Barrier materials
Barrier materials Emerging circular biobased barrier solutions Multilayer plastic packaging films are commonly used to pack sensitive food products. Their share on the packaging market is increasing as they enable lightweighting and increase resource efficiency in their primary use in comparison to rigid packaging. However, multilayer packaging concepts are currently not recyclable. Indeed, high purity fractions are needed for reprocessing and the vast majority of them end up in land fill or in energy recovery systems. In addition, most of the barrier materials such as Ethylene Vinyl Alcohol (EVOH) or polyamides (PA), are fossil based. In this article, emerging solutions in recent research and innovation initiatives will subsequently be reviewed, first in terms of new biobased feedstocks from which barrier materials can be sourced and second on how using them can positively affect the end of life of the derived laminates. An array of potential sources in nature Many biopolymers made of polysaccharides or proteins offer good barrier properties against oxygen permeation and can be used as edible coatings such as chitosan, proteins from dairy, fish, potatoes or legumes. In addition, those can be extracted from non-edible food fractions or agro-food industry by products. For example, in the project DAFIA [1], marine rest rawmaterials such as salmon skin and backbones are harnessed to develop cost-efficient isolated and purified gelatin and hydrolysates. Gelatin is a denatured polypeptide extracted by hydrolysis from pre-treated collagen sources, mainly animal skins and bones, which is mostly affected by its amino acid composition and molecular weight distribution. The fractionation and lipids separation pre-treatment protocols have been optimized in mild conditions. The coating was formulated comparing different natural plasticizers, pH and temperature as well as drying condition. Furthermore, the mechanically separated salmon muscle has been hydrolysed with proteases as potential active compound. The addition of hydrolysates has shown positive antioxidant activity (Gallic acid equivalent GAeq of 66 +/-7 ppm and Ferric Reducing Ability of Plasma FRAP of 189 +/-17 µmol/L), but no antibacterial effects were observed. The coating application and lamination have been successfully carried out at pilot scale by AIMPLAS resulting in laminates with promising oxygen barrier (1.58 OTR (cm³/(m²·day) at 23°C, 1 atm and 50 % relative humidity for a 10 µm coating). This shows that biomacromolecules from marine sub-products have a great potential to be used as high added value active barrier coatings for multilayer packaging or edible coatings directly applied on food. Previously reported Wheylayer ® barrier materials have also been obtained from whey protein [2] (which can be extracted from a cheese by-product). Further development also allowed obtaining thermoformable versions of the same (Thermowhey) [3]. In the recent project OptiNanoPro [4], nano-enhancement of the whey protein coating was performed adding food contact approved nanoclays. Those were converted into a so-called “ready-to-use” formulation by means of a solid-state pre-dispersion process using ball-milling. The process yielded a nearly dust-free, freeflowing powder containing agglomerated particles, which can easily be mixed with water. The preparation of a coating Oxygen transmission rate °C/50% RH (cm 3 · 100µm (STP) m -2 d -1 bar -1 ) Fig 1. top: microscopic picture of the cross-section picture of a laminate including PET 23 µm and 4 µm of whey proteins nanocomposite coatings produced semi-industrial-scale, and bottom: Scanning electron microscopy (SEM) images at a magnification of 50,000 on the nanocomposite coating Fig. 2: Permeability values for different whey coatings vs. standard and biobased polymers (all normalized to 100 μm) 10000 1000 100 10 1 0.1 PE-HD PP (oriented) PA 12 PE-LD PC PUR-elastomer Celluloseacetate Wax/paper PA 11 PS (oriented) PVC-U PA 12 PET (oriented) PA 66 PVC-U (oriented) PA 6 EVOH 44% PVDC EVOH 38% Wheylayer Cellulose-acetobutyrate Thermowhey OPTIANOPRO EVA-copolymer, VAC 20% 0.01 0.01 0.1 1 10 100 1000 Water vapour transmission rate 23°C/85 0% RH (g · 100µm · m -2 d -1 ) 44 bioplastics MAGAZINE [05/19] Vol. 14
Barrier materials By: Multilayer Film Elodie Bugnicourt, Simona Neri IRIS Technology Solutions Barcelona, Spain Esra Kucukpinar Fraunhofer IVV Freising, Germany Markus Schmid Faculty of Life Sciences, Albstadt-Sigmaringen University Sigmaringen, Germany Patrizia Cinelli, Andrea Lazzeri INSTM, University of Pisa Pisa, Italy Fig. 3: Illustration of the materials recyclability of whey coated laminates Grinding Wheylayer Removal Density Separation Recycled PE Recycling Recycled PET formulation and its upscaling for roll-to-roll converting at pilot- and semi-industrial scale was also successfully implemented [5]. This process resulted in a good dispersion and orientation of the nanoparticles (Fig. 1) and an interesting barrier improvement that allowed resulting coating laminates matching the properties of EVOH (Fig. 2). Nevertheless, as seen from the graph (Fig. 2), the developed protein coatings are not able to compete with standard plastics in terms of water vapour barrier. In BIOnTop [6], to reach such performance, the previously developed whey protein coatings will be improved by nano-coatings of fatty acids applied by a resource efficient grafting technology. But what about the End Of Life? All the previously mentioned protein-based coatings are compostable by nature. Indeed, their composition makes them ideal for metabolization by microorganisms. They can be applied on a range of biodegradable or nonbiodegradable substrate films and the end of life of the later is what mainly determines that of the whole laminate. Fig. 4: Representation of the end of life scenarios that will be compatible with the new BIOnTop materials, some of them coated with barrier materials Biontop Copolymers & Compounds Coating Organic & Materials Recycling Indeed, when applied for example on PLA, the nitrogen (as amino-acid rich component) of the coating was even reported to speed up the biodegradation of the overall multilayer films [7] resulting in industrially compostable packaging solutions. When the protein coating is applied on conventional substrates, its removability using enzymatic detergent during the washing step of the packaging recycling can be exploited (Fig. 3). In that case, the cleaned layers of e.g. PE and PET can then be separated by density and reprocessed separately with a minor loss of properties [8]. After showing the capability for automatic sorting of the packaging containing the new biobased barrier coatings, BIOnTop aims at upscaling the recycling process of the barrier multilayer packaging. In addition, to match virtually any controlled waste management demand, PLA copolymers suitable for home composting are also being developed. Such end of life versatility, depicted in Fig. 4, is key in the view of the difficulty to remove the organic content in specific packaging formats such as tea bags or when fruits or vegetables get rotten in their trays or nets. It is also key to be able to adjust to the most sustainable end of life option depending on the packed products and the actually feasible waste management for which available logistics are extremely variable between regions. Conclusion lead Home Composting Echoing the increasingly stringent legislations and public demands, the packaging industry is requesting more sustainable barrier solutions. This is boosting the research in renewably sourced materials which in turn also have the ability to support the circular economy transition by enabling improved organic or materials recycling routes. Different protein solutions based on cheese or fish byproducts have been discussed and to barrier properties close to their fossil counterpart while making laminates recyclable organically or in terms of materials. bioplastics MAGAZINE [05/19] Vol. 14 45
