Minimally processed date palm (Phoenix dactylifera L.) leaves as natural fillers and processing aids in poly(lactic acid) composites designed for the extrusion film blowing of thin packages

A bio-based and biodegradable film was manufactured by extrusion blowing of polylactic acid (PLA) based thermoplastic resin (PLSF) compounded with natural fillers obtained from minimally processed date palm leaves (DPLF). A neat PLSF reference film and films with different filler contents (1, 2 and 5 wt. %) were prepared and tested in tension along three directions: Machine direction (MD), transverse direction (MD) and 45 degrees direction (45D). Adding DPLF up to 2 wt.% has a reinforcing effect, with an optimum around 1 wt.%. This optimum reinforcement translates in the enhancement of the apparent Young's modulus, the tensile strength and the elongation at break, of about + 29 % and + 12 %, respectively, along the MD direction. Above 2 wt. % DPLF, the mechanical properties decrease because of a loss in film crystallinity, additional PLA thermal degradation triggered by the addition of the natural fillers and the poor adhesion between the fillers and the matrix. The mechanical anisotropy of films (larger tensile strength and elongation at break along MD) was increased by the addition of DPLF. This anisotropy was essentially explained by the amorphous polymer chain orientation along MD during blowing, which is promoted by the filler confining effect. Overall, this study shows that a waste from date palm leaves can be valorized for biodegradable film packaging applications.