MECHANISMS OF FORMALDEHYDE GENERATION FROM WOOD AND IMPLICATIONS TO BIOMASS TREATMENT

摘要

In the realm of non-structural wood-based composites, thernstringency of new formaldehyde emissions regulations makesrnnecessary a complete accounting of all formaldehyde sources,rnsynthetic and biogenic. Research in our lab has considered lignin’srncontribution to biogenic formaldehyde formation via the hypotheticalrnreaction pathway shown in Figure 1. It is known, and we have furtherrndemonstrated, that common industrial heating processes stimulaternformaldehyde generation and emission. The implications in thernwood-based composites industry are great; but perhaps those for thernfuture biofuels industry have not been considered. Extensive ligninrnmodel compound studies reveal two acidolysis pathways with one ofrnthem generating formaldehyde. As these studies suggested, acidrntypes influence the acidolysis pathway, perhaps due to the acidrncounter ion size effects. In light of this, we applied different acidsrninto solid wood, and demonstrated their capabilities to manipulaternformaldehyde generation. To further validate the hypothesis shownrnin Figure 1, efforts were devoted to search for homovanillinrnendgrouds, which resulted in a series of model compounds synthesesrnand verifications. There is also an indication of chain cleavage inrnFigure 1 if the resulting endgroups don’t react, which should lead tornthe decrease of lignin glass transition temperature (Tg). By usingrndynamic mechanical analysis (DMA), we investigated thernrheological properties of heat-treated wood with or without thernpresence of external acid including Tg, and Arrhenius activationrnenergy (Ea) at glass transition. Meantime, we also focus on thernproperties of in situ lignin due to these treatments using wetrnchemistry methods, such as thioacidolysis and DFRC, combined withrnvarious analytical instrumentations, such as GC, GC/MS, NMR, UVVis,rnand Fluorometer. Lignin undergoes dramatic chain cleavagernduring heat treatment, while repolymerization or condensationrnreactions also occur simultaneously.