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Biobased Building Materials


Today increasing attention is turning to biobased building materials, which offer lightweight strength and are a renewable resource, able to deliver material where and when it is needed. The best-known biobased building material is clearly wood, although it is a resource renewable only over decades, or even centuries. Other, less familiar, biobased materials are beginning to play an important role in the building materials market, because they are rapidly - even annually-renewable. In the field of biobased building materials the ideas of sustainable agriculture and environmentally responsible building converge. The future for biobased building materials is bright, and several new agricultural fiber-based building materials are already making their mark on the building industry.

Building materials derived from plants aren't a completely new idea. Fibrous plants like bamboo and thatch reeds have been either gathered or cultivated for centuries. Today farmers are turning attention toward cultivating crops specifically for their fiber. Two fibrous crops increasing in popularity because of their varied manufacturing applications and comparatively low-input production include industrial hemp and kenaf. Both plants produce long, strong fibers that can be used as reinforcement in composite materials. Although cultivation of industrial hemp is against the law in the United States, Canada now allows the crop, and there is increasing acreage in cultivation, as well as a growing market for hemp fiber.

Not only can useful fibers be derived from specialty crops, but they can also be obtained from the residues of crops already being produced - particularly from straw remaining after cereal grains are harvested. By one report, as much as 350 million tons of agricultural residue, consisting of stalks, straw and stovers, is produced annually in North America. Much of this material is currently burned or discarded, but applications are being developed to make use of this rapidly-renewable and abundant source of fiber

If you want to find agricultural fiber in a building product today, the first place to look is the fiberboard market, where innovative companies have been offering strawboard for the past several years. Fiberboard is typically manufactured in 4' x 8' panels that can be made not just from wood, but also from a range of plant fibers such as wheat straw, industrial hemp, grass stems, sugar cane bagasse, sunflower seed hulls or cornstalks. The fibers are bonded under heat and pressure with a resin binder to form panels used in cabinetry, shelving, furniture, countertop substrate, and flooring underlayment.

In the past few years the number of agricultural fiberboard producers in North America has increased rapidly, and more plants are planned for the coming years. World leaders in panel equipment are now offering specialized technology for handling agricultural fiber. Their interest stems from worldwide attention turning to agricultural residues as possible substitutes for diminishing or inaccessible wood supplies.

Agricultural fibers also hold promise as reinforcing fibers within composite materials. These composites, especially those that contain recycled plastic, can be extruded into shapes with a variety of construction uses, from furniture to window frame parts. One company already offers a recycled plastic lumber containing rice hulls for use in decks.

Other crops have strong market potential not for their fiber, but rather for their chemical composition. One of the most versatile of these is the soybean. Soy-based products for construction include water sealants for concrete and biodegradable concrete form release agents, as well as soybean oil paints and solvents.

Soy is also playing an important role in adhesives for engineered wood products. The United Soybean Board funded research for soy-based adhesives that led to a soy adhesive that can fingerjoint green or dry wood. Soy adhesives reduce formaldehyde and are likely to cost less than conventional resin binders now used in construction products.

Even as known uses for agricultural fiber crops and residues become better established in the building material market, additional new uses are emerging. As one example, research in California identified potential benefits from using rice hull ash as an additive to fly-ash cement. In another effort, researchers are reported to have created rigid urethane foam from soybean oil, of the type that could be used for building insulation. Additional research has shown that milk unfit for consumption can be recovered for use in paint. These products begin to provide an idea of the significant impact that agricultural products could have on the building material market.

CRBT is a project of the National Center for Appropriate Technology, NCAT. CRBT is dedicated to promoting environmentally responsible practices in construction