Bio-based barriers from wood hydrolysates : A pilot-scale approach

Sammanfattning: Wood hydrolysates (WHs) are liquids extracted from the hydrothermal treatment of wood. They exist as the byproduct of forestry industries such as the dissolving pulp and fiberboard industries. WHs are hemicellulose-based with a large share of lignin in the chemical composition. In this thesis, methods for utilizing pilot-scale produced WH are shown for production of oxygen barriers. The key materials for fabricating oxygen-barriers are WHs with minor upgrade through ultrafiltration/diafiltration. These barriers have a great potential to be used in the food packaging industry.WHs were produced via hydrothermal treatments of spruce and birch chips in a pilot-scale digester, which mimicked a prehydrolysis plant in a dissolving pulp mill. The produced WHs were used in their crude state or after upgrading through ultrafiltration/diafiltration to form freestanding films and coatings. As shown in previous studies from our group, WHs can provide an inexpensive alternative for the production of oxygen barriers. Compared with purified hemicellulose, they perform better due to the presence of the lignin and lignin carbohydrate molecular interactions forming a denser and less permeable matrix.     Careful analyses and characterizations were conducted on the WHs to assess the influence of cooking conditions and upgrading parameters on the chemical composition and molecular weight of the WHs, which consequently affect the oxygen barrier and mechanical properties of the freestanding films. The optimum cooking and upgrading parameters were chosen to produce pilot-scale WH, which were further used in coating formulations applied in multilayer barriers. Three different green co-components were chosen to blend with the WH to mechanically reinforce the matrix: carboxymethyl cellulose and microfibrillated cellulose (MFC) were blended with spruce and/or birch WH, and poly L-lactide (PLLA) was blended with softwood hydrolysates from a fiberboard mill (Masonite AB). Freestanding films with different formulations were produced through casting, and the mechanical and oxygen barrier properties were compared.To proceed toward industrialization of the oxygen barrier, barrier coatings based on pilot-scale produced WH along with different carboxymethyl celluloses as co-component were applied using a semi-pilot scale Hirano coater to form multilayer barriers. The oxygen barrier properties, mechanical properties and coating/substrate interaction were analyzed for the multilayer barriers.     In a different approach, softwood hydrolysate from Masonite AB fiberboard mill was functionalized through a ring-opening polymerization of L-lactide in which L-lactide oligomers were grafted from the acetylated galactoglucomannan (AcGGM) backbone. This copolymer was then used as a compatibilizer in the hydrolysate/PLLA blend films. The introduction of only a minor amount of copolymer (1% w/w) into hydrolysate/PLLA matrix caused a significant increase in the tensile ductility (~ 400%).Freestanding films based on spruce and birch hydrolysates containing carboxymethyl cellulose and/or MFC as co-component demonstrated excellent barrier performances with oxygen permeability (OP) values as low as 0.3 cm3 µm day-1 m-2 kPa-1 at 50% relative humidity (RH). Although at higher RH (80%) the barrier properties of the films diminished, the OP values were still less than 30 cm3 µm day-1 m-2 kPa-1; hence, they were still considered good barriers. These good barrier properties cause these films to be ready to compete with most petroleum-based polymers such as polyethylene terephthalate (PET) and Ethylene vinyl alcohol (EVOH) for the packaging industry.