Preparation, Properties And Applications Of PBO Nano Fiber Membrane

Polybenzoxazole (PBO) polymers have been attracted broad attention for the excellentperformance of high-strength and high-modulus, high temperature resistance, and fire-resistancecapability. Besides the high performance PBO fiber, Zylon, commercialized by Toyobo, thepreparation and potential applications in various fields of PBO polymers have been widelyinvestigated and developed. Polybenzoxazole (PBO) nano fiber membranes could be preparedfrom the polyhydroxyamide (PHA) precursor by electrospinning and thermal cyclizationprocesses.In this dissertation，based on the successful synthesis of PHA precursor, the novel PBOnanofiber membrane with excellent thermal stability, mechanical property, solvent and fireresistant were fabricated. The structure, thermal stability, mechanical property, dielectric propertyand application in proton exchange membrane of PBO nano membrane were investigated anddiscussed. The main contents are as follow:1. PHA was synthesized by conventional polycondensation of2,2’-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BisAPAF) and isophthaloyl dichloride (IC). Thestructure of PHA was verified by FT-IR and1H-NMR analysis. High molecular weight PHApolymer with an intrinsic viscosity of0.33dL/g was synthesized, which could fulfill the spinningrequirements.2. PBO nanofibers with uniformly diameter distribution were successfully prepared from PHAnanofiber by electrospinning and thermal cyclization process. FT-IR analysis indicated PHApolymer was transferred to PBO after thermal cyclization. The TGA results showed that PBOnanofiber has excellent thermal stability with a decomposition temperature of550oC undernitrogen atmosphere. PBO nano fiber membrane showed excellent mechanical and thermalstability. Tensile Strength and Young’s modulus of PBO nanofiber blended with MWCNTs was35.77MPa and1.11GPa, respectively. TGA analysis indicated the decomposition temperature wasabove550oC under nitrogen atmosphere. At the same time, PBO nanofiber couldn’t be dissolvedin ethanol, acetone, chloroform, the majority of the acid solution and other organic solvents,showing excellent solvent and chemical resistance. 3. Potential application of PBO nanofiber membrane in low dielectric field was investigated.The obtained PBO nanofiber membrane was fluorine contained and processed submicron-scaleporous structure, which is an effective method to reduce the dielectric constant of materials. Thedielectric constant of PBO nano membrane was3.0at the frequency of1MHz-1GHz. When0.8-1.0wt%MWCNTs was added, the dielectric constant decreased to1.2-1.5. The lowerdielectric content of PBO nano membrane indicated a potential application as electronic packagingmaterials.4. PBO nano fiber/sulfonated polyphenylene sulfone (SPPSU) composite membrane wasprepared and characterized. The proton conductivity and direct methanol fuel cell performance ofNafion117membrane, pure SPPSU and SPPSU/PBO composite membrane were analyzed andcompared. The proton conductivity of all samples in100%relative humidity (RH) were stronglydependent on temperature, The proton conductivity of SPPSU/PBO at80oC was as high as0.15S/cm, which was nearly closed to that of comercialzed Nafion membrane. Direct methanol fuelcell performance of membrane electrode assembly (MEA) fabricated from SPPSU/PBO in DMFCmode was measured and compared with Nafion membrane. The highest power density ofSPPSU/PBO at room temperature reached9mW/cm2, which was still higher than Nafion and pureSPPSU (7mW/cm2). The higher open circuit voltage (800mV) of SPPSU/PBO than Nafion andpure SPPSU indicated PBO nanofiber has a very high resistance to alcohol, which made greatsignificance to DMFC.