The structure-property relationships of LLDPE–EVOH blend films fabricated by multiplication extrusion

Abstract

The blend of linear low density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with weight fraction of 50–50 is extruded through a series of multipliers to fabricate thin films. Different numbers of multipliers are utilized to tailor the morphology of the extruded blend films. We discover that as the number of multipliers increases, the blend film morphology evolves dramatically. The elongated and layer-like structure is gradually replaced by well-dispersed nano-blend morphology when the number of multipliers reaches eight. The domain size of each component decreases due to the effect of multiplication process. This is because during the multiplication process, multipliers behave similar to static mixers that physically break the elongated and layer-like structure of LLDPE and EVOH into tiny domains. Along with the morphological evolution, the physical properties of the extruded blend films change greatly. Atomic force microscopy (AFM) and wide angle X-ray scattering (WAXS) are utilized to investigate the morphology and crystalline structure of the blend films. Oxygen gas permeability and water vapor transport rate (WVTR) are measured by MOCON units. The transmission rate and mechanical properties are studied by the UV–vis and a mechanical tensile stretcher (MTS) respectively. We report that both oxygen permeability and WVTR increase as the number of multipliers increases. The transparency is improved as more multipliers are used. The last but not the least, tensile mechanical behaviors gradually become isotropic at different deformation directions as the morphology changes.