The influence of UV irradiation on the properties of chitosan films containing keratin A. Sionkowska * , J. Skopinska-Wisniewska, A. Planecka, J. Kozlowska Nicolaus Copernicus University, Faculty of Chemistry, Gagarin 7, 87-100 Torun, Poland article info Article history: Received 7 June 2010 Received in revised form 29 July 2010 Accepted 6 August 2010 Available online 14 August 2010 Keywords: Chitosan Keratin UV radiation Surface properties Mechanical properties abstract The mechanical, thermal and surface properties of chitosan and chitosan containing keratin hydrolysates have been studied and the influence of UV irradiation on these properties has been compared. The surface properties of chitosan films containing 5%, 15% and 30% of keratin hydrolysate before and after UV irra- diation (l ¼ 254 nm) were investigated by means of contact angle measurements allowing the calculation of surface free energy. The chemical and structural changes during UV irradiation were studied by UVevis and FTIR-ATR spectroscopy. The changes in mechanical properties such as breaking strength, percentage elongation and Young’s modulus have been investigated. The results have shown that the mechanical properties of the chitosan/ keratin films were greatly affected by UV irradiation, but the level of the changes of these properties was smaller in the blend than in pure chitosan and strongly dependent on the time of irradiation and composition of the samples. The contact angle and the surface free energy were altered by UV irradiation, which indicates photooxidation and an increase of polarity of specimens. The range of these changes point to greater susceptibility of chitosan to photooxidation in the presence of keratin. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Chitosan is a natural polymer (polysaccharide) prepared from chitin by deacetylation. One of the most promising features of chitosan is its excellent ability to be processed into porous struc- tures and thin films for use in cell transplantation and tissue regeneration. In medical and pharmaceutical applications chitosan is used in bandages, sponges, membranes, artificial skin, contact lenses, control release drugs, bone disease treatment and surgical sutures [1e3]. Chitosan properties can be modified by addition of another polymer, like collagen, PVA, PVP, and PEO [3e18]. The properties of chitosan can be modified also by UV irradiation, mechanical treatment and heating [19e21]. During UV irradiation of polymers, the excited molecules are formed in the first step and then, the secondary processes such as chain scission, cross-linking, oxidation take place [22,23]. Chitosan and keratin do not exist together as blends in nature, but the specific properties of each may be used to produce synthetic blends that confer unique structural and mechanical properties. The uses of relatively low cost, low pollution biomaterials with specific properties has great potential, for instance in developing a new generation of biomaterials [24,25]. Keratin is one of the most abundant proteins in animal population. It is the major component of hair, feathers, nails and horns of mammals, reptiles and birds. This fibrous protein is composed of several amino acids residues along its chain. The sequence of amino acids defines the possibility of intermolecular links and the access of amino acids to the chemical reaction. A pivotal role in photochemistry of keratin play aromatic amino acids (tryptophan, tyrosine, phenylalanine) and cystine (amino acid containing sulphur). The presence of cystine in the keratin chain leads to characteristic inter- and intramolecular disulphide bonds which can decide about several properties of keratin. From the point of view of polymer science, keratin is a biopolymer that is insoluble in water. In our case, for the inves- tigation of photochemical properties of insoluble keratin, we used keratin hydrolysates dissolved in water. The aim of this study was to compare the mechanical and surface properties of chitosan/keratin films with mechanical and surface properties of chitosan films and to determine the influence of UV irradiation on these properties. Contact angle is a well-known technique for investigating and controlling adhesion, surface treatment and cleaning as well as polymer film modification. The wetting of solid substrates is a basic feature of many natural and industrial processes and contact angle is a simple, rapid, and sensitive method of characterizing the wettability of a solid surface. * Corresponding author. E-mail address: as@chem.uni.torun.pl (A. Sionkowska). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2010.08.002 Polymer Degradation and Stability 95 (2010) 2486e2491