Field of the Invention
Background to the Invention
The present invention relates to systems containing a halogen bleach source, for
example for use as household cleaning products.
It is well known to use hypochlorite bleaches in household hard surface cleaning
compositions, for example as kitchen surface cleaners typically containing 0.1-1.5% by
weight of sodium hypochlorite at a pH of approximately 11.5-13.0, or at higher levels,
e.g. up to 3% by weight of hypochlorite for mould removal. However, there remains a
need to produce hypochlorite bleaching compositions giving the same high standards of
cleaning (and hygiene) performance as these standard sodium hypochlorite household
cleaning products but with lower hypochlorite levels to provide better sensory, safety
and environmental properties.
The present invention solves this problem by reducing the pH of the hypochlorite
solution at the point of delivery, by admixture with an acid.
WO-A-98/21308 describes the use of a dual-compartment pack to separate alkaline
hypochlorite and a chlorine 'de-activating agent' such as sulphamic acid. The mixed
formulation has a pH of around 6 and is said to give good bleaching of mould and
food/beverage stains on hard and soft surfaces but, as sulphamic acid acts as a chlorine
scavenger, without the risk of producing toxic chlorine gas. A hypochlorite to
sulphamic acid ratio of 3.6 to 2.5 is specified to ensure adequate bleaching activity. The
use of thickening agents in conjunction with these formulations, to provide "cling" to
vertical surfaces, is also disclosed.
The present invention differs from that disclosed in WO-A-98/21308 in that the usage
pH range is greater than 6 and for this reason the formulation need not contain an amine
compound as a chlorine 'de-activating agent'.
Also, as disclosed in WO-A-99/32596, an aqueous solution of "a source of unipositive
chlorine ions", typically sodium hypochlorite, contains a chlorine stabilising agent such
as sulphamic acid or a salt thereof, or an organic sulphonate or sulphonamide, and an
acidic buffer, typically a mono-, di- or polycarboxylic acid or phosphoric acid. The pH
is buffered to be from around 2 to 6.5.
The present invention differs from that disclosed in WO-A-99/32596 in that being in
two-pack form, the hypochlorite is stored at a more alkaline pH and therefore, does not
require the chlorine stabilising agent.
Definition of the Invention
There are several known examples of low pH hypochlorite bleaching systems in other
applications. US-A-4 236 891 describes the use of magnesium hypochlorite maintained
at a pH in the range 3.5-7.7, by addition of mineral or organic acids, for industrial or
domestic bleaching of textiles. CA-A-1 087 955 relates to use of hydroxycarboxylic
acid salts in reducing hypochlorite pH to between 5 and 8 for cleaning and disinfecting
substrates including human skin and clothing.
The present invention now provides a dual container delivery system comprising a first
container containing a first aqueous solution comprising a hypochlorite bleach or a
source thereof and having a pH of at least 13, a second container containing an aqueous
solution comprising an acid and delivery means for delivering the first and second
solutions to a surface such that they mix just before or upon impacting the surface, the
amount and strength of the acid in the second solution being such that the pH of the
resulting mixture is from 8 to 13, preferably from 9 to 12.
The pH of the first aqueous solution, i.e. that containing the hypochlorite, is at least 13.
Furthermore, the pH of the composition resulting from mixing of the two aqueous
solutions can also be as high as 13. However, it is to be understood that whatever the
pH of the first aqueous solution before mixing, the pH of the resultant mixed solution
will always be lower than that of the first aqueous solution, by virtue of the acid from
the second aqueous solution.
Without being bound by any particular theory or explanation, the applicants have
conjectured that the stability of sodium hypochlorite is optimised at high alkalinities
where self-decomposition (disproportionation) and reactions with other formulation
components are slow. Hypochlorite reactivity however increases with decreasing pH due
to the increased levels of the conjugate acid, hypochlorous acid HOCl, which is a highly
reactive electrophilic oxidant. These conflicting requirements for optimised reactivity
and stability mean that standard hypochlorite based household cleaning formulations,
which are delivered from single compartment formulations, use a combination of
relatively high hypochlorite concentrations to maximise cleaning and hygiene activity,
and relatively high alkalinities to maintain storage stability.
