ALBERT

Description: Summary The α-hydroxyl group in lignin model compounds 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) and 1-(4-hydroxy-3-methoxyphenyl)ethanol (3), and the α-carbonyl group in 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethan-1-one (5) are removed by treatment of the model compounds with trifluoroacetic acid (CF3CO OH) and triethylsilane (Et3sih) in methylene chloride. The reaction is highly chemoselective and it tolerates the lignin γ-hydroxyl group, phenol and β-O-4-aryl ether linkage. The α-hydroxyl group in 1 has also been removed with triethylsilane in aqueous trifluoroacetic acid (CF3CO OH : H2o = 75 : 25). The combination of trifluoroacetic acid and sodium borohydride, or sodium triacetoxyborohydride, is also effective in removing the α-carbonyl group in 5 and the α-hydroxyl group in lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethanol (7) and in milled wood lignin. The selective removal of the lignin α-hydroxyl and α-carbonyl groups may potentially be used, in conjunction with the protection of the lignin phenol, to inhibit the light and/or heat-induced yellowing of mechanical pulps.

Description: Summary A special furnace for smoke-heating logs, with increased far-infrared radiation (FIR), was produced to improve the wood quality. Green sugi (Cryptomeria japonica D.Don) logs were smoke-heated with the direct use of this system. In a short time, this process increased the temperature inside the logs up to 80–100 °C uniformly, without any damage to the wood. The great increase in steam pressure inside the log resulted in the rupture of pit membranes (PMs) with a high frequency, leading to a decrease in the moisture contents of the logs. It was found that when a temperature of 80 °C is attained inside the log, the rupture of PMs occurs. The rupture proceeds from the outer sapwood towards the pith, accompanied by the radiation heat transfer within the log. By the rupture of PMs, smoke-heated sugi wood showed a large improvement in permeability.

Description: Summary Relative proportions of cellulose in the Iα and Iβ molecular packing forms were estimated through a relationship between molecular packing and the center of gravity of a 13C NMR signal assigned to C-4 of cellulose. An alternative method, based on generation of linear combinations of spectra of 2 samples of wood, was too time-consuming for routine use but provided data for calibration purposes. NMR spectra of algal, tunicate, bacterial and commercial fibrous-powder cellulose were also used for calibration purposes. Mass fractions of the Iα form were estimated as 0.51 for Pinus radiata wood and 0.25 for Castanea sativa wood. The difference is too small to have an important effect on moduli of elasticity.

Description: Summary The cork from the outer bark of Douglas-fir (Pseudotsuga menziesii) was exhaustively extracted and submitted to a mild CaO-catalyzed methanolic depolymerization. The solubilized material (2.5 % yield) was derivatized and analysed with GC-MS. Glycerol was the main component (41.2%), followed by aliphatic acid monomers (30.6%) and glyceryl and feruloyl dimers (14.5%). Monoacylglyceryl esters of α,ω-diacids were dominant (68% of glyceryl dimers), followed by monoacylglyceryl esters of alkanoic acids and of ω-hydroxyacids (respectively 20% and 9%). For all cases 1- and 2-monoacyl-glyceryl esters were present. Dimers of ω-hydroxyacids esterified to ferulic acid through their primary hydroxyl were also found. The feruloyl ester of docosanol could also be identified. The relative abundance of the dimers followed the proportion of acid monomers. The direct evidence found here for P. menziesii, and previously for Q. suber, that glycerol is esterified to all suberinic acids and that ω-hydroxyacids are esterified to ferulic acid supported the discussion of a suberin structure developing on glyceryl-diacyl-glyceryl and glyceryl-hydroxyacyl-feruloyl backbones.

