The Research Of Low Temperature Plasma Modification Of Surface Properties Of PBI Fibers

Polybenzimidazole(PBI) fiber is widely applied in aerospace, aviation,military defense, power generation, environmental purification and other areas. Not only because of the unique rigid molecular structure but also the properties of benzimidazole ring itself make PBI fibers own many excellent properties, especially the high-temperature flame retardant property. However, due to the high molecular rigidity, strong hydrogen bonds between molecules and the lack of side group, PBI fiber is poor in compression resistance and adhesion. Low-temperature plasma modification has been adopted in this paper to modify the surface properties of PBI.Firstly, the effects of air plasma discharging pressure, power and treatment time on the PBI fiber strength and the friction coefficient have been analyzed through a single factor experiment. the orthogonal experiment and Range Method were used to detect all the indexs(breaking strength, static and dynamic friction factor, wicking height, the contact angle). Finally the better optimization parameters are determined: the discharge power is125 W, the treatment time is 210 s and discharge pressure is 25 Pa, namely A1B3C3. Then by means of scanning electron microscope(SEM), XPS, FTIR, TG-DSC, densitometer on different modification conditions(untreated, better optimization, weak, violent) to analyze the fiber properties. The result shows that with the plasma modification process increasing,the surface of fibers vary from smooth, “frosting” likely small layers, “frosting” likely small layers plus bubbling raised cortex to “nubbles”. Meanwhile, C,N elements have decreased while content of O elements and carboxyl-groups have increased. Thermal properties and fiber density did not change significantly after treatment.After the low-temperature plasma modification treatment, adhesion between PBI fibers and other materials was highly increased. We use shear strength between PBI fiber and epoxy resin, peeling strength and peeling power between PBI fiber and PTFE membrane to characterize this change. Under the optimization program(A1B3C3), shear strength,peeling strength and peeling power were 19.51 Mpa, 39.62 c N and 394.08?J respectively. The increasing rate is separately 111.4%, 109.3%, 71.4%. SPSS statistical software analysis indicates the correlation between the static friction coefficient, dynamic friction coefficient and shear strength, peeling strength, peeling power. The results prove that the optimum curve between static, dynamic friction coefficient and adhesion is: xy-=133.6761.49, thecorrelation coefficient R is 0.899.Timeliness of plasma treatment is existing. So as to explore the timeliness factors, the change of wicking height and contact angle was discussed under different conditions. The study reveals that with the extension of storage time, the superior properties after modification have gradually disappeared. Low temperature, high humidity and keep in dark place can help suppress the timeliness.