Technical lignins are widely available as side-streams from pulping and biorefining processes. The aromatic structure of such lignins could be exploited in coating formulations to provide antioxidant or UV-blocking functionalities to packaging films. In this study, six technical lignins sourced from different plant species by given isolation/modification methods were compared for their composition, molar mass and functional groups. The lignins were then used to prepare thin spin-coated films from aqueous ammonia media. All the lignins formed ultrathin (< 12 nm), smooth (roughness < 2 nm) and continuous films that fully covered the solid support. Most of the films contained nanometer-sized particles, while those from water-insoluble lignins also presented larger particulate features, which likely originated from macromolecular association during solvent evaporation. These latter films had water contact angles (WCA) between 40º and 60º, corresponding to a surface energy of 42-48 mJ/m2 (determined by Zisman plots). For comparison, the water wettability measured on lignins pellets obtained by mechanical compression tracked closely with the WCA obtained from the respective thin films. Considering the widely diverse chemical, molecular and structural properties of the tested lignins, comprehensively documented here by using a battery of techniques, the solubility in water was found to be the most important and generic parameter to characterize the thin films. This points to the possibility of developing lignin coatings with predictable wetting behavior.

The transition to sustainable, biodegradable, and recyclable materials requires new sources of cellulose fibers that are already used in large volumes by forest industries. Oat and barley straws provide interesting alternatives to wood fibers in lightweight material applications because of their similar chemical composition. Here we investigate processing and material forming concepts, which would enable strong fiber network structures for various applications. The idea is to apply mild pretreatment processing that could be distributed locally so that the logistics of the raw material collection could be made efficient. The actual material production would then combine foam-forming and hot-pressing operations that allow using all fractions of fiber materials with minimal waste. We aimed to study the technical features of this type of processing on a laboratory scale. The homogeneity of the sheet samples was very much affected by whether the raw material was mechanically refined or not. Straw fibers did not form a bond spontaneously with one another after drying the sheets, but their effective bonding required a subsequent hot pressing operation. The mechanical properties of the formed materials were at a similar level as those of the conventional wood-fiber webs. In addition to the technical aspects of materials, we also discuss the business opportunities and system-level requirements of using straw as an alternative source of lignocellulosic fibers.

The effects of xylan extraction from birch kraft pulp on the manufacture and properties of cellulose nanofibril (CNF) films were here investigated. Hot water extractions of bleached and unbleached kraft pulps were performed in a flow-through system to remove and recover the xylan. After the extraction, the pulps were oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and fibrillated in a high-pressure microfluidizer. Compared to CNF from bleached kraft pulp, the CNF dispersions obtained from water-extracted pulps were less viscous and generally contained a higher amount of microfiber fragments, although smaller in size. In all cases, however, smooth and highly transparent films were produced from the CNF dispersions after the addition of sorbitol as plasticizer. The CNF films made from water-extracted pulps showed a lower tensile strength and ductility, probably due to their lower xylan content, but the stiffness was only reduced by the presence of lignin. Interestingly, the CNF films from water-extracted bleached pulps were less hydrophilic, and their water vapour permeability was reduced up to 25%. Therefore, hot water extraction of bleached birch kraft pulp could be used to produce CNF films with improved barrier properties for food packaging, while obtaining a high-purity xylan stream for other high-value applications.

The use of chemical additives (1- and 2-naphthol, formaldehyde) in hydrothermal pre-treatments of pine, birch, and willow wood was evaluated to minimize lignin condensation reactions and consequently improve the saccharification of the pre-treated materials. The residual hydrolysis lignins were then tested in the preparation of polylactic acid (PLA)-based composites. The results showed that addition of 2-naphthol to the hydrothermal pre-treatment increased the saccharification of pine wood by twofold compared to water-only experiments, but the sugar yield was only 50% of the carbohydrate content in the pre-treated pine. The use of 2-naphthol and formaldehyde also improved somewhat the saccharification of bark-containing willow wood, while the use of 1-naphthol had no effect on the saccharification of any of the pre-treated materials. In birch and willow (without bark), almost complete saccharification could be achieved even without additives. Analyses of hydrolysis lignins from birch revealed structural changes caused by the additives, which were consistent with a reduction of condensation reactions. Selected lignins were successfully used at 20% loading in PLA/lignin composites; however, variation in mechanical properties among composites prepared with different lignins was only minor. In general, the use of lignin decreased the strength and ductility of PLA but increased the stiffness. Based on these results, the use of additives may only be beneficial in the pre-treatment of pine or other softwoods to improve the sugar yields.