Preparation And Properties Of Polyimide Fiber/Hybrid Epoxy Composites

As a new type of organic fiber,high performance polyimide fiber(PIF)has excellent mechanical and dielectric properties,good resistances to heat,chemical corrosion,and irradiation,making it an ideal reinforcement for light-weight wave-transmitting composites.Epoxy materials have good balanced properties,good processability,low cure shrinkage and relatively low cost,and are the most widely used resin-based matrix for composites.Therefore,PIF reinforce epoxy-based composites are very important for wave-transmitting appliations.The main research conents are as follows.1.A fluorine-containing epoxy,FDE,was synthesized and added into DGEBA/MNA system as a low-k modifier.Effects of FDE addutuib on cure kinetics and properties were investigated.Results showed that the curing process was barely affected by addition of FDE.After kinetic study,the optimum cure scheme was established,i.e.,110℃/2h +130℃/2h+150℃/3h +190℃/1h.At 10wt%FDE loading,the dielectric constant decreases ca.0.3,the impact strength increases from 20 kJ/m2to 25 kJ/m2,ana at the same time,no obvious reauction in glass transition temperature was found.2.Prepregs composed of S35 polyimide fiber and DGEBA/MNA matrix were prepared by wet winding method,and optimized processing parameters were established.The prepreg by the wet wound method suffers from non-uniform resin distribution and high VOC emission;thus,the prepreg was also prepared by the glue film method.The optimized film-forming condition is achieved by adding 3wt%fumed SiO2 and then procure at 85℃ for 60 mins.The optimized processing parameters for the hot-melt prepreg machine are:55℃,4MPa,and lrpm.The thus prepared prepreg is stable and can be used in the next step.3.Laminates were prepared by applying heat and press to the layered pregregs in a a molding press.The optimized processing condition is applying 4MPa when heating up to 80℃.The interlaminar shear strength,ensile strength,tensile modulus,compression strength,compression modulus,bending strength and lexural modulus of laminate are 50MPa,1.37GPa,56GPa,234MPa,50.5 GPa,580 MPa,and 50 GPa,respectively.4.Using DGEBA/MNA as matrix,two composites reinfornced with Kevlar29 and S3 5 polyimide fiber were prepared.Results showed that,at the same condition,the mechanical and dielectric properties as well as heat resistance of the S3 5 reinforned composite were better than that reinfornced with Kevlar29.5.Effect of FDE addition on the performance of S3 5 reinforced DGEBA/MNA composite was studied.When 10wt%FDE was added,the dielectric constant of the composite decreases from 3.4 to 3.2 without notable decreases in mechanical and thermal properties.