Surface Graft Modification Of PBO Fiber And Properties Of PBO Fiber Reinforced Thermosetting Resin Composites

The new material industry is promoting the development of science and technology,economic growth and social progress.In China,the new material industry is listed as a new national strategic industry.Compared with traditional metal or ceramic materials,advanced polymer matrix composites have higher specific strength,specific modulus and designability.Poly-p-phenylene benzobisoxazole(PBO)fiber,as reinforcing material for high-performance advanced composite materials,is widely used in national defense and aerospace.However,the surface of PBO fiber is high crystallinity and chemically inert,and the interface bonding of composite material is poor.Therefore,to expand the application of PBO fiber,the surface of PBO fiber should be modified to improve the interface bonding strength with resin matrix.Graft modification of PBO fiber was based on improving the interfacial bonding strength of PBO fiber reinforced thermosetting resin matrix composites.There were three aspects:1)Aliphatic chain was combined with imide polyurethane to make polyurethane compatible with epoxy resin which has lots of carbon-carbon single bonds and carbon-oxygen single bonds in molecular structure to improve the interface bonding strength of polyurethane grafted PBO/EP composites.Aromatic ring is combined with the polycarboxyimide polyurethane to make the polyurethane compatible with the bismaleimide which has lots of benzene ring structure in molecular structure,and exists at the interface during the BMI curing process to improve the interface bonding strength of the composite material.2)The aliphatic imide type polyurethane was grafted onto the surface of PBO fiber by air dielectric barrier discharge(DBD)plasma.The effect of sizing agent on the grafting reaction was studied.3)The aromatic polycarboxyimide polyurethane was grafted onto the surface of PBO fiber by DBD plasma at atmospheric pressure,and the effect of aging on the grafting reaction was studied.First,aliphatic chain imide polyurethanes and aromatic polycarboxyl polyurethanes were synthesized.The polyurethanes were characterized by Fourier transform infrared spectroscopy(FTIR):The backbone structure of HDIE,HDITE,IPDIE,HMDIE,HMDITE and IPDITE is mainly urethane bond structure with a small amount of imide.There are carboxyl groups and imides in the backbone of TDIEC,TDIBC and TDIHC.The aliphatic imide polyurethanes were successfully grafted onto the surface of domestic PBO fiber by atmospheric DBD plasma.The modification process was combined with dry winding to realize online continuous modification and winding process.The effect of plasma grafting aliphatic imide polyurethane on the surface of domestic PBO fiber,and grafted PBO fiber reinforced epoxy resin composite material was studied.The PBO fibers without sizing(PBOs)were characterized by X-ray photoelectron spectroscopy(XPS)and total reflection Fourier transform infrared spectroscopy(ATR-FTIR).The content of C,N and O elements in grafted PBOs fiber were different from the only DBD treated fiber.The content of carboxyl groups on the surface of the treated fiber was obviously increased.After grafting,the oxazole ring in the molecules on the surface of the PBOs fiber and nearly surface layer were damaged obviously.Scanning electron microscope(SEM)images showed that etching and graft on PBOs fiber,which was beneficial to the surface infiltration.The failure mode of the modified composites changed from interfacial debonding to partial cohesive energy failure.The interlaminar shear strength(ILSS)of the grafted PBOs/EP composites increased from 59.9%to 76.7%,and the IPDITEs sample reached 43.8 MPa.The results of XPS and SEM of grafted PBO fiber with sizing agent were consistent with PBOs fiber.However,ATR-FTIR results showed that there was no grafting and damage in the near surface layer.The results showed that the plasma grafting treatment only affects the outermost surface and sizing agent of PBO fiber.The ILSS of the grafted PBO/EP composites increased from 65.7%to 99.5%.Plasma grafting of aliphatic imide polyurethane onto PBO fiber can effectively improve the interfacial bonding properties of PBO/EP composites.The surface modification effect of plasma grafted aromatic polycarboxylic polyurethane on domestic PBO fiber and interface properties of grafted PBO fiber reinforced bismaleimide(BMI)resin composites were studied.TDIEC,TDIBC and TDIHC were successfully grafted onto the surface of PBO fiber by air DBD plasma.Interlaminar bonding properties of PBO/BMI composites were improved after grafting,and ILSS of TDIEC value increased by 55.2%.XPS showed that the content of O element in PBO fiber increased after grafting.The content of carboxyl group increased and then decreased with the increase of the concentration of graft solution.The highest value was 5%Vol.ATR-FTIR showed that the destruction of oxazole ring on PBO fiber surface was the main reaction of plasma treatment.The aging effect of TDIEC grafted PBO fiber was studied.The results showed that the aging effect of TDIEC grafted PBO fiber disappeared,ILSS value remained unchanged with time,while the activity time of PBO fiber only treated by DBD plasma was shorter.The SEM results showed that the surface of PBO fiber was more irregular after grafting.The failure mode of the composites changed from interlayer delamination to partial cohesive energy failure.PBO Fiber grafted with aromatic polycarboxylic polyurethane can improve the interfacial properties of PBO/BMI composites.