Abstract
Materials with high barrier properties against oxygen are required for the packaging of many sensitive foods. Since commodity polymers lack these properties, additional barrier materials are used in plastic-based barrier packaging. These are usually more expensive than commodity polymers and, in higher fractions, also make recycling more difficult. Current developments, therefore, aim at barrier layers that are as thin as possible but retain the barrier properties. One approach is to incorporate nanoparticles into these layers. In this study, the barrier properties of nanocomposite coatings, consisting of unmodified polyvinyl alcohol (PVA), and dispersed stick-shaped halloysite (Hal) or platelet-shaped montmorillonite (MMT) silicate nanoparticles, were investigated. The PVA was dissolved in aqueous nanoparticle dispersions, which were prepared by mechanical shearing, to produce the so-called “nanolacquer.” Nanolacquers with nanoparticle concentrations of 7, 30, and 47 vol% with respect to PVA were applied in a single process step with k-bar on a polypropylene substrate film. The integration of 30 vol% platelet-shaped MMT enhances the barrier performance in comparison to pure PVA by a factor of 12 and 17 for oxygen and helium, respectively. Scanning electron microscopy (SEM) shows a homogeneous distribution and a parallel alignment of the nanoparticles within the coated layer. An increase in the crystallinity of PVA was observed due to the nanoparticle integration as demonstrated by x-ray diffraction (XRD) measurements. The investigation by Fourier transform infrared (FTIR) spectroscopy and the activation energy of the permeation coefficient indicate an interaction between the nanoparticles and the PVA. The theoretically calculated values for barrier enhancement accord well with the experimental values, which emphasizes that the gas barrier improvement for oxygen and helium is mainly dominated by the tortuous path effect.
Highlights
Some sensitive foods are described by consumers as sensory impaired already at an oxygen intake of less than mg kg [1].For such products, packaging materials with oxygen permeability down to cm3 m2(STP) d bar are needed to ensure a sufficiently long shelf life [2]
To measure the extension in the z-direction (W), Scanning electron microscopy (SEM) images of cross-sections of the coatings were analyzed. The assumption for this is that the degree of exfoliation of the nanoparticles is not effected during the mixing process of the dispersion with polyvinyl alcohol (PVA) [20]
The thickness of these white lines indicates the W of the platelets and a value of 25 nm was measured for both MMT-ball mill (BM) and MMTUT samples
Summary
Some sensitive foods are described by consumers as sensory impaired already at an oxygen intake of less than mg kg [1].For such products, packaging materials with oxygen permeability down to cm m2(STP) d bar are needed to ensure a sufficiently long shelf life [2]. Some sensitive foods are described by consumers as sensory impaired already at an oxygen intake of less than mg kg [1]. For such products, packaging materials with oxygen permeability down to cm m2. If one wants to achieve high barrier properties, lightweight, and good recyclability for the corresponding packaging at the same time, different solutions are available. The most common are polymer barrier layers made of polyvinyl alcohol (PVA). These PVA barrier layers are targeted to be as thin as possible without having to sacrifice the barrier properties, because of two main reasons. Since the incorporation of platelet-shaped nanoparticles has already shown a significant improvement in many polymers, especially in the oxygen barrier properties [3], this approach was pursued in this study
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