Control of the crystalline morphology of polyphenylene sulfide in secondary thermoforming by the strong memory effect of crystallization

Polyphenylene sulfide (PPS), as a typical resin for aerospace thermoplastic composites, often undergoes repeated melting and crystallization during thermoforming. Thermal histories can introduce the self-nucleation (SN) effect in certain circumstances, which will significantly accelerate the overall crystallization rate of PPS. In this article, the SN behavior of PPS and its influence on nonisothermal and isothermal crystallization behavior were studied by differential scanning calorimetry, and the multiscale crystalline morphology and structure were characterized. A unique SN domain within the temperature range of 292 degrees C-323 degrees C was identified, where the melting endo-therm reaches the melt baseline and the peak crystallization temperature remains stable, while the spherulite size is several hundred nanometers. The mechanisms of the impact of molecular chain topology at different melting temperatures on the SN behavior were proposed. This work provides guidance for the design of PPS crystalline structure and suggests a stable thermoforming processing region, approximately 20 degrees C above the melting point.