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

✍ Scribed by Carlos Arrieta; Eric David; Patricia Dolez; Toan Vu-Khanh

• Publisher: Society for Plastic Engineers
• Year: 2011
• Tongue: English
• Weight: 465 KB
• Volume: 32
• Category: Article
• ISSN: 0272-8397
• DOI: 10.1002/pc.21041

✦ Synopsis

Abstract

A previous study of the effects of thermal aging on the tensile properties of a fabric made of a 60–40 wt % blend of Kevlar and PBI fibers has shown that exposure to elevated temperatures between 190 and 320°C results in a rapid decrease in tensile breaking force retention. In this article, X‐ray diffraction and Raman spectroscopy analyses were carried out to evaluate the consequences of thermal aging on the material's crystallinity. Differential thermal analyses were also undertaken to examine the evolution of the glass transition temperature of PBI following thermal exposure. X‐ray diffraction profiles show a gradual increase in the crystallinity with temperature and aging time, whereas a complete disappearance of spectral lines for aged samples in Raman analysis suggests instead a decrease in crystallinity as a consequence of exposure to elevated temperatures. The seemingly contradictory outcome obtained when using the two techniques led to the proposal of a new, alternative hypothesis to explain the observed results. This hypothesis involves two simultaneous events that occur during thermal aging: the increase of crystallite size in the direction parallel to coplanar sheets, and the disruption of the crystalline lattice in the direction perpendicular to those sheets. The glass transition temperature of PBI was found to shift towards the lower temperatures after thermal aging, a phenomenon that can be associated with random polymer chain scission caused by thermal aging. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers