CA1059359A - Treatment of waste paper and similar materials - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for recycling waste-paper products is disclosed which involves subjecting the products to a high pressure environment and then rapidly opening a a restricted transfer line to a low pressure environment whereby the rapid passage of the products results in liberation of the cellulosic fibres of which they are composed.

Description

; l~S5~359 This invention relates to a method for recovering cellulosic fibre from paper products and similar cellulose-containlng materials in a form suitable for use in the manufacture of new cellulosic products. In general, the invention is concerned with the defibra-tion of substantially clean waste paper products, the defibration of waste paper products contaminated with contraries, the ~ -simultaneous defibration and removal of ink and other encrustants from waste paper products,and the partial defibration and segregation of various waste cellulosic materials. r ', The increasing restrictions applied to the fores-t based industries has intensified the pressure upon paper and paper board manuEacturers to seek alternative sources of cellulosic fibre for their products. As a consequence, the recycling of cellulosic fibre from waste-..... ..
paper and paper-board is becoming of primary importance.
In 197~, for example, some 35~ by weight of all paper ~`
and paper-board manufactured in Australia was accounted for by recycled fibre and this proportion is likely to increase in the ~uture (see R.W. Maddern, ~ppita ~ournal, 29, No. 3, 196-200, Nov. 1975).
The waste-paper and paper-board for recycling derive from a wide range of industrial, commercial and - f2omestic sources. Commonly encountered types of material include box and cart:on boards, fine papers, newsprint, packaging papers and consumer container boards. In some specific instances, the waste paper and paper-board is substantially free of contaminants however in many cases the waste-paper and paper-board are contaminated with .,,~ .

1~593S9 ` undesirable contraries. The extent and type.s of contraries are widely diversified and depend upon the source of the : .
paper products but commonly encountered contaminants ..
include metal, ylass, plast.ics, rags, pressure sensltive tapes, asphalt, laminates, carbon papers, grit, stones and domestic refuse. In certain instances, print and ink on : `
the surfaces of the waste-paper are also regarded as -contaminants. All of these unde~ired components must be removed or rendered innocuous before the recycled cellulosic fibre can be introduced to a paper or paper-board making ::.
machine. :
Present machines for recoverlng .Eibre, whether from cl~an or contaminated furnishes, generally rely upan dispersing the waste-paper fibres into aqueous suspension.
The dispersed fibres so produced (known as "stock" or "pulp") ~
may then be addi`tionally treated to remove or disperse any .
contaminants pre~sent in the original feed material.
Descriptlons of a number of currently used machines :~
for converting waste-paper and paper-board into pulp 91urry are given in J~.N. Stephenson's "Preparation of Stock for Papermaking", pages 100-1~6 (ls-t Ædition, McGraw-l-lills, .. :
N.Y. 1951). A widely used machine, and one W]liC}I typifies .
the action of many of the others, is known as the "Hydrapulper". ~..
The Hydrapulper basically consists of a vertical, bowl shaped tank with a multivaned rotor fitted through -the base. The waste-paper and paper-board are charged into t~e bowl together with sufficient water to give a final .
3 to 5 per cent pulp slurry. The multivaned rotor keeps the contents of the ~Iydrapulper in constant agitation in such a manner as to gradually liberate the-fibres from the feed : . `' ';

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material. In batchwise operation, a defibration cycle may ' ', '' take one hour or longer and fibre liberation is frequently~ ,`,' ' aided by heating and the addition of approprlate chemicals. ~,' ;
Heating and chemicals addition become mandatory when the defibration is performed concomi-tantly wi-th ink liberation. ~ ' With contaminated furnishes, contraries removal ln' the Hydrapulper proceeds in a number of different ways. The, light contraries, such as matchsticks and foamed plastics, ' float to the top and can be'recovered by skimming. Heavy , .
contraries, such as metals and glass, sink to the bottom ,,~
and into a specially designed'compartment from where they , ;,:r, are removed by hucket elevator. Larger and substantially ,`
~ .
neutral buoyancy materials such as sheet plastic,ropes, 5trings an,d rags are encouraged to wrap around a length oE
barbed wire which is then gradually drawn out of the ~; Hydrapulper bowl.
Waste-paper materials and contaminants particularly ',;
difficult to deal with in a Hydrapulper are high wet ~' strength papers, pressure sensitive tapes, waxed cartons, , glassine papers, papers laminated with thin layers of -' plastics or metal,and any material containing asphalt either `~
as an adhesive or a water proofing agent. ~"
High wet strength papers, in which the natural bonding of the cellulosic fibres is augmented by the presence of resins, are not easy to disperse in the Hydrapulper. The high wet strength papers tend to break into small flakes ' rather -than individual fibres. Whether the wet strength ', papers constitute a major or minor proportion of the feed, the flakes have to be removed by additional treatment, after the llydrapulper and before the stock is sultable for re-use . ,~ .

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~q)59359 :
.;- ~ .
. on the paper or board machines. Maddern (see R.W. ~addern, '' -Appita Journal; 30,.. No.. 4, 303, Jan. 1977.) has estimated , ~:
; -- .. . . .
that the power requirements for dispersing high wet strength ~. papers with a Hydrapulper type of system are 450 kwhr/tonne ,' greater than the power requirements for dispersing air dried .''~.
..
kraft pulp. .`, .
: The particular.problems encountered with pres~ure ;,','"~
'~ sensitive tapes, waxed cartons and asphalt containing ..
. materials is that when these are present as contraries, i.,~
. . . .
the adhesives, waxes and asphalt disperse in conjunction with the fibres in-to the pulp suspension within the Hydra~
.1 ~ ., .
J pulper. These aahesives, waxes and asphalt (collectively 's.: ., ' known as i'bitumen") are not removed in the subsequent stages ,, ' of pulp pr,ocessing and appear as imperfections in the Einal ', ., . paper or paper-board. Industry experience has sho~An that ...
.: , as little as 1 kg of bitumen per 200 tonnes.of recycled ,'',, . paper can render the whole batch unsuitable for h1gh grade ',", '-'' , consumer packaging board. ~part from appearance, the 'I presence of flecks of bitumen renders the final paper or ',~
,.~ 20 paper-board difficult to print. Consequentl~, contamination "' !~
of this type can relegate the recycled fibre to a much ~ ':
lower grade application than might be warranted by the ,.;' ' i~ ' lntrinsic mechanical properties of the fibre itsçlf. ,"
! ' In summary, established waste-paper and paper-board recycling techniques as exemplified by Hydrapulper operation ,... ; .
suffer from a number of shortcomings, namely:- . '~,.:.
'.` 1. The défibration rate is relati~ely slow, ~ :
'. defibration periods of one hour or longer ~r.~ . .
being common in batchwise operation. ~' '`' '.
.. ...

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l~S~?359

2. The intrinsic nature of the ~ydrapulper type methods requires a relatively high degree of dilution of the `
stock, generally to the range of 3 to 5~ solids consistency. -~ ;
This, in turn, leads to liquid effluent disposal problems, particularly if chemicals have been used to aid the ;-~
; operation of the Hydrapulper. ~
~: ,.,':

3. The means of contaminant removal are varied and compli- ~
:~ ;
~; ~ cated.
.

4. Difficulties are encountered in recycling high wet strength ~ materials and the energy demand with such materials is high.

; 5. Bitumen is inadequately removed from the stock and appears as imperfeations in the final product. `~

6. The Hydrapulper type systems have no provision for seg- `~
regating the original waste-paper or waste paper-board furnishes into fibre fractions of differing strengths other than by initially hand sorting the furnish components prior to introduction to the Hydrapulper.
The present invention is based upon the discovery that paper ;
products and similar cellulose-containing materials can be completely or partially defibrated by a technique of pressure pulping.
Thus according to the present invention there is provided a a method for defibrating waste-paper which comprises loading waste-:, . ( paper into a digester vessel together with sufficient aqueous liquor ;
to submerge the waste-paper; pressurizing the digester vessel with a j: .
gas from an external source to achieve a rapid and uniform perme- ~
ation of the aqueous liquor into the interstices of the waste-paper ~ ~i ~ and thereby weaken the interfibre bonds between the cellulosic fibres of the waste paper; subjecting the weakened waste-paper to a turbulent x :"
,~

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discharge by rapidly opening a valve in an exit line of the digester vessel leading to a collector vessel of lower internal pressure than the digester vessel, said discharge being sufficiently turbulent to impose shear and tensile forces on the weakened waste-paper to there- ~ 4 .;
by liberate the cellulosic fibres from the waste-paper, the said dis-charge being carried out while maintaining the gas pressure with the --digester vessel at an elevated value; and separating the cellulosic fibre from the product collected in the collector vessel.
The high pressure environment may be a liquid and/or gaseous :~
environment.
In the case where it is desired to simultaneously remove ink and/or other encrustants from a cellulose-containing furnish, the furnish must be initially impregnated with an aqueous liquor and then heated either prior to or simultaneous with the step of subjection to the high pressure environment. ;;
In the case where the cellulose-containing furnish comprises a mixture of strong and weaker cellulosic fibres and it is desired to `~;
separate such fibres from one another the resultant product stream is separated into underflow and overflow fractions respectively con- ;
.... .
; 20 taining the weaker and stronger cellulosic fibres. ~
.. . ..
The medium of transfer of the cellulose-containing materials `

may be gaseous, liquid or a mixture of gas and liquid. The aellu-.~, . .:
lose-containing furnish may be at ambient or elevated temperature prior to the transfer from the high pressure environment to the lower ~ ;
pressure environment and the method of the invention may be practised ~:
in the presence or absence of added chemicals. ~
', When the invention is concerned with the simultaneous removal ~ ;
of ink and/or other encrustants, the initial impregnatlon of the ~ ~
aellulose-containing furnish is usually effected with plain water _ ; ;
but small quantities of alkali may also be added.
The final stage of separating the cellulosic fibres A

~V5935~
,s from the particles of ink and other encrustants may be ~;
proceeded with by any of a number of known methods. ~
Thus, in one embodiment, the present invention - provides a deinking and de-encrusting method in which none !~
or only a relatively small quantity of deinking/de-encrusting .
, chemicals is used. Consequently, the effluent disposal problems associated with the present invention are less - severe than with other methods. Furthermore, the method of deinking of the present invention is fast and well adapted to the treatment of a wide range of differing types of paper products either simultaneously or consecutively, with the type of paper product having only a marginal effect upon the speed and efficiency of the deinking/de-encrusting process.
To summarize, the present invention may be applied ... .
to achieve the following results:-1. Substantially defibrate waste-paper and paper-;,:
board furnishes to give a wet, dry or mois-ture ~ ;
regulated product.
2. Substantially defibrate high wet strength papers ,;
with no or minimal chemical usaye and give a pulp `
product requiring minimal secondary treatm~nt before introduction to the paper or paper-board machine '~
.,: : .
systems. ' 3. Separate cellulosic fibres from contraries in a simplified manner relative to existing processing ``
and simultaneously remove the majority of the bitumen type substances from the furnish.

