Jute and kenaf

Urena and Abutilon. These are less important vegetable fibers of a jute-like nature. Urena lobata (Cadillo) of the mallow family (Malvaceae) is a perennial that grows in Zaire and Brazil to a height of 4—5 m with stems 10—18 mm in diameter. Because of a lignified base, the stems are cut 20 cm above the ground. The plants are defoflated in the field and retted similarly to jute and kenaf. The retted material is stripped and washed and, in some cases. 

Stout has written a detailed review on jute and kenaf. X-ray diffraction patterns show the basic cellulose crystal structure, although in jute and kenaf the crystalline orientation is high and the degree of lateral order is lower than in flax. Batra" in a comprehensive review has highlighted the morphological structures and physical, mechanical and chemical properties of other long vegetable fibers. 

The term wood-plastic composites (WPCs) refers to wood as a proxy for fibrous materials of plant origin. It can be wood flour or sawdust, or agricultural plant residues, typically cut, milled, or ground, or other types of natural fiber, such as hemp, jute, and kenaf, commonly as a by-product of the respective industrial process. 

The secondary wall found in wood cells is composed of two or three layers, known as SI, S2, and S3, respectively. In each of these layers, the cellulose microfibrils are "spirally-wound" at a different angle to the major axis of the tracheid. This variation in microfibril angle imparts strength to the fiber structure in a variety of directions. Within the bast or schlerenchyma cells found in flax, hemp, jute, and kenaf, the secondary wall is less thick than that of wood, but contains layers of similarly spirally-wound microfibrils embedded in a hemicellulose and pectin-rich matrix. This "composite structure" imparts potentially high strength to regions of the cell wall. Figures 9.1 and 9.2 show a schematic representation of flax fiber and a section of an elementary fiber with its fibrillar structure in its secondary cell wall [31]. 

Both jute and kenaf grow to 2.5-3.5 m in height at maturity, but kenaf, although it still requires a long day length for vegetative growth, flourishes in drier conditions than jute and can adapt to a wider variety of soils and climates. As a result, it is preferred to jute as a fiber... 

Jute and kenaf fibers develop in the phloem, or bast, region of the stem of the plants, and they appear as wedge-shaped bundles of cells intermingled with parenchyma cells and other soft tissues (Figure 7.1) in the transverse sections of the stem. In the growing part of the stem, a circumferential layer of primary fibers develops from the protophloem, but, as vertical growth ceases in the lower parts, secondary phloem fibers develop as a result of cambial activity. In mature plants, which reach a height of 2.5-3.5 m and a basal diameter of about 25 mm, the secondary fiber accounts for about 90% of the total fiber bundles. 

Retted fibers such as jute and kenaf have three principal chemical constituents, namely, a-cellulose, hemicelluloses, and lignin. The lignin can be almost completely removed by chlorination methods in which a soluble chloro-lignin complex is formed, and the hemicelluloses are then dissolved out of the remaining holocellulose by treatment with dilute alkali. The final insoluble residue is the a-cellulose constituent, which invariably contains traces of sugar residues other than glucose. 

Along with the three principal constituents, jute and kenaf contain minor constituents such as fats and waxes, 0.4-0.8%, inorganic matter, 0.3-5%, nitrogenous matter, 0.8-1.5%, and traces of pigments. Totally, these amount to about 2%. Table 7.2 shows the chemical composition of both kenaf and jute reported by different laboratories in the United States, India, and Bangladesh [15b]. 

Jute and kenaf, like most vegetable fibers, contain a proportion of acetyl groups that are readily hydrolyzed by dilute alkali to acetic acid. Estimation of the quantity of acetic acid produced per unit weight of fiber then provides an index of the acetyl content. 

Soutar and Brydon s results show no significant difference between H. cannabinus and H. sabdariffa, which is, perhaps, surprising in view of the difference between the two jute varieties, but the acetyl content does appear to offer a means of differentiating between jute and kenaf. For such a comparison to be valid, of course, there must have been no prior treatment of the fiber with alkali, which occasionally happens in chemical retting experiments. 

Source From Man, J.S.., and Rowell, J.S., Paper and Composites from Jute and Kenaf Resources, CRC/Lewis Publishers, Boca Raton, FL 1997, MS 83. ... 

An alternative method of distinguishing between jute and kenaf is by means of the crystals in the ash of the fiber after incineration. These crystals are present in the parenchyma and retain their original form during asking. In kenaf, cluster crystals are commonly found in the ash, whereas they are relatively uncommon in the case of jute. Jarman and Kirby [18], however, have shown that jute can be distinguished by the fact that the ash contains solitary crystals occurring in chains. Solitary crystals may occur in kenaf, but not in chains. 

Jute and kenaf are strong fibers, exhibiting brittle fracture, but having only a small extension at break. They have a high initial modulus, but show very httle recoverable elasticity. Tenacity measurements recorded in the literature vary widely, and, although some of this... 

The grading and classification of base fibers such as jute and kenaf for commercial purposes has a long history, but is still done subjectively by hand and eye. Official standards have been formulated, but these are purely descriptive and no quantitative values are assigned to the... 

Because the properties of the jute and kenaf fiber result from the chemistry of the cell wall components, the basic properties of a fiber can be changed by modifying the basic chemistry of the cell wall polymers. 

Medium- to high-density mats can also be used as filtering aids to take partieulates out of waste and drinking water or solvents. Figure 7.11 shows a filter unit that is in plaee to remove metal ions from water that has come from an abandoned coal mine. Jute and kenaf fibers can also be modified to beeome more effieient in removing a wide variety of contaminates from water. 

Tests are presently underway to use jute and kenaf sorbents to remove heavy metals, pesticides, and oil from rain water run off in several cities in the United States. Medium-and high-density mats can also be used for oil spill clean up pillows. It has been shown that the core material from kenaf preferentially sorbs oil out of seawater when saturated with water. There are many other potential sorbent applications of agrofiber and core resources such as removal of dyes, trace chemicals in solvents, and in the purification of solvents. 

It is also possible to use core materials as sorbents in cleaning aids such as floor sweep. While this is not a composite, it does represent another way in which jute and kenaf resources can be used as sorbents. 

Structural composites can range widely in performance from high-performance materials used in the aerospace industry down to wood-based composites, which have lower performance requirements. Within the wood-based composites, performance varies from multilayered plywood and laminated lumber to low-cost particleboard. Structural wood-based composites intended for indoor use are usually made with a low-cost adhesive, which is not stable to moisture, while exterior-grade composites use a thermosetting resin that is higher in cost but stable to moisture. Performance can be improved in wood-based as well as jute and kenaf composites by using chemical modification techniques, fire retardant, and decay control chemicals, etc. 

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