Carboxymethylated-, hydroxypropylsulfonated- and quaternized xylan derivative films
Introduction
Xylan is an important polysaccharide used for composite preparation, film and package applications (Hansen and Plackett, 2008, Köhnke et al., 2012, Saxena et al., 2010, Saxena et al., 2011, Šimkovic, 2013). Carboxymethyl and quaternary xylan (CQX) was recently studied for preparation of an amphoteric polysaccharide derivative of water soluble xylan from bamboo in two steps using microwave (Peng, Ren, Zhong, & Sun, 2012). Carboxymethyl xylan (CX) was also prepared from birch kraft pulp after extraction of xylan and subsequent carboxymethylation (Alekhina, Mikkonen, Alén, Tenkanen, & Sixta, 2014). The reaction has been previously performed, but fully substituted CX was not prepared. By the repeated “slurry” method DSC = 1.90 was reported without considering the molar mass of the produced derivatives (Petzold-Wecke, Schwikal, Daus, & Heinze, 2014). Carboxymethyl xylan (CX) was also prepared from birch kraft pulp (Alekhina et al., 2014).
Because our beech wood xylan was isolated by NaOH extraction and is only partially soluble in water we used conventional heating instead of microwave to prevent the dramatic molar mass degradation. From our previous studies on the preparation of trimethylammonium-2-hydroxypropyl xylan (QX), 2-hydroxypropylsulfonate (SX) and trimethylammonium-2-hydroxypropyl xylan sulfate (QXS) we have learned that the numerical molar masses (Mn) of the produced material were larger than the water-soluble part of the used xylan (Šimkovic et al., 2011a, Šimkovic et al., 2011b, Šimkovic et al., 2014). In this work we have used a method in which several ion-exchanging substituents were introduced in one step and the degree of substitution (DS) values were compared with values when single substituent was introduced under analogous conditions. The mechanical properties of the prepared films were studied and compared with data in the literature. The goal was to understand the relation between the chemical structure of the polysaccharide, the type of substituent, molar mass and water solubility together with the effect of chemical modification on thermal stability, optical and mechanical properties of the films.
Section snippets
Materials
Xylan (X) was extracted from beech sawdust holocellulose with 10% NaOH as previously described for hornbeam wood (Ebringerová, Kramár, & Domanský, 1969). It was characterized as described before (Šimkovic et al., 2011a, Šimkovic et al., 2011b, Šimkovic et al., 2014). All the chemicals used were of analytical grade and were used without further purification.
CX was prepared by mixing X (1.654 g; 10 mmol) with water (18 ml; 1 mol), containing NaOH (3.2 g, 80 mmol). Subsequently 4.7543 g of ClCH2COONa (40
Carboxymethylation and multiple derivatization
According to the results from 1H-NMR spectroscopy of CX in D2O solution when the molar ratio of reactants was at X/NaOH/ClCH2COONa/H2O = 10/80/40/1000, the DSC = 0.63 was determined by integration of the anomeric signals. Based on HSQC, COSY, TOCSY and HMBC experiments CX was assigned with the predominant substituent at C-2 of xylopyranose unit (Table 1). By using the integration of anomeric signals except the determined DSC also 4-O-methyl-d-glucuronic acid content was determined to be 20% of
Conclusions
The CQX, CSX, QSX and CQSX films were prepared in one step by using up to three alkylating agents. When singly-substituted under identical conditions the DS decreases in the order: DSC > DSQ > DSS, while when all three alkylating agents are introduced in one step the obtained DS's were decreased differently (DSQ > DSC > DSS). For doubly substituted derivatives the yield decreased in order CQX (90%) > QSX (53%) > CSX (52%). This could be explained by the difference of the reaction mechanism of negatively
Acknowledgements
The authors are pleased to acknowledge the State programs # 2003SP200280203 and 2003SP200280301 and Slovak Granting Agency VEGA (Project No 2/7030/7, 2/0087/11and 2/0007/13) for the support. We acknowledge Eva Špyrková-Hadzimová for runing the TG/DTG/DTA experiments. This contribution is the result of the project implementation: Centre of excellence for white-green biotechnology, ITMS 26220120054, supported by the Research & Development Operational Program funded by the ERDF.
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