ABSTRACT:The optimization of three-layer films (PE/ binder/PA) manufactured by extrusion blow molding presents significant industrial challenges. The main issue consists in combining use properties (e.g., impermeability to water steam and oxygen, welding properties) with high mechanical, optical, and adhesion performances, while maintaining cost-effectiveness. This article shows that the introduction of EVA in the PE layer improves the heat sealing ability and optical properties without degradation of the mechanical and adhesion performances. In the most favorable case, this modification leads to a 40% reduction of the heat sealing time, the other performances remaining either identical or higher. This leads to cost reduction of this manufacturing step while improving the flexibility of the process (wider process temperature window). The properties modifications observed can be explained by microstructure modifications (crystallinity, orientation, and molecular mobility).

ABSTRACT:The second part of this series shows that the incorporation of EVA in the tie layer of extrusion blowmolded three-layer (PE/binder/PA) improves the adhesion properties, while reducing the film cost by 6% and preserving the performances previously (Part I) obtained by addition of EVA in the PE layer only, such as optimal improved seal ability, optical properties, and satisfactory mechanical properties. The improvement of adhesion between the binder and the PA layers could be related to a modification of the type and the density of the intermolecular interactions between binder, PA, and EVA.

The optimisation of food packaging films requires the films to be designed with excellent barrier properties to gases (usually water vapour and oxygen) and high mechanical and optical performances, without significant cost increase. Polymer nanocomposites may offer an interesting opportunity in this respect. This solution is studied in the present paper for both polyamide-6 (PA6) single-layer films and polyethylene/maleic anhydride grafted polyethylene/polyamide-6 (PE/PEgMAH/PA6) multilayer films. The addition of 2 wt.% of nanoclay in PA6 simultaneously improves the mechanical properties (tensile modulus, yield stress and strength), optical performances (gloss, haze and clarity) and oxygen impermeability. The processing conditions have no major influence on the studied properties, except for the optical properties. The cost increase induced by this solution is balanced by the benefits obtained in terms of overall improvement of film properties.

The potential of a fracture mechanics approach (Essential Work of Fracture or EWF method) to determine the toughness of PE/PEgMAH/PA multilayer films has been investigated. The films had been modified either by blending EVA in the PE and PEgMAH layers or by inserting clay nanoparticles in the PA layer. The method was first calibrated on PE and PA single layer films. An analysis of the sensitivity of the toughness, assessed by the EWF method, to both sample geometry and test conditions has been carried out, so as to optimise the testing procedure for these materials. Then these optimal test conditions have been used to characterise PE- and PA-based multilayer films. The results show that the Essential Work of Fracture method is relevant for this type of structure, and may be more sensitive to the film composition variations than standard tensile mechanical tests, especially when the composition modification affects the layer of lowest rigidity and tensile strength.

The slippability of packaging films has to be controlled to facilitate confectionary operations and guarantee an easy opening for filling. In the case of singlelayer polyethylene (PE) films, the addition of slip agents made of fatty acid amides such as erucamide or oleamide usually allows the tailoring of the coefficient of friction (COF) in the film to match industrial targets, which depend on the final application. The coupling of Fourier transform infrared spectroscopy and atomic force microscopy analysis showed that this method has a limited efficiency and may even be detrimental in the case of multilayer PE þ ethylene vinyl acetate (EVA)/maleic anhydride grafted polyethylene (PEgMAH) þ EVA/polyamide films. The reason is that the migration of the slip additives toward the outermost surface of the PE layer, which leads to a reduction in the COF, are strongly affected by both the existence of the adjacent layers and the presence of EVA in the PE and PEgMAH layers. Nevertheless, a proper knowledge of the effect of this perturbation allows one to reach a slippability level that is required for some confectionary operations and/or for an easy opening for filling without the degradation of the heat sealability.