The Preparation And Crystallization Behavior Research Of WF/iPP Composites

Crystallization behavior has a great influence on the mechanical properties of polymer matrix. In this paper, watermelon vine was chosen as raw material. And Watermelon vine fiber(WF) was extracted as reinforcing material to prepare WF/propylene(iPP) composites. Then, the effects of WF on crystallization of WF/iPP composites were investigated. The main work included in this study is as following:1. Extraction processes and properties of WF:Dilute acid solutions were used to dissolve non-cellulose so as to obtain the WF with high cellulose content. The effects of treatment on the thermal stability, composition and crystallinity were analyzed by means of Thermal gravimetric analysis(TGA), Infrared spectroscopy(FTIR) and Wide angle X-ray diffraction(WAXD). A set of optimal conditions was obtained through orthogonal experiments.2. Preparation processes and performance analysis of composites:WF/iPP composites were prepared by HAAKE Mixer. The effects of WF contents, surface treatment of WF, isothermal crystallization temperatures and cooling rates on crystal morphology, crystallinity, et al were performed by POM, DSC and WAXD. TGA was used to analyze the thermal stability of WF/iPP composites. The Avrami equation and Caze method were chosen to describe the isothermal and non-isothermal crystallization kinetics of composites. The crystallization activation energy was determined by Kissinger method.The main conclusions of this research are:1. WF had optimum performance when the process steps were Boiling in acid solution—Alkali treatment—Bleachig—Alkali treatment—Bleaching, in which the alkali concentration were 7.5% and 12.5% respectively, and both of the temperatures were 130℃during alkali treatment.2. WF is an effective nucleating agent of iPP:(1)With the increasing of WF contents, the spherulite size decreased, crystallization peak temperature increased and the half-time of crystallization shortened. In addition, transcrystallization was found on the surface of WF. (2)Silane treatment improved the nucleation rate of WF. (3)The higher the isothermal crystallization temperature, the slower the crystallization rate was. Moreover, the formation of transcrystallinity became difficult with the increasing of crystallization temperature. The faster the cooling rate, the lower the crystallization peak temperature was. (4)Both the WAXD and DSC results showed that the crystallinity of WF/iPP decreased with the increasing of cooling rate. Besides, the addition of WF made the crystallinity of composites lower than that of pure iPP. With the increasing of WF content and cooling rate, the relative content ofβcrystal decreased,βcrystal was almost disappeared with WF whose surface was treated with silane. (5)The crystallization activation energy of composites which added with WF is higher than that of pure iPP.3. The existence of WF increased the thermal stability of iPP:The TGA results showed that the addition of WF increased the thermal stability of iPP. During the process of thermal decomposition, WF decomposed prior to iPP.