Study Of Carbon Foam Derived From Ally Novolac -modified BMI Resin

Carbon foam, due to its excellent properties, such as light weight, high temperature resistance, corrosion resistance, good microwave absorption, aseismic performance, electrical and chemical properties, can be used in many fields ranging from aeronautics, astronautics, chemicals, electronics, energy, environmental protection to catalysis. Carbon foam was directly prepared by atmospheric pressure pyrolysis of the ally novolac (AN)-modified bismaleimide (AMB) resin, which was prepared by performing a series of procedures including prepolymerization, bubble removal, casting and curing. The effects of temperature, aging time and bismaleimide (BMI) content on the viscosity of the AMB prepolymer were studied, and the structures of the AMB resin after curing was analyzed. In addition, the influence of pyrolysis temperature on the structures and compositions of the AMB resin was investigated. In addition, the structures and properties of the carbon foam from the AMB resin prepared with different amount of BMI were discussed, as well as heat-treatment at high temperature.FT-IR,’H-NMR, TG-DTG and DSC were adopted to analyze the structures, components and properties of the AMB resin. The results show that the glass transition temperature of the AMB resin is about 290℃, the maximum decomposition rate temperature is 413℃, the decomposition temperature range is 362-632℃, and the char yeld of the AMB resin is 37%. The viscosity of the AMB prepolymer within a certain temperature range decreases with increasing temperature. In addition, the viscosity of AMB prepolymer and the glass transition temperature of AMB resin increase when prolonging the testing time and increasing BMI content, respectively.FT-IR, XRD, SEM and elemental analysis were used to analyze the effects of temperature on the structures, compositions, dimensions of the AMB resin at different pyrolysis temperatures. The results show that AMB resin possesses self-foaming characteristics at high temperatures. The pyrolysis process of the AMB resin was made up of three stages including free water volatilization, side chain breaking and rearrangement, and carbon formation by aromatic ring condensation, the weight loss of the resin mostly occurs in the temperature range of 500-600℃. With the increase of pyrolysis temperature, the shape of resin sample keeps well. It is found that the bubbles change from irregular shape to spherical shape, and therefore the size of bubbles become more and more homogeneous.The effects of BMI content and heat treatment on the structures and properties of the carbon foam prepared from AMB resin were investigated using SEM, XRD, thermal conductivity meter, four-probe tester and electronic universal testing machine. The results show that the carbon foam belongs to vitreous carbon though it has a certain degree of graphitization structure. With the increase of BMI amount, the bulk density and compressive strength of the carbon foam increase whereas its porosity, thermal conductivity and electrical resistance decrease. After heat treatment at 1800℃, the resulting carbon foam has an improved degree of order and increased electrical, thermal and mechanical properties. Meanwhile, the bulk density of the carbon foam increases but its porosity decreases.