Wood hydrolysate Barriers

Abstract: Wood hemicellulose is an abundant but fairly unexploited renewable feedstock. Recent studies have shown that hemicelluloses have a large potential for use in the food packaging industry as a sustainable alternative to the conventional oxygen-barrier materials used today. Such hemicelluloses are the main components of wood hydrolysates (WH), which are released in large quantities in many forestry process side streams. Recovering these hemicellulose-rich WH fractions and turning them into food packaging materials would be beneficial from both, an environmental and an economic point of view. However, in the development of packaging materials for large-scale applications, the high production costs to obtain the highly purified hemicellulose and their high moisture sensitivity are considered to be the two main limiting factors.In this study, a selective choice of the upgrading conditions during the recovery of WH and the incorporation of layered silicate particles in WH-based films and coating formulations are used as tools to control and tailor the barrier and tensile performances of the materials, enabling the design of renewable oxygen-barrier materials that are cost-effective and with improved properties. The WH originated from the aqueous liquor from hardwood hydrothermal treatment and upgraded according to one of three alternative routes (ultrafiltration, ultrafiltration followed by diafiltration, and ethanol precipitation) resulting in hemicellulose-rich fractions with different structures, compositions, and properties, which in turn resulted in different performances in terms of mechanical and oxygen-permeability properties. WH in its crudest form gave rise to coatings with the best oxygen-barrier performance, higher than the oxygen-barrier performance of pure hemicellulose coatings. The addition of montmorillonite or talc layered silicates as mineral additives in the WH-based films resulted in better water-vapor-barrier properties, and considerably improved oxygen barrier performance at a relative humidity as high as 80 %. The application of the WH-based films was therefore extended to a wider range of relative humidity conditions.