AU463580B2 - Preparation of woodpulp - Google Patents

Description

3.4 6 0 73 63,

to a method The present invention relates generally them to a high-yield of treating whole-wood fibers to convert More particularly pulp useful in paper-making operations. for converting whole-wood the invention relates to a process treatment with a fibers to pulp which comprises sequential and to a method of chlorine-containing compound and ozone; lignin-preserving bleaching these pulps by treatment with bleaching agents. a carbohydrate Wood is composed of two main parts portion com- or cellulosic portion and a non-carbohydrate this latter portion being prising phenolic-type compounds, commonly referred to as lignin. wood must For use in paper-making processes the can be defined as wood fibers first be reduced to a pulp which and then deposited capable of being slurried or suspended methods employed to accom- on a screen to form a sheet. The a physical or chemical plish this generally involve either of the two treatments. treatment of the wood, or a combination ground against a In mechanical pulping, wood is physically pulp of low purity, grindstone resulting in a high-yield fragments of fibers, with comprising mainly fiber bundles and the individual fibers. considerable damage being done to to as groundwood pulp, The resulting pulp, most often referred made from it tend to has low bonding strength, and papers on aging. deteriorate in strength and turn yellow 4635.8

63,4 60/73 In chemical pulping wood chips are treated with a and chemical solution which attacks the non-fibrous materials are reacts with the lignin to form soluble compounds which

removable by washing. This type of treatment results in a

purity low-yield pulp having less fiber damage and a higher

than mechanical pulp. Besides the low yield, chemical pulping

wood chips processes require cooking digesters wherein the hours to are treated for periods of time ranging from three

seven hours.

The production of semi-chemical or chemi-mechanical mechanical treat- pulp involves a combination of chemical and treat- ments 4 n which the wood is first subjected to a chemical refiberizing ment to soften the lignin, followed by mechanical

to complete the fiber separation. The resulting pulp is of an

damage to the intermediate to high yield with little if any

individual fibers. The high yield pulps can readily be bleached loss in to an acceptable brightness without any significant is low and yield, but the bonding strength of these pulps charac- papers produced from them have very poor strength

teristics. At lower yields the pulps have improved bonding acceptable bright- strength but are difficult to bleach to an

ness. be It is also known that whole wood fibers can removal of produced without chemical treatment and without of the weight of lignin, resulting in a yield close to 100% treatment of the the wood employed, by a preliminary steam a pressure disc re- wood chips followed by a defiberizing in

finer. These fibers are useful in making fiber insulation bonding strength and and wallboard, but due to their lack of of as pulp low brightness they are not generally thought 4 635. S

3.4 60 /73 useful in the preparation of paper products. The whole wood fibers used in the present invention prior to sepa- are produced by treating wood chips with steam disc refiner. ration of the individual fibers in a pressure together to form The resulting fibers are incapable of bonding since they an acceptable sheet and are also low in brightness original wood. contain most or all of the components of the In accordande with the present invention, to con- excessive vert these fibers to a high-bonding pulp, without one loss of yield, they are first treated with at least chlorine chlorine-containing compound consisting of chlorine, treated with dioxide or a hypochlorite salt and subsequently

ozone. Pulps produced by this method are readily bleached opera- to a brightness useful in conventional paper-making agents. tions by treatment with lignin-preserving bleaching In carrying out this invention whole wood fibers in the are prepared according to any of the methods known fibers as art. It is especially preferred to prepare the follows: Wood chips are fed to a digester where they are of maintained in contact with steam at a gauge pressure then passed 100 psi for four to six minutes. The chips are 10 to through a disc refiner with an energy input of from set to reduce horsepower days per ton and clearances are the wood to substantially single fibers. The fibers separator. passed through a blow valve and into a cyclone In converting these fibers to a pulp useful in is preferred: paper making processes the following procedure The fluffed fibers, at a consistency of from

