Resin impregnation of cellulose nanofibril films facilitated by water swelling
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ORIGINAL PAPER
Resin impregnation of cellulose nanofibril films facilitated by water swelling Yan Qing • Ronald Sabo • Zhiyong Cai Yiqiang Wu
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Received: 17 August 2012 / Accepted: 24 October 2012 / Published online: 8 November 2012 Ó Springer Science+Business Media Dordrecht (outside the USA) 2012
Abstract Flexible composite films were produced by impregnating aqueous phenol formaldehyde (PF) resin into water-swollen cellulose nanofibril (CNF) films. CNF films were prepared using a pressurized filtration method in combination with freeze drying. The freeze-dried films were swollen with water then impregnated with PF resin by soaking in aqueous resin solutions of varying concentrations. Small amounts of PF slightly enhanced the tensile properties of CNF films. The formulation with the best mechanical properties was CNF/PF films with 8 wt % resin exhibiting tensile stress and toughness of 248 MPa and 26 MJ/m3, respectively. Resin concentrations higher than about 8 % resulted in composites with decreased tensile properties as compared to neat CNF films. The wet strength of the composite films was significantly higher than that of the neat CNF films. The resulting composites showed greater resistance to moisture absorption accompanied by reduced thickness swelling when soaked in water as compared to
Y. Qing Y. Wu (&) School of Materials Science and Engineering, Central South University of Forestry and Technology, 498 Shaoshan South Road, Changsha 410004, China e-mail: [email protected] Y. Qing R. Sabo Z. Cai (&) Forest Products Laboratory, United States Department of Agriculture, 1 Gifford Pinchot Drive, Madison 53726-2398, WI, USA e-mail: [email protected]
neat CNF films. The composites also showed decreased oxygen permeability at low humidity compared to neat films, but the composites did not show improved barrier properties at high humidity. Keywords Cellulose nanofibril Phenol formaldehyde Water swelling Mechanical properties Wet strength Morphology Oxygen permeability
Introduction Cellulose nanofibril (CNF) has recently been receiving increased attention for their use in composite materials (Siro´ and Plackett 2010). These nano-scale fibers have been reported to have remarkable mechanical properties, including an elastic modulus measured to be about 150 GPa (Iwamoto et al. 2009). Such mechanical properties suggest that CNF has the potential to compete with other inorganic reinforcements, such as glass fibers. In addition, films and composites made from CNFs have low thermal expansion (Nogi et al. 2009), provide effective gas and oil barrier (Syverud and Stenius 2009; Aulin et al. 2010; Rodionova et al. 2012), and exhibit excellent light transparency (Nogi et al. 2009; Zhu et al. 2011). The particular mechanical and physical properties of cellulose nanofibrils lend themselves to a wide range of potential applications, including packaging and coatings (Syverud and Stenius
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2009; Aulin et al. 2010), reinforced nanocomposites (Svagan et al. 2007; Iwatake et al. 2008; Gong et al. 20
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