Crystallization kinetics of polyamide 66 at processing-relevant cooling conditions and high supercooling

• Published in: Thermochimica acta 2015-03, Vol.603, p.103-109
• Main Authors: Rhoades, Alicyn Marie, Williams, Jason Louis, Androsch, René
• Format: Article
• Language: English
• Subjects: Crystallization kinetics; Fast scanning chip calorimetry; Polyamide 66
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2014.10.020

[Display omitted] •PA 66 will crystallize from the melt upon cooling at rates less than 1000K/s.•PA 66 undergoes separate high and low temperature ordering processes.•Heating rates above 10,000K/s prevent cold crystallization from vitrified state. Processing of polyamide 66 (PA 66) by injection molding includes cooling of the melt at rates between 100 and 103K/s and its solidification at high supercooling. The kinetics of crystallization at such conditions is unknown and has been evaluated in this work using fast scanning chip calorimetry. Slow cooling of the melt of PA 66 leads to formation of crystals, with the maximum crystallinity being about 30%. It has been found by analysis of the crystallinity as a function of the cooling rate that crystallization is suppressed on cooling faster than about 300K/s. Isothermal analysis of the crystallization rate revealed a bimodal temperature dependence, with maxima obtained at about 165 and 110°C. It is suggested that the observation of two distinct crystallization-rate maxima is related to a change of the nucleation mechanism on temperature variation or the formation of different crystal polymorphs exhibiting different growth rate. The findings provide a fundamental step towards accurately predicting the solidification behavior, the skin–core morphology, and properties of injection moldings of PA 66.