BAST FIBER APPLICATIONS FOR COMPOSITES

Authored by: Erwin H. Lloyd and David Seber

 

 

ABSTRACT:

In today's market, the cost, quality, and availability of fiber are of utmost importance. A number of companies currently are developing manufacturing operations that utilize alternative fibers for panel products. This paper surveys the crop and fiber technical characteristics of the temperate bast family of plants, as well as an overview of the potential products and markets from these markets. These materials include kenaf, hemp, and flax.

This report investigates the ongoing research and development of prolific bast fiber crops noted for the strength of their fiber bundles. These materials hold strong potential, particularly in applications demanding substantial strength.

This session is valuable to senior plant management, investors in the composite industry, and raw material procurement and product development personnel interested in utilizing alternative fibers and materials as either supplemental or primarily raw materials.

INTRODUCTION:

Over the past decade, allowable harvests of old growth in the Pacific Northwest have been reduced. In light of this restriction, it has become increasingly difficult to provide end users with the quality lumber they once enjoyed. Furthermore, diminished supply of larger dimension timbers has created high pricing. Through these changes, new products and producers have emerged to fill this need with composite and engineered wood products. This report presents the current state of work in the development of bast materials and processes to assist in filling the need for high end structural building products. The opportunities to incorporate bast products into both established and innovative products and processes in the marketplace also will be discussed.

PERSPECTIVES:

When one considers the use of alternative materials, several perspectives may be taken. Many people take what could be considered a market driven approach. In this case, one first considers a traditionally established product, and then looks at how alternative materials could be substituted for the traditional raw material. A second approach is resource driven in which applications are sought for a particular, often non-traditional, fiber crop or residue. In both cases, one must work under a framework of technical feasibility and economic viability.

A third approach, suspends the current and future projected supply and demand for various related products and simultaneously considers the specific characteristics of a material or crop. This especially helpful when one considers the development of a plant to be grown specifically for its fiber. In this arrangement, one could consider a number of possibilities and evaluate each one in a cursory fashion to determine the combinations with the greatest economic return. These best-fit synthesized solutions rely on a combination of raw materials and strategies to form the final product. The price and demand for the raw material and the performance requirements also may vary depending upon market conditions.

One must also consider whether targeting a niche or commodity market is best for their particular situation. Generally, larger scale operations benefit dramatically from significant economies of scale especially in regard to capital equipment, and to a lesser extent other on-going costs. This arrangement favors the commodity-based market. Mature and brand new markets and products, distinctive raw materials, market uncertainties, or limitations in available raw material supply or funding would favor often smaller-scale operations producing a specialty product for a niche market.

PROFITABLE RETURNS:

Three ways exist to expand markets in composite products. The first is to gain increased sales through expanded markets through a stronger sales and market penetration effort. A second is to add value to existing products through performance enhancing features. The third is to develop new products having improved performance characteristics developed to expand into new markets previously occupied by more expensive materials. This presentation focuses on the opportunities we have discovered through the pursuit of the latter two methods.

When we evaluate alternative materials, several issues must be kept in mind. The combination of these issues will determine the relative feasibility of a product's success in the marketplace. These are the following:

1. The average amount of yield/acre/year, as well as the degree of viability and stability of this yield.

2. The real delivered to plant costs of this material. These include harvesting, "baling", and transportation costs, as well as nutrient replenishment of the soil.

3. The ability this material has to be available in sufficiently large quantities to enable a manufacturing plant to possess economies of scale.

4. The quality of this product for a particular application.

5. The degree of ease or difficulty with which this material may be processed into a composite material due to a species distinctive characteristics.

6. The degree of ease with which this material could smoothly transition into broadly accepted usage in an existing process, plant, and product. This includes the geometries of materials, physical, thermal and chemical binder compatibility during processing, and appearance in the final product.

7. Binder compatibility-the ease with which economically viable binders at sufficiently low levels can be mixed with the fibrous material.

8. Binder compatibility within a specific plant. When alternative materials are used as a supplement to an established furnish, such as wood, it is strongly preferable for the current, established adhesive in the plant to be compatible with the supplemental material. When this is not achievable, plant management is often quite reluctant to consider the incorporation of this feedstock.

9. The in-plant hygiene and environmental effects both within the mill and in the finished board resulting from the use of a particular binder.

10. The technical feasibility to utilize this material to produce a particular product having a certain set of product characteristics.

11. Any regulation that could favor or detract from this material's entry as a raw material or acceptance as a finished product.

From another perspective, over the past 15 years great changes have taken place on the following fronts:

1. Allowable timber harvesting on federal, state, provincial, and even private timberlands have been significantly reduced in certain regions.

2. These reductions have led to increased costs for lumber, plywood, and other wood products which makes products made from other materials more viable. Some of these materials such as steel, plastic, and concrete are manufactured using completely different processes and thus different equipment and plants. As wood costs remain high, these other products will gain an ever greater share of construction materials.

3. Strong political and environmental public perceptions of the value in employing whatever means necessary in order to reduce the harvesting of forests, especially old-growth areas containing the better quality timber.

BAST PLANTS AS A FIBER RESOURCE:

Bast fiber plants provide a means for traditional forest products companies to maintain market share and even capture new markets through the use of alternative raw materials which possess unique and beneficial properties which are particularly fitting for certain applications. They also provide the perception of improved environmental stewardship of our resources.

Bast fibers have been grown for centuries throughout the world. Bast plants are characterized by long, strong fiber bundles that comprise the outer portion of the stalk. Bast plants include flax, hemp, kenaf, sunn-hemp, ramie, and jute. The focus of our research has been on the species that can grow in temperate regions of the world, namely flax, hemp, and kenaf. These fibrous plants have long been noted for their exceptional strength in cordage and paper. The primary focus of our research will be from a North American perspective, although occasional references will be made to applicable international developments.

