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.