Effect of silver nanoparticles on hardness in medium-density fiberboard (MDF)

Abstract

© iForest -Biogeosciences and Forestry IntroductionThe harvested wood of fast-growing trees is not usually suitable for the furniture industry; however, they provide a sustainable source for paper and composite-manufacturing industries, and natural regeneration would help the process (Ruprecht et al. 2012, Maresi et al. 2013). Wood-composite panels offer the advantage of a homogeneous structure which may be important for many design purposes (Valenzuela et al. 2012). Due to the low thermal conductivity coefficient of wood (Taghiyari et al. 2013a), some studies have so far been carried out to decrease the maximum pressing time or increase the heat-transferring rate to the core section of the mat (Lehmann et al. 1973, Taghiyari et al. 2013b. Hot press time is dependant on the thickness of the composite mat, press temperature, closing rate, and most importantly, moisture distribution throughout the mat (Doost-Hoseini et al. 2013, Taghiyari et al. 2013b). There is a limit to moisture content of the mat because of two main reasons: (i) increase in the hotpress time; and (ii) occurrence of blows in wood-composite panels. A blow occurs when excess moisture in the board explosively evaporates at temperatures greater than 100 °C, once pressure is released. Furthermore, for urea-formaldehyde (UF) resin, there is a limitation of MC level (Papadopoulos 2007, Stockel et al. 2012. Therefore, rapid transfer of heat to the core section of the mat, and polymerization of resin, has always been a challenge.Many areas of science have used nanotechnology to enhance the effectiveness of materials at nano scales. Heat-transferring property of metal nanoparticles (Khojier et al. 2012) and mineral nanofibers (Haghighi Poshtiri et al. 2013) was reported to improve some properties in solid wood as well as wood-composite materials. However, little study has so far been carried out to practically investigate the effects of different nano-materials in wood-composite panels. The present research project was therefore conducted to study the effects of silver nanoparticles as well as different hot-press times on the hardness of medium-density fiberboards. The relations between the hardness and some physical properties of the panels were investigated as well. Materials and methods Specimen preparationWood fibers were obtained from the Sanaye Choobe Khazar Company (MDF Caspian Khazar, Amol, Iran). The fibers were a mixture of beech, alder, maple, hornbeam, and poplar from forests of the Gillan province (Amol, Iran). The raw materials were free from fungi deterioration. This material was used to prepare boards that were 16 mm thick and had a density of 0.68 g cm -3. A laboratory hot press produced by the Mehrabadi Machinery Mfg. Co. (Tehran, Iran) was used to prepare test specimens. The size of the hot plates was 50 × 50 cm. The total nominal pressure applied by the hot plates was 160 bars at a fixed plate temperature of 150°C. Hot-pressing continued for 6, 8, and 10 minutes. Urea-Formaldehyde resin (UF) was supplied from Pars Chemical Industries ...

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