Characterization and properties of epoxidized natural rubber toughened poly (lactic acid) reinforced by graphene nanofiller

Abstract

The unvulcanized and dynamically vulcanized poly (lactic acid)/ epoxidized natural rubber (PLA/ENR, PLA/ENR-TPV) blends and a new ternary nanocomposite system based on PLA/ENR/graphene and PLA/ENR-TPV/graphene were prepared. The effect of ENR and ENR-TPV contents (10-30 wt%) on the morphological and mechanical properties of the blends were investigated. On the top of that, the effects of graphene loadings (0-2.0 phr) and different processing methods on the morphological, mechanical and thermal properties of nanocomposites were evaluated. The blends were prepared using a nano-single screw extruder whereas PLA/ENR/graphene and PLA/ENR-TPV/graphene nanocomposites were prepared using both nano-single screw extruder and internal mixer. The tensile and the impact test were carried out to determine the mechanical properties, while the differential scanning calorimeter (DSC) and the thermogravimetric analysis (TGA) were used to investigate the thermal properties. Meanwhile, scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM) were used to observe the morphologies of the blends and nanocomposites. The PLA/ENR and PLA/ENR-TPV blends at 10 wt% of ENR and ENR-TPV loadings showed the highest impact and tensile properties. Thus were selected as basic materials to prepare the nanocomposites. The PLA/ENR/graphene nanocomposites prepared using the internal mixer gave higher mechanical properties and thermal stability than the nano-single screw extruder. The tensile strength, elongation at break and impact strength of the PLA/ENR/graphene and PLA/ENR-TPV/graphene nanocomposites were increased until 1.0 phr of graphene loading. Beyond that these mechanical properties decreased. The PLA/ENR-TPV/graphene nanocomposite exhibited higher tensile strength, elongation at break and impact strength compared with PLA/ENR/graphene nanocomposite. The thermal stabilities of the PLA/ENR/graphene and PLA/ENRTPV/ graphene nanocomposites prepared by both nano-single screw extruder and an internal mixer have improved as the graphene loading increased. From DSC analysis, it was found that the melting temperature, Tm remained unchanged while heat of fusion, AHm and degree of crystallinity, Xc increased as the graphene loading increased since graphene acted as a nucleating agent. The FESEM micrographs revealed good dispersion and distribution of graphene in the PLA/ENR and PLA/ENR-TPV matrix at 1.0 phr of graphene loading that resulting in good interaction between the components. Furthermore, the nanocomposites that prepared using the internal mixer showed better dispersions and distributions of graphene in the matrix thus further enhancing the properties of the nanocomposites.