ENZYMATIC PRE-TREATMENT OF WOOD CHIPS FOR ENERGY SAVINGS IN TMP REFINING

Enzyme pre-treatment of wood chips before refiner mechanical pulping has been shown in previous work by the authors to reduce energy consumption by 15%-36%. The enzyme cocktail used to achieve the reported energy savings contains a mix of cellulolytic and hemicellulolytic enzymes which can hydrolyze the various carbohydrate polymers found in wood. The key to industrial implementation of enzyme-aided mechanical pulping is to improve enzyme efficiency by gaining a more thorough understanding of enzyme action in respect to fibre development and energy savings. Light mechanical treatments, including downsizing and compression/decompression cycles, were used before enzyme application to determine whether they could help improve enzyme penetration into wood chips. Using a fluorescent molecular probe of dimensions similar to the enzymes used in the experiments to help visualize penetration, it could be seen that the treatments did improve accessibility to potential enzyme attack sites by creating cracks and forcing the enzyme solution into fibre walls. Pulps prepared using these enzymatically and mechanically pre-treated wood samples demonstrated that fibre separation during refining occurred at locations which enabled development of more favourable pulp physical properties, as observed with SEM/TEM. These results were supported by pulp characterization and paper properties analyses. Furthermore, FT-Raman and NMR analyses were used to investigate lignin and lignin-carbohydrate-complex (LCC) structural changes caused by enzyme treatment. First, FT-Raman analysis showed that with increasing enzyme dosage, native lignin peaks became more pronounced, indicating that lignin was being dissociated from the LCC within the wood cell walls. CP-MAS NMR results also indicated that certain bonds related to LCC, along with peaks representative of beta-glycosidic bonds, were being increasingly cut with as the enzyme dosage increased. These changes in molecular connectivity within cell walls could help explain how enzyme treatments can affect fibre material strength properties and also explain observed changes to fibre bundle fracture patterns, which in turn would explain the mechanisms behind the reduction in specific energy consumption (SEC).