e-book Identification of Vegetable Fibres

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This comprehensive practical guide to the identification of vegetable fibres will be of use to forensic scientists, archaeologists, conservators of antiquities.
Table of contents

The fibre is derived from the inner bast tissues of the stem.

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The bast of ramie cannot be removed from the woody tissue in which it is embedded by a simple retting process such as is used for flax, hemp and jute. Instead, it must first undergo a severe pounding or scraping to remove the outer bark, which is administered by hand or by one of the many types of decorticating machines. The decorticator and decorticated ramie fibre is shown as in Fig.

Classification and properties

By decortication, the outer bark, the central woody core and some portion of the gums and waxes of the bast are mechanically removed. In principle, any machine which is used for sisal or kenaf decortications can be adjusted for ramie. The decorticator consists of a beater or breaker plate and a metal drum, which is equipped with steel beater blades or knives that are set at equal intervals on the periphery of the drum. The quality of decortication and fibre recovery also depend largely on the efficiency of the operator as well as condition of the plants.

Stalks becoming dry after harvest cannot be properly decorticated. Decortication should be completed on the day of harvest and if there are some left over, they should be kept moist by sprinkling water till decortications is done on the following day. Decortication is to be done immediately after harvest and therefore, a harvesting schedule is planned in relation to the decortications capacity of the machines used 9.

A number of small machines have been designed in various countries with the objective of extracting bast fibre from the green stems of jute and similar fibre plants and thus eliminating the need of retting. Decorticators developed for ramie include small mobile types suitable for use in the field and larger machines designed for central operation.

Use of decorticators in the field saves the cost of transporting unwanted plant material to soil Some have been in use for a long while, but they all have drawbacks for commercial big scale production. Either the fibre is imperfectly cleaned so that it can only be put to use for limited local purposes, or the output is much too low, or there too much wastage of fibre during the process of decortications The ribbons of partially separated but not yet degummed fibre, are known as "China grass" and it is in this form that ramie is normally exported from China to European and other markets.

The extracted fibrous material, after washing, should be immediately dried or degummed to prevent the development of mildew. As mentioned above, ramie is not retted in the same way as are other stem fibres such as jute, hemp, flax, etc. Due to the presence of gum, the fibre becomes stiff and brittle. It acts as an inhibitor for water and other chemicals to enter inside the fibre.

So, it is always better to remove the gum content of ramie fibre before going for the processing of the fibre. The process of removal of gum from the fibre is known as degumming. Degumming can be done with chemicals like sodium hydroxide 13 , 14 or with enzymes 15 - 19 or with microbial action The tenacity, wet strength, extensibility are increases. Removal of the gum enables the fibre to take a more crystalline form. On gum removal, the crystallites increase in width but deteriorate with regard to their alignment along the fibre axis The ribbons of ramie, on their arrival at the factory, are greenish yellow to yellowish-white strips.

They may be used in this form for coarse products, but if ramie is to be spun into yarns suitable for fine fabrics, the first process in the mill is to degum the ribbons. Generally caustic soda is used for degumming process.

The gums of ramie are composed of araban and xylans which are insoluble in water but easily soluble in alkaline solutions. A slight mistake in the degumming process can spoil the quality of fibre, since the major component in ramie is cellulose and is sensitive to alkali. It is essential to remove the excess of alkali by acetic acid treatment after chemical degumming, otherwise the fibre strength will be reduced.

After the fibre has been submitted to the degumming action, it is thoroughly washed and dried. The separated cells of ramie, known as "filasse" although white and clean, are still somewhat harsh and dry. In order that the fiber may lend itself more readily to the subsequent manufacturing operations, it is usually treated with an oily preparation composed in most cases of water, glycerine, wax and soap, when it is thoroughly softened, ramie is ready for processing The SEM images showing the effect of combined degumming and bleaching is shown in Fig.

From the figure it is observed that after the chemical treatment, the fibres are found to be clean. In a study the degumming of ramie with sodium metasilicate, alone or in combination with other alkali solutions such as sodium carbonate, trisodium phosphate and sodium metasilicate phosphate, has been reported The most significant factors involved in ramie degumming are the concentration of the chemicals, temperature, time and the methods employed to ensure that the degumming liquor penetrates to all parts of the ribbons.

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The decorticated and chemically degummed fibres are as shown in Fig. There is no international grading system is available for grading of ramie fibre and the grading is done as per the standards developed by the ramie producing countries. Ramie fibre will be graded before taken in to processing industry. The existing jute grading system can also be adoptable in the case of ramie.

Generally two methods of grading are adopted. Hand and eye method and instrumental method. During grading, the following parameters are to be checked. Colour, strength, softness, length, fibre separation and defects major, minor. The market prize of ramie fibre is determined by grading system. Ramie is a unicellular cellulosic bast fibre. Among all the bast fibres, major content of cellulose is found in the ramie.

Ramie Fibre Processing and Value Addition

Cellulose is a polysaccharide i. The chemical composition of ramie fibre is as shown in Table 1. The fibre possesses some very valuable properties because of its silky, luster, unparallel strength, durability and its suitability to blend with all other natural and manmade fibres. It is almost 6 times stronger than cotton, 2 times that of flax and almost equals silk in its lustre.

