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The decay resistance of chemically modified aspen composites to the white rot fungus Coriolus versicolor (L.) Quelet
1998 - IRG/WP 98-40122
Chemical modification of Aspen wood (Populus tremula L.) in the form of solid wood, veneers and sawdust was undertaken by a two step procedure consisting of esterification with maleic anhydride (MA) and subsequent oligoesterification with MA and glycidyl methacrylate (GMA) or allyl glycidyl ether (AGE). Modified wood was thermoplastic and was thermally formed by hot-pressing to produce veneer or solid wood samples with smooth glossy surfaces, while plastic-like wafers were obtained by hotpressing modified sawdust. Chemical modification alone was shown to enhance the biological resistance of Aspen to decay by Coriolus versicolor. In addition, hot-pressing enhanced decay resistance of both unmodified wood and esterified wood veneer samples, although no improvement was found by hot pressing oligoesterified wood. The most effective treatment for the improvement of decay resistance was chemical modification of the sawdust in conjunction with hot-pressing. A microscopic examination of chemically modified and control samples following exposure to the fungus showed more extensive colonisation and decay in untreated, unpressed samples.
M C Timar, A J Pitman, M D Mihai

Photo-discoloration and Degradation of Wood and its Stabilisation by Modification with Benzoyl Chloride
2004 - IRG/WP 04-40274
Photo degradation of Pinus roxburghii (chir pine) and Hevea brasiliensis (rubber wood) was studied under artificial accelerated weathering conditions in a Xenon test chamber. The irradiated samples were analyzed for color changes and chemical changes. Analysis of colour changes in wood surfaces by UV-Vis. irradiation was carried out using a colour measuring (CIELAB) system and chemical changes were monitored using FTIR and fluorescence spectroscopy. Irradiation modified physical and chemical characteristics of wood surfaces and resulted in rapid colour changes, reduction in lignin content and increased concentration of chromophoric groups on the wood surfaces. Colour changes were correlated with formation of carbonyl groups and lignin decay rate determined by FTIR measurements. Fluorescence emission spectra measured from un-weathered wood shows excitation wavelength dependence. Photo irradiation leads to a rapid reduction in the emission intensity, broadening of spectra and a significant red shift in the emission maximum. Photo stability of wood surfaces esterified with benzoyl chloride was also assessed. The modification was characterized and analyzed by fluorescence and FTIR spectroscopy and photo-stability of modified wood was assessed. Esterification of wood by benzoyl chloride suppressed the colour changes (photo-discoloration) and also reduced the lignin degradation and generation of carbonyl groups on irradiated wood surfaces. Results show esterification of wood with benzoyl chloride was effective at inhibiting photo-degradation of wood polymers.
K K Pandey

Bioefficacy of boric acid grafted onto wood
1999 - IRG/WP 99-30202
The use of borate treated wood in outdoor is limited because of the migration of borate. The objective of this study is to investigate the fixation of boric acid in wood using polyethylene glycol (PEG-400) to form polyester borate and isocyanato group as coupling agent. FT-IR was used to monitor the reaction between boric acid and PEG. Elemental analysis was conducted to evaluate the C, H, and N variation in weight before and after treatment. Very low to undetectable level of boron was leached from the grafted sample suggesting a good fixation of boron to the wood compounds through 4,4'-Methylenediphenyl isocyanate (MDI) coupling agent. Laboratory soil block tests were conducted using white and brown rot fungi. At retention level of 0.79% BAE (Boric Acid Equivalent), an adequate protection against brown rot was obtained.
Weining Cui, D P Kamdem

Vinyl Benzoate Photostabilizes Wood Whereas Vinyl Cinnamate and Vinyl 4-T-butylbenzoate are Less Effective
2009 - IRG/WP 09-40452
Thin wood veneers were esterified to different weight gains with three different aromatic vinyl esters, vinyl benzoate, vinyl cinnamate and vinyl 4-T-butylbenzoate and the photostability of the modified wood was examined. There was a linear relationship between the level of esterification of wood with vinyl benzoate and the photostability of the modified veneers exposed to natural weathering. Vinyl benzoate protected lignin and cellulose in wood from photodegradation at high weight gains (>30%) whereas modification of wood with vinyl-4-T-butylbenzoate provided no such protection and vinyl cinnamate increased the photodegradation of wood. We provide an explanation for why these effects occurred and discuss the implications of our findings for the development of weather-resistant wood materials.
M Jebrane, G Sèbe, I Cullis P Evans

Elucidation of reactive sites of wood modified with acetic anhydride: Insights from density functional theory calculations
2020 - IRG/WP 20-40892
Density functional theory (DFT) was employed to investigate the interaction of cellulose and lignin with acetic anhydride for explaining the wood modification process. Atoms in molecules (AIM) and reduced density gradient (RDG) along with non-covalent interaction (NCI) plots were used to analyse the intermolecular bonding characteristics. Cellulose was modelled with a cellobiose unit (dimer of glucose) and dibenzodioxocin was used to represent lignin model. This typical lignin model has three predominant linkages such as β-O-4, α-O-4 and 5-5’. All DFT calculations were performed at dispersion-corrected wB97X-D/6-311g(d,p) level of theory. The obtained results revealed that interaction energy of cellobiose-acetic anhydride was higher (about 20 kJ mol-1) than lignin-acetic anhydride. Structural analysis demonstrated that acetic anhydride undergoes a conformational change in lignin-acetic anhydride conformer to avoid steric repulsion from lignin aromatic moieties. Hydrogen bonds are studied to provide detailed information about strength of the interaction between cellobiose/lignin and acetic anhydride using AIM, RDG and NCI. The results showed that H-bond between cellobiose-acetic anhydride is stronger than lignin-acetic anhydride, and those H-bonds have a non-covalent character. It is observed from AIM analysis that electron density and its Laplacian for cellobiose-acetic anhydride is two-fold higher than lignin-acetic anhydride. A similar result was found in RDG analysis, and the calculated eigen value from electron density is more negative for cellulose-acetic anhydride case. This work suggested that acetic anhydride strongly bound to cellobiose during acetylation of wood rather than lignin model, and the detailed investigated data provides the interaction mechanism of acetic anhydride treatment of wood to some extent.
V Ponnuchamy, A Sandak, J Sandak, R Herrera Diaz