Page 28 - HPIC India

Cover Story

situation both physical and chemical The Dutch used potash lye and rous acid, depending on the pH (alka-
methods of removal are combined. buttermilk as a bleaching agent, linity) of the resultant solution.
There are situations when the soil which that was eventually replaced
consists of substances that cannot by dilute sulphuric acid in 1756. Sub- The stability of hypochlorite solu-
be removed by chemical treatment, sequent developments gradually cul- tion is achieved by use of 1-2%
but can be dislodged only by inter- minated in the introduction of mod- sodium hydroxide in the final resultant
facial processes, using modern deter- ern chemical bleaches toward the bleach mixture. Stability is affected
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gents containing quality surfactants, end of the 18 century when Javelle by light and trace amounts of heavy
water-soluble complexing agents, water was accidentally discovered. metals, copper, nickel, cobalt, chro-
water-insoluble ion exchangers, en- In 1792, a French national based in mium, iron, manganese and so care
zymes, etc. Javelle near Paris found that addition should be taken to avoid contact of
of caustic potash to chlorinated water the bleach solution with materials
Commonly encountered stains in the ratio of 1:8, produced a solu- made of the above metals. It is advis-
in daily life usually consist of sub- tion that was effective as a bleach. able to fill and store the bleach solu-
stances belonging to the plant king- This solution was called as “Eau tion in opaque glass bottles, plastic
dom, viz., tea, coffee, wine, fruit de Javelle” and was commercially containers, glazed porcelain or rub-
juice, beer, spices, grass, vegetable sold to textile bleachers even though ber or glass-lined vessels to maintain
sauce, egg yolk, etc. These soils the potassium hypochlorite solution stability.
compounds that can be bleached to formed was not very stable.
reduce them to colourless products. Hypochlorite decomposes into
Sometimes these colourless products In 1799, Charles Tennant of Eng- sodium chloride (NaCl) and nascent
regain their colour due to air oxida- land produced a more stable “Chlo- oxygen [O], which is the active bleach-
tion. Stains of Urobilin and Urobilino- ride of Lime or Bleaching powder” by ing agent. In case no bleaching takes
gen, derived from blood haemoglobin absorbing chlorine on wet lime. By place then nascent oxygen produced
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degradation, is excreted though hu- the end of the 19 century sodium combines slowly to form inactive
man urine. Perspiration stains are hydroxide and chlorine were electro- Oxygen (O ). During the decomposi-
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another major stain associated with lytically produced from brine, leading tion of hypochlorite some amount of
humans that have to be eliminated. to the commercial manufacture of an chlorate is also produced.
Stains of certain commercial products inexpensive, but relatively stable,
used by individuals in their daily life sodium hypochlorite solution in 1820 One major disadvantage of hypo-
like cosmetics, hair dyes, nail polish/ to be used as an inexpensive bleach- chlorite bleach is that it has to be
enamels, shoe polish, ink, tobacco, ing agent for household purposes. added separately in the wash liquor
etc. are also sometimes required to and cannot be incorporated directly
be eliminated from fibres. The perennial quest to achieve into a detergent formulation. More-
cleaner and brighter laundry, led over, chlorine bleach solution is de-
Historical development mankind to continuously improve, pendent of user experience and strict
During the pre-historic times, the and the concept of whiteness was adherence to the manufacturers’ re-
bleaching agent used was wood ash, revolutionised by the development commendations is required to derive
consisting mainly of potash, as a fat of Fluorescent Whitening Agents, the maximum benefit; wrong usage
cleaving or lipolytic agent to remove along with greatly improved chemi- can lead to serious laundry damage.
oily stains. At about 70 AD, bleachers cal bleach systems.
in Rome effectively made use of urine Concentration of hypochlorite
that contains ammonium carbonate as Chemical bleaches for laundry solution is usually specified in terms
a mild alkaline detergent. The use of of its available chlorine content. This
urine as a cleaning agent was so popu- Chlorinated Bleaches is usually expressed as the amount
larised by the bleachers of Rome that Sodium Hypochlorite, bleaching of chlorine produced when hypo-
Emperor Vespasian taxed the commer- powder, chlorinated isocyanurates, chlorite solution is acidified. House-
cial collection of urine by the bleach- isocyanuric acid, dichlorodimethyl hold hypochlorite bleaches are sold
ers. Croft-bleaching, in which bleach- hydantoin, chlorinated phosphates, in strengths up to 10% (maximum)
ing takes place due to the formation chloramines, lithium hypochlorites, of available chlorine. Hypochlorite
of hydrogen peroxide by the action of etc., are some bleaching chemicals, has good reactivity and high oxida-
sunlight on moist fabric spread out on which in an aqueous medium, pro- tion potential and so is effective at
Croft grass was also practised. duce hypochlorite ions or hypochlo- low temperature. Nevertheless, it
28 Home, Personal & Institutional Care India November 2020