Fourier transform infrared spectroscopy, scanning electron microscopy, and the weight-loss method were utilized to propose a novel kinetic model for PMMA decomposition by microwave digestion with HNO₃ as a digestion reagent. By Newton's method, the experimental results of the remaining weight of PMMA is closely fitted by the model combined with zero-order and first-order kinetics, in which the former dominates the reaction at lower temperatures (423-443 K) and the latter at higher temperatures (≧ 453 K). Accordingly, a mechanism for PMMA decomposition is proposed in this study. Kinetic parameters of PMMA decomposition under 423-453K including rate constants and the mass fractions (α) via main-chain scission were determined by this model. Activation energies of PMMA decomposition estimated by Arrhenius equation are 2.45-2.81 and 23.5-27.0 kcal mol⁻¹, respectively, for the zero- and first-order reactions. The pre-exponential factors of the zero- and first-order reactions are 1.96×10⁻² to 2.92×10⁻² g min⁻¹ and 1.31×10¹¹ to 7.08×10¹² min⁻¹, respectively. Effect of HNO₃ volume on PMMA decomposition was investigated at 423-473 K. The digestion efficiency apparently increases as HNO₃ volume is more than 3mL at these temperatures. At 473 K, the digestion efficiency has increased to 100% as HNO₃ volume is ≧3 mL. The estimated α values of the decomposition with 2-7mL of HNO₃ at 423-473K are increasing with HNO₃ volume at 423 and 443 K, yet varying insignificantly at 453 and 473 K.
關聯:
Materials Chemistry and Physics vol. 108, no. 2-3 pp.382-390
