Kenaf Core as a Board Raw Material

Terry Sellers, Jr., George D. Miller, and Marty J. Fuller

In the United States, more than 60% of all timber harvested is manufactured into pulp and paper products (1). Increasing costs and decreasing quantities of desired species have led to some pulp fiber importation into the United States. For example, the United States now imports more than 50% of its newsprint paper stock, particularly from Canada (5). Kenaf fiber has been suggested as a supplemental fiber source for newsprint pulp as well as a potential raw material for board manufacture (2, 4, 6).

As a raw material in test runs by several newspapers, the whole­stalk kenaf fiber is reportedly as sturdy as wood pulp paper, but is generally brighter, requires less ink and has less ink rub­off (2). More recently, it was determined that separation of the bast and core fractions would be necessary for kenaf to become commercially viable as wood pulp (3). This separation allows the development of markets, primarily specialty pulp, which was not possible with the unseparated product. As a result of the separation process, a considerable amount of core material is generated.

The objective of this work was to evaluate kenaf core material in low­density composites. Such use in a value­added product would also enhance the overall success of kenaf as a viable agricultural crop.

Kenaf core material was secured, dried, and made into 16­ lb/ft3 panels. No problems in processing (adhesive application, felting, or pressing) were encountered. Panels were made at two press times (7.4 and 5.7 minutes) for comparison. The assembly time (time from resin application to panel full hot­press pressure) was 20 to 30 minutes. Two panels per press cycle were made for a total of four. Two boards, one from each press cycle, were cut into specimens suitable for testing strength properties, dimensional stability, and water absorption properties and acoustical properties. One panel (long­press time type) held in reserve as a display panel was later tested for compression

strength and modulus of elasticity.

The panel internal bonds were stronger in the panel with the longer press time. Such results sometimes indicate improved resin curing with longer press cycles. For a panel of this density, the internal bonds were apparently quite good.

The water absorption after a 2­hour soaking was about 120% and after a 24­hour soaking, nearly 250% for the panel with the longer press time. Water absorption by the panel pressed at the short press cycle was greater. The water absorption after 2 hours was 220% and water absorption after 24 hours was 325%.

The kenaf core appears to be a potential raw material for low­density panels suitable for sound absorption type products. More research is needed for definitive judgments on its efficacy for construction panels and other uses. Further work is needed to explore blends of the core and bast fibers for these interior­type products. Since some insulation/acoustical tiles are made with cold press curing, work is needed to explore the use of kenaf in these processes.

Literature Cited

1. American National Standards Institute. 1985. American National Standard: Cellulosic Fiberboard ANSI/AHA A194.1. American Hardboard Association, 520 North Hicks Road, Palatine, IL. 60067.

2. American Society of Heating, Refrigerating, and Air Conditioning Engineers. 1989. Typical thermal properties of common building and insulating materials­­Design values: Table 4. 1989 ASHRAE Handbook: Fundamentals, I­P Edition. American Society of Heating, Refrigerating, and Air Conditioning Engineers, Atlanta, GA. p. 26.6­26.9.

3. Center for Applied Engineering. 1992. Personal correspondence from R.G. Miller to Terry Sellers, Jr.; St. Petersburg, FL.

4. Department of Agricultural Economics. 1992. Personal correspondence from M.J. Fuller to Terry Sellers, Jr.; Mississippi State University, Mississippi State, MS 39762.

5. Ellefson, P.V. 1989. Trade, price, and consumption of timber in the USA. Concise Encyclopedia of Wood and Wood­Based Materials. Arno P. Schniewind, ed., Pergamon Press, Oxford, United Kingdom. p. 309­317.

6. Forest Products Laboratory. 1987. Manufacturing, properties, and uses of insulation boards. Agriculture Handbook No. 72. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory; Madison, WI. p. 21.2­21.7.

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Terry Sellers, Jr., is a Professor and George D. Miller is a Research Assistant, Mississippi Forest Products Utilization Laboratory; Marty J. Fuller is Professor and Agricultural Economist, Department of Agricultural Economics, Mississippi State University.