Pretreating poly(p‐phenylene benzobisoxazole) fibre with polyphosphoric acid and dyeing with disperse dyes

Abstract

In recent years, many advanced composite materials based on poly(p‐phenylene‐2,6‐benzobisoxazole) fibres have become prominent in applications requiring high‐strength and flame‐retardance such as body armour, industrial reinforcement materials and military camouflage. However, the application of these fibres used as protective clothing is limited due to difficulties in dyeing and printing. In the present work, a process for pretreating poly(p‐phenylene benzobisoxazole) fibre with polyphosphoric acid was applied, and the pretreated fibre was then dyed with disperse dyes via dip dyeing. Effects of pretreatment temperature and time on structure and properties were investigated. Surface morphology, crystallinity, chemical structure and degree of orientation of fibres were characterised. The results indicated that the supramolecular structure of the fibre was relaxed or swelled by polyphosphoric acid in the pretreatment process, so that the dyeability of poly(p‐phenylene benzobisoxazole) fibre was improved, with satisfactory dye exhaustion, K/S values and dyeing fastness. Also, with the appropriate pretreatment process, the swelling effect of polyphosphoric acid on the structure of poly(p‐phenylene benzobisoxazole) fibre was limited, so as to control the decrease in tensile strength and limiting oxygen index of the dyed fibre.