Description: Summary Specimens of Pinus sylvestris have been subject to decay by the brown rot fungus Coniophora puteana, the white rot fungus Phanerochaete chrysosporium, and to doses of γ irradiation sufficiently high to cause significant molecular damage. Specimens of Picea abies have been subject to decay by the brown rot fungus Postia placenta. The dynamic mechanical properties of the decayed and degraded materials have been assessed between −100 °C and 120 °C using in some cases a natural frequency instrument and in other cases a driven frequency instrument. The results obtained have allowed calculation of the temperature coefficients of modulus for the materials at various stages of decay or degradation, and these are relatively constant regardless of the history of the specimen. Such changes as do occur can be explained by modulus dependent frequency effects. The static mechanical properties of some specimens were also assessed by three point bending at 20 °C. Measured changes in dynamic stiffness and flexural modulus have been compared with the weight changes and the proportionality constant relating strength and stiffness loss to weight loss obtained for each situation. These show that in the case of fungal attack the dynamic stiffness falls more quickly than flexural strength, and that, as would be expected, the brown rot fungi are the more effective at reducing mechanical properties.

Description: Summary The moisture related properties of wood-coating composites have been studied to evaluate the influence of coating penetration on the protection of wood against moisture. Pine sapwood samples were vacuum-impregnated with 7 pigmented and unpigmented coatings, both water and solvent borne. The retention and void filling of the coating have been determined. After drying, the samples were exposed to relative humidities between 33 and 98 % and to liquid water and equilibrium moisture content and dimensional changes were measured. The rate of swelling and moisture sorption has been measured, the latter was also used to calculate diffusion coefficients. The sorption isotherms were analysed by the Hailwood-Horrobin equation. In order to obtain additional information on the hygroscopicity of coatings, similar measurement were made on free coating films. The void filling of wood with coating material has the strongest impact on the uptake of liquid water. A limited reduction was observed for the equilibrium moisture content, the diffusion coefficient during adsorption and the rate of dimensional change. No influence on the equilibrium swelling have been found but the shrinkage during desorption was however often slightly increased for the wood-coating composites. The limited impact of the penetrated coating on moisture related properties can to a large extent be explained by the low void filling after drying (20–60%) and the relatively high moisture sorption and swelling of the coating film itself. In general, it can be concluded that the moisture protection of penetrated coating material is low in comparison to coating applied as a film on the surface of wood.

Description: Summary The mechanism of wood degradation by white-rot fungi is not understood in detail other than it is involving phenol oxidases (which are lignin-degrading enzymes) and cellulases. The possible role of hydroxyl radicals in degradation by the white-rot fungus Phanerochaete chrysosporium was studied. The production of a low-molecular-weight substance that is secreted was measured periodically. The substance catalyzes a redox reaction between O2 and an electron donor producing hydroxyl radicals in the culture fluid of this fungus with glucose or wood as the carbon source. We examined the possible role(s) of one-electron oxidation activity by phenol oxidases and hydroxyl radicals in wood degradation by this fungus. Assays of phenol oxidase activity showed that P. chrysosporium produced much manganese peroxidase in wood culture, and that the activity peaked early in incubation. The generation of hydroxyl radicals in the redox reaction was related to the rate of wood degradation, but the activity of phenol oxidases was not related. Therefore, hydroxyl radicals are important in wood degradation by this fungus.

Description: Summary Polyhydric alcohol pulping was developed to separate components of low-quality softwoods that are produced by thinning and improvement cutting as well as to establish a self-supporting pulping system. Propylene glycol (PG) was superior to ethylene glycol (EG) as solvent for polyhydric alcohol pulping at atmospheric pressure. PG pulping of fir, larch and cedar, with sulfuric acid as a catalyst, gave satisfactory pulps with few rejects and a very low level of residual lignin as compared with EG pulping. The PG pulps were readily bleached to approximately Kappa number 1 and 80% brightness by one treatment with sodium chlorite. The yield of bleached pulp from fir was 44.7% based on chips. The bleached pulps had very high α-cellulose content and crystallinity, and their mechanical properties were similar to those of kraft pulp. Therefore, polyhydric alcohol pulping appears to be promising for pulping of softwoods by an organosolv method.