PET foam cores undergo crystallinity changes during thermoforming or thermal bonding; how does this affect mechanical properties?

PET is a semi-crystalline thermoplastic. The as-foamed board has low crystallinity (about 5–15%) and is translucent. When heated above 120°C, molecular chains rearrange, increasing crystallinity to 30–40%, manifested as whitening, hardening, and embrittlement. Moderate crystallization (crystallinity ~25%) can improve compressive modulus without excessive toughness loss; but excessive crystallization (>35%) drastically reduces elongation at break from 50% to 5% and impact strength by 60%. During composite sandwich panel production, if using an autoclave to cure prepregs (180°C), rapid cooling quenching is necessary to retain some amorphous regions. DSC testing is recommended for each batch.

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PET foam cores undergo crystallinity changes during thermoforming or thermal bonding; how does this affect mechanical properties?

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