Study On Preparation And Properties Of Thermal Conductive Polyethylene Composites

Carbon nanotubes have excellent mechanical properties and high thermal conductivity and electrical conductivity and boron nitride is one of the best ceramic materials with good thermal conductivity.In order to improve the mechanical properties and thermal conductivity at the same time,high density polyethylene modified composites were prepared by adding carbon nanotubes and boron nitride particles in the polymer matrix.In this thesis,firstly,high density polyethylene(HDPE)was used as the matrix material,and carbon nanotubes and boron nitride particles were used as heat conducting fillers;the effects of the ratio of carbon nanotubes and boron nitride particles on the mechanical properties,thermal conductivity,melt flow rate,heat resistance,melt crystallization and thermal stability of the composites were studied.The results showed that when the mass ratio of carbon nanotube and boron nitride was1:1,the thermal conductivity of the composite was the highest;when both of the carbon nanotube and boron nitride content were 10%,the thermal conductivity of the composites increased 62.64%(test temperature of 100?);hybrid fillers not only improved the thermal conductivity of the composites,but also improved the tensile strength,the flexural strength and thermal stability.Polyethylene polypropylene composites were prepared by melt blending method with high density polyethylene and polypropylene as matrix materials and carbon nanotubes and boron nitride particles as thermal conductive fillers.The effects of different ratios of polyethylene and polypropylene on the mechanical properties and thermal conductivity of the composites and the effects of single filler boron nitride onmechanical properties,thermal conductivity,melt flow rate,heat resistance,thermal stability and melt crystallization behavior of composites were studied.Meanwhile,the effects of the ratio of carbon nanotubes and boron nitride particles on the mechanical properties,thermal conductivity,melt flow rate and heat resistance of polyethylene/polypropylene composites were investigated.The results showed that the thermal conductivity of composites decreases with the increase of polypropylene content;boron nitride can improve the tensile strength,flexural strength,thermal conductivity and thermal stability of the composites;when the mass ratio of carbon nanotubes and boron nitride was 7:3,the thermal conductivity of the composites was the highest,and it was 30.5% higher than that of the composites without thermal conductive fillers.With high density polyethylene as matrix,carbon nanotubes as conductive filler,the thermal conductive HDPE/CNTs composites were prepared by melt blending and solution blending methods.The effects of carbon nanotubes content and size on mechanical properties,thermal conductivity,Vicat softening temperature and melt flow rate of the composites were studied.And the effects of the two processing methods on mechanical properties and thermal conductivity of the composites were compared.The results showed that with the increase of carbon nanotubes content,the tensile strength,flexural strength and thermal conductivity of the composites increased obviously.Carbon nanotubes with big diameter were more favorable for the improvement of the performance.The tensile strength,flexural strength and thermal conductivity of the composites were increased by 33.4%,36.3% and 52.5%(60?)respectively when carbon nanotubes content is 10%.The improvements of the properties of the composites prepared by melt blending method were more obvious.