The present invention involves delivery of hypochlorite formulations of 'reduced'
alkalinity by mixing an alkaline hypochlorite solution with an acid at the point of
delivery. The alkaline hypochlorite and acid solutions are stored separately in the
compartments of a dual-compartment pack and mix together during application onto the
surface. In this way, the stability problems associated with use of reduced alkalinity
hypochlorite are avoided. The higher reactivity of the less alkaline hypochlorite
formulation allows a reduction in the level of hypochlorite required to achieve current
standards of cleaning and hygiene.
Detailed Description of the Invention
Systems according to the invention are applicable for use in a range of products where
relatively high concentrations of hypochlorite bleach are currently required to achieve
acceptable cleaning and hygiene performance. Specific product types include mould
removers, wc and kitchen cleaners.
Preferred forms of the first and second containers, the delivery means and the first and
second aqueous solutions, will now be described in more detail.
The first and second aqueous solutions need to be kept in different containers so that
their components do not react until use. This could be achieved by providing them in
respective separate containers. The consumer could then apply each to the surface,
either sequentially or simultaneously.
However, it is more convenient to provide the products in a dual-compartment container
in which the aqueous solutions are stored in separate compartments. The delivery
means then allows them to be delivered to the surface so that pH reduction of the
hypochlorite solution occurs or is initiated as they are exiting the delivery means and/or
in mid-air as they are directed to the surface and/or on the surface itself. Preferably,
they are delivered to be mixed in approximately equal volumes, i.e. typically from 0.5 :
1 v/v to 1 : 0.5 v/v.
A particularly preferred delivery means, especially for non-thickened systems, is a
trigger spray head. In the case of a dual compartment system, this will preferably have
two siphon tubes, respectively leading into each compartment and either a single nozzle
with a mixing chamber or two separate nozzles substantially adjacent to each other. If
desired, a dispensing nozzle or nozzles configured to promote foaming may be used.
For thickened systems a pouring dual compartment packaging form is generally
The hypochlorite or hypochlorite source is preferably present at about from 0.01% to
10% by weight, more preferably from 0.1% to 2%, most preferably from 0.05% to 0.5%
by weight of the first aqueous solution. In the second solution, the amount of acid will
depend on the alkalinity of the hypochlorite (first aqueous) solution. However, for
typical commercial sources of hypochlorite solution, in the case when the acid in the
second aqueous solution is a monovalent mineral acid, this will be typically present at
about from 10 mole% to 200 mole%, more preferably from 50 mole% to 150 mole%
based on the molar concentration of the hypochlorite present. The quantity of acid
required to achieve a specific pH will of course depend on the quantity of additional
alkali added to the first solution. For n-valent mineral acids, these values will be
divided by n. In the case of organic acids, these amounts are more difficult to express as
the range of strengths of such acids is quite large. However, for a dicarboxylic acid such
as malic, maleic or succinic acid, typical ranges might be from 10 mole% to 300 mole%,
more preferably from 50 % to 150 mole%.
The hypochlorite or source thereof in the first solution may be a simple hypochlorite salt
such as those of the alkali or alkaline earth metals or a compound which produces
hypochlorite upon hydrolysis, such as the organic N-chloro compounds. Mixtures of
such materials may also be used.
The acid in the second solution may be a mineral acid such as hydrochloric, sulphuric,
phosphoric or nitric acid. The term "acid" includes acidic salts such as sodium
hydrogen sulphate. Alternatively, it may be organic acid such as a mono-, di- or
polycarboxylic acid. Forms of any of these which are hydroxylated and/or contain keto
and/or ester and/or amide groups may also be used. Saturated and unsaturated forms are
included within these definitions.
Simple monocarboxylic acids such as formic acid and acetic acid may be used but are
less preferred because of their unpleasant odours. A non-exhaustive list of typical
suitable organic acids includes propanoic, lactic, glycolic, pyruvic, crotonic, isovaleric,
cinnamic, salicylic, carbanic, methylcarbanic, benzoic, glucanic, malic, maleic,
sulphonic, methane sulphonic, toluene sulphonic, fumaric, malonic, itaconic, oxalic,
tartaric, glutamic, aspartic and succinic acids. However, citric acid is a generally
preferred organic acid.
