Formation And Heat Simulation Of Polyimide Foams

In this paper,a novel polyimide foam was prepared successfully by using3,3?,4,4?-benzophenonetetracarboxylicdianhydride(BTDA)and4,4'-diaminodiphenylmethane(MDA)as the main raw materials via the method of two-step process.The structures of BTDA,esterification product of BTDA and polyamide esters were analyzed by Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance spectroscopy(~1H-NMR),respectively.The morphology of polymer powder was observed by scanning electron microscope(SEM).The foaming kinetic parameters of polymer powder were determined by Ozawa dynamics calculation method according to differential scanning calorimetry(DSC)data.The foaming temperatures of polymer powder were determined by thermal gravimetric analysis(TGA)curve.The results indicated that the appropriate esterification time of BTDA was 1h.The polymer powder consisted of most of polyamide ester and a small amount of polyamide salt.The morphology of polymer powder presented microspheres,and the particle size of microspheres were from 0.5?m to 40?m.The range of foaming temperature was100??250?as drying temperature was 80?,90?,and 100?,respectively.The activation energy(E_a)and pre-exponential factor(A)of three stages of foaming process for polymer powder were 2.52 KJ/mol,17.01 KJ/mol and 35.32 KJ/mol,15126,2286 and1101,respectively.The effects of drying temperature of polymer powder,the type and dosage of blowing agent on polymer powder foaming were investigated.The structures and properties of polyimide foam were characterized by FT-IR,SEM,TGA,dynamic mechanical properties analyzer(DMA),limiting oxygen index meter(LOI)and computer-controlled electronic universal testing machine.The results had shown that the drying temperature of polyamide ester determined was 80?,the dosage of blowing agent DOW was 0.5%.Thermal decomposition temperature(T_d)and glass transition temperature(T_g)of polyimide foam were 526?and 284?,respectively,indicating that the polyimide foam was a kind of organic foam materials with excellent thermal stability.Limiting oxygen index(LOI)of polyimide foam with different densities were more than 40%,indicating polyimide foam has good flame retardant properties.The compress load-deformation curve of polyimide foam with different densities exhibited three deformation phases,i.e.the elastic deformation stage,"platform"stage and the"hardening"of the tight stage.The tensile strength and of polyimide foam was more than 0.25 MPa,elongation at break less than15%.Thermal conductivities of polyimide foams with density of 0.0124g/cm~3,0.0138g/cm~3and 0.0141g/cm~3 and 0.0144g/cm~3 were measured by thermal conductivity measuring meter,and their thermal conductivities were 2.61×10~-22 W/(m·k),2.80×10~-22 W/(m·k),2.96×10~-22 W/(m·k)and 3.08×10~-22 W/(m·k),respectively.The heat conduction of polyimide foam was simulated by ANSYS software,the results showed that the simulated temperature close to the measured temperature value.The simulation of foam unit was conducted,indicating heat conduction mainly conducted through matrix skeleton,air has played an important role in impeding heat conduction.