Wood-based hemicelluloses for packaging materials

The need for biobased polymers is increasing. The raw materials from agricultural and forest resources are renewable and abundant in nature. Among forest-based biomass, hemicelluloses form a scarcely utilized but extensive material source. Over one million tons of hemicelluloses could be extracted annually in Finland from pulp or wood chips without reducing the fiber quality for papermaking. Significant amounts of polysaccharides can also be found in mechanical pulping process waters. In order to tailor hemicelluloses to valuable compounds, chemical modification is often needed. The aim with the chemical derivatization was to adjust the degree of molecular branching and hydrophobicity. The purpose of adjusting the branching was to create internal plasticization and to provide thermoplasticity. Hemicellulose derivatives were tested as e.g. aqueous coatings. In general the grease resistance was excellent and water resistance mediocre. Oxygen and water vapor barrier depended on the modification. Water-soluble xylan derivatives and crosslinked galactoglucomannan provided film formation and the best barrier in the case of pigment-coated paperboard. The best coatings provided similar barrier properties than polyester used as a reference. Also hydrophobic xylan derivatives provided relatively good water vapor barrier on uncoated board. Hydrophobically modified xylans had both thermoplastic properties and extremely good water resistanc