The acid component in the second aqueous solution may contain mixtures of two or
more acids. However, whatever acid or acids are used, they preferably should not be of
a type which would be oxidised within a few minutes of admixture with the
hypochlorite. Again, mixtures of such materials may be used. The weight ratio of the
hypochlorite or its precursor to the acid is typically from 0.01 : 1 to 100 : 1.
The hypochlorite (or source thereof) and acid solutions are stored separately using dual-compartmentalised
packaging and react together on mixing during application onto the
surface. The resulting mixed formulations give efficient bleaching from the relatively
low levels of the hypochlorite. In a typical embodiment, the hypochlorite is present in
alkaline solution, in order to minimise decomposition, while the acid is present at a level
sufficient that on mixing the final pH of the formulation is optimised for the specific
usage scenario. It is important that the mixing process be carefully controlled so that the
pH of the final mixed solution is constrained not to fall below a value of 8. Attempts to
achieve lower pH values could result in incomplete mixing and localised areas of very
low pH with the consequent risk of generating toxic chlorine gas. The mixed
composition may also contain surfactants, polymers and other formulation components
such as a perfume, or dye. Some or all of these additional components can be stored
separately from hypochlorite, i.e. together with the acid, allowing use of formulation
ingredients that do not have long term stability in hypochlorite solution and are therefore
not used in conventional single compartment hypochlorite bleach formulations.
The composition according to the invention optionally may comprise detergent actives
(surfactants). These may be chosen from a wide range of anionic, nonionic, cationic,
amphoteric or zwitterionic surfactants well known in the art.
Suitable anionic surfactants are e.g. water-soluble salts, particularly alkali metal,
alkaline earth metal and ammonium salts, of organic sulphate esters and sulphonic acids
having in the molecular structure a C8-C22 alkyl radical or a C10-C22 alkaryl radical.
Examples of such anionic surfactants are alcohol sulphate salts, especially those
obtained from the fatty alcohols derived from the glycerides of tallow or coconut oil;
alkyl-benzene sulphonates such as those having a C9-C11 radical. Examples of such
anionic detergents are alcohol sulphate alkyl group attached to the benzene ring;
secondary alkanesulphonates; sodium alkyl glyceryl ether sulphates, especially those
ethers of the fatty alcohols derived from tallow and coconut oil; sodium fatty acid
monoglyceride sulphates, especially those derived from coconut fatty acids; salts of 1-6
EO ethoxylated fatty alcohol sulphates; salts of 1-8 EO ethoxylated alkylphenol
sulphates in which the alkyl radicals contain 4-14 C-atoms; the reaction product of fatty
acids esterified with isethionic acid and neutralised with sodium hydroxide.
The preferred water-soluble synthetic anionic surfactants are the alkyl benzene
sulphonates, the olefin sulphonates, the alkyl sulphates, and the higher fatty acid
monoglyceride sulphates and fatty acid soaps.
A special class of anionic surfactants which may be used in the cleaning compositions
according to the invention are hydrotropes which are known in the art specifically for
their thickening or liquid structuring capabilities. Well known examples of such
compounds are the alkali metal salts of toluene-, xylene- and cumene-sulphonic acid.
Suitable nonionic surfactants can be broadly described as compounds produced by the
condensation of alkylene oxide groups, which are hydrophilic in nature, with an organic
hydrophobic compound which may be aliphatic or alkylaromatic in nature. The length of
the hydrophilic or polyoxyalkylene radical which is attached to any particular hydrophobic
group can be readily adjusted to yield a water-soluble or water dispersible compound
having the desired balance between hydrophilic and hydrophobic elements.
