Washing And Heat Treatment Processes Of High Performance PBO Fibers

Poly (p-phenylene benzobisoxazole)(PBO) fibers possessing excellent thermalstability and extraordinary mechanical properties have been widely applied in highperformance composite materials. In the industrial process, washing and heattreatment are the key factors affecting fiber properties.In this article, PBO fibers were spun by dry-jet wet-spinning after thepolymerization of DAR and TPA in PPA solution. The as-spun PBO fiber was washedwith different washing medium. The relationship between washing conditions and theproperties of PBO fiber was studied by changing the washing time and washingmedium. At the same time, ultrasonic was tried to enhance the washing effects.The phosphorus content of washed samples was measured using inductivelycoupled plasma atomic emission (ICP) method, the results shows that washing caneffectively remove the residual polyphosphoric acid in PBO fiber, achieving therequirement of the phosphorus content of0.8%or less. The measurement results ofultrasonic treatment samples show that the effect of phosphorus removal by ultrasonicwashing is better and more efficient. As the phosphorus content decreased, fibermechanical properties have a certain degree of improvement. The experiment alsofound that washing in the dilute alkali solution or ultrasound time is too long cancause fiber mechanical properties reduced.Phosphorus removal effect and cost analysis show that the ultrasonic applied tothe PBO fiber washing is feasible.Heat treatment of PBO fiber was studied by setting different heat treatmenttemperature and time. The Fourier infrared spectrum analysis, phosphorus contentanalysis, X-ray diffraction (XRD) analysis of samples found that the tension heattreatment can promote the cyclization reaction of PBO molecules, improve theregularity of molecular chain and the length of the polymer chain in conjugatedsystem, improve the crystallization and orientation of fiber and defect reduction. Scanning electron microscopy (SEM) analysis and micro-pull-outed test found thatheat treatment can make the fiber surface roughness, and increase the interfacial shearstrength (IFSS) of PBO fiber/epoxy resin composites, the highest can be increased by40%.Mechanical performance tests show that heat treatment can significantly improvethe mechanical properties of PBO fiber, but for the influence of modulus is even moresignificant. The modulus of PBO fiber processed under550℃up to167GPa,increased by nearly50%than the as-spun fiber, but only about7%of the fracturestrength up to ascension. Increasing the heat treatment temperature and time all canimprove the mechanical properties of PBO fiber, but too high temperature or longtime will result in lower mechanical properties.In order to determine the best condition of heat treatment process, the heattreatment parameters are optimized by genetic algorithm. First, adopting the methodof multiple regression analysis established the mathematical model of the targets, andthen using the genetic algorithm to calculate the fitting model, getting the optimal heattreatment temperature of520℃and the heat treatment time of28s, implementing theoptimization of PBO fiber heat treatment process.