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Hindi Editorial, J Nanomater Mol Nanotechnol Vol: 4 Issue: 1
Effects of Nano-Materials on Gas and Liquid Permeability in Wood and Wood Composites
| Hamid R. Taghiyari* | |
| Wood Science & Technology Department, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran | |
| Corresponding author : Dr. Hamid Reza Taghiyari Wood Science & Technology Department, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Lavizan, Shabanloo St., Tehran, Iran Tel: (+ 98) 930-2005235; Fax: (+ 98-21) 22970021 E-mail: htaghiyari@srttu.edu & htaghiyari@yahoo.com |
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| Received: February 21, 2015 Accepted: February 24, 2015 Published: February 26, 2015 | |
| Citation: Taghiyari HR (2015) Effects of Nano-Materials on Gas and Liquid Permeability in Wood and Wood Composites. J Nanomater Mol Nanotechnol 4:1. doi:10.4172/2324-8777.1000e107 |
Abstract
Effects of Nano-Materials on Gas and Liquid Permeability in Wood and Nano-Materials
As a naturally regenerated and biodegradable material, wood and wood composites will be deteriorated in nature. Different poisonous materials, called wood preservatives, are therefore forced into the texture of wood and wood composites to prevent the attack of biological deteriorating agents. Moreover, their hygroscopic property causes absorption of water and water droplets, and even the vapor in the air by the hydroxyl groups in the cell-wall polymers; this process of water absorption would eventually result in dimensional instability and deformation of shape. Water absorption and thickness swelling of wood composites, as their main shortcomings, are also closely correlated to their permeation towards the transfer of different liquids and gases. The susceptibility of woody materials against fire hazards also causes immense losses to both life and property, making it necessary to impregnate wood with fire-retardants. The porous structure and permeability of solid wood species is also practically important for drying wood. Improvement in the permeability of wood, as a porous media, is therefore vital to improve its biological resistance against wooddeteriorating agents, consequently increasing its service life, to improve its dimensional stability, and to increase its fireretardancy. Based on the above mentioned facts, it can be concluded that permeability is a physical property that affects preparation and treatment of solid woods and wood composites, as well as many of their final applications. Over decades, different preservatives and fire-retardants were introduced to wood industry, overcoming many of the above mentioned disadvantages. The increased specific surface area resulted from the breaking down of materials to nano-scale provides more effectiveness of their properties. The present study tries to shortly sum up some of the latest research and projects on the effects of impregnation and/or treatment of wood and wood composites with different nanomaterials on the gas and liquid permeability to overcome some of the above mentioned shortcomings.
Keywords: Nanomaterials; Nano-Materials; Liquid permeability
Effects of Nano-materials on Permeability in Solid Woods |
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| Wood species have porous structures that are significantly different in terms of the volume of woody mass/void spaces, in terms of the extractive content, and in terms of the blockage of vessels and pits with tyloses and other cell wall components [1,2]. Both types of continuous and isolated pores exist in wood, however, their proportion differs in each species. Impregnation of wood species with nano-suspensions and liquids is therefore carried out in vessels and under high pressure. The pressure forces the suspension to be inserted deep into the void spaces and texture of solid wood species. The high pressure in the impregnation process distorts and tears up the tyloses, perforation plates, and other physical obstacles along vessels and tracheids, as main pathways through which previously sap could run, eventually increasing permeability [3,4]. Moreover, extractives are sometimes dissolved in the aqueous nano-suspension (like nano-silver), leaving pits and perforation plates wide open for the transfer of fluids, eventually increasing permeability. However, in some wood species, tyloses and extractives are accumulated along vessels, blocking the paths, resulting in significant decrease in permeability [5,6]. It should therefore be kept in mind that the final increasing or decreasing trends in permeability of solid woods are entirely related to the porous structure and cell wall components of the wood species. | |
| Besides, metal nano-particles (silver, copper, and zinc-oxide nanoparticles) were reported to increase the effectiveness of heat-treatment, as the most commercially used wood modification method and modified cure of the resin [7-9]. The high thermal conductivity coefficient of metal nano-particles facilitated the transfer of heat to the inner parts of wood bodies, resulting in formation of micro-checks in the cell-wall [10], eventually increasing permeability. Moreover, the accelerated process of thermal degradation of hemi-cellulose caused by the facilitated transfer of heat resulted in a significant reduction of water bonding with cell-wall polymers [11]. Cluster analysis of the treatments based on gas and liquid permeability measurement revealed significant effect of impregnation with metal nanosuspensions on permeability in solid woods [5,6]. | |
Effects of Nano-materials on Permeability in Wood Composites |
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| In wood composites, nano-materials act in several ways to decrease permeation to water and water vapors, improving the physical properties and service life of wood-composite panels [12]. First, nanomaterials can chemically make bonds with the compounds in the cell wall structures. This would provide a more integrated compositematrix, decreasing the possibility of the fluid to pass through. Mineral and organic nano-materials were reported to provide such decrease in permeability of composite panels [13,14]. | |
| Moreover, the high thermal conductivity of metal and mineral nano-materials facilitates the transfer of heat to the core section of wood-composite mats, resulting in a better cure of the resin. With the resin being completely cured, there would be lower free space/void through which fluids can flow [15]. Furthermore, some mineral and organic materials are originally water-repellant, namely wollastonite and silane. Addition of these materials at nano-scale was reported to significantly improve the water-repellant property of the composite panels produced, resulting in significant decrease in liquid permeability. | |
Conclusion |
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| Based on the short review above, it can be concluded that impregnation with aqueous nano-materials have a great potentiality in increasing permeability in solid woods, resulting in a higher effectiveness of preservatives and fire-retardants, eventually increasing the service life. Also, they can decrease permeability in wood composites, resulting in substantial decrease in water absorption and thickness swelling, again increasing the service life of cabinets and furniture. Until now, many nano-materials have been tested on wood and wood composites. However, there are lots of others that can be tested to find the most ultimate nano-materials for particular purposes. | |
Acknowledgments |
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| Author appreciates the scientific support of Dr. Jack Norton as his valued mentor (retired from Horticulture & Forestry Science, Queensland Department of Agriculture, Forestry and Fisheries, Australia). | |
References |
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