6. Fibers from Palm Trees

Palm trees are grown for oil in about 15 million hectares, and about 11 tons of dry mass are produced per hectare of palm grown. Cultivation of palm trees generates by-products called fronds (leaves) shown in Fig. 6.1, and about 164 million tons of fronds are estimated to be produced every year in the world [00Dah, 00Lin, 08Kha]. In addition to the fronds, the palm plants provide two additional sources of fibers. After harvesting the seeds, the fibrous empty fruit bunches (oil palm empty fruit bunch) (OPEFB) have been studied as potential sources for fibers. A kilogram of fruit bunch produces approximately 22 g of palm oil but results in about a kilogram of OPEFB [09Gun, 13Kit]. Similarly, the mesocarp left in the seed after squeezing for oil is also considered a source for fibers. On an average, about 400 g of fibers can be obtained from each OPEFB by natural retting [97Sre]. OPEFB fibers typically are composed of about 63 % cellulose, 18 % hemicellulose, and 18 % lignin. Natural cellulose fibers have been extracted from various types and parts of the palm tree. Native to upper Africa, Hyphaene thebaica (doum palm) was used as a source to extract fibers from the folioles and leaf stalks. For mechanical extraction, the plant parts were separated into fibers by beating and grating to liberate the fibers that were later dried in air [09Sgh]. After mechanical extraction, fibers were further treated with NaOH (3 N) for 2 h at 90 °C and later with sodium hypochlorite at room temperature [09Sgh]. As seen in Table 6.1, considerable variations in fiber properties can be seen between the foliole fibers and the leaf stalk fibers. Similarly, alkali treatment resulted in fibers with considerably finer diameter and higher strength, elongation, and modulus for the fibers obtained from the folioles. Morphologically, the fibers contain pores on the surface that were more evident after alkali treatment as seen in Fig. 6.2 [09Sgh].