The Influence Of Reinforcement Type And Molecular Weight On The Crystallization Behavior And Morphology Of Poly(Ether Ether Ketone)

Poly(ether ether ketone)(PEEK)is one of the semi-crystalline high performance thermoplastic polymers,widely used in high performance applications such as automotive,aviation and biomechanics.The addition of glass fiber or carbon fiber to PEEK is also a commonly used method to further improve its tribological and mechanical properties.A high degree of crystallinity is required to ensure optimal mechanical performances for PEEK.In this context,the crystallization behavior of PEEK has been investigated extensively in literature.This thesis focuses on the influence of reinforcement type(carbon fiber or glass fiber),and molecular weight on the crystallization behavior of PEEK.The main results are as follows.(1)The influence of reinforcement type(carbon fiber or glass fiber)on the crystallization behavior of PEEK.The crystallization behavior of neat PEEK,30% carbon fiber reinforced PEEK,and 30% glass fiber reinforced PEEK were investigated by differential scanning calorimetry(DSC),polarized optical microscope(POM),fourier transform infrared spectrometer(FTIR),wide angle X-ray diffraction(WAXD),and small angle X-ray scattering(SAXS).The results of DSC revealed that,during cooling process from the melt,the crystallization peak temperature of carbon fiber reinforced PEEK shifted to higher temperature.While the behavior of glass fiber reinforced one was in reverse direction,compared with which of neat PEEK.The crystallization half-time increased in the following order: glass fiber reinforced PEEK< carbon fiber reinforced PEEK(27)neat PEEK.The optical microscopic images showed that the carbon fiber(or glass fiber)did not induce the formation of the transcrystalline layer in the PEEK matrix.The results of FTIR showed that the incorporation of carbon fiber(or glass fiber)did not cause significant changes in the characteristic peaks of PEEK.The results of WAXD and SAXS revealed that the incorporation of carbon fiber(or glass fiber)also did not cause significant changes in the crystal structure and the long period of PEEK.(2)The influence of molecular weight on the crystallization behavior of PEEK.The crystallization behavior of high molecular weight PEEK(PEEK-H),medium molecular weight PEEK(PEEK-M),and low molecular weight PEEK(PEEK-L)were investigated by DSC,POM,FTIR,and WAXD.The results of DSC revealed that,during cooling process from the melt,the crystallization peak temperature of PEEK-M shifted to higher temperature,compared with which of PEEK-H,while the crystallization peak of PEEK-L almost was same with which of PEEK-H.The crystallization half-time increased in the following order: PEEK-L(27)PEEK-H(27)PEEK-M.The optical microscopic images showed that the crystal density was high for the three different molecular weight of PEEK.The results of FTIR showed that the molecular weight had no significant effect on the characteristic peaks of PEEK.The results of WAXD revealed that the molecular weight also did not cause the change of PEEK crystal structure.