Improving the resistance to hydrothermal ageing of flame-retarded PLA by incorporating miscible PMMA

Three flame-retarded systems based on PLA, PMMA and PLA/PMMA blend have undergone hydrothermal ageing. The miscibility of the blend as well as the crystallization behaviour of PLA were studied by DSC. The impact of ageing in terms of weight variations, melt viscosity, molecular weight distribution, morphology, and thermal degradation was investigated. Results showed that crystallization of PLA and significant hydrolysis phenomenon occurred during ageing. Flame retardant content determined by EDX and ICP revealed a loss of phosphorus during ageing, especially for flame-retarded PLA (91 wt% phosphorus loss after ageing). Incorporation of 50 wt% PMMA moderated the negative impacts observed. Fire properties evaluated using cone calorimeter revealed almost no impact of ageing on flame-retarded PMMA, contrary to flame-retarded PLA (increase of pHRR from 291 to 487 kW/m2). Flame-retarded blend shows intermediate properties. It revealed the positive effect of incorporation of PMMA in PLA, by limiting the water diffusion and by reducing the loss of phosphorus.