Milled wood

Extraction of hemiceUulose is a complex process that alters or degrades hemiceUulose in some manner (11,138). Alkaline reagents that break hydrogen bonds are the most effective solvents but they de-estetify and initiate -elimination reactions. Polar solvents such as DMSO and dimethylformamide are more specific and are used to extract partiaUy acetylated polymers from milled wood or holoceUulose (11,139). Solvent mixtures of increasing solvent power are employed in a sequential manner (138) and advantage is taken of the different behavior of various alkaUes and alkaline complexes under different experimental conditions of extraction, concentration, and temperature (4,140). Some sequences for these elaborate extraction schemes have been summarized (138,139) and an experimenter should optimize them for the material involved and the desired end product (102). 

In solution, lignin is most conveniendy analyzed quaUtatively and quantitatively by uv spectroscopy. Typical absorptivity values, D, at 280 nm for milled wood (MW) lignins and other types of lignins are Hsted ia Table 4. These values are used for quantitative determination of the lignins ia suitable solvents. 

Table 5. Phenolic and Aliphatic Hydroxyl Contents of Milled Wood and Technical Lignins ...

The polydispersity of softwood milled wood lignin, as measured by M /M = 2.5, is high compared with that of cellulose and its derivatives. 

Solution Properties. Lignin in wood behaves as an insoluble, three-dimensional network. Isolated lignins (milled wood, kraft, or organosolv lignins) exhibit maximum solubiUty in solvents having a Hildebrand s solubiUty parameter, 5, of 20.5 — 22.5(J/cm ) (10 — ll(cal/cm ) > and A// in excess of 0.14 micrometer where A]1 is the infrared shift in the O—D bond when the solvents are mixed with CH OD. Solvents meeting these requirements include dioxane, acetone, methyl ceUosolve, pyridine, and dimethyl sulfoxide. 

Charcoal is produced commercially from primary wood-processing residues and low quaUty roundwood in either kilns or continuous furnaces. A kiln is used if the raw material is in the form of roundwood, sawmill slabs, or edgings. In the United States, most kilns are constmcted of poured concrete with a capacity of 40 to 100 cords of wood and operating on a 7- to 12-d cycle. Sawdust, shavings, or milled wood and bark are converted to charcoal in a continuous multiple-hearth furnace commonly referred to as a Herreshoff furnace. The capacity is usually at least 1 ton of charcoal per hour. The yield is - 25% by weight on a dry basis. 

Milled wood lignin (MWL) is produced by grinding wood in a rotary or vibratory ball mill. Lignin can be extracted from the resulting powder using solvents such as methylbenzene or... 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

Comparisons made between unpurified spruce milled-wood lignin fractions and unfractionated poljrmers made from coniferjd alcohol alone already revealed the great qualitative similarity between natural and biosynthetically duplicated lignins [see, for example, K. Freudenberg in 94), pp, 125—126]. When a purified lignin fraction is compared tvith an identical fraction made from a mixture of all three -coumaryl alcohols, the resemblance is of course much greater. 

Kawamura, /., and T, Higuchi Comparative Studies of Milled Wood Lignins from Different Taxonomical Origins by Infrared Spectroscopy. In (10), pp.439--f56. 

Okay, A. Hydrogenation Products of Spruce Milled-Wood Lignin and of Related Model Compounds. Holzforschung J7, 105—110 (1963) J. Org. Chem. 27, 1783-1786 (1962). 

Biorenewable wastes Agricultural wastes, crop residues, mill wood wastes, urban wood wastes, urban organic wastes... 

Konishi et al. (4,5) reported that milled wood lignin (MWL) treated with the laccase from C. versicolor suffered oxidative polymerization, depolymerization producing... 

No differences were found between the native and deglycosylated enzymes for the characteristics of pH range of stability, optimum pH, and adsorption to cellulose and milled wood. It can be concluded that the most important role of the carbohydrate chains in laccase III is the resistance to proteolysis in wood decay (15),... 

Figure 1. Among the five resonance structures shown, Ra, Rb and Rc will undergo random coupling reactions more readily than Rd and Re, since the radicals Rd and Re are sterically hindered. Indeed, this is what is found experimentally, since only minor amounts of 0-1 structures (derived from Rd) have been found in milled wood lignin (22,23), and demethoxylation does not occur to any appreciable extent during lignin formation (21). The reactivity of the phenoxy radical, Ra, will be affected greatly by pH since it can be masked by protons under acidic conditions, and its reactivity will thus be diminished. On the other hand, the reactivity of Rb and Rc will not be affected appreciably by pH. Thus more frequent coupling of Rb-Rc, Rb-Rb and Rc-Rc can be expected at low pH, and more of Ra-Rb and Ra-Rc coupling at high pH.

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