Moisture Content
Also called: Moisture, water content, residual moisture
Moisture content is the percentage of water in plastic material; too much causes bubbles, splay and degradation, especially in PET, nylon and PC.
Moisture content is the amount of water held in or on a plastic material, usually reported as a percentage by weight. It can be surface water left after washing or water absorbed into the polymer itself.
Which plastics are sensitive
- Hygroscopic plastics such as PET, nylon, PC and ABS absorb moisture from air and must be dried before processing.
- In PET, nylon and PC, moisture at melt temperature breaks polymer chains, lowering IV and strength.
- Polyolefins such as PP and PE do not absorb much water, but washed flakes and film agglomerate can still carry surface moisture.
Why it matters when buying recycled plastic
- Wet material causes bubbles, voids, silver streaks and unstable extrusion.
- You pay for water by weight. Agree a maximum moisture limit for washed flakes.
- Ask how material was dried and packed, and whether bags are sealed against humidity in transit.
- Moisture can be checked by loss on heating or with a moisture analyser. Include it in your quality checklist.