Extraction and characterization of indigenous Ethiopian castor oil bast fibre

Bast natural fibers have gained importance in the recent years mainly due to their ecofriendliness and their potential availability as raw materials for textile industries. In the present study extraction and characterization of fibers from the stem of Ethiopian indigenous castor oil plant is conducted for possible utilization in textile and related industrial applications. Among the different fiber extraction methods chemical retting using aqueous alkaline media (NaOH) is used for the extraction of the bast fiber. In this study the extraction was carried out by setting appropriate retting conditions of concentration of alkali, temperature and time. The extracted fibers for experimental analysis under the combined conditions were tested for chemical composition, gross morphology, mechanical and thermal properties. The analysis on chemical composition revealed that the castor oil bast [COB] fiber is composed of 64.5–67.3% cellulose, 16.4–21.5% hemicellulose, 15.8–17.2% lignin, 0.3–0.9% extractive with 4.9–5.3% ash content. FTIR spectra of the extracted fibers also confirmed the presence of cellulose, hemicellulose, lignin and extractives. Analysis on dimensional characteristics of the fiber showed that the extracted fiber has a diameter of 14.2–30.8 µm and fineness of 4.5–13.5 tex with fiber length ranging from 1.3 to 10 cm; the moisture content and moisture regain of the fiber are 7.0–9% and 8.1–10% respectively. Tests on mechanical properties of the extracted COB fiber show a tensile strength of 250–700 MPa with tenacity in the range of 57.80–86.89 cN/tex, elongation of 1.2–5% and elastic modulus of 2114.55–2625.44 cN/tex. TGA results for thermal property analysis indicated that the COB fiber has very good thermal stability with a thermal decomposition temperature in the range of 386.5–498.9 °C. The reasonably high cellulose content, good dimensional and moisture characteristics of COB fiber and its very good mechanical and thermal properties in comparison with conventional natural fibers such as jute, flax, hemp and cotton indicate the possibility for versatile conventional and non-conventional applications of COB fiber such as in textiles and in fiber reinforced composites.