AGRICULTURAL FIBERS IN COMPOSITION PANELSIn: Maloney, Thomas M., ed. Proceedings of the 27th international

particleboard/composite materials symposium; 1993 March 30-31; April 1;Pullman, WA. Pullman, WA: Washington State University; 1993:133-152.

J. A. YOUNGQUIST B. E. ENGLISHUSDA Forest Products Laboratory USDA Forest Products Laboratory

Madison. Wisconsin Madison, Wisconsin

H. SPELTERUSDA Forest Products Laboratory

Madison, Wisconsin

ABSTRACT

This paper addresses options for using agri-cultural materials alone or in combination withwood to produce composition panel products.Past research and technology available on a re-gional basis throughout the world is reviewedfirst. Agricultural fiber options for North Amer-ica are discussed and a brief review of perform-ance properties that can be obtained using thesefibers is provided.

P. CHOWUniversity of Illinois

Urbana-Champaign, Illinois

Commercial standards for particleboard andhardboard are used as a baseline by which tocomparatively judge the panels. Alternative ag-ricultural fibers that seem most appropriate andavailable in North America are bagasse, cerealstraw, corn stalks, cotton stalks, kenaf, rice husks,rice, straw, and sunflower hulls and stalks. Tech-nically speaking, these agricultural fibers can beused to manufacture composition panels. How-ever, it becomes more difficult to use certain

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kinds of fibers when restrictions in quality andeconomy are imposed.

In general, it can be concluded that compo-sition panels made from agricultural fibers are ofsomewhat poorer quality than those made fromwood; however, blending in small amounts ofagricultural fibers (e.g., 10% to 20% by weight)may have no significant impact on quality. Ba-gasse, cereal straw, and kenaf appear to have themost promise for continued panel development.

INTRODUCTIONNever before has there been so much demand

placed on the world’s fiber resource. Worldwideeconomic growth and development have gener-ated unprecedented needs for converted forestproducts. Congruently, the energy needs of de-veloping countries are creating increasing de-mands for fuelwood, which now represents 50%of all wood fiber consumption. At the same time,global fiber production systems, in total, arcdemonstrating the capability to meet these de-mands. In other words, regardless of tremendouspressures for fiber resource, there is not a globalfiber shortage or crisis. However, there are someserious local and regional fiber shortages andresource management conflicts that will play acritical role in the immediate and long-term fu-ture.

In the latter part of the 20th Century, peopleare concerned about the future of their forests–their health, wildlife diversity, productivity forwood, environmental roles, and aesthetics. As aresult of these concerns, forestry practices arechanging, resulting in localized wood fiber sup-ply shortages. The challenges are how the woodfiber demand is balanced and how, simultane-ously, the earth’s population and ecologicalneeds are met (McNutt 1992).

Additionally, many developing countries donot possess adequate forest reserves to covertheir needs for fuelwood, industrial wood, sawnwood, and wood-based composition panels.However, many of these countries do have rela-tively large quantities of other lignocellulosic

materials available in the form of agriculturalresidues from annual crops. Several of theselignocellulosics have been used to successfullyproduce particleboards, fiberboards, and, tosome extent, inorganic-bonded boards.

This paper addresses options for using agri-cultural materials alone or in combination withwood to produce composition panel products.Past research and the technology available on aregional basis throughout the world is reviewedfirst. Agricultural fiber options for North Amer-ica are discussed and a brief review of perform-ance properties that can be obtained using thosefibers is provided. The paper closes with a dis-cussion of economic considerations affecting theuse of agricultural fibers in panels.

GLOBAL PERSPECTIVEGlobally, many fiber options arc available. A

literature search was conducted at the USDAForest Service, Forest Products Laboratory(FPL), to survey the worldwide use of agricul-tural fibers. A total of 1,039 citations were se-lected from the vast number available. Fromthese citations, it was learned that the world isbusy producing and conducting research oncomposition panels from agricultural fibers.

Composition panels made from agriculturalmaterials are in the same product category aswood-based composition panels. These catego-ries are low density insulation boards, mediumdensity fiberboards, hardboards, and particle-boards. Composition panel binders may be syn-thetic thermosetting resins or modified naturallyoccurring resins like tannin or lignin, starches,thermoplastics, or inorganics. There seems to belittle restriction on what has been tried and whatmay work.

The following materials are selected high-lights, by region, from the literature search.These highlights are categorized by geographi-cal area, which may be a region or a country, andare presented alphabetically.

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Africa (Botswana, Nigeria, Sudan)Port Harcourt, Nigeria (Odozi et al. 1986).

was the site of a study to determine if particle-board could be made from agricultural wastes.In this study, naturally occurring tannins frommangrove and red onion skins were used tomodify and reduce the costs of synthetic resins.Reportedly, particleboards with high strengthwere made with combinations of bagasse, man-grove bark, wood shavings, and corncobs. InSudan (Gabir et al, 1990), a study to make com-position boards from guar and sorghum stalkswas undertaken. In Botswana, the Ministry ofAgriculture searched for alternative uses for sor-ghum (Kgotlele 1987).