Particular examples include the condensation product of straight chain or branched chain
aliphatic alcohols having 8-22 C-atoms with ethylene oxide, such as coconut oil fatty
alcohol/ethylene oxide condensates having from 2 to 15 moles of ethylene oxide per mole
of coconut alcohol; condensates of alkylphenols whose alkyl group contains 6-16 C-atoms
with 2 to 25 moles of ethylene oxide per mole of alkylphenol; condensates of the reaction
product of ethylenediamine and propylene oxide with ethylene oxide, the condensates
containing from 40 to 80% of ethyleneoxy groups by weight and having a molecular
weight of from 5,000 to 11,000. Other examples are: tertiary amine oxides of general
structure RRRNO, where one R is a C8-C22 alkyl group (preferably C8-C18) and the other
Rs are each C1-C5 (preferably C1-C3) alkyl or hydroxyalkyl groups, for instance
dimethyldodecylamine oxide; tertiary phosphine oxides of structure RRRPO, where one R
is a C8-C22 alkyl group (preferably C8-C18) and the other Rs are each C1-C5 (preferably C1-C3)
alkyl or hydroxyalkyl groups, for instance dimethyl-dodecylphosphine oxide; dialkyl
sulphoxides of structure RRSO where one R is a C10-C18 alkyl group and the other is
methyl or ethyl, for instance methyltetradecyl sulphoxide; fatty acid alkylolamides;
alkylene oxide condensates of fatty acid alkylolamides and alkyl mercaptans. Amine
oxides are especially preferred because they blend very well with inorganic electrolytes
and show good stability to hypochlorite bleach.
Suitable amphoteric surfactants are derivatives of aliphatic secondary and tertiary amines
containing a C8-C18 alkyl group and an aliphatic group substituted by an anionic water-solubilising
group, for instance sodium 3-dodecylamino-propionate, sodium 3-dodecylaminopropane
sulphonate and sodium N-2-hydroxydodecyl-N-methyl taurate.
Suitable cationic surfactants are quaternary ammonium salts having at least one C8-C22
aliphatic or alkyl-aromatic group, e.g. dodecyl-trimethylammonium bromide or chloride,
cetyltrimethyl-ammonium bromide or chloride, didecyl-dimethyl-ammonium bromide or
chloride, octyl-benzyldimethyl-ammonium bromide or chloride, dodecyl- benzyldimethyl-ammonium
bromide or chloride and (higher alkyl)- benzyldimethyl-ammonium bromide
or chloride. Many quaternary ammonium salts have antimicrobial properties and their use
in cleaning compositions according to the invention leads to products having exceptionally
effective disinfection properties against a wide range of micro-organisms. They are used in
the cleaning compositions according to the invention in an amount of 0-10%, preferably
0.1-8%, more preferably 0.5-6%. Since virtually all cationic surfactants would be unstable
in the presence of hypochlorite, when they are used, they should be incorporated in the
second aqueous solution (i.e. the acid solution).
Suitable zwitterionic surfactants are derivatives of aliphatic quaternary ammonium,
sulphonium and phosphonium compounds having a C8-C18 aliphatic group and an
aliphatic group substituted by an anionic water-solubilising group, for instance 3-(N,N-dimethyl-N-hexadecylammonium)propane-1-sulphonate
betaine and 3-(cetylmethyl-phosphonium)-ethane-sulphonate
Further examples of suitable surfactants are given in the well-known textbooks "Surface
Active Agents", Volume I by Schwartz and Perry and "Surface Active Agents and
Detergents", Volume II by Schwartz, Perry and Birch.
Detergent surfactants often play an important role in thickening systems. Apart from
that they are preferably added also for their wetting properties on hard surfaces and for
their cleaning properties. Thus, preferably surfactants are present even if a non-surfactant
thickening system is used. If not required for thickening, the total surfactants
content is preferably between 0.1 and 20%, more preferably between 0.5 and 10%. If
part of the thickening system the minimum total amount of surfactant will be at least
0.5%, preferably at least 1%.
Electrolytes, particularly inorganic salts, are part of many thickening systems. Suitable
salts are alkali metal carbonates, sulphates and halogenides. Electrolytes are used in an
amount of 0-20%, preferably 0-15%, more preferably 0-10%.
Many thickening systems have been used in thickened hypochlorite bleach
compositions. Such systems often consist of two or more different detergent surfactants,
or of one or more such surfactants in combination with an electrolyte such as an
inorganic salt. Many thickening systems comprise as one of their components tertiary
amine oxides containing one long alkyl chain e.g. having 8-22 C atoms and two shorter
alkyl chains e.g. having 1-5 C-atoms, often in combination with an anionic surfactant.
