Study On High Performance Foams Based On Bismaleimide Resin

High performance foams are ideal lightweight structural materials, which play more and more inportant role in fields required light-weight such as aerospace and aviation. High performance foams should have outstanding thermal resistance, high strength and outstanding flame retardance, however, present foams do not completely meet those requirements. Therefore, developing a new kind of high performance foams has been a hot and important subject in the field of material science and technology.Bismaleimide resin is one kind of heat-resistant thermosetting resin, but few investigations are related on developing high performance foams based on bismaleimide resin. In this thesis, high performance foams based on diallyl bisphenol A modified bismaleimide (BDM/BA) were developed in the first time, and the structure-properties relationship of BDM/BA foams were intensively studied.The preparation technology of BDM/BA foams was firstly investigated. In detail, the effects of prepolymerization condition of BDM/BA foams on morphology and structure of resultant foams, such as the decomposition rate of blowing agent (AC135), gelation time of prepolymer as well as blowing temperature and time, have been discussed. Judging from the results, the optimum prepolymerization condition is 140°C for 60 min, and the foaming condition is 160°C for 35 min.The effects of the content of blowing agent on the morphology, thermal behaviors, dielectric properties and mechanical properties were also investigated. Results show that the resultant foams have outstanding thermal stability and mechanical properties, while the morphology and dielectric properties of BDM/BA foams are depended on the content of blowing agent. The BDM/BA foam with 9wt% AC135 has uniform cell distribution, low density, high porosity as well as low dielectric constant and loss.Flame-retardant BDM/BA foams were prepared by using carbon nanotubes (MWNTs) and clay as combined flame-retardants for the first time. Results show the incorporation of MWNTs into BDM/BA foam can not only increase the mechanical strength, but also improve the flame-retardancy of the foam. The foam with 1%MWNTs has the minimum peak release rate and total heat release value, and the maximum compressive strength. In addition, the incorporation of MWNTs into BDM/BA foam does not affect the ignition time; with the increase of MWNTs content in foams, the mass loss rate declines significantly. When both MWNTs and clay are added into foams, they not only show obvious synergism effect to reduce the peak heat release rate, the total heat release value and the mass loss rate, but also lead to form a whole carbon layer.