A study of the microscopic structure of the fiber strands of common Indian bast fibers and its economic implications

Abstract

Natural fibers, used since the dawn of civilization, are obtained from different plant organs. They are classified as stem (bast), leaf, seed, or fruit fibers. Fibers vary in their mode of origin, in yield, and in quality, which makes them suitable for different purposes. Each kind of plant fiber is present in a definite pattern within the specific plant organ. Fibers obtained from the stem (commercially known as bast fibers) lie embedded in the softer tissue of the bark and may be classified into two categories: some are primary in origin (ramie, flax, sunnhemp), others are secondary. Those of the second category are derived mostly from cambial meristematic activity which cuts off fiber initials that grow longitudinally along the axis within the bark. Each of these cells, pointed at both ends and with a lumen at the center, is called an ultimate fiber cell (Maiti, 1968). These ultimate fiber cells, connected end to end with the help of cementing materials of hemicellulose and pectose, form the fiber strands of commerce. The fiber strands thus formed are connected here and there along their longitudinal course to form the meshy structure of bast fibers. In stem transverse sections, the fiber strands appear as fiber bundles which are embedded in the soft parenchymatous tissue of the bark. Why different bast fibers vary in yield and quality (Wilson, 1967; Maiti & Chakravarty, 1977) is a question not yet fully answered although some attempts have been made in this direction. Differences may be due to variation of cellulosic fractions in the crystalline regions and non-cellulosic substances in the paracrystalline part. Fiber structure indicates to some extent the spinning and the yarn quality (Hearle & Peters, 1963). Structural organization of the fiber strands plays some role in governing the quality as demanded and defined by technologists. The main quality parameters of vegetable fibers are strength, fineness, surface structure, meshiness, color, and lustre. Attempts have been made to predict some of these quality parameters from anatomical structures in some fibers (Maiti, 1968, 1970a, 1970b, 1970c, 1974). Different jute and mesta varieties show variation in microscopic structure correlating with quality function (Maiti, 1970c; Maiti & Dasgupta, 1972). Ultimate fiber cells with higher length to breadth ratio (L/B) are related to higher strength not only in different fiber crops but also in the same species at different regions (Maiti & Basu, 1968). The morphology of ultimate fiber cells indicates their suitability of utilization in the manufacture of different types of papers (Maiti, 1973a). Cross-sectional area of fiber strands indicates the fineness of fibers (Maiti, 1973b). In the present study of microscopic structure of widely divergent fiber crops, the objective is to see whether variation in structure is related to quality and to make possible microscopic grading of quality.