Page 29 - HPIC India

Cover Story

has problems with textile dyes and cial production of stable peroxide perature than 60°C acylating agents
Fluorescent Whitening Agents that compounds in 1925. The bleaching or bleach activators like, tetraacetyl-
are unstable to chlorine. This re- action of H O , like that of hypochlo- glycouril (TAGOU), tetraacetyl-
2 2
stricts the widespread usage of hypo- rite bleach, also depends on factors ethylenediamine (TAED) or sodium
chlorite bleaches for coloured and like temperature and pH. Bleaching p-isononanoyloxybenzene sulfonate
superior quality fabrics. Sodium hypo- takes place due to an active form (iso-NOBS) are incorporated. Among
chlorite is still used as an inexpen- referred to as “active oxygen.” them TAED at 5% max. level is the
sive bleaching agent and a sanitizer most widely used. Bleach activators
for household purposes, although in Crystalline sodium perborate at an alkaline pH of 9-12 preferen-
many developed countries it is being (sodium peroxyborate tetrahydrate, tially react with H O to form organic
2 2
replaced by oxygenated bleaches and 25% max) is the most widely used peroxyacid (PAA) that has a higher
photobleaching agents. oxidative bleach in laundry detergents oxidation potential when compared
worldwide. The perborate ion hydro- to H O showing better bleaching
2 2
Reduction bleaches lyses in the aqueous wash liquor to activity at lower temperature. Organic
Sodium dithionate, sodium or zinc form hydrogen peroxide. It exhibits a peroxyacid bleaching agents in situ
formaldehyde sulfoxylates, formadine superior shelf life compared to other are also less aggressive to fabric dyes
sulfinic acid, and sodium hydrosul- oxidative bleaches like sodium per- and optical brighteners than sodium
phite are some of the commercial carbonate (Na CO 1.5H O ), sodium hypochlorite bleaches. Unwanted
3
2 2
2
materials available for use as reduc- perphosphate (Na P O 3H O ), per- impurities like ions of copper, man-
4 2 7
2 2
tive bleaches to treat specific types of carbamide (CO(NH ) H O). Peroxo- ganese, and iron, if present in the
2 2
2
discoloration. They are usually used mono- and peroxodi- sulphuric and bleach liquor catalyse the release
in textile, dyeing industry or institu- phosphoric acid salts are not popular of oxygen that reduces the effect of
tional settings and very rarely used because of their poor bleaching power bleach and damages the fabrics. To
for household detergent formulations. and low oxidation potential. The salts, suppress this, 0.1-5% of finely divid-
sometimes fail to hydrolyse to hydro- ed magnesium silicate is added along
Oxygenated bleaches gen peroxide in the alkaline wash with small amounts of complexing
They are complex persalts of or- liquor of a detergent formulation. The agents like ethylenediaminatetraace-
ganic or inorganic compounds with activity of sodium perborate increases tic acid (EDTA) or Nitrilotrimethy-
hydrogen peroxide (H O ). Alkali per- with increasing, pH and temperature. lenephosphonic acid (NTPO) that ex-
2 2
carbonate, perborates, persulphates, The bleaching activity significantly hibit a significant stabilising effect.
perpolyphosphates, organic peroxides, increases with higher ratio of perbo-
etc., produce hydrogen peroxide in rate concentration in the wash liquor Photobleaching Agents (PBA)
aqueous medium, which, in turn, and so in the detergent formulation. Aluminium or zinc tetrabenzo-
decomposes to produce active oxygen tetraazaporphine derivatives repre-
that provides the bleaching activity. Unfortunately, sodium perborate sent another form of laundry bleach.
The discovery of hydrogen peroxide exhibits low bleaching effect at tem- Tinolux BS, a tetrabenzotetraazapor-
(H O ) in 1818 by Thenard as a perature below 60°C. To improve phine derivative, which can readily
2
2
bleaching agent triggered commer- the bleaching efficacy at lower tem- exhaust on to a cellulosic fibre from
the detergent wash liquor, is used in
present day detergents for superior
bleaching effect. Unlike in the other
bleach systems described above, in
photobleaching, oxygen from the
atmosphere is catalytically made
active by the photobleach and the
active oxygen in turn bleaches oxi-
dizable stains on the fibre. Further,
the bleaching performance from PBA
is obtained when the damp washed
laundry is exposed to light in pre-
sence of water, i.e., during soaking,
washing or drying. The PBA absorbs
light energy from the reddish part
Home, Personal & Institutional Care India November 2020 29