701 The Polymer Society of Korea www.springer.com/13233 pISSN 1598-5032 eISSN 2092-7673 Macromolecular Research, Vol. 22, No. 7, pp 701-709 (2014) Regenerated Cellulose Fibre Reinforced Casein Films: Effect of Plasticizer and Fibres on the Film Properties Sung-Woo Cho 1,2 , Mikael Skrifvars * ,1 , Kumar Hemanathan 1 , Pirabasenan Mahimaisenan 1 , and Kayode Adekunle 1,3 1 School of Engineering, University of Borås, SE-501 90 Borås, Sweden 2 ABB AB, Corporate Research, 721 78 Västerås, Sweden 3 Michael Okpara University of Agriculture, Umudike, P.M.B. 7267, Umuahia Abia State, Nigeria Received November 27, 2013; Revised January 26, 2014; Accepted February 21, 2014 Abstract: The idea of using man-made cellulosic fibres as reinforcement for casein films in this study was inspired by their well defined fibre diameter and availability in large quantity, eventually leading to a homogeneous high quality composite at low cost. The casein biofilms were fabricated by solution casting from an aqueous alkaline solu- tion of the bovine milk protein casein in the presence of glycerol as a plasticizer, and the fibre-reinforced biocom- posites were prepared by the addition of regenerated cellulose fibre to the casein casting solution with various amounts of glycerol. The effects of glycerol content and cellulose fibre reinforcements on the mechanical, thermal and physiological properties were characterized. The results showed that increasing glycerol content decreased the film strength, Young’s modulus and thermal stability with a gradual increase in the elongation. However, the tensile properties were noticeably improved when reinforced with cellulose fibre. The composite with 20 wt% glycerol and 20 wt% cellulose fibre showed the maximum tensile strength of 23.5 MPa and Young’s modulus of 1.5 GPa. The corresponding values for the composite with 30 wt% glycerol and the same fibre content were 15.1 MPa and 0.9 GPa, which were 2.3- and 3.2-fold higher compared to 30 wt% glycerol plasticized film. The thermal analysis revealed that the glass transition temperature and the thermal stability were decreased when the glycerol content was increased. Addi- tion of cellulose fibres increased the glass transition temperature as well as the thermal stability. The gel electropho- resis (SDS-PAGE) analysis indicated that there was no significant decrease in the molecular weight of the casein protein during sample preparation. Scanning electron microscopy showed that the obtained composites with low glycerol content had adequate interfacial bonding, and Fourier transform IR spectroscopy confirmed the formation of molecular interactions between the cellulose fibres and the casein. Keywords: casein, regenerated cellulose fibre, biocomposite, film extrusion. Introduction The traditional crude-oil based synthetic polymeric mate- rials have during the recent years been under debate, regard- ing their environmental impact due to non-biodegradability and pollution. For packaging materials, which are typically of short life length before disposal, this has led to the devel- opment of the packaging films made of biobased materials. 1 Proteins play the vital role as a structure or biological activity in living organisms, 2 which cover the wide range among all poly- meric materials. Proteins have been traditionally used in techni- cal applications such as fibres, adhesives, paints and coatings. Proteins are commonly derived from plant and animal sources on large industrial scale. Casein is one such protein, which is the major protein present in the bovine milk, representing about 80% of the total milk protein content. Casein is a globular protein made up of four different sub units like  s1 -,  s2 -, -, and -casein; each subunit will differ in their pri- mary, secondary and tertiary structure with the molecular weight ranges from 19-25 kDa. 3,4 Casein has the property to form films readily due to its random coil nature and also has the ability to form intermo- lecular hydrogen and electrostatic bonds. 5 The films made of proteins are usually brittle and stiff due to strong protein- protein and protein-water interactions. Plasticizers can be added to control the protein-protein interaction, resulting in increased protein flexibility and elongation. The most widely used plasticizers for making edible films are sucrose, sorbitol, fatty acids, mono-glycerides and glycerol, wherein glycerol is a common one. However incorporation of plasticizer has some drawbacks on the film properties, such as decrease in the tensile strength and decreased ability to act as a barrier DOI 10.1007/s13233-014-2091-0 *Corresponding Author. E-mail: mikael.skrifvars@hb.se