Abstract: The effect of heat treatment at 50 and up to 150°C was studied on dowel-shape specimens prepared from beech (Fagus orientalis), poplar (Populus nigra), and fir (Abies alba) wood. Specimens were cut into two diameter sizes (18 and 25 mm) to explore the effect of diameter size on permeability. Separate sets of specimens from each size and species were prepared to be first impregnated with a 200 ppm aqueous nanosilver (NS) suspension to investigate the effect of facilitated heat-transfer on permeability at different temperatures. Specimens were heated in five consecutive steps at 50, 75, 100, 125, and 150(C and for 24 hours in each step. High variance was found in the specific gas permeability between each treatment group, thus indicating probable high fluctuation in settlement of extractives at different spots of a log. Heat treatment only affected gas permeability at the first steps of heating (50 and 75°C), where loss of moisture content resulted in a permeability increase in nearly all species. Consecutive steps of heating up to 150(C did not significantly affect the permeability in either normal or NS-impregnated specimens.

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.

Effects of tensile and compression loading on the overall strength of two miter frame corner joints, namely V-nail and dovetail joints, with and without adhesive were studied for medium-density fiberboard and particleboard. Two sizes of V-nails were chosen, sizes 7 and 10. Tensile and compression load-carrying capacity values were measured on the internal and external corners of the joints. Results showed that both wood-composites had greater load-carrying capacities for compression stress in comparison to tensile stress. Medium-density fiberboard demonstrated higher strength compared to particleboard specimens because of its higher compactness of fibers and more integrity in the composite matrix. Application of adhesive resulted in a significant increase in the strength of all joints and both composites. The increase in medium-density fiberboard was significantly higher in comparison to particleboard because lower permeability in medium-density fiberboard did not let adhesive to be uselessly penetrated into the texture. In particleboard specimens, however, adhesive penetrated into the voids and spaces in the composite, and the adhesive line was weakened between the surfaces of the composite bodies. It was concluded that V-nails are recommended for craftsmen in case adhesive is used. However, dovetail joints provide higher strength if the production process necessitates not to use adhesive in joints.

RESUMO Nanopartículas são amplamente aplicadas em compósitos de polímero-madeira (WPCs) nos últimos anos para melhorar algumas das desvantagens das espécies de madeira sólidas. No presente estudo, os efeitos de nanopartículas de ZnO nas propriedades de retardamento do fogo, propriedades físicas e mecânicas da madeira polimerizada de Populus foram investigadas. Espécimes de Poplar foram impregnados com monômero de estireno, contendo quatro diferentes conteúdos de óxido de nano-zinco (ZnO) (0, 0,5, 1 e 1,5%, com base no peso seco do monômero). A microscopia eletrônica de varredura (SEM) revelou homogênea dispersão das nanopartículas de ZnO na matriz WPC. O ZnO melhorou propriedades físicas da madeira tais como a absorção de água e estabilidade dimensional. Além disso, as propriedades mecânicas aumentaram em comparação com as amostras de controle. O processo de impregnação também significativamente melhorou algumas das propriedades retardadoras de fogo, incluindo o tempo de ignição; no entanto, a natureza de inflamabilidade do estireno agravada alguns outros, como a área carbonizada. Concluiu-se que embora a maioria das propriedades foram melhoradas, a aplicação final do WPC deve ser tomada em consideração antes de tomar a decisão sobre a impregnar a madeira de Populus com estireno ou não.

ABSTRACT Nanoparticles have been vastly applied in wood polymer composites (WPCs) in the recent years to improve some of the drawbacks of solid wood species. In the present study, the effects of ZnO nanoparticles on fire retarding, physical, and mechanical properties of polymerized poplar wood were investigated. Poplar specimens were impregnated with styrene monomer, containing four different contents of nano-zinc oxide (ZnO) (0, 0.5, 1 and 1.5%, based on the dry weight of monomer). Results of the scanning electron microscopy (SEM) showed homogeneous dispersion of ZnO nanoparticles in the WPC matrix. Nano-zinc oxide improved physical properties such as dimensional stability and water absorption. Moreover, mechanical properties increased in comparison to the control specimens. The impregnation process also significantly improved some of the fire-retarding properties, including the ignition time; however, the flammability nature of styrene aggravated some others, such as carbonized area. It was concluded that, although most of the properties were improved, the final application of WPC should be taken in to consideration before making decision on whether or not to impregnate populus wood with styrene.

The effects of wollastonite fibers on the physical and mechanical properties of medium-density fiberboards composed of wood fibers with up to 10 % camel-thorn chips were studied. Approximately 30 % of the wollastonite fibers were less than 100 nm while the remainder were less than 1 μm. Wollastonite fibers significantly improved most of the physical and mechanical properties while addition of camel-thorn produced more variable effects on panel properties. Up to 10 % camel-thorn could be added to panels without negative effects. A combination of 10% camel-thorn and 5% wollastonite fibers produced panels with the best properties.

The present study is focused on the effects of the shape and size of Fagus orientalis wood flour on physical and mechanical properties of HDPE based wood plastic composites (WPC). Variables included two mesh sizes (20 and 60), as well as five different contents of ground shavings (0, 25, 50, 75, and 100%) mixed with sawdust; totally 10 treatments. HDPT content was 40% in all formulations. Panels were compression molded and physical and mechanical tests were carried out in accordance with ASTM D2240 standard specifications. Results showed that mesh size can only significantly affect the hardness in the studied wood-plastic composites. On the other hand, increasing the proportion of the ground shavings possessing higher aspect ratio (l/d) increased both flexural strength and hardness. This increasing effect however was not observed for ground shavings beyond 50%. It was also concluded that while the addition of ground shavings up to 50% could improve the mechanical properties, higher proportions would reduce some of the properties, particularly the impact strength. In was concluded that the panel made of 50% wood flour combined with 50% ground shavings exhibited overall suitable properties for most applications.