The word "bast" refers to the outer portion of the stem of these plants. This stringy, vascular portion comprises 10 - 40% of the mass of the stem depending upon the species of bast plant, as well as the particular variety, or cultivar, within a bast plant.

The remainder of the stem inside this bast layer is a different type of fibrous material, which has different names depending upon the species selected. This inner material is known as shives when referring to flax and sometimes hemp, as hurd in the context of hemp, and as core when from kenaf. For the purpose of simplicity and consistency, we will use the word "core" when discussing this portion of the bast plant.

Overall Advantages of Bast Plants:

In general, bast plants possess the following benefits:

1. High tensile strength in bast portions, especially in fiber varieties.

2. Bast plants have a relatively low specific gravity of 0.28 - 0.62, yielding an especially high specific strength, i.e. strength to weight ratio, (Kozlowski, Mieleniak, Przepiera, 1994).

3. Generally high fiber productivity rates, rivaling and even surpassing that of the most commercial tree species.

4. Potential for even greater productivity, bast portions, and mechanical properties through focused genetic breeding.

Overall Limitations of Bast Plants:

In general, bast plants also have the following limitations:

1. Rotations at least every other year generally required.

2. Limited research for composite applications in North America.

3. Lack of related agricultural infrastructure in North America.

4. Relatively high absorption of moisture in core portion.

5. Diminished board properties when using core for particleboard.

6. Difficulty in handling long fiber bundle lengths for processing.

7. Difficulty in applying binder to long fiber bundle lengths.

Comparative Properties of Bast and Wood Species:

The following graphs illustrate the attractive properties of these bast plants relative to common wood species. These graphs illustrate first the relative cellulose contents and then the tensile strength. The final graph illustrates the specific strength that is the tensile strength relative to the specific gravity. Both tensile strength graphs compare fiber bundle characteristics, as well as those of the individual fiber. Both of these types of particles may be used depending upon the specific processes and end products produced.

FLAX:

Flax, Linum usitatissimum, is one of the bast fibers grown in temperate regions. Flax has two general markets, one group grown for its textile, and a second type grown for its seed, which is converted to linseed oil for paints and other industrial products, with a smaller but growing portion converted into linseed meal and oil as a health supplement. Flax plants range in height from 12 to 40 inches, and have shallow taproots. The same species is used for both fiber and seed, with breeding of specialized cultivars for the two different products. The seed-producing varieties have shorter stems and are heavily branched. The fiber varieties pursue stem development resulting in a taller plant more sparsely branched.

Flax has been cultivated for nearly 10,000 years, and was grown in North America as early as 1626. With the invention of the cotton gin in 1793, cotton became an inexpensive substitute, and largely displaced flax as a fiber source in the United States and Canada. Subsequently, flax has been cultivated in North America primarily for its seed, (Mo, 1969).

An estimated 12 million hectares grow textile flax, while 500,000 hectares are cultivated for the oil-seed variety (Wong, 1990). This crop has a specific gravity of 0.32 - 0.68, somewhat greater than jute and hemp, but comparable to bagasse. In light of nutrient requirements, flax can only be grown once every five years on a particular acreage, (West, 1995).

Textile flax is primarily grown in Europe. Textile flax often has a relative high percentage of its stem that is bast fiber, up to 40%. A new textile hybrid, Heiya 8, has been developed which has a stem yield of 6.5 tons/hectare and is drought resistant, (Gu, 1994.) This indicates that certain varieties of flax when grown for textile can produce moderate yields. Decorticated textile bast fiber demonstrates exceptional mechanical properties including high tensile strength as well as a large proportion of bast material. The relatively low productivity, however, create a quite expensive bast fiber, which sells for $2,000 - $4,000/ton.(Domier, 1996). This high cost effectively prohibits its use for most, if not all, composite material applications. The core, however, finds considerable use as furnish in particleboard.

Virtually all the flax grown in North America is for seed-oil. Argentina, India, The Commonwealth of Independent States, and China also grow flax for oil-seed, (Wilkins, 1988). Saskatchewan and Manitoba are the primary regions that grow flax in North America, although Alberta, North Dakota, and South Dakota grow flax as well. Over two million acres are grown in Canada, with lesser amounts grown in the United States. Of this 26%, 65,000 tons, are used for pulp in specialty applications such as cigarette papers. Oil-seed flax is somewhat distinctive from the other temperate bast fibers, kenaf and hemp, on several different fronts. First, the diameter of the stalk of the oil seed flax is much less than kenaf or hemp, making the flax stalk much more slender. Secondly, the bast fiber yields per acre are also considerably lower than other bast varieties, generally reaching only 1,000 - 1,500 bone dry pounds per acre, (Wong, 1990).

Since North American flax is grown for its seed from which is made linseed oil, the remaining flax stalk effectively is a residue. Fiber flax, as with other bast fiber products, is harvested earlier in order to maximize the quality and quantity of its fiber. Flax or other bast crops grown for its oil are harvested later in the season. During this time of reproductive development of the seeds, bio-chemical changes occur which increase the lignin content from a very small amount to a much greater proportion, (Domier, 1996). This, and perhaps other bio-chemical changes, decrease the tensile strength of the flax to a level approximately one-half of that enjoyed a few weeks earlier prior to seed development, (King, 1996). Now as a residue, the price of the decorticated bast fiber from flax is generally less expensive than other bast fiber crops, reaching only around $200/bone dry ton. Thus, the diminished structural qualities are roughly compensated by a lower price.

Stem Yields (dry tons/acre)

Location

0.5 - 0.75

North Dakota, Manitoba, and Saskatchewan

Sources: Wasylciw 1996 and Wong 1990.