The Americas (Cuba, Mexico, Peru,United States, Venezuela)

The literature search showed that bagasse,the residue fiber from sugar cane processing, isthe agricultural fiber of choice in much of theAmericas. The first bagasse composition panelplant was built by Celotex1 in Lousiana (UnitedStates) in 1920. Since then, more than 20 bagasseparticleboard plants have been built throughoutthe world (Atchison and Lengel 1985). In Vene-zuela, Tablopan de Venezuela started producinga line of bagasse fiberboards in 1958 (Smith1976). Production boards included those of low,medium, and high density. As a result of in-creased prosperity in Venezuela and a decreasein wood fiber availability, the company purchaseda second line in 1975. Sidney (1986) describedan insulation board and hardboard plant in Na-volato, Mexico. In 1987 (Valdes et al. 1989),bagasse particleboards from the three main fac-tories in Cuba were tested. The board quality wasreported to be quite high, with 21 of 24 samplespassing Cuban Standard NC43 18:86, which gen-erally agrees with international standards.

1 The use of trade or firm names in this paper is for readerinformation and does not imply endorsement by the U.S.Department of Agriculture of any product or service.

Bagasse is not the only agricultural fiberbeing utilized in the Americas. In Peru, prefabri-cated panelized construction was developed thatutilized bamboo and wood (Kuroiwa 1984). Inthis type of construction, prefabricated panels ofbamboo and wood are produced using low tech-nology methods. The finished structures areplastered with cement mortar and are earthquakeresistant. Wheat and ryegrass straw were used forthe production of panels in the Northwest regionof the United States (Loken et al. 1991). Gertje-jansen and others (1972, 1977) experimentedwith sunflower stalks and hulls in Minnesota(United States).

Asia (China, Japan, Taiwan, Thailand)Although bamboo is given limited use in the

Western Hemisphere, its use in Asia is wide-spread. A special building center was establishedin Kyoto, Japan, after World War II for the de-velopment of building materials from bamboo(Iwai 1983). The building center was formedthrough the cooperation of bamboo wholesalers,producers, and manufacturers.

Bamboo has been made into a variety ofcomposition panels. A study conducted in Tai-wan (Chen and Wang 1981) determined the fea-sibility of producing oriented and random three-layer boards from bamboo and wood waste. Asimilar study (Tsai et al. 1978) showed that Mosobamboo residue and red cypress shavings exceededthe National Chinese standard. A stressed-skinpanel-type product was produced using ply-bamboo as faces and polyurethane or polysty-rene foam for a core (Wang and Joe 1983).

Other agricultural materials are also used inAsia. Currently, bagasse particleboard is made inChina (Jingxing 1988). Soybean stalks were in-vestigated (Shi et al. 1988). and hardboards wereproduced from Thai hardwoods and coconut fi-ber that met or exceeded Japanese standards(Krisnabamrung and Takamura 1972).

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Europe (Bulgaria, former Republic ofCzechoslovakia, Sweden, former

West Germany)Wood fiber shortages and lumber price in-

creases make bagasse particleboard an attractivesupplement to wood fiber in Sweden. In Sweden,as well as other countries, there is a growinginterest in compact, versatile, particleboard plantsthat can handle wood, wood waste, and agricul-tural materials (Dalen et al. 1990). Sweden is notthe only country in Europe that has looked intocomposition panel production utilizing bagasse.In the former Republic of Czechoslovakia, re-searchers addressed many production parame-ters involved with bagasse particleboard produc-tion (Lois Correa 1979) This study addresseddepithing and year-round storage.

Europeans also felt that there were opportu-nities for building materials that contain a certainamount of straw. Researchers in the former WestGermany produced a variety of wood and strawand straw composition panels (Hesch 1978). Inthis work, boards made from straw at the sameresin content and density as those made fromwood generally had better properties. In anotherWest German study (Troger and Pinke 1988), aseries of three-layer boards using straw and soft-wood particles had slightly different results. Inthis study, straw boards did not perform as wellas wood, but all straw boards nearly met or meetEuropean standards for particleboards.

Interest by the Europeans in agricultural fi-bers was not limited to bagasse and straw. ABulgarian study (Tsolov 1985) examined a mul-titude of agricultural waste fibers. In this study,fiberboards were produced by mixing varyingamounts of beech fibers with hemp, vine, to-bacco, cotton, raspberry, maize, or sunflowerstalks. All these wastes were suitable for boardproduction, but the best results were obtainedwith hemp and tobacco. Bamboo was also exam-ined in West Germany (Heinrichs 1989). Specialwinter-hardy varieties were studied to use inbuilding materials.

