Forest products particleboard

Approximately one million metric tons of urea-formaldehyde resin are produced annually all over the world. More than 70% of this urea-formaldehyde resin is consumed by the forest products industry. The resin is used in the production of an adhesive for bonding particleboard (61% of the urea-formaldehyde used in the industry), medium-density fiberboard (27%), hardwood plywood (5%), and as a laminating adhesive (7%) for bonding furniture case goods, overlays to panels, and interior flush doors, for example. 

Forest products industries know that temperature increases in piles of sawdust and bark. In pulp and paper mills, self-heating develops in amassed tree chips. Paper rolls stacked hot tend to self-heat, as occasionally do stored bales of waste paper. The wood-base panel products particleboard, hardboard, and fiberboard self-heat after being stacked too hot in the factory. Where in structures the framing lumber, wood-base panels, and lignocellulosic insulation is heated by items such as steam pipes, temperatures tend to rise above that of the heat source. 

Baumann, M.G.D., Batterman, S.A. and Zhang, G.-Z. (1999) Terpene emissions from particleboard and medium-density fiberboard products. Forest Products Journal, 49 (1), 49-56. 

Koontz, M.D. and Hoag, M.L. (1995) Volatile organic compound emissions from particleboard and medium density fiberboard. Measuring and Controlling Volatile Organic Compounds and Particle Emissions from Wood-Processing Operations and Wood-Based Products, Proceedings No. 7301, Forest Products Society, WI, pp. 76-87. 

The most recent state-of-the-art report was published last year under the sponsorship of the Bark and Residues Committee of the Forest Products Research Society. The author, Bhagwat (17), included a section on particleboard, hardboard, and molded products where bark was a constituent in the furnish. 

Interest in pine bark as a source of adhesive components began to accelerate following the oil crisis of 1973. Sodium hydroxide extracts of southern pine bark were successfully used in replacing up to 40% of the phenolic resin for bonding of particleboards, oriented strandboards, and composites with a flakeboard core and veneer facing (50f51). Similar results were obtained with extracts from patula pine (52). Encouraged by results of this type, the New Zealand Forest Products Ltd. Corporation expanded their radiata pine bark tannin pilot plant to full-scale operation in 1981 to produce an extract trademarked Tannaphen. This material was crosslinked with paraformaldehyde and used as an adhesive... 

Lehman WF (1986) Outline of a fast durability test for UF and PF adhesives in composite materials. In Maloney T (ed) Proceedings of the 20th Washington State University Particleboard Symposium, Pullman, Washington, 105-22 Leicester RH (1988) Timber engineering standards for tropical countries. Proceedings of 1988 International Conference of Timber Engineers, Seattle. Forest Products Society, Madison, Wisconsin, Vol. 1 177-85... 

Product tests. Clearly, the best product test is full-scale testing of finished panels under actual use conditions. This has been done (27,38) but is expensive, because several full-sized panels of each product must be pre-conditioned at constant temperature and humidity for at least a week. The next best approach is to test product samples in air chambers under standardized conditions. A summary of such methods is contained in Table I. A very large effort has been made over the last three decades world-wide to develop quick, reliable and meaningful product tests. Wittmann (16), Zartl (20), Plath (17), Verbestel (1, Neusser (21,22), Roffael (25), HUD, the U.S. Forest Products Industry (39,40), many standaraization organizations (41-43) and others have published many viable methods, but the testing involves a combination of complex factors and there is simply no single test that fulfills everybody s specific needs. Table I list some of the currently accepted test methods for formaldehyde emission from particleboard, plywood and medium density fiberboard. 

Rybicky, J. Horst, K. Kambanis, S. "Assessment of the 2 Hour Desiccator Test for Formaldehyde Release from Particleboard" Forest Products Journal, Sept., 1983, 33, pp. 50-54. 

In 1973, K.C. Shen of the Eastern Forest Products Laboratory in Ottawa, Canada, proposed sulfuric acid as a curing agent for SSL waferboard. The pressing conditions were the same as those of conventional PF particleboard, when poplar wafers were first sprayed with 1% of 15 to 20% sulfuric acid and then with 4 to 5% SSL powder, which adheres at the surface of the wet wood wafers. Later [9], concentrated sulfuric acid (9%) was added to the SSL before spray drying, and the powder adhered to the wax-coated wafers. 

Isocyanates are used in the forest products industry to adhesively bond wood chips, which are then pressed to form particleboard and oriented strandboard. Urethanes are also used to fill knotholes and surface defects in finished plywood boards ( plywood patch ). These filled systems must cure rapidly and be sanded easily. 

M.D. Koontz and M.L. Hoang, Volatile Organic Compound Emissions from Particleboard and Medium Density Fiberboard, Proceedings of Measuring and Controlling VOCs, No.7301, Forest Products Society, WI, USA, 1995, p.76-87. 

Most of the recent efforts to develop uses for the condensed tannins have centered on their application in wood adhesives. Reviews by Pizzi (182, 186) and others (15, 78, 87, 93, 208) provide references to several hundred papers and patents on this subject. Despite world-wide research efforts on other sources of tannins, particularly since the 1972-1973 petroleum shortage, the mimosa or wattle tannins extracted from the bark of black wattle Acacia mearnsii) remain the major source of condensed tannins exploited commercially for adhesive manufacture. Of the approximately 100000 tons of wattle tannin produced annually, only about 10000 tons are used in wood adhesives, predominantly in South Africa but also in Australia and New Zealand (186). The extensive use of wattle tannins by the wood products industry of South Africa is impressive indeed, as these tannins have partly replaced phenol and resorcinol usage in adhesives for bonding of particleboard, plywood, and laminated timbers (182, 186, 213). Three factors have contributed to the success in use of wattle tannin-based adhesives, namely the comparatively high costs of phenol and resorcinol in the Southern Hemisphere, their resorcinolic functionality and low molecular weight and, perhaps most importantly, the commitment by the research and industrial communities of these countries to reduce the reliance of the forest products industry on petroleum-based adhesives. 

One of today s fastest growing segments of the wood composition board industry is production of medium density fiberboard (MDF) using a dry process similar to that used for particleboard. First mention of the possibility of utilizing bark for MDF came in a presentation by Brooks in 1971 (43). He described a process in which a homogenous board with superior properties could be made from such raw materials as mixed, unbarked hardwood pulp chips unbarked pine chips, if bark content was less than 30% forest thinnings, branches, and so on and hardwood bark. Furnish was prepared by double-disk pressurized refiners. Brooks concluded a plant could be built to operate on 100% hardwood bark. 

Oil based resins such as AESO are a good choice for making straw particleboards. Wheat straw particleboard bonded with AESO resin has high mechaitical and physical properties in comparison to UF bonded straw particleboard. It can be a substitute for wood particleboard this product is a good solution for countries with little or no forest resources but have considerable agricultural waste. AESO and wheat straw as substitutes for UF and wood, respectively, can decrease the consumption of petroleum and also wood resources. 

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