Molding Process
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Product stress whitening when bent
Problem Phenomenon
The product locally whitens when subjected to bending or impact loads
Cause Analysis
Debonding occurs at the interface between fibers and the PP matrix, producing micropores that scatter light; long fiber ends are strong stress concentration points initiating silver streaks; residual stress from molding superimposed with external load
Solution
Improve the interfacial bonding strength between glass fiber and PP (coupling agent + grafted PP); optimize the fiber aspect ratio; anneal to eliminate molding internal stress
Key Takeaway
Stress whitening is the macroscopic manifestation of fiber-matrix interfacial debonding
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