Preparation And Properties Of Polypropylene/Boron Nitride/Alumina Thermal Conductive Composites

Polymer-based thermally conductive（TC）composites have become a study hotspot in the area of TC such as 5G communication instruments,electronic packaging and energy transmission due to their merits of light weight,easy processing and corrosion resistance.Nowadays,it is still a simple and efficient measure to prepare new TC composites by using high TC fillers to polymers.Polypropylene（PP）composites were prepared by melt blending using PP with inexpensive and widely source as the matrix and boron nitride（BN）and alumina（Al₂O₃）as fillers.The effects of filler particle size,content on the thermal and mechanical properties of PP composites were studied by laser thermal conductivity meter,differential scanning calorimeter（DSC）,universal testing machine and scanning electron microscope（SEM）.Meanwhile,the influence of fillers on the thermal conductivity of composites was further discussed by numerical simulation technology,which provided a reference for the preparation of new thermal conductive composites.The details of the work are as follows:（1）A series of PP/BN composites were prepared using four kinds of BN as fillers.It was found that the addition of BN could improve the TC and crystallinity of PP/BN,enhance its bending modulus and impact strength,but the tensile properties became poor.The TC of PP/BN reached 0.4540 W·m^-1·K^-1 when the filling a mount of BN was 20%and the particle size of BN was 20μm;while BN has different heterogeneous nucleation in the PP matrix with different synthesis processes at the same particle size,which has a greater influence on the crystallinity of PP in PP/BN.（2）PP/Al₂O₃ composites were prepared using three types of Al₂O₃ with particle sizes of45μm,20μm and 5μm as fillers.With the increase of Al₂O₃ filling amount,the TC and bending modulus increased,the bending strength decreased first and then increased,and the impact strength and elongation at break tended to increased first and then decreased.The crystallization front temperature of PP/Al₂O₃ prepared by adding Al₂O₃ with particle size of45μm is 9°C higher than that of pure PP,the melting limit is the narrowest,and its elongation at break,bending modulus and impact strength are better than those of Al₂O₃ with smaller particle size at the same filling level.（3）In order to explore the synergistic effect of filler type,morphology and particle size on the properties of PP composites,the TC pathway was optimized by filler compounding to accelerate the propagation of hot carriers,resulting in a 158.78%increase in the TC of PP/BN/Al₂O₃compared to pure PP,while further increasing the crystalline front temperature of PP in the composite.In addition,adding a small amount of Al₂O₃ to PP/BN was able to substantially improve the bending and impact properties of the composites,but reduce the tensile strength.In the heat dissipation experiment of LED lamp,it showns that LED working temperature can be effectively reduced by PP/BN/Al₂O₃,which has certain practical value.（4）In order to further study the influence of fillers on the TC of PP composites,the equivalent TC of the composites was calculated by finite element analysis technology,and the feasibility of the model was verified by comparing with the experimental results and the classical theoretical model.At the same time,by observing the temperature cloud diagram,it is found that the mixed filler filling can further optimize the internal heat conduction network compared to the single filler,thereby improving the TC of the composite material.