Obtaining spruce hemicelluloses of desired molar mass by using pressurized hot water extraction.

There is growing interest in utilizing galactoglucomannan, the main hemicellulose in softwoods, for various applications such as cosmetics, pharmaceuticals, textiles, alimentary, and health products, as well as for the production of fuels. For fuel production and for using the rare sugars as platform chemicals, the hemicelluloses need to be hydrolyzed to sugar monomers, and for this purpose, low-molecular-mass extracts are favorable. However, for the other applications high molecular masses are required, which presents an even greater challenge for extraction. The ability to optimize the extraction process according to the needs of further processing, by using solely water as the solvent, is a key issue in the environmentally friendly utilization of this versatile raw material. The goal of this work is to study how the average molar mass of hemicelluloses extracted from spruce sapwood can be influenced by altering the experimental conditions. The main parameters influencing the extraction and hydrolysis of the hemicelluloses, namely, extraction time, temperature, pH, and chip size, were studied. The results show that it is feasible to develop an extraction process for harvesting spruce hemicelluloses, also of large molar masses, for industrial applications by using pressurized hot water extraction.