Examples of such thickening systems are described in EP-A-079697, EP-A-110544, EP-A-137551,
EP-A-145084, EP-A-244611, EP-A-635568, WO95/08611, DE-A-19621048
and the literature cited in these patent applications.
Other suitable thickening systems comprise polymeric substances which in solution
thicken in response to an increase in pH or electrolyte concentration. Examples thereof
are polymers of acrylic acid known for their thickening properties such as those sold
under the trademark "Acusol".
In the case of the dual container systems of the present invention, the final composition
may be thickened if desired, preferably by a multi-component thickening system of
which the components are divided over at least two partial compositions, such that on
mixing of the partial compositions on delivery to the surface to be cleaned the
combination of the components of the thickening system causes the final composition to
thicken. This will improve the composition's ability to cling to a non-horizontal surface
and prevent it from draining off before proper cleaning is obtained. Usefully the
viscosity of the final composition after dispensing is at least 50 mPa.s, more preferably
at least 100 mPa.s. On the other hand the viscosity is preferably not more than 1000
A large number of multicomponent thickening systems is known in the art. For them to
be suitable for the cleaning compositions according to the invention, preferably at least
one component should be storage stable in the same partial composition as the
hypochlorite bleach. The total thickening system should be sufficiently stable in the
final composition to enable it to thicken and remain on the surface for long enough to
perform its cleaning action.
Another way to improve cling of the final composition to a non-horizontal surface is to
cause it to foam on dispensing through the addition of a foaming surfactant to at least
one partial composition and the use of an appropriate dispensing device such as foaming
trigger sprays known in the art.
Surfactants which are storage stable in combination with the hypochlorite or
hypochlorite source may be combined in the same (first) partial composition.
Surfactants which do not have such stability should be made part of the other (second)
Other Optional Components
The cleaning compositions according to the invention may also usefully contain a
sequestering agent suitable for binding Ca ions. Suitable sequestering agents for this
purpose are well known in the art and include compounds such as: alkali metal
tripolyphosphate, pyrophosphate and ortho- phosphate, sodium nitrilotriacetic acid salt,
sodium methylglycine-diacetic acid salt, alkali metal citrate, carboxymethyl malonate,
carboxymethyloxysuccinate, tartrate, mono- and di-succinate and oxydisuccinate.
The mixed composition on the surface may also contain polymers and other formulation
components such as a perfume, colourant and foam control agents. Some or all of these
additional components can be stored separately from the hypochlorite or hypochlorite
source, i.e. together in the second solution with the acid, allowing use of formulation
ingredients that do not have long term stability in strong oxidising agents and are
therefore not used in conventional single compartment hypochlorite bleach
Example 2a and 2b
A typical non-limiting formulation suitable for delivery from a dual-compartment pack
would be as follows:
- Partial composition A: sodium hypochlorite - 1.0%, pH adjusted to 13.0 (in order to
minimise hypochlorite decomposition).
- Partial composition B: hydrochloric acid - 0.55%, pH 0.8.
- Solutions A & B when dispensed from a suitable dual-compartment and mixed in equal
proportions will produce a 'hypochlorite' solution with a pH of 11.0.
Example 2a is the composition of a two-pack reduced alkalinity 'low' hypochlorite
mould remover or kitchen cleaner formulation suitable for delivery from dual-compartment
spray pack. Compositions A & B are stable over extended periods and
Example 2b is the composition of the mixed formulation on delivery from the dual-compartment
pack onto the surface.
