Method for deinking printed waste paper using soybean peroxidase

DETAILED DESCRIPTION OF THE INVENTION As described herein, it has been discovered that newsprint such as newspapers, magazines, etc.
can be reclaimed as secondary fiber for use in the production of high quality fine paper for printing and writing by treating an aqueous slurry of pulped newsprint with a peroxidase enzyme and a peroxide such as hydrogen peroxide.
Preferably the original newsprint contains up to about 5% moisture.
Any of a variety of peroxidases can be used in the present invention.
Soybean peroxidase is preferred because tests have shown that it is more reactive and that it is more chemically and thermally resistant than other peroxidases.
Furthermore, soybean peroxidase (SBP) exhibits a higher redox potential than some other enzymes such as horseradish peroxidase (HRP) as shown in Table 1:
TABLE 1
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Redox Potential of Soybean Peroxidase (SBP) vs.
Horseradish
Peroxidase (HRP)
Substrate (.
lambda.
max)
E1/2 (V) SBP* HRP*
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pentamethoxybenzene (300 nm)
1.
07 8.
76 2.
50
1,2,3,5-tetramethoxybenzene
1.
09 3.
02 0.
30
(295 nm)
1,2,4-trimethoxybenzene
1.
12 9.
23 1.
64
(450 nm)
hexamethoxybenzene (425 nm)
1.
24 0.
22 0
1,4-dimethoxybenzene (315 nm)
1.
34 0.
072** 0
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*all values in .
DELTA.
Abs/(mg enzymemin).

**curve of .
DELTA.
Abs/time slopes upward as reaction proceeds.

Although soybean peroxide is preferred, the invention is also open to the use of peroxidases such as peroxidases from other legumes, horseradish peroxidase, rice peroxidase and peroxidases from malvaceous plants such as cotton.
The aqueous slurry of the printed waste paper pulp fibers may be treated with the peroxidase in the form of a plant extract or, in the case of soybean peroxidase, the soybean seed hulls may be employed directly