Mechanical and Barrier Properties of Thermoplastic Whey Protein Isolate/Ethylene Vinyl Acetate Blends Markus Schmid, 1,2 * Kerstin M€ uller, 1,3 * Sven S € angerlaub, 1,2 Andreas St € abler, 1 Vanessa Starck, 1 Felix Ecker, 3 Klaus Noller 1 1 Fraunhofer Institute for Process Engineering and Packaging IVV, Giggenhauser Strasse 35, Freising 85354, Germany 2 Chair for Food Packaging Technology, Technische Universit€ at M€ unchen, Weihenstephaner Steig 22, Freising 85354, Germany *These authors contributed equally to this work. 3 Department of Food Technology, Hochschule Fulda—University of Applied Sciences, Marquardstraße 35, Fulda 36039, Germany Correspondence to: M. Schmid (E - mail: markus.schmid@ivv.fraunhofer.de) ABSTRACT: Crude oil is becoming scarcer and more expensive, resulting in alternative biobased or partially biobased materials gaining importance in the field of plastic packaging and encouraging the development of naturally derived, protein-based plastics (Endres, 2009; Jones and McClements, Compreh. Rev. Food Sci. Food Safety 2010, 9, 374; Khwaldia et al., Compreh. Rev. Food Sci. Food Safety 2010, 9, 374). A strategy to improve extrusion processing behavior of proteins is the blending with other polymers. In this study eth- ylene vinyl acetate (EVA) was used for such purpose. The aim of this study was to determine the properties of blends of thermoplas- tic whey protein (TPP) and ethylene vinyl acetate (EVA). Mechanical and barrier properties were tested. Blends of differing TPP/EVA ratio were produced and extruded into flat films. Morphological analysis of the blends shows immiscibility of the TPP and EVA, greatly influencing the mechanical properties. Young’s modulus measurements shows the values approached that of pure EVA with increasing EVA ratios. At values of about 21 MPa, corresponding to EVA ratios of 30% (w/w) and above, continuous extrusion including material take-off was possible. At higher whey protein ratios in the blends the water vapor transmission rate increased, i.e., the higher water vapor transmission rate of whey protein compared with EVA dominated this property. This study showed that whey proteins can be utilized for extrusion by blending with EVA. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41172. KEYWORDS: blends; extrusion; films; functionalization of polymers; mechanical properties Received 14 April 2014; accepted 12 June 2014 DOI: 10.1002/app.41172 INTRODUCTION Because of the high amount of plastic trash and the scarcity and rising cost of fossil fuels, the development of biodegradable and/or bio-based polymers is gaining importance. Biopolymers based on renewable resources such as starch, cellulose and pro- teins are considered promising for the processing to packaging materials. The differing molecular structure of proteins causes different properties of films made thereof such as specific bar- rier and mechanical properties. 1–3 This means that packaging materials can be produced with a wide range of functional properties. 4 For this reason, protein-based materials might be suitable for replacing or complementing the hitherto used fossil fuel-based polymers in food packaging applications. Whey is one of the biggest sources of food protein, but only a small fraction of this is consumed by humans. 5 Approximately 92% of the produced whey is an unused by-product of cheese production. 6 There is a growing demand to find ways of using that whey. Up until now several processes for forming whey pro- tein based films and coatings and their properties have been stud- ied. The barrier properties were one focus of these studies. 7–13 Recent studies showed that whey protein based layers generated by lacquering processes have excellent barrier properties with oxy- gen permeability (OP) Q 100 < 1.5 cm 3 (STP) m 22 d 21 bar 21 and water vapor transmission rate (WVTR) Q 100 < (223) g m 22 d 21 85!0 % relative humidity, 23  C, 14–20 making them suitable for use in sensitive food packaging applications. 21 Extrusion is another continuous processing technique of practi- cal industrial use for whey protein based films or separate layers in multilayer films. However, the materials here must have ther- moplastic properties. As proteins have no natural thermoplastic behavior, the use of additives is indispensable for extruding pro- teins. 22 Proteins can undergo a large number of interactions due to the different functional groups in the amino acid side chains. These allow a vast number of interactions and chemical V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.41172 41172 (1 of 9)