Abstract

Sawdust is an abundant high-quality residue from sawmills, representing 20–30 % of sawn products by volume. In this study, the chemical pre-treatment of pine sawdust with Fenton’s reagent, formed from hydrogen peroxide and iron catalyst under moderately acidic conditions, was found to intensify the microfibrillation process in terms of energy consumption and improve the grade of the high-yield lignin-containing microfibrillated cellulose (LMFC) produced.

With a minor yield loss of 5.5 wt.%, Fenton pre-treatment increased the microfibrillation rate and bonding potential of LMFC, indicating that the ultrastructure of the lignocellulose cell walls had been modified. Linear dependency between the growth of specific surface area and energy consumption was seen, i.e. microfibrillation followed Rittinger’s law of comminution. In comparison with the reference without any pretreatment,the total grinding energy consumption to a particle size of 14 µm was about 30 % lower (10.7 vs. 15 MWh/t) while the tensile strength and stiffness of LMFC films were 50 % (100 vs. 66 MPa) and 35 % higher (6.6 vs. 4.9 GPa), respectively. The advantageous effects of Fenton chemistry were assumed to originate from the cleavage of lignin-carbohydrate bonds, mainly between lignin and hemicelluloses. This phenomenon was supported by the substantially increased solubility of polysaccharides in dilute alkali.

The calculated manufacturing costs of LMFCs (using the above-mentioned specifications) was € 850/t, of which the raw material, chemical and electricity costs accounted for 10 %, 2 % and 88 %, respectively. Without any chemical pre-treatment, manufacturing costs were € 1100/t of which raw material accounted for 7 % and electricity 93 %.