IndiaBinderless particleboards from bagasse were

produced in India (Shuala and Chandra 1986).The boards were produced by cooking the ba-gasse in a 1% to 2% alkali bath and then temper-ing the pressed boards with oil. When comparedto other agricultural residue panel products inIndia, bagasse also proved to make a good insu-lation board (Srivastava and Gupta 1990).

Inorganic boards appear to be growing inpopularity in India. Researchers and industryteamed up to develop a variety of building ma-terials using industrial and agricultural wastesthat incorporated cement and cementitious ma-terials as binders (Mohan 1978). The resultingcombinations were used to produce compositionboards, roof sheathing, flooring tiles, and weath-erproof coatings.

The Middle East (Eqypt,Iraq, Saudi Arabia)

Rice straw is the main lignocellulosic mate-rial in Egypt. This country uses rice straw toproduce fiberboard, most of which is inferiorquality compared to that made of wood fiber.This is due to the high percentages of nonfibrousmaterials included in the straw. When care istaken to fiberize the rice straw, board propertiescan increase significantly (Fadl and Rakha1990). Other lignocellulosic materials availablein the Middle East include cotton stalks, bagasse,and kenaf. One study (Fahmy and Fadl 1974)showed that hardboards prepared from these ma-terials were generally better than those made ofcommercial rice straw.

In Iraq, particleboards were made with vary-ing mixtures of reed or cattail mixed with wood.Properties were significantly impacted by theaddition of the reed, with strength propertiesincreasing, but water resistance properties de-creasing. At 50% reed levels, most properties ofthe panel met or exceeded specifications (Al-Sudani et al. 1988). In Saudi Arabia, bagasse isconsidered an attractive source of fiber for com-posites for building materials (Usmani 1985).

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Philippines

The Forest Products Research and Develop-ment Institute in Laguna, Phillipines, has anactive research program that examines the utili-zation of agricultural fibers in the production ofcomposition panels. Much of the research at theInstitute has focused on coconut coir (or husk)and banana stalk. In one study, coconut coir andpineapple fiber were blended with wood wastesfor the production of particleboard (Pablo andLovian 1989). In another study of underutilizedagricultural species (Pablo et al. 1975), bananastalk was blended with wood chips to makeparticleboard. Finding uses for banana stalk iswarranted because each banana tree plant pro-duces only one banana bunch, and the stalks aregenerally burned.

Former USSR

In the former USSR, building materials withhigh compressive and bending strength weremade using wastes from flax or cotton fabricsand phenol-formaldehyde resin (Inyutin et al.1983). Rice straw boards with excellent proper-ties were also produced (Kluge 1978). The ricestraw was treated with steam and ammonia toincrease the natural thermosetting properties ofstraw. When pressed to high density, the boardshad excellent bending strength and minimumwater absorption.

ALTERNATIVE FIBER OPTIONS FORNORTH AMERICA

The first major awareness of the importanceof resources and the environment came from ourforebearers working in forestry and conserva-tion. The early leaders in this area can be de-scribed as militants with a tremendous con-sciousness of their mission. The FPL and majorforestry schools came into existence because ofthe direct personal involvement of these pioneersof resource management. If such inheritancecounts for anything, this audience should bedeeply concerned with what seems to be a con-servation renaissance in this country.

As managers of the wood resource, we wishto make sound decisions. But in the face of thepresent flood of diverse and divergent opinions,good decisions are more and more difficult tomake. What will be the need for timber when thepresent crop or the next crop matures? Our pro-fessional responsibilities and native instinctsforce us to be extremely aware of the environ-ment. Forests provide great aesthetic pleasureand other values, and it is obvious that the futureof forest life will depend overwhelmingly on ourability to balance conservation and utilization.

Today in the United States, wood fiber is themain source of material for composition panels.However, as has been shown, other sources offiber are available. These alternative fiber op-tions have the potential to alleviate regionalwood fiber shortages. Shortages that have beenpartially created because of renewed concernsabout how forests should be used.

For the purpose of this paper, the discussionof agricultural fibers is limited to those that seemmost appropriate and available in North Amer-ica. These materials are bagasse, cereal straw,corn stalks and cobs, cotton stalks, kenaf, ricehusks, rice straw, and sunflower hulls and stalks.Technically speaking, these agricultural fiberscan be used to manufacture composition panels.However, it becomes more difficult to use certainkinds of fibers when restrictions in quality andeconomy are imposed. The remainder of thissection addresses the issues of quality, whichinvolves harvesting, handling, manufacturing,and properties of the finished panel. Commercialstandards are used only as a baseline by whichto comparatively judge the panels.