 

Advantages of Oil-Seed Flax:

Oil-seed flax possesses the following benefits:

1. Relatively low cost for bast fiber portion since it is a residue of the seed-oil.

2. Currently, commercially available in production level quantities.

3. Best developed infrastructure for composites supply.

4. Oil-seed flax is an established crop resulting in less risk for farmers to grow.

Limitations of Oil-Seed Flax:

Oil-seed flax also has the following limitations:

1. Low yields per acre.

2. Limited rotations, generally three years.

3. Lower tensile strength of the oil-seed variety, as compared to other bast plants, such as hemp.

KENAF:

Kenaf, Hibiscus cannabinus, originating from Africa, has traditionally been a source of bast fiber in India, China, The Commonwealth of Independent States, Iran, Nigeria, and Thailand. Kenaf is a newer crop to the United States that shows good potential as a raw material for use in composite products. Presently, around 4,300 acres of kenaf are cultivated in the United States. 2,000 acres are grown in Mississippi, 1,200 acres in Texas, 560 acres in California, with lesser amounts in Louisiana, New Mexico, and Georgia. Traditionally, kenaf has been known as a cordage crop or jute substitute. Research on kenaf first began in the United States in 1957 and has continued sporadically since that time, (White, Higgins, 1964). Newer advances in decortication equipment which seperates the core from the bast fiber combined with fiber shortages has renewed recent interest in kenaf as a fiber source.

 Stem Yields (dry tons/acre)

Location

7 - 12

Southern Florida, Southern Texas, Southern California, and Hawaii

6 - 8

Mississippi, Central-northern Texas, Louisiana, Northern Florida, and Georgia

5 - 7

Arkansas and New Mexico

Sources: U.S.D.A., Agricultural Research Service. 1970; Bledsoe 1996; and Cook 1996

 

Agronomic Characteristics:

Kenaf is a member of the Malvaceae family, and may grow 8 to 20 feet in height and is generally unbranched in thick stands. By 1965, the areas of adaptation without supplementary water supply were low-elevations sections of North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and eastern Texas. Excellent yield potentials should exist in warm, dry areas with irrigation, (USDA, ARS, 1970).

No known diseases or insect pests seriously injure kenaf, however, it has been highly susceptible to root-knot nematodes and other nematode species. New genetic research in Texas shows considerable improvement in nematode resistance in that region. Although kenaf is a fast-growing, competitive crop, chemical weed control is highly advisable in most production areas with exceptions being wide, bedded rows in Florida flatwood soils, (USDA, ARS, 1970).

Kenaf has some promising characteristics along with certain limitations. Nutrient requirements are low, with no significant improvement in yield at nitrogen levels above 33.5 pounds per acre, (USDA, ARS, 1970). The length of the vegetative phase is determined by daily length of the dark period. A growing period of 90 -150 days is needed, with fastest growth at temperatures of 20 - 22 C, (68 - 72 F), and approximately 6000 m3 water per hectare, (Vannini, Venturi, 1992). Growth becomes quite minimal when temperatures reach below 50oF, (USDA, ARS, 1970; LeMahieu, Oplinger, and Putnam, 1991).

Kenaf contains a bast fiber portion comprising 26 - 35% (by dry weight) of its stem, (Columbus, 1996; Sellers, 1996; Fuller, 1996; Fisher, 1996; Bledsoe, 1996). This bast crop shows potential as a substitute for hardwood species as shortages may become more pronounced in various locales of the Southeast and Mid-South. Bast fibers average 2.5 mm in length, very similar to southern pine species, while the core, with lengths of 0.5 mm closely matches that of hardwoods. This composition provides a desirable blend for many pulp and paper applications, spurring continued interest and development, (Schroeter, 1994).

Advantages of Kenaf:

Kenaf possesses the following benefits:

1. Excellent yields in southern regions. For example, 15 tons/acre were grown at College Station, Texas in research plots, (Berger, 1969). Actual production yields of 7 -9 bone dry tons/acres can be expected in the warmer regions of Texas.

2. Low harvested whole stalk costs in favorable climatic regions such as southern Texas.

3. Genetic strains have been developed which yield 35% or greater bast portions. This is a relatively high proportion.

4. Considerable progress has been made in developing nematode resistance in the Texas growing region. Nematode susceptibility has long been an encumbrance to the viability of kenaf development.

5. Is competitive showing favorable weed control characteristics.

6. Is viewed favorably by the USDA as a prime candidate for alternative fiber development and has consequently received greater research funding.

7. Strong federal political support.

Limitations of Kenaf:

Kenaf also has the following limitations:

1. Low productivity in cooler climates. Its growing season can be as short as 90 - 120 days, and consequently it will grow in almost any region of North America if sufficient moisture is available. The yields of kenaf in Rosemount, Minnesota, south of the Twin Cities, yielded only 2.5 tons/acre in a research plot, compared to the 15 ton/acre yield in College Station, Texas, (Le Mahieu, Oplinger, Putnam, 1991; White, Higgins, 1964). Actual production yields are roughly 60-70% of those in test plots, (Blodsoe, 1996; Cook, 1996).

2. High moisture requirements. 600 mm, (23.6 in) of water is preferable during its growing cycle of 120-150 days, (Vannini, Venturi, 1992).

HEMP:

Agronomic Characteristics:

Another notable bast fiber crop is hemp. This plant was probably first grown in Central Asia from where it spread to China where it is thought to have been grown for 4,500 years. It was originally grown for its fiber, then around 900 BC also became known for its narcotic qualities. Hemp is a strong, durable, though harsh bast or phloem fiber, having a core which is characteristic of hardwood fiber. The bast portion is typically 14%. Hemp is an annual plant which at maturity develops a rigid, woody stem ranging in height from 1.2 - 5 m, (3.9 - 16.4 ft), and having a diameter from 4 to 20 mm, (0.16 - 0.79 in), (Hayward, 1948; Berger, 1969).

