receiving record under the same lot number. When a customer reports a problem, you want to name the lot, pull its COA and retest its retain within an hour, not spend a week reconstructing it.
How we can help
Every lot we supply ships with a COA, and labels carry the grade and lot number. Samples of about 50 lb are available upon credit approval for your qualification trial, and a polymer chemist reviews every request. Orders start at one gaylord, FOB the warehouse. We aim to send your quote within one to three business days.
Common questions
What should I check when resin arrives?
Match the PO, packing list and COA to what is on the truck, check every package label for grade, color and lot number, look for crushed boxes, torn liners or water, and note any damage on the bill of lading before you sign.
How much melt flow difference from the COA is acceptable?
The producer's specification range is the limit that counts. Many molders flag an in-house result more than about 10–20% away from the COA value, because melt flow repeatability between labs is wide; dry hygroscopic resins first, or the result reads high.
Why keep a retain sample of every resin lot?
A sealed, labeled retain lets you retest the actual lot if parts fail months later, compare it with a new lot, and settle a dispute with the supplier with evidence rather than memory.
How long should I keep resin retain samples?
As long as your quality system or customer requires. Many shops keep them for at least the warranty or service period of the parts, and automotive and medical customers often set a minimum.
What should I do if a resin lot fails incoming inspection?
Tag it on hold and keep it apart, photograph it, keep a retain, and contact the supplier with the lot number and your test data before you use or return any of it.
Does a new resin source need PPAP?
For production automotive parts, a change of material or material source normally requires customer notification and, unless the customer waives it, a new PPAP submission before you ship parts. Check your customer's requirements.
Is the same grade from a new distributor a new source?
It is the same product, so it is usually not a material change, but it is a new supplier, and many automotive customers want notice of a supplier change. Check that it arrives in the producer's original packaging with lot traceability, and confirm whether your customer wants notice.
Tell us the grade you want to qualify
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province