ABSTRACT The present study investigated the effect of heat treatment on the relative amount of cellulose in untreated and nanosilver-impregnated poplar wood (Populus alba). The impacts on physical and mechanical properties were further studied. Specimens were heated at 145°C and 165°C in hot air medium. In order to enhance heat transfer to the inner parts of specimens, separate sets of specimens were first impregnated with nanosilver suspension in a pressure vessel. Differential scanning calorimetry (DSC) analyses showed that due to high thermal resistance of cellulose, the cellulose relative volume percent increased along with the increase in thermal temperature and the consequent degradation of other wood polymers (hemicellulose and lignin). High correlation was found between the cellulose relative volume percent versus different physical and mechanical properties. Impregnation with nanosilver increased thermal conductivity in the specimens resulting in an enhanced thermal degradation of hemicellulose and lignin, translated into an increased cellulose relative volume.

Abstract Effects of Aspergillus niger was investigated on the strength of cotton textile specimens impregnated with nano-wollastonite, and then compared with normal specimens. Cotton strips were cut and prepared in warp and wept directions according to the standard specifications ASTM D-5035. Results showed that incubation of A. niger on specimens for three months resulted in a significant decrease in tensile stress as well as weight mass change in both directions. Impregnating specimens with NW ameliorated the negative effects of fungal attack on tensile stress to a considerable extent. Moreover, weight change was significantly decreased. It is concluded that NW positively protect cotton textile against A. nigra; the ultimate NW-content should be studied in complimentary studies.

RESUMO Efeitos da adsorção de nano wollastonite (NW) na superfície de celulose foram estudados nas propriedades físicas e mecânicas de placas de fibra de madeira de média densidade (MDF); as propriedades foram então comparadas com aqueles de painéis de MDF sem NW. A amplitude de tamanho de NW foi 30-110 nm. A interação entre NW e celulose foi investigada usando a teoria do funcional da densidade (DFT). Foram efetuados testes físicos e mecânicos em conformidade com as especificações do Iranian Nacional Standard ISIRI 9044 PB tipo P2 (compatível com ASTM D1037-99). Resultados de simulações de DFT mostraram forte adsorção de NW em superfície de celulose. Além disso, propriedades mecânicas demonstraram melhora significativa. A melhoria foi atribuída à forte adsorção de NW na superfície de celulose prevista pela DFT, agregando força e integridade entre fibras de madeira de painéis de MDF com NW. Concluiu-se que NW melhora propriedades mecânicas em painéis MDF como um material compósito de madeira, além de ser eficaz em melhorar a sua condutividade térmica e biológica.

ABSTRACT Effects of nanowollastonite (NW) adsorption on cellulose surface were studied on physical and mechanical properties of medium-density fiberboard (MDF) panels; properties were then compared with those of MDF panels without NW-content. The size range of NW was 30-110 nm. The interaction between NW and cellulose was investigated using density functional theory (DFT). Physical and mechanical tests were carried out in accordance with the Iranian National Standard ISIRI 9044 PB Type P2 (compatible with ASTM D1037-99) specifications. Results of DFT simulations showed strong adsorption of NW on cellulose surface. Moreover, mechanical properties demonstrated significant improvement. The improvement was attributed to the strong adsorption of NW on cellulose surface predicted by DFT, adding to the strength and integrity between wood fibers in NW-MDF panels. It was concluded that NW would improve mechanical properties in MDF panels as a wood-composite material, as well as being effective in improving its biological and thermal conductivity.

Effects of nano-wollastonite (NW) on physical and mechanical properties of medium density fiberboard (MDF) were studied. NW was applied at 5, 10, 15, and 20 g/kg dry weight basis of wood fibers; the results were then compared with control specimens. Two application methods of NW were used: surface and internal applications. Density was kept constant at 0,67 g/cm³ for all treatments and tests were carried out in accordance with ASTM D-1037. Addition of NW contributed in improving the physical and mechanical properties of the panels, both when applied internally or as surface treatment. It was concluded that NW contents of 10% and 15% were the optimal levels for industrial purposes for internal and surface applications, respectively.

Effects of alfalfa-intercropping and nanosilver-impregnation were studied here on the specific gas permeability of 10-year old Populus nigra var. betulifolia. Specimens were impregnated with a 200 ppm aqueous dispersion of silver nanoparticles under 250 kPa pressure; the results were then compared with the un-impregnated specimens. The size range of silver nanoparticles was 10 to 80 nm. After the initial measurement, specimens were kept in vaporized chamber for six months (43±2°C, and 80±3% relative humidity); permeability was measured every month. Results showed that maximum specific longitudinal gas permeability was observed in the nanosilver-impregnated inner-wood specimens of the treatment with alfalfa (1614,4 × 10-13 m³ m-1), and minimum permeability was found in the un-impregnated outer-wood specimens of the treatment without alfalfa (491,7 × 10-13 m³ m-1) before the vaporization. Vaporized chamber made permeability decrease permeability at the first phases because of the absorption of water vapors and the consequent swelling; however, due to the proliferation of pits and perforation plates by fungi and molds, permeability was eventually increased. Antibacterial property of silver did not significantly decrease the growth of molds and fungi in the nanosilver-impregnated specimens.

