Effects of compatibilizer on morphology, mechanical and thermal properties of polylactic acid/natural rubber blend

Abstract

The primary focus of this study was to prepare two types of compatibilizers, i.e. polylactic acid-grafted-maleic anhydride (PLA-g-MA) and natural rubbergrafted- maleic anhydride (NR-g-MA) for PLA/NR blends. In the first phase of the study, PLA/NR blends with different NR concentration in the range of 5 to 20 wt% were fabricated. Experimental results showed that PLA/NR blend containing 5 wt% of NR concentration (designated as PLA95/NR5) was the optimum blend due to its higher impact strength (35.74 J/m) and elongation at break (1.84%) as compared to other PLA/NR blends. In the second phase of the study, the two types of compatibilizers (PLA-g-MA and NR-g-MA) with different MA concentrations in the range of 3 to 12 phr were prepared using melt grafting free-radical polymerization method. It was found that the optimum MA concentration for grafting PLA and NR were both 9 phr with the degree of grafting of 1.63% and 5.02%, respectively. In the third phase, the PLA95/NR5 blend was incorporated with different compatibilizers (PLA-g-MA and NR-g-MA) at various loadings (1-10 phr). The experimental results of the mechanical properties, i.e. impact strength, elongation at break and storage modulus of the PLA95/NR5 blend did not show significant enhancement upon addition of PLA-g-MA in the blend. Scanning electron microscope results showed better interfacial adhesion between PLA and NR phases upon addition of 3 phr PLAg- MA into the blend. The improvement in the interfacial adhesion of the blend could be attributed to the good dispersion of the NR particles in the PLA matrix with the aid of PLA-g-MA compatibilizer. On the contrary, the addition of NR-g-MA did not show much improvement in the mechanical properties of the PLA95/NR5 blend but thermal stability of the blend was increased as compared to the PLA95/NR5. In all tests, further increased of PLA-g-MA and NR-g-MA up to 5 phr and 10 phr, respectively in the PLA95/NR5 blend caused the blend stiffness to increase. This possibly due to an increase in the amount of MA and the reduction of NR elasticity.