Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer (pdf)

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Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer

Cellulose (2016) 23:1189–1197 DOI 10.1007/s10570-016-0887-0 ORIGINAL PAPER Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer Yutao Yan . Hassan Amer . Thomas Rosenau . Cordt Zollfrank . Jörg Dörrstein . Cornelia Jobst . Tanja Zimmermann . Jozef Keckes . Stefan Veigel . Wolfgang Gindl-Altmutter . Jianzhang Li Received: 14 October 2015 / Accepted: 12 February 2016 / Published online: 17 February 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract In order to produce dry and hydrophobic microfibrillated cellulose (MFC) in a simple procedure, its modification with alkyl ketene dimer (AKD) was performed. For this purpose, MFC was solventexchanged to ethyl acetate and mixed with AKD dissolved in the same solvent. Curing at 130 °C for 20 h under the catalysis of 1-methylimidazole yielded a dry powder. Scanning electron microscopy of the powder indicated loss in nanofibrillar structure due to aggregation, but discrete microfibrillar structures were still present. Water contact angle measurements of films produced from modified and unmodified MFC showed high hydrophobicity after AKD treatment, which persisted even after extraction with THF for 8 h. The hydrophobized MFC was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and X-ray analysis. In summary, strong indications for the presence of AKD on the surface of MFC before and after extraction with solvent were found, but only a very small amount of covalent b-ketoester linkages between the modification agent and cellulose was revealed. Y. Yan J. Li MOE Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Beijing 100083, China e-mail: T. Zimmermann Applied Wood Materials, Empa, Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerland Y. Yan J. Li Beijing Key Laboratory of Wood Science and Engineering, Beijing Forestry University, Beijing 100083, China Y. Yan J. Li MOE Engineering Research Centre of Forestry Biomass Materials and Bioenergy, Beijing Forestry University, Beijing 100083, China H. Amer T. Rosenau Department of Chemistry, BOKU - University of Natural Resources and Life Science Vienna, Vienna, Austria J. Keckes Department of Materials Physics, University of Leoben, Leoben, Austria H. Amer Department of Natural and Microbial Products Chemistry, National Research Centre, P.O. 12622, Dokki, Giza, Egypt S. Veigel W. Gindl-Altmutter (&) Department of Materials Science and Process Engineering, BOKU - University of Natural Resources and Life Science Vienna, Vienna, Austria e-mail: C. Zollfrank J. Dörrstein C. Jobst Chair for Biogenic Polymers, Technische Universität München, Straubing, Germany 123 1190 Keywords Microfibrillated cellulose Alkyl ketene dimer Surface modification Hydrophobicity Dry powder Introduction Microfibrillated cellulose (MFC) has been discussed for many potential applications (Eichhorn et al. 2010; Dufresne 2012), among which polymer reinforcement is one of the most obvious. Because of its high strength and stiffness, high aspect ratio, web-like structure, and its bio-based and renewable characteristics, MFC has been widely used in polymer preparation as an excellent reinforcement material (Fakirov et al. 2008; Iwatake et al. 2008; Lu et al. 2008a, b; Nakagaito et al. 2009; Wang and Drzal 2012; Miao and Hamad 2013; Pandey et al. 2013). However, as demonstrated in a recent comprehensive overview, a break-through towards bulk use of MFC in polymer reinforcement has not been realized to date (Lee et al. 2014). One major limitation to be overcome lies in the poor surface-chemical compatibility of cellulose with many widely used fossil-based consumer polymers, such as polyolefins as well as important biopolymers from renewable resources such as polylactic acid (PLA). The pronounced hydrophilicity of MFC, caused by the presence of abundant hydroxyl groups, limits its dispersibility in hydrophobic polymers and solvents (Yang et al. 2014), and subsequently entails poor reinforcement efficiency in composites. Chemical surface modification efficiently tackles this problem (Habibi 2014). Among the many different routes for surface modification reported, esterification with acetic anhydride or long chain carboxylic acids (Rodionova et al. 2010; Lee et al. 2011; Bulota et al. 2012);grafting of polymers (Lönnberg et al. 2008; Littunen et al. 2011; Missoum et al. 2012);cationization (Hasani et al. 2008; Syverud et al. 2010); silylation (Goussé et al. 2004; Andresen et al. 2006; Lu et al. 2008a, b), and TEMPO oxidation (Saito et al. 2006; Fukuzumi et al. 2009) are mentioned as important examples. Even though highly successful at the laboratory scale, the up-scaling of these wetchemical approaches to industrial dimensions, involving partly pricey reagents and repeated solvent transfers is most probably quite cost-intensive. 123 Cellulose (2016) 23:1189–1197 Another significant obstacle for high-volume MFC application is the fact that MFC cannot be dried directly from suspension in water by simple evaporation at atmospheric pressure, because this may cause an irreversible agglomeration, also termed hornification, during drying, affecting its unique properties related to size and nanofibrillar geometry (Spence et al. 2011; Beck et al. 2012). Preparation of dry microfibrillated cellulose powder without hornification could be of great interest in industrial application. Freeze-drying represents a potential option, because it largely preserves the fibrillary structure of MFC without agglomeration during the drying process (Peng et al. 2012). Nanocellulose powder was prepared by combining freezing drying and surfactant treatment, and it was re-dispersed in PLA-chloroform solution to prepare PLA composites (Petersson et al. 2007). Drying in supercritical CO2 is also a good way to produce dry NFC, as it keeps the dimensions in nano size (Peng et al. 2012). However, both of these two methods are of high cost and impractical to scale up. By carboxymethylation and mechanical disintegration, water-redispersible MFC in powder form was prepared by Eyholzer et al. (2010). Though the MFC powder maintained its original properties, the carboxymethylated sample displayed a loss in crystallinity and a strong decrease in thermal stability. In summary, the hydrophilicity of MFC greatly hinders its large-scale application in polymer reinforcement, as it limits dispersion and reinforcement efficiency, and prevents the production of a dry fibrillary product required for convenient industrial processing. We propose a novel approach to significantly reduce this hurdle for MFC utilization by using AKD as a modifier. In the paper industry, sizing agents such as alkyl succinic anhydride (ASA), alkyl ketene dimer (AKD) and rosin are used to provide a certain degree of hydrophobicity and printabili (...truncated)