Vol.:(0123456789) 1 3 Journal of Polymers and the Environment https://doi.org/10.1007/s10924-018-1221-8 ORIGINAL PAPER Efcient Acetylation of Xylans by Exploiting the Potassium Acetate Formed During the Alkaline Extraction Merve Akkus 1  · Necati Ozkan 2,3  · Ufuk Bakir 1,4 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Isolation of hemicelluloses through alkaline extraction results in formation of salts, which usually necessitates additional salt removal steps. In this study, acetylation of xylans was studied without the removal of potassium acetate (KAc), a commonly produced salt during the alkaline extraction, to fnd a facile method to alter the hydrophilic characteristics of hemicelluloses. The acetylation reaction was carried out solely with acetic anhydride without any catalysts or solvents added. The weight gain and ATR–FTIR analyses verifed the acetylation of xylans in the presence of KAc. A signifcant decrease in water solubil- ity and moisture uptake was observed upon acetylation in the presence of KAc which is also accompanied by an increase in thermal stability, disclosing an easy, efcient and environmentally friendly method to obtain hydrophobically modifed xylans without the use of toxic catalysts and costly salt purifcation steps. Keywords Lignocellulosic biomass · Hemicellulose · Potassium acetate · Acetylation · Hydrophobic modifcation Introduction Lignocellulosic biomass is considered to be one of the best alternatives to non-renewable fossil-based resources since it has the potential to displace both petroleum and petroleum derived materials. Among its constituents, hemicelluloses receive particular interest as a replacement for petrochemical polymers due to their biodegradability and structural diver- sity. Hemicelluloses can be extracted from lignocellulosic biomass by various methods but mainly steam treatment, acidic or alkali solutions [1]. Extraction procedures with alkaline solutions are often preferred to isolate high molecu- lar mass hemicelluloses [2], which consist of dissolution, neutralization and ethanol precipitation steps [3–5]. Besides those, an additional purifcation step is usually applied to remove the salts that are formed during the neutralization step, since the presence of salts may deteriorate mechanical properties of hemicellulose-based materials [6, 7]. However, a recent study by Bahcegul et al. [8] showed that potassium acetate (KAc), which is formed during the neutralization of potassium hydroxide (KOH) and acetic acid, improves both flm formation and mechanical properties of xylan-based flms revealing that an additional purifcation step might not always be necessary depending on the type of salt. Being the most common type of hemicelluloses, xylans receive particular interest in food packing applications due to their superior oxygen barrier properties [9, 10]. One of the main obstacles in the application of xylans for pack- ing applications is their inherent hydrophilic nature which makes polymeric materials sensitive to water, causing func- tionality problems. Structural variations among diferent types of hemicelluloses and presence of reactive hydroxyl groups make hemicelluloses ideal targets for chemical modi- fcations [11]. Etherifcation [12], benzylation [13], car- boxymethylation [14] and esterifcation [15] methods are being used to overcome problems with increased oxygen permeability and decreased mechanical properties at humid * Necati Ozkan nozkan@metu.edu.tr * Ufuk Bakir ufukb@metu.edu.tr Merve Akkus mcinar@metu.edu.tr 1 Department of Chemical Engineering, Middle East Technical University, Ankara 06800, Turkey 2 Department of Polymer Science and Technology, Middle East Technical University, Ankara 06800, Turkey 3 Central Laboratory, Middle East Technical University, Ankara 06800, Turkey 4 Department of Biotechnology, Middle East Technical University, Ankara 06800, Turkey