Properties of plasticized composite films prepared from nanofibrillated cellulose and birch wood xylan
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Xylans, an important sub-class of hemicelluloses, represent a largely untapped resource for new renewable materials derived from biomass. As with other carbohydrates, nanocellulose reinforcement of xylans is interesting as a route to new bio-materials. With this in mind, birch wood xylan was combined with nanofibrillated cellulose (NFC) and films were cast with and without glycerol, sorbitol or methoxypolyethylene glycol (MPEG) as plasticizers. Microscopy revealed some NFC agglomeration in the composite films as well as a layered nanocellulose structure. Equilibrium moisture content in plasticized films increased with glycerol content but was independent of xylan:NFC ratio in unplasticized films. Sorbitol- and MPEG-plasticized films showed equilibrium moisture contents of approximately 10 wt% independent of plasticizer content. Tensile testing revealed increases in tensile strength with increased NFC content in the xylan:NFC composition range from 50:50 to 80:20 and plasticizer addition generally provided less brittle films. The oxygen permeability of unplasticized xylan-NFC films fell into a range which was similar to that for previously measured pure NFC films and was statistically independent of the xylan:NFC ratio. Water vapor permeability values of 1.9–2.8·10−11 g Pa−1 m−1 s−1 were found for unplasticized composite films, but these values were significantly reduced in the case of films plasticized with 10–40 wt% sorbitol.
KeywordsXylan Nanofibrillated cellulose Composites Films Plasticizer Tensile
The research reported here was supported by the Danish Science Council under the project # 09-065804 entitled “Advances in Sustainable Materials – Chemical and Physical Modification of Hemicellulose Sugars”. Thanks are due to Mikael Ankerfors at Innventia AB, Stockholm and Tom Lindström at KTH, BiMac Innovation Centre, Stockholm for their assistance in providing the carboxymethylated NFC. Lotte Nielsen and Sokol Ndoni (Department of Micro- and Nanotechnology, Technical University of Denmark) are acknowledged for the development of the SEC protocol which was used for xylan molecular weight analysis. The authors wish to express their gratitude to Frank Friedrich (Karlsruhe Institute of Technology, Karlsruhe, Germany) for obtaining FEG-SEM images using the FEI Quanta 200 MKII instrument. Assistance from Zsuzsa Sarossy (Department of Chemical and Biochemical Engineering, Technical University of Denmark) in carrying out the thermal analysis of xylan as well as the acid hydrolysis and sugar analysis experiments is also gratefully acknowledged.
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