2.1. Bleaching of cotton textiles

Cotton material (the fabric or a yarn), presoak in a solution containing, g/1:

caustic. . . . . . . . . . . . . . . . . . . . . . .2,0

sodium silicate (square 1,44) . . . .30,0

surface-active substance. . . . . . . . 0,5

hydrogen peroxide. . . . . . . . . . . . . 2,0

water. . . . . . . . . . . . . . . . . . . . . . . . .X

The liquor ratio of a bath 50, temperature 40 °C. Then the solution heats up to 85 -90°C and reaction time textiles at this temperature within 1 hour. Then samples wash out warm and cold water, dry up and define whiteness degree. For this purpose measure factor of reflexion of textiles with use of photometers, spectrometers, leicometers, etc.

2.2. Mercerization

Mercerizing is one of the major processes of preparation. The size and type of merceriser depends on the output required and whether a high luster is required or simply improved dye affinity. It is processing of cellulose materials by the concentrated solutions NaOH (concentration 220 - 300 g/L) at a room temperature. After such processing hygroscopicity of a fiber, shine, luster, silkiness, durability, ability to be painted raises. Mercerizing materials in the severe and boiled kind can be exposed. Processing spend under a tension. Quality mercerization is estimated on change affinity Ba(OH)₂. The relation affinity this reagent mercerizing and not mercerizing of fiber increased on 100, is called barium as number which depending on a substratum (the yarn or a fabric) makes from 120 to 160%. Last years it is developed warm and hot mercerization which allows to lower concentration caustic and sharply to reduce duration of process. It will positively affect quality of a material and will lower pollution of sewage.

It is known mercerizing for liquid ammonia NH₃. Thus duration of processing makes 1 second instead of 2 mines, its full regeneration that will exclude environmental contamination is thus possible.

To define shrink a material, mercerized by tensionless Performance order. The sample of the boiled or bleached material place in a glass with solution NaOH concentration 220 - 300 g/1 at a room temperature for 2 minutes Then samples wash out water, process a solution of sulfuric acid H₂S0₄ concentration 5 g/1 at a room temperature during 2 mines for neutralize caustic, then again wash out water. The sample dry up, define degree shrink, %, on the formula:

At = (L_int - L_fin) / L_int 100 %,

where L_int, - L_fin - initial and final length of the sample.

Then the sample mercerizied and not mercerizied paint in one bath a solution of dye direct blue or another concentration 1 g/l at temperature 90 °C during 10 mines at constant stir of samples. After dyeing samples to wash out, wring out and dry up.

To compare intensity of coloring of samples, to remove spectral characteristics.

3. Application of optical bleaches

3.1. Optical bleaching substances

The whiteness of textile materials as an indicator of visual perception of quality of production is generally characterised by four indicators: lightness, color tone (a whiteness shade), evenly and stability of a whiteness. The chromaticity role is shown that the textile materials classified as white, can be perceived in comparison with the white standard as a bit yellowish, reddish, greenish, etc. the Most white the materials having not achromatic, but slightly bluish color tone (with the dominating length of a wave 446 nanometers) are perceived.

Presence in textile materials of the polluting impurity absorbing light radiation in a short wave part of a spectrum owing to what materials look yellowish, influences their whiteness. On a whiteness indicator it is possible to spend an influence estimation blue pigment or optical bleaches.

Optical bleaching substances (OOS) represent the colorless fluorescing organic connections, capable to eliminate yellowness of fabrics increase in quantity of dark blue beams in reflected light. They transform invisible short-wave ultra-violet light in visible dark blue, green or violet. Behavior OOS at processing of textile fibers submits to laws of dyeing and ways of application same, as ways of application of those or other dyes at processing of corresponding fibers. They should be steady against action of various temperatures, a wide range pH, to influence of finishing preparations, should not decay from action of bleaching substances, and should not weaken a fiber.

Let out OOS at type powders, solutions or highdisperse pastes in a mix with various fillings or without them. In quality filling apply substances which promote the best solubility, to reception of optimum dispersion, improve selection OOS by a fiber.

At work with OOS it is possible to apply water of average rigidity, but not containing salts of iron, manganese, copper, at concentration of iron 40 mg/1 there are more fluorescence is completely extinguished.

