Enhancing the transparency and tensile properties of immiscible poly(methyl methacrylate)/ethylene-vinyl alcohol copolymer blends by lithium salt addition

To improve the transparency and tensile properties of immiscible poly(methyl methacrylate) (PMMA) and ethylene-vinyl alcohol copolymer (EVOH) blended films, lithium (trifluoromethane sulfonyl) imide (LiTFSI) was added in small amounts. The addition of LiTFSI improved the transparencies of the PMMA/EVOH blends. However, scanning electron microscopy (SEM) images revealed that the blends with LiTFSI still maintained a sea-island morphology of the PMMA and EVOH phases with strong interfacial adhesion. A comparison of the SEM and energy-dispersive X-ray spectroscopy (EDS) images revealed the localization of LiTFSI in the EVOH domains. By comparing the refractive index data for the EVOH/LiTFSI blends, we established that the refractive indexes of the EVOH phases at LiTFSI concentrations of 20 or 30 wt% matched that of pure PMMA, which accounted for the improvement in transparency. The localization of LiTFSI interrupted the intra- and intermolecular hydrogen bonds of the OH groups in EVOH, resulting in a decrease in crystallinity. Consequently, the amorphous and flexible EVOH domains dispersed in the PMMA matrix prevented stress concentration during tensile deformation, improving the tensile properties. We added lithium (trifluoromethane sulfonyl) imide (LiTFSI) salt into an immiscible poly(methyl methacrylate) (PMMA)/ethylene-vinyl alcohol copolymer (EVOH) to improve the transparency and tensile properties. The addition of LiTFSI reduced the refractive index of EVOH, which matched the refractive index of PMMA, resulting in high transparency. In addition, LiTFSI interrupted the intra- and intermolecular hydrogen bonds between the OH groups in EVOH, resulting in decreased crystallinity. Consequently, the amorphous and flexible EVOH domains in the PMMA matrix changed the tensile properties from brittle to ductile by suppressing the stress concentration.