KENAF COMPOSITION BOARDS WITH TERMITE RESISTANCE P. Chow1, F.S. Nakayama2, T.A. Coffelt2 and S.H. Vinyard2 1Department of Natural Resources and Environmental Sciences,
University of Illinois, Urbana, IL 61801, USA
2U.S. Arid Land Agricultural Research Center, USDA-ARS, Maricopa, AZ 85138, USA
Introduction Composition boards resistant to insect damage are a desirable feature for their use in industrial and home construction. Such material should greatly reduce the costly replacement of termite damaged wood and insure the structural integrity of the building. Acceptance of such products would be further enhanced by using raw materials that are cheap and environmentally acceptable. We propose to combine fibers from kenaf (Hibiscus cannabinus L.) and resinous material of guayule (Parthenium argentatum Gray), both of which can be considered as secondary products from the primary ones, i.e., paper from kenaf and latex from guayule. Previous studies indicate that wood treated with guayule resin [1 and 2] and composite boards containing guayule plant fiber  could provide termite protection. Thus, the objective of this investigation was to fabricate termite-resistance, medium density kenaf composition boards.
Experimental Two most common types of commercial wood- or bio-based composition board, so called ‘Flake-board’ and ‘Fiberboard’, were made. Kenaf stalks consisting of four different cultivars were used to make the boards. ‘Flake-board’ was made by cutting the green stalks into 7.62-cm sections and flaking with a disc type of flaking machine. Later these flakes were dried to a moisture level of 5 to 7% and screened to remove any impurities and fines. The average length and thickness of kenaf flakes was 6.69 cm and 0.99 cm, respectively. The ratio of bast and core fiber in kenaf stem was around 35:65 on a dry weight basis. Phenol-formaldehyde (PF) thermosetting resin (6%) and wax (2%) were mixed with the kenaf flakes. The flake-board composition was three layered oriented strand-board (OSB). Two laboratory flake alignment devices were constructed using a series of parallel metal fins to keep the flakes in alignment until they were aligned and deposited on mat. The mat for the OSB was obtained by rotating the device at 90 degree for each layer. An oil-heated hydraulic hot press was used to press the mat to a pressure of 3.8 MPa at about 204°C press temperature. The final thickness of the flake-board was 11 mm with a specific gravity of about 0.70. Kenaf fiberboard was made using the steam-pressure refined kenaf stalk fibers. The hammer-milled kenaf stalks were fiberized in a single disc pressurized refiner. The wet refined kenaf fibers were dried to a moisture content of about 8%. Seven percent of PF resin and 1 percent of wax emulsion were mixed with the dried kenaf fibers. Resin and wax were applied separately; the wax was applied first. The fiberboard was made using 6.0 MPa pressure at 185°C. Fiberboards with an average thickness of 3.2 mm and specific gravity of 1.00 were produced. Both flake-boards and fiberboards were cut into specimens for tests on mechanical and physical properties. Standard test methods for evaluating properties of wood-based fiberboard and particle panels materials were used . Sections (2.54 x 2.54 cm2) of flake-board and fiberboard were treated with de-rubberized guayule resin in a treatment chamber. The chamber with the wood sample was first evacuated for 5 to 10 min and then the resin-acetone solutions of different concentrations were introduced into the chamber to impregnate the blocks. Pressure in the chamber was maintained for 30 min at 690 kPa. After exposure, the excess resin was wiped off the treated blocks, and the blocks dried in a vacuum oven to remove the acetone carrier solvent. The resin-treated and untreated blocks were exposed to the Eastern subterranean termites (Reticulitermes spp.) following methods described in American Society for Testing and Materials  procedures. More than 200 active termites were put into each specimen bottle consisting of sand. The termite activity in each bottle was observed and monitored daily for four weeks. The rating of the approximate termite mortality was: Slight (0 to 33%), Moderate (34 to 66%), and Heavy (67 to 99%).
Results and Discussion A. Mechanical Property Tests
The results of physical and mechanical properties test indicate that flake-board and fiberboard made from kenaf stalks have promising potential as alternative fibrous materials for the wood products industry for making fiberboards and composition panels. In particular, the test results show that kenaf fiberboard panels can be made to perform at acceptable levels for some types of commercial hardboard applications [6 and 7].
The resin-treated kenaf flake-board and fiberboard were found to be resistant to termite damage. Termite survival after a 1-week exposure is shown in Table 1. Survival was zero after a 2-week exposure.
Table 1 Termite mortality of kenaf composite
treated with guayule resin.
Note: Termite alive (in %) after one week
Conclusion A combination based on two new crops, kenaf and guayule, provided the means of producing medium-density flake-board and fiberboard that were resistant to termites. When the raw materials are considered as waste or by-product sources, the fabrication of termite-resistant, medium-density flake-board and fiberboard appears to be economically feasible. Also, the possibility exists of blending guayule bagasse that still contains the resin with kenaf fiber to produce higher density composition panel products.
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3. Bultman, J. D.; Chen, S-L. and Schloman, Jr., W. W. Anti-termitic efficacy of the resin and rubber in fractionator overheads from a guayule extraction process. Ind. Crops Prod.8 (1998) 133-143.
4. American Society for Testing and Materials (ASTM). Standard Test Methods for Evaluating Properties of Wood-based Fiber and Particle Panel Material. D-037. Book of ASTM Standard. Section 4 (2008) Vol. 04.10-Wood. ASTM. West Conshohocken, PA.
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6. Chow, P. and Bajwa, D.S. Oriented strandboard (OSB) panel made from kenaf stalks and aspen. J. Natural Fibers 2 (2005) 83-89.
7. Muehl, J. H., Krzysik, A. M., Youngquist, J. A., Chow, P. and Bao, Z. Performance of Hardboards Made From Kenaf. In Book of Kenaf Properties, Processing and Products.Edited by Seller, T., Jr. and Reichert, N.A., Mississippi State, (1999) Pp. 367-379.