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Lignin rich nanocellulose fibrils isolated from parenchyma cells and fiber cells of western red cedar bark Yanhui Huang, Sandeep Sudhakaran Nair, Heyu Chen, Benhua Fei, Ning Yan, and Qiming Feng ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b03634 • Publication Date (Web): 15 Aug 2019 Downloaded from pubs.acs.org on August 24, 2019
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ACS Sustainable Chemistry & Engineering
Lignin rich nanocellulose fibrils isolated from parenchyma cells and fiber cells of western red cedar bark Yanhui Huanga, *, Sandeep S. Nairb, Heyu Chenb, Benhua Feic, Ning Yanb,d *, Qiming Fenga a
MOE Key Laboratory of Wooden Material Science and Application, Beijing Forestry
University, Qinghua East Road 35, Beijing 100083, China b
Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontario M5S3B3,
Canada c
International Center for Bamboo and Rattan, No. 8 Futong Dongdajie, Wangjing Area,
Chaoyang District, Beijing 100102, China d
Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200
College Street, Toronto, Ontario M5S 3E5, Canada * Corresponding
Authors:
E-mail:
[email protected] Tel.: +861062337192. E-mail: ning.yan@ utoronto.ca Tel.: +14169468070. Fax: +14169783834.
ABSTRACT: Mild alkaline treatment followed by micro grinding are employed to isolate lignin (23 wt%) containing nanocellulose fibrils (LNF) from bark of Western Red Cedar. Microscopic images of the cross section of bark revealed the high abundance of thin walled parenchyma cells
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followed by fiber cells. The mild alkaline treatment resulted in separated cell corners, reduced cell wall thickness, loose and, layered cell wall structure for all the cells. Confocal and AFM-IR images confirmed that the lignin mainly moved out from the cell corners, parenchyma cells and S1 layer of fiber cells. Within a few passes through grinder, most of bark were disintegrated to smaller fibrils. The extracted bark was homogenized to LNF with diameter less than 15 nm. The dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) results showed the high thermal stability of LNF films, compared to those made from bleached nanocellulose fibrils (BNF). In addition, the LNF films retained the bulk of mechanical and water vapour barrier properties at high humidity. The films made from LNF exceeded the tensile performance of most of other biopolymers reported in literature.
KEYWORDS: Lignin containing nanocellulose fibrils, Atomic force microscope infrared spectroscopy, Mechanical property, Thermal stability,Water vapor transmission rate INTRODUCTION Plant fibers are made of elementary fibrils or microfibrils, which are bundles of cellulose molecules held together by strong hydrogen bonds. These microfibril or aggregates of microfibrils with diameter less than 100 nm, known as cellulose nanofibrils (CNFs) have garnered considerable attention in the past few decades due to its promising applications. In addition to its renewable and biodegradable nature, CNFs possess high mechanical strength and have been widely considered as a viable green alternative for various composites, coatings, membranes and packaging materials.1,2,3 However, the breaking down of plant fibers to CNFs using strong shearing force is a highly energy consuming process with reported values ranging from 1550 to 21000 kWh/tonne.4 In addition, the highly polar nature and poor thermal stability have also limited the use of CNFs in various composite applications.5
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Lignin acts as a strong adhesive between the cellulose fibers, providing mechanical strength to the plant cell walls and by augmentation to the entire plant. The presence of lignin with its strong covalent bonding of cellulose acts as a barrier for cellulose nanofibrillation ,6 and therefore most of the studies use either completely bleached cellulose or cellulose with less lignin content for CNF production.7 However, the presence of lignin on cellulose has lots of beneficial effects. Lignin with its high amount of non-polar hydrocarbon and benzene groups impart enhanced hydrophobicity and thermal stability to cellulose.5,8 Also, the use of unbleached cellulose for nanofibrillation with high amount of lignin have additional benefits such as high yields, low production costs, and limited generation of chemical waste. Only few efforts have been successful in extracting lignin (>5 wt%) containing nanocellulose fibrils (LNF). Some of the recent studies include using fibers subjected to SO2–ethanol solvent process,8 acid hydrolysis,9 and Tempo oxidation
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for obtaining LNF. The use of high amounts of chemicals,
depolymerization of cellulose, or use of expensive reagents are some of the disadvantages associated with these efforts. Recently, Visanko et al.11 used high temperature grinding process using a microgrinder to extract LNF from never dried unbleached ground wood. The storage and transportation of never dried pulps are not always economical. Some studies used thermomechanical pulp (TMP) for LNF production. However, only a fraction of fibers was fibrillated to nanoscale (
