Recycling of carbon fibers inserted in composite of DGEBA epoxy matrix by thermal degradation

Abstract

In this study, carbon fibers inserted into an epoxy resin derived from diglycidyl ether of bisphenol-A (DGEBA) were recovered based on the complete removal of the matrix by thermal treatment. The degradation of the composite was carried out at various experimental conditions and the ideal one was obtained at 450 °C for 2 h. Under this condition, all of the resin was removed without degrading the C fibers to any significant degree. The results of thermogravimetric analysis revealed several stages of thermal decomposition depending on the material analyzed. It was established by thermogravimetry analyses that the epoxy matrix starts to experience intense degradation at temperatures above 280 °C with maximum loss in the temperature range of 360–410 °C. In the case of composite samples above 800 °C a residue of approximately 50% by weight can be observed, which is related to carbon fibers. Confirmation of the removal of the resin from the carbon fiber was obtained by means of scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The kinetic of release of CH4, CO2 and N2O gases during degradation process was accompanied by gas chromatography. The concentrations of methane and carbon dioxide increased significantly during the first 10 min of the processing and after this, no released quantities were verified. On the other hand N2O continues to be released even after 3 h of the process of burning the composite in air atmosphere. The treatment proposed in this study can be considered to be a low-cost one as well as being interesting for the recovery of C fibers present in DGEBA matrix which would normally be discarded after use.