4. Segregate mixed waste-paper and paper-board :j .
furnishes into strong and weaker fibre components on r,, ~''' .~ .

~; ~$9359 `..: `
., - -.
the basis of the response of the mixed waste material to the method of the invention.

5. Provide a rapid method of simultaneously defibrating ~;
and deinking recycled materials to give a pulp `-~
- product substantially free of ink and other encrustants or a pulp product with a reduced quantity of associated :;
ink and encrustants.
It will be apparent from what has been said above and the following discussion that the invention exhibits the ~;
following advantages over known waste-paper and paper-board recycling processes~
1. A rapid defibration cycle, ; ;~
2, Minimal use of heat and chemicals, 3. :A simplified contaminants removal scheme, 4. Reduced water usage, ;~
5. A substantial removal of bitumen from the stock, ~

6. The facllity to segregate waste-paper and waste ~ -; -- paper board components without prior manual r~
sorting of the furnish. .
~20 The invention will now be described with reference to the acccmpanying drawing.
ReEerring to the drawing, recycled cellulosic material enters the system at 1. If the ma-terial is heavily '!
~ ' contaminated with glass, metals or similar gross contraries some of these contraries may be removed in unit 2 by known msthods. Known methods may include magnetic separation, ~`;
air attrition or flotation. Unit 3 in the processing line -,;.
is a coarse shredder to give some size reduction in the furnish if necessary. Although not essential, the shredder 3 ., ,~ - '. ~,, .
,. ..
_ 9_ .... , . . , . i .... , .. , .. ~, . ,.,, . :., .. ... : . . ...

~!~)5935~ / ~
is advantageous for certain classes of waste which, as received, might lead to inefficient packing and volume utilization in the subsequent stages of treatment.
From the shredder 3, the recycled cellulosic material enters the digester 12 which is capable of withstanding the temperature, pressure and chemical conditions pertaining `
to~the practice of the present invention. Although shown as a batch digester in the drawing, the digester 12 may be ~ of a batch or continuous design. This does not affect the principle of the invention. However, for adequate `~
performance of the inventi~n, the digester must be of such a design as to permit rapid discharge of the digester contents at the termination o~ the pre-selected processing conditiona.
In batchwise operation, after charging the digester 12 with the recycled cellulosic material, water or liquor `
may be added from tank 6.
For defibration only, the addition of water or liquor is not essential to the practice of the invention and may be omitted if a dry or moisture controlled product is required. However, in most instances, the use of water or liquor is preferred since this will decrease the energy demand of the subse~u~nt de~Cibration step. If .
water or liquor is added, sufficient water or liquor should ~ ~`
be introduced to give uniform fibre saturation. In practice, this would preferably be a minimum of four parts by weight ~;
of water or liquor to 1 part of cellulosic material.
.. ,~: :
If the process of defibration is to be simultaneous : :
~, . . ..
With substantial ink and/or encrustant removal,then the use - ; ;
of Iiquor becomes essential. The chemicals used for deinking ~;
~,''.' :', ,, ~' _ I O~

1059359 !y ~ !l liquors may include alkalis such as soda ash, caustic soda, ; . - . .
sodium silicate, sodium peroxide and sodium sulphite and may -~
also include bleaching agents such as hydrogen peroxide and may further include surface active agents. The concentration and nature of the deinking liquor will be determined by -specific feed materials, heavily printed materials for ; ~
instance requiring a more concentrated liquor than lightly ~ -printed feedstocks. However, in the majority of applications, the combined total of the dissolved liquor components is :. . . .
lO unlikely to exceed five weight per cent of the total liquor and will generally be less.
For non-deinking applications of the present invention in which water is added to the digester, the performancq of the invention may be improved in certain 15 circumstances by dissolving small quantities (less than two weight per cent by weight of the water) of alkalis andjor i.
surface active agents in the water. This is advantageous, although not essential, when treating high wet strength papers .
or paper-boards or other relatively moisture impervious `
20 feed stocks.
When watér or liquor is used, the water or liquor ;
may be added hot or cold. ~lot liquor or water is advantageous j`~
if the digester contents are to be subsequently heated as this will decrease the required processing times.
After charging the digester 12 with the recycled ~ ~
cellulosic material and water or liquor if required, the i ~ 5 digester is sealed. The contents of the digester may then be heated. Heating is necessary if the method of the invention is to be used for the simultaneous difibration and deinking of printed material or for the defibration of ,~
: ,:
-l~S93~9 high wet strength materials. The digester 12 may be heated by any known means but the preferred method of heating ',s by the direct injection of steam from steam inlet 13 into the base of the digester 12. ' ', , If heating is employed, the rate of heating should ' ,~
preferably be as rapid as practicable; a heatup time of ,, , ~, a few minutes being preferable to a more prolonged approach to temperature. ~;, The maximum temperature to which the digester contents ~10 are heated will be governed by nature of the material ~,, "
being processed. The deinking or de~ibrating of high wet :, strength materials and thick papers or boards will neecl a higher processing temperature than thinner and more readily wetted grades, but in most instances a maximum digester contents temperature of 180C or lower will - ?, ' sufice for the practice of the present invention. ',' ' Upon attaining the required operating~temperature, the contents of the digester 12 may then be maintained ~;
- , . : . .
~ ' for a short period at that temperature if required. Otherwise ,;