BagasseBaggasse is the residue fiber remaining when

sugar cane is pressed to extract the sugar. Somebagasse is burned to supply heat to the sugarrefining operation, some is returned to the fields,and some finds its way into various board prod-ucts. Bagasse is composed of fiber and pith. Thefiber is thick walled and relatively long (0.03 to

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0.12 in., 1 to 4 mm). It is obtained from the rindand fibrovascular bundles dispersed throughoutthe interior of the stalk (Hamid et al. 1983). Forthe best quality bagasse fiberboard and particle-board, only the fibrous portion is utilized. Asmay have been ascertained by the continual ref-erence to bagasse in this paper, it is the agricul-tural residue that might offer the greatest oppor-tunity for composition panel production in NorthAmerica. In what could be considered a defini-tive work, Atchison and Lengel (1985) told ofthe history and growth of bagasse fiberboard andparticleboard at the 19th Washington State Par-ticleboard/Composite Materials Symposium. Intheir paper, the authors described the varioussuccess and failure stories of bagasse utilization.

Bagasse is available wherever sugar cane isgrown. In North America, that constitutes justabout everywhere between Canada and Mexico.As such, almost no harvesting problems exist.Large volumes of bagasse are available at sugarmills. In the United States, the cane harvestusually lasts about 2-1/2 months. During thistime, bagasse is readily available. For the re-mainder of the year, the material must be stored.Special care must be taken during storage toprevent fermentation, because bagasse doeshave a high sugar content. To reduce the sugarcontent and increase storage life, bagasse is usu-ally depithed before storage. The pith is an ex-cellent fuel source for the sugar refining opera-tion. Generally, if the bagasse is depithed, dried,and densely baled, it can be stored outside. Ifhandled in a careful manner, bagasse can also bestored wet. In the wet method, large bales ofbagasse are specially fabricated and stacked toinsure adequate air flow. Heat from fermentingsugars effectively sterilize the bales. Bagasse canbe stored for several years using this method(Chapman 1956). Other storage options areavailable, including some that keep the bagassewet beyond the fiber saturation point.

As previously mentioned, only bagasse fiberis utilized for the production of high-qualitycomposition panels. As such, various schemes

are available to separate the bagasse fiber fromthe pith. The fibers after depithing are moreaccurately described as fiber bundles. These fi-ber bundles can be used, as is, to make particle-board, or they can be refined to produce fibersfor fiberboard. In either product, dry or wet layupis possible. Some properties of bagasse compo-sition panels are shown in Figure 1. Specifica-tions for these panels are 92% bagasse, 8% urea-formaldehyde, 0.74 specific gravity, and 0.3 in.(10 mm) thickness (Salyer and Usmani 1982).

Cereal StrawCereal straw is probably the second most

used agricultural fiber for reconstituted panelproduction. For the purposes of this paper, cerealstraw is meant to include straw from wheat, rye,barley, oats, and rice. Straw, like bagasse, is anagricultural residue. Unlike bagasse, large quan-tities of cereal straw, generally, are not availableat one location. Storage is accomplished usuallyby baling. Straws have a high ash content (Tablel), tend to fill fireboxes in boilers, and increasethe wear rate on cutting tools. Their high silicacontent also tends to make them naturally fireresistant (Opel 1992).

Plants exist in. several countries to makethick (5 to 15 cm; 0.2 to 0.6 in.) straw panels withkraft paper faces (United Nations Industrial De-velopment Organization 1975). The panels aremade by heating the straw to about 200°C, atwhich point springback properties are virtuallynil. The straw is fed through a reciprocating armextruder and made into a continuous low density(0.25 specific gravity) panel. Kraft paper is gluedto the faces and edges of the panels. These panelscan then be cut for prefabrication into housingand other structures. The low density of thepanels makes them fairly resilient and test datashow that housing built using these panels isespecially earthquake resistant. In the 1980s,such a plant to produce straw panels from wheatand rye straw was set up in California (Galassco1992).

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Figure 1.—Some properties of bagasse composition panels. Thickness swell and water absorption valuesbelow dotted line are desirable. (Source: American National Standard Institute [for standards] 1989a[particleboard Standard] and 1989b [American Hardboard Association]; Salyer and Usmani 1982 [for data])

Table 1 .—Chemical composition of selected lignocellulosic fibersCompositiona (%)

Fiber Type Alpha Cellulose Lignin Ash SilicaRice strawb 28 to 36 12 to 16 15 to 20 9 to 14Wheat strawb 38 to 46 16 to 21 5 to 9 3 to 7Oat strawb 31 to 37 16 to 19 6 to 8 4 to 7

Bagasseb

Kenafb

Cotton stalksC

32 to 44 19 to 24 2 to 5 1 to 431 to 39 14 to 19 2 to 5 na

na 22 5 3

Rice husksd 38 22 20 19Softwoodsb 40 to 45 26 to 34 <l --Hardwoodsb 38 to 48 23 to 30 <l --a na is not available: - - is negligible valueb Source: TAPPI 1983c Source: Fadl et al. 1978d Source: Govindarao 1980

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Straw can be used to supplement part of thefiber content in particleboard. A large particle-board plant in the United States, located in LaGrande, Oregon, substituted straw at a rate of 8%and found no major problems except that thesander dust from the faces deposited additionalash in the boiler. This plant then stopped usingstraw in the face and used it only in the core. Ata rate of 10% or less, the effect on tool wear wasnot significant (Knowles 1992).

