Structuring poly (lactic acid) film with excellent tensile toughness through extrusion blow molding

Abstract

We reveal a convenient and feasible processing technique to blow polylactide (PLA) film with excellent tensile toughness, which was: PLA granules were isothermally crystallized and then were blown at a temperature lower than the complete melting temperature. The initial crystalline state of PLA granules was changed by adjusting isothermal crystallization temperature, which was a key point to influence the condensed structures and mechanical properties of films. The results showed that a lower annealing temperature was beneficial for tension toughness of films. When the temperature was set at 90 °C, the elongation at break of film reached 114% and 127% along transverse direction (TD) and machine direction (MD), respectively. The mechanical performances of films were related with their condensed structures. The residual crystals effectively induced tensile crystallization and mesophase during blow molding. Crystals, acting as physical linked points, increased the stress transfer. Cohesive entanglement was an important factor causing PLA film embrittlement, which was suppressed by mesophase.