Material Drying
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Silver streaks and bubbles from insufficient PPO drying
Problem Phenomenon
Silver streaks, bubbles, and internal voids appear on the surface of PPO products, distributed along the flow direction near the gate; in severe cases, the impact strength decreases and the product becomes brittle.
Cause Analysis
Although PPO has low water absorption, trace moisture vaporizes under high-temperature melting at 260~310℃ and triggers degradation; when the moisture content exceeds 0.05%, silver streaks and bubbles are produced; flame-retardant and glass fiber reinforced grades are more sensitive to moisture.
Solution
①Dry ordinary modified PPO at 90~110℃ × 4~6 hours, and raise to 110~120℃ for flame-retardant glass fiber grades; ②verify the moisture content is below 0.05%; ③after drying, keep sealed and heat-preserved to prevent secondary moisture absorption; ④when silver streaks appear, check drying first before adjusting the process.
Key Takeaway
PPO's low water absorption easily makes people relax drying management; the 0.05% moisture content red line must be quantitatively verified; drying is the lowest-cost defect prevention means.
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