Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE
Characterization, Synthesis, and Modifications
Self-sustaining cellulose nanofiber hydrogel produced by hydrothermal gelation without additives Shin Suenaga, and Mitsumasa Osada ACS Biomater. Sci. Eng., Just Accepted Manuscript • DOI: 10.1021/acsbiomaterials.8b00026 • Publication Date (Web): 12 Mar 2018 Downloaded from http://pubs.acs.org on March 13, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Biomaterials Science & Engineering
Self-sustaining cellulose nanofiber hydrogel produced by hydrothermal gelation without additives Shin Suenaga, Mitsumasa Osada* Department of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, 3-15-1, Tokida, Ueda, Nagano 386-8567, Japan
*Corresponding Author E-mail:
[email protected]; Tel.: +81-268-21-5458; Fax: +81-268-21-5391
ACS Paragon Plus Environment
1
ACS Biomaterials Science & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 34
Abstract We prepared a self-sustaining hydrogel from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)oxidized cellulose nanofibers (TOCNs) via hydrothermal treatment at 160 °C. The selfsustaining hydrogels could be obtained at less than 1 wt% TOCNs without any additives. Brownish hydrogels obtained after the hydrothermal treatment could be rendered transparent by immersing them in distilled water at 5 °C. The compressive modulus of the hydrogel increased with increasing heating time. X-ray diffraction studies reveal that the crystal structure of the internal layers of the TOCNs remained intact after the hydrothermal treatment and depigmentation. The hydrothermal treatment caused the hydrolysis of molecules, especially the glucuronate units, from the external layer of TOCN. The elimination of the glucuronate units decreased the net negative surface charge of the TOCNs, resulting in their aggregation into a three-dimensional network structure owing to the predominance of attractive forces. Such additive-free hydrogels which can be shaped into diverse forms are promising for medical applications.
Keywords: Nanocellulose, hydrogel, hydrothermal treatment, green chemistry
ACS Paragon Plus Environment
2
Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Biomaterials Science & Engineering
1. INTRODUCTION Cellulose is the most abundant biomass and has been utilized for a long time owing to its various beneficial properties such as renewability, nontoxicity, and chemical stability. Recently, high-value-added cellulose has been studied toward the effective utilization of thinned wood or lumbering waste.1–3 Cellulose nanofibers (NFs) are a promising example of high-value-added cellulose. Individualized cellulose NFs, viz., fibers with widths less than 10 nm and lengths more than several hundred nanometers, are easily prepared by treating wood pulp with 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO) radicals.4 TEMPO selectively oxidizes the hydroxyl group at C-6 position of glucose in the cellulose microfibrils to generate a carboxylate group.5 This process introduces dense negative charges on the surfaces of cellulose microfibrils and the microfibril structure could be completely disintegrated via simple mechanical shearing owing to the electrostatic repulsion between the TEMPO-oxidized cellulose nanofibers (TOCNs).6 TOCNs with widths of several nanometers have advantageous properties such as a low density (1.6 g cm– 3
), high elastic modulus (140 GPa),7 high specific surface area (600 m2 g–1),8 and low coefficient
of thermal expansion (0.6 × 10–5 K–1).9 TOCNs are not only used as dispersions, but also converted into films,10 aerogels,8,11 and hydrogels12,13 for potential application in flexible display panels, biodegradable packaging films, thermal insulators, drug delivery systems, catalytic systems, scaffolds, and seed growing media. Hydrogels comprise three-dimensional (3D) network structures produced by water-insoluble polymers that can swell and retain a large amount of water within their network structures.14,15 TOCN or chitin NF dispersions form 3D networks, even at low concentrations (
