Modified formaldehyde-based resin adhesives for rice hull-wood particleboard.
A study was conducted to develop an effective and economical resin system to improve the physical and mechanical properties of rice hull-wood composites. Boards 0.5 inch (12.5 mm) thick were made from a mixture of rice hulls and pine particles with three main resin types: urea formaldehyde (UF), phenol formaldehyde (PF), and polyisocyanate (ISO), in various adhesive formulations. Results indicated that conventional UF and PF resins did not perform well with rice hull-wood composites. However, a modified resin system with IS0 as minor component significantly improved the boards’ strength properties and dimensional stability. Resin content had a significant effect on the quality of the boards, with the higher resin content resulting in stronger boards. The boards bonded with the l%ISO / 6%UF resin system had higher internal bond strength, and attained the best dimensional stability and the highest bending strength (MOR) and stiffness (MOE). As global population increases and developing countries increase their use of wood and paper products, there is new interest in producing and conducting research on composite board from agricultural fibres. Rice hull is quite fibrous by nature and requires little energy input to prepare, so its suitability for the manufacture of particleboards has been assessed in a number of studies (Vasishth 197 1; Hancock and Chandramouli 1974; Mahanta et al. 1980; Viswanathan et al. 1987). However, particleboards made from rice hulls have not found commercial acceptance because substantially more adhesive is needed for rice hulls than for wood flakes to yield boards with acceptable properties (Vasishth 197 1; Chen 1979). The reason for the higher resin requirement for bonding rice hulls is not completely understood, ‘Southern Research Station, USDA Forest Service, Pineville, Louisiana, 7 1360, USA. School of Forestry, Wildlife, and Fisheries, Louisiana State University Agricuhural Center, Baton Rouge, Louisiana, 70803, USA. Email: chse@fs.fed.us but a comparison between wood and rice hull showed that rice hull has less holocellulose and a much higher ash content (Houston 1972). The predominant component of its ash is silica (Luh 1991). The silica covers almost the entire outer layer of the rice hull surface which also contains the water repellent cuticle (Juliano 1985). This silica layer and the partially hydrophobic surface of rice hull are incompatible with aqueous urea formaldehyde (UF) or phenol formaldehyde (PF) resins and prevent the formation of a good bond between rice hull surfaces. Thus, a new and improved resin adhesive system is needed to produce high quality rice hull particleboards. Urea formaldehyde resins are often fortified with melamine to increase the bond strength and water resistance of particleboard. More recently, highly reactive polyisocyanate (ISO) has been used to modify UF resins (Deppe and Ernst 1971; Deppe 1977; Pizzi 1981; Liu and Binglye 1992) and PF resins (Hse 1978, 1980) for board products. IS0 modified adhesives improve the bond strength and performance of wood particleboards, so they might have similar beneficial effects on the bonding of rice hulls. Therefore,
Rice Hull Reinforced Building Boards Using Formaldehyde-Free Adhesive Resins Derived From Whey
The disposal of rice hulls from harvesting and use of rice, and the disposal of whey and whey permeate from the cheese industry represents a serious eco nomic and environmental problem. This project looks at the feasibility of pro ducing rice hull-reinforced particle boards using resins derived from whey permeate. Results indicate that low quality boards may be prepared using un- ground rice hulls, but may be improved by grinding the rice hulls and/or adding saw dust to the formulation. The proposed utilization of whey permeate in this manner would favor re placement of formaldehyde-based resins currently used in the forest products building board industry in addition to conserving non-renewable energy re sources in the form of petroleum and natural gas.
Occupational Skin Disease
Dr Adams has performed a remarkable service. He has put together, in encyclopedic fashion, the many environmental allergens that can disrupt the integrity of the integument through occupational exposure. Although he expects his audience to be conversant with the skin changes caused by irritation and allergic sensitization and their identification, he does lead the reader through the approach to various cutaneous changes and the more common causes of them. A course in basic dermatology is not provided, nor should it be expected. The focus is on the factors that evoke the dermatologic disease. The worth as well as the technique of diagnostic patch testing are underscored. Considerable time is given not only to the treatment and prevention of occupational skin diseases but also to the correct approach of the physician consultant who investigates the workplace in search of occupational hazards that relate to the skin. Many in glancing through Dr