Catalytic degradation of a carbon fibre reinforced polymer for recycling applications

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 C[dbnd]N 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.