Effect Of Hollow Glass Microsphere On Thermal Insulation Performance Of Polyimide Film

Hollow glass microsphere(HGM)consists of outer stiff glass and inner inert gas,which results in some unique properties.Owing to its light weight,low density and dielectric constant,excellent thermal and sound insulation,HGM filled polymer-matrix composites has been employed to fabricate polymer composites for wide applications.Polyimide(PI)is an important engineering plastic with excellent properties including thermal stability,low thermal expansion coefficient,superior mechanical and dielectric properties,as well as favorable chemical resistance properties.Therefore,polyimide has been widely used in the microelectronics,aerospace,and other fields.The main aim of this work is to improve thermal insulation property of PI/HGM composite films by combining polyimide and hollow glass microsphere.The thermal insulation properties,thermal stability,dimensional stability,dielectric properties and mechanical properties of PI composite films were studied.First,HGM filled polyimide composite films were prepared by blending HGM with polyamic acid and imidization with heat treatment.The effects of the content and density of HGM on the thermal and dielectric properties were investigated,it is found that the thermal conductivity,dielectric constant and dielectric loss of composite films decrease with increasing HGM content or decreasing HGM density.Compared with neat polyimide,the maximum decrease of 50%for thermal conductivity,40%for dielectric constant and70%for dielectric loss is obtained at the HGM content of 30 vol%and the density of 0.15g/cm~3.In addition,the experimental trends of thermal conductivity of the composites are analyzed by using different models,the results from Maxwell model show close correlation with the experimental values.Then,the microstructure,thermal properties and tensile properties were studied by scanning electron microscopic images,thermogravi metric analysis,thermal mechanical analyzer and stretch tester.The results show that HGM is uniformly dispersed into polyimide matrix,the composite films have good thermal stability.In addition,introducing the HGM,the tensile strength of composite films decreased dramatically.This work indicates that thermal conductivity,thermal properties,dielectric and tensile properties of polyimide-matrix composites can be tailored by adjusting hollow glass microsphere content and density,which provides theoretical guidance for structural design and molding process optimization of high performance polyimide film.