The time of harvest for the straw is importantto board quality (Rexen 1977). The quality of thestraw is highest when the grain is at its optimumripeness for harvesting. Under-ripe straw has notyet yielded its full potential and over-ripe strawbecomes brittle. A small amount of ryegrassstraw particleboard was produced commerciallyin the United States in Oregon (Loken et al.1991). The product has a density of 0.6, is quitestiff, and has a Class 3 fire rating (Opel 1992).Some properties of straw composition panels areshown in Figure 2. Specifications for these pan-

els are 97% pulped rice straw, 3% urea-formal-dehyde resin, 0.98 specific gravity, and 0.08 in.(2.8 mm) thickness. Thickness swell and waterabsorption time values are unknown (Fadl et al.1984).

Corn Stalks and Cobs

Based on the literature search, currently thereis no commercial utilization of corn stalks orcobs in composition panel production. A three-layer board having a corn cob core and woodveneer face was produced for a short time inCzechoslovakia after World War II (United Na-tions Industrial Development Organization1975). Records show that the process was toolabor intensive and was discontinued.

Corn stalks., like many agricultural fibersources, consist of a pithy core with an outerlayer of long fibers. Currently, in the UnitedStates, corn stalks are chopped and used forforage, left on the field, or baled for animalbedding. The cobs are occasionally used for fuel.

Figure 2—Some properties of straw composition boards. (Source: American National Standard Institute[for standards] 1989a [Particleboard Standard] and 1989b [American Hardboard Standard]; Fadl et al.1984 [for data])

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Research shows that corn stalks and cobs can bemade into reasonably good particleboard andfiberboard (Chow 1974). In the research, cornstalks and cobs were either hammermilled intoparticles or reduced to fibers in a pressurizedrefiner. Some panels were laminated with 0.09in. (3.2 mm) pine veneers, and three-layer panelswere made with stalk faces and cob cores. Se-lected results of this research are shown Figure3. Specifications for these composition panelsare 92% hammermilled and depithed corn stalks,7% urea-formaldehyde resin, 1% wax, 0.74 spe-cific gravity, and 0.5 in. (16 mm) thickness(Chow 1974).

Cotton Stalks

Cotton is cultivated primarily for its fiberused in textiles and little use is made of the cottonplant stalk. Stalk harvest yields tend to be lowand storage can be a problem. The cotton stalk isplagued with parasites and stored stalks canserve as a home for the parasites to winter overfor next year’s crop. Attempted commercializa-

tion of cotton stalk particleboard in Iran wasunsuccessful for this reason (Brooks 1992).

If the parasite issue could be addressed, cot-ton stalks can be an excellent source of fiber.With regard to structure and dimensions, cottonstalk fiber is similar to common species of hard-wood fiber (Mobarek and Nada 1975). As such,debarked cotton stalks can be used to make highgrades of paper. The stalk is about 33% bark andquite fibrous. Newsprint quality paper can bemade from whole cotton stalks. Some propertiesof composition panels made from undebarkedcotton stalks are shown in Figure 4. Specifica-tions for these composition panels are 97% re-fined undebarked cotton stalk, 3% phenolicresin, 0.82 specific gravity, and 0.08 in. (2.8 mm)thickness. Thickness swell and water absorptiontime values are unknown (Fadl et al. 1978).‘Recently (Frazier 1993), Carl Schenk GmbHconstructed a plant based on cotton stalks inChina (in De Zhou, 300 km east of Beijing). Theplant is providing a board meeting or exceeding

Figure 3.—Selected results of corn stalk composition board research. (Source: American National StandardInstitute [for standards] 1989a [Particleboard Standard] and 1989b [American Hardboard Standard]; Chow1974 (for data])

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property specifications for wood particleboar.The plant size is 110 m3 with an 8.2 by 33 ftsingle opening press. An identical plant is nowunder construction in Heze in Shandong Prov-ince and a third plant is on order.

Kenaf

Kenaf is a plant that is similar to jute or hemp.It has a pithy stem surrounded by fibers. Thefibers make up 20-25% of the dry weight of theplant (LaMahieu et al. 1991). Kenaf grows wellin the southern United States. Growth in thenorthern United States fluctuates with variationsin the growing season. Mature kenaf plants canbe 17 ft (5 m) high.

Currently, kenaf is generating a great deal ofinterest from government and industry. The U.S.Department of Agriculture is promoting kenaf,and other nonfood, nonfeed agricultural crops,because these crops are not subject to subsidies(Alternative Agricultural Research and Com-mercialization 1992). Historically, kenaf fiberwas first used as cordage. Industry is exploring

the use of kenaf in papermaking and nonwoventextiles. Kenaf fiber can be used to make letter-head quality paper; whole kenaf stalk can be usedto make newsprint grade paper. With the pithremoved, kenaf and other fibers can be blendedtogether to make nonwoven textile mats. As anonwoven textile mat, kenaf can be used forerosion control, seedling mulches, and oil spillabsorbents. When a resin is added to the kenafmats, they can be pressed into flat panels ormolded into shapes, such as interior car doorsubstrates.

