The changes of structure and mechanical properties of poly(p-phenylene benzobisoxazole) (PBO) fibers with different heat-treatment condition involving temperature, level of tension and duration was investigated. The results revealed that the modulus of fibers was affected greatly by the heat treatment, while the strength of fiber was insensitive to the applied parameter during the heat treatment. It was also found that the heat treatment could promote the ring-close reaction of PBO molecules to completion and impelled the molecular chains to adjust and slide along the stress direction for further orientation, which could make the molecular chain more stretched, regularize the structure of PBO fibers and improve the mechanical properties of PBO fiber.

The interface of two low-density materials is bent in the forming process, which decreases the performance of materials. The theoretical analysis of the interface state in the forming process was taken to solve this problem, and the results indicated that the viscosity of the low-density material was very important to the interface state. The finite element simulation was also used to investigate the factors that affect the interface state. The results revealed the viscosity of material and the pressure were the main factors that affected the interface state; the stress and displacement at the interface could be accurately predicted by the finite element models. The ultimate aim was to modify the relevant parameters in a way that could obtain the required interface states.