X-ray Microdiffraction Study of Chain Orientation in Poly(p-phenylene terephthalamide)

Single fibers of poly( p -phenylene terephthalamide) (PPTA; trade names: Kevlar 29, Kevlar 49, and Kevlar 149 ) have been scanned through a 3 μm diameter X-ray beam and the degree of orientation ( f c ) determined at every point. All samples show a gradient in f c values from the skin to the core. The highest degree of orientation was found at the edges of the fibers. This effect is particularly strong for Kevlar 29 . In addition, ripples in orientation were observed along the fiber axis for Kevlar 29, but on a smaller scale than the transversal gradient. Upon tensile deformation up to about 3 GPa applied stress, the transversal f c anisotropy is gradually reduced and disappears at the highest stress values. Kevlar 29 attains at about 1.5 GPa applied stress the same degree of orientation as Kevlar 49 .