Paper: Polymer crystallinity and the ductile to brittle transition

The effects of crystallinity and molecular weight on the ductile-brittle transition of a semi-crystalline polyamide were de-coupled. Low molecular weight organic acid solutions were used to accelerate the molecular weight degradation of polyamide-11 to be faster than with water aging at 120 °C. The mass average molecular weight (Mm) of the aqueous acid aged polyamide-11 (PA-11) polymerized from 11- aminodecanoic acid degraded 4 times faster in acetic and 8 times faster in butanoic acid solutions than aging in water. With accelerated Mm degradation, crystallinity increased due to chemi-crystallizaion but at a slower rate than decreases in molecular weight. These accelerated molecular weight degradation techniques made it possible to separate the role of crystallinity from molecular weight on PA-11 ductility. This research on degradation of a semi-crystalline polyamide in acidic solutions and in water shows that reaching a critical crystallinity determines the ductile to brittle phase transition, not chain length as measured by molecular weight.

Our paper has been published in the journal Polymer (2018 impact factor: 3.771).

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