As an indication of the interest in kenaf, arecent bibliography devoted solely to kenaf had241 scientific citations (United States Depart-ment of Agriculture 1992). Also, the Interna-tional Kenaf Association is devoted to the studyand promotion of kenaf (Taylor 1993). Researchon the use of kenaf for composition panels hasbeen somewhat limited, although encouraging.In the literature search, two references containeddata on composition panels made from kenaf.

Figure 4.—Some properties of undebarked cotton stalk composition panels. (Source: American NationalStandard Institute [for standards] 1989a [Particleboard Standard) and 1989b [American HardboardStandard]; Fadl et al. 1978 [for data])

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Research at the FPL (unpublished) showed thatkenaf can be used to make fiberboard nearlyequal or equal to American National StandardInstitute, American Hardboard Association, ba-sic hardboard standards. Some properties forkenaf composition panels are shown in Figure 5.Specifications for these panels are 92% depithedkenaf bast fiber, 7% urea-formaldehyde, 1%wax, 0.74 specific gravity, and 0.5 in. (16 mm)thickness. Thickness swell and water absorptionvalues reflect 2 hours of immersion (Chow1974).

Rice Husks Sunflower Stalks and Hulls

Rice husks are an agricultural residue that is The University of Minnesota was the site ofavailable in fairly large quantities in one area. several studies to examine the properties of par-Rice usually comes to the plant at about an 8% ticleboard made with varying amounts of sun-moisture content level (Vasishth and Chandra- flower stalks and hulls. In Gertjejansen et al.moule 1974). Rice husks are quite fibrous by (1972). particleboards from 50% aspen and 50%nature and require little energy input to prepare sunflower hulls were produced. Gertjejansenthe husks for board manufacture. To make high- (1977) focused on sunflower stalks, preparedquality boards, the inner and outer husks are and depithed in different ways and blended withseparated and broken at their “spine.” Resin is aspen flakes. The results indicated that most

applied and the rice husk particles are air laid likeother lignocellulosic materials.

Rice husks or their ash are used in cementblock and other cement products. The additionof the hulls increases thermal and acoustic prop-erties (Govindarao 1980). Some properties ofselected rice husk composition panels are pre-sented in Figure 6. Specifications for these com-position panels are 0.94 specific gravity and 0.2in. (6.2 mm) thickness. Husk and resin contentare unknown (Govindarao 1980).

Figure 5.—Some properties of kenaf composition panels. (Source: American National Standard Institute[for standards] 1989a [Particleboard Standard] and 1989b [American Hardboard Standard]; Chow 1974[for data])

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Figure 6.—Some properties of rice husk composition panels. (Source: American National Standard Institute[for standards] 1989a particleboard Standard] and 1989b [American Hardboard Standard]; Govindarao1980 [for data])

physical and mechanical properties increasedwhen adding the fibrous sunflower stalks.

The literature search found only one citationfor sunflowers outside the United States. Withinthe United States, two citations were found forhulls and one was found for stalks. At the timeof this writing, no commercial use is known forsunflower stalks or hulls in composition panels.Properties of composition boards made fromsunflower stalks and hulls are shown in Figures7 and 8, respectively. Specifications for thesesunflower stalk composition panels are 90% de-pithed sunflower stalks, 10% phenol-formalde-hyde resin, 0.74 specific gravity, and 0.4 in. (12mm) thickness (Gertjejansen 1977). Specifica-tions for these sunflower hull composition pan-els are 92% sunflower hulls, 7% urea-formalde-hyde resin, 1% wax, 0.78 specific gravity, and0.3 in. (10 mm) thickness. Thickness swell andwater absorption values reflect 2 hours of im-mersion (Chow 1974).

FIBER AVAILABILITY ANDECONOMICS

Knowing that agricultural residues and othernonwood fibers can be used to make panels ofcomparable mechanical properties, the question is,“are these fibers available and economical to use?”The material that follows will discuss briefly theavailability, economics, fiber yield, bulk density,alternative use, and price comparison.

AvailabilityConsiderable amounts of agricultural resi-

dues are generated each year in the United States(Table 2). If the unlikely assumption was madethat 75 wood composition panel plants decidedto change entirely to agricultural fiber and, onaverage, each particular plant required 135 × 103

metric tons (t) of fiber a year, the total fiberrequirement would be approximately 10 x 106 t.Relative to the amount of residues generated,more than 30 times as much agricultural fiberwould be available as would be consumed. This

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Figure 7.—Some properties of sunflower stalk composition panels (Source: American National StandardInstitute [for standards] 1989a [Particleboard Standard] and 1989b [American Hardboard Standard];Gertjejansen 1977 [for data])

