WO2009015704A1

WO2009015704A1 - Bleached fibrous material

Info

Publication number: WO2009015704A1
Application number: PCT/EP2008/002575
Authority: WO
Inventors: Esa-Matti Aalto; Hans-Ludwig Schubert
Original assignee: Voith Patent Gmbh
Priority date: 2007-07-31
Filing date: 2008-04-01
Publication date: 2009-02-05
Also published as: DE102007036376A1

Abstract

The invention relates to bleached fibrous material from wood having a degree of brightness, according to ISO, of > 80% and a buIk of more than 1.3 cm3/g, a breaking length of more than 7.5 km at 15 °SR and a lignin content of at least 13% in relation to the oven-dry fibrous material for coniferous wood in the bleached state and having a tearing length of more than 5.0 km at 20°SR and a lignin content of at least 10% in relation to the oven-dry fibrous material for hardwood in the bleached state. Said fibrous material is characterised in that it is bleached after pulping, maintaining as much lignin as possible.

Description

Bleached pulp

The invention relates to a bleached pulp.

Bleached pulps are measured on known fibers, especially wood pulp and pulp. During the production of pulp, the lignin, the cement substance, is leached out between the cells of the lignocellulosic raw material, which largely consist of cellulose and hemicelluloses, during the digestion. The leading process for producing pulps is the kraft process. The digestion is carried out in the kraft process with sulfides. Other pulp digestion processes are the sulfite process or the soda process. The sulfite process can be carried out with different process variants from the acidic to the neutral to the alkaline pH range. During digestion, a reduction of the original lignin content of the lignocellulosic raw material from about 20% to 28% based on the otro mass of the raw material to about 2.5% to 5% is sought.

The lignin content of the raw material can thus be reduced in the digestion readily to about 20% of the original lignin content. However, the digestion conditions with the intermediates and degradation products of lignin and the residual lignin remaining in the pulp cause the pulp to have whiteness of 15% ISO to 60% ISO after digestion. The pulp is therefore too dark for most industrial applications.

Bleaching with chemicals that do not degrade the remaining lignin and the various degradation products of lignin has proven to be uneconomic. Therefore, in most pulp mills today, an oxygen stage is connected to the digestion. Under alkaline reaction conditions, a significant portion of the residual lignin and degradation products of lignin are degraded in the presence of oxygen. However, the reaction conditions require pressure reactors which are operated at high temperatures and thus considerable expenses for plant engineering and energy. Only after the oxygen stage is the use of bleaching agents economical that do not degrade lignin.

Wood pulps, to which refineries and high-yield pulps are reckoned at this point, are produced as far as possible without loss of yield, ie obtaining as high a native lignin content as possible. Wood pulps are bleached only with chemicals that do not degrade lignin to any appreciable extent. White levels of 8 O% ISO and above are not achievable for wood pulp.

For industrial applications there are thus two groups of fibers available. Pulp fibers have high static and dynamic strengths and high degrees of whiteness. The fiber optic properties such. B. Opacity or Buil are not good for pulp fibers. Wood pulp fibers generally have low strengths at the same degrees of whiteness. But they offer good optical properties.

The object is to provide fibers which have good optical properties at high strengths and whitenesses at the same time.

This object is achieved with a pulp according to claim 1. According to the invention a bleached wood pulp is proposed which has a whiteness of> 80% ISO and a buik of 13 cm ₃ / g and at the same time a breaking length of more than 7.5 km at 15 ⁰ SR and a lignin content of at least 13% based on the otro pulp for softwood bleached and having a breaking length of more than 5.0 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp for hardwood in the bleached state, wherein the pulp bleached as possible ligninerhaltend after digestion becomes.

A pulp that bleaches to high whiteness while maintaining good fiber optic properties and strength properties, is z. B. prepared by lignocellulosic raw material is mixed with a sulfite solution and digested at high temperatures. The digestion is completed in time so that the yield at over 75% based on the otro raw material. The pulp thus produced has a tenacity of more than 7.5 km at 15 ^° SR and a lignin content of at least 13% based on the otro pulp for softwood in the bleached state. For hardwood, such a pulp produced has a breaking length of more than 5.0 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp in the bleached state.

According to a preferred embodiment of the invention, the pulp after bleaching has a whiteness of at least 85% ISO for softwood pulp with a lignin content of more than 13% based on the otro softwood pulp and for hardwood pulp with a lignin content of more than 10% based on the otro hardwood pulp. In particular, when the pulp is prepared by the above-described method using a sulfite solution, the pulp can be bleached even with a high lignin content to very high whiteness.

Preferably, a bleached pulp is proposed, which has a tenacity of more than 9 km, preferably of more than 10 km as a softwood pulp at 15 ⁰ SR, and as a hardwood pulp at 20 ⁰ SR a breaking length of more than 5.5 km having. If a fibrous material which has been digested with a sulfite solution is bleached, then the pulp can be lightened so gently that high strengths are retained.

The requirement for overall high strength properties is preferably followed by a bleached pulp which, as a softwood pulp, has a lignin content of more than 13% at 15 ^° SR a tearing strength of more than 60 cN, preferably more than 70 cN, and which is hardwood. Fiber has a lignin content of more than 10% at 20 ⁰ SR a tear strength of more than 50 cN. Thus, the pulp according to the invention has both high static strength (tear length) and high dynamic strength (tear strength).

