Preparation And Characterization Of Thermal Conductive Polyvinylidene Fluoride Based Composites

Due to their excellent corrosion resistance, good processing ability and low manufacturing cost, polymers exhibit a wide range of applications in electronic packaging and other related fields. With the rapid development of microelectronics integration and packaging technology, the volume of electronic components and logic circuits has been shrinking thousands of times, while the operating frequency of the components is increasing rapidly. As a result, the heat generated by electronic equipment is largely accumulated, which makes the devices operate with sharply decreased efficiency, crash and even lead to fires and other hazards. Polymer materials exhibit poor thermal conductivity in general, which make them can’t meet the demand for industrial production. Filling polymer matrix with high conductive fillers has become a common method to improve the thermal conductivity of the materials. Thus, the preparation of highly thermal-conductive polymer materials is of great significance.The present thesis is focused on investigating the influencing mechanism of the interfacial resistance, filler networks, and crystal structure on thermal conductivity of Polyvinylidene fluoride (PVDF)-based polymer composites, aimed to explore new methods and techniques to improve the thermal conductivity of PVDF-based composites and further understand the mechanisms of improvement of thermal performance. It is expected to provide theoretical guidance for the development of thermal conductive polymer materials in industrial production. The main results obtained in the present thesis are listed as follows:(1) In this work, CNTs@PVP was prepared by physically treating carbon nanotubes (CNTs) using polyvinylpyrrolidone (PVP) firstly. Then composites PVDF/CNTs and PVDF/CNTs@PVP were prepared by melt blending method. The effects of PVP on dispersion of CNTs and interfacial thermal resistance between PVDF and CNTs were studied through the thermal conductivity measurement and the characterization of crystallization behavior, rheological behavior and microstructures. The results showed that when the content of CNTs and PVP were 10wt% and lwt%, respectively, the thermal conductivity of the composite was increased to 0.63 W/mK, which is 3 times of that of pure PVDF. The crystallization behavior showed that the addition of PVP will not change the crystal form of PVDF. Morphology characterization and rheological behavior showed that the introduction of PVP greatly improved the dispersion of CNTs and helped CNTs build denser thermal networks. The formation of hydrogen bonding between PVP and PVDF was proved by FTIR. The more integrated CNTs network structure and the intensified interfacial interaction were suggested the main mechanisms for the largely enhanced thermal conductivity of the PVDF/CNTs@PVP nanocomposites.(2) A small amount of graphene oxide (GO) was introduced into poly(vinylidene fluoride) (PVDF)/Carbon nanotube (CNT) composites through solution compounding. The morphology characterization and rheological behavior showed that GO facilitate the dispersion of CNTs, and the CNTs formed a denser three-dimensional network structure. The thermal conductivity and EMT theoretical simulation results showed that three-dimensional network structure constructed by GO and CNTs is the main reason for the improvement of thermal conductivity. In addition, the crystallization behavior demonstrated that GO induced the formation of polar y crystal. Therefore, the introduction of GO can not only reduce production cost of thermal conductive polymer composites, but also broaden the potential applications of PVDF.(3) The ionic liquid (IL) was added to PVDF to prepare the PVDF/IL blends. Results of crystallization behavior characterization showed that IL induced the formation of polar β crystal of PVDF, and the relative crystal content of β form increased with increasing IL content. Thermal conductivity mesurement results showed that polar crystals benefited the thermal performance of PVDF. The effects of polar crystal on thermal conductivity was preliminarily explored. This work provides a new strategy to improve the thermal conductivity of PVDF.