Co-extrusion of multilayer poly(m-xylylene adipimide) nanocomposite films for high oxygen barrier packaging applications

Multilayer packaging films incorporating a montmorillonite layered silicate (MLS)/poly(m-xylylene adipimide) (MXD6) nanocomposite as the oxygen barrier layer and low-density polyethylene (LDPE) as the moisture resistant layer were produced through the co-extrusion process at the laboratory and pilot scale level. Extrusion screw speeds were varied from 30 to 130 rpm in order to produce samples with varying layer thicknesses. The multilayer film structure was scaled up from the laboratory scale to the pilot-level scale based on oxygen transmission data obtained from the laboratory-scale process parameters. Laboratory-scale film results indicated that the film which demonstrated an optimal oxygen transmission rate (OTR) of 0.3 cm3/(m2 day) at 60%RH and water vapor transmission rate (WvTR) of 1.4 g/(m2 day) at 90%RH had a structure that contained a core barrier film layer of nanocomposite MXD6 that makes up roughly 34% of the total film thickness, with the remainder of the film material consisting of maleic anhydride grafted polyolefin tie layers and LDPE skin layers. The OTR of the films changed as the relative humidity of the test environment was varied from 0 to 90%. However, for the pilot-scale trial it was necessary to reduce the target thickness of the core nylon barrier layer to 22% due to layer-to-layer melt flow instabilities that occurred during processing. The barrier properties of the multi-layer co-extruded films were highly dependant on overall film thickness. The highest performing oxygen barrier pilot-scale film had an OTR of 0.3 cm3/(m2 day) (60%RH) and a WvTR of 2.4 g/(m2 day) (90%RH) with a core nylon layer of 1.5 mil and a total thickness of 7.7 mil. Correlation of the layer thicknesses to the barrier and mechanical properties of the pilot-scale multilayer films indicated that an increased nanocomposite core layer thickness improved the oxygen barrier performance and decreased film elongation while improving the tear resistance of the films.