Example 2a: Typical partial compositions for a reduced alkalinity 'low' hypochlorite
mould remover or kitchen cleaner
| Chemical Name || % active level in formulation as delivered from pack |
| Partial Composition A: |
|Sodium xylene sulphonate ||1.20 |
|Sodium hydroxide ||0.60 |
|Sodium hypochlorite ||1.00 |
|Decyl-dimethyl amine oxide ||0.40 |
|Sodium laurate (soap) ||0.20 |
|Water ||to 100% |
| Partial Composition B: |
|Hydrochloric acid ||0.55 |
|Water ||to 100% |
Example 2b: Formulation of a prototype reduced alkalinity 'low' hypochlorite mould
remover or kitchen cleaner on delivery to the surface formed upon mixture of the
components of example 2a:
| Chemical Name || % active level in formulation as delivered from pack |
|Sodium xylene sulphonate ||0.60 |
|Sodium hydroxide ||0.30 |
|Sodium hypochlorite ||0.5% |
|Decyl-dimethyl amine oxide ||0.20 |
|Sodium laurate (soap) ||0.10 |
|Hydrochloric acid ||0.275 |
|Water ||to 100% |
|The mixed formulation had a pH of 11.0 |
B. CLEANING APPRAISAL DATA
Further, if desired, viscous products suitable for providing 'cling' to vertical surfaces,
such as wc bowls, are prepared by use of suitable surfactants or thickening agents. These
are added to partial compositions A & B such that the partial compositions are non-viscous
during storage but develop viscosity on mixing, during delivery from the pack.
Examples showing the enhanced cleaning efficacy of the reduced alkalinity/low
hypochlorite solutions will now be described.
Cultures of hyphal Cladosporium cladosporioides were prepared on agar jelly. Warm
water was used to dissolve the jelly and separate it from the mould hyphae, which were
then autoclaved. A little distilled water was added to the hyphae which were crushed to
a 'paste' using a pestle and mortar. The 'paste' consisted of a mixture of fine particles
of hyphal cell wall together with a dark black mould ink. Once prepared, the mould
paste was stable to storage for several weeks at 5°C.
A small amount of the 'mould paste' was applied to the surface of a porous ceramic tile
and a small amount of distilled water added. This mixture was evenly spread across and
rubbed into the surface of the tile using a flexible plastic spatula. Additional mould
paste or water was added to ease the soiling process as necessary. The final appearance
of the soiled tile was a uniform dark grey. The tiles were left to dry overnight in the
dark and then large tiles were then cut into smaller test pieces using a standard 'tile
Small circular pieces of single ply tissue paper were cut to a convenient size and placed
on the surface of the 'mould tile' test pieces, such that the edges of the test pieces
remained uncovered. A fixed quantity of the test solution was allowed to drop onto the
surface of the tissue and allowed to soak into the tile. The test solution only contacted
that area of the tile that was originally covered by the tissue paper, thus preserving a
background of untreated 'mould paste' around the periphery of the test piece about 1
cm3 of bleach liquor was required to cover a circular area around 3 cm in diameter).
The test solution was allowed to remain in contact with the soil for a fixed contact time,
i.e. about 3 minutes or 20 minutes, after which the test piece was immersed in 1.0M
sodium thiosulphate solution for 10 minutes (to quench the reaction and prevent further
bleaching). The test pieces were then immersed in distilled water for 10 minutes before
rinsing with further distilled water and air drying.
Test pieces were assessed for the level of mould bleaching by an expert panel, using a
integer scale running from 0 (no decolorisation) to 6 (complete bleaching). Panel test
data for each system were collated and analysed statistically to provide mean scores for
each test system. Each test (bleaching) system was tested using at least 3 replicate tiles.
Typical test data showing the effect of pH on mould bleaching are shown in Table 1.
Example 4: Application as a Kitchen Cleaner
The data show that the bleaching activity of a standard commercial sodium hypochlorite
product (3.0% sodium hypochlorite, pH 13) can be achieved from just 0.5% sodium
hypochlorite if the pH is reduced by a few units.
