Preparation And Study On Mechanical Properties Of High Temperature Rigid Polyimide Foam

With the demand for new types of cellular polymer materials in the fields of aerospace,shipbuilding and other fields,it is imminent to prepare a kind of rigid polyimide foam(RPIF)with good using safety and excellent high and low temperature resistance.In this paper,a new approach to preparing RPIF has been developed,and the effect of cell structure and semi-interpenetrating network structure of RPIF on its mechanical properties also has been studied.Firstly,the optimum preparation conditions of high temperature resistant RPIF were selected.Then,the effect of different surfactant additions on the microcellular structure and mechanical properties of RPIF was studied.Finally,the semi-interpenetrating network structure was introduced into the polymer by adding a linear polyimide during the preparation process of RPIF.And the effect of semi-interpenetrating network structure on the mechanical properties and using safety of RPIF was also investigated.The major works of this paper are listed in detils as follows:1.A novel rigid polyimide foam which both with high temperature resistance and excellent mechanical property is successfully prepared from aromatic dianhydride and polymethane polyphenyl isocyanate(PAPI).The effect of the various factors such as the foaming technique,species and initial concentration of reaction monomer,reaction temperature on the chemical structure,cell structure,thermal property and mechanical property of RPIF were studied in detail,respectively.The results show that the optimal condition are: The best foaming technique is determined by combining the microwave and high temperature foaming technique,the optimum reaction monomer is 3,3’,4,4’-benzophenone tetracarboxylic dianhydride(BTDA),the optimum preparation temperature and concentration of reaction monomer was 50℃ and 60 wt%,respectively.2.First,the effect of the amount of surfactant on the microcellular structure and other properties of the prepared RPIF was studied.As a result,the addition of surfactant has no obvious effect both on the molecular structure and thermal properties of RPIF.The scanning electron microscope examination showed that the addition of surfactant is important to form a uniform and fine microcellular structure.The compressive strength of the prepared RPIF shows a trend of rising first and then decreasing with the increasing amount of surfactant.And the compressive strength of the RPIF sample reached 5.54 Mpa when the addition of surfactant was 6%.By establishing the relationship between the mechanical properties and the microcellular structure of the RPIF samples,it is found that the compressive strength shows a contrary trend to the porosity of the prepared RPIF.The higher the closed cell rate of foam materials is,the better mechanical properties will be obtained.Samples with thicker edge thicknesses and smaller average cell sizes have higher mechanical properties.Moreover,the regular microcellular structure will also be beneficial to better load bearing.3.A linear poly(amic-acid)(PAA)was first synthesized by BTDA and di-(4-aminophenyl)ether(4,4’-ODA),then a series of rigid RPIF with semi-interpenetrating polymer network structure were prepared with different blending ratios of linear PAA and polyimide precursor which derived from BTDA and PAPI were.The results showed that the RPIF samples before and after modification have high flame retardancy,and a small number of linear polymers can obviously enhance the thermal and mechanical properties of RPIF.The RPIF with an addition of 10% PAA shows a significantly improving in mechanical and thermal properties than pure RPIF.The maximum compressive strength and the themperature at 5 wt% weight loss can reach 6.71 MPa and 508°C,respectively.