Molds & Tooling
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PBT notch-sensitive brittle cracking
Problem Phenomenon
PBT products crack immediately upon impact at notches and sharp corners, and notched impact strength is significantly lower than the unnotched value.
Cause Analysis
The benzene ring and ester group in PBT molecules form a large conjugated system making the molecular chain poorly flexible, and the polar ester group and carbonyl group increase intermolecular forces; high molecular rigidity leads to poor toughness and notch sensitivity.
Solution
①Polymerization modification to introduce flexible segments (copolymerization/grafting/block); ②blending modification adding reactive compatibilizers such as POE-g-GMA for in-situ compatibilization with PBT terminal carboxyl groups; ③structural design to avoid notches and sharp corners; ④select toughened grades for stressed parts.
Key Takeaway
Notch sensitivity is an inherent weakness determined by PBT's molecular structure; modification and structural design are the two major solution paths, and toughened grades should take priority over process adjustment.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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