Aqueous Dispersions from Wood-Derived Biopolymers for Barrier and Packaging Applications

Synthetic polymers (e.g., polyethylene, polyvinylchloride, and polystyrene) are well-known to exhibit excellent structural properties such as durability and barriers, and these biopolymers can be used in many applications. Yet, they are neither biodegradable nor sustainable. They cause accumulation in landfills and end up in the oceans. Meanwhile, the degradation of plastic into microplastics can harm the health of human beings. Innovation to develop sustainable and green biopolymers and materials is urgently needed as one route to reduce greenhouse gas emissions and dependency on petrol-based materials. This thesis is dedicated to using renewable wood-derived polymers (e.g., cellulose, hemicelluloses, lignin, and suberin) to produce bio-based aqueous dispersions, addressing some of the current limitations in certain applications. Furthermore, these bio-based aqueous dispersions are utilized to provide barrier properties of fiber-based materials in packaging applications. To achieve redispersible nanocellulose, here as cellulose nanofibrils (CNF), an integrated fibrillation process using the addition of water-soluble hemicelluloses and their derivatives was established. Particularly, carboxymethylated-galactoglucomannan (CM-GGM) facilitates fiber fibrillation enabling a good flowability during homogenizing, thus saving energy. Moreover, hemicellulose addition improved the water redispersibility that was validated by comparing size distribution, morphology, viscosity and film properties with neat nanocellulose. Furthermore, this thesis demonstrates the use of as-prepared nanocellulose in the presence of hemicelluloses as coatings materials for dispersion coating, achieving a good barrier property of fiber-based materials in decrease of heptane vapor and increase of grease resistance. In this thesis, an approach to prepare bio-based aqueous dispersion coating of CNF/lignin was developed, where lignin was in situ polymerized in proximity to the CNF surface in its dispersion via laccase-catalyzed oxidation. A dispersion of nanocellulose with its fiber network evenly coated by aligned lignin nanoparticles was obtained, in particular with isopropyl alcohol (iPrOH)-soluble fractions of lignin, and the thus-prepared films of CNF/lignin dispersion showed high hydrophobicity and low water vapor transmission rate (WVTR) compared to the neat CNF films. More importantly, varying lignin fractions, obtained by the sequential solvent fractionation method, were attempted to prepare coating dispersions to unveil the structure-property relationship between CNF surface decoration and coating performance. The coating formulation using iPrOH lignin fractions outperformed those using other fractions in enhancing the barrier properties of coated paperboard. Suberin fractions, isolated from birch outer bark, were used to prepare aqueous dispersion coatings. Aqueous suberin dispersions were produced by thermomechanical dispersing at 55−75 °C with the assistance of a dispersing agent. The obtained stable aqueous dispersions had particle size distribution in the range of 1 to 100 μm. More importantly, this thesis demonstrated the possibility of aqueous dispersions of suberin as coating formulations that can be applied on the fiber-based substrates in a pilot-scale coating process. The resulting suberin-coated paperboard sample showed promising barrier properties for water vapor (18 g/m2/day), heptane vapor (below the detection limits), grease resistance (KIT number of 12), and oil penetration (24−168 h). Collectively, this thesis reveals the promising possibility of bio-based components from wood-derived polymers in aqueous dispersions that can be applied as coating formulations for fiber-based materials.