Material Analysis
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Dimensional Change of PU Products During Long-Term Storage
Problem Phenomenon
PU products stored 3 months show dimensional change ±2-3%, exceeding the ±0.5% requirement
Cause Analysis
PU physical aging relaxation causing continuous dimensional change; secondary crystallization slowly changing density and dimensions; low molecular substances slowly migrating changing local density
Solution
1) Anneal products at 80°C/4h before shipment to stabilize dimensions; 2) Select high molecular weight grade to reduce low molecular substances; 3) Slight crosslinking to reduce molecular chain mobility and inhibit aging; 4) Control storage environment temperature at 23±2°C to reduce temperature change effects
Key Takeaway
Dimensional change is caused by physical aging; annealing and slight crosslinking are the measures to stabilize dimensions
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