In this study we present a rapid method to prepare robust, solvent resistant nanofibrillated (NFC) cellulose films that can be further surface modified for functionality. The oxygen, water vapor and grease barrier properties of the films were measured and in addition mechanical properties in dry and wet state, and solvent resistance were evaluated. The pure unmodified NFC films were good barriers for oxygen gas and grease. At relative humidity below 65%, oxygen permeability of the pure and 2 unmodified NFC film was below 0.6 cm 3 µmm -2 d -1 kPa -1 , and no grease penetrated the film. However, the largest advantage of these films was their resistance to various solvents, like water, methanol, toluene and dimethylacetamide. Although they absorbed a substantial amount of solvent, the films could still be handled after 24h of solvent soaking. Hot-pressing was introduced as a convenient method to increase not only the drying speed of the films but also enhance the robustness of the films. The wet strength of films increased due to the pressing. Thus they can be chemically or physically modified through adsorption or direct chemical reaction in both aqueous and organic solvents. Through these modifications the properties of the film can be enhanced introducing e.g. functionality, hydrophobicity or bioactivity. Herein a simple method using surface coating with wax to improve hydrophobicity and oxygen barrier properties at very high humidity is described. Through this modification the oxygen permeability decreased further and was below 17 cm 3 µmm -2 d -1 kPa -1 even at 97.4 % RH and the water vapor transmission rate decreased from 600 to 40 g/m 2 day. The wax treatment did not deteriorate the dry strength of the film. Possible reasons for the unique properties are discussed. The developed robust NFC films can be used as a generic, environmentally sustainable platform for functional materials.

BackgroundWood cell walls are rich in cellulose, hemicellulose and lignin. Hence, they are important sources of renewable biomass for producing energy and green chemicals. However, extracting desired constituents from wood efficiently poses significant challenges because these polymers are highly cross-linked in cell walls and are not easily accessible to enzymes and chemicals.ResultsWe show that aspen pectate lyase PL1-27, which degrades homogalacturonan and is expressed at the onset of secondary wall formation, can increase the solubility of wood matrix polysaccharides. Overexpression of this enzyme in aspen increased solubility of not only pectins but also xylans and other hemicelluloses, indicating that homogalacturonan limits the solubility of major wood cell wall components. Enzymatic saccharification of wood obtained from PL1-27-overexpressing trees gave higher yields of pentoses and hexoses than similar treatment of wood from wild-type trees, even after acid pretreatment.ConclusionsThus, the modification of pectins may constitute an important biotechnological target for improved wood processing despite their low abundance in woody biomass.

Certain xylanases from family GH10 are highly expressed during secondary wall deposition, but their function is unknown. We carried out functional analyses of the secondary-wall specific PtxtXyn10A in hybrid aspen (Populus tremula × tremuloides). PtxtXyn10A function was analysed by expression studies, overexpression in Arabidopsis protoplasts and by downregulation in aspen. PtxtXyn10A overexpression in Arabidopsis protoplasts resulted in increased xylan endotransglycosylation rather than hydrolysis. In aspen, the enzyme was found to be proteolytically processed to a 68 kDa peptide and residing in cell walls. Its downregulation resulted in a corresponding decrease in xylan endotransglycosylase activity and no change in xylanase activity. This did not alter xylan molecular weight or its branching pattern but affected the cellulose-microfibril angle in wood fibres, increased primary growth (stem elongation, leaf formation and enlargement) and reduced the tendency to form tension wood. Transcriptomes of transgenic plants showed downregulation of tension wood related genes and changes in stress-responsive genes. The data indicate that PtxtXyn10A acts as a xylan endotransglycosylase and its main function is to release tensional stresses arising during secondary wall deposition. Furthermore, they suggest that regulation of stresses in secondary walls plays a vital role in plant development.

To understand the limitations occurring during enzymatic hydrolysis of cellulosic materials in renewable energy production, we used wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), X-ray microtomography, and transmission electron microscopy (TEM) to characterize submicrometer changes in the structure of microcrystalline cellulose (Avicel) digested with the Trichoderma reesei enzyme system. The microtomography measurements showed a clear decrease in particle size in scale of tens of micrometers. In all the TEM pictures, similar elongated and partly ramified structures were observed, independent of the hydrolysis time. The SAXS results of rewetted samples suggested a slight change in the structure in scale of 10-20 nm, whereas the WAXS results confirmed that the degree of crystallinity and the crystal sizes remained unchanged. This indicates that the enzymes act on the surface of cellulose bundles and are unable to penetrate into the nanopores of wet cellulose.

All-polysaccharide composite films were prepared from native, unmodified cellulose nanofibrils (CNF) mixed with various natural water-soluble polysaccharides like carboxymethyl cellulose, galactoglucomannan, xyloglucan and guar gum. Composite films were manufactured by pressurized filtration and hot pressing. The mechanical properties of the films were systematically evaluated in the dry and the wet state. GG was furthermore selectively oxidized using galactose oxidase (EC 1.1.3.9), and the effect of the degree of oxidation on the final composite film properties was shown.It was found that all the tested polysaccharides increased the strength and toughness of the dry composite films at 2 weight percent (wt-%) addition to CNF. After soaking the samples for 24h in water, striking differences between the samples were found: already at 2 wt-% CMC the wet strength of the composite films diminished, while the uncharged polysaccharides improved the wet strength. For example, the addition of 2 wt-% GGM increased Young's modulus by a factor of 1.3, the tensile strength by a factor of 2.8, and the toughness by a factor of 3.4. The results are discussed in relation to the amount of water absorbed in the films and possible reasons for the improved properties are suggested.

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Native cellulose nanofibrils (CNF) were prepared from bleached birch pulp without any chemical or enzymatic pretreatment. These CNF were modified by adsorption of a small amount of watersoluble polysaccharides and used to prepare nanopapers, which were processed into composites by lamination with an epoxy resin and subsequently cured. The results were compared to the properties of composites prepared using bacterial cellulose nanopapers, since bacterial cellulose constitutes highly pure and crystalline cellulose. It was found that both types of nanopapers significantly improved both the thermal stability and mechanical properties of the epoxy resin. As anticipated, addition of only 2 wt% of watersoluble polysaccharides efficiently hindered crackpropagation within the nanopaper and significantly improved the tensile strength and work of fracture compared to composites containing a conventional nanopaper reinforcement. The mechanical properties of the composites thus reflected the improvement of the nanopaper properties by the polysaccharides. Moreover, it was possible to predict the properties of the final composite from the mechanical performance of the nanopapers.