Why PC/ABS must be dried
PC/ABS pellets absorb moisture from the air. In injection molding the melt is above 230 °C. At that temperature, moisture:
- turns into steam, forming splay and bubbles on the surface;
- breaks the PC molecular chains (hydrolysis), lowering impact strength.
The second is more dangerous. The part may look normal but break in a brittle way when dropped or when screws are driven.
Drying conditions
Typical values. Refer to the actual TDS.
| Item | Standard PC/ABS | Flame-retardant PC/ABS |
|---|---|---|
| Drying temperature | 100–110 °C | 80–100 °C (per the grade TDS) |
| Drying time | 3–4 h | 3–4 h |
| Target moisture content | ≤ 0.02 % | ≤ 0.02 % |
| Recommended equipment | Desiccant dryer | Desiccant dryer |
Target moisture reached ≤ 0.02 %
Key points:
- In humid seasons and in southern China, hot-air drying is often not enough; a desiccant dryer is recommended.
- Do not leave dried material in the hopper too long. A hopper dryer feeding the machine directly is recommended.
- Do not dry for too long. Long drying at high temperature can make the flame retardant migrate or the material yellow in flame-retardant grades.
- Spot-check moisture content with a rapid moisture analyzer and record it in the batch record.
Temperatures and processing window
Typical values. Refer to the actual TDS.
| Item | Standard PC/ABS | Flame-retardant PC/ABS |
|---|---|---|
| Melt temperature | 250–280 °C | 230–260 °C |
| Mold temperature | 60–90 °C | 60–80 °C |
| Back pressure | Low to medium | Low |
| Screw speed | Medium-low | Medium-low |
| Residence time | As short as possible | As short as possible; avoid going straight into production after a long stop |
Mold temperature
A higher mold temperature improves surface gloss and weld lines and reduces internal stress.
Injection speed
Thin-wall parts need a fairly high speed. Too high a speed causes burning, so good venting is needed.
Stops
After a stop of more than 10–15 minutes (typical value), purge the degraded material into the air before restarting production.
Special requirements for flame-retardant PC/ABS
Flame retardants are temperature sensitive. Too high a temperature or too long a residence time causes:
- flame retardant decomposition, producing gas and mold deposits;
- whitening and blooming on the surface;
- a loss of flame retardancy, so the part fails the burn test.
Recommendations:
- Keep the melt temperature below the upper limit in the grade TDS;
- Match barrel capacity to shot size, with the shot at about 30–70 % of barrel capacity (typical value);
- Clean the mold vents regularly;
- Purge the barrel thoroughly when changing color or material.
Defect troubleshooting table
| Defect | Possible cause | What to adjust |
|---|---|---|
| Splay, bubbles | High moisture content; temperature too high; too much shear | Check drying; lower the melt temperature; lower screw speed and back pressure |
| Brittle part failure | Hydrolysis; temperature too high; too much regrind; stress concentration at sharp corners | Check moisture content; lower the temperature; use less regrind; add fillets |
| Yellowing, black specks | Long residence time; high temperature; residue in the barrel | Shorten residence; lower the temperature; purge the barrel |
| Mold deposits, surface whitening | Flame retardant decomposition or blooming | Lower the temperature; improve venting; shorten residence |
| Visible, weak weld lines | Low mold temperature; poor venting | Raise mold temperature and injection speed; add venting |
| Screw boss cracking | Internal stress; chemical contact; screw choice | Raise mold temperature; check lubricants and cleaners; adjust the hole diameter |
| Flammability failure | Flame retardant degradation; walls thinner than the test thickness of the flammability rating; too much regrind | Control temperature; check wall thickness; use less regrind |
How to use regrind
- The regrind ratio is usually no more than 20–25 % (typical value); keep it lower for flame-retardant parts, and validate it.
- Regrind must be dried too.
- Mix regrind evenly with virgin material.
- Regrind only once. Repeated regrinding accumulates degradation.
Mass production checklist
Related grades
GRN-PCA-T310 (heat resistant), GRN-PCA-H320 (low-temperature high impact), GRN-PCA-W310 (weather resistant), GRN-PCA-N510 / GRN-PCA-N520 (halogen-free flame retardant), GRN-PCA-S520 (silicone-based flame retardant, without PTFE anti-drip agent). Processing parameters for each grade follow the TDS, to be verified by GREENPOLYMER.
Related pages: PC/ABS material page | UL 94 and thickness Need processing support? Contact hello@greenpolymer.com.
References
- Injection molding of high-quality molded parts: dryingCovestro
- The Troubleshooter: the role of moisture in injection molding splay defectsPlasticsToday
- PC/ABS drying and moisture control in injection moldingsalesplastics.com
Accessed 2026-10-19.