Ciba Specialty Chemicals Corporation

Pulp and Paper Research Institute of Canada

Cyril Heitner

Raymond R Seltzer

Jean-Pierre Wolf

Glen T Cunkle

Randall B Nelson

Peter F McGarry

John A Schmidt

David Devore

Norman Liebergott

Chemical pulps or papers, especially kraft pulps or papers, which may still contain traces of lignin, have enhanced resistance to yellowing when they contain an effective stabilizing amount of a N,N-dialkylhydroxylamine, an ester, amide or thio substituted N,N-dialkylhydroxylamine or N,N-dibenzylhydroxylamine or an amminium salt thereof. This performance is often further enhanced by the presence of one or more coadditives selected from the group consisting of the UV absorbers, the polymeric inhibitors, the nitrones, the fluorescent whitening agents and metal chelating agents. Combinations of hydroxylamines or their salts, benzotriazole or benzophenone UV absorbers and a metal chelating agent are particularly effective. N,N-Diethylhydroxylamine and N,N-dibenzylhydroxylamine and their acid salts are surprisingly effective for this purpose.

Inhibition of pulp and paper yellowing using hydroxylamines and other coadditives

Pulps or papers, especially chemimechanical or thermomechanical pulps or papers, which still contain lignin, have enhanced resistance to yellowing when they contain an effective stabilizing amount of a hindered amine compound which preferably is a nitroxide, a hydroxylamine or an ammonium salt thereof. This performance is often further enhanced by the presence of one or more coadditives selected from the group consisting of the UV absorbers, the polymeric inhibitors, the nitrones, the fluorescent whitening agents, metal chelating agents, sulfur containing stabilizers, metal salts and diene compounds. Combinations of nitroxides, hydroxylamines or their salts, benzotriazole or benzophenone UV absorbers and a metal chelating agent are particularly effective. Selected derivatives of 1-oxyl-2,2,6,6-tetramethyl-piperidin-4-ol and selected hydroxylamine salts are novel compounds and are surprisingly effective for this purpose.

Inhibition of pulp and paper yellowing using nitroxides, hydroxylamines and other coadditives

Pulps or papers, especially chemimechanical or thermomechanical pulps or papers, which still contain lignin, have enhanced resistance to yellowing when they contain an effective stabilizing amount of a hindered amine compound which preferably is a nitroxide, a hydroxylamine or an ammonium salt thereof. This performance is often further enhanced by the presence of one or more coadditives selected from the group consisting of the UV absorbers, the polymeric inhibitors, the nitrones, the fluorescent whitening agents, metal chelating agents, sulfur containing stabilizers, metal salts and diene compounds. Combinations of nitroxides, hydroxylamines or their salts, benzotriazole or benzophenone UV absorbers and a metal chelating agent are particularly effective. Selected derivatives of 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol and selected hydroxylamine salts are novel compounds and are surprisingly effective for this purpose.

A multistage process for bleaching high-yield and ultra high-yield pulps is described whereby the pulp is treated sequentially with a peroxygen compound, a reducing compound and a final peroxygen compound to achieve higher brightness levels.

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Pierrefonds, Canada

Cyril Heitner