Catalytic degradation of a carbon fibre reinforced polymer for recycling applications

Abstract

A range of alkaline and weak Lewis acid solutions were used in conjunction with an acetone / water solvent system in order to decompose a carbon fibre reinforced epoxy resin. The initial concentration of the additives in the mixture was varied between 0.01 to 0.40 M at temperatures and pressures of 280 to 320 °C and 13 to 20 MPa. Under these conditions and a reaction time of 1 h, KOH and NaOH did not accelerate the decomposition of the matrix relative to the neat solvent, however, 0.05 M solutions of ZnCl2 and MgCl2 and a 0.005 M solution of AlCl3 facilitated the recovery of clean fibres at 300 °C. Under these conditions, the degradation achieved with acetone / water alone was just 33 wt%. By changing the process temperature and reaction time, the minimum necessary conditions for complete degradation were identified as 290 °C, 1.5 h or 300 °C, 45 min for all metal chlorides investigated. This represents a reduction in temperature of 40 °C when compared to a neat acetone / water solvent mixture. The reaction kinetics were studied through the application of a first order rate equation and a shrinking core model with the results demonstrating that 0.05 M ZnCl2 reduces the activation energy of the reaction by 30%. Analysis of the organic liquid fraction using infrared spectroscopy suggests that this is due to the cleavage of the CN bonds in the epoxy resin by the metal ions. Gas chromatography with mass spectrometry identified the presence of cyclic compounds and low concentrations of amine derivatives.