about 3% to about 6 are treated with from about 3% to 4635.80

63.460 73 compound con- one chlorine-containing about 6% of at least a hypochlorite salt. chlorine dioxide or sisting of chlorine, from about out at a temperature of This treatment is carried about from about 5 to 0 at times ranging 0 F. to about 80 F. on be varied depending The times employed can minutes. of compound, and the concentration the chlorine-containing pre- compound. It is especially said chlorine-containing and 6% solution of between 4% ferred to employ an aqueous to 45 minutes. time of from 30 chlorine at a treatment fibers is adjusted of these treated The consistency is comminuted 45 This thickened stock to approximately 35- are the resulting fluffed fibers in a disintegration mill and stream, with oxygen containing treated, in a countercurrent 0 to 80 F. for a temperature of from 600 from 2% to 4% ozone at of ozone is equal minutes. The take-up from 2 to about 40 fibers. of the weight of the to from 2% to 10% in excess which is generally The pulp produced, employed, has a bright- of the weight of the wood chips of 75% when measured on a range of 50-60 G.E. units nes. in the ness in the range o ith TAPPI Standard accordance with TAPPI Standard General Electric Photometer in to pulp have been found prepared from this T 217m. Sheets approximatley 4000 to 6000 exhibit a breaking length of to the length of a uni- meters. This length is equivalent held at one end, would of paper which, if formly wide strip under its own weight. This just cause the strip to break paper and is calcu- the strength of the is an indication of the basis weight of the tensile break load and lated from T 220m. in TAPPI Standard sheet as specified by way of the of the pulp obtained The brightness with can be increased by treatment process of this invention 4635.80

63.460/73 preferred bleaching agents. To avoid any loss in yield it is agents such as peroxide, to use "lignin-preserving" bleaching sodium hydrosulfite, and peracetic acid, zinc hydrosulfite, treatment is especially sodium borohydride. The following

preferred. ozone, the pulp After treatment with chlorine and solution to increase the pH is treated with a dilute alkaline about 8 and the stock is ad- to a value of from about 6.5 to about 30% to 35%. An alkaline justed to a consistency of from the ratio of alkali, calculated peroxide solution, in which is from about 2.2 to 1 to as sodium hydroxide, to peroxide so that from 0.8% to about 2.8 to 1, is added in an amount on the bone dry weight of the 1.2% hydrogen peroxide, based with is allowed to remain in contact pulp, is added. The pulp of from 7 00-1200F. the peroxide solution at a temperature hours. The pulp is then washed for a period of from 20 to 25 yield with a dilute solution of sulfurous acid. The of the weight of the wood of the pulp is from 65 to 85% prepared from this.pulp chips originally employed. Sheets have an increased brightness. invention so that In order to describe the present the following examples it may be more clearly understood, set forth primarily for are set forth. These examples are and any specific enumeration of the purpose of illustration, not be interpreted as a detail contained therein should invention. limitation on the concept of this EXAMPLE I treated with satu- Mid-western poplar chips were of 75 psi for 4.44 minutes. rated steam at a gauge pressure at a gauge pressure of The softened chips were then fed,

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S3.46 0 psi, into the eye of a double disc refining apparatus with

the discs rotating in opposite directions at 1200 rpm. The

disc diameters were 36 inches and had a separation of 0.01

inches. The defiberized wood was discharged from the refin-

ing equipment and into a cyclone separator. The product

isolated consisted essentially of single, intact fibers with

a composition very similar to the original wood and little,

if any, bonding characteristics.

The lignin content of the fibrous fraction was

reduced by diluting the defiberized wood product to a consis-

tency of 1% and screening the product through a Sweco gyrating i 31 L A c&

screen with 801 mesh wire. Essentially ligneous material

passed through the screen.

The whole wood fibers, at 4% consistency, were then

treated with an aqueous solution of chlorine so that The chlorine was added based on the weight of the fibers.

chlorinated material was dewatered, without subsequent wash- the ing, to a consistency of 40% in a basket centrifuge and The product was fluffed in a high speed fiber separator. stream fluffed fibers were then treated with a countercurrent

of from 2% to 4% ozone in oxygen. The gas velocities and

a the rate of feed of the fibers were adjusted so that at and residence time in the ozonation equipment of 30 minutes

a temperature of 77°F. the amount of ozone consumed was

of the bone dry weight of the fibers. Hand-sheets were

TAPPI prepared from the resulting pulp in accordance with T 281m Standard T 205m for physical tests and TAPPI Standard

for optical tests. Sheets produced in this manner had a Photometer and brightness, as measured on a General Electric and 60 when expressed in terms of G.E. units, of between 50

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63.460 73 measured in accordance with TAPPI Standard T 217m. The break-

ing length of the sheet was approximately 5000 meters.

