Preparation And Properties Of PBO/Two-dimensional Carton Materials

Poly(p-phenylene benzobisoxazole)(PBO) fiber has a very high thermal stability,mechanical strength as well as good flame retardant due to its rigid rod-like structure,which has a wide application in aerospace and some advanced composite materials fields.Although PBO fiber deliver such excellent performance,it still has some obstacles to overcome,such as a large gap between the actual modulus and the theoretical modulus(only 15% can be achieved).Therefore,in this thesis,in order to further improve the mechanical and thermal properties of PBO fiber,the parameters during fabrication process,including polymerization,fiber spinning and heat treatment,to improve the PBO fiber's performance were optimized.Meanwhile,inspired by multi-walled carbon nanotube(MWCNTs)-enhanced PBO fiber's performance,the PBO composite fibers with different sizes of 2D carbon nanomaterial such as nanographene oxide(NGO),graphene oxide nanoribbon(GONRs) and graphene oxide(GO) were designed and synthesized.The relationship between structure and properties of these three kinds of composite fibers were analyzed.In addition,the differences in performance between PBO composite fibers prepared via in-situ polymerization and blending methods were also studied.Throughout these studies,it will benefit to develop more excellent performance composite fibers.The optimized spinning conditions were determined by studying the process parameters of PBO fiber in polymerization,spinning,water washing and heat treatment.Observing the changes of viscosity of the PBO polymer during the polymerization process,reaction time and reaction temperature in each stage were ensured.As a result,a high molecular weight of PBO polymer of 26400 was achieved which is higher than those of other published PBO composites.The optimized conditions were determined at the polymer concentration of 12 mass%;the air bath length of 20-25 cm;the coagulation bath of 10-30% phosphoric acid solution;the spinning speed of 100 m/min and the heat treatment temperature of 350?.The average tensile strength of obtained original PBO fiber is 5.20 GPa,and 6.22 GPa for PBO composite fiber.Currently,this is the highest tensile strength value compared with other published PBO composite fibers.The NGO was prepared by hydrolysis glucose at high temperature and high-pressure,the size controlled at 18-26 nm.Due to the excellent mechanical properties of NGO,the composite fiber of PBO-NGO was synthesized to further improve the fiber's tensile and heat resistance properites.Based on mechanical and thermal the tests,the PBO-NGO composite fiber exhibited an obvious improvement on tensile strength,tensile modulus and heat resistance compared with original PBO fiber,11.1% improvement for tensile strength;22.6% enhancement for tensile modulus;35? mprovement for the initial decomposition temperature.The GONRs were prepared by oxidative unzipping of MWCNTs,the walls of MWCNTs were opened by cutting MWCNTs which increases the external specific surface area.PBO-GONRs and PBO-MWCNTs composite fibers with different MWCNTs and GONRs contents were prepared via in-situ polymerization.Although,the molecular weight of the two composite polymers are similar,PBO-GONRs fiber displayed better properties on mechanical and heat resistance.When the loading of GONRs is 1.0 wt%(based on the total composite weight),the tensile strength and tensile modulus of the PBO-GONRs fiber are 6.02 GPa and 235 GPa respectively,which are superior to 5.72 GPa and 216 GPa for PBO-MWCNTs composite fiber.In addition,compared with the mechanical properties of original PBO fiber,PBO-GONRs fiber has an 15.8% improvement for tensile strength and 29.8% enhancement for tensile modulus.Two kinds of PBO-GO composite fibers were fabricated and compared via blending and in-situ polymerization methods.The GO sheet has a good dispersibility in PBO polymer via in-situ polymerization method,and the corresoponding composite fiber demonstrated higher mechanical properties and heat resistance than those of fiber fabricated by blending method.Moreover,compared with the original PBO fiber,the performance of composite fiber also has been improved,about 19.6% enhancement for the tensile strength,35.9% for tensile modulus and 52? improvement for initial decomposition temperature.In contrast,the performance of the composite fiber via blending method exhibited inferior performance,about 10.5% decreased for tensile strength;6.6% decreased for tensile modulus;and 12? decreased for initial thermal decomposition temperature.Meanwhile,the enhancement effects of PBO fiber with different sizes and shapes of 2D carbon materials were also compared.The results showed that PBO-GO fiber prepared via in-situ polymerization possess better mechanical property than those of other PBO composite fibers.