The ability of Raman spectroscopy to nondestructively evaluate thermal degradation in graphite reinforced epoxy composites was examined. A series of composite samples, exposed to temperatures ranging from 150 to 400 °C for periods of 2 to 20 minutes, were analyzed by Fourier transform Raman and reflectance infrared spectroscopies. The intensity of the Raman and infrared polymeric backbone vibration at 1 600 cm' diminishes with increasing thermal exposures and can be correlated to failure strain and flexural strength measured by four point bending tests, as well as acoustic emission events. These data, along with infrared transmission spectra of species evolved from composite pyrolysis, suggest that thermal degradation occurs in three stages: 1) polymeric fragmentation (possibly microcracking), 2) advanced polymer degradation observed as delamination between the four ply layers, and 3) final composite failure with fiber fracture.
A piezoelectric crystal thermogravimetric analyzer Is described which allows analysis of microgram samples at rates up to 100 °C/min. Samples are deposited as films from solution In a volatile solvent. The variation in frequency as a function of crystal temperature Is measured and subtracted
A bench-scale instrument has been constructed which provides a fire hazard and combustion product profile of polymers and composites used in advanced construction. Novel to the instrument is that a standardized test of material flammability (oxygen index) can be measured as a function of sample exposure temperature up to 800°C. Sample mass loss is measured concurrently ; and Fourier transform infrared (FT-IR) spectroscopy is used for on-line quantification of evolved gas species during heating, burning, and smoldering of the sample. The instrument has applications for industrial quality control of the fire characteristics of processed materials, and research and development of new building materials. This article describes the instrument and presents measurement results for several materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.