Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer
Cellulose
Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer
0 Y. Yan J. Li Beijing Key Laboratory of Wood Science and Engineering, Beijing Forestry University , Beijing 100083 , China
1 Y. Yan J. Li MOE Key Laboratory of Wooden Material Science and Application, Beijing Forestry University , Beijing 100083 , China
2 Stefan Veigel
3 S. Veigel W. Gindl-Altmutter (&) Department of Materials Science and Process Engineering, BOKU - University of Natural Resources and Life Science Vienna , Vienna , Austria
4 H. Amer Department of Natural and Microbial Products Chemistry, National Research Centre , P.O. 12622, Dokki, Giza , Egypt
5 J. Keckes Department of Materials Physics, University of Leoben , Leoben , Austria
6 T. Zimmermann Applied Wood Materials, Empa, Swiss Federal Laboratories for Materials Science and Technology , Duebendorf , Switzerland
7 C. Zollfrank J. Do ̈rrstein C. Jobst Chair for Biogenic Polymers, Technische Universita ̈t Mu ̈nchen , Straubing , Germany
8 H. Amer T. Rosenau Department of Chemistry, BOKU - University of Natural Resources and Life Science Vienna , Vienna , Austria
9 Y. Yan J. Li MOE Engineering Research Centre of Forestry Biomass Materials and Bioenergy, Beijing Forestry University , Beijing 100083 , China
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.
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
(Lo¨nnberg et al. 2008;
Littunen et al. 2011; Missoum et al.
2012)
;cationization
(Hasani et al. 2008; Syverud et al. 2010)
;
silylation
(Gousse´ 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.
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 indu (...truncated)