Vegetable fibre

As it is now possible by choice of suitable conditions to prepare most compounds in this form, the colloid state should be considered as a physical state in which all substances can be made to exist. Many ma terials such as proteins, vegetable fibres, rubber, etc. are most stable or occur naturally in the colloidal slate. In the colloidal stale the properties of surface are all-important. 

AA.TCC Technical Manual, Vol. 59, American Association of Textile Chemists and Colorists, Research Triangle Park, N.C., 1984. D. M. Colling and J. E. Grayson, Identification ofi Vegetable Fibres, Chapman and Hall Ltd., London, 1982. 

It is this action alone which enables a relatively small number of dyes, the so-called substantive cotton dyes, to be absorbed directly by the unmordanted vegetable fibre. The most important of these dyes are the bis-azo dyes, such as Congo-red and related compounds, which are derived from doubly diazotised benzidine. In aqueous solution they are present as sols and are colloidally adsorbed by the fibres as irreversible gels. 

Cellulose differs from amylose principally in the stereochemistry of the acetal linkages, which are a in amylose but P in cellulose. a-Amylase is specific for al 4 bonds and is not able to hydrolyse pi 4 bonds. An alternative enzyme, termed cellulase, is required. Animals do not possess cellulase enzymes, and thus cannot digest wood and vegetable fibres that are predominantly composed of cellulose. Ruminants, such as cattle, are equipped to carry out cellulose hydrolysis, though this is dependent upon cellulase-producing bacteria in their digestive tracts. 

To reduce the density, a larger amount (6-12%) of light woodmeal, peat meat or vegetable fibre (e.g. cellulose) is sometimes added. This brings about a considerable reduction in density (to 0.70) and increases the sensitiveness of the explosive to detonation. 

V. Nitroglycerine low-density powder. This is a modification of Group IV. Low density (ca. 0.7) is obtained by incorporating vegetable fibre or peat. A low density form of ammonium nitrate and sodium chloride may also be used. A 1 Roun-kol is an example of an explosive of this group. Sheathed Rounkol has been replaced by Unikol. They are used for soft coal, for maximum lump production. Their water resistance is the same as that of Group IV. 

Preparation of Sections of the Fibres.—Identification of animal or vegetable fibres is based mainly on the physical characters, the fibres being mostly so transparent that their form and structure, and particularly the thickness of the walls and the form of the internal canal or lumen, are easily observed. In some cases, however, owing to the close resemblance between certain fibres, recognition is doubtful. This is the case, for instance, with the poorer qualities of flax and hemp, and with certain types of artificial silk. In these instances the transverse sections of the fibres are studied, these permitting of observation of the thickness of the walls, the strata... 

If a little of the sample, when brought near to a flame, bums with an odour of burnt horn and leaves a spongy carbonaceous residue adhering to the unbumt part of the fibre, it consists of animal fibres. If, however, it bums rapidly with emission of an empyreumatic odour and leaving no carbon but only a slight ash, it is composed of vegetable fibre. 

A little of the sample is boiled for a few minutes with 10% caustic potash solution, which dissolves animal but not vegetable fibres. 

See A Cappelli Behaviour to tintonal analysis of naturally coloured animal and vegetable fibres. Ann. Labor. Chtm. centrale GabeUe, Vol. VII, p. 213. 

Green s method includes two series of tables, one for colouring matters fixed on wool and the other for those fixed on cotton. The former series may serve also for the examination of dyestuffs on silk and the latter for those on the other principal vegetable fibres, excepting that small variations are necessary in both cases for certain groups of colouring matters. 

The common elements in the cited examples are the mechanical characteristics and the insulation properties. These advantages come, not only from macroscopic configuration of these materials (the hollow cylindrical structure of stubble for instance), but, mainly, from their microscopic structure. Most the vegetal fibres can be described by two models wood fibres and cotton fibres, which will be presented later. In order to better understand the mechanical properties of these fibres, let us first consider their molecular constitution, then their hierarchical structure. 

The fibre characteristics depend on the source. Table 5.2 gathers the main characteristics of industrial vegetable fibres. A short description of every type of fibre and their applications are given in the following paragraphs. 

Vegetable fibres (including wood fibres) represent a good replacement solution for glass and carbon fibres for the reinforcement of composites based on a thermoplastic matrix. The advantages of vegetable fibres are economically and ecologically important ... 

Figure 5.24 (a) Maleinated polypropylene and (b) the adduct formed with vegetable fibres by... 

The product is shipped in tank cars or in glass carboys. The solution must be stored cold and protected from sunlight. It is used for bleaching vegetable fibres, in laundries and textil factories. This hypochlorite solution is also used for the sterilization of water. 

It is almost paradoxical that in the history of mankind composite materials were earlier used than their "homogeneous" rivals. The earliest "engineering materials" were bone, wood and clay. Wood is a composite of matrix lignin and a cellulosic reinforcement bone is a natural composite where fibres of hydroxyapatite reinforce the collagen matrix and the oldest building material was adobe clay as a matrix, reinforced by vegetable fibres. After the industrial revolution other composites were added reinforced rubber, reinforced concrete, reinforced asphalt, etc. 

The plant material can be used as herbal material, once dried, e.g. marijuana. Low-quality products, which contain stalks, seeds, leaves and flowering tops, may be compressed into blocks (West African and Caribbean material), it may occur as loose herbal material (from Central and Southern Africa), or it may be rolled into a so-called Com Bob , wrapped in vegetable fibre (again from Central and Southern Africa). Higher-quahty materials, composed of fruiting tops and flowers alone, may also be encountered. If tied around bamboo sticks, this material is known as Buddha Sticks or Thai Sticks , and arises from South-East Asia. A central bamboo cane is used, around which up to 2 g of herbal material can be tied. The materials can be seized in bundles of up to 20 sticks. An African equivalent is to wrap the material in a small roll of brown paper such rolls frequently contain less than 0.5 g of cannabis per roll. Sieved products may also be encountered. This process removes the stems and the leaves, producing Kif, a material derived from North Africa, for example, from Morocco. 

The animal fibres absorb the vapour of benzyl chloride in greater quantities than do the vegetable fibres. Following this absorption, the resistance of the vegetable fibres is notably lowered, while that of the animal fibres is practically unchanged. The benzyl chloride vapour is only partly removed by a current of air. The limit of insupportability is 85 mgm. per cu. m. of air, according to Flury. 

The animal fibres absorb more bromoacetone than do the vegetable fibres. The absorption capacity is fairly high and textiles are discoloured. It is found that textiles which are merely air-dried absorb more bromoacetone than those which have been completely freed from all water. ... 

Dimethyl sulphate does not attack metals. It is only to a slight extent absorbed by animal and vegetable fibres cotton absorbs more than wool. ... 

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