Persalts sodium perborate

This is the basis for the use of the solid forms of H2O2, that is, persalts such as sodium perborate (PBS) and sodium percarbonate (PCS). 

If sufficient heat and/or time is available, peroxide alone is an effective bleach. This is typically delivered into the formulation in the form of solid persalts. The two most commonly encountered forms are sodium perborate and sodium percarbonate. Sodium perborate is more storage stable than sodium percarbonate. To obtain satisfactory storage stability for commercial use, the latter is typically coated. 

Sodium perborate is available as the so-called tetrahydrate (NaB03 4H20 or PBS4) or monohydrate (NaBOs H2O or PBSl). The monohydrate is produced by dehydration of the tetrahydrate. The perborates are true persalts, having the structure shown in Fig. 1 [7]. It can be seen from the structure that the monohydrate is actually an anhydrous salt and the tetrahydrate is a hexahydrate. The nomenclature of PBSl and PBS4 arose before the true structures of these salts were known. 

Sodium percarbonate (PCS, NazCOa 1.5 H2O2) is not a true persalt but a simple addition compoimd and, consequently, is less storage stable, as is, than perborate (PBSl or PBS4). It has an active oxygen content of 15% (approximately equal to that of PBSl). Its solubility at 20°C is 120 g/L (i.e., about five times more soluble than PBS4). Its rate of dissolution, in the uncoated form, is about the same as that of PBSl, and its bulk density is somewhat higher (0.9-1.2 kg/L, depending on the method of manufacture). The carbonate liberated contributes to the alkalinity of the wash bath. 

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