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Materials 2016, 9(6), 473; doi:10.3390/ma9060473

Recyclability of PET/WPI/PE Multilayer Films by Removal of Whey Protein Isolate-Based Coatings with Enzymatic Detergents

1
National Research Council, Institute for the Chemical and Physical Processes UoS Pisa, Via G. Moruzzi 1, Pisa 56124, Italy
2
Department of Civil and Industrial Engineering, University of Pisa, Via Diotisalvi 2, Pisa 56122, Italy
3
Fraunhofer Institute for Process Engineering and Packaging IVV, Giggenhauser Strasse 35, Freising 85354, Germany
4
Chair of Food Packaging Technology, Technische Universität München, Weihenstephaner Steig 22, Freising 85354, Germany
5
Innovació i Recerca Industrial i Sostenible (IRIS), Parc Mediterrani de la Tecnologia, Avda. Carl Friedrich Gauss 11, Castelldefels 08860, Spain
*
Authors to whom correspondence should be addressed.
Academic Editor: Marek M. Kowalczuk
Received: 23 March 2016 / Revised: 30 May 2016 / Accepted: 6 June 2016 / Published: 14 June 2016
(This article belongs to the Special Issue Biodegradable and Bio-Based Polymers)
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Abstract

Multilayer plastic films provide a range of properties, which cannot be obtained from monolayer films but, at present, their recyclability is an open issue and should be improved. Research to date has shown the possibility of using whey protein as a layer material with the property of acting as an excellent barrier against oxygen and moisture, replacing petrochemical non-recyclable materials. The innovative approach of the present research was to achieve the recyclability of the substrate films by separating them, with a simple process compatible with industrial procedures, in order to promote recycling processes leading to obtain high value products that will beneficially impact the packaging and food industries. Hence, polyethyleneterephthalate (PET)/polyethylene (PE) multi-layer film was prepared based on PET coated with a whey protein layer, and then the previous structure was laminated with PE. Whey proteins, constituting the coating, can be degraded by enzymes so that the coating films can be washed off from the plastic substrate layer. Enzyme types, dosage, time, and temperature optima, which are compatible with procedures adopted in industrial waste recycling, were determined for a highly-efficient process. The washing of samples based on PET/whey and PET/whey/PE were efficient when performed with enzymatic detergent containing protease enzymes, as an alternative to conventional detergents used in recycling facilities. Different types of enzymatic detergents tested presented positive results in removing the protein layer from the PET substrate and from the PET/whey/PE multilayer films at room temperature. These results attested to the possibility of organizing the pre-treatment of the whey-based multilayer film by washing with different available commercial enzymatic detergents in order to separate PET and PE, thus allowing a better recycling of the two different polymers. Mechanical properties of the plastic substrate, such as stress at yield, stress and elongation at break, evaluated by tensile testing on films before and after cleaning, were are not significantly affected by washing with enzymatic detergents. View Full-Text
Keywords: whey protein isolate; enzymatic detergents; recyclability; protease; multilayer films; polyethylene terephthalate (PET); polyethylene (PE) whey protein isolate; enzymatic detergents; recyclability; protease; multilayer films; polyethylene terephthalate (PET); polyethylene (PE)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Cinelli, P.; Schmid, M.; Bugnicourt, E.; Coltelli, M.B.; Lazzeri, A. Recyclability of PET/WPI/PE Multilayer Films by Removal of Whey Protein Isolate-Based Coatings with Enzymatic Detergents. Materials 2016, 9, 473.

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