Hemp varieties planted in the temperate zones fall into two groups, namely the northern and the southern varieties. The latter require high temperatures and a long vegetative period, and consequently grow taller and yield more fibre. Overall, hemp is a tough plant that grows quickly and produces abundant seed and readily adapts to different niches or areas.

Stalk Yields:

According to the latest European statistics, Hungary has some of the greatest yields of hemp stalk. The yield of hemp stalk from Hungary can readily produce 9 metric tons/hectare, (4 tons/acre). Highest yields in Hungary reach 11 metric tons/hectare, (4.9 tons/acre). Hemp varieties have a growing season of approximately 143 days, (Berger, 1969; Helm, 1995; de Meijer, 1993).

Data suggests that hemp, a vital part of the cordage industry throughout the world over a century ago, once had higher yields than those common today. The United States and Canada in recent decades are well noted for their ability to develop high levels of production of agricultural crops relative to the rest of the world. Limited energies by genetic agricultural research organizations in North America have thus far been applied to enhancing the productivity of hemp. With a concerted effort from the North American agricultural research community, it is reasonable to conclude yields substantially greater than those present in Hungary can be achieved in 4 - 10 years of genetic development.

Stem Yields (dry tons/acre)

Location

4.0 - 4.9

Hungary

2.5 - 3.0

Canada

Source: Nelson 1996 and Personal Communication.

 

Advantages of Hemp:

Hemp shows the following strengths:

1. Hemp requires less moisture to grow than kenaf.

2. Hemp's fiber-bundles are stronger and tougher than those of kenaf, generally comparable to varieties of flax, and most other known fiber species.

3. Hemp is generally pest resistant, drought resistant, and light frost resistant.

4. With proper leaf removal, hemp has low net nutrient requirements and requires minimal cultivation.

5. Hemp provides greater fiber yields in areas generally north of the 40th latitude than most other fiber crops, generally surpassing flax by 10%.

Disadvantages of Hemp:

Hemp also has the following weaknesses:

1. Restrictions of its growth and cultivation in North America, especially in the United States.

2. Lower fiber yields than kenaf and other tropical species in the warmer portions of the United States and more southerly regions.

3. Lower bast fiber portions relative to kenaf and flax.

LEGALIZATION OF HEMP:

Virtually all of Western Europe, including The United Kingdom, France, The Netherlands, and Germany, as well as Australia, have legalized low THC varieties of hemp to be grown for industrial purposes. THC is the drug producing substance found in traditional varieties of hemp.

Beginning in 1998, Canada has now legalized the growth of hemp for commercial production and processing. The legalization of the production of industrial hemp is proceeding in several state legislatures in the United States at this time. Industrial hemp that contains only non-leafy material is currently allowed in all of the states for industrial processing.

BAST PLANT MATERIAL SOURCES, AS A RESIDUE OR A FIBER CROP:

One key agronomic and economic issue is whether bast material is better suited to come from oil-seed varieties, or from fiber crops, especially for flax and hemp. At this time, the product development and markets for oil extracted from the kenaf seed is quite limited. Flax and hemp, on the other hand, produce an economically viable oil-seed crop. In these varieties, the fiber is of lower quality, due to bio-chemical changes that occur as the magnitude and proportion of daylight hours decreases. A critical time is reached within a species when the plant shifts from a fiber producing role to a self-preservation one of seed production. As this develops, the lignin content increases and the strength and chemical nature of the cellulose changes adversely.

Because the primary purpose of such a product is for the oil, its fiber may be treated as a residue with corresponding lower value and cost attached to that raw material. The material still demonstrates considerably higher strength properties than wood, so even in this state such material appears suited for moderately improved strength applications of structural products, with lower raw material cost gained as well. These products could be using a bast fiber exclusively, although this type of fiber is probably better suited for combinations with wood to act in a supplementing role.

At this early stage of development, several principles appear evident. In North America, virtually all flax grown is for oil. Thus, residue from these sources is inevitable. The market for hemp oil as a nutritional supplement is small, but appears poised for rapid growth. This results in a reasonable amount of flax and potentially hemp oil-seed residue material is and will be available for testing and commercial applications. The demand for oil from flax, a seemingly stable market, as well as for hemp will be the driving force in determining the amount of resulting residue available. Continued product development from these sources will determine the value and potential applications of this lower cost bast fibrous material.

For product applications in which the high performance of the bast fiber is desired to be maximized, the fiber varieties are best suited. Within a species, the fiber costs for a particular form of processed material will be higher; however, the physical and chemical composition will be correspondingly improved as well. Further product and economic comparisons are necessary to develop a more complete understanding of the viability's and applications best suited for each of these forms of material.

BAST FIBER APPLICATIONS:

Fibre Alternatives are developing applications in which bast plants can supplement and complement wood structural products. We have selected processes that are best suited for the high-end performance characteristics of these species. Table 1 compares the chemical composition of these bast plants with that of wood.

 

Table 1: Comparative Chemical Composition:

FIBROUS MATERIAL:

CELLULOSE

HEMI- CELLULOSE

LIGNIN

EXTRACTIVES

ASH

FLAX

78.5

9.2

8.5

2.3

1.5

HEMP

68.1

15.1

10.6

3.6

2.5

KENAF (bast)

60.8

20.3

11.0

3.2

4.7

CONIFEROUS

48.0

15.0

25.3

11.5

0.2

DECIDUOUS

52.8

21.8

22.3

2.7

0.4

Source: Danforth International, and TAPPI

 

Research at Washington State University is on-going in the development and testing of these materials. The results from these tests are not yet complete. Hence, the following material is based on our current understanding combined with data from additional sources.

