Bleaching and dyeing; fluid treatment and chemical modification – Bleaching
Reexamination Certificate
2000-01-12
2003-07-29
Kopec, Mark (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Bleaching
C008S107000, C008S110000, C162S158000, C162S100000, C162S091000, 16, 16, 16, 16, 16, 16
Reexamination Certificate
active
06599326
ABSTRACT:
The instant invention pertains to a method for preventing the loss of brightness and for enhancing resistance to yellowing in pulp or paper, particularly pulp or paper which may still contain traces of lignin, by the addition of N,N-dialkylhydroxylamines, an ester, amide or thio substituted N,N-dialkylhydroxylamine or N,N-dibenzylhydroxylamine, or their salts and other coadditives.
BACKGROUND OF THE INVENTION
High-yield and ultra-high yield wood pulps undergo rapid light-induced discoloration, particularly when they are exposed to near ultraviolet light (wave lengths 300-400 nm) in indoor fluorescent light and daylight. This characteristic restricts their use to short-life, low-value paper products. High-yield and ultra-high yield wood pulps can be bleached to a high level of whiteness. If this whiteness could be stabilized against discoloration, these bleached high-yield pulps could displace significant amounts of more expensive fully-bleached, low-yield chemical pulps.
This discoloration is ascribed to the substantial lignin content of high-yield pulps totally about 20-30% by mass. Phenoxy radicals are the key intermediates in the reaction mechanism. Several light-induced reactions have been proposed to account for their formation such as cleavage of the aryl ether bond of phenacyl aryl ether groups, or breakdown of ketyl radicals formed from saturated aryl-glycerol &bgr;-aryl ether structures in lignin. The phenoxy radicals are oxidized by other oxygen-centered radicals (alkoxy and perhydroxy) to form yellow chromophores.
I. E. Arzkin et al., Khymiya drevesiny (Chemistry of Wood), 1982, No. 2, 114 and A. D. Sergeev et al., ibid, 1984, No. 5, 20 disclosed that the use of iminoxyl radicals such as TEMPO (1-oxyl-2,2,6,6-tetramethylpiperidine) is useful in the delignification of wood using the one-stage oxygen-soda (alkaline) process, but made no mention or suggestion of any activity provided by TEMPO on preventing light-induced discoloration of paper or pulp made from such treated wood.
V. 1. Khodyrev et al., Vysokomol soyed, A29, No. 3, 616 (1987) [Polymer Sci. U.S.S.R., 29, No. 3, 688 (1987)] show that the photoinitiated oxidation by oxygen causes weathering of cellulosic textile materials such as flax or cotton, and that the light stability of the cellulose could be improved by photostabilizers such as the UV absorbers, benzophenols and 1-oxyl-2,2,6,6-tetramethylhydroxypiperidine. The UV absorbers offer no protection, and are actually detrimental. The authors noted that the stable nitroxyl radical interacts with alkyl radicals in the cellulose to afford its salubrious stabilizing activity. There is no suggestion by the authors that this stabilizing activity could be applied successfully in wood pulp and/or paper made therefrom.
M-K. Syler et al., J. Assn. Paper Pulp Tech, 29, 135 (1990) show that selected metal salts such as magnesium sulfate and lower alkanoic acids inhibit color reversion in bleached pulp.
P. Fomier de Violet et al., Cellulose Chem. Tech., 24, 225 (1990) show that the use of UV absorbers and hydrogen donor agents such as thiols, ascorbic acid, etc. help prevent the photoinduced discoloration of hydrogen peroxide bleached wood pulp, but that chain breakers such as hindered phenols and hindered amines (having >N—H or >N—CH
2
— moieties) had no or even a detrimental effect on preventing photoinduced discoloration.
R. Agnemo et al., 6th International Symposium on Wood and Pulping Chemistry, Appita, 1991, confirmed that free hydroxyl radicals plus lignin lead to undesirable photoyellowing in pulp and paper.
S. Omori et al., J. Assn. Paper Pulp Tech, 48, 1388 (1993) describes the effect of antioxidants and UV absorbers on light reversion and concludes that the combination of an antioxidant and UV absorber prevents color reversion and has a synergistic effect in that activity.
