A new class of bleaching and brightness stabilizing agents. Part III: Brightness stabilization of mechanical pulps

Recently, we discovered that water-soluble tertiary hydroxyalkyl phosphines and quaternary hydroxymethyl phosphonium salts were capable of providing a bleaching effect similar to or higher than that achievable with hydrosulphite on mechanical pulps over a wide range of pH, consistency and temperature. Now, we have found that mechanical pulps bleached with these phosphorus (P) compounds are more stable than those bleached with hydrosulphite, not only when exposed to heat and moisture, but also during ambient dark storage. One of the P compounds, tris(hydroxypropyl)phosphine (THPP), P(CH2CH2CH2OH)(3), is also effective in providing additional brightness gains to, and in improving the light stability of papers made from peroxide-bleached mechanical pulps.