Nanocomposite Films of Hemicellulose and Nanocelluloses with Improved Barrier Properties for Packaging Applications

In this project, nanocomposite films and coatings, based on renewable resources, were prepared. A hemicellulose biopolymer, based on xylan, was used as the matrix, and cellulose nanowhiskers (CNWs), as the functional additive. The xylan based matrix is an oxygen, grease and aroma barrier, making it a suitable raw material for packaging applications. Cellulose nanowhiskers were used to improve the mechanical properties and thermal stability of the hemicellulose while improving the barrier properties at high relative humidity. The focus of this thesis was processing and characterization of xylan based nanocomposites’ films and coatings. Two grades of xylans, A and B, and food contact approved plasticizer were used to prepare homogeneous films and coatings of nanocomposites, containing 2.5, 5 and 10 wt% of CNWs. The microscopy study showed no aggregations of CNWs in micro scale. Crosslinking was efficiently performed on A films and coatings, and a crosslinking density of about 70% was obtained. X-ray diffraction studies revealed a semicrystalline structure for A matrices and an amorphous one for B. The addition of CNWs resulted in an increase of crystallinity in both A and B samples. Dynamic mechanical thermal analysis showed that addition of whiskers tended to increase the storage modulus at high temperature (90°C) region. Furthermore, crosslinking as well as small amounts of whiskers (2.5 to 5 wt%) resulted in a shift of tan δ peak of nanocomposites to higher temperatures. Mechanical testing revealed a trend of improved mechanical stability in nanocomposites with small amounts of whiskers, whereas the Young’s modulus, maximum strain and maximum stress increased. However, the mechanical properties decreased at 10 wt% CNW content, probably due to aggregation of whiskers. Moreover, barrier tests, like crisp bag, grease permeability and especially oxygen permeability, indicated improved barrier properties of the materials at moist conditions. In general, improvements in barrier and mechanical performance of the material were observed, resulting from combination of CNW addition and crosslinking.Validerat; 20111121 (anonymous