Polymer Matrix Composites Reinforced with Natural Fibers

Turkchem 02 May 2018 95 7 dk okuma

TURKCHEM

Abstract

Physical and mechanical test results for innovative coconut/polyester and coconut-glass fiber/polyester sandwich structures were investigated, as well as the advantages of using woven glass fiber as external layer reinforcement.

Introduction

Natural fibers are sustainable resources that can be grown in short time periods. Therefore, compared to carbon, glass and other synthetic fibers, natural fibers can provide unlimited source materials for the production of polymer matrix composites. 1,2 To date, numerous studies have been conducted on the use of natural fibers as reinforcing elements in composite materials.3-5 Natural fibers are classified as lightweight materials due to their low density, which is a significant advantage. 6, 7 However, composite materials reinforced solely with natural fibers have insufficient mechanical properties. The optimal solution for addressing both economic and environmental problems is the combined use of natural fibers with synthetic fibers in composites. Figure 1. (A) Sandwich-structured composite with non-woven fabric made of coconut fiber in the interior and polyester on the exterior (B) Glass fiber structure forming the outer part of the composites (C) Schematic diagram of composites containing non-woven fabric made of varying amounts of glass fiber and coconut fiber used in this study. The composition of the composites is explained by the initials of the structures it contains. For example; the letter C represents coconut fiber, and the letter G represents glass fiber. (D), (E) Photographs taken during the vacuum-assisted resin transfer molding process of fibers made from coconut and glass fibers Composites reinforced with natural fibers find application in products where low cost is required, the automotive industry, and low-cost construction.3,8 To date, a wide variety of natural fibers (coconut fiber, sisal, jute, ramie, pineapple leaf, kenaf, abaca, palm, bamboo, palm tree, banana, hemp, flax, rice husk fiber, and cotton) have been used in composites. These composites are intended to replace steel or synthetic fiber-reinforced composite materials. 9–12 This study aimed to examine the mechanical properties of sandwich-structured composite materials. The sandwich structure in question uses coconut fibers in the interior and glass fibers on the exterior. 13 To investigate the effect of the produced sandwich structure on mechanical properties, the mechanical properties of polyester matrix composite containing only coconut fibers were compared with sandwich-structured polyester matrix composite under the same conditions. The obtained results are expected to be decisive regarding the use of polyester/coconut fiber/glass fiber composite product in final applications. Coconut fiber is a lignocellulosic fiber used in a wide variety of agricultural and horticultural applications. These fibers are particularly obtained from the shells of coconut palms grown in tropical regions.14 The reason it is the focal material of this study is that it has advanced properties as a reinforcing element for composite materials. For example, due to its high lignin content, it is more moisture-resistant compared to other fibers.15,16 To explain in more detail, coconut fibers contain higher lignin content (40-45%) and lower cellulose content (32-43%) compared to other fibers, and this gives them high moisture resistance.15 Coconut fibers are typically 10-30 cm in length and therefore have a high length-to-diameter ratio. Additionally, the 450 spiral arrangement of microfibrils allows coconut fibers to stretch more beyond their elastic limits without breaking.17 For the sandwich composites in Figure 1, non-woven fabric made of coconut fiber was used in the interior. Specimens were produced using vacuum-assisted resin transfer technique. To determine the mechanical and physical properties of coconut/polyester and coconut-glass fiber/polyester composites, reinforcement ratio, resin ratio, basis weight, and thickness were measured. Physical test results showed that for coconut-glass fiber/polyester sandwich structures, thickness variation, water absorption, and moisture content generally have lower values compared to coconut/polyester composites (Figure 2). In mechanical tests, tensile strength, open hole tensile strength, and flexural strength were measured for all specimens. Coconut-glass fiber/polyester sandwich structures (70 MPa) exhibited significantly higher tensile strength compared to coconut/polyester composites (8 MPa).Figure 2. Water absorption properties and mechanical performance of coconut-reinforced sandwich composites. (a) tensile modulus and open hole tensile modulus, and after 2, 24, 48, and 96 hours (b) thickness change and (c) water absorption. The experiments demonstrated that using woven glass fiber as the external layer in coconut/polyester composites significantly improved mechanical and physical properties. For example, after 96 hours, the thickness change of the specimen decreased from 13.3% to 1.85%. Similarly, water absorption and moisture content were reduced. Conversely, the tensile strength, tensile modulus, and flexural strength of the composites increased substantially with the use of woven glass fiber as the external layer. These increases ranged from 4.2 MPa to 69.2 MPa for tensile strength, from 2 GPa to 6 GPa for tensile modulus (Figure 2(a)), and from 31.8 GPa to 131.5 MPa for flexural modulus. The increase in flexural strength can be explained by the I-beam concept. Under bending load, the flanges in an I-beam structure carry tensile and compressive loads. This condition resembles the effect of the external layer in the sandwich composite and carries shear stresses in the internal layer. Thus, bending rigidity increases.

Conclusion

In summary, in this study natural coconut fiber was used as an innovative reinforcing element in polymer composites. Furthermore, physical and mechanical properties were examined for the produced coconut/polyester and coconut-glass fiber/polyester composite structures. The results showed that coconut-glass fiber/polyester specimens have significantly higher tensile strength compared to coconut/polyester specimens. Additionally, the properties of both composite structures were substantially improved through reinforcement with woven glass fiber as the external layer. Thus, innovative natural fiber-reinforced composites were found to be suitable for different application areas (such as construction, automotive, and furniture industries). In the coming period, it is planned to increase the ratio of natural fiber reinforcement and to use natural material as resin in composites with coconut reinforcement. Assist. Prof. Dr. Ali Kilic - Faculty of Textile Technology and Design - Istanbul Technical University Dr. Tamer Hamouda - Textile Research Department - National Research Centre Dr. Ahmed H. Hassanin - Department of Textile Engineering - Alexandria University Assoc. Prof. Dr. Zeki Candan - Department of Forest Products Engineering - Istanbul University