BULETIN TEXTILE.COM/ Jakarta – For industry players, we are familiar with various types of fiber, one of which is carbon fiber.
Carbon fiber is one of the technical textile fibers. As the name implies, carbon fiber is composed of an arrangement of carbon atoms. The carbon atoms are bound in a crystalline structure which has a degree of orientation parallel to the fiber axis.
What makes this carbon fiber special is its high working properties, such as resistance to chemical degradation, heat resistance, low thermal expansion, and excellent tensile strength. Another prominent property of this fiber is that carbon fiber has very high fiber strength to weight ratio.
Carbon fiber has high strength with light weight. With these properties, this one fiber is often used as a material for making composites and reinforcing materials in technical textiles. Carbon fiber has a strength in the range of 5000 MPa, with a modulus of up to 250 GPa and a volume density of 1.76 gram/cm3.
One well-known application of carbon fiber is its use in the manufacture of composite panels for aircraft parts. Carbon fiber has made it possible for engineers to obtain a material that is both strong and light at the same time.
What Is Lignin?
Lignin or wood substance is one of the constituent components of plants. The composition of these constituents varies depending on the type. Lignin mainly accumulates in the stems of trees and shrubs.
In stems, lignin functions as a binding material for other constituent components, so that a tree can stand upright (like cement on a concrete rod).
In contrast to cellulose which is formed from carbohydrate groups, the chemical structure of lignin is very complex and does not have the same pattern. The aromatic group is found in lignin, which are interconnected by aliphatic chains, which consist of 2-3 carbons.
Availability of Lignin in Industry
Environmental impacts and air pollution caused by petroleum-based fuels have prompted the need to develop alternative renewable fuel resources. Bioethanol is a renewable alternative fuel resource obtained from non-fossil sources.
It is a form of renewable energy that can be produced from agricultural raw materials, which can be made from very common crops such as hemp, sugarcane, potato, cassava and corn.
In the process of extracting cellulose to convert it into bioethanol (a bio-based gasoline additive), lignin is produced in large quantities as the main by-product (process waste material) – which actually has the potential to be used as a feedstock in sustainable material processing applications.
In addition to the bioethanol process, lignin can also be obtained as a waste material in the paper pulp industry production line.
Even so, the lignin obtained from the rest of the production process in the industry cannot be used immediately, but it still has to go through the washing and purification stages to remove the rest of the chemical substances and contaminants it contains.
Lignin Material and Carbon Fiber Production
The need for carbon fiber is increasing along with technological developments and the application of carbon fiber in the world of composites and other technical materials. The manufacture of carbon fiber is nothing new today. Currently, carbon fiber production processes have been carried out in bulk using synthetic fiber-based raw materials made from PolyAcryloNitrile (PAN) polymers.
Polyacrylonitrile itself is a polymer product derived from petroleum products. In addition to PAN raw materials, carbon fiber can also be produced with raw materials in the form of rayon fiber. Currently, around 90% of carbon fiber on the market is mostly produced with synthetic fiber raw materials made from PAN. Carbon fiber produced through the PAN raw material process has advantages in terms of quality and strength.
Based on this, to this day the production process of carbon fiber with PAN raw materials is still mostly carried out by manufacturers in the world. Broadly speaking, the total costs that contribute to the price value of carbon fiber are the cost of raw materials and the cost of the carbonization process that is carried out.
Therefore, researchers around the world are currently focusing on studying the search for renewable raw materials that are cheaper and more cost-efficient processes to produce carbon fiber. Lignin chemically has an aromatic carbon ring structure in its molecule (with a carbon content value of 60-65%). This makes lignin a potential candidate for use as a raw material in carbon fiber production, both in terms of its chemical characteristics and in terms of its availability.
If lignin from industrial process residues can be used as a raw material in the carbon fiber manufacturing process, then the resulting carbon fiber can have a higher sustainability aspect.
Carbon Fiber Production with Lignin Raw Materials
Production of carbon fiber with lignin biopolymer as raw material can be done in several techniques. However, in general it includes several stages, including (1) the process of forming raw material fibers through the spinning process, (2) the oxidative stabilization process and (3) the carbonization process. The process of forming fibers is carried out to form fibers from lignin material. The forming process can be carried out using melt spinning or wet spinning.
Furthermore, the fiber is subjected to thermal treatment until the carbonization process occurs at a very high temperature of 1000oC with an inert atmosphere of nitrogen gas. This series of processes will then produce carbon fiber with its distinctive color, which is black.
Although the production process of carbon fiber with lignin offers a fairly good sustainability solution, the fact is that the quality produced from this series of processes cannot compete with PAN-based carbon fiber. To overcome this problem, researchers from Izmir Katip Celebi University have succeeded in finding a way to improve the quality of this lignin-based carbon fiber. The innovative solution offered by the researchers is to mix PAN and Lignin together as raw materials for the carbon fiber manufacturing process.
Researchers revealed that carbon fiber made from pure lignin only ranges from 1-3 GPa. A mixture of lignin and PAN as a raw material in the manufacture of carbon fiber has succeeded in increasing the fiber up to 3.25 GPa. This is close to the quality of carbon fiber made from PAN with a strength range of 5 GPa. Although carbon fiber made from lignin – PAN has lower strength, raw material costs from the production process can be reduced by up to 75%.
This shows that carbon fiber made from lignin – PAN has a much greater economic value by utilizing residual production waste that has not been used.
(Red B-Teks/Andrian Wijayono)