https://www.sciencedirect.com/science/article/abs/pii/S0964830506000229
Abstract
In this study both the anti-bacterial properties and strength of cockroach avoidance of laminate wood floorings containing colloidal silver is evaluated. The laminate wood flooring manufactured with the overlay added with resin containing colloidal silver ion showed an antibacterial activity of up to 98.9%. For colloidal silver-treated, laminate wood flooring, the relative avoidance rate was 87±1%. With colloidal silver treatment onto the surface of the laminate wood flooring, using melamine-formaldehyde resin for overlay paper impregnation, laminate wood flooring was developed as an environmentally friendly material for residential application.
Introduction
There are three types of wood flooring: laminate wood flooring, engineered flooring and solid wood flooring. The laminate wood flooring consists of high-density fiberboard (HDF) as the core material, while the engineered flooring consists of plywood with a thin fancy veneer bonded onto the face of the plywood using urea-formaldehyde and melamine-formaldehyde (MF) resins as hot-press adhesives (Kim and Kim, 2005a).
Interior fitment and furniture manufacturers are using more surfacing materials for decoration of fiberboard. This material is manufactured as uniform, flat panels that provide excellent surfaces for the application of coating materials. These coated panels are used in the construction of cabinets, furniture, paneling, kitchen worktops, and floorings in offices, educational institutions and houses. The purposes of coating fiberboard surfaces with decorative overlays are to suppress the absorption of water and humidity, and eliminate the release of formaldehyde. The performance of the coated panels is dependent on the quality of wood-based panel and the type of coating material (Nemli and Çolakoğlu, 2005; Sparkes, 1993; Hoag, 1993).
A laminate wood floor is a composite floor with either a chipboard or HDF core that is bonded to a film of wood-effect veneer and covered with a laminated surface. It is not to be confused with wood veneer flooring, which has a real wood veneer bonded on top; this is a different type of flooring altogether. Most wood laminate floors are simply a photographic representation of wood grain. Unlike wood veneers, laminates cannot be sanded or refurbished once any wear begins to show. Laminate wood flooring consists of four main components that are bonded together. A wear resistant, decorative surface made of resin-based MF resin and aluminum oxide. This material is bonded to a moisture resistant, wood composition based core. A balancing backing is bonded to the underside of the core. On the top is a clear cap sheet of aluminum oxide, which provides the protection and stain resistance (Kim and Kim, 2005b).
It has been known that among metallic elements, heavy metals such as silver, zinc, copper, mercury, tin, lead, bismuth, cadmium, chromium, and thallium possess antibacterial properties and the exchange with these metals imparts antibacterial activity to the zeolites (Top and Ülkü, 2004).
Silver has a long history of use in medicine as an antimicrobial agent. Silver ions have been found to have antibacterial effects on some microbes. Several studies have demonstrated that silver ions are selectively toxic for prokaryotic microorganisms, with little effect on eukaryotic cells (Park and Jang, 2003; Spadaro and Becker, 1976; Webster et al., 1981; Marino et al., 1974).
Silver exhibits good anti-bacterial properties and in recent years has been used in a variety of medical applications ranging from wound dressings to urinary catheters. The anti-bacterial activity of silver is dependent on the balance between the activity of the Ag+ ions which kill bacteria and the total amount of silver released from the coating, which if too high results in cytotoxicity The anti-bacterial activity of silver is dependent on the silver cation (Ag+), which binds strongly to electron donor groups on biological molecules containing sulfur, oxygen or nitrogen. The silver ions act by displacing other essential metal ions such as Ca2+ or Zn+ (Betts et al., 2005; Dowling et al., 2001, Dowling et al., 2003; Zhao and Stevens, 1998).
Colloidal silver consists of a very fine particle suspension of the metal in water. When silver particles are suspended and evenly dispersed throughout a solution, all the particles are microscopic and are electrically charged with a positive potential. This suspension can be prepared by the following electrical method. Pass 12–30 V through two silver electrodes in mineralized (salt) water for 2–3 min per glass. Put a small light bulb in the circuit. If the bulb lights, the water is conducting and the process has started. If not, add a little salt to disinfect any unhygienic water as is done while camping. The highest quality colloidal silver is produced by the electro-colloidal/non-chemical method. The silver particles and water have been completely “colloided” and evenly dispersed and held in suspension by an electrical current sent through the combination. This process is the only known method to create a truly homogeneous, i.e., evenly distributed, solution containing super-fine silver particles in the range of 0.005–0.015 μm in diameter, suspended in water, without the need of any chemical, stabilizer, dye, or other ingredients (Becker, 1985).
Researchers in the past have used various methods, including physical and chemical modification of the material surface, to try and prevent bacterial adhesion and slime production on materials. Bridgett et al. (1993) tested bacterial adhesion to cerebrospinal fluid shunts coated with a hydrogel material that created a more hydrophilic surface. This coating, although effective in reducing bacterial adhesion, was difficult to apply uniformly. Silver-impregnated cuffs on catheters have been another approach based on the anti-microbial activity of silver ions (Maki et al., 1988). However, this approach is limited by the degradation of the cuff resulting in the loss of the coated silver ions and thereby the antimicrobial activity (Raad 1998; Baveja et al., 2004).
In this study, we manufactured anti-bacterial, laminate wood flooring with colloidal silver, and then tested its anti-bacterial properties and examined the strength of its cockroach avoidance.
Section snippets
Colloidal silver treatment onto the laminate wood flooring
Despite the importance of functionality for laminate wood flooring, it should not be the only factor under consideration. When it is approached without thinking about the production line and equipment, many obstacles can arise during manufacturing despite high functionality. Many anti-bacterial substances have been developed and are applied into different products. However, because most anti-bacterial substances are ceramic powder, it is very difficult to apply on surface of laminate wood
Anti-bacterial test
Before testing for the antibacterial activity of colloidal silver, antibacterial, laminate flooring, the antibacterial activity of the non-treated laminate was tested first. As shown in Table 2, the antibacterial effect was 25–35%, which was very low. The very low formaldehyde emission was notable. It is claimed that common laminate floorings have a high antibacterial activity probably because of high formaldehyde or VOC emission rate, creating a harsh environment for bacteria to survive in. In
Conclusion
We blended MF resin and colloidal silver to manufacture environmentally friendly laminate wood flooring for enhancing anti-bacterial function. The productivities of the MF resin-impregnated papers and laminate wood floorings were not obstructed by adding colloidal silver. It was merely added like the water that is used when MF resin is produced because it is colorless and transparent liquid state silver ion (colloidal silver). The laminate wood flooring manufactured with the overlay added with
Acknowledgements
This work was supported by the Brain Korea 21 project.
