Research And Application On High Thermal Conductivity Of Functional Polymer Materials

The thermal conductive materials have been widely applied in various departments of the national economy and industrial departments. The traditional thermal conductive materials are based on metal materials, inorganic materials. Metals of thermal conductive materials such as Al, Cu, Ag, etc. When referred to inorganic materials such as SiC and AlN, etc. With the industrial development and technological advances, more requirements on the thermal conductive materials were put forword, e.g, electrical insulation, corrosion resistance, light weight and easy processing. The trend of high-tech electronic products is becoming smaller, lighter and thinner; however, the board connects large numbers of electronic components, so heat distributing issues must be resolved. The traditional material can't solve the problems above, for the reason that though the metallic materials have good heat distributing property, it is also good for electricity conducting, and this will affect the work of the circuit. Both with the thermal conductive and insulating polymer materials are excellent to solve these problems.At present, the photovoltaic (PV) modules packaging material is mainly taken by EVA film, but its thermal conductivity is low, the surface temperature of silicon cells improved will reduce the efficiency of converting, so it's urgent to solve the thermal issues of PV modules. The target of this paper is to research, design and preparation for a new thermal conductive encapsulation material in PV modules, and to solve the cooling, easy aging problems of current package material of PV modules.In the first part of this paper, the nano ZnO was prepared by several ways, and surface of multi-walled carbon nanotubes (MWNT) was treated by mixed acids. Morphology of ZnO surface was observed by scanning electron microscopy (SEM) analysis, while the functional groups of the surface of carbon nanotubes were characterized by Fourier transform infrared spectroscopy (FTIR) instrument. The result showed that the carboxyl group (-COOH) and others were successfully added to the carbon nanotube surface. The purity of carbon nanotubes after mixed acids treatment was observed by X-ray diffraction analyzer. Besides, dispersion of chemical modified MWNT in common solvents also was studied. Finally, ZnO, SiC, AlN fillers and so on were proposed by coupling agents.In the second part, on the basis of the carbon nanotube surface modified by -COOH group, the SOCl2 reacted–COOH through chloride reaction, then reacted with the acrylamide and the double bound was got. Finally, by free polymerization of butyl acrylate and vinyl acetate, the copolymer-coated carbon nanotubes (the MWNT-PBV) were prepared. The MWNT-PBV was charactered by the transmission electron microscopy (TEM) and thermogravimetric analyzer (TGA). The photos of TEM showed that the diameter of carbon tubes were thicker, TGA measurements found that between 310 ~ 410℃the carbon nanotubes had large mounts of thermal weight loss. It's approving that the MWNT had been coated with polymer. In addition, selecting appropriate raw materials for preparing EVA film applied for PV modules encapsulation.In the third part, the thermal conductive fillers prepared before were mixed with EVA and masticated, and then by molding compression the thermal conductive film for the PV module encapsulation was obtained. The effection of ZnO on the degree crosslinking of EVA was carried out, and found that ZnO can improve the EVA crosslinking. The crosslinking degree of ZnO/EVA Co-film can reach 95.2%. Focusing on the influence of different fillers on the thermal conductivity of EVA film, and the result indicated that different filler, different size, different surface morphology of thermally conductive fillers, can do an effect on the thermal conductivity of the composites. When the volume fraction of MWNT-PBV was 30vol%, the thermal conductivity of the co-film got as high as 4.18 W / (mK), it's much bigger than the best inorganic filler SiC filled co-film's thermal conductivity (2.90 W / (mK), 60vol %), while the volume fraction of MWNT-PBV was just half of the SiC. The maximum tensile strength was up to 0.75MPa .By the cooling simulation test, the result was basically the same as the thermal conductivity tester. The thermal conductivity of ZnO / EVA co-film was forcasted by the Maxwell equation and found that when the ZnO volume fraction is low (less than 15%), the measured data was consistent with the theoretical curve of the Maxwell equation. If the volume fraction of ZnO was over 15% , the Maxwell equation was not fitted and then the modified equation was put forward.The performance of high thermal conductive EVA film of this research was excellent, was abled to be applied in PV modules encapsulation, and the marketing value is better.