| In recent years, more and more attention has been paid for Polylactic acid which is a biodegradable polymer materials. And compared to the traditional plastic. Polylactic acid has excellent performance, such as its good compatibility, biodegradability and good mechanical properties. However, PLA has some shortcomings, such as hard and brittle mechanical properties, relatively low crystallization rate and so on, which limit its development and practical application. Crystallization of polylactic acid can significantly improve its stiffness, strength, heat distortion temperature, chemical resistance and permeability, etc. Many researchers have selected different nucleating agents to improve the crystallization properties of polylactic acid, but often neglected the impact of processing technology. In order to improve the shortcomings of PLA, in this work, the effect of uniaxial orientation process conditions on the crystallization and the oxygen permeability of pure and plasticized poly (lactic acid) film had been investigated with PLA as raw material. The main results are as follows:(1) When stretching ratio and stretching rate were constant, with the increasing of temperature, the crystallinity of pure and plasticized PLA was first increased and then decreased. The optimal stretching temperature of pure PLA and plasticized PLA was respectively90℃,90℃and100℃. Comparing with pure PLA film, plasticized PLA films showed lower sensitivity of crystallization to stretching temperature.(2) When stretching temperature and stretching rate were constant, the crystallinity of pure and plasticized PLA increased with the stretching ratio increasing, and the crystallinity of plasticized PLA was higher than that of pure PLA.(3) When stretching temperature and stretching ratio were constant, the crystallinity of pure PLA increased when stretching rate was improved. But the crystallinity of plasticized PLA decreased with stretching rate increased.(4) Stretching temperature, stretching ratio and stretching rate did not change a crystal form in pure and plasticized PLA samples.(5) The analysis results of polarizing microscope photographs showed that pure PLA and PLA samples with TEC content5wt%all had ellipsoidal spherulites. But the spherulite size of plasticized PLA was larger than that of pure PLA.(6) When the content of plasticizer was constant, oxygen permeability coefficient of pure and plasticized PLA decreased with increasing crystallinity. But when stretching temperature was constant, oxygen permeability coefficient decreased with the content of plasticizer increased. |
