Preparation And Research Of Highly Thermal Conductive CNT/PVA Nanofibrous Film

With the continuous development of microelectronics industry,the heat flux of circuit board is rising continuously.The existing thermal conductive and diffusive materials are unable to keep pace with the development of the electronic industry.The thermal management of electronic components has become a research hotspot.The traditional metal-based,ceramic-based and carbon-based thermal conductive materials have the disadvantages of poor corrosion resistance,poor insulation performance and poor impact resistance.Therefore,the polymer-based thermal conductive materials with small size,light weight,strong deformability,good insulation performance and high corrosion resistance have become the focus of research.However,the intrinsic thermal conductivity of polymer materials is low,and the thermal conductivity is mainly enhanced by adding highly thermal conductive fillers.The preparation of polymer-based thermal conductive materials with excellent performance is the key to solving the heat diffusion problem of highly integrated electronic components.In this paper,we used electrospinning technology to prepare carbon nanotube(CNT)/polyvinyl alcohol(PVA)nanofibrous film.We achieved the multi-level ordered structure including aligning PVA polymer chains,highly thermal conductive fillers(CNT)and nanofibers to prepare CNT/PVA nanofibrous film with high thermal conductivity.For PVA polymer chain’s disentanglement and orientation,we researched the effects of the ultrasonic treatment,the mechanical stirring treatment and the shear extrusion treatment on the disentangling of PVA macromolecular chains in fiber.By analyzing the characterization results of the two-dimensional wide-angle X-ray diffraction(2D WAXD),we found that the PVA macromolecular chains could be effectively disentangled by the ultrasonic treatment.So the PVA macromolecular chains could be stretched to be straight and orient in the subsequent preparation process.For the orientation degree of CNT as a thermal conductive filler in the composite fiber,we first ly improved its dispersion stability in water by adding water dispersing agent of carbon nanotubes and ultrasound-assisted treatment.We finally obtained CNT/PVA composite spinning solution with uniform dispersion of CNT.When observing the arrangement of CNT in the composite fiber,it was found that after effective dispersion treatment,CNT had a high orientation degree in the axial direction within the PVA fiber.When studying the arrangement of CNT with different length-diameter ratio in the composite fiber,it was found that the CNT with smaller length-diameter ratio had higher orientation degree in the fiber.Further,comparing the thermal conductivity of composite films with different CNT contents,we found that when the CNT content was 8 wt.%,the thermal conductivity of CNT/PVA composite films reached the optimal value of 2.59 W/(m·K),while the thermal conductivity of pure PVA electrospun films without CNT was only 0.7 W/(m·K).For the orientation of the composite fiber in the film,we improved the fiber collecting device.We finally prepared the film with highly oriented fibers by using the cage rotor.With the increase of the fiber ’s orientation degree,the thermal conductivity of the film increased to 3.17 W/(m·K),which was 23% higher than that of film collected by the drum.Further,in order to enhance the thermal conductivity of the CNT/PVA composite film,we improved the orientation degree of the macromolecular chains,fillers and fibers in the film by hot stretch treatment.When comparing the effects of the same CNT concentration and different hot stretch ratios on the thermal conductivity of the CNT/PVA composite film,it was found that hot stretch could effectively improve the thermal conductivity of the film.When the hot stretch ratio was 8 times,the thermal conductivity of the film could reach 7.79 W/(m·K),which was about 150% higher than that of the non-hot stretch ratio.When comparing the thermal conductivity of samples with different CNT contents under the same hot stretch ratio(8 times),it was found that the thermal conductivity generally increased.We thought the effect of hot stretch on the samples with various CNT contents was related to the state when they were not stretched.The sample with good original arrangement and moderate thermal conductive fillers got more benefits when subjected to the hot stretch.