Subscriber access provided by Kaohsiung Medical University
Article
In Search of Stronger/Cheaper Chitin Nanofibers through Electrospinning of Chitin-Cellulose Composites Using an Ionic Liquid Platform Julia L. Shamshina, Oleksandra Zavgorodnya, Hemant Choudhary, Brandon Frye, Nathaniel James Newbury, and Robin D. Rogers ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03269 • Publication Date (Web): 12 Sep 2018 Downloaded from http://pubs.acs.org on September 16, 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 26 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 Sustainable Chemistry & Engineering
In Search of Stronger/Cheaper Chitin Nanofibers through Electrospinning of ChitinCellulose Composites Using an Ionic Liquid Platform Julia L. Shamshina,1 Oleksandra Zavgorodnya,2 Hemant Choudhary,2 Brandon Frye,3 Nathaniel Newbury,3 and Robin D. Rogers2,4,* 1 2
Mari Signum Mid-Atlantic, LLC, 3204 Tower Oaks Boulevard, Rockville, MD 20852, USA College of Arts & Sciences, The University of Alabama, Tuscaloosa, AL 35487, USA
3
Anton Paar USA, Inc., 10215 Timber Ridge Drive, Ashland, VA 23005, USA
4
525 Solutions, Inc., PO Box 2206, Tuscaloosa, AL 35403, USA
*Email:
[email protected] Keywords: biopolymers, chitin, cellulose, composites, ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), electrospinning, nanofibrous mats (nanomats), strength, elasticity
Abstract The ability of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) to solubilize natural biopolymers (e.g., chitin and cellulose) without any chemical modification has been used to develop a one-pot process to prepare a spinning dope by extracting chitin from shrimp shell, co-dissolving microcrystalline cellulose (MCC, DP = 270), and electrospinning nanomats from shrimp shell-extract/MCC solutions. The resulting spinning dopes were prepared with optimal viscosity of 380 to 900 cP, and conductivity and surface tension of ~2.8 mS/cm and ~ 36 dyn/cm, respectively, however, nanofibers could only be prepared when the chitin/MCC ratios in SS-extract/MCC solution were between 9/1 and 6/4. Compared to nanomats electrospun from shrimp shell-extract solution, 7/3 chitin/MCC composite nanomats demonstrated a 2-fold improvement in hardness and 3-fold improvement in elasticity, although further increases in MCC content resulted in lowering both parameters which nonetheless were higher than the pure chitin nanomats. This one pot process for preparing spinning dopes directly from shrimp shellextract is a viable method to prepare chitin/MCC composites of improved strength/elasticity at lower costs. 1 ACS Paragon Plus Environment
ACS Sustainable Chemistry & 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 26
Introduction Accumulation of non-degradable polymeric waste in both landfills and oceans is a major environmental concern raised in the last decade.1,2 Using biomass feedstock or its waste products for recovering of biopolymers to be used as substitutes to synthetic polymers is a more sustainable approach that has been applied to make different products.3-6 In our own efforts of plastic replacement, we have developed technologies for the preparation of fibers, films, and beads via solution processing of biopolymers dissolved in the ionic liquid (IL) 1-ethyl-3methylimidazolium acetate ([C2mim][OAc]).7-10 Recently, as a continuation of these efforts, we have shown that high molecular weight (MW) regenerated chitin extracted from shellfish waste9 could easily be processed into nanomats through electrospinning from [C2mim][OAc].11-13 We have not only demonstrated the concept of electrospinning of the biopolymer from the IL, but also achieved scale up of the process,12 and have shown that fiber formation depends primarily on the solution properties (i.e., conductivity, surface tension, and viscosity or polymer concentration).13 However, wide application of biopolymers in material development in general, and chitin nanomats in particular, are still limited due to often insufficient mechanical strength as compared to synthetic analogs and the expense of isolating and purifying the chitin from raw crustacean shells. Our previous work has focused on electrospinning of regenerated chitin that we obtained by first extracting the chitin from raw shrimp shells using an IL, and then coagulating it in an antisolvent to remove solids, salts, and proteins.12,13 The extra purification steps of coagulating, isolating, and then redissolving it in fresh IL add cost and thus for practical commodity materials and applications, it would be advantageous to be able to conduct electrospinning directly from the original chitinous extract solution. Electrospinning a solution of chitin crustacean biomass right after the extraction step with simple centrifugation to remove any solids, would significantly reduce the costs, however, nanofibers electrospun from such shrimp shell-extract solution (abbreviated SS-extract) are anticipated to be weaker than necessary for certain applications due to the presence of impurities, thus requiring reinforcement.14 Indeed, dry-wet jet spun monofilament fibers, pulled from SS-extract solution exhibited ca. 1.8-times inferior strength than fibers obtained by the same method using regenerated purified and then redissolved, chitin.9 2 ACS Paragon Plus Environment
Page 3 of 26 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 Sustainable Chemistry & Engineering
We hypothesized that desirable strength improvement could be achieved using another biopolymer, cellulose, known for its remarkable strength and often used as a reinforcement polymer in composite materials. 15 - 18 For example, microcrystalline cellulose (MCC) with Young’s modulus of 29-36 GPa has been shown to reinforce numerous biopolymeric materials,19-23 and is often used in industrial applications in place of unrefined cellulose directly from plants. Due to its low cost and commercial availability, MCC is often used as a binding filler in, for example, drug delivery systems and as additive to commodity plastics to increase materials rigidity.
