Crystallization Kinetics Of Carbon Fiber-reinforced Thermoplastic Polymer Composites

Carbon fiber reinforced polymer(CFRP)composites offer a number of potential technical advantages,such as high strength,light weight,easy processing,high production efficiency and so on.These advantages enable CFRP to be utilized in aerospace,wind power and automotive engineering fields.However,polymer can form complicated interfacial structure(transcrystalline and cylindrites)on the surface of carbon fiber(CF)due to the influence of processing conditions during machining.The interfacial structure of the composites has great influence on the properties.However,the existing crystallization kinetics models cannot accurately predict the structure evolution of the products during machining in the material design,which limits the development and application of CFRP materials.Based on the above background,the crystallization behavior of polypropylene on the surface of CF was systematically investigated.Then,the nucleation and crystallization kinetics models for CFRP have been deduced and verified.The main works were summarized as follows:(1)The nucleation kinetics model on CF surface was proposed.The crystallites morphologies of polypropylene on the CF surface were systematically studied.The relationship between number of nuclei on CF and transcrystalline length was deduced based on the extended volume,and the relationship between number of nuclei and fraction of CF covered by transcrystalline was obtained.The nucleation kinetics model was obtained by fitting the curves of fraction of CF covered by transcrystalline.Based on the results of the model and isothermal rheological experiment of polypropylene,the mechanism of enhanced nucleation on the CF surface was analyzed by microrheological model.The higher content of helical chain on the CF surface was the direct induction of enhanced nucleation.(2)The crystallization kinetics model for CFRP was presented.The crystallites morphologies on the CF surface were simulated by 3D pixel coloring method.And then the extended volume model of transcrystalline was proposed.A crystallization kinetics model for CFRP was proposed by combining the extended volume of transcrystalline and Kolmogorov model.The model was verified by pixel coloring method and differential scanning calorimetry experiment,and the influence of transcrystalline on the crystallization behavior of CFRP composites was summarized.Transcrystalline can accelerate the crystallization rate during isothermal crystallization,shorten the induction period of non-isothermal crystallization.The effect is more significant at higher temperature and lower cooling rate.(3)The crystallization behavior of CF reinforced polypropylene during cooling process was investigated,and the influences of CF and cooling rate on crystallization were analyzed.The effects of cooling rate and CF content on the crystallization of CF reinforced polypropylene during cooling were analyzed by using the crystallization kinetics model proposed and pixel coloring method.CF can significantly influence the crystallites morphologies and temperature of composites.The effect was more significant at a lower cooling rate.