Preparation and properties analysis of polycaprolactone/polylactic acid blend for agricultural biodegradable film

Poly lactic acid (PLA) is a kind of environment-friendly high polymer material with the characteristics of biodegradability and good processability, which can be used in producing agricultural film. However, the PLA perform brittleness leads to several defects of PLA film, which might be overcome by addition of polycaprolactone (PCL). This study aimed to find the optimal PCL and PLA ratio for PCL/PLA blend preparation. The preparation and performance tests in the study were all completed in the key laboratory of bio-composite materials of College of Materials Science and Engineering in Central South University of Forestry and Technology in Changsha, Hunan. PCL and PLA mass ratio including 0: 100, 30: 70, 40: 60, 50: 50, 60: 40, and 100: 0 was designed. The PCL/PLA blend was prepared through melt blending and injection molding process. Measured indicators included mechanical properties such as tensile strength, tensile elongation at break and the impact strength. Meanwhile, the micro interface bonding, thermal stability, melting and crystallization behavior as well as the surface wetability of the PCL/PLA blend were tested and analyzed. The analysis of mechanical property tests showed that, with the increase of PCL mass fraction, the tensile strength of PCL/PLA blend decreased gradually, while the tensile elongation at break and impact strength increased first and then decreased. The blend tensile elongation at break and impact strength reached the maximum value of 11.2% and 6.3 MPa, respectively when the PCL mass fraction was 50%. Scanning electron microscopy analysis showed a poor micro interface bond, indicating an inferior compatibility between PLA and PCL. Moreover, it was found that the mechanical properties of PCL/PLA blend were influenced by both the kind and characteristics of the continuous phase of polyester. Thus the results that tensile fracture of blend with the 50% PCL presented the best bonding situation of the 2 continue phases were consistent with results of the mechanical property test. Thermogravimetry analysis showed that the PCL effectively reduced the pyrolysis rate of the blend, improved the pyrolysis temperature and the carbon content of blend increased with the increase of mass fraction of PLA. Differential scanning calorimeter analysis showed that, compared to PLA and PCL, PLA/PCL blend glass transition temperature, melting temperature and crystallization temperature had changed, but effect of the mass ratio on 3 kinds of temperature was not obvious. While the contact angle analysis showed that the contact angles of PCL/PLA blend increased compared to PCL and PLA, reducing the water wettability. When the mass ratio of PCL and PLA was 50: 50, the contact angle of PCL/PLA blend was highest (96.2°). In a comprehensive consideration, PCL/PLA blend performed the best properties with the PCL and PLA mass ratio of 50: 50, and in the other words, the PCL modified the toughness of the composites effectively. The study could provide valuable information for biodegradable plastic film preparation. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.