SEPARATING/DECORTICATION TECHNOLOGY AND TRENDS:

One important issue is whether the bast fiber should be decorticated, that is, separated into bast fiber and core fiber portions. A whole stalk lends itself to certain products that include composite building materials, especially particleboard and MDF. When the bast and core portions are separated, the significantly different characteristics of the two types of fibers become obvious, each best suited for rather different products and applications.

Historically, the vast majority of decortication equipment was produced in the developing world and suffered from an inability to separate the larger diameter bast fibers such as kenaf and hemp with mechanical reliability, efficiency of separation, and purity of separation. Recent developments in decortication equipment design in Italy and the United States show promise in significantly improving this situation.

Whole stalk usage appears most favorable with kenaf. At this time, kenaf offers the lowest price whole stalk temperate bast material. In addition, decortication equipment may be better developed for flax, and its smaller diameter is better suited for mechanical reliability. Furthermore, the high tensile strength of hemp's bast portion does cause considerable challenges in the cutting of the whole stalk.

As equipment improves, decortication offers a workable mechanism to separate the fibers efficiently and effectively. The trend appears to favor decorticated material being the primary material form. A certain portion, mainly of kenaf, may survive as a viable application for whole stalk usage. This will depend upon production and processing cost as well as the final product and process directions which develop over the coming years.

BINDERS:

Traditionally MDI, that is isocyanate, is the best, most effective binder for agricultural materials. MDI is also viewed as being one of the few binders along with melamine that allows a product to perform acceptably well in exterior applications. MDI releases no formaldehyde within the plant or the board after manufacturing which yields an important advantage. Recent work with agricultural-based binding supplements may considerably reduce the amount of MDI required allowing this binder to be that much more economically viable.

The ability to use several different binders for bast fibers is quite helpful in expanding the utility and applications of bast-based products. These alternative adhesives further expand the economic and performance viability as well as expanding the utilization in a wide range of existing wood composite processing plants.

Testing at Washington State University indicates a strong potential exists to use urea formaldehyde and probably phenol formaldehyde with agricultural materials when properly pre-conditioned.

Lignin also has potential to be used as an adhesive. For decades, many groups have tried to utilize lignin as an adhesive with limited success. Today, several groups have developed promising advancements in a viable product both from a performance as well as from an economic perspective. At least one of these companies has developed promising results using agricultural-based fibrous materials.

Presently, several organizations are pursuing a protein-based binder using soybeans as the base for an adhesive. Five mid-western universities have formed a consortium to further pursue the development of a soy-based adhesive. Several companies and state organizations are also working with isolates and complementary combinations of soy products with other adhesives.

PARTICLEBOARD AND FIBERBOARD APPLICATIONS:

Flax Board Properties:

We have worked on a joint project with Medite to test the performance of flax-based MDF. The results yielded good aesthetic and generally fine performance characteristics. Some of these board properties are shown in Table 2. The high ash and insoluble silica content of flax do create some challenges by increasing machine tool wear. Nevertheless, the board properties are of generally good quality, and the lower density of the flax-wood combination does add a quite desirable feature of a lighter density, (Allen, 1993).

Composite panel plants in a number of locations throughout the world use flax cores to produce particleboard. Four French and Belgian particleboard plants have used flax core as a supplement to wood furnish. China and The Commonwealth of Independent States produce particleboard which exclusively use flax core. The Czech Republic, Slovakia, Bulgaria, and Poland mix the flax core with either hemp core or wood sawdust. The use of wood does help improve the qualities of the boards produced using cores, especially in furniture applications. In light of this issue, both Eastern and especially Western European particleboard manufacturers have shifted to the use of greater proportion of wood in their furnish mix, (Kozlowski, Mieleniak, Przepiera, 1994).

 

Table 2: Properties of Flax MDF:

 RESIN TYPE

RESIN LEVEL (%)

DENSITY (PCF)

IB (PSI)

MOR (PSI)

MOE (KPSI)

UF

9

49

78

4210

458

UF

9

49

80

5140

576

 MUF

9

48

59

4770

582

 MDI

4

49

106

4400

428

 MDI

4

51

171

6590

684

 MDI

4

40

86

3430

377

Source: Medite Corporation

 

A major corporation in the flax industry is currently exploring the use of both the bast and core portions of flax in industrial products including composite building materials.

Kenaf Board Properties:

In one series of low-density board production tests, the core of the kenaf performed without problems in processing including adhesive application, felting, and pressing. The kenaf panels also demonstrated good performance characteristics in low-density, (256 kg/m3), board applications, having encouraging in comparison with current industrial insulation boards. The kenaf core appears to be a potential raw material for low-density panels suitable for sound absorption and thermal resistance or corkboard-type products, (Sellers, Miller, Fuller, 1993). The structural properties of kenaf medium-density particleboard when utilizing different binders are shown in Table 3.

Table 3: Properties of Kenaf Medium-Density Particleboard:

RESIN TYPE

RESIN LEVEL (%)

DENSITY (PCF)

IB (PSI)

MOR (PSI)

MOE (KPSI)

PF

10

44

72

1675

3650

MDI

10

31

88

1035

2517

UF *

10

51

109

2800

5407

* Board made with kenaf core and southern yellow pine face. Source: Bledsoe, 1996

 

Hemp Board Properties:

One example of hemp's application in composite materials is from the sole particleboard plant in Hungary. This facility exclusively uses decorticated hemp core that primarily comes from the sizable Hungarian hemp textile industry. The three-layer particleboard shows distinct stratification of each layer. One notable flaw in the particleboard sample was the extensive proportion of oversized particles, commonly known as shives, in the face. These shives appear to result from lower quality raw material preparation equipment, such as hammermills, as opposed to inherently poor quality raw material. Plant management hopes to improve the capital equipment and process as soon as sufficient funds are available.