the digester 12 is then further pressurized by the admission ,, , ~`.:. .
of a moderately water-soluble gas or gas mixture from the ' , "
compressed gas tank 9. It is within the scope of the ~'`
present invention for the gas or gas mixture to be admitted prior to the heating of the digester contents but in ,;-, practice it is generally preferred to admit the gas after ~'','~
the required operating temperature has~been reached. ", ';
I the digester contents have not,been,heated, then the moderately water soluble gas or gas mixture i5 '~
~..'.' .. :~ .
introduced immediately after the digester 12 has been sealed. '' ;
,,,: .
Gases suitable for the practice of the invention `';~ , , ,~
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1~59359 .
. . ..
include carbon dioxide, nitrogen, halocarbons~ h~drocarbons ' ! '. ' and gas mixtures such as particulate free, low oxygen content flue gas. Air may be used if desired, but in all :: . . .
gas mixtures containing free oxygen, it is advisable to limit the final digester pressure to such a level as to -render the system safe from uncontrolled oxidation and explosion. If liquors containing a strong alkali such as caustic soda are .~eing used, then it may be advantageous . ~ ... .
to restrict the carbon dioxide and sulphur dioxide of the admitted gas to a level where the reactions between the admitted gas and liquor alkali components become inconsequential.
The pressure of the gas or gas mixture should be such as to give adequate fibre liberation during the subsequent transfer operations. The optimu~ gas pressure $
will be governed by the exact nature of the rec~cled `~
cellulosic material being treated and the temperature,~
time and liquor composition variables pertaining to the -~
I ~ ... .. .
particular embodiment of the invention but in most instances an applied gas pressure of 20 MPa or less Will suffice for the practice of the invention.
If liquor or water has been added to the digester, then after pressurizing the digester 12 with gas from tank ~, the digester contents are ieft to soak for a few minut~es under the applied gas pressure. During this soaking pe`riod the applied gas press~ure forces the water or liquor into : -- the interstices of the waste paper, waste paper-board or similar material. This serves to weaken the interfibre hydrogen bonds in the case of untreated paper and paper-board or the resin cemented bonds in the case of high wet strength .. ''' ''' _1,~ .. ` ;' ' 16~5935 materials. The hyarolysis of resin cemented bonds is ~-further aided by heat and the presence of alkali chemicals in the liquor. A similar mechanism occurs in the treatment of printed ma-terial. The influx of hot liquor into the printed paper or board is promoted by the applied gas ~ ~i pressure. The hot liquor swells the cellulosic fibres ;
within the paper or paper-board and then the chemicals , in the liquor further attack and loosen the ink - fibre bonds.
.
;~ At the end of the soaking period, the digester exit valve 15 is opened and the applied gas pressure within the digester rapidly transfers the contents of the digester into vessel 16. '~
If no water or liquor has been added to the digester, ,' then no soaking period is required and the valve 15 may be opened as soon as the required gas pressure has been attained in the digester 12.
The diameter of the transfer line connecting the digester 12 to the vessel 16, the design of the dlgester ; exit valve 15 and the pressure differe~tial maintained ;
between the digester 12 and the vessel 16 during the transfer period should be sUch as to maintain a highly turbulent state of flow during the transfer period. This ?' ~ ~ ' , is essential to the practice of the inven~ion.
The highly turbulent flow of the transfer process ' imposes shear and tensile forces upon the discharging i~
paper or paper~-board. These forces serve to liberate the cellulosic fibres from the treated material and also, in -;
the case of printed feedstock, serve to liberate ink and ~ , other encrustants from the surfaces of the cellulosic fibres.
For a fixed digester system geometry, the extent of ;,~' :'' .

~.0593~9 -,~
turbulence obtained during the transfer process is directly proportional to the pressure of the gas applied to the digester 12. Higher pressures will promote a higher degree of-turbulence and hence more effective fibre liberation and ink removal. For a fixed gas pressure, the extent of turbulence during the transfer process may be increased by the installation of turbulence promoting devices such as 1~ -shaped vanes within the transfer line.
The rapidity of the transfer process and hence the efficiency of fibre liberation is influenced by the design 1~ of the digester exit valve 15. For maximum effectiveness, I ~ valve 15 should be of a full flow type such as a plug valve I or a ball valve. Valve 15 should open as rapidly as possible. The maximum opening time from fully closed to ~`
ully open should not exceed one second and preferably should be less than 0.2 seconds.
The energy for the rapid transfer of the digester contents is supplied by the compressed gas. The diameter -of the line connecting the gas tank 9 to the digester 12 and the design of valve 8 should be such as to permit a ~'~
free 1ow of gas from tank 9 to the digester 12 during the transfer operation. For gas economy, valve 8 may be closed once the digester aontents have been fully discharged.
The design of vessel 16 should be such as to give .
a rapid disengagement of the gaseous stream from the product stream. In the drawing, vessel 16 is depicted as a cyclone but a large volume collecting -tank, or example, ~ ;
j- - .
j could equally well be used.
The efficiency of defibration attained during the ~' '`

