Influence of Carboxymethylation on the Surface Physical–Chemical Properties of Glucuronoxylan and Arabinoxylan Films Nena Velkova, 1 Ale s Doli ska, 2 Lidija Fras Zemljic ˇ, 3 Alenka Vesel, 4 Bodo Saake, 5 Simona Strnad 3 1 TT Okroglica d.d., 5293 Volc ˇja Draga, Slovenia 2 Frutarom Etol d.o.o.,  Skofja vas 39, SI-3211  Skofja vas, Slovenia 3 Faculty of Mechanical Engineering, Institute of Engineering Materials and Design, University of Maribor, 2000 Maribor, Slovenia 4 Jo zef Stefan Institute, Ljubljana, SI-1001 Ljubljana, Slovenia 5 Chemical Wood Technology, Department of Wood Science, University of Hamburg, 21031 Hamburg, Germany Xylans were carboxymethylated in order to increase their anionic nature and thus tune their surface free energy (SFE) and hydrophilicity, which are of crucial importance in the majority of special applications. Fourier transform infrared spectroscopy and polyelectrolyte titration results confirmed the successful carboxymethylation of the xylan samples. The main aim of this study was to investigate the influences of carboxymethylation of glucuronoxylan and arabinoxylans on the surface physical and chemical properties of the films made from them. Films were pre- pared by the casting method, and their surface morpholo- gies were analyzed by atomic force microscopy. The surface chemical compositions of the films were investi- gated using X-ray photoelectron spectroscopy, and their influences on SFE, i.e., Lifshitz–van der Waals and elec- tron donor and acceptor contributions, were determined using goniometry. The introduction of 2 mmol/g of car- boxyl groups into the glucuronoxylan or arabinoxylan molecular structures had a significant influence on the chemical and physical surface properties of the prepared films. Higher amounts of the carboxyl group present on the films’ surfaces and higher surface roughness contrib- uted to a significant increase (by 270%) in the electron donor component of SFE and to 40% improvements in the hydrophilicities of the films’ surfaces. POLYM. ENG. SCI., 00:000–000, 2015. V C 2015 Society of Plastics Engineers INTRODUCTION Xylans are the main hemicellulose components of secondary cell walls, constituting about 25%–35% of the dry biomass from the woody tissues of dicots and lignified tissues of monocots and occur up to as much as 50% in some tissues of cereal grains [1]. Xylans are heteropolymers possessing b-(1-4)-D-xylopyra- nose backbones, which are branched by short carbohydrate chains comprising D-glucuronic acid or its 4-O-methyl ether, L- arabinose, and/or various oligosaccharides. Xylans are available in huge amounts as by-products from the forestry, agriculture, wood, pulp, and paper industries [2], and thus also the largest source of renewable hemicellulose on earth. Research into xylans has recently focused on special applica- tions like pharmaceutical [3, 4], biomedical (especially as hydrogels) [5, 6], food [7], and improvement of the pulps’ char- acteristics in the pulp and paper industries [8, 9]. Some researchers have discussed films made from xylans, especially their mechanical, oxygen, and moisture barrier properties [10]. The carboxymethylation of glucuronoxylans and arabinoxy- lans has been studied in detail in order to obtain xylans with anionic properties [11, 12]. The structural characterization and carboxymethylation of arabinoxylan under different reactive conditions were described by Saghir et al. [13]. It was discov- ered by Alekhina et al. [14] that one of the advantages of using the carboxymethylation of xylans is the improvement of its film-forming properties. The authors investigated the mechanical and optical properties, water vapour, and the oxygen permeabil- ity of films made from carboxymethylated xylans. In many applications of films and foils in the fields of food- packaging, biomedicine, and pharmacy, the most important aspect is solid–liquid surface interactions, which are mainly dependent on the surface physical and chemical properties of the solid phase. Within this context, the surface charges, surface morphologies, and surface free energies (SFEs) of the solid surfaces are of major importance. These properties dictate not only the strengths of the solid–liquid interactions but also the control of the processes like the stability of the aqueous colloidal suspensions, the dynamics of molecular self- assembly, and the wetting, spreading adhesion, and adsorption prop- erties. Characterization of the surface properties, especially the SFE components, is therefore of crucial importance for understanding the mechanisms of the various surface-based phenomena. To the best of our knowledge, to date, no thorough study has been performed regarding the influences of the carboxymethyla- tion of different xylans onto their film formations or onto the films’ physical and chemical properties. Therefore, the main aim of this study was to investigate the influence of introduced carboxymethyl groups onto the film forming properties and especially onto the SFE and its electron donating and accepting components’ parameters, which are of crucial importance for the majority of potential xylan films’ applications. MATERIALS Xylan Samples 4-O-methyl glucuronoxylan from beech wood (BX) (M w 5 19,400 g/mol and M w /M n 5 1.9) was obtained by the extraction Correspondence to: Simona Strnad; e-mail: simona.strnad@um.si Contract grant sponsor: Slovenian Technology Agency (TIA); contract grant sponsor: Slovenian Research Agency (ARRS). DOI 10.1002/pen.24059 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2015 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2015