Our initial research and testing began by considering the performance of bast fibers in an MDF application. The bast fiber from hemp was first pre-chopped followed by atmospheric refining. An MDI binder was then added to make a traditional prototype. In the initial testing 4 -6% of the MDI was applied. While this level of MDI is high for a production operation, it is typical for most materials in this stage of product and process development. The performance of some of these sample boards is shown in Table 4. As you can see, the properties of these samples generally meet and often exceed the ASTM standards for MDF. This demonstrates the performance viability of bast fiber in such composite applications.

Table 4: Properties of Hemp MDF:

 RESIN TYPE

RESIN LEVEL (%)

DENSITY (PCF)

IB (PSI)

MOR (PSI)

MOE (KPSI)

PF

8

51

30

1130

-

UF

14

55

85

3010

-

MDI

6

50

97

4020

-

 MDI

6

48

147

3190

438

 MDI

6

45

91

4310

541

MDI *

6

47

131

6310

575

* 50/50 mix hemp fiber + wood fiber. Source: WSU, WMEL, 1991-1995.

Equipment Manufacturers for Bast Core Panel Boards:

Verkor, of Belgium and Siempelkamp, of Germany, have played a major role in providing appropriate processing equipment and technology to produce particleboard from core material. Polish and perhaps other East European manufacturers have produced plant equipment as well.

Economic Viability for Particleboard and MDF Furnish:

At this time, most of these bast fiber crops have not yet enjoyed the concerted genetic and (agricultural) horticultural development to maximize their potential for bast fiber yields. Consequently, the decorticated bast fiber generally sells for $250 - $500/ bone dry ton. Until further plant development and harvesting efficiencies are realized this material is too costly for such a furnish-based application.

The use of the core does hold some potential for composition board raw material as its cost can be lower than the bast portion. Traditional harvesting and processing techniques offer poor retrieval efficiency of the core. The more efficient harvesting and decortication techniques used in kenaf provide much greater efficiency in core collection and separation. In the warmer regions of the United States and farther south, the productivity of kenaf appears sufficiently high that economical use of either the core, or, more likely, of the entire stalk as a furnish base for particleboard or MDF.

Fiber Crop Supplements to a Strawboard Facility:

Another approach to enhance the capacities of such a plant would be to supplement the straw raw material base with a crop especially bred to provide fiber bundles of large yields and possessing attractive characteristics for use in composite products. Thus, land would need to be dedicated, probably on a rotating basis. If land which the USDA has placed in the Set Aside Program were used for the development of a fiber crop, this would be a prudent way to save tax dollars, while also improving the economies of scale for a strawboard plant. The flax industry in Canada is actively improving their technology, and has the best developed infrastructure to serve the composite industry at this time.

Bast Panel Conclusions:

A series of issues exist which may preclude the potential use of a kenaf, hemp, or flax in furnish-based panel applications at the present time. The lab prototypes mentioned in Tables 2, 3, and 4, however, demonstrate the technical feasibility of using these fibers as a either supplement or substitute to wood in providing panels having well accepted physical characteristics.

Tests conducted at Mississippi State University show good success using kenaf as 100% furnish for low-density boards, (Sellers, 1996). Perhaps ceiling tile applications may be well suited for such a product. Turning to MDF, the primary performance categories such as S.G., (Specific Gravity), I.B., (Internal Bond), MOR, (Modulus of Rupture), and MOE, (Modulus of Elasticity) for flax and hemp are all well within accepted parameters for wood-based particleboard or MDF. With pressurized refining, surface quality was acceptable as well. The bast-based panels are of different shades of tan than wood. The color was slightly darker than that of wood for some samples of hemp, and was lighter for other samples of hemp, and all those of flax. In any case, this difference is minor, and may be used as a distinctive marketing feature. Naturally, this difference decreases as the percentage of wood furnish increases. Furthermore, wood could be used on the faces with no problems with compatibility.

Use of the whole stalk of bast material may be necessary to provide sufficiently high performance characteristics for the bast material. The value in using the whole stalk is further strengthened by the fact that the both Eastern and especially Western Europeans have minimized the use of only flax core as a furnish material. The whole stalk appears a more promising option for furnish in light of its improved performance characteristics. The whole stalk must be competitive in terms of raw material costs, however, some cost may well be saved by removing the decortication step from the processing of the whole stalk.

At this point, kenaf appears most economically viable as a potential furnish. Further genetic development in yield productivity show promise in expanding the commercial economic viability of both kenaf and hemp, and possibly flax. In summary, the bast plant materials show favorable technical viability for panelboard products.

TENSILE STRENGTH:

In our initial testing we became aware of the strength of the fiber bundles of the bast fibers. Table 5 illustrates the fiber bundle tensile strength properties of the various bast fibers are significantly higher than those of wood species. (Douglas fir, Southern Pine, Aspen vs. Hemp, Kenaf, Flax). In light of this issue, higher structural applications appear the most promising. This value is an excellent measure of the structural performance we can expect in a particular size and configuration of a product.

Moreover, Table 5 also indicates desirable Length/Diameter Fiber Ratio's, and Table 1 shows relatively high cellulose contents along with lower hemi-cellulose portions. These may also contribute to the favorable structural characteristics including MOE.

