Friday, July 1, 2011

BEST FIBERS

           The fibers known in the textile trade as best fibers are the stiffening elements associated with the phloem tissues in plant stems leaf stalks and leaves . They can be divided botanically into two groups  (1) cells occurring in the bast of the stalks or stems (2) the fibers occurring as serendipitous tissue in leaves . They are generally characterized by having a ratio of length to diameter of from 500 to 2000 They occur in bundles disposed longitudinally wherever stiffening is required .

The cells in the bundles are embedded are embedded in a median layer which cements the fibers together . This may be almost absent as in the case of New Zealand flax or very thick as in the case of nuns hemp. It consists of lining or nitrocellulose or in th cease of flax of calcium spectate.

The bundles themselves are embedded in a packing structure consisting of cuboid parenchymatous cells of no textile value .
External to the phloem is a layer of cortex which may be regarded as a skin or bark.The commercial methods used in the production of bast fibers consist in general of  ,mechanical removal of the cortex , mechanical removal the whole or most of the median layer. In commercial production the cortex parenchyma and median structures are rarely removed quite completely and examination for identification purposes should not neglect a search for residual non bast cells which are often characteristic.

Chemically the bast fibers are all cellulose but differ from cotton in that they also contain varying proportions of lining or nitrocellulose. This proportion may very from almost zero in the case of ramie to a proportion of 40% lining in the case of jute hemp may be regarded as typical of an intermediate type containing from 5 to 10 % nitrocellulose.

Microscopical methods of identification consist in measurement of the mean cell diameter observation of the shape of the cell ends , consideration of the width of the lumpen relative to that of the cell walls examination of the cross section and determination of the characteristics of special constituents such as the stigmata in manila .Chemically the most useful reaction for identification is this specific staining of nitrocellulose by means of phloroglucinol.

Some of the fiber names are used very loosely fo example matthews ( textile fibers ) lists more than thirty plants giving fibers known commercially as hemp. The most important textile bast fibers are ramie flax hemp and jute these together with sisal manila New Zealand flax and raffia are considered in detail below . For other bast fibers Matthews should be consulted.

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