|Bleaching of 'autoclaved mould paste' by various hypochlorite containing systems (ambient temperature, 3 minutes contact time) |
| || Mean score |
| || pH |
|Concentration of sodium hypochlorite (% w/w) ||13.0 ||12.0 ||11.0 ||10.5 ||10.0 |
|0.2% ||0.0 ||0.6 ||1.7 ||--- ||--- |
|0.5% ||1.3 ||2.2 ||3.1 ||4.2 ||5.6 |
|3.0% ||5.4 ||6.0 ||--- ||--- ||--- |
A length of pre-stained cotton cloth was cut into square swatches (2 cm x 2 cm). Four
replicate cloths were placed in the bottom of a clean glass beaker and covered with the
cleaning liquor at room temperature. After a contact time of 2 to 5 minutes has elapsed,
the cloths were removed from the cleaning solution using tweezers and immediately
immersed in distilled water. The cloths were stirred in the water, and washing procedure
repeated twice more using fresh water each time. Washed cloths were then pressed
between two filters to remove excess water and placed on fresh filter papers, in the dark,
Reflectance measurements were carried out on a Spectraflash 400 instrument. ▵R
measurements were calculated using '40ptspec' software, using a portion of untreated
cloth from the same cloth batch as a standard. Results obtained from each of the four
replicate test cloths were then statistically analysed to obtain mean ▵R values for each
bleach system. Test data showing the effect of reducing the pH of the sodium
hypochlorite are shown in Table 2.
|Bleaching of tea stained cotton cloth (BC-1) by 'acidified' hypochlorite (1 minute contact time ambient temperature, c.a. 20°C). |
| || Mean Δ R (460nm) |
| || pH |
|Concentration of sodium hypochlorite ||13.0 ||12.0 ||11.0 ||10.0 ||9.0 |
|0.1% ||4 ||8 ||13 ||16 ||18 |
|1.0% ||10 ||22 ||26 ||27 ||28 |
Example 5: Bactericidal Performance of Mixed Systems on Dilute Application
The results show that bleaching efficacy of the hypochlorite significantly enhanced by
controlled acidification. By this means, a ten-fold reduction in sodium hypochlorite
content can be made whilst maintaining bleaching performance by reducing the 'in-use'
pH by a few units. Thus a 0.1% sodium hypochlorite formulation at pH 11.0 can
provide performance parity with a typical commercial based kitchen cleaner formulation
containing c.a. 0.5% - 1.5% sodium hypochlorite at a pH of 11.0-13.0.
The test was designed to reflect the European Suspension Test protocol (European
Standard EN1276). The bacterial test suspension contained between 1.5 and 5.0 x 108
Testing was performed under conditions of heavy soil. A stock solution of 3% bovine
albumin was prepared as an interfering substance. The test formulation was pre-diluted
to the relevant concentration in sterile Water of Standard Hardness (24° French Hard).
The presence of the bacterial test solution and interfering substance resulted in a further
1 : 1.25 dilution of the formulation in the test procedure.
Test Procedure: A volume of the interfering substance was pipetted into a sterile
container and an equal volume of the bacterial test suspension was added and contents
of the tube were mixed. The bacteria and soil were allowed a contact time of 2 min ±
10s. At the end of this contact time, a volume of the diluted formulation was added to
produce an overall 1:10 dilution of both the bacterial test suspension and interfering
substance and the contents of the tube were mixed again. The formulation was allowed
a bactericidal contact time of 5 min ± 10s.
At the end of the contact time an aliquot was removed and diluted 1:10 into a sterile
container containing a suitable chemical quenching solution. The contents were mixed
thoroughly and left for a contact time of 5 min ± 1 minute. The dilution process was
repeated a further five times into a suitable diluent to produce a series of six dilutions of
the bactericidal stage ranging from 10-1 to 10-6.
Total viable counts were enumerated by a suitable method and the reduction in number
of viable cells elicited by the test formulation was calculated. Table 3 shows the
biocidal activity of hypochlorite delivered from stock solutions at pH 13.4 and 9.0. The
results were achieved after 1 : 40 dilution of the test formulation.
| Biocidal activity |
| || || Log Reduction (SD) |
| || || S. aureus || E. hirae |
| ||NaOCl (%) |
| pH 13.4 ||1.2 ||2.03 (0.36) ||0.23 (0.09) |
| ||1.6 ||3.53 (0.89) ||1.27 (1.03) |
| ||2.0 ||4.67 ||4.78 |
| pH 9 ||1.2 ||3.18 (0.45) ||1.58 (0.49) |
| ||1.6 ||4.67 ||4.34 (0.89) |
| ||2.0 ||4.67 ||4.78 |
A reduction in pH from 13.4 to 9.0 when the two solutions were mixed prior to dilution
resulted in increased bactericidal activity from low levels of hypochlorite (<2.0%).