 

Table 5: Comparative Mechanical/Physical Properties of Bast and Wood Materials:

 FIBROUS MATERIAL

 DENSITY (g/cm3)

 LENGTH (mm)

DIAMETER (um)

 L/D RATIO

TENSILE STRENGTHS (psi)

 FIBER

BUNDLE

RANGE

 AVG

RANGE

AVG

 FLAX

1.51

1.2

10 - 65

32

10 - 25

18

1,778

51,000

KENAF (bast)

-

1.2

1.4 - 5

2.6

14 - 23

21

124

58,000

KENAF (core)

0.31

-

0.4 - 1.1

0.6

18 - 37

30

20

-

HEMP

1.48

1.2

7 - 55

25

13 - 30

18

1,087

118,000

S.Y. PINE

0.51

-

2.7 - 4.6

3.7

32 - 43

38

97

11,600

D. FIR

0.48

-

2.7 - 4.6

3.7

32 - 43

38

97

15,600

ASPEN

0.39

-

0.7 - 1.6

1.2

20 - 30

25

48

7,400

Sources: Wood Handbook; Danforth International; W.S.U., WMEL; Columbus, 1996, Institute of Natural Fibers, U.S.D.A., A.R.S.; The BioComposite Center.

 

PRODUCT DEVELOPMENT DIRECTIONS:

In light of the strength properties of bast materials, which directions and strategies are best to pursue? Ultimately, should bast fibers be developed for use in a more conventional, established product such as particleboard or MDF; and if so, which one? In this arrangement, we believe the unique properties of the bast fibers would not be utilized to their greatest extent. Should we pursue instead a course in which the bast fibers' special characteristics, namely its strength and to a lesser extent its toughness, are strongly utilized to their greatest benefit. This more innovative course presents a new series of challenges and questions difficult to answer at this time. Erwin Lloyd and associates including Paul Skillicorn and David Seber are considering these options and have developed some proprietary developments. Those interested in such pursuits may contact Erwin Lloyd at (360) 734-4240 for additional information.

The Advantages of Bast Fibers:

Approaching product development efforts from the perspective of the characteristics of the material, bast fibers' primary assets appear to lie in the following areas:

1. The vigorous competitiveness and limited care necessary to grow bast plants.

2. Potentially high productivity per acre per year.

3. Long, strong fiber bundles.

Item 1 already exists and does not require much attention. Item 2 probably will require more time to fully develop, and are in an area apart from our expertise and less directly affect the area of product development to pursue. Item 3, the bast plant's long, strong fiber bundles, however, are a crucial issue, especially in light of the need to choose directions for product development efforts.

Pultrusion/Extrusion Composite Technology:

Other applications, particularly pultrusion, are viable. Cordage is an area in which some bast fibers, especially jute, sisal, and hemp, has historically been strong. Consequently, pultrusion with its use of thread-like material is especially applicable to these fibers. Cordage machinery having a spectrum of sophistication and associated processing costs is available to convert these bast fiber bundles into the appropriate form for such pultrusion products.

French textile data indicates the specific strength that is the strength to density ratio, of the bast portion of textile flax is comparable to that of carbon fiber, although the E-modulus is considerably less. The specific strength of the bast fiber flax is 23% greater, and also 18% greater in E-Modulus than E-glass fiber, (Bolton, 1990). Germany has invested large sums of money into flax research over the past six years, (Domier, 1996). This country now appears poised to shift to extensive research into hemp with the recent legalization of this fiber crop.

The BioComposites Centre at The University of Wales, Bangor, United Kingdom has also begun to research the viability of bast fibers for high end structural composite applications as substitutes for man-made fibers. According to their initial research bast fibers provide "strong, low-cost, lightweight alternatives" to synthetic fibers. Such plant fibers also have the advantage of a very reactive surface chemistry and a high work of fracture of over 104 J/m2. Moreover, these fibers are renewable, recyclable, or can be combustible to allow recovery of their energy content unlike glass fibers. Such bast fibers also offer reduced tool wear and safer handling and work conditions.

Wood fibers offer the advantage of being uniform, quite inexpensive, readily available, and well known, along with the disadvantage of being short, (mean fiber length of 2.7 mm). Bast fibers are relatively inexpensive, and offer either long individual fibers or long fiber bundles; however, these plant fibers lack a heterogeneous cell structure. Development efforts stem from the agricultural community seeking higher value crops and industry in developing less expensive raw materials, (Bolton, 1990).

A major German automotive manufacturer also is reported to have developed products for automotive interiors that utilize bast fibers. At this time, little information has been released regarding their development efforts.

COMPARISON OF FIBER FROM TREES TO OTHER PLANT SPECIES:

One perspective to consider is the issue of quantity, quality, and growing expenses of various fiber-producing plants compared to particular tree species. Both the productivity and tenacity of kenaf, hemp, and any tree species are generally inversely related to one another on a continuum. Oil-seed flax is relatively sensitive, yet also low yielding in its fiber. This type of flax, however, is a residue that effectively puts it in a different category relative to kenaf and hemp fiber crops. Considering for a moment only kenaf, hemp, and trees, in warmer regions, kenaf has the higher productivity, yet it is the most delicate and most susceptible to damage and requires higher maintenance in its cultivation. Trees on the other hand are much more durable and rugged; able to readily withstand both extreme and even extended changes in temperature and moisture availability, all with minimal cultivation. Trees, however, lack the potential productivity. Hemp is between that of kenaf and trees in all of these areas in the warmer temperate and sub-tropical regions. If we consider tropical regions, the dynamics change somewhat, with several other plants showing promising characteristics.

SYNTHESIZED SOLUTIONS:

As we seek the best and most viable raw materials and resulting products, some of the best answers may rest in a combination of several types of raw materials. One newer raw material could be the supplement for an existing raw material such as the use of straw to supplement wood in the Willamette Valley of Oregon. Likewise, a bast fiber plant could supplement a strawboard plant. Such a material could provide increased production through a more concentrated quantity of material while enhancing some of its physical and structural characteristics. This approach may involve a more complicated raw material sorting, refining, forming, and bonding system, although it may not be that difficult. One illustration of where this combining is occurring is the engineered I-beam in which OSB is used as ribbing and LVL as flanges; another example is ComPly utilizing a veneer face and a particleboard core.