A sodium hydroxide solution was added to the re-

sulting unbleached pulp to raise its pH to 7.5 and the pulp

was then dewatered to 34% consistency. A peroxide bleach

solution having an alkali, calculated as sodium hydroxide,

to peroxide ratio of 2.5 to 1 was applied to the pulp so that

1% peroxide was added based on the bone dry weight of the 0 pulp. After 23 hours at 95 F. the pulp was washed with water

containing 0.1% sulfurous acid. The bleached pulp had a

yield equal to 78% of the weight of the poplar chips used.

Sheets prepared as with the unbleached pulp had

the following properties:

Breaking Length 5444 meters

Brightness 83.5 G.E.

Reverted Brightness, as measured by re- reading the brightness after aging the sheets at 105 0 C. for one hour 80.9 G.E.

EXAMPLE II

Whole wood fibers were prepared from poplar chips

as in Example I. The resulting fibers, at 3% consistency,

were treated with an aqueous solution containing 2% chlorine

dioxide and 3% chlorine based on the weight of the fibers. 0 After 30 minutes at 77 F. the chlorinated material was washed,

dewatered to a consistency of 48.2% in a basket centrifuge

and fluffed in a high speed fiber separator. The fluffed

fibers were then treated with a countercurrent stream of from

2% to 4% ozone in oxygen. The gas velocities and the rate

of feed of the fibers were adjusted so that, at a residence

time in the ozonation equipment of 30 minutes and a tempera-

43 5,8 0

63.460 73 0 ture of 77 the amount or ozone consumed was 3.2% of the bone dry weight of the fibers. The resulting product was a pulp and was useful in forming sheets as in Example I. An alkaline solution was added to this pulp to raise the pH to 7.0 and the pulp was then dewatered to consistency. A peroxide bleach solution having an alkali, calculated as sodium hydroxide, to peroxide ratio of 2.5 to 1 was applied to the pulp so that 1.16% peroxide was added based on the bone dry weight of the pulp. After 24 hours at 770 F. the pulp was washed with water containing 0.1% sulfurous acid. The yield of bleached pulp was equal to 77.5% of the weight of the poplar chips employed. Handsheets prepared as in Example I had the follow- ing properties: Breaking Length 4393 meters Brightness 79.2. G.E. EXAMPLE III Whole wood fibers were prepared from poplar chips as in Example I. The resulting fibers were dewatered to 0 consistency in a basket centrifuge and dried in air at 77 F. The air-dried fibers were suspended in carbon tetrachloride and were treated with a solution of 5% chlorine gas in carbon tetrachloride. The final consistency of the fibers in carbon tetrachloride was The mixture was agitated for 0 minutes and then allowed to stand, at 77 for an addition- al 30 minutes. The fibers were separated by filtration, di- luted with water to a consistency of 1% and dewatered. The

fibers were then treated with ozone as in Example I and the conditions adjusted so that the amount of ozone consumed was 5.6% of the bone dry weight of the fibers. Sheets could

46 0

63.4 60 Ir be formed from the resulting pulp. to The pulp was washed with an alkaline solution consistency. raise its pH to 6.5 and then dewatered to 36.5% as A peroxide bleach solution having an alkali, calculated was applied sodium hydroxide, to peroxide ratio of 2.5 to 1 on the to the pulp so that 1.16% peroxide was added based 0 bone dry weight of the pulp. After 23 hours at 95 F. the acid. The pulp was washed with water containing sulfurous weight of the yield of bleached pulp was equal to 80% of the poplar chips employed. Handsheets prepared as in Example I had the fol-

lowing properties: Breaking Length 4387 meters

Brightness 80 G.E.

