Hydrogen Peroxide (H2O2) Bleaching

The H2O2 bleaching is the most common bleaching method, and is environmentally friendly (degradable into water and oxygen). The best bleaching whiteness can be obtained at pH 11 adjusted using caustic soda.

However, if metal ions, such as iron ions and copper ions are present in fabrics or in water, catalytic action of these metal ions causes abnormal degradation of H2O2, which may sometimes cause embrittlement of fabrics until holes (pin-holes) are generated due to the excessive degradation.

Usually, the abnormal degradation of H2O2 and the resulting generation of pin-holes are prevented by adding a chelating agent. Also, as a stabilizer for H2O2, sodium silicate has been conventionally employed. The obtained bleaching whiteness is favorable. However, the use of sodium silicate has the following disadvantages. Silica scales are generated due to calcium ions and magnesium ions reacted with silica ions. The generated silica scales are adhered to machinery, damaging fabrics, or undermining hand of the fabrics.This case, however, suffers from a contradiction that complete removal of calcium ions and magnesium ions will undermine the stability of H2O2.

To solve the disadvantages and contradiction, a non-silicate type stabilizer containing no sodium silicate has been developed, although the cost is higher than sodium silicate.

Furthermore, when dyeing is performed without a drying process after the H2O2 bleaching, the problem of residual H2O2 arises. 10ppm of residual H2O2 or more causes dyeing problems, although it depends on a type of dye. To degrade the residual H2O2, a reducing agent or the like, or an enzyme (catalase) can be used. The enzyme appears as a current mainstream.