FIBER SHORTAGES:

A number of existing plants are currently experiencing shortages in their supply of fiber. When such plants can only operate five rather than seven days a week, managers are painfully aware of the additional start-up costs and more importantly the lost potential profits from a process designed to be continuous. The incorporation of some of these agricultural crops could readily supplement their current fiber supply. Many more plants could readily increase their throughput through further incorporation of mat conditioning technology, or faster curing binders, however, their current fiber supply restricts them from taking advantage of these improvements. Again, supplemental agricultural fibers could fill this need. A transitional period of accommodation would be necessary, as a plant would make the technical adjustments necessary to utilize this new material. A sufficient foundation, however, has already been laid by research universities and other organizations to allow for the speedy acclimation of these alternative fiber crops.

PRODUCT CATEGORIES OF BAST MATERIALS:

Bast materials offer distinctive and valuable characteristics for certain applications. A summary of these applications is listed in the following sections.

Whole Stalk Applications:

1. Particleboard, probably better suited for kenaf.

2. MDF, probably better suited for kenaf.

3. Additional proprietary pursuits. (Contact Erwin Lloyd for additional information.)

Core Fiber Products:

The present market conditions allow for a premium to be realized for the core material when used as an animal bedding material, and especially as an absorbent material. Other potential applications including a corn starch substitute and as animal feed stock also may be realized. Several of these applications may well provide strong, higher value-added capabilities to the core material, thereby diminishing its opportunity to serve as a component in building materials.

Nevertheless, certain potential applications of the core material are possible. These include:

1. Low-density insulation boards.

2. Ceiling Tiles

3. Substrate for lightweight furniture.

4. Components in manufactured housing.

5. Office partitions.

6. Core materials for doors.

7 Possibly particleboard and MDF.

Bast Fiber Applications:

1. Reinforcing Fibers to other Materials such as Concrete, Wood, or Straw

2. Pultrusion Products

3. Reinforcements for Thermoplastics

4. Insulation

5. Additional proprietary pursuits. (Contact Erwin Lloyd for additional information.)

 

PRODUCT CATEGORIES OF BAST MATERIALS:

As one reflects upon all of the different raw materials and types of products that can be produced, five categories of alternative materials come to mind:

1. Cementitious products. Cement and lime of a proper pH mixed with a bast material. Testing and production from Europe demonstrate a high strength, lightweight material may be developed.

2. Specialty applications that service a niche market. Higher cost products can be viable due to their unique applications. One example is "Environ," from Phenix Bio-Composites, a granite substitute composed primarily from soybeans and recycled-newsprint.

3. Inexpensive residue that may be refined into small particle sizes and made into particleboard, or more likely MDF. The product from this material will have a smooth finish. The material may exist as a small particle, as in the case of sawdust, and it need not possess a great deal of strength. Examples would be sawdust, shavings, and pin chips from wood, straw, corn stalks for cornboard, and possibly whole stalk and core fibers.

4. Fast growing and especially low value species, such as aspen, derived from wood possessing a moderate amount of strength for use in products of intermediate structural application such as oriented-strand board, OSB.

5. Raw materials having very high strength fiber bundles for use in demanding structural applications. Such an example would include bast fibers, including kenaf, flax, and hemp, used in high-performance applications.

SUMMARY:

In terms of inexpensive materials for the MDF and particleboard markets, residual wood products appear to hold the greatest potential. Such plants have overcome their technical obstacles to produce a product of very good quality having low raw material costs. Other products such as strawboard and products made from recycled urban waste may gain a similar position. The ability of any of these products to overcome technical challenges and economic disadvantages listed previously, however, has not yet been conclusively proven.

Kenaf, hemp, and flax all have physical fiber characteristics that may well make it viable for demanding structural applications. Nevertheless, specific agronomic conditions must be carefully evaluated to ensure that kenaf inherent sensitivities are not too detrimental for a particular application.

CONCLUDING REMARKS:

A number of viable alternative materials for composite material applications do exist. Some have been tested and used more thoroughly than others. Often much of this testing and experience is from overseas. These alternative materials do pose certain limitations and they require a certain degree of adjustment in the equipment to accommodate their use.

These materials, when properly selected, however, do hold meaningful promise as either primary or secondary raw materials for a composite facility. The physical properties of agricultural products are sufficiently broad that these materials may be used as possible binding agents, and as low-cost materials for MDF or particleboard.

Bast plants can provide competitively low-cost material suitable for particleboard and MDF applications. Furthermore, the desirable combination of physical, mechanical, and chemical aspects lend the bast fiber plants quite well to high-end structural composite applications. Exciting and profitable opportunities await those who pursue these applications further.

ADDITIONAL INFORMATION:

For further information on these and other related subjects, you may contact the author at the following address of Fibre Alternatives/BioComposite Solutions:
Erwin Lloyd
Director
BioComposite Solutions
2408 Kentucky Street
Bellingham, WA 98226-3998 USA
(360) 734-4240 - Tel
(530) 618-6984 - Fax
E-mail: biocomp@home.com

ACKNOWLEDGMENTS:

We thank Tom Maloney, Marty Lentz, Mike Wolcott, Roy Pellerin, and the entire staff of the Washington State University's Wood Materials and Engineering Laboratory for their gracious support and assistance of this ongoing work. In addition, we also wish to thank William Conde and David Seber of Conde's Redwood Lumber, Daryl Eherensing of Oregon State University, Agricultural Extension Office, David West of GamETec, and Frank Riccio Jr. and Richard Cook of Danforth International Trade Associates Inc.

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