EXAMPLE IV

Western hemlock chips were fed through a rotating were in direct pocket pressure valve into a chamber where they of 100 psi contact with saturated steam at a gauge pressure at a gauge for 4.99 minutes. The heated and softened chips, a double disc pressure of 100 psi, were fed into the eye of opposite direc- refining apparatus with the discs rotating in

tions at 1200 rpm. The disc diameters were 36 inches and

had a separation of 0.015 inches. The defiberized wood was a cyclone discharged from the refining equipment and into fibers which separator. The product was essentially single sheet. were incapable of bonding together to form a

The whole wood fibers, at 3% consistency, were 3% treated, for 5 minutes, with an aqueous solution of fibers and there- chlorine dioxide, based on the weight of the based on after with an aqueous solution of 3% chlorine also 4 63 5, ca oi 0 the dry weight of the fibers. After 30 minutes at 77 F. the chlorinated material was dewatered to a consistency of and the product was fluffed in a high speed fiber separator.

The fibers were then treated with ozone as in Example I

and the conditions adjusted so that the amount of ozone con-

sumed was 8.8% of the bone dry weight of the fibers. Fol-

lowing this treatment the product was a pulp and handsheets

prepared as in Example I had a breaking length of approximately

6000 meters. The pulp was washed with an alkaline solution to raise its pH to 7 and then dewatered to 36% consistency. A peroxide bleach solution having an alkali, calculated as sodium hydroxide, to peroxide ratio of 2.5 to 1 was applied to the pulp so that 2.0% hydrogen peroxide was added based on the bone dry weight of the pulp. After 23 hours at 950 F. the pulp was washed with water containing sulfurous acid. The yield of bleached pulp was equal to 80% of the weight of the western hemlock chips employed. Handsheets prepared as in Example I had the fol- lowing properties. Breaking Length 6139 meters Brightness 73.1 G.E. EXAMPLE V Whole wood fibers were prepared from poplar chips as in Example I. The resulting fibers, at 3% consistency, were treated with an aqueous solution of 3% sodium hypo- chlorite based on the weight of the fibers. After 5 minutes

at 770 F. the chlorinated material was washed, dewatered to a consistency of 40%, and fluffed in a high speed fiber sepa- rator. The fluffed fibers were treated with ozone as in -11- 4635,80

63.4 60/73 of adjusted so that the amount Example I and the conditions the fibers. of the bone dry weight of ozone consumed was 8.45% which handsheets could be prepared The result was a pulp from

as in Example I. adjusted to 6.7 with a The pulp, after the pH was solution was treated with a bleach sodium hydroxide solution,

comprising 1.5 gs hydrogen peroxide 1.0 gms sodium hydroxide 5.0 gms sodium silicate 100 cc water was applied so that 1.25% peroxide The bleach solution was weight of the pulp. After added based on the bone dry containing hours at 104°F. the pulp was washed with water

sulfurous acid. ng in Example I had the followi Handsheets prepared as

properties: 78.0 G.E. Brightness 76.1 G.E. Reverted Brightness

-12- 4 6 35,8 0

Claims (1)

1. Ii 9 0, C, A /77

   The claims! defining the inventiol are as follows' from whole wood 1. A process for Freparing wood pulp of steamed fibers prepared by pressure defiberization treating the whole wood chips, said process comprising compound wood fibers with at least one chlorine-containing dioxide or a hypochlorite consisting of chlorine, chlorine the fibers with an ozone, sa.lt, and subsequently treating

   oxygen mixture. in which the 2. A process according to claim 1, chlorine gas. chlorine-containing compound is 1 or 2, in which the 3. A process according to claim 6% of the dry weight of chlorine is equal to from 4% to

   the fibers. 1, in which the chlorine- 4. A process according to claim of chlorine and containing compound is a combination chlorine dioxide. one of the preceding A process according to any weight of fibre from 2% claims, in which based on the dry the fibers. to 10% ozone is taken up by of the preceding 6. process according to any one treating the resulting pulp claims, which further comprises agent. with a lignin preserving bleaching 6, in which the lignin 7. A process according to claim an alkaline peroxide solution. preserving bleaching agent is

   19 Dated this 10th day of December, NY SCOTT PAPRR COMPA

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