Surface Modification of Bacterial Cellulose Nanofibers for Property Enhancement of Optically Transparent Composites:  Dependence on Acetyl-Group DS

Abstract

Bacterial cellulose (BC) nanofibers were acetylated to enhance the properties of optically transparent composites of acrylic resin reinforced with the nanofibers. A series of BC nanofibers acetylated from degree-of-substitution (DS) 0 to 1.76 were obtained. X-ray diffraction profiles indicated that acetylation proceeded from the surface to the core of BC nanofibers, and scanning electron microscopy images showed that the volume of nanofibers increases by the bulky acetyl group. Since acetylation decreased the refractive index of cellulose, regular transmittance of composites comprised of 63% BC nanofiber was improved, and deterioration at 580 nm because of fiber reinforcement was suppressed to only 3.4%. Acetylation of nanofibers changed their surface properties and reduced the moisture content of the composite to about one-third that of untreated composite, although excessive acetylation increased hygroscopicity. Furthermore, acetylation was found to reduce the coefficient of thermal expansion of a BC sheet from 3 x 10(-6) to below 1 x 10(-6) 1/K.

Topochemical acetylation of cellulose nanopaper structures for biocomposites: mechanisms for reduced water vapour sorption

“…In a previous study, moisture sorption of acetylated cellulose was high for specimens with high bulk-DS (Ifuku et al 2007). High bulk-DS may cause extensive derivatization and degradation of fibril structure.…”

“…Biocomposites with unmodified NFC adsorbed more moisture than pure resins, due to the hydrophilic character of NFC surfaces and disordered regions (Fig. 10) (Ifuku et al 2007;Zhang et al 2011). However, the moisture content is much lower than for typical plant fiber biocomposites (Gaceva et al 2007;Nguong et al 2013), pointing to the advantage of nanocomposites based on cellulose of fairly high purity.…”

“…A previous study by Ifuku et al (2007) on bacterial cellulose (BC)/acrylic resin composites demonstrated that increasing degree of BC acetylation decreased composites moisture sorption at RH = 55 %. However, for high degrees of substitution (DS) [ 0.56 the moisture sorption started to increase.…”

Chitin Nanofibers with a Uniform Width of 10 to 20 nm and Their Transparent Nanocomposite Films

“…By the introduction of hydrophobic functional groups into hydrophilic hydroxyl groups on chitin fibers, it is expected that dispersibility in nonpolar solvents, hygroscopicity, adhesion properties with hydrophobic matrices for fiber-reinforced composite materials are improved (Glasser et al, 1994). In chemical modification, acetylation is considered to be a simple, popular, and inexpensive approach to change the surface property (Kim et al, 2002;Ifuku et al, 2007). However, there have been no reports regarding acetylation of chitin nanofibers.…”

Novel cellulose-based composites based on nanofibrillated plant and bacterial cellulose: recent advances at the University of Aveiro – a review

“…BC has a high degree of poly merization and crystallinity, extremely high water holding capacity, high tensile strength, and high surface area (George et al 2005a,b ). BC is well suited as a reinforcing element in nanocomposites in several polymeric matrices, namely, cellulose acetate butyrate (Gindl and Keckes 2004 ), acrylic thermosetting resins Ifuku et al 2007 ), phenolic resins , poly(ethylene oxide) (Brown and Laborie 2008 ), plasticized starch (Wan et al 2009 ), PLA (Kim et al 2009 ), and epoxidized soybean oil matrix (Retegi et al 2012 ), just to mention a few examples.…”