Extrusion Scorching and Discoloration: The Problem Is Usually in One of These Places

1. First, Tell Them Apart: Scorching or Discoloration?

Extrusion problems look similar, but they are actually two different things. Scorching is localized charring: black spots, scorch marks, a burnt smell, and in severe cases burnt material and line breakage. Discoloration is overall yellowing, darkening, and an unclean base color. If you can't tell them apart, you can't fix them properly: scorching usually points to temperature and residence time, while discoloration points first to whether heat stability is sufficient and initial coloring is good.

2. Troubleshoot in Order

First, temperature. Are the barrel section temperatures too high? Is there localized overheating? Check set temperatures against actual measured temperatures first.

Second, residence time. Low output, dead spots in the machine, or clogged screens keep material in the machine longer, and it burns easily. Reducing residence time and cleaning dead spots usually works better than adding more material.

Third, stabilizer dosage and grade selection. Check the dosage against the recommended range in each grade's TDS to see if enough was added, then check whether the grade matches the product type. Hard products take more, soft products take less; fine-tune within the recommended range in combination with your own formulation.

Fourth, lubrication. Roll sticking, exudation, or poor flow — look at lubrication first; lubrication may need fine-tuning after a switch.

Fifth, the raw materials themselves. Pigments, fillers, and recycled material differ in heat resistance; if problems start after changing a raw material batch, check the raw materials first.

3. Grade Selection from the Stabilizer Side

All dosages and performance figures below are verified figures; refer to each grade's TDS for specifics:

Transparent extrusion: T-230P, total 1.0–2.0 phr; oven aging at 190℃ for 35 minutes shows discoloration ≤15%, and dynamic two-roll stability at 180℃ for 35 minutes shows discoloration ≤15%.

Cable extrusion: GB-200 (4-6 phr) and GB-300 (4–6 phr) meet the national 70-degree standard, GB-313 (8–12 phr) meets the national 90-degree standard; 200℃ heat stability time is over 90 minutes for GB-200 and GB-300, and over 200 minutes for GB-313.

Pipe extrusion: S-510 (pipe grade); other rigid grades include S-530 (3.0–4.0 phr) and S-580 (4–6 phr).

Foam products: S-300, dosage 4–7 phr.

Calendered film roll sticking: T-600P, no roll sticking at 180℃ for 45 minutes.

4. Verify Before Switching Stabilizers

Don't switch a whole batch at once. Take free samples and run them on your own formulation and process first, compare discoloration and processing windows, and finalize the dosage only after confirming there are no problems. If roll sticking or exudation appears after switching, look at lubrication first; equipment that previously ran lead must be thoroughly cleaned before running Ca-Zn, to avoid lead residue mixing into new products and affecting environmental testing.

5. Conclusion

YesPVC has worked on PVC heat stabilizers for 18 years, is a national high-tech enterprise (recognized since 2018), implements the ISO 9001 quality management system, and its products have passed SGS testing certification and comply with RoHS and REACH regulations. We provide free samples and formulation support, with trial orders from 100 kg. If you are unsure about the cause of extrusion discoloration or scorching, submit your product type and process through our contact page, and we will recommend grades by application.