As to the importance of permeability in the preservation process of solid woods, the effects of diffusion drying schedule with three different initial moisture contents (MC) on fluid flow in the sapwood and heartwood of paulownia wood (Paulownia fortunei) were studied here. Boards with initial MCs of 113 % (D-1), 75.5 % (D-2) and 53.5 % (D-3) were dried to the final moisture content of 8 ± 2 %. Results showed a significant difference in the specific gas and liquid permeability of paulownia wood dried with these different initial MCs. Although gas permeability of sapwood and heartwood specimens was significantly different, no significant difference was seen in liquid permeability between these two parts. D-2 and D-1 showed the highest specific gas and liquid permeability, respectively. It was therefore concluded that the initial MC has a significant effect on the gas and liquid permeability of paulownia boards dried under diffusion schedule with different MCs. Furthermore, the presence of tyloses plays a more important role in permeability than vessel size and frequency by forming an impermeable barrier, resulting in a significant decrease in gas and liquid permeability in paulownia wood.

En cuanto a la importancia de la permeabilidad en el proceso de preservación de maderas macizas, se estudiaron los efectos del programa de secado de difusión con tres diferentes contenidos de humedad (MC) iniciales en el flujo de fluido en la albura y el duramen de la madera de paulonia (Paulownia fortunei). Los tableros con MC iniciales de 113 % (D-1), 75,5 % (D-2) y 53,5 % (D-3) fueron secados al contenido de humedad final de 8 ± 2 %. Los resultados mostraron una diferencia significativa en la permeabilidad específica del gas y del líquido de madera de paulonia secada con estos diferentes MC iniciales. Aunque la permeabilidad al gas de la albura y duramen fue significativamente diferente, no se observó ninguna diferencia significativa en la permeabilidad a los líquidos entre estas dos partes. D-2 y D-1 mostraron la mayor permeabilidad al gas y a los líquidos, respectivamente. Por tanto, se concluyó que el MC inicial de paulonia tiene un efecto significativo sobre la permeabilidad al gas y al líquido de la madera secada con programas de difusión con diferentes MC. Además, la presencia de tilosis juega un papel más importante en la permeabilidad que el tamaño y la frecuencia de los vasos mediante la formación de una barrera impermeable, lo que resulta en una disminución significativa en la permeabilidad de gas y líquido en madera de paulonia.

In this research, effects of screw diameter, screw type, panel type, and end distance on lateral resistance of the joints made with drywall and sheet metal screws were studied in bagasse particleboard and the results were compared to those obtained from commercial medium density fiberboard (MDF). The accuracy of EYM in prediction of lateral resistance was then investigated. The drywall screws comprised of size 8 with coarse thread and size 10 with fine thread; the sheet metal screws comprised of size 8 and 10 with normal thread. Results indicated that lateral resistance increased with the increase in the diameter of both screw types, although not statistically significant. The lateral resistance obtained from MDF specimens was 20% more than that of bagasse specimens. Increase in the end distance also resulted in an increase in the lateral resistance. In all cases, sheet metal screws showed higher lateral resistance in comparison to those obtained from drywall screws. It can be concluded that Mode IIIs is more accurate than Mode Is in the prediction of lateral resistance in two-member screwed joints (single shear plane) for both MDF and bagasse boards.

The effects of heat-treatment on permeability are the main topic of the present study. Longitudinal dowel shape pairs of specimens were prepared from three native species and their specific gas permeability values were measured. From each pair, one specimen was kept for heat-treatment and the other was impregnated with 200 ppm nano-silver suspension; the size range of nanoparticles was 20-80 nm. In six consecutive steps, each pair was heated at 50, 75, 100, 125, 150, and 185°C. Results showed that gas permeability increased when specimens were heated at 50°C as a result of the loss of bond-water and consequent shrinkage. Permeability sharply decreased when the specimens were heated at 75°C and gradually increased at each step up-to 150°C. At 185°C, permeability again decreased in. The sharp decrease in permeability at 75°C was possibly due to irreversible hydrogen bonding in the course of water movements within the vessel perforations and pore system of cell walls. The gradual increase in permeability at higher temperatures, though, might be due to higher internal stresses that are released as micro-cracks develop, thus leading to a greater capability of fluid-transfer. Nano-silver impregnation intensified this process.

Heat-treatment, a major method of wood modification for improving dimensional stability and natural durability, has been studied considerably in the scientific literature. This study will focus on the effect of heat-treatment on permeability, an important physical property of wood by subjecting beech samples to two different mediums of hot water and steam, as well as in two buffered hot water of pH 7 and 8. Hydrothermal treatment caused gas permeability to decrease to its lowest value among the treatments (91.6% decrease comparing the control treatment). Hydrothermal treatment in buffered hot water of pH 8 made the lowest impact on gas permeability (12.3% decrease). The decrease in gas permeability was due to settlement of extractives on vessel perforation plates. Gas permeability showed a highly significant correlation with the amount of swelling in radial direction. Low correlation was found between liquid permeability with water absorption and the amount of swelling. Gas permeability is considered a suitable criterion for predicting the amount of swelling in beech wood.