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':
~)59359 ~ i transfer process may be further lmproved by fitting a roughened plate near the entry of vessel 16. If the ejected digester conten-ts st~ike this plate, then further turbulence is created and additional defibration achieved.
The gaseous stream 17 from vessel 16 is either vented to atmosphere or may be recycled to the compressed gas tank 9. The product stream from vessel 16 proceeds to secondary processing. ~' The nature of the secondary treatment given to the ~ ;
product from vessel 16 will be determined by ~hich ~i particular émbodiment of the present invention is being practiSed. The embodlments and secondary treatments are summarized in Table A Which follows: ~

TABLE A ;
SECONDARY TREATMENT OF DIGESTER PRODUCT - ~
~`:''' ~ ' .' .:
Embodiment of Secondary treatment invention Defibration of dry Air elutriation or tumble material screening by known means to ~
give a dry fibre and a dry -oversiæed product stream.
Oversized product recycled for further defibration. ; ;
_ , Defibration of clean Material wet screened by known furnishes with added means to separate fibres from water or liquor undefibrated fragments, Unde~
fibrated material discarded or recycled to digester. ~, . ,"'" . .: ,"
Defibration of Produc-t screened by known means contaminated furnishes to give a screen accepts fraction of fibres and a screen rejects fraction enriched with contraries. -~
Screen rejects discarded.

. .

. . .
'' ' "'' ,. ., , , ,. . . ,.. -. , . . , . , . ... , ,, ,. ,, :, , : .. ... .. ~ .. . . . . . . . : . ~

~5g~9 ` ' ~

TABLE A (continued) ..
...~ .

Segregation of mixed Product screened by known means furnishes to yield a screen accepts stream of liberated fibres and a screen rejec-ts stream of undefibrated material. The undefibrated ~`
material recy~led for further defibration. , . '~
'~
.
Ink and encrustants Product washed by known means removal to remove liberated ink particles ~;
and other encrustan-ts such as ~ - , clay particles, starch fragments etc. Washed pulp then screened to remove any undefibrated feed , material The method of the invention is further illustrated ~', by reference to the following examples:- ;
EXAMPLE l This example relates to the defibration of recycled news print and corrugated box board by the method of the invention.
The materials to be defibrated were charged together w1th water at 18C into the digester, the digester sealed and then further pressurized with nitrogen. After a soaking period of 3 minutes under gas pressure, the contents of the digester were rapidly transferred to a collecting vessel at atmospheric pressure by opening the digester exit valve in less than O.l sec. The extent of fibre liberation :
!, , obtained was measured by screening the discharged material over a 0.25 mm opening slotted screen. The fraction of the discharged material passing through the slotted screen was substantially composed of liberated cellulosic fibres. ~ ;

,.

~)5~359 ,~`
The extent of defibration obtained with both samples was directly proportional to the applied gas pressure, the ,;~
higher pressure giving the better fibre release ~Table lA, ~.
beloW)- (i;,. ' - -TABLE lA ~
EFFECT OF APPLIED GAS PRESSURE ON THE ,:: .
.: . . , DEFIBRATION OF RECYCLED NEWSPRINT AND . z CORRUGATED BOX BOARD .,~. --Digester operating temperature = 18C
. ~ Water : wastepaper solids charged to . :
~L0 the digester = 12.7:1 ~ ~:

Recycled Gas pressure applied Wt.~i discharged product furnish to digester (MPa) passiny through 0.25mm :
. slotted screen ,, _ "~ "
Newsprint 4.83 67.2 `~:
2.07 47.3 ''; ';~
'`
Corrugated 4.83 59,0 ` ~`
box board 3.45 45.2 1.
2.07 28.4 ~
., ~ .
. . , , ~'.', ;`," .
The defibration o the recycled material at a given pressure was influenced by the temperature, higher operating temperatures giving better defibration. Table lB
summarizes the results of heating the digester contents to 50C and 110C before release. ~ :
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~.~)Sg359 TABLE lB `,~
- ~
EFFECT OF TEMPERATURE ON THE DÆFIBRATION ~ ~
OF RECYCLED NEWSPRINT AND CORRUGATED .; ~``-`., -, : - ~ !
! BOX BOARD .: .
;
,~ .- ' igester pressure prior to transfer = 4.83 MPa Water : wastepaper solids charged to the digester = 19.2:1 ~ A~ '' " '`
` . '. .

RecycledTemperature of wt,% dlscharged ~.
furnishdigester contents product passing (C) through 0.25mm .~
:~ . . slotted screen` ' :
,~ ~ `, i Newsprint SQ 88.Q , ~ 110 98~6 :, _ .,, ' ', Corrugated 50 83.1 box board 110 98.6 ' .

