Morphology of poly(p‐phenylene terephthalamide) fibers

Abstract

Fibers of poly(p‐phenylene terephthalamide) (PPTA) have a fibrillar morphology, the individual fibrils having a high proportion of extended chains passing through periodic defect layers. A pleat structure is superimposed. The fibers are fully crystalline (within the limits of determination) with a small fraction of randomly oriented crystalline material. The major distinction between PPTA and conventional fibers lies in the high level of extended chains passing through the defect layers of the former structure. These extended chains result in crystallographic register being maintained between adjacent ordered zones. Quantitatively, a measure of this order is obtained from a comparison of the correlation length, obtained from meridional x‐ray peak widths, and the defect spacing. In conventional fibers the defect spacing, i.e., long period, is longer than the correlation length (i.e., crystal size). In PPTA, the analog of the long period, the defect spacing (about 35 nm) is smaller than the correlation length, which is over 80 nm.

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

“…Comparing the three models of the PPTA fiber structures given by Panar et al 40 , Morgan et al 52 and Northolt and Sikkema 55 we can observe that the 600 nm fibril diameter deduced by Panar et al is ten times larger than the 60 nm fibril diameter deduced by Morgan et al…”

“…The value 35 nm of the defect spacing in the banding of the PPTA fibers is observed by Panar et al 40 by using etching techniques in refluxing hydrochloric acid solutions plus small angle X-ray scattering (SAXS). The defected layer and its relationship to chain extension are crucial to understanding the structural features of PPTA fibers which are most closely related to the high strength of these fibers.…”

“…Figure 16 illustrates the skin-core structure of etched PPTA fibers -shown by the scanning electron microscope (SEM). Panar et al 40 used the plasma technique to cut the ends of the fiber so as to study the skincore structure of PPTA fibers. They found that, the surface fibrils are uniformly axially oriented, while the core ones are imperfectly packed and are ordered (so, voids will be formed in the core): Figures 17 and 18.…”

Strength and toughness of structural fibres for composite material reinforcement

“…In this case, the residual strength of the Kevlar KM2 notched fibres was not significantly affected by the presence of the defect introduced, suggesting involvement of other nonlinear energy dissipation mechanisms (3194 and 3816 MPa for notched and unnotched strength, respectively). This notch insensitivity behaviour could be attributed to the fibrillated structure that allowed sliding mechanisms in the fibre direction, which could produce a homogenization of the stress field around the notch region [7,14]. As a result, individual bundles of the aramid fibre were loaded almost homogeneously and regardless of the presence of the notch, resulting in a less sensitive behaviour of the fibre (figure 6b).…”

Moisture Sorption Mechanism of Aromatic Polyamide Fibers. (Part 4). Effect of Water on the Crystal Structure of Regular Kevlar.

“…In the case of Pn symmetry, however, the structural factor for the 001 reflection is not zero. (14,15,18,19,24). From these data, the average number paper, we will report on the WAXD study on the dehydration process using an as-spun wet PPTA fiber to detect the formation of the crystal lattice.…”