Study on photoaging of poly(p‐phenylene benzobisoxazole) fiber

As a kind of rig‐rod‐like polymer, poly(p‐phenylene benzobisoxazole) (PBO) has received great interest because of its excellent mechanical properties and good thermal stability. The use of PBO fibers, however, is limited due to its low sunlight stability. In this work, the photoaging of PBO fibers, as well as the effects of oxygen and moisture on their photoaging, is investigated by tensile strength measurements, infrared spectroscopy, molecular mass determination, and scanning electron microscopy. It is first time to find that the photoaging of PBO fibers includes two development stages. The physical aging is the dominate factor at the first stage of photoaging relative to the second stage, in which the chemical aging is the dominate factor. In the first degradation stage, long defects appear and develop parallel to the fiber axis. Little chemical change occurs in this stage. In the second degradation stage, the molecular mass of PBO decreases and chemical degradation occurs. Oxygen accelerates the occurrence of chemical degradation. It is also found PBO fibers are more stable for photoaging when moisture and oxygen are isolated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012