M. Paulsson et al., 8th International Symposium Wood and Pulping Chemistry, Helsinki, 1995, show that efficient photostabilization of unbleached paper or hydrogen peroxide bleached TMP pulp can be achieved by acetylation.
There have been a number of different approaches proposed to inhibiting the yellowing of mechanical pulps. These include: radical scavengers and antioxidants; UV screens; elimination of chromophores after their formation; chemical modification of lignin by alkylation or acetylation; polymeric inhibitors; and two types of coadditives used in combination. Z-H. Wu et al., Holzforschung, 48, (1994), 400 discuss the use of radical scavengers like phenyl-N-tert-butylnitrone to reduce the formation of chromophores during mechanical pulping and give a more light-stable pulp.
C. Heitner, Chemistry of Brightness Reversion and It Control, Chapter 5, TAPPI, Atlanta, 1996, pp 183-211, summarizes the state of the art in the thermal and light-induced yellowing of lignin-containing pulps such as thermomechanical (TMP) and chemithermomechical (CTMP) pulps, showing the seriousness of these undesirable effects discusses generally the then current prior art methods used to attack this problem. These include bleaching, the use of phosphites, UV absorbers, polyalkylene glycols and free radical scavengers such as ascorbic acid, thiols, thioethers, dienes and aliphatic aldehydes and chelating agents such as ethylenediaminetetraacetic acid (EDTA). The author concluded that, although much progress had been made, much still remains to be done before a successful and practical solution to this loss of brightness and undesirable yellowing of lignin-containing pulp and/or paper is found.
Copending application Ser. No. 09/119,567 describes a potential solution where the use of selected hindered amine nitroxides, hindered amine hydroxylamines or their salts in combination with selected UV absorbers and metal chelating agents is seen to prevent loss of brightness and to enhance resistance to yellowing in chemimechanical or thermomechanical pulp or paper still containing lignin.
Canadian Patent Application No. 2,164,394 and WO 97/36041 teach a multi-component system for modifying, degrading or bleaching lignin-containing materials. This system includes an oxidation catalyst as an essential component. The catalysts are selected enzymes such as oxidoreductases of classes 1.1.1 to 1.97. The system also includes a number of mediators which inter alia include lower N,N-dialkylhydroxylamines and N,N-dibenzylhydroxylamine.
The instant invention describes another approach to this important problem where the use of N,N-dialkylhydroxylamine, an ester, amide or thio substituted N,N-dialkylhydroxylamine or N,N-dibenzylhydroxylamine or their salts in combination with selected coadditives also prevents the loss of brightness and enhances resistance to yellowing in pulp or paper, especially pulp or paper still containing lignin. The ester, amide or thio substituted N,N-dialkyl-hydroxylamines are described in U.S. Pat. Nos. 4,612,393; 4,720,517 and 5,019,285.
DETAILED DESCRIPTION OF THE INVENTION
Hydroxylamines are known to be efficient free radical traps and may limit the production of o-quinones; UV absorbers limit photochemistry in the underlying substrate to which they are applied, and ultimately reduce the production of free radicals. UV absorbers and hydroxylamines are each effective at stemming some of the free radical chemistry leading to paper yellowing when used singly. However, when they are used together, hydroxylamines and UV absorbers can act synergistically to effectively stop photochemical yellowing of lignin containing papers. The hydroxylamines show enhanced inhibiting activity when combined with a metal chelating agent such diethylenetriaminepentaacetic acid or citric acid, or polymeric inhibitors such as polyethylene glycol.
More particularly, the instant invention pertains to a composition having enhanced resistance to yellowing which comprises
(a) a chemical pulp or paper, especially a kraft pulp or paper, which may still contain traces of lignin, and
(b) an effective stabilizing amount of an N,N-dialkylhydroxylamine, an ester, amide or thio substituted N,N-dialkylhydroxylamine or N
Cunkle Glen T.
Devore David
Heitner Cyril
McGarry Peter F.
Nelson Randall B.
Ciba Specialty Chemicals Corporation
Hall Luther A. R.
Hamlin Derrick G.
Kopec Mark
Stevenson Tyler A.
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