Thermal and physical properties of poly(lactic acid) PLA micro-ground paper recyclable blends

A candidate for hot food packaging applications is poly(lactic acid), PLA, which possesses insufficient heat deflection temperature (HDT) unless fully crystallized. Correlations were determined for the observed enhancement in HDT for PLA and melt-blended composites thereof after annealing. The kinetic parameters of crystallization were obtained by fitting the Avrami equation to DSC data. The reaction order for all the systems were n ~ 3, which is consistent with heterogeneous nucleation and spherulitic crystal growth. The addition of paper and talc did not change the model but did change the rate of crystallization. The smaller particle sized fillers offered the greatest improvement in the rate of crystallization. PLA and all the composites thereof formed containing micro-ground paper or talc had identical melting temperatures (Tm). The variations in the HDTs of the composites were not found to be mirrored in the Tm. Annealing increased crystallinity from 10-15% to 30-40%. Moduli enhanced via annealing were determined using dynamic mechanical spectroscopy (DMS), the results for which support the DSC findings. Blends containing micro–ground paper were found to be tougher than those containing talc by roughly 50–100% depending on the method of test. The annealed PLA/paper composites were found to be superior overall to the PLA/talc composites and are, importantly, sustainable.

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