Kong Haijuan

Microstructural developments of poly (p-phenylene terephthalamide) fibers during heat treatment process: a review

Poly (p-phenylene terephthalamide) fibers prepared by wet or dry-jet wet spinning processes have a notable response to very brief heat treatment (seconds) under tension. The modulus of the as-spun fiber can be greatly affected by the heat treatment conditions (temperature, tension and duration). The crystallite orientation and the fiber modulus will increase by this short-term heating under tension. Poly (p-phenylene terephthalamide) fibers have a very high molecular orientation (orientation angle 12-20°). Kevlari and Twaroni fibers are poly (p-phenylene terephthalamide) fibers. This review reports for PPTA fibers the heat treatment techniques, devices and its process conditions. It reports in details the structural relationships between the fiber properties which are influenced by the heat treatment process. In particular, focused deeply on the effect of the crystal structure and the morphology of the fibers on the mechanical properties of PPTA fibers.

Surface modification of poly(p-phenylene terephthalamide) fibers with HDI assisted by supercritical carbon dioxide

A process of surface modification of poly(p-phenylene terephthalamide) fibers was reported to improve the adhesion to epoxy, in which the fibers were treated in supercritical carbon dioxide (ScCO2) with hexamethylene diisocyanate (HDI). After the modification, the surface chemical composition of the fibers was identified using X-ray photoelectron spectroscopy (XPS), and the results showed Ph-NH2 groups are formed on fibers after treatment in ScCO2 with HDI. From the scanning electron microscope (SEM) and atomic force microscope (AFM) results, we can find the surface of fibers treated with HDI in ScCO2 became much rougher. The interfacial properties of aramid/epoxy composites were investigated by microdebond test, the results showed that the interfacial shear strength (IFSS) was improved by 22%. It is beneficial for the application of the fiber material as reinforcement in an epoxy system that can improve the interfacial property of PPTA fibers with epoxy.