Can One PA66 Grade Replace Another? And Why Does PC/ABS Go Brittle?

Can one PA66 grade replace another?

Technically yes: regular production lots of local PA66 resin match the grade you run today in tensile strength, flexural modulus and HDT after glass reinforcement. Two things must be validated, though.

First, batch-to-batch consistency. Automated lines are sensitive to melt flow variation, so confirm MFR and ash content — the glass loading — across at least three consecutive lots. Second, long-term heat ageing: retained strength after 1000 hours at 120 °C, where the original grade usually carries a fuller data package.

Four usual causes of brittle PC/ABS

One, under-drying hydrolysing the PC phase — the most common cause, showing silver streaking alongside brittle failure.

Two, thermal degradation from excessive melt temperature: PC begins to deteriorate after more than roughly 15 minutes residence, especially with small presses running large shots.

Three, high residual stress from design or processing, cracking at stress concentrators in drop tests. Anneal to verify — 80-90 °C for 2 hours for PC/ABS.

Four, excessive regrind. Keep regrind below 15% for flame-retardant PC/ABS and always re-dry it.

Suggested troubleshooting order

Start with moisture content, the fastest discriminator. Next confirm barrel residence time — actual shot volume divided by part weight divided by cycle time.

Then run an annealing comparison: if impact recovers after annealing the issue is stress; if nothing changes, degradation.