.:
Another factor influencing the extent of defibration -:
:,;' . r ~ .
obtained by the method of the invention was the ratio of ~,`
~20~. water to wastepaper solids charged to the digester. The I;
results of varying this ratio for newsprint are given in Table lC. A11 of the e~xperiments listed in Table~lC , were at 18C and an initial digester pressure of 4.83 MPa.
.
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~L05~35~-~, ,. i. ~ .. , .~ TABLE lC . . :~
. EFFECT OF WATER : WASTEPAPER SOLIDS RATIO . ,~
,. ~
" ON THE DEFIBRATION OF NEWSPRINT ~ : :
, ;~ .
Water : Solids wt.% discharged product ~ passing through 0.25 mm .~ slotted screen O.l:l 15.4 `7.0:l 62.3 i, ~ . i. , ,:, ,~ 10~ 12.7:1 ~ 67.2 ' ;' `~ ~` 19.2:1 69.1 The experiment with a water:solids ratio of Q.l:l ~
was with air dried newsprint, no additional water being ~; ;;
added to the digester. The resul~ing defibration was '' . ., j~ relatively poor (15.~%) but a dry product was obtained.
The extent of defibration improved rapidly as water was added at a water:solids ratio of 7:1, the newsprint was completely water saturated and the defibration ;"
increased to 62.3%. Some further improvement in defibration ~
; ~ :; : , could be obtained by increasing the water:solids ratio to ~ -19.2:l, but the gain was small relative to the improvement between air dried newsprint at O.l:1 and water saturated newsprint at 7.0:1. ,~

An inherent feature of the method of the present æ~
invention is the ability to defibrate waste paper or board at either a specified moisture content or with a lower water:solids ratio than is possible with Hydrapulper type ~ of operations (where the water:solids ratios typically f:30 vary from 20:1 to 33:1).

:~ ' ;~
_ 21)-- r ~ I

~)59359 : :-When air-dried furnishes are defibrated by the . . . ,: .
method of the present inven-tion, higher initial digester pressures are required to obtain the same extent of defibration that is obtained when treatlng water saturated furnishes. Alternatively, if the initial digester pressure is maintained constant, then a number of passes of the air dried furnish through the digester ;``~
become necessary. Hence, after the first discharge, the partially defibrated product is returned to the dlgester for a second discharge and so on. Table lD summarizes the results of successively discharging air-dried newsprint from an initial digester pressure of 48.3 MPa. ;

SUCCESSIVE DISCEIARGES OF ~IR DRIED NEWSPRINT

No. of times discharged Wt.~ discharged product through digester passing through 0.25 mm slotted screen . ~ .

1 15.4 `~
2 32.8 3 47.9 ~ `
' When processing an air-dried feedstock, the cholce of adding water to the digester will be determined by the . ~ -end use of the liberated fibres. If the fibres are to be used for paper or paper-board manufacture by conventional ~ i - -means, then water saturating the digester contents is advantageous. However, if the fibres are to be subsequently used for dry forming operations, then defibration of the :. . . . , ~ .

~ 5~359 ; ;:
~ ... .
recycled paper or paper-board in an air-dired condition ', will yield a light, fluffy fibre mass well adapted to this type of a~plication. ;

The role of turbulence promoting devices in the , transfer line is illustrated by the following example relating to the defibration of recycled corrugating paper.
The diameter of the transfer line of the digester ~;
- system used in the experiment was 51mm. This was constricted to 9.5 mm diameter by fitting a sharp edged -circular choke into the line. The results of this are ~ .
indicated in Table 2. Both experiments were a-t 18C with c a w~ter:wastepaper solids ratio of 11.0:1 and an applied ~ ;
gas pressure o~ ~.83 MPa. The corrugated paper was allowed to soak under the applied gas pressure Eor 3 mins.
!`~ . .
in both experiments before the digester exit valve was opened.
TABLE 2 `, ;; ... . .
~ EFFECT OF CONSTRICTING THE TRANSFER LINE :;t ' ~' ~ ' Constriction . Wt.~ discharged product passing through 0.25mm slotted screen . . ...
_ .

None 77.3 9.5mm diameter 82.8 -circular choke '~
. '~

The 9.5 mm diameter choke intensified the flow turbulence during the-transfer period and hence inareased .,,, '` . ~;. , :, . . .
_22-' ' ; `
`` 11t~9359 `
the forces acting upon the discharging wastepaper. This, -~
in turn, gave improved defibration relative to the experiment in which no choke-was used.

Many of the contraries encountered in contaminated waste paper have a high wet strength. Thus, when the .! `~
method of the invention is applied to contaminated waste ~ paper or waste paper-board and sufficient water is added-j~ to the digester to submerge the recycled material, the subsequent pressurized soaking period considerably weakens , the structure of the untreated waste paper or waste paper-. . .... .
board whilst having minimal effects upon the contraries. ', During the subse~uent trans~er process, the forces induced by the turbulent Elow considerably defibrate the water saturated waste paper or waste paper-board whilst leaviny the contraries relatively unaffected.
Table 3 summarizes the effect of treating contaminated waste paper and waste paper-board by the method of the invention. Sufficient water was added to submerge the furnish, the digester sealed, pressurized to 4.83 MPa with~l ;
nitrogen and the digester contents left '-o soak under the applied gas pressure for 2 mins. before opening the digester exit valve. The digester contents were not heated, the process being conducted at the ambient temperature of 18C. ~~`
From Table 3 it can be seen that the majority of the contraries were unaffected by the rapid discharge from the digester. Ready separation between the contraries and the liberated fibres could be obtained by a simple screening operation. -~,, ,'`~' .
, .~ .

