Journal of Cleaner Production 250 (2020) 119458 Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro Propionylation-modified chitin with improved solubility in green ethanol/water binary solvents for sustainable film and coating applications * Tuhua Zhong a, Michael P. Wolcott a, Hang Liu a, b, Jinwu Wang a, c, a Composite Materials & Engineering Center, Washington State University, Pullman, WA, 99164, USA b Department of Apparel, Merchandising, Design and Textiles, Washington State University, Pullman, WA, 99164, USA c Forest Products Laboratory, U.S. Forest Service, Madison, WI, 53726, USA article info abstract Article history: The use of less-toxic solvents is highly desirable for biopolymer processing and applications to meet Received 29 July 2019 sustainability while alleviating environmental burdens. In this study, chitin was propionylated to Received in revised form improve its solubility. The highly propionylated chitin exhibited considerably improved solubility (up to 20 November 2019 96%) in a binary ethanol/water solution as compared to almost insolubility in a single solvent (either Accepted 24 November 2019 ethanol or water). Transparent films were prepared with acidified solutions and possessed excellent Available online 25 November 2019 mechanical properties with a tensile strength up to 40 MPa and Young’s modulus of 1.3 GPa. When the Handling Editor: M.T. Moreira solution of the chitin propionate solution was employed as a coating on a paper substrate, the chitin propionate coating was found to improve the tensile strength of the paper from 64 MPa up to 84 MPa, Keywords: and it also significantly decreased the surface energy to improve water resistance. These results suggest Acylation that chitin propionate that is dissoluble in ethanol/water binary solvents has potential use for new Chitin propionate sustainable bio-based films and coatings in practical applications. Ethanol/water binary solvent Published by Elsevier Ltd. Transparent films Coatings 1. Introduction products based on chitin and chitin derivatives may be used as a potential replacement for petroleum-based products, thus Sustainable packaging materials based on polysaccharides or benefiting the environment. However, chitin cannot dissolve in their derivatives have received much attention in recent years due common organic solvents because of its supramolecular structure to their renewability and biodegradability, which can help to alle- that formed by ample inter- and intramolecular hydrogen bonds, viate land and ocean pollutions generated by petroleum-derived which makes it difficult in the processing and restricts its appli- packaging products. Chitin is the second most abundant cations (Rinaudo, 2006). Although chitin can dissolve in a few biopolymer on earth and commonly obtained from shrimp, lobster solvents such as dimethylacetamide/lithium chloride (DMAc/LiCl), and crab shells which are produced at a rate of 6e8 million tonnes or ionic liquids, these solvents are either toxic or expensive, which globally every year; these shells, containing 15e40% chitin, are make them impractical in industrial applications (Barber et al., often discarded as food waste from the canning industry (Kumar, 2013; Poirier and Charlet, 2002; Qin et al., 2010). The poor solubi- 2000; Yan and Chen, 2015). Efficient use of this underutilized and lity of chitin is still the main barrier to its practical applications. The abundant biopolymer can create more economic and environ- presence of a large number of hydroxyl groups in chitin offers a mental benefits. Chitin is biodegradable, which can be degraded wide range of possibilities for its chemical modifications aiming at and depolymerized by various enzymes such as chitinases, chito- improving its solubility in common organic solvents, thereby sanases, and non-specific enzymes like carbohydrases and pro- leading to new chitin derivatives. teases (Kaczmarek et al., 2019). Sustainable and biodegradable Acylation chemistry has been widely used in chemical modifi- cations of cellulose, which produces a wide range of cellulose esters for coating additives and plastics (Edgar et al., 2001). Chitin has a * Corresponding author. Forest Products Laboratory, 1 Gifford Pinchot Dr, Madi- similar structure to cellulose, but it has an acetamido group at the son, WI 53726, USA. C2 position instead of a hydroxyl group in the pyranose ring (Kurita, E-mail address: [email protected] (J. Wang). https://doi.org/10.1016/j.jclepro.2019.119458 0959-6526/Published by Elsevier Ltd. 2 T. Zhong et al. / Journal of Cleaner Production 250 (2020) 119458 1998). Well-developed acylation chemistry for cellulose could be propionate. This study aims to investigate the dissolution of chitin adopted to modify chitin