The density of fibre ranges from 1. The tensile strength varies from MPa. Form the table 1 it is observed that the cellulosic content in ramie is much more than other bast fibre like Jute and Hemp. It is highly crystalline fibre. The mechanical properties of plant fibres largely depend on the amount of cellulose, which is closely associated with the degree of crystallinity and the crystallite orientation of the fibre with respect to the main fibre axis Ramie fibre is easily identified by its coarseness, thick walls, lacks twist and has striated surfaces It is resistant to bacteria, mildew, mild alkalis, rotting 26 , sunlight and insect attack.

It is having good wetting strength but poor in elasticity, abrasion resistance and wrinkle recovery. Degumming is essential after fibre extraction. Prolonged treatment with strong alkali and strong acids causes loss in strength of the fibre and also hydrolysis of cellulose. Properties of degummed ramie fibres make it more attractive and better than cotton. Acid hydrolysis of native ramie cellulose fibre leads to aqueous suspensions of elongated nano crystals with high aspect ratio.

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  • Ramie can be used, generally speaking, for those purposes for which flax and hemp are normally used-particularly for twines and threads, for which purposes its properties of strength and lack of stretch make it most suitable. From the Fig. The weight loss is mainly because of evaporation of water and volatile substances low molecular weight waxes and fats.

    Table 2 shows weight loss percentage of ramie fibre subjected to heating in varied temperature, indicating nature of thermal decomposition. During eighteenth and nineteenth centuries, ramie cultivation became established in many areas of the western world.

    Spinning mills were operated in England, France and Germany towards the end of the nineteenth century. But it is only in comparatively modern times that the production of ramie fabric has become established on a commercial scale. Before spinning, the fibres are sorted into three lengths, i. This long fibre is spun separately. The medium-length fibre is either spun on its own, or spun together with the short fibre and any waste which is obtained during the dressing of the long fibre. To make them suitable for spinning, the decorticated ramie fibre has to be degummed in an effort to separate the individual fibres free from gums, waxes and pectins and leave them in a soft, clean state with their strength and other textile characteristics intact.

    Methods of spinning ramie may vary, in different countries and mills and are determined to a large extent by the type of spinning system available in a particular mill. In the current scenario, there is no specialized spinning system in India is available for ramie and is spun in jute system. Attempts have been made by various researchers to spin ramie in blends with jute, silk, viscose and polyester fibres using jute and woollen spinning systems 32 - Because of this variable length, before the fibre is subjected to spinning process, it is cut in to uniform size.

    The finest yarns are produced on the spun silk system developed by the Japanese, but this system is labour intensive. In Europe, Brazil and the Philippines, some modifications are made. This produces coarser count yarn but much less labour is required. Ramie is also suitable for blending with both natural and synthetic fibres in different proportions.

    The blended yarns have good scope in the areas like home furnishing, upholstery and industrial fabrics. In another work 36 , degummed ramie fibre of cut staple length 20 cm was processed in flax carding system and subsequently blended with jute fibre during drawing stage.

    After three passages of successive drawing, the sliver was processed through jute roving machine and finally spun in to a yarn of 84 tex. Ramie may also be spun on the worsted and long draft cotton systems, but in the latter case stapled noils are used and usually blended with cotton or synthetic fibres 37 , Ramie is most often blended with other fibres for its unique strength, absorbency, lustre and dye affinity.

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    Long staple fibres can be used for spinning, where as short fibres are using for the manufacture of papers, composites, non woven and other products 39 , In spite of the undoubtedly good properties of ramie fibre, the wide occurrence of the plant and the enormous amount of publicity which has been given to the subject from time, the fibre has not so far been developed or used on any large scale outside of China and Japan.

    Ramie is a labour intensive and input intensive crop in terms of planting material, plant nutrients and machines. In ramie crop, return comes mainly from the second year onwards. The individual growers may not be in a position to make such investment for raising the crop. Ramie fibre is extracted through decorticator machine. Now, the main problem of decorticating machine is, availability and that too at reasonable or affordable price by farmers. For proper extraction of fibre, efficient decorticating machines or decorticators are needed to be made available to the growers at reasonable price.

    Another important problems associated with the ramie fibre is the removal of gums from the un-degummed crude fibres.

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    • Degumming is still treated as trade secret by the mills that have perfected this art. Mistakes in degumming process can ruin the fibre and cause a spinner considerable loss since the know-how for carrying the degumming operations are not freely available. Of course, numerous patents have been published relating to the degumming of ramie and there is certainly death of information on the subject.

      Another difficulty with the crop is its very low production by itself. Some users textile mills have lost interest in the fibre mainly because of the problems of irregularity of quality supply and as well as processing difficulties and these have further discouraged the industrial sector from promoting the use of ramie.

      However, the development of a greater ramie industry has been hampered, first, by technical difficulties resulted from the nature of the fibre and secondly, by commercial difficulties attendant upon the introduction of most new textiles. The technical difficulties may be summarized as:. Apart from any economic or technical reasons, the development of any new fibre needs market development work of some kind.

      The use of ramie is limited by its price and spinning properties. A manufacturer can place an order for as much as, say, one million lb on the spot for cotton.