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Method for reducing brightness reversion of mechanical pulps and high-yield chemical pulps

a technology of mechanical pulp and brightness reversion, which is applied in the field of fibrous products, can solve the problems of reducing reflectivity, negative effect on other properties of products, or being uneconomical, and achieves the effect of improving brightness reversion and not significantly impaired by yellowing

Inactive Publication Date: 2007-07-19
KEMIRA OY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0008] It is an aim of the present invention to eliminate the problems of the prior art and to provide a new method of reducing or preventing yellowing. The method aims at effectively reducing both light- and heat-induced brightness reversion of mechanical pulps and high-yield chemical pulps.
[0010] Thus, the present invention provides a method of modifying fibres by bonding of new compounds to the oxidized fibres via radical pathways. In particular, the aim of the bonding of the compounds is to stabilize the structure by forming a colourless lignin derivative unable to participate in yellowing reactions.
[0015] contacting the oxidized fibre material with a modifying agent containing at least one first functional site, which is capable of bonding to oxidized fibre material, said modifying agent being capable of imparting to the lignocellulosic fibre material improved resistance to brightness reversion caused by light or heat or combinations thereof.
[0017] Another embodiment of the invention provides a method of reducing light or heat induced brightness reversion of mechanical or high-yield chemical pulp, comprising the steps of enzymatically or chemically oxidizing phenolic groups of the pulp and bonding to the oxidized phenolic groups a substance capable of forming a colourless lignin derivative unable to participate in yellowing reactions.
[0019] The present invention provides important advantages. Importantly, the invention makes it possible to produce novel kinds of fibrous materials having improved brightness reversion. By means of the process, the modifying agents can be reliable attached to the fibres, and the improved resistance to yellowing will not be significantly impaired by, e.g., extensive washing of the fibres prior to forming the material into a paper or cardboard web.

Problems solved by technology

Usually, such changes result in reduced reflectivity, particularly in blue light.
Heat and damp are the main causes of the brightness reversion of chemical (lignin-free) pulps, whereas mechanical pulps mostly yellow when they are exposed to light.
Many of the additives that have been found to prevent yellowing are expensive or problematic from an environmental point of view; others are only effective when introduced in so large amounts that they may have a negative effect on other properties of the product or be uneconomical.

Method used

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  • Method for reducing brightness reversion of mechanical pulps and high-yield chemical pulps

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0049] A 5 g portion of bleached spruce TMP was suspended in water. The pH of the suspension was adjusted to pH 4.5 by addition of acid. The suspension was stirred at RT. Laccase dosage was 1000 nkat / g of pulp dry matter and the final pulp consistency was 7.5%. After 30 minutes laccase reaction, 0.15 mmol linoleic acid / g of pulp dry matter was added to the pulp suspension. After 1 h total reaction time, the pulp suspension was filtered and the pulp was washed thoroughly with water. Handsheets were prepared. For comparison purposes, reference treatments were carried out using the same procedure as described above but without addition of laccase or linoleic acid or both. The light-fastness on the pulps was tested with Xenotest 150S light exposure and weathering test instrument using “window glass” filter. The brightness of the handsheets was measured as function of irradiation dosage. The results are presented graphically in FIG. 1.

[0050] From the results presented in FIG. 1, it is a...

example 2

Bonding of New Compounds to TMP

[0051] A 5 g portion of spruce TMP was suspended in water. The pH of the suspension was adjusted to pH 4.5 by addition of acid. The suspension was stirred at RT. Laccase dosage was 1000 nkat / g of pulp dry matter and the final pulp consistency was 7.5%. After 30 minutes laccase reaction the new compound was added to the pulp suspension. After 1 h total reaction time, the pulp suspension was filtered and the pulp was washed thoroughly with water. Handsheets were prepared. For comparison purposes, reference treatments were carried out using the same procedure as described above but without addition of laccase or the new compound. The light-fastness on the pulps was tested with Xenotest 150S light exposure and weathering test instrument using “window glass” filter. The changes in the ISO brightnesses after irradiation are summarized in Table 1.

TABLE 1Δ BrightnessIrradation(as ISO-Treatment(Whm2)Brightness)TMP Reference126010TMP + laccase + ferulic acid...

example 3

[0052] Sample A: Peroxide bleached aspen-CTMP-pulp was treated with sodium persulphate (dosage 5 kg / ton of pulp) and linoleic acid (5 kg) at 80° C., at pH 5 for 60 minutes. The treatment was carried out at a consistency of 10%.

[0053] Sample B: The pulp sample was treated in the same way as Sample A except that ammonium persulphate (5 kg) was used instead of Na-persulphate.

[0054] Sample C: The pulp sample was treated in the same way as Samples A and B except that hydrogen peroxide was used instead of persulphate. The pH of the test was 4.

[0055] Sample D: The pulp sample was treated as Sample A but t-butanol (5 kg) was used instead of linoleic acid.

[0056] Sample E: The pulp sample was treated in the same way as Sample A, but no linoleic was added. After the treatment with persulphate, a separate treatment was made with linoleic acid (5 kg) at 80° C. at a consistency of 10%. The duration of the treatment was 30 min, and the pH was 5

[0057] Sample F: The sample was prepared as Sampl...

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Abstract

The present invention concerns a process for reducing the susceptibility of lignocellulosic material to unwanted yellowing, particularly yellowing caused by light and heat. According to the invention, the fibres are activated enzymatically or chemically and then contacted with a modifying agent capable of bonding to the oxidized fibre material, rendering the lignocellulosic fibre material improved resistance to brightness reversion. By means of the invention, brightness reversion caused by light or heat or a combination thereof can be retarded and even stopped.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to fibrous products. In particular, the present invention concerns a process for reducing the susceptibility of lignocellulosic material to unwanted brightness reversion, in particular to brightness reversion caused by light or heat. [0003] 2. Description of Related Art [0004] It is well-known in the art that light (UV light in particular), heat, moisture and chemicals can give rise to changes in the brightness of cellulose pulps. Usually, such changes result in reduced reflectivity, particularly in blue light. This phenomenon is known as brightness reversion or yellowing and can be caused by various factors depending on which type of pulp is concerned. Heat and damp are the main causes of the brightness reversion of chemical (lignin-free) pulps, whereas mechanical pulps mostly yellow when they are exposed to light. The brightness reversion of mechanical pulps also varies depending on t...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): D21C9/00D21C5/00D21H11/20D21H21/14
CPCD21C5/005D21H21/143D21H11/20D21C9/005
Inventor BUCHERT, JOHANNAVIIKARI, LIISAGRONQVIST, STINASVEDMAN, MIKAELPAREN, ARTOVUORENPALO, VELI-MATTI
Owner KEMIRA OY
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