Stabilization of PE/PEO Cocontinuous Blends by Interfacial Nanoclays

Organomodified clays are known to be effective in polymer blend compatibilization if located preferentially at the domain interfaces, but little is known regarding the origin of their localization. In this study, we investigate the effect of organomodifier, clay loading, and shear environment on the compatibilization extent in nonreactive polyethylene (LDPE)/poly(ethylene oxide) (PEO) and reactive maleic anhydride functional polyethylene (PE-g-MA)/PEO polymer blends. We pose important questions: If clay is to compatibilize blends by interfacial localization, how does organomodifier affect its localization? How does an increase in clay loading affect the shape and elasticity of the interface? What is the shear intensity needed to overcome the equilibrium distribution of clays and delaminate it from the interface? We utilize laser scanning confocal microscopy and 3D image analysis to calculate characteristic phase size and gain unique insights into the connection between the clay loading and the interfacial curvature. Our experiments demonstrate that 1 wt % of interfacially localized clay is sufficient to suppress coarsening and greatly reduce phase domains. However, further increase of clay loading only saw a marginal reduction in phase size compared to 1 wt % clay loading. The interfacial curvature calculations showed that with increase in clay loadings beyond 1 wt % the shape of the interface does not change significantly; however, slight broadening of curvature distribution and increasing asymmetry are observed from 3D images. This can be attributed to the multiple layers of clay jammed at the interface at higher clay loadings. When reactive PE-g-MA was substituted for LDPE, graft copolymers were generated via in situ coupling at the interface. These copolymers combined with clay resulted in the smallest phase domains. In addition, we show that clay dispersion and localization were largely independent of shear intensity, which suggests that clay does not delaminate from the interface even in high shear environments.