Adhesion, Permeability, and Mechanical Properties of Multilayered Blown Films Using Maleated Low-Density Polyethylene Blends as Adhesion-Promoting Layers

Abstract

W eh av ef abricated three-layer films, comprising a varying content of ethylene-vinyl alcohol copoly- mer (EVOH) as the internal layer and blends of low-density polyethylene (LDPE) and low-density ethylene grafted with maleic anhydride (LDPE-g-MAH) as the external layers, by ac oextrusion blown-film process. We chose to use blends to promote the adhesion between EVOH and LDPE and to reduce the number of layers in the coextrusion system. The peel strength increased sharply when the amount of LDPE-g-MAH was greater than 12.5 wt% and we associate it with the promotion of adhesion between layers brought about by specific interactions between EVOH and LDPE- g-MAH. FT-IR spectroscopic analysis showed an increase in the intensity of the absorbance of the ester band upon increasing the content of LDPE-g-MAH, which indicates that a chemical reaction occurs that promotes adhesion at the interface. The tensile strength did not change significantly with increasing LDPE- g-MAH content, which had a small effect on elongation and modulus in both the machine direction (MD) and transverse direction (TD). Tear strength decreased continuously with in- creasing LDPE-g-MAH content, in both the MD and TD, as a result of the greater ease of crack propagation in the EVOH layer. The oxygen permeability of the three-layer films remained alm ost constant upon varying the amount of LDPE-g- MAH. These three-layer fi lms all followed the theoretical prediction made by the inverse additivity rule. The water vapor permeabilitie so ft he three-layer films, however, were affected by the degree of hydrogen bonding, which was analyzed by FT-IR spectroscopy. The effects of this hydrogen bonding resulted in a discrepancy between the experimental findings and the theoretical predictions, especially when the EVOH content was increased. Coextrusion is a process in which two or more poly- mers are extruded simultaneously and joined together to form a single structure having different properties in each layer and to achieve a broad range of properties that are not available in any of the individual materi- als alone. In recent years, the packaging and container industries have paid increasing attention to the devel- opment of new or improved products formed by coex- trusion, such as multilayer sheets, multilayer films, and