Effect Of Microwave Irradiation On Structure And Property Of Polyolefin And Fluororesin Composites

In this paper, the 'sandwich-like'model and 'package-like'model are built for the purpose to simulate the micro structure change in the interface between the filler and the polymer matrix of the composites under the influence of microwave irradiation. Through attenuated total reflection FTIR (ATR-FTIR), infrared dichroism, thin film X-ray diffraction (TF-XRD), dynamic contact angle (DCA), X-ray photoelectron spectrum (XPS) and thermal analysis etc. the thermal effect and non-thermal effect (plasma effect) of microwave on the gradient change of the physical structures and chemical composition of the polymer interface and matrix were investigated, the microwave processing mechanism of polyolefin and fluororesin composites was discussed, the relationship between micro phase structures and macro physical properties of polyolefin and fluororesin composites was also explored. 1. The influence of microwave irradiation on the crystal structure of HDPE (or iPP) interface of Al/HDPE/Al (orAl/iPP/Al) composites was studied. During irradiation, the orthogonal phase in the crystal phase of HDPE interface is changed to hexagonal phase, the crystal transformation does not happen in the interface of HDPE films under the same irradiation condition; the grain size and the crystallinity are raised up; with the depth increasing, the microwave effect becomes weaker. The macro residual stress of HDPE interface decreases, the micro residual and lattice static distortion stress goes to the maximum at 75min. The crystal transformation (α→β) of iPP interface in iPP/Al happens. The order level of βphase crystal lattice increases, the defaults within the βcrystals reduces, D[300] (stand for β-form phase) becomes larger, βcrystals become more perfect. The microscopic distortion, micro residual stress and lattice static distortion of βcrystals are smaller than those of αcrystals under the same irradiation condition. The residual stress change promotes the crystal transformation. Microwave irradiation does not have apparent influence on the crystal structure such as crystallinity, grain size etc. of HDPE or iPP matrix in HDPE/Al/Al or iPP/Al/Al composite. 2. During microwave irradiation, the PTC intensity of polyolefin/carbon black (CB) composites increases, the area of the resistivity-temperature loop reduces. High PTC effect is achieved by microwave irradiation; the room temperature resistivity decreases under proper irradiation, the linear expansion coefficient also becomes less. An approach for researching the interface change in 'package-like'and 'sandwich-like'model between polyolefin and CB was proposed to investigate the structure reasons about composites properties improving. The results show that some polar groups (mainly -NH group) are induced on the molecular chain of interfacial HDPE, and the interfacial free energy of HDPE increases, the chemical interaction is thus enhanced. During microwave irradiation no remarkable change in grain size, crystallinity as well as, the melting and crystallization rate of polyolefin matrix. The crystal transformation (α→β) caused by the plasma effect of microwave is observed in iPP matrix, this kind of transformation only happens in iPP interface during microwave irradiation, similar influence on the crystal phase of polyolefin/CB composite. During irradiation, the crystallinity decreases, the grain size increases, the lamellar becomes thinner, the melting and crystallization behavior slows down; some part of orthogonal crystal of interfacial HDPE changes to hexagonal, the conformation isotacticity of interfacial iPP rises, then change wears off with the depth increasing.3. After microwave irradiation, the dielectric permissivity and loss reduce, the piezoelectric constant does not change sharply, favorable for improving the sensitivity of the pyroelectricity and the passive transducer materials. The dielectric loss peak of PVDF/PZT composites shifts to the low frequency, the dielectric relaxation energy increases, showing that the macromolecular chain of PVDF is restricted. An approach for researching the interface change in 'package-like'and 'sandwich-like'model between PVDF and PZT was proposed to investigate the structure reasons about composites properties improving. The experimental results show that some polar groups are observed after irradiation in the interface between PVDF and PZT due to plasma effect of microwave; the interfacial free energy raises up, the difference between the surface free energy drops down, the chemically interfacial adhesion is thus enhanced. The crystallinity of PVDF matrix in PVDF/PZT composites increases, the grain size decreases during irradiation; the crystallinity of PVDF interface in PVDF/PZT 'sandwich-like'model reduces. The crystal transformation (α→β) of PVDF happens both in PVDF matrix and interface, more obvious in PVDF interface. The thermal and non-thermal effects of microwave irradiation promote the physical and chemical interaction between PVDF and PZT fillers, the interfacial PVDF chain is bounded firmly, the response sensitivity to the mechanical excitation such as outside force, electricity, heat etc. is thus greatly improved.