Preparation And Life Cycle Assessment Of Environment-Friendly Wooden Composites Based On Modified Industrial Lignins

With the rapid growth of world economy and improvement of human life, the wood-based panel industry is developing rapidly. However, the problems of of forest resources scarcity, high production energy consumption, formaldehyde emission, which limit the industry development and threaten the room environment and human health. Nowadays, developing green bio-modified technology is proved to be an effective method to resolve this problem. It is significant for clean production of wood-based panel and low-carbon processing.The industrial lignin was modified by laccase-mediator system and hybrid modified technology respectively. The green wooden composites were prepared by the method of high speed mixed-flat of hot pressing using wood fiber as the main materials and modified industrial lignin as a natural binder. This research focused on four aspects, which were:(1) based on the single-factor test of enzymatic and hybrid modification conditions, instrumental analysis and performance analysis of physics and chemistry, the optimization conditions of modified ammonium lignosulfonate were determined; (2) response surface methodology (RSM) was used to develop the quadratic regression model between the influencing factors and board performance. The suggested optimal modified conditions were obtained respectively; (3) the binding mechanism of green wooden composites was explored by FTIR, XRD, SEM, DMA and contact angle measuring instrument; (4) based on essential technology framework of Life Cycle Assessment (LCA) in ISO 14040-2006 and GB/T24040-2008, a comparative LCA of the traditional MDF and the green wooden composites were performed by the LCA GaBi 6.0 software. The conclusions of this research were as follows:(1) The chemical structure and reactivity of ammonium lignosulfonate were changed and improved in both modified conditions. Under the laccase-vanillin system, the main reaction was hydrogen atom shift with increasing the hydroxyl group and decreasing the phenolic hydroxyl group; under the basicity conditions, the main reaction was dominated by oxidative degradation. The hydroxyl group and methoxyl group were decreased greatly, while the intensity of phenolic hydroxyl group and carbonyl group was increased. The modified conditions had a clear effect on physical and mechanical properties of the materials. The optimum conditions were as follows:under the laccase-vanillin system, laccase dosage is 140 U/g· lignin, vanillin dosage is 1 wt%, activation temperature is 45 ℃, activation time is 2.5 h; under the hybrid modified technology, H2O2 dosage is 20 wt%, mass ratio of OMIL to PEI is 7:1, pH value is 10 and oxidation time is 2.0 h.(2) Based on two modified methods, modified ammonium lignosulfonate were used as a binder in the manufacture of the green wood-based composite. The objective of this study was to investigate the effects of modified lignin dosage, hot press temperature and time on physical and mechanical properties of the composites. The test results were statistically analyzed and optimized by using response surface methodology. A quadratic regression model was developed between the influencing factors and board performance. The results showed that physical and mechanical properties of the composites was prominently affected by the modified lignin dosage, hot press temperature and time and some interactions between the influencing factors. The suggested optimal conditions were about 32 wt% for LMIL dosage, 170℃ for hot press temperature, and 5.5 min for hot press time for the LMIL/WF composites; 30 wt% for HMIL dosage,170℃ for hot press temperature, and 5.5 min for hot press time for the HMIL/WF composites.(3) The original contact angles of UMIL/WF was less than that of LMIL/WF and HMIL/WF, and the difference was increased by time prolonging. The main reactions of the polycondensation and coupled reaction were observed between wood fibers and the modified ammonium lignosulfonate. Under optimum processing, although the X-ray diffraction analysis showed that the addition of either unmodified ammonium lignosulfonate (UMAL), LMIL or HMIL 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 HMIL/WF composites had higher storage modulus and tanS values than did the LMIL/WF and UMIL/WF composites. Moreover, SEM analysis showed that the LMIL/WF and HMIL/WF composites had better bonding strength characteristics than did the UMAL/WF composites.(4) For pushing forward clean production of forestry industry, according international standard 14040-2006 and national standard, the LCA systems of the wooded composites were set up from theory to the clean production with sustained design and reform. GaBi 6.0 software was used to perform the LCA on production stage of the traditional MDF and HMIL/WF composites. The results were showed that the most serious stage was fiber production. Three stage significantly influenced the environment burdens of the production system:electricity production, thermal production, and binder production. As environment-friendly productions, the GWP value of the two productions was negative. Compared with MDF production, the energy saving and emission reduction of HMIL/WF composites was better except whole higher environmental loads.