Clay‐induced Preferred Orientation in Polyethylene/Compatibilized Clay Nanocomposites

Migration of Quaternary Ammonium Cations from Exfoliated Clay/Low-Density Polyethylene Nanocomposites into Food Simulants

Clay/polymer nanocomposites (CPNs) are polymers incorporating refined clay particles that are frequently functionalized with quaternary ammonium cations (QACs) as dispersion aids. There is interest in commercializing CPNs for food contact applications because they have improved strength and barrier properties, but there are few studies on the potential for QACs in CPNs to transfer to foods under conditions of intended use. In this study, we manufactured low-density poly(ethylene) (LDPE)-based CPNs and assessed whether QACs can migrate into several food simulants under accelerated storage conditions. QACs were found to migrate to a fatty food simulant (ethanol) at levels of ∼1.1 μg mg^-1 CPN mass after 10 days at 40 °C, constituting about 4% total migration (proportion of the initial QAC content in the CPN that migrated to the simulant). QAC migration into ethanol was ∼16× higher from LDPE containing approximately the same concentration of QACs but no clay, suggesting that most QACs in the CPN are tightly bound to clay particles and are immobile. Negligible QACs were found to migrate into aqueous, alcoholic, or acidic simulants from CPNs, and the amount of migrated QACs was also found to scale with the temperature and the initial clay concentration. The migration data were compared to a theoretical diffusion model, and it was found that the diffusion constant for QACs in the CPN was several orders of magnitude slower than predicted, which we attributed to the potential for QACs to migrate as dimers or other aggregates rather than as individual ions. Nevertheless, the use of the migration model resulted in a conservative estimate of the mass transfer of QAC from the CPN test specimens.

Interfacial interaction exploration and oxygen barrier potential of polyethylene/poly(ethylene-co-vinyl alcohol)/clay hybrid nanocomposites

Hybrid nanocomposites based on high-density polyethylene (HDPE)/poly (ethylene-co-vinyl alcohol) (EVOH)/clay were prepared and fully characterized. Morphological (WAXS and TEM), calorimetric (DSC), and dynamic mechanical thermal (DMTA) analyses were applied to investigate potential of nanocomposites as barrier against oxygen. Co-existence of ingredients of different nature, i.e. HDPE (general-purpose non-polar component), EVOH (engineering polar component with excellent barrier properties), nanoclay (planar one-dimensional mineral barrier nanofiller), and maleated HDPE (PE-g-MA) as coupling agent, brings about serious intricacies in view of interaction between existing phases. Conceptual/experimental analysis was performed to explore the interdependence between microstructure and oxygen barrierity of HDPE/EVOH/clay nanocomposites through the lens of interaction state in the system. Morphological measurements confirmed formation of an intercalated nanostructure, while investigations on complex viscosity, storage modulus, permeability, thermo-mechanical properties, and nanoclay interlayer galleries were all indicative of dependence of nanocomposites’ properties on molecular interactions. The performance of nanocomposite sheets as oxygen barriers was mechanistically explained.