Preparation, Structure And Properties Of Swcnts And Graphene Reinforced PBO Fibers

Poly(p-phenylene-2,6-benzobisoxazole)(PBO) fiber is one of high-performanceorganic polymer fibers, which is characterized by low density, superior mechanicalproperties, excellent thermal and thermo-oxidative stability and good flameretardance. It is widely applied in various frontier fields. However, there are someflaws in PBO fibers, such as a large gap between the actual tensile modulus and thetheoretical tensile modulus, weak interfacial property with resin, et al. In this paper,the main aims are to improve the mechanical, thermal properties and interfacialproperty of PBO fibers. So, PBO composite fibers reinforced by SWCNTs orgraphene were designed and synthesized, the microstructure and the properties ofcomposite fibers were studied. The researches are beneficial to develop morecomposite fibers with excellent comprehensive performance.SWCNTs were acid-treated by the two methods, concentrated H2SO4/HNO3system or20%SO3oleum/concentrated HNO3system. The process is in order toachieve the purifying, cutting short and carboxylation of SWCNTs. Threefunctionalized SWCNT I-III were obtained through chemical grafting of aminodicarboxylic acid including L-Aspartic acid (I), L-glutamic acid (II) and5-amino-isophthalic acid (III) onto SWCNTs surface, respectively. The functionalizedSWCNTs (SWCNT I-III) is to overcome the issues of limited dispersivity andprocessibility of SWCNTs in polymerization system.Graphene oxide (GO) sheets were successfully prepared through modifiedHummers method. The obtained GO sheets have not been further deoxidized andstill retained the active groups for the next functional treatment. The DADHB-is-(GO/TPA) inner salts were synthesized through the special composite inner saltsmethod. DADHB-is-(GO/TPA) inner salts were designed to improve the dispersionof GO in polymerization system and processibility of GO with PBO matrix. Theresults show that GO sheets disperse well in the inner salts. GO sheets work as thenucleating template agents in the composite inner salts, which effectively avoid theaccumulation of GO sheets and lay a solid foundation for the dispersion of GO inthe following polymerization procedure.The SWCNT I-III&PBO composite fibers were synthesized through in situpolymerication of dehydrochlorinated monomers. The chemical composition,intrinsic viscosity and viscosity average molecular weight, surface and crosssection morphology, crystallization behaviors of the SWCNT I-III&PBOcomposite fibers and the SWCNTs distribution in composite fibers were analyzed.The results show the additions of functionalized SWCNTs (SWCNT I-III) have the obvious effects on the structures of PBO fibers. The mechanical enhancements ofPBO fibers by functionalized SWCNTs (SWCNT I-III) were investigated by tensilestrength, tensile modulus and elongation at break. The results indicate that tensilestrength and modulus of all composite fibers have a certain extent increment, inwhich adding SWCNT III into PBO matrix has increased by the largest margin.The effect of SWCNT I-III in the thermal stabilities for PBO fibers were studied.All the results indicate that the enhancement effects of SWCNTs graftedrigid-chain molecules on mechanical and thermal properties are much better thanthat of SWCNTs grafted flexible-chain molecules. The effects of adding SWCNTI-III on the interfacial properties of PBO fibers composite materials were evaluatedby surface wettability, surface free energy and interfacial shear strength.The GO-co-PBO composite fibers with different GO contents were synthesizedby in situ polymerization of a novel composite inner salts. The structures andproperties of GO-co-PBO composite fibers were lucubrated and systematicalanalyzed. The intensification mechanism of GO in PBO fibers is proposed andsimply discussed. The effects of different GO contents on PBO fibers structureswere evaluated by chemical composition, the intrinsic viscosity and viscosityaverage molecular weight, surface and cross section morphology, the crystalliz-ation behavior of the compositite fiber and the GO distributions in composite fiber.The mechanical enhancement of PBO fibers with differen GO contents werestudied by tensile strength, tensile modulus and elongation at break. Comparedwith PBO fibers, tensile strength and modulus of composite fibers have asignificant increments with GO content. The thermal stabilities of GO-co-PBOcomposite fibers were studied and it was found that the incorporation of GOimproved the thermal stabilities and flame retardancy of PBO fibers. The effects ofGO on the interfacial properties of PBO fibers composite materials were evaluatedby surface wettability, surface free energy and interfacial shear strength.