Chemistry Reference
In-Depth Information
these products were used in two companies with which agreements had
been made to perform experiments in an industrial environment. Apart
from the commercial additive mixtures, the generally used products, such
as water glass, magnesium sulphate and sodium persulphate were also
studied as single substances.
Each selected additive was investigated in the presence and absence of
hydrogen peroxide. Based on these experiments, it was verified as to
whether or not the additive has electroactive properties and whether it
interferes with the hydrogen peroxide signal, which can be possible in an
electrochemical way or through another route. Once the behaviour of the
different groups of additives is known, they are combined into real bleach-
ing solutions, where, once again, a number of experiments are performed
for reasons of control. In these, it is not only the concentration of the addi-
tives that is varied but also the hydrogen peroxide concentration and the
pH. The aim is to verify whether the sensor works correctly, whether a pos-
sibly occurring interference was intercepted and/or eliminated in an appro-
priate way, and whether Equation 5.2, obtained in absence of additives,
needs to be adapted.
Inorganic additives
Sodium hydroxide is the most important inorganic additive in solution, not
only to obtain optimal bleaching effects but also because this particle is pH-
determining and the latter parameter strongly influences the current signal.
This interference, which was thoroughly investigated in the absence of other
additives (as was described in the previous sections of this chapter), appears
not to be influenced by the presence of these other additives. Consequently,
the influence of the sodium hydroxide concentration as is represented
in Equation 5.2 is still valid. Besides an activator (sodium hydroxide), a
stabiliser is also required, as is indicated in Chapter 4, section 4.2.2. To
this end, mainly MgSO
4
in combination with water glass is used. These
components do not appear to have electroactive properties in the studied
potential area, and do not perceptibly influence the hydrogen peroxide
signal.
Sodium persulphate (desizing agent) does, however, appear to have elec-
troactive properties. However, these are manifested only in the sensor not
the relevant reduction region. In an oxidation region, sodium persulphate
behaves indifferently. It does not display electroactive properties, and it
does not influence the hydrogen peroxide signal in a non-electrochemical
way either. It can be concluded that the inorganic additives do not inter-
fere with the electrode signal originating from the hydrogen peroxide oxi-
dation reaction, with the exception of sodium hydroxide. Considering the
importance of this reagent in the bleaching process, its influence was thor-
