Study of the Properties of Rosella Hibiscus sabdarriffa L Fibers as a Reinforcing Component and as a Structural Material

Abstract

This research studied the feasibility of using Karkade (Roselle), an agricultural waste with glass fiber as hybrid reinforced polymer composite material and using Karkade fiber alone as structural material. For that purpose, the research contains four parts. The first part refers to the extraction method and characterization of Karkade fiber. In this part the fiber was extracted using water retting process with different duration times (15 to 30 days). The second part refers to characterization of Karkade fiber as a reinforcement material in terms of its physical, thermal, morphology and chemical properties. In this part, the Karkade fiber had been compared to other established natural fibers, such as Kenaf and Jute. The results obtained indicated that the chemical composition of Karkade fiber contained 67.6% cellulose, 12.27% hemicellulose and 12.21% lignin which are comparable with the composition of other established natural fiber. The water absorption and moisture content were found to be 70.43% and 1.26% respectively. These percentages showed superiority compared to other natural fibers. The density of Karkade fiber was found to be 1.56 g/cm3 which is close to the density of cotton fiber from the same family of Karkade. The diameter of the Karkade fiber was measured using scanning electron microscope. The results varied between 110μm and 149μm. This appears to be slightly higher than the diameter of other natural fibers. In morphology analysis there were a lot of bur in the structure surface with impurities that may be due to use of untreated fibers. Again, the structure of Karkade fiber appears to be the same as that of other natural fiber. In thermal analysis, the decomposition of Karkade fiber component happened between 220°C-600°C with two peak temperature points 350° and 425°C. The results proved that, Karkade fibers have good thermal properties that enable their use in composite fabrication. The third part of this research evaluated the mechanical properties of hybrid Karkade/glass/polyester composite. The composite was prepared using different fiber contents (0%, 5%, 7.5%, 10% and 20%) weight, as well as without fiber (neat polyester). Generally, the use of hybrid Karkade /glass / polyester composite showed an improvement in tensile and flexure strengths. The highest tensile and flexure strengths were achieved at 15% wt. of glass fiber with 5% wt. of Karkade fiber. This may be due to good interfacial bonding between fiber and matrix. However, decreasing strength values were observed with other percentages. Further, Karkade composite showed improvement in mechanical properties compared to the neat polyester. The fourth part of this research investigated the use of Karkade natural fiber in engineered cementitious composite (ECC) in terms of mechanical and physical properties as well a visual study of the ECC ductility. Taguchi method was used to determine the parameters controlling the mechanical properties of ECC. Based on Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) based Taguchi method the optimum experiment parameter was cement sample3 (CS3) because of its value of overall performance coefficient was the closest to the ideal solution 0.889, and the optimum parameters were A1 (2% of fiber content), B1 (0.6 W/C ratio) and C2 (40mm fiber length). Moreover, compared to optimum value obtained from (TOPSIS) based Taguchi experiments results, it can be seen that the compressive and flexure strengths increased by 28.37% and 47.93% respectively, while impact strength decreased by 18.53%. In density decreasing by 1.98% was recorded. It can be observed that there was significant effect of W/C ratio on compressive strength. Also, fiber content and fiber length had significant effect on flexure and impact properties of Karkade cementitious composite board. Furthermore, using of Karkade natural fiber in ECC improved the ductility of composite in flexure and compression and reduced the small cracks that occurred during flexure test. As a study being conducted for the first time in Sudan to find out the properties of Karkade fiber, it can be summarized that the results had shown that this fiber is a promising fiber in the field of composite as well as a structural material. Also, the use of this waste helps in reducing toxic gas emissions, which is positively reflected in enhancing the environment.