According to a preferred embodiment of the invention, the pulp is bleached by a combination of bleaching agents, in particular by oxidizing and reducing chemicals. The combination of several bleaches allows an individual Adaptation to the requirements of the bleached pulp. Whiteness, builing, opacity and other properties of the bleached pulp can be individually adjusted in this way.

Suitable bleaching agents are both reductive and oxidative bleaches, preferably peroxide, formamidine sulfonic acid (FAS), dithianite, borole and / or peracetic acid. These bleaching agents can be used with economically justifiable plant and energy costs. A pulp bleached with these bleaches is very competitive in comparison to pulp and pulp.

The lignocellulosic bleaching of a wood pulp alone with lignin-containing chemicals helps to maintain a high bulk. The BuIk remains above 1,3 cm3 / g for wood pulp with a breaking length of more than 5 km at 20 ° SR for hardwood and softwood pulp with a breaking length of more than 7,5 km at 15 ⁰ SR not yet known, especially when it comes to bleached fibers with a whiteness of more than 75% ISO.

The lignocellulosic bleaching of lignocellulosic fibers, which were produced in particular using sulfites, with lignocellulosic bleaches is explained in more detail below using exemplary embodiments.

The examples described below were evaluated according to the following rules:

The yield was calculated by weighing the raw material used and the pulp obtained after the digestion or the bleaching, in each case dried at 105 ^° C. to constant weight (atro).

The paper technology properties were determined on test sheets which were produced according to Zellcheming leaflet V / 8/76. - The degree of grinding was recorded according to Zellcheming leaflet V / 3/62.

The density (BuIk) was determined according to Zellcheming regulation V / 11/57. The tear length was determined according to Zellcheming regulation V / 12/57. The tear resistance was determined according to DIN 53 128 Elmendorf. The whiteness was determined by preparing the test sheets according to Zellcheming leaflet V / 19/63, measured according to SCAN C 11:75 with a Datacolor elrepho 450 x photometer; the whiteness is given in percent according to ISO standard 2470. - The opacity was determined according to the specification Zellcheming leaflet VI / 1/66. The term "otro" in this document refers to "oven-dry" material which has been dried at 105 ^° C. to constant weight.

The chemicals for bleaching are given in weight percent, unless otherwise explained. -

Eucalyptus high yield pulp with an initial whiteness of 61% ISO was initially treated with a Q-grade. This was followed by peroxide bleaching and a final bleaching with formamidine sulfonic acid (FAS bleach).

Q-stage

The Q-step was performed with 0.2% DTPA at 3% consistency for 60 minutes and at a reaction temperature of 70 ⁰ C. The pH was adjusted to between 5 and 5.5 using 4 N sulfuric acid. At the end of the Q-stage the whiteness was 65% ISO.

P-stage

The subsequent peroxide stage was carried out with 3% peroxide, 1.5% NaOH, 0.1% MgSO 4 and 0.05% DTMPA. Consumption of 64% of the peroxide used reached a brightness of 81% ISO. The P-stage was carried out for 180 minutes at 8o C and a consistency of 10%.

FAS stage

The final FAS-stage was carried out at 99 ⁰ C over a period of 30 minutes at the consistency of 10%. Based on the otro eucalyptus high yield fiber, 0.4% NaOH, 0.3% Na 2 SiO 3 and 0.5% FAS were used. At the beginning of the bleaching, a pH of 10.2 was established. At the end of bleaching was measured a pH of 9.35. The final whiteness was determined to be 86.5% ISO.

The thus-bleached pulp was milled to a freeness of 20 ° SR within 4 minutes. At this freeness, a tearing length of 5.51 km and a tearing strength of 55.0 cN (100 g / m ² ) were measured. The opacity is 82.5%. The BuIk was determined to be 1.39 cm ³ / g.

Claims

claims

l. Bleached wood pulp with a whiteness> 75% ISO and one

BuIk of over 1.3 cm ₃ / g with a breaking length of more than 7.5 km at 15 ⁰ SR and a lignin content of at least 13% based on the otro pulp for softwood bleached

Condition and with - a tearing length of more than 5.0 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp for hardwood in the bleached

Condition, characterized in that the pulp is bleached as possible lignin-preserving after digestion.

2. Pulp according to claim 1, characterized in that the pulp after bleaching has a whiteness of at least 80% ISO for softwood pulp with a lignin content of more than 13% based on the otro softwood pulp and - at least 85% ISO for hardwood pulp with a lignin content of more than 10% in relation to otro hardwood pulp.

3. Pulp according to claim 1, characterized in that the bleached pulp as softwood pulp at 15 ⁰ SR has a tearing length of more than 9 km, preferably of more than 10 km, and as hardwood pulp at 20 ⁰ SR one Tear length of more than 5.5 km.

4. Pulp according to claim 1, characterized in that the bleached pulp as a softwood pulp with a lignin content of more than 13% at 15 ⁰ SR has a tear strength of more than 60 cN, preferably greater than 70 cN, and as hardwood Fiber having a lignin content of more than 10% at 20 ° SR has a tear strength of more than 50 cN.

5. Fiber according to claim 1, characterized in that the pulp has been bleached by oxidizing and reducing chemicals.

6. Pulp according to claim 5, characterized in that the pulp is bleached by peroxide, formamidine sulfonic acid (FAS), borole and / or peracetic acid.