Tensile and compressive behavior of poly(p‐phenylene benzobisthiazole) fibers

Abstract

SYNOPSISHeat treated poly(p-phenylene benzobisthiazole) (PBZT) fibers tested in tension result in two types of failure modes. In failure mode I, the fiber exhibits a relatively sharp break; mode I1 is characterized by significant axial fiber splitting. Approximately 20% of the fibers failed in mode I1 when tested at 2.54,7.62, and 12.7 cm gage lengths. At 1.25 cm gage length all the fibers failed in mode I. Tensile strength decreased from the 1.25 to 7.62 cm gage length, but tensile strength of the fibers tested at 7.62 and 12.7 cm gage lengths were similar. The two failure mode observation is supported by the Weibull statistical distribution. Fiber tensile properties were also measured at 150°C. Axial compressive strength of the PBZT fibers as determined from the recoil test is also reported and is found to be independent of fiber tensile modulus and fiber diameter. As-received heat-treated fibers were post heat treated between 700 and 775°C. Structural changes in the fiber were studied using infrared spectroscopy, small and wide angle x-ray scattering, and swelling studies. 0

Liquid crystalline organic fibres and their mechanical behaviour

“…On the other hand, PBO fibres reach values of about 6-7 and PBZT fibres values of about 7-10. In any case the shape parameter appears to be slightly lower than that of Kevlar fibres which is in the range 8-14 (Sahafeyan and Kumar, 1995;Leal;.…”

Rigid‐Rod Polymers

“…In mode II, significant splitting is observed with lower tensile strength. Both of the modes fit the Weibull statistical distribution (181,182). The distribution of PBO fiber strengths can be expressed as a Weibull distribution function with two parameters (187).…”

“…With increasing molecular weight, the tensile strength and the elongation at break of both PBZT and PBO fibers increase (31,180). In addition, defects, such as impurities, voids, surface damage, and misaligned crystals, affect the strength of rigid-rod polymer fibers (181,182). When the intrinsic viscosity of PBO/PPA spinning solution increases to approximately 30 dl/g, the resulting fibers have the highest tensile strength and modulus (31).…”

“…However, the PIPD fiber shows improved compressive properties due to the intra-and intermolecular hydrogen bonds in its molecular structure (10). For PBZT fibers, no significant compressive strength dependence on either fiber tensile modulus or diameter was observed (181,182).…”

“…(1) Cross-linking PBZT fiber through post-heat-treatment, to enhance the lateral connection and improve the compressive strength (181,265,266). (2) Cross-linking PBZT through functional groups, which can create free radicals:…”