Pine Extractives Strongly Affect Lignin Thermochemical Pathways

Abstract

Interactions between Pinus virginiana wood and the corresponding extractives played a large role in lignin thermochemistry and selectivity of lignin acidolysis pathways, as determined by thioacidolysis and biogenic formaldehyde analysis. Heating wood (dry wood, 200 °C, 10 min) generates formaldehyde, principally via lignin acidolysis; this was studied as a function of extractives removal. Formaldehyde generation in P. virginiana and P. radiata woods was substantially reduced by extractives removal, but extraction had no effect on yellow-poplar (Liriodendron tulipifera). Isolated P. virginiana extractives generated thermochemical formaldehyde at low levels; but the greater extractives effect appeared to be catalysis of formaldehyde generation in whole wood, probably by lignin acidolysis. According to thioacidolysis, lignin in P. virginiana wood was thermally stable when extractives were present; whereas substantial lignin degradation occurred after extractives removal. In nearly opposite fashion, yellow-poplar extractives were associated with minor lignin degradation, while extractives removal promoted lignin thermal stability. The nearly opposite thermochemical behavior of P. virginiana and L. tulipifera highlighted extractive/ wood interactions that were particularly strong in P. virginiana. The implications are lignin catalytic complexities promoting certain acidolysis pathways through natural endogenous effects or exogenous treatments.

Formaldehyde from Lignin Acidolysis Might Be Useful for In-Line Control of Industrial Biomass Processing

“…We confirmed this in whole tissue, but the pathway selectivity is much lower, probably, because in situ lignin substructures exhibit a broader range of bond-rotational conformations than do dimeric models . The C2/C3 pathway selectivity is also strongly affected by wood extractives, for instance much more so in Pinus virginiana than in Liriodendron tulipifera . Since the formation of lignin-borne formaldehyde is facile and subject to catalytic manipulation, it is feasible that formaldehyde generation might always be associated with biomass processing that induces lignin acidolysis.…”

“…Our prior work involved quantitation of lignin-borne formaldehyde generated during thermal processing of wood. , We found that lignin-borne formaldehyde accounts for a small percentage of lignin acidolysis, where two major and competing pathways occur. Considering β-O-4 linkages (β-aryl ethers), lignin acidolysis begins with benzyl cation formation; thereafter, either C2 or C3 cleavage (as in C6C2 vs C6C3 products) can occur .…”

“…The former produces formaldehyde, and both pathways generate a free phenol (Figure ). The ease with which native lignin generates formaldehyde has been known since about 1927, and the observation was central to the early elucidation of lignin structure. , In fact explanation of lignin-borne formaldehyde was the source of considerable debate; formaldehyde was hypothesized to originate from the dioxymethylene structure in piperonyl groups, presumed to occur in lignin. − This was disproven, and the accurate characterization of lignin-borne formaldehyde solidified the understanding of the 3-phenyl-1-propanol structural motif in lignin. , Wood polysaccharides and extractives can also generate formaldehyde but not as easily as lignin because the readily formed lignin benzyl cation activates the γ-carbinol in β-O-4 and β-5 (phenylcoumarin) linkages. ,, Delignified lignocellulose generates far less formaldehyde than whole tissue and isolated lignins that retain some native character. ,,, Indeed the fact that lignin is the nearly exclusive source of lignocellulosic formaldehyde was why the topic was central to early lignin structural studies. , …”

Energy potential of wood waste from a tropical urban forest

“…Extractives are nonstructural phytochemicals and affect many wood properties and their variety and quantities can differ among softwoods and hardwoods (Jankowska et al, 2017;Quinteiro et al, 2019;Wan & Frazier, 2019). The content and composition of wood extractives is a relevant factor for in energy production since it influences volatile materials and compounds emitted to atmosphere during burning (Moulin et al, 2017;Wan & Frazier, 2019).…”

Improvement in mechanical, physical and biological properties of eucalyptus and pine woods by raw pine resin in situ polymerization

“…The raw pine resin has high viscosity, low melting point, and selfsolidifies at about 160− 180 • C, which can be catalysed using an alcohol, although its polymerization has not yet been fully understood (Huang et al, 2018;Okon et al, 2017). Recent research on pine resin focuses on resin derivatives obtained by thermochemical processes (Aldas et al, 2020;Wan and Frazier, 2019) or in improving the tapping process (de Oliveira Junkes et al, 2019;Zas et al, 2020). In this work, the raw pine resin was used to impregnate two different fast-growing solid woods (Eucalyptus grandis Hill Maiden and Pinus elliottii Engelm) and in situ polymerized to improve their hygroscopic, chemical, morphological, mechanical, and thermogravimetric properties.…”