Lateral growth of microparacrystals in kevlar 49 fibers irradiated by Co⁶⁰

Abstract

SynopsisWide-angle x-ray diffraction experiments on Kevlar 49 fibers, irradiated with y-rays from a Corn source, indicated that radiation-induced cross-linking in the form of H-bonding occurred within the microparacrystals (mPC) in the lateral direction b of the unit cell and had led to an increase in the mPC size in this direction. On the other hand, the mPC size Zzoo along the axis and normal to the [200] netplanes did not change by radiation. In effect, the mPC size normal to the [110] netplanes increased from 4.23 nm to a maximum value of 6.04 nm at the 600 MRad dose level, after which it decreased. The mPC size in the direction of the fiber axis was 102 nm and did not change significantly by radiation (102-109 nm). Thus, essentially, the mPCs grew solely in the b direction. The paracrystalline distortion parameter (g) in the direction of the fiber axis was 2.8% and was not changed significantly by radiation (g = 2.9 f 0.2%). The equatorial "crystallinity" maintained a value of 76% until a dose of 50 MRad and then became 73% at 100 MRad and 70% after this dose level The netplane distances were not affected by radiation.

X‐ray diffraction, Raman, and differential thermal analyses of the thermal aging of a Kevlar®‐PBI blend fabric

“…This decrease may play a central role in explaining the significant loss of tensile strength after thermal aging. The proposed hypothesis offers an explanation of the effects of thermal treatments on the crystallinity and mechanical properties of Kevlar fibers that both synthesizes the conflicting results found in previous studies [4–9], and agrees with the experimental facts described in this paper. Such a fitting explanation, to the best of our knowledge, has never been reported in the literature concerning Kevlar fibers.…”

“…Previous studies on the effects of thermal treatments on Kevlar crystallinity have produced some conflicting results. Hindeleh et al [4, 6, 7] studied the crystallinity and the lateral crystallite size of Kevlar after thermal aging in air and thermal annealing under nitrogen atmosphere. They measured a decrease in crystallinity after aging Kevlar at 150°C for periods ranging between 7 and 150 days.…”

Influence of Hydrolytic and Chemical Treatment on the Mechanical Properties of Aramid and Copolyaramid Fibers

“…From this result, we may conclude that some lateral growth in the lamellae takes place at a cost to their thickness. Hindeleh and others reported similar structural variations [5,7] when Kevlar 49 was annealed at high temperatures or irradiated with Cob°-y rays, respectively. This process may be initiated by cracking tie molecules, leading to a diminished correlation of supermolecular order parallel to the fiber direction.…”

Effect of the factors affecting high-performance p-aramid fibre dyeing and their optimization

“…The molecular chains in p-aramid fibre are ordered and dense due to which it contains high crystalline structure and high glass transition temperature (T g ) (Lei et al , 2014). In the synthetic fibres, the dye diffusion depends on the polymer chain mobility which ultimately depends on the glass transition temperature (Hindeleh et al , 1990).…”