Of all the indicators on the published specification, residual vinyl chloride is the one that decides whether a resin can be used at all in a regulated application. It is also the figure most buyers have questions about, because it is a chemical limit rather than a processing one. This guide covers what it measures, what the manufacturer commits to, and how to check it on arrival.
What the figure measures
Vinyl chloride monomer is the raw material of PVC polymerisation. Polymerisation converts the great majority of it into the polymer, but a small amount remains trapped in the resin grains after the reaction — the residual vinyl chloride, quoted in milligrams per gram of resin.
It is a specification figure like impurity count or volatile matter: measured per batch, reported on the certificate of analysis, and held within the limits published for the grade level.
The published limits
| Grade level | Residual vinyl chloride |
|---|---|
| Premium | 8 mg/g |
| First grade | 10 mg/g |
| Qualified | not specified |
The limits apply across the whole range — SG1 to SG8 alike — so the grade you choose does not change this figure; the grade level does.
The qualified row is the one to read carefully. Like the fish eye figure, the residual vinyl chloride limit is simply not specified at the qualified level. That is not a promise that qualified resin exceeds 10 mg/g; it is a statement that the specification makes no commitment at all at that level. For any application where the figure matters — and if you are reading this guide, it probably matters — the qualified level is not the right specification. Order premium or first grade and get the commitment in writing.
Why it tends to sit at the top of the buyer's checklist
Vinyl chloride is a regulated substance, and finished-goods standards for PVC products — particularly anything with a food-contact, drinking-water or medical-adjacent use — put a limit on the residual monomer in the product. When a downstream customer or an import inspector reviews a PVC product, this is among the first figures they ask to see.
That makes the resin figure an input to your own compliance work rather than a formality. The lower and better-documented the incoming figure is, the less explaining your finished product has to do.
Checking it on the certificate
The certificate of analysis that travels with each shipment reports the measured value for the batch. Compare it against the published limit for the grade level you ordered — 8 mg/g on a premium order, 10 on first grade.
Two practical points:
- Check the grade level on the certificate matches the order. A premium price paid against a first-grade certificate is a claim waiting to happen, and the residual figure is where the difference shows first.
- File it with the batch. If your finished product is ever asked to demonstrate compliance, the trail runs from your product back through your formulation to the resin certificate. Reconstructing that trail afterwards is far more expensive than keeping it as you go.
The claim window for quality disputes is 30 days from discharge in writing, so the certificate check belongs at arrival, not at the point of use.
Resin figure versus finished-product figure
The specification limit applies to the resin. Processing changes the picture: the heat history the compound sees in extrusion or moulding reduces the residual monomer further, so the finished product normally carries a lower figure than the resin it came from. What that final figure is, and what limit it has to meet, depends on your process and your market — the resin certificate is the starting point of that calculation, not the end of it.
If your application has a residual limit attached to it, tell us the end use when you enquire and we will confirm which grade level we can hold the figure for, batch by batch.