Natural fibers have been used in construction since ancient times for enhancing the properties of building materials. Coir, sisal, flax, straw, jute, and cane have been actively used due to their availability, physical and mechanical properties. In recent years, the innovations in the methods of enhancing physical and mechanical properties of the natural fibers allow to expand the applications in construction and replace concrete materials providing opportunities for sustainability.
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Understanding the hazards synthetic construction materials are causing to the environment results in the growing interest in the development of eco-friendly options. The commercial use of natural fiber in different industrial sectors has increased due to this tendency. Natural fibers are renewable, biodegradable, and efficient materials extracted from various sources. The low cost and weight of the natural-composite materials are essential factors for increasing the demand for them.
The properties of natural fiber building materials are modified and enhanced with the help of new technologies and approaches. The possibility of molding 3D shapes using natural fiber composites sparks particular interest in construction as well as other industries. Natural fibers are widely used to build roofs, rear walls, panel linings, and furniture. Hemp, sisal, jute, coir, plants, and animals are among the common sources used for the extraction of natural fibers.
Sources of natural fibers:
- Hemp is a plant about 1-4 meters high and 2 centimeters in diameter going through a particular mechanical process to extract the necessary core content and forming yarn or bundles. Hemp is frequently used for the production of composites, ropes, textiles.
- Cotton is an agricultural crop known to most for the application in the textile industries but also receiving ever-growing use for the composites in industrial applications.
- Kenaf is a plant cultivated for over 4000 years, used for the textiles, boats, ropes in ancient times. Today these fibers are made as composites for construction, furniture, and textiles.
- Ramie is a fast-growing plant about 1-2 meters high. Ramie fibers are utilized for the production of composites, furniture, and upholstery.
- Palm tree fibers category consists of coconut fibers, oil palm fibers, and date palm fibers. Coconut fibers are known for their insulation properties and durability, and date palm fibers for their increased water absorption.
- Cereal straw comprises wheat straw, barley straw, and oat straw and has a long-lasting history of being used for strengthening mud bricks. Improved resistance against fire and energy efficiency are among the main benefits of these fibers.
- Bamboo is an extensively available tree represented by over 400 species. Bamboo fiber is utilized for polymeric materials reinforcement, building houses, bridges, and oats.
Although the use of natural fibers in construction has a long history and numerous advantages, poor durability due to the natural origin, degradability and hydrophilic are mentioned as the disadvantages of such materials. To diminish these harmful properties, the improvements in the methods of treatment and coating help create natural fiber building materials for the new generation.
The treatments of the natural fibers enhancing their properties:
- Alkaline treatment to enhance thermal and mechanical properties by altering the structure of the natural fibers;
- Silane treatment provides high tensile strength;
- Acetylation treatment is applied to reduce the hydrophilic nature of the fibers by stabilizing the composites;
- Peroxide treatment is carried out after alkalization to enhance the mechanical properties of the cellulose fibers;
- Benzoylation treatment is applied to decrease the hydrophilic nature and raise the thermal stability of the fibers.