24 , 25
In this way, MCC-reinforced low density polyethylene (LDPE)
demonstrated an ca. 1.6-times increase in the Young’s modulus when compared to non-modified LDPE.20 A similar increase in mechanical strength was observed by others for regenerated chitin/MCC films, when composites were prepared through an IL process.26 Based on the solubility of both chitin9 and MCC27 in [C2mim][OAc], we settled on the codissolution of both polymers in the same IL. Such attempts of simultaneous processing of chitin and MCC from ILs have been shown to be possible in certain applications, such as making macrofibers (via dry-wet spinning), beads, and films (via biopolymer dissolution and casting or via ion-gel coagulation methods) from 1-ethyl-3-methylimidazolium propionate, 1-butyl-3methylimidazolium chloride, and [C2mim][OAc].28-32 Both chitin and cellulose have each been successfully electrospun from IL solution,33-37 however, we are unaware of any reports where composites of these were electrospun from a single solution of both biopolymers. To test our hypothesis, we electrospun a series of SS-extract/MCC solutions with different biopolymer ratios from [C2mim][OAc], and employed regenerated chitin and SS-extract without MCC as our benchmarks. Our investigation of the effects of low MW MCC on solution properties, observations on fiber formation, and testing of mechanical properties of the resultant materials, suggests this approach is a viable method to electrospin composite SS-extract/MCC dopes and prepare chitin/MCC composites of improved strength at lower costs.
Results and Discussion In order to conduct electrospinning using regenerated (purified) chitin, the chitin needs first to be isolated through multiple steps including microwave-assisted extraction in [C2mim][OAc], centrifugation of undissolved calcium carbonate residue and proteins, coagulation of the supernatant using an anti-solvent, multiple washing steps to remove the IL, and drying (Scheme 3 ACS Paragon Plus Environment
ACS Sustainable Chemistry & 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 4 of 26
1). The purified regenerated chitin must then be ground and re-dissolved in fresh IL prior to electrospinning.12,13 Our first intent with this work was to reduce the time, costs, energy, and solvent usage by eliminating the many isolation and purification steps. We questioned whether simple centrifugation to remove the solids from the SS-extract would obviate the need for the chitin purification steps. The main difficulty is that crustacean shells contain not only chitin, but also large amounts of proteins (often covalently bound), mineral salts, and a small amount of lipids.
Scheme 1. Electrospinning of regenerated chitin (left) compared to electrospinning of shrimp shell-extract (SS-extract) solution (right).
Our earlier work had already suggested that microwave-assisted chitin extraction using [C2mim][OAc] followed by centrifugation would completely remove IL-insoluble calcium carbonate.9 In reality, electrospinning into a water bath is not much different from the coagulation process noted in Scheme 1 and we have previously shown this coagulation step provides regenerated chitin of high purity.9
Preparation of Spinning Dopes Shrimp Shell-Extract To prepare SS-extract for the electrospinning trials, shrimp shell biomass was first obtained from raw uncooked shrimps (see Experimental for details). The collected washed, oven-dried (80 °C), ground, and sieved (95%) was used as received from IoLiTec, USA (Tuscaloosa, AL). Microcrystalline cellulose (MCC, DP = 270) was obtained from Sigma (Sigma-Aldrich, St, Louis, MO). Deionized (DI) water was obtained from a 16 ACS Paragon Plus Environment
Page 17 of 26 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 Sustainable Chemistry & Engineering
commercial deionizer (Culligan, Northbrook, IL) with specific resistivity of 16.82 MΩ·cm at 25 °C. Biomass Frozen shrimp used for chitin extraction were purchased from Skinner’s Seafood, Dauphin Island, AL. The shrimp were thawed; peeled, and visible shrimp meat removed. The backs of the shells were collected and washed 5-times with tap water followed by oven-drying (Precision Econotherm Laboratory Oven, Winchester, VA) at 80 °C for 2 days. The dry shells were ground with a Janke & Kunkel mill (Ika Labortechnik, Wilmington, NC) for 5 min and sieved through 1000 µm, 500 µm, 250 µm, and 125 µm brass sieves with wire mesh (Ika Labortechnik, Wilmington, NC). Shrimp shell particles
