Mechanical, thermal, morphological and rheological properties of POLY (LACTIC ACID) / natural rubber/ carbon nanotube nanocomposites

Abstract

Inherent brittleness in poly(lactic acid) (PLA) largely limit its wide applications as common biodegradable plastic materials. Thus, PLA toughening through melt blending was prepared by incorporating different ratio of natural rubber (NR) (0% to 20%) as toughening agents to investigate the mechanical, thermal, morphological and rheological properties of the PLA/NR blends. This approach used 9 wt.% of two different types of compatibilizers natural rubber-grafted-maleic anhydride (NR-g-MA) and polylactic acid-grafted-maleic anhydride (PLA-g-MA) in the system to enhance compatibility between PLA and NR. Then, to improve stiffness and strength of the blends, addition 1-8 phr of nanofiller pristine carbon nanotube (CNT) was added into the system to prepare PLA/NR nanocomposites. The result of mechanical properties the blends showed good performance significantly for impact strength. Additionally, thermal properties of the blends and nanocomposites were investigated by using thermogravimetric analysis and differential scanning calorimetry. The results showed an increase in glass transition temperature and thermal stability by addition of CNT. Scanning electron microscopy and nanoscanning electron microscopy were conducted and revealed good dispersion of CNT particles in the PLA matrix at higher amount (8phr). Moreover, X-ray diffraction analysis was carried out for microstructure properties determination for nanocomposites and showed good interactions between PLA and CNTs. Finally, melt flow index and rotational rheometer were used to characterize the rheological properties of the blends and nanocomposites. Increasing for storage modulus and loss modulus were observed in the system with addition of CNT. Experimental data obtained from rheological analysis for all these three systems were used for mathematical model approaches using Power Law and Carreau - Yasuda models to study the rheological behaviour of blends. Power Law model has the best fit and more suitable for shear-thinning behaviour because of low range shear rate system for this particular study compared to Carreau-Yasuda. As a conclusion, additional of compatibilizer and CNT led blend properties to increase significantly in impact strength and thermal stability.