This research focuses on the microstructure (at the micrometer, nanometer, and Angstrom scale) and mechanical properties of biodegradable polylactide acid (PLA) and compares these properties with those from hydrocarbon derived polymers. The materials are poly-L-lactide acid (supplied by Nature Works), high density polyethylene (HDPE) and low-density polyethylene (LDPE). Extruded films, from 10-30 mm thick, were kindly supplied by Polimeros del Sur SA de CV (Cuernavaca Mor. Mexico). Thermal transitions were determined by differential scanning calorimetry (DSC) analysis, whereas the microstructure was determined via wide and small-angle X-ray scattering (WAXS and SAXS), and small-angle light scattering (SALS). The mechanical properties were determined under uniaxial testing at room temperature using the mini-tensile tester TST-350 (Linkam, England), and the influence of rate of deformation on Young modulus and yield stress was investigated, varying the strain rate from 1 mm/min to 20 mm/min. The results showed for PLA bag an increase in yield stress at higher strain rates, suggesting a strain hardening phenomenon probably associated to stress-induced crystallization. Moreover, the biodegradable polymer PLA also has significantly higher yield stress and Young's modulus relative to the PE samples. Tensile testing along and orthogonal to the extrusion direction revealed anisotropic properties in PLA, and LDPE but this was not the case for HDPE. The mechanical behavior will be discussed in correlation with the micro and nano-scale structure.

Mechanical properties and nanostructure in extruded films of polylactide acid and polyethylene: Influence of rate of deformation

246th National Meeting (2013)

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