Figure 8.—Properties of sunflower hull composition panels. (Source: American National Standard Institute[for standards] 1989a [Particleboard Standard] and 1989b [American Hardboard Standard]; Chow 1974[for data])

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Table 2.—Residue estimates of U.S. major cropsa

Estimated 1990Harvested Yield per ha Residue Weight

Crop (ha) (acre) (t/ha) (t/acre) (×106 t)

Corn 26 65 5 to 7 2 to 3 167Wheat 24 60 2 to 5 1 to 2 106Sorghum 6 16 5 to 7 2 to 3 23Oats 6 14 2 to 5 1 to 2 9Barley 4 11 2 to 5 1 to 2 11Rice 1 2 2 to 5 1 to 2 2

TOTAL 318a Source: Goldstein 1981

calculation of availability does not take into ac-count baggasse or agricultural fibers from non-residue sources like kenaf. Thus, from the view-point of potential availability, the amount ofresidues generated by U.S. agriculture far ex-ceeds present and future composition panel fiberrequirements.

However, not all the gross potential supplyis freely available. For instance, to participate inFederal farm programs, all farms must have anapproved conservation plan by 1995. In somecases, this entails leaving some portion of theresidue mass on the ground as cover for soil pro-tection. Also note that these fibers are availableonly on a seasonal basis. Storage issues for manyindividual fiber types are addressed in this paper.

EconomicsIn North America, composition panels come

primarily from wood residues and secondarilyfrom roundwood obtained from traditionallymanaged forests. How alternative fiber sourcescompare in cost with these traditional sourceswill determine the extent to which they can beconsidered as a wood fiber substitute. Alterna-tive agricultural fiber comes from two mainsources: agricultural crops grown for fiber (e.g.,kenaf) and residues of crops grown for otherpurposes (e.g., wheat, cotton).

Fiber YieldIntensively managed hybrid poplar grown

under short rotations can produce yields of fiberranging from 4 to 6 t/acre (10 to 15 t/ha) per year.Conventionally managed aspen stands yieldabout 1 t/acre (2.5 t/ha) per year (Dawson et al.1975, Turhollow 1991). From the viewpoint ofmaximum yields, kenaf appears to be preemi-nent. Yields of up to 20 t/acre (50 t/ha) on thebest sites were reported (Corkern 1971), al-though 6 t/acre (15 t/ha) is more realistic. Whenfiber yields of crop residues were examined, therange of harvestable fibers varied from 1 to 3t/acre (2 to 7 t/ha), depending on plant speciesand local growing conditions (Table 2).

Bulk DensityA major difference between wood and non-

wood fibers is bulk density. One obstacle toagricultural fiber utilization for relatively low-value commodity products, like composite pan-els, is low bulk density. Low bulk density canincrease transport costs significantly. A standardcord contains 128 ft3 (3.6 m3) of space of whichapproximately 76 ft3 (2.1 m3) is wood. Thisyields a gross bulk density (dry basis) of 15 to20 lb/ft3 (240 to 320 kg/m3). The economics ofprocessing and transporting small-diameter tim-ber with such bulk density indicates a practicalprocurement radius of about 40 miles (65 km)(Vaagen 1991).

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In contrast, annual fiber stems of a plant suchas kenaf or straw cannot be compacted muchbeyond 8.4 lb/ft3 (135 kg/m3), which limits thefeasible supply basin to a range of 15 to 20 miles(25 to 35 km) (Sandwell 1991). By analogy,similar ranges could be expected to hold forresidue fibers as well, if the same high densitybaling equipment as assumed in the Sandwellstudy were available. This effectively reducesthe availability of fiber to a single plant to an areaof approximately 800,000 acres (320,000 ha).Assuming that 70% of this land was devoted toagriculture and fiber-producing plants wereplanted on one-third the acreage in a given year,the available supply, based on a 2 t/acre (5 t/ha)yield, would be about 375,000 t. This provides acoverage ratio of 2.75 for a typical plant’s needs,based on the previous assumptions.

Alternative Use

Not all the fiber produced in U.S. agricultureis valueless by product. For example, uses andmarkets for baled straw exist where animal bed-ding needs are high, such as in states wheredairying is strong. In Wisconsin and Pennsylva-nia, two states where the availability of straw

relative to the number of cows in dairy herds issmall. Baled straw delivered to central auctionsites is priced from US$50 to US$90/dry t (Table3). In North Dakota, straw is generally left on theground. The small amount of straw that is baledmarkets for only US$25 to US$35/t. In otherareas, although straw is not priced, it plays avaluable role in agriculture as a mulch to retardrunoff and soil erosion. The use of straw for theseconservation purposes is mandated by Federalfarm programs. These conservation purposesmust be established by 1995 for a farm to benefitfrom Federal farm programs. Nevertheless,mulch straw has little economic value and wouldbe available for other off-site uses at low cost.

Corn stalk residue has lower absorbency thandoes straw and thus, is not as well suited forbedding purposes. Estimates show that cornstalks could be obtained for as little as US$5/t,unbaled (on the stump). Factoring in harvestingand transport costs, such material should be ob-tainable for US$25/t.