359 ~- ~

TABLE 3 ~ ~ -RESPONSE OF VARIOUS MATERIALS WHEN SUBJECTED -TO THE METHOD OF THE PRESENT INVENTION . - :

~ .
Material Response :
. , Writing paper Substantial separation into :.
Newsprint individual cellulosic fibres. -~
Uncoated carton board .
Corrugated carton board Polyethylene laminated Unaffected by treatment drink carton . .
Waxed drink carton ..
~X` " '' ~
High wet strength Torn into fragements some paper 20 to 50 mm square '' '.:':''.. :
Asphalt impregnated Some tearing at the edges but packaging paper otherwise intact -:

Clear contact tape Undamaged, with the tape Masking tape retaining substantially all ~.
P.V.C. insulating of the adhesive. .:
tape Asphalt backed tape ~ ~

Polystyrene foam Virtually unaffected .. . . ..
Brittle P.V.C. Some breakage but the majority .
unaffected .:
Metal staples Released from writing paper and carton board - ".:.
'30 Polyethylene bags Unaffected by treatment Cotton rags ., ,., :', ~:

_2~_ :

~L~5~359 ~ :~
When compared with the ~Iydrapulper, the method of the present invention has the advantage of yiving minimal dispersion of asphalt, adhesives, waxes and other bitumen ,,' forming substances~ These remain associated with the ,, contraries and are removed in the subsequent screening of .'' the product. Consequently, the method of the present invention can be used to satisfactorily process more heavily bitumen contaminated furnishes than are acceptable for Hydrapulper'type processing. ,~
LO ' ~''' EXAMPLE~
' The principle of selective defibration can also be ' ' applied to the segregation of mixed waste-paper furnishes. ~' Compound carton boards, such as,corrugated box ',' boards', are fabricated from differing grades o material.
~lence, in a corrugated box board, the corrugated paper in " ~' the core of the board is generally enriched with neutral sulphite pulp whilst the outer liner plies are enriched with stronger kraft pulp. Upon water saturating such a carton board according to the method of the invention and then rapid~ly discharging the satura-ted board from the , digester, it has been found that the differing components of the corrugated box board respond difEerently to the -' discharge.
Under conclitions of incomplete defibration, the weaker corruga-~ed paper has been found to defibrate more read.ily than the stronger outer plies. Upon screening the partially defibrated product, the screen oversiæe material gives a stream enriched with the stronger kraft fibres whilst the screen aCCQptS are enriched with the .

';
~ 2~

.

,i 1~9359 ; ~
weaker neutral sulphite fibres.
Table 4A summarizes the result of treating coxrugated box board according to the method of the invention. The ;.. ; :.
box board was charged to the digester together with 12.7 '~
parts of water per weight of board, the digester sealed, pressurized to 4.83 MPa with nitrogen and the board left to soak for 3 mins. under gas pressure before dlscharge.
The discharged product was then screened over a 0.25 mm ~:
slotted screen and -the screen oversize and undersize ,~
fractions separately collected. The screen oversize fraction was further defibrated in a stirred tank defibrator to complete the fibre liberation and then papermakin~ ?; ~ i pro~erites o~ the two Eractions Were evaluated by Appi-ta Rtandard methods. ~ ~ .
As can be .seen from Table ~A, the higher kraft fibre ;~.
content of the screen oversize fraction is reflected in J`
the higher papermaking strength of that fraction.

TABLE 4A ;
~ .
CORRUGATED BOX BOARD SEGREGATED BY THE METHOD ~

OF THE PRESE1.~T INVENTION
Digester operating temperature = 18 C ,~.

Fraction wt. fractlon Freeness- Tear Burst Break Fold of original (Csf) index index length ., x l00 . (mN/gsm) (kPa/gsm) (km) _ .
Screen ' :
oversize 41 2-~ 11.3 2.7 4.5 Screen .
accepts 59 . 250 9.l 1~3 2.8 9 ' ' .

. . .

.,~ ,"

._26_ .

:.. . , .: ;;., ~ .......................... ,. , , :, .

~!~5~335~ ~
,. ` `~; :
... .
The method of the invention is not confined to ~.`
-.
to the separation of components from compound carton boards but can be applied to any mixture of papers or ~i paper-boards where fractions of the mixt~re exhibit differing responses to the turbulence associated with the , .. . ,., ~
discharge of the digester. `, The method of the invention is also not confined ~` ~
- to the treatment of wet or moist paper or paper-boards - -but can also be applied to dry furnishes. , ;~
' Table 4B refers to a 50/50 wt.~ mixture of kraft wrapping paper and newsprint which was treated in an air-'~ dried condition wi~hout the addition of water to the`~
; digester. The digester was gas pressurized (at ambient temperature) to 4.83 MPa and the Waste paper mix~ure discharged. This process was repeated for a total of three discharges and then the product screened. The ~,.
screen undersize and oversize fractions were separatel~
collected, reslushed with water and evaluated for paper-' making properties according to standard Appita methods.
~ TABLE 4B ;
, A 50/50 WT ~ KRAFT W~APPING PAPER / NEWSPRINT `~
;, MIXTURE SEGREGATED B~ TREATMENT IN THE AIR-DRIED
CONDITION

J Fraction wt. fraction Freeness Tear Burst ~reak _ of original (Csf) index index length , -material x 100 (mN/gs~) (kPa/gsm) (km) -Screen 67 150 8.8 4.0 6.1112 overslze . .

