Study Of Shear-induced Interfacial Crystallization In Fiber/isotactic Polypropylene Composite Through In-situ Monitoring Interfacial Shear Stress

Polymer/fiber composites have drawn great attentions due to their comprehensive properties in the past decades. As for the polymer-based composites, characteristics of interphase, e.g., interfacial crystallization, play an important role in determining the mechanical properties. Moreover, tunning of interfacial crystallization provides a promising method to obtain polymer/fiber composites with desirable properties. Particularly in polymer/fiber composites, transcrystallinity is regarded as one of the most interesting interfacial issues, which has attracted extensive interest in academic sector. Researchers built fiber-pulling device to prepare sandwich-like samples, and investigate the crystallization morphology of polymer and the property of resultant composite samples. However, the device and method they used are far from perfect.In order to further and efficiently investigate shear-induced interfacial crystallization of polymer-based composites, an improved fiber-pulling device was designed and built in our lab. Moreover, a new way to investigate shear-induced crystallization is explored. This paper consists of several aspects as following:1) Establishing of the modified fiber-pulling device. A force transducer is assembled to in-situ monitor the variation of interfacial shear stress between the polymer matrix and pulling fiber. Thus, the relationship between interfacial shear stress and the subsequent crystalline morphology can be quantitatively established. Function of the modified device is demonstrated by a series of experiments.2) Effect of shear on subsequent crystallization morphology. GF was pulled at different speeds or different pulling time at134℃, and then isothermally crystallized. Different crystallization morphologies were found to be the result of different shear stress level or different fiber pulling time. The results indicate that interfacial crystallization kinetics is promoted by the presence of interfacial shear stress and the fiber pulling time. Furthermore, there are two thresholds of interfacial shear stress for interfacial crystalline morphology.3) Effect of pre-shear on subsequent crystallization morphology. GF was pulled at different speeds and different temperatures above melt point of iPP, and then crystallized at134℃. Different crystallization morphologies were obtained. The relation of two opposite effects, shear and relax, was discussed.4) The mechanism of β-iPP or so-called "cylindrite" was discussed based on the results of this study. We analyzed the mechanism which was proposed by Varga, and found two problems according to his mechanism. So we suggest another mechanism to solve these two problems. We consider both a-iPP and P-iPP are induced by interfacial shear, and grow on their own nuclei.