Overall Price ComparisonCurrent costs of pulpwood were used as a

frame of reference. Pulpwood in the United

Table 3.—Various cereal straw pricesa

U.S. StateCereal Straw Availability Number of Milk Price Range

per Year (×106 t) Cows (×106) Ratio (straw/cow) (US$/t)b

Kansas 24.5 0.10 250 - -North Dakota 23.3 0.09 250 25 to 35Washington, Oregon 15.2 0.31 50 - -Montana 12.9 0.23 55 - -Texas 11.6 0.38 30 - -Oklahoma 11.4 0.10 110 --Minnesota 10.2 0.78 15 - -Illinois, Indiana 10.2 0.38 25 - -California 8.9 1.10 8 - -Nebraska 7.6 0.11 70 - -Wisconsin 2.2 1.76 1.2 60 to 90Pennsylvania 1.6 0.77 2.0 50 to 95aSource: Goldstein 1981, Frank 1993, Hoffman 1993b- -, price not available

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States is usually marketed in terms of cords, thusa conversion to weights, based on species den-sity, was made to facilitate comparsion with ag-ricultural residues. The results of the comparisonare in Table 4.

Recent pine, mixed hardwood, and aspenpulpwood delivered prices range from US$43 toUS$52/cord (3.6 m3). When converted to a weightbasis, prices range from US$40 to US$47/t.

Intensively cultivated hybrid poplar planta-tion prices are estimated at US$60/t, exceedingpine and hardwoods prices. Hybrid poplar esti-mates assume a 6 t/acre (15 t/ha) yield and twoharvest rotations following initial harvest in-volving coppice regeneration (which eliminatesreplanting costs).

Among the agricultural fibers, kenaf is gen-erally the highest in estimated price because allcultivation and harvest costs are born by the fibercomponent of the output. Kenaf calculations arebased on 6 t/acre (15 t/ha) yields, and the price

is between those of hybrid poplar and pine orhardwood pulpwood. Straw and corn generallycost less than do crops grown specifically fortheir fiber content because the grain portion ofthe output bears the expense. An exception to thisis where the fiber has value for other uses, suchas animal bedding. In those cases, straw pricescan be almost twice as high as pulpwood and notcurrently within economic reach of particleboardproducers.

CONCLUDING REMARKS

A new era of wildland stewardship is emerg-ing in the United States. Its philosophy is broaderthan sustained yield and multiple use and it shouldnot reject the contributions and future utility ofthose concepts and practices that have charac-terized good land management. In fact, the emerg-ing ecosystem management builds directly onthe foundation established by previous policies,concepts, and accomplishments. Because ofwhat prior generations of scientists and resource

Table 4.—Relative prices of wood and agricultural fibersPrices (US$/t) (US$/cord)a

Pulpwood/Fiber Stumpageb Harvested and Delivered Total

PulpwoodSouthern Pinec 16 20 25 32 41 52Southern hardwoodc 8 9 31 34 40 43Lake Statesd

Aspen 13 12 34 33 47 45Hybrid poplar 40 na 20 na 60 naKenaf 36 na 19 na 55 na

Agricultural fibere

Cereal strawCorn stalks

5 to 70 na 20 na 25 to 90 na5 na 20 na 25 na

a Conversions based on 77 ft3 (2 m3) per cordb Stumpage is growing cost plus return to land and farmer; for kenaf, straw, and corn, cost of harvest isincluded in stumpagec Prices from Timber Mart South (1992)d Aspen prices from Wisconsin and Minnesota state forestry officials; hybrid poplar based on Turhollow(1991); kenaf based on Sandwell and Associates (1991)e Based on partial survey of state agricultural extension economists

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managers created, we can now move to landmanagement that considers more than selectedresource outputs and single species utilization.

In this paper, the uses of alternative agricul-tural fibers from a global perspective were ex-plored. Agricultural fibers that have been orcould be used in North America were discussed.Also discussed were those issues in which aproducer of wood-based composition panelswould have the most interest. In summary:

1. There is no global wood fiber shortage. How-ever, several examples of localized supplyshortages exist throughout the world.

2. A large amount of literature reports on thesatisfactory use of agricultural fibers incomposition panels.

3. More than enough agricultural fiber resi-dues are available to support compositionpanel manufacturing needs within NorthAmerica. However, the fibers may not be inthe right place at the right time.

4. In general terms, composition panels madefrom agricultural fibers are of somewhatpoorer quality than those made of wood, butblending in small amounts of agriculturalfibers (10% to 20%) may have no signifi-cant impact on quality.

5. Bagasse, cereal straw, and kenaf appear tohave the most promise for continued paneldevelopment.

ACKNOWLEDGMENTSWe thank Diana Hess for assembling data

and constructing Figures 1 to 8 and Table 1.

REFERENCES CITED

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