to yield chitin esters. Acylation enables propionate in ethanol/water binary solvents with various ethanol the substitution of the hydrogen of hydroxyl groups of chitin with concentrations. Subsequently, chitin propionate in aqueous ethanol an acyl group to form less hydrophilic esters, which can weaken or solutions was employed in the transparent film preparation; in the break down the hydrogen bonds and thus leading to improvement meantime, it was also applied as a coating material on the paper in its solubility in organic solvents (Draczynski, 2011; Sugimoto substrate. We investigated microstructure, mechanical properties et al., 2010; Van Luyen and Rossbach, 1995; Yang et al., 2009). and surface energy of chitin propionate films. The surface Synthesis reactions may occur in a heterogeneous process or a morphology, mechanical properties and surface energy of chitin homogeneous process. In the heterogeneous process, chitin may be propionate coated paper were also determined. treated with an organic acid anhydride and a catalyst (usually sulfuric acid or perchloric acid) in the absence of solvents. For 2. Materials and methods example, Draczynski (2011) produced chitin acetate/butyrate by the heterogeneous process in which the mixture of two organic 2.1. Materials acid anhydride as acylation agents and perchloride acid as a catalyst in the presence of non-solvent for the starting chitin. The homo- Chitin from shrimp shells (powder, practical grade), propionic geneous process often requires the dissolution of chitin prior to the anhydride (97%), perchloric acid (ACS reagent, 70%), diiodomethane reaction with an organic acid anhydride or acyl chlorides. For (ReagentPlus, 99%), N,N-Dimethylacetamide (DMAc, anhydrous, example, Teramoto et al. (2006) produced different chitin esters 99.8%) were purchased from Sigma-Aldrich. Glacial acetic acid (ACS fi under homogeneous conditions: chitin was rst dissolved in DMAc/ reagent) was purchased from EMD Millipore Corporation. Ammo- 5%LiCl solution, subsequently, the acylation occurred with the nium hydroxide was purchased from J.T. Baker. Glyceryl triacetate addition of pyridine as a catalyst. To date, different chitin esters (GTA) was kindly provided by Siegwerk USA Co. Paper (Multipur- have been reported in the literature, but the information on the pose paper, standard 92, recycled 100%) was from Georgia-Pacific. practical use of these chitin esters are still rare. It is well known that Ethanol (200 proof, anhydrous) was purchased from Decon Labs, commercially available cellulose esters, cellulose acetate, cellulose Inc. Lithium chloride (LiCl, lab grade) was purchased from Fisher propionate, cellulose acetate propionate, and cellulose acetate Science Education. butyrate have been widely applied in coatings, additives, plastics, optical films, membranes, and composites, because cellulose esters can provide qualities such as good flow and leveling, inter-coat 2.2. Synthesis of chitin propionate adhesion, sag resistance when applied as coating additives, meanwhile, cellulose ester films are optically clear, very tough and A reaction mixture was prepared with the 1.0/6.6/0.5 wt ratio of hard, and possess a high degree of ultraviolet stability (Edgar et al., chitin/propionic anhydride/perchloric acid. Twenty grams of the 2001). Structurally similar to cellulose esters, chitin esters might chitin power was used for each batch, around 12.3 wt% of the re- also have great potential to be used in the coatings and plastic film action mixture. Propionic anhydride and perchloric acid were pre- À packaging applications. In this research, we are searching for less- cooled at 4 C for 1 h. Then, the perchloric acid was added toxic organic solvents for processing chitin esters and exploring dropwise into the propionic anhydride; subsequently, the chitin the applicability of chitin esters in film and coating applications. powder was added. The mixture was placed in a water/ice bath at fi There are some investigations on the solubility of chitin esters in 0 C for the rst 30 min and then at room temperature under organic solvents. For example, chitin acetate with a degree of acetyl stirring for 2.5 h. After the propionylation, the diluted acetic acid substitution of 2 was found to be only soluble in acids such as solution was added to the mixture to hydrolyze unreacted propi- formic acid (Van Luyen and Rossbach, 1995). Chitin propionate, onic anhydride. The product water-insoluble chitin propionate was chitin butyrate, chitin valerate, and chitin caproate were found to separated from the mixture through water precipitation, then washed and repeatedly filtered until the pH was neutral, and finally be soluble in DMAc, dimethylformamide (DMF), dimethyl sulfoxide (DMSO),