Tensile behavior of extruded poly (lactic acid) films during stretching at different conditions

As a commercially available biodegradable and bio-based polymer, Poly (lactic acid) is accepted to be a promising potential to replace conventional polymers in packaging applications. Oriented PLA films are obtained through stretching at temperatures above the glass transition temperature. The present study evaluates the effects of both temperature and drawing speed during stretching on the tensile behavior and surface morphology of PLA films. Increasing the drawing speed enhances the strain hardening behavior. Conversely, there is a noticeable reduction in strain hardening as stretching temperature increases from 70 to 80 °C. Besides, stretching at 90 °C eliminates, thoroughly, the strain hardening behavior at lower drawing speeds. However, stretching the PLA film at 90 °C and at a high drawing speed (30 mm/sec) stimulates the strain hardening behavior demonstrating chain extension exceeds the chain relaxation at such a high drawing speed. The surface morphology of PLA films observed by scanning electron microscopy (SEM) reveals no crystalline structures on the film surface of PLA films stretched at 70 and 80 °C. The SEM image of PLA film stretched at 90 °C indicates formation of crystalline lamellae which is attributed to cold crystallization during stretching.