Thermal Degradation of Polylactide Composites Containing Plant Fibers

Due to its compostability, biocompatibility and high deformation and strength properties, polylactide (PLA) has found wide application in various industries. However, unsatisfactory thermal stability of PLA, its tendency to hydrolysis, low hydrophilicity, low values of crystallization rate and impact toughness significantly limit its application. To eliminate the above disadvantages, fillers based on clay, nanocellulose, metals, metal oxides/hydroxides and silicon are used. Particularly noteworthy are plant fibers consisting of cellulose, hemicellulose, lignin, waxes and pectin, which can be used to reinforce polymer matrices in order to improve their properties. Fillers based on plant fibers are low cost, low density and are obtained from widely available renewable raw materials. The results of the analysis of the literature sources discussed in the review showed that untreated plant fibers, which have hydrophilic properties, in most cases reduce the thermal stability of the hydrophobic PLA matrix. Poor compatibility of cellulose-containing fillers with the polyester matrix, causing agglomeration of plant fiber particles in compositions with PLA, contributes to the deterioration of the thermal stability of PLA. However, chemical modification of plant fibers (treatment with sodium hydroxide, silane, acetic anhydride, etc.) can improve the compatibility of plant fillers with the polylactide matrix. This is confirmed by TGA data (namely, an increase in the temperature of the maximum decomposition rate Tm.s.r., corresponding to the stage of thermal degradation of PLA, with the introduction of modified plant fibers) and kinetic analysis (the effective values of the activation energy of thermal decomposition of PLA compositions with modified plant fibers are higher than those of the original PLA).