Friday, May 9, 2008

Colour and colouration

Colour has been playing a dominant role in life from time immemorial. Right from the prehistoric times man has noticed the abundance of multitude of colours worn by nature. With progress in times it was realised that the colours in nature were not permanent. The process of colouration began with application of natural colouring matters to dye clothes prepared from different natural textile fibres like cotton, linen, wool, silk etc. It was soon realized that the method of extraction of natural dyes and their application were lengthy and laborious. This gave the impetus to development of synthetic dyestuffs. Colouration in textiles ranges from apparel fabrics and other end uses like carpets, furnishing fabrics, automotive textiles, military textiles and so on. Textile colouration industry is a service that alters the appearance and aesthetics of textile materials. Colourants in textile application are principally based on organic dyestuffs and pigments, with some inorganic pigments also in use. Dyestuffs are mainly used in traditional dyeing and printing of textile material. Coloured textiles are produced today on a large industrial scale. Although modern automation techniques have been introduced for colour measurement, metering of dyes and auxiliaries and automatic control of dyeing processes much human invention is still required. Fibres can only be standardized to a limited extent due to biological and environmental factors like growing of cotton, raising of sheep etc. New developments in fashion and application have required constant modification in various procedures. Goal of every dyeing is to produce coloured textile of desired shade, homogeneous depth and hue with due consideration to economy and ecology.

Wednesday, May 7, 2008

emulsion in textile formulation

A lot of textile auxillaries used are in the form of emulsions. Emulsions are disperse systems consisting of two (or more) mutually insoluble or sparingly soluble liquids. The liquid present in excess is termed the closed, continuous or external phase, while the liquid dispersed in it is termed the internal or dispersed phase. The preparation of an emulsion is termed emulsification and the agents used for this purpose are termed emulsifiers. Normally the emulsions which are encountered in textile industry are oil in water (o/w) and the vice versa (w/o).

To prepare eumulsion emulsifiers are required. So what is the exact role of emulsifier? The polar (hydrophilic) aqueous phase and the polar (lipophilic) lipid or oil phase of an emulsion cannot be combined stably and homogenously without additives. The surface tension at the interface between these two phases must be reduced by the addition of emulsifiers. Emulsifiers are surface active substances that reduce the surface tension between polar and apolar phases by penetrating into the interface between the oil and the water phase. This occurs because of their amphiphilic molecular structure, i.e. they consist of both hydrophilic (polar) and lipophilic (a polar) molecular regions and are thus soluble in both the hydrophilic and the lipophilic phase.
Whether a w/o or an o/w emulsion is formed depends essentially on the stability of the emulsifier layer surrounding the droplets. If a water stable emulsifier envelope is formed around the oil droplets in a system containing water, oil and emulsifier, an o/w emulsion is produced. On the other hand the formation of an oil-stable envelope around the water droplets produces a w/o emulsion. Thus emulsifying agent should show following properties,
It should be surface active and reduce surface tension to below 10 dyne/cm
It should be adsorbed quickly around the dispersed drops as nonadherent film which will prevent coalescence
impart to the droplets an adequate electric potential so that mutual repulsion occurs
It should increase the viscosity of the emulsion
It should be effective in a reasonably low concentration
be stable
be compatible with other ingredients
be non-toxic

An emulsifier consists of water-soluble hydrophilic parts and water-insoluble, oil-soluble lipophilic parts within its.When an emulsifier is added to a mixture of water and oil, the emulsifier is arranged on the interface, anchoring its hydrophilic part into water and its lipophilic part into oil.
On the interface surface of water and air and of oil and air, the hydrophilic part and the lipophilic part are adsorbed and arranged around the interface. The emulsifier reduces the interfacial tension.That is, the force to separate the oil and water is thus weakened, resulting in the easily mixing of oil and water.

Friday, May 2, 2008

Wool Fiber

The word wool was wull in Old English, wullo in Teutonic, and wlna in pre-Teutonic days. Wool is the fiber from the fleece of domesticated sheep. It is a natural, protein, multicellular, staple fiber. The fiber density of wool is 1.31 g/cm3, which tends to make wool a mecfiurn weight fiber.

The wool fiber is a crimped, fine to thick, regular fiber. Fine wools may have as many as 10 crimps per centimeter, whilst coarse wools have less than 4 crimps per 10 centimeters. As the diameter of wool fibers increases, the number of crimps per unit length increases. The number of crimps per unit length may be taken as an indication of wool fiber diameter or wool fiber fineness.

Wool fibers may vary from off-white to light cream in colour. This variation in colour is due to the disulphide bonds which seem to be able to act as chromophores. As a result the incident light may be modified to cause the reflected light to have a tinge of yellow, giving the wool fibers their off-white appearance. When the fiber is cream to dark cream in colour, this is due more to polymer degradation on the surface of the fiber. This can readily occur, as the wool polymer is chemically very sensitive to atmospheric oxygen and air pollutants.

Fibre length to breadth ratio can be critical with wool, since the short, coarse fibers spin into less attractive yarns than do those of fine wools. In general, fiber length to breadth ratio ranges from 2500:1 for the finer, shorter wools to about 7500:1 for the coarser, longer wools.