Modified ammonium lignosulfonate (MAL) and polyethylenimine (PEI) were combined and used as a binder in the manufacture of a woodbased green composite. The effects of hot pressing temperature (150 ºC to 190 ºC), hot pressing time (3 min to 11 min), binder content (10 wt.% to 30 wt.%), and MAL/PEI weight ratio (1:1 to 1:9) on the physicomechanical properties of the composites were investigated. The composites met the mechanical property requirements for furniture grade medium density fiberboard (MDF-FN REG) under the following parameters: hot pressing temperature of 170 ºC, hot pressing time of 7 min, binder content of 20 wt.%, and MAL/PEI weight ratio of 7:1. Under optimum processing, although the X-ray diffraction analysis showed that the addition of either unmodified ammonium lignosulfonate (UMAL) or MAL did not change the crystalline structure, this addition markedly improved the relative crystallinity of the composites in comparison to that of pure wood fiber. The DMA results indicated that the MAL/PEI composites had higher storage modulus and tanδ values than did the UMAL/PEI composites. Moreover, SEM analysis showed that the MAL/PEI composites had better bonding strength characteristics than did the UMAL/PEI composites.

The tests on physical and mechanical properties of fiberboards made of wood fiber with ammonium lignosulphonate/urea as filling material are performed according to requirement of EU standards EN 622-2-2004 "Fibreboard-Specifications Part 2: Requirements for hardboard" reveal the reaction mechanism of formaldehyde-free fiberboards with ammonium lignosulfonate /urea as filling material through analysis of characteristics of chemical reactions on ammonium lignosulfonate and urea by FTIR and the chemical reaction analysis of C atom by ESCA. The results show that physical and mechanical properties of fiberboards with ammonium lignosulphonate/urea as filling material have reached the requirement of EU standards EN 622-2-2004, the forming of furan resin, the results of reaction between urea and furfural substances is main reason for the better physical and mechanical properties of lignin-based formaldehyde-free fiberboard.