Effects of kraft lignin addition in the production of binderless fiberboard from steam exploded Miscanthus sinensis

Kraft lignin was added to Miscanthus sinensis steam-exploded pulp to improve the properties of fiberboards and determine whether pulp can be substituted by lignin without deteriorating the board's properties. Lignin - M. sinensis fiberboards were produced on laboratory scale by adding powdered lignin to the material that had previously been steam exploded and explored how the amount of lignin and the pressing conditions affect the physicomechanical properties of lignin hardboards. Response surface methodology was used with a central composite design. The variables and their respective ranges were as follows: pressing temperature, 120-170°C; final pressing time 3-8 min; and lignin amount, 13.2-46.8%. To a certain extent, increasing the amount of lignin had a good effect on the board's properties, although at high pressing temperatures there was a tendency for intern bubbles to form, and these bubbles reduce the quality of the fiberboards. Most of the boards we obtained were of good quality (modulus of elasticity (MOE) up to 6590 MPa; modulus of rupture (MOR) up to 54 MPa; internal bond (IB) up to 2.9 MPa; thickness swelling (TS) up to 8% and water absorption (WA) up to 15%). The addition of kraft lignin before steam explosion was also studied. This seemed to be a better method, possibly because low molecular weight substances were eliminated and mixing with cellulosic fibers was better (MOE up to 8200 MPa; MOR up to 61 MPa; IB up to 3.5 MPa; TS up to 2.3% and WA up to 11.3%).