A technology for manufacturing a reinforcement (strengthening) composite from a waste coconut leaf sheath (CLS) has been uncovered by an international research team from Russia, India and Thailand. Due to its lightness and strength, it can be used to cover autobahns, create interiors for railway cars and airplanes. Also, it can be used for domestic needs.
Natural fibers – coconut, sisal, coir, jute, banana, hemp, bamboo – are increasingly in demand in the industry due to their high mechanical strength and stiffness, excellent thermal stability and corrosion resistance. Use of these natural fibers are increasing to replace synthetic fibers as a cost-effective, affordable and environmentally friendly solution.
King Mongkut’s University of Technology North Bangkok jointly with the NUST MISIS Department of Engineering of Technological Equipment conducted the study on green composites. The leading scientists from Thailand are Dr. Sanjay Mavinkere Rangappa, Senior Research Scientist at KMUTNB, and Prof. Dr. -Ing. habil. Suchart Siengchin, President of KMUTNB.
“The superior properties of composite made of natural fibers are driven especially by a good interfacial bonding at the interface of fiber and matrix. To obtain it the natural fibers, which belong to hydroxyl groups containing lignin and cellulose are generally chemically modified. By using chemical or surface modification, it is possible to improve the degree of interlocking of at the interface of fiber with a matrix, which results in excellent resistance to failure of the materials,” said Sergey Gorbatyuk, Co-author of the study, Professor of the Department of Engineering of Technological Equipment at NUST MISIS.
Coconut fiber composites with 60% and 40% phenol formaldehyde were made by hand lay-up technique followed by compression molding ad the study was carried out by testing tensile, flexural, impact strength, as well as measuring the rate of water absorption and biodegradability characteristics.
According to the developers, the results confirm the superior mechanical properties of the green composite compared to natural coconut fiber are driven by the low content of hydrophilic hydroxyl groups and reduced impurities.
To optimize the technology two types of fibers – untreated and mercerized – treated with a concentrated solution of caustic soda (which is the most common alkali) and washed with hot and cold water. The mercerized composite samples showed an elastic modulus of about 45–60% and a 30–40% higher tensile strength compared to the untreated sample. This is due to the formation of a special rough surface on the fibers as a result of processing, which provides a better arrangement of the fibers and adhesion to the matrix.
The study showed clearly that the created composite is a good candidate for domestic and industrial applications in the decoration of cabins and railway cars, highway construction, in commercial interior design as environmental wall and floor coatings.
In Russia, developers plan to adapt the technology using flax, hemp and nettle fibers as raw materials.