Some marks OOS give to a product a weak color shade. Different colorists depending on requirements of the consumers prefer this or that shade. Some OOS possess antimicrobic activity.

Bleaching substances have critical concentration above which the visible bleaching effect starts to weaken, i.e. process of the concentration clearing connected with the various difficult phenomena begins. Occurrence of strongly appreciable undesirable shade is thus possible. The maximum of curves of reflexion on textile materials is between 425 and 460 nanometers, the smaller length of waves corresponds to a reddish shade, and big - green-blue. OOS - the connections similar to dyes at which chromofor the system possesses ability of fluorescence. Ability of connections to fluoresce depends on a chemical structure and can be established from the formula and depends, first of all, on presence in a molecule of system not less than 4 interfaced double communications and absence of the groups causing coloring of connections. The increase in quantity of the interfaced double communications in a molecule shifts a spectrum of fluorescence towards long waves. Presence of free amino groups reduces OOS, presence acetyl - benzoil - groups, triazin rings and so forth testifies about high steady to light. Solubility and an ion charge (anion - or cationactivity) are defined by character of assistants in a molecule.

OOS belong to various classes of aromatic and heterocyclic connections with the developed system of the interfaced communications. The chemical classification based on the maintenance in OOS of chemical groups is widely applied. Depending on a structure they possess affinity to fibers and get out of a bath like dyes.

The whiteness in the big degree depends on properties of a textile material, its surface. Intensity of fluorescence on a brilliant surface above, than on the matte. The materials painted in pink color, at processing OOS become more pink, dark blue - is brighter, green - more dark blue and bright, grey - dark blue, pastel than tone - is more gentle. Colorings it is light yellow and cream tones it is not recommended to process OOS since they become less bright, faded.

Critical concentration of bleaching substances makes 0,1 - 0,3 % (from weight of bleached materials).

Bleaching of products from cellulose fibers there begin with warming up of a bath to temperature 40-50 °C. After soakings of products in a bath add solution OOS and salts (NaCL or Na₂S0₄), and spend bleach during 20-30 mines at temperature 50° C, then a product wash out in cold water. Bleaching it is possible to combine with processing in solutions hydrogen peroxide, precondensates of pitches, anionic and notionic softing; it is not recommended to apply with cationicactivity material..

At bleach products from a clap quantity OOS of 0,05-0,4 %, a viscose fiber 0,1 - 0,8 % from weight of fabric. The whiteness of a cotton fabric defined by leikometer f. K.Ceiss at length of a wave of 457 nanometers, makes: severe - 59 %, the boiled 60 %, bleached NaClO 75 - 78 %, bleached on hydrogen peroxide to a way 81-88 %, the blued blue 92 %, processed by optical bleaching preparations approximately 114%.

At bleach a wool take 0,2 - 1,0 % a optical bleaching preparation, 3-4 % of 85 % of ant acid or acetic 80 % . Optical bleaching spend during 20-30 mines at temperature of a solution 60 -70 °C. Then products wash out.

Like a wool bleach natural silk, but without acid.

PET textiles bleach in the solutions containing 0,5 - 1,0 g/l of leeling agent and 0,5 - 2,0 % of optical bleaching preparations, at boiling during 45 - 60 minutes

To an estimation of bleaching effect apply Fotometer, supplied with a mercury lamp, color comparators. By means of the device for color measurement define co-ordinates of color of the sample in system CIE and count an indicator of a whiteness and an indicator of a shade of a whiteness in conformity from GOST P ИCO 105-J02-99.

Prior to the beginning of measurements define presence (or absence) of optical bleach with use of an ultra-violet source. If on a fabric there is an optical bleach measurement spend on the device which shines test by polychromatic light and has the relative distribution of spectral energy approximately corresponding to standard light source CIE D65 in a range of lengths of waves from 330 to 700 nanometer.

For the approached definition of efficiency of optical bleach on a way of a falling light stream establish the filter cutting an ultra-violet part of a spectrum. The difference between instrument readings before filter installation can serve as a measure of increase in visually perceived whiteness owing to the additive of an optical bleach.