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,
Influence of Adhesive Type and Content on the Properties of Particleboard Made from Sunflower Husks
The suitability of using milled sunflower husks as a wood substitute for producing medium-density particleboard was investigated. Additionally, the impact of the adhesive type and the amount used on the properties of the panels were evaluated. Urea-formaldehyde (UF) in three commercial variants (UCL, U96, and AG), phenol-formaldehyde (PF), modified melamine urea-formaldehyde (VM), and polymeric diphenylmethane diisocyanate (pMDI), as well as mixtures of VM/AG and of PF/pMDI, were used to manufacture the panels. The adhesive content was varied between 3% and 6% for pMDI, and from 9% and 12% for the other adhesives. Higher thickness swelling (TS) and water absorption (WA) values were observed with the UF panels compared with the PF and pMDI panels. The lowest mechanical strength properties were observed for the UF panels, with the commercial variants ranking (from highest to lowest): UCL > VM/AG > U96. Increasing the adhesive content level resulted in better dimensional stabilities and mechanical properties for the pMDI and PF panels, which met some of the performance requirements for interior uses prescribed by the relevant standard.
Thermosetting adhesives resins from whey and whey by-products
Preparation d'adhesifs thermodurcissables a partir de lactoserum de l'industrie du fromage, d'uree ou de phenol ou de melange des deux