Heat resistant synthetic fiber Kevlar and its composites
Kevlar is a synthetic material created from a chemical known as poly-para-phenylene terephthalamide. Here, we discuss this strong and heat-resistant synthetic Kevlar fiber, its properties, limitations, applications, and recent relevant studies.
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What are composites?
Composites are heterogeneous materials made up of several distinct constituents bonded together, giving rise to better properties. These constituents are generally divided into two main categories: the matrix and the reinforcements. As the name suggests, reinforcements are the load or impact bearing components, while the matrix binds them together and provides a cushioning effect in some cases. The properties of a composite can vary from one part of the material to another, depending on the phase of the material, the shapes and alignment of the fibers, and the type of matrix-reinforcement combination used.
There are three main types of basic matrices: polymer matrix, ceramic matrix and metal matrix, while the reinforcement can be made of particles or fibers. Different combinations of these produce composites with different unique properties, hence the endless applications.
Composite materials with a high strength-to-weight ratio used in structural applications are best classified as high performance systems and often require regulated production parameters for maximum performance. Additionally, a composite can be specially designed to meet the precise mechanical requirements of each particular project, using different matrix-reinforcement combinations or varying the matrix-reinforcement ratio, resulting in much higher efficiency for applications. finals.
Natural, aramid, carbon and glass fibers are now the most widely used fibers, followed by polyester and nylon fibers. Short fiber reinforced epoxy resin composites offer interesting mechanical qualities. They are used in various industries including, but not limited to, friction materials, defense, aerospace, automotive, sporting goods, and chemical engineering.
What is Kevlar?
Kevlar pulp is a kind of short fiber with a high strength-to-weight ratio that is tough and resistant to impact loads. Kevlar is a brand of commercial fibers made up of para-aramids, which are strong, lightweight materials bonded to aramids like Technora and Nomex. It is often used in cotton fibers, textiles and fabrics or as an important component of composite materials.
The strong and weak bonds of the electronic system in the linear and lateral orientations of the polymer chains combine to give Kevlar (KF) fiber its yellow hue. Also, the fibers twist internally if they are bent into a loop. These specific fiber qualities are carried over into composites. For example, Kevlar-epoxy multilayer unidirectional fibers have lateral weaknesses while being linearly strong.
Limits of Kevlar
The production of poly-para-phenylene terephthalamide (PPTA) (Kevlar) is expensive. Other disadvantages of Kevlar include low compressive strength, sensitivity to environmental factors compared to other materials, and puncturing obstacles (special drill bits are required once it is rolled).
Properties of Kevlar
Kevlar has proven to be resistant to high temperatures as a fibrous polymer. However, it loses 10-20% of its tensile/tensile strength at high temperatures, which is lost again after a few hours. For example, it exhibits a 10% drop in performance at 160°C over 500 hours of continuous use, and 50% of its strength is lost in 70 hours at 260°C.
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Spun Kevlar produces fibers with a relative density of 1.44 and a tensile/tensile strength of approximately 3620 MP. The Kevlar structure includes relatively hard molecules that are often woven into flat webs. Kevlar is available in different forms which can be used alone or in combination with other fibers like glass and carbon fibers to create a composite, depending on the application. Kevlar fibers have low weight, high tenacity and exceptional thermal stability.
Carbonyl groups and nitrogen-hydrogen generate intermolecular hydrogen bonds. By stacking the interactions between neighboring aromatics, more resistance is created. The arrangement and orientation of links and chains create specific properties including excellent wear and friction resistance, very low creep, low thermal shrinkage, flame resistance and self-extinguishing, resistance high chemical resistance, high tear strength, low electrical conductivity, excellent dimensional stability, high modulus, good toughness, low elongation at break, high tensile strength and low weight.
In a study published in 2018, researchers investigated the effects of different matrix combinations on blunt trauma and energy absorption by Kevlar fiber reinforced polymer laminates. To test the Kevlar fiber reinforced polymer composites against a 9mm bullet, samples of the material were made using epoxy and varying percentages of rubber and epoxy.
Compared to pure fabric, Kevlar composites and Kevlar with different amounts of rubber exhibit distinct ballistic impact behavior and backside signature measurements. Test results indicate that adding rubber to the matrix has good effects on energy absorption, backside signature removal, and damage-causing mechanisms during ballistic impact events. .
Applications and conclusion
Kevlar is a durable, impact-resistant short fiber with a high strength-to-weight ratio. Para-aramids, which are strong and lightweight materials bonded to aramids, are the basis of this commercial fiber. It is frequently used to create cotton fibers, textiles and fabrics and to form an important part of composite materials.
Kevlar fiber reinforced polymer composites have been used for various applications in several industries. For example, they have recently been mainly used in the defense industry to make body armor and helmets. Different weave patterns are produced and stacked to create an excellent composite structure that can resist bullet penetrations and minimize impact. Additionally, compacted Kevlar fabrics are suitable for sheathing, reinforcement and fabric roofs of buildings as they are strong, lightweight and rigid. In addition, Kevlar and its composites are expected to play an important role in space applications in the near future to protect space shuttles and communication satellites from the impact of space debris.
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References and further reading
Al-Furjan, MSH, Shan, L., Shen, X., Zarei, MS, Hajmohammad, MH & Kolahchi, R. (2022). A review of manufacturing techniques and tensile properties of fiberglass, carbon and Kevlar reinforced polymer composites. Journal of Materials Research and Technology.
Jang, BZ (1992). Control of interfacial adhesion in continuous polymer composites reinforced with carbon fibers and Kevlar. Composites Science and Technology, 44(4), 333-349.
Pasha, RA, Nasir, MA, Anjum, NA and Sardar, HW (2018). Effect of rubber particles on polymer composite reinforced with kevlar fibers against high velocity impacts. Technical Journal, 23(1).
Kowsari, E., Haddadi-Asl, V., Ajdari, FB and Hemmat, J. (2019). From aramid fiber composites to innovative sustainable materials for biomedical applications. In Materials for Biomedical Engineering (pp. 173-204). Elsevier.