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Exclusion of anions from the wood cell wall
1991 - IRG/WP 3661
Anionic components of wood preservatives and fire retardants such, as arsenates and phosphates, equilibrate at much lower concentrations in the cell wall bound water than in the free solution in the cell lumens. A degree of anion exclusion is expected in wood, due to the Donnan membrane effect. Fixed anions in the wood cell wall, produced by pH-dependent dissociation of the weak acid groups in wood, are not free to diffuse into the lumens, resulting in a chemical potential that limits migration of the mobile anions into the cell wall. The extent of exclusion, measured as "solute free water" (d) or by a molal partitioning coefficient (Km), decreases with increasing solute concentration, as expected from Donnan exclusion effects. However, the expected pH dependence (lincreased exclusion with increased pH) is not observed. In fact, there is an apparent anomalous effect of high cell wall penetration at pH's > 9.
P A Cooper

Probing red maple pit membrane pore size at FSP and OD using polystyrene macromolecules
2001 - IRG/WP 01-40217
A modified solute exclusion technique was used to pressure impregnate a polystyrene molecular weight (MW) series dissolved in styrene into red maple samples at approximately the fiber saturation point (FSP) and oven dry (OD). Radial penetration was less than tangential and FSP less than OD. There was a marked penetration change with MW in the tangential direction, although there appeared to be a slight decrease in FSP penetration at the higher MW tested.
A Omidvar, M H Schneider, A R P Van Heiningen

A new process for in situ polymerization of vinyl monomers in wood to delay boron leaching
1998 - IRG/WP 98-40110
Efforts were accelerated on effective use of boron compounds in wood preservation owing to their environmentally safe characteristics and relatively low costs in addition to their well-known high bioactivity and fire resistant properties. Although having these unique favorable properties, they are readily leachable from treated wood at humid conditions. Therefore, they had limited market for exterior applications. A supplementary combination treatment with vinyl monomers; styrene (ST) and methylmetacrylate (MMA) was studied in order to extend the service life of boron treated wood. Sapwood specimens of Japanese cedar (Cryptomeria japonica D. Don) first treated with boric acid (BA) at 1.00% aqueous solution concentration. Vinyl monomers were impregnated after air-drying of BA-treated wood at ambient temperatures. Polymerization was performed during compression of monomer impregnated wood to a 50 to 70% dry set of radial dimension under a hot-press heated to the polymerization temperatures of 60 and 90°C required by the selected catalysts VAZO (a, a' - Azobis-isobutyronitrile) and benzoyl peroxide, respectively. Wood acquired a perfect dimensional stability and remarkably high moisture exclusion efficiency with the minimum water holding capacity with the compressed-wood polymer composite (CWPC) process that was approved by submerging of the test specimens in tap water, boiling water exposure to a 10 cycles accelerated severe weathering. As a result, boron leaching rate from CWPC pretreated with BA was considerably slower than that from ordinary WPC. Scanning electron microscope (SEM) observations were found explanatory for controlled-but-continuous boron leaching determined analytically. An effective bulking was found necessary to accompany to polymerization in cell wall with an even distribution of monomer in wood. Grafting to cell wall components can be tried further to achieve an envelop polymerization of boron deposited sites in WPC for better boron immobility.
M K Yalinkilic, W Dwianto, Y Imamura, M Takahashi

Influence of artificial and natural weathering on water exclusion efficacy of wood
2015 - IRG/WP 15-20559
Water exclusion efficacy (WEE) is one of the most important properties of wood that contributes to the overall performance of naturally durable wood species in outdoor above ground applications. WEE is in strong correlation with moisture dynamics of wood, its hydrophobicity and can indicates susceptibility against wood decay fungi. Despite of the importance of this parameter, WEE is not completely understood. The main question was, how WEE changes within time, artificial or natural weathering, fungal exposure, etc. In order to elucidate this question Norway spruce (Picea abies), European larch (Larix decidua) and Scots pine (Pinus sylvestris) sapwood specimens were prepared. WEE of spruce wood was upgraded with thermal modification and/or with impregnation with cupper-ethanolamine, tung oil and montan wax suspension. Weathering was accelerated with different methods. After conditioning, specimens were exposed to blue stain fungi Aureobasidium pullulans and Sclerophoma pithyophila, wood decay fungi Schizophyllum commune and Gloeophyllum trabeum, artificially accelerated weathering and outdoor weathering. After weathering, mass loss and color changes were determined and compared to unexposed material. WEE was determined with surface sessile drop method, short term and long term water uptake. The results indicates that WEE can be considerably improved with proper hydrophobic treatment. Different ageing agents have ununiformed influence on the WEE. The highest decrease of WEE was determined after artificial and natural ageing. This is somehow expectable, as both ageing reflects synergistic effect of different factors.
M Žlahtič, M Humar

Decay and water resistance of Siberian and European larch wood
2019 - IRG/WP 19-10941
The occurrence of larch wood is rather frequent in civil engineering. Namely, in building façades, terraces and balcony fences. In Slovenia and other central European countries, the use of the Siberian larch is especially popular. In this research, the durability against decay fungi in laboratory conditions and water exclusion ability of plantation-grown and naturally grown Siberian larch (Larix sibirica) and the European larch (Larix decidua) was investigated. Various tests related to moisture absorption were performed (contact angle, short- and long-term water uptake and water vapour uptake). In addition, the resistance dose DRd, as the product of the critical dose Dcrit and two factors taking into account the wetting ability of wood (kwa) and its inherent durability (kinh) was determined in the laboratory. Results show no significant difference of the wood durability to decay fungi between larch species from a different origin. The higher difference was shown in water performance tests, especially, long-term exposure to the water resulted in a significant difference, which is clearly correlated to the wood density. Combinate effect of wetting ability and inherent durability of tested materials exhibited in resistance dose, where European larch show the highest resistance dose.
B Lesar, D Krzisnik, M Humar

Studies on the material resistance and moisture dynamics of Douglas fir and Sitka spruce from Slovenia
2021 - IRG/WP 21-20677
Wood in outdoor applications is subject to various decomposition factors. Wood degradation can be prevented by construction details, biocide protection of wood, wood modification, or selection of naturally durable wood species. Unfortunately, the majority of timber species in Europe do not have naturally durable wood. Imported tree species represent a new pool from which we can draw wood species with better natural durability. Wood performance in the outdoor application is a function of biologically active compounds (extractives) and water exclusion efficacy. Based on these parameters, we can estimate the resistance dose that reflects the material property of wood. Recently, the model most commonly used for this purpose is Meyer-Veltrup. Literature data indicate that the durability of the wood from native and new sites is not always comparable, so it is necessary to determine the resistance of non-native wood species from new sites. This paper presents original data on the overall wood durability of American Douglas fir (Pseudotsuga menziesii) and Sitka (Picea sitchensis). Experimental data show that the adult heartwood of Douglas fir is more durable than the wood of European larch (Larix decidua), and Sitka spruce is more durable than the wood of Norway spruce (Picea abies). Among the wood species considered, the wood of the American Douglas fir shows the greatest potential for outdoor use.
M Humar, B Lesar, D Krzisnik, E Kerzic, R Brus