علی یادگاری

As a commercially available biodegradable and bio-based polymer, Poly (lactic acid) is accepted to be a promising potential to replace the conventional polymers in packaging applications. Oriented PLA films are obtained through stretching at temperatures above the glass transition temperature. The present study evaluated the effects of both temperature and drawing speed during stretching on the tensile behavior and surface morphology of PLA films. The results showed that increasing the drawing speed enhanced the strain hardening behavior. Conversely, there was a noticeable reduction in strain hardening as stretching temperature increased from 70 to 80 °C. Besides, stretching at 90 °C eliminated, 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) stimulated the strain hardening behavior demonstrating chain extension exceeded the chain relaxation at such a high drawing speed. The surface morphology of PLA films observed by scanning electron microscopy (SEM) revealed 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 showed the formation of crystalline lamellae which is attributed to the cold crystallization during the stretching.