Bleaching hydrogen peroxide determination

Methods. A typical hydrogen peroxide bleaching operation consists of treatment of a 20% HPL solution in 60-75% aqueous ethanol with 25-50% hydrogen peroxide (by weight) on lignin derivative at 80°C. The reaction medium is adjusted to pH 2 by the addition of HC1, or to pH >12-13 by NaOH. Color loss is determined by UV/VIS absorbance measurements on suitably diluted samples. 

We undertook the study of this reaction, employing conditions where limited amounts of oxygen (or hydrogen peroxide) were allowed to react with mercaptoacetate in the presence of iron ions. The amount of Fe(III) (OH) (RS)2-2 produced was determined spectrophotometrically. Since the rate of bleaching of this complex was fast under some of the conditions, a rapid-mixing device was employed. This consisted of a spring-actuated syringe, patterned after one described by Stem and Du Bois (12), which injected one of the reaction mixtures into the other contained in a spectrophotometer cell. 

Apart from the basic products, hydrogen peroxide and sodium hydroxide, an industrial bleaching bath contains many additives, the most important of which are discussed below. From an analytical point of view, it is evident that, for the development of a sensor for hydrogen peroxide, each of the additives used must be investigated to determine whether and to what extent they can interfere. 

Measurement of the hydrogen peroxide concentration during bleaching processes determined by means of the sensor system (—) and titration (x). The smaller figure represents the measured data during the first 500min. 

Use thermochemical Equations a and b to determine AH for the decomposition of hydrogen peroxide (H2O2), a compound that has uses ranging from bleaching hair to energizing rocket engines. 

Regarding exploitation of the isosbestic point in DWS for the analysis of turbid samples, a good example is the determination of hydrogen peroxide in wood pulp bleaching streams relying on peroxide association with the molybdate ion [22]. The influence of dispersed lignin in the pulp bleaching stream, a critical spectral interferent in the analytical procedure, was quantitatively circumvented. 

Therefore, it was of interest to determine which of these two parameters— permeability or mercaptan content—might contribute more to the rate of polymer add-on. Hair was bleached to varying extents with alkaline hydrogen peroxide and then treated with a bisulfite-cumene hydroperoxide system, using methyl methacrylate monomer. The data clearly show increasing polymer add-on with decreasing disulfide cross-links (Table... 

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