Graphene Modification Of High Performance PIPD Fibers And Its Structure And Properties

Poly{2,6-dimidazo[4,5-b:4',5'-e]pyridinylene-1,4(2,5-dihydroxy)phenylene}(PIPD)is a rod polymer with rigid structure,which has 2,5-dihydroxy phenylene and imidazole pyridine as the repeating units.PIPD fibers show superior mechanical properties,good aging resistance and excellent flame retardance.However,there are some flaws in PIPD fibers,such as PIPD polymer monomers are easily oxidized,the viscosity of the system is large and the reaction activity in the later stage of the polymerization is low.To improve the performance of the PIPD fiber by increasing the molecular weight is limited.In contrast,nano-enhanced modification is more simple and effective.Graphene oxide(GO)contains a large number of polar functional groups.GO can participate in the polymerization to achieve the effect of copolymerization enhancement.Based on the principle of nano-modification enhancement,PIPD fiber was modified by in situ copolymerization and blending of graphene oxide and graphene,and the mechanical properties,heat resistance and interfacial properties of PIPD fiber were enhanced.In this paper,graphene oxide(GO)was successfully prepared by chemically modified Hummers method,and some of the obtained graphene oxide was reduced to obtain reduced graphene(rGO).By studying the effect of time and temperature on the inherent viscosity of the PIPD polymer in the polymerization process,the results showed that the polymer molecular weight rose fastest with a polymerization time of 15 h.In the temperature range of140°C-180°C,the inherent viscosity of the PIPD polymer increases with increasing temperature and reaches a maximum of 12.25 dL/g at 180°C.The prepared PIPD fibers were heat-treated at different temperatures in the range of 200-300°C.The effect of heat treatmenttemperature on the structure and mechanical properties of PIPD fibers was studied.The results show that the increase of temperature is beneficial to improve the crystallinity of PIPD fiber,and the mechanical properties of the fiber also increase from the original 2.16 GPa to2.73 GPa,an increase of 26.4%.Graphene oxide and reduced graphene oxide were added into PIPD polymerization system by in situ copolymerization-blending method to obtain different contents of GO/PIPD and rGO/PIPD composite fibers.The influences of the addition of GO on the structure and properties of the composite fibers were studied.Moreover,the structures,mechanical properties and thermal stabilities of GO/PIPD composite fibers were compared with the same content of rGO/PIPD composite fibers.In addition,a preliminary discussion of the mechanism of GO modification to enhance PIPD fibers was conducted.The mechanical properties of different contents GO/PIPD composite fibers were studied by tensile strength.Compared with pure PIPD fibers,there is some improvement with addition of GO.When the content of GO is 1wt%,the tensile strength of composite fibers reaches a maximum of2.43 GPa.When the content is the same,the mechanical properties of GO/PIPD are better than those of rGO/PIPD composite fibers.With the addition of GO,the surface energy of GO/PIPD composite materials is improved.When the content of GO is 2wt%,the maximum value is 53.20mN/m.The interfacial shear strength of PIPD fibers/epoxy composite materials is higher than pure PIPD fibers.When the GO addition amount is 1wt%,the interfacial shear strength reaches a maximum of 51.27 MPa.The addition of graphene oxide is beneficial to increase the initial decomposition temperature of the composite fiber.When the content of GO is 2wt%,the composite fiber has the highest residual carbon content of 57%,which is 4%higher than that of pure PIPD fiber.