Screen 33 150 7.4 2.3 4.723 undersize ___ _ _ ' ~.

_27_ :i The kraft wrapping paper was less readily defibratedby the method of the invention than the newsprint and this was reflected in the higher strength properties of the screen oversize fraction.

When operated at ambient temperatures, the method -of the present invention is inefficient in defibrating `~
high wet strength papers. However, the method of the invention readily defibrates high wet strength papers when operated at elevated temperature.
Table 5 shows the results of defibrating high ~ :
wet strength kraft bag papers. In the first experiment, the paper was loaded into the digester with sufficient 10 g/l caustic soda solution to cover the paper, the digester temperature raised from ambient to 120C in ~
8 mins. and then the contents of the digester maintained -~ -.. ..
at 120C for a further 5 mins before discharge. The applied gas pressure was 2.01 MPa. The second experiment was similar except that water rather than caustic soda solution was charged to the digester. , DEFIBRATION OF HIGH WET STRENGTH BAG KRAET PAPER
, , .

Liquor charged to wt.% discharged product passing digester through 0.25 mm slotted screen . '~ ' '~' .:
10 g/l NaOH 100 .. ,:
water 99 _ ' ''.'; ' .

.~

. i ;. ' .' ' ;' '' ' ', '. ' , , ' : 1 . . ~,, " . ' .. ' . ' . 1 ' ,, : , " i , . , - . , . . : . . . ~ . ~ .. . . .. . ...

93~i9 `: ~`

The high wet strength ~ag kraft paper was completely defibrated when 10 g/l caustic soda solution was used and 99% defibrated when water was used.
EX~MPLE 6 A problem allied to the defibration of waste paper and paper-board is the defibration of dried pulp.
Particular difficulties arise in the reslushing of pelletised pulp, where the pulp is received as pellets some 10 mm in diameter and 25 mm long. If any residual , I
0 black liquor has been left in the pulp as a result of poor ~
pulp washing, then -this tends to act as a cement in the r `'' dried pellets and inhibits reslushing of the pulp. In `
these circumstances the reslushing of -the pellets can take several hours in ~Iydrapulper -type of equipment.
The method of the present invention may be used to ..
readily reslush pulp pellets and similar materials. The operating conditions summarized in Table 6 gave complete defibration of eucalypt neutral sulphite pulp pellets `
without the use of any added chemica].s.
o TABLE 6 DEFIBRATION OF EUCALYPT NEUTRAL SULPHITE
-PULP PELLETS
. . . ., Variable Amount Wt. of water:pellets - charged to digester 7 Time for digester to reach 120C from ambient 12 mins.

Time digester maintained o at 120C 5 mins, ; .' ;.''. ' _ 2')-~S9359 : ~:
.:
TABLE 6 (continued) ,'~
.
Applied digester gas pressure 2.01 MPa ~
Degree of defibration of pulp pellets 100 Another embodiment of the method of the invention is ~
the removal of ink and other encrustants such as pigments, ;, L0 ', clays and starch granules from waste paper and waste `
paper-board. The loosening of the ink particles and other ,' encrustants from the r'ecycled material proceeds simultaneously with the defibration of the rec~cled material and then the loosened ink particles and other encrustants are,~' removed from the liberated cellulosic ibres b~ washing '-- , according to known techniques.
, Some loosening of the ink and encrustants occurs `
,~
when the recycled paper and paper-board is defibrated in the presence of water at elevated temperatures.
, , Table ~A summarizes the results of treating newsprint ,~
with water at various temperatures. Sufficient water was added to the'digester to submerge the'newsprint, the '~
digester pressurized -to 4.83 MPa with nitrogen and -the ,, digester contents then heated to the predetermined temperature. The digester contents were discharged to'-atmospheric pressure immediately the predetermined ~,;
temperature was attained. The pulp so produced was further washed on a vibratory screen to remove any loosened ink '~
particles. The pulp was then made into handsheets by , , ', .. ,j~ '' , f~

Appita standard methods and the brightness measured by the Elrepho photometer using the green filter.
The control sample was prepared by defibrating a . .
further sample of newsprint in a British standard ~
::
Disintegrator.
hs can be seen from Table 7A, the brightness of the pulp product progressively decreased as the cooking temperature was raised to 130C and above. T'lis was due ..
to progressive condensation of the li~nin within the ground wood component of the newsprint to give an increasingly dark product until at 200C the pulp .. .
brightness had dlminished to 26.7%.

EFFECT OF TEMPERATU~E ON INK.~EMOVAL
FROM NEWSPRINT

Digester liquor:- water '-; Applied digester pressure = 4~83 MPa ~ . . , ' ''; :~ ' ~ Maximum digester Time to reach Elrepho green 'A`, ' ' `; contents temperature maximum temperature filter bright~
( C) from ambient (mins) ness of pulp . _ _ I (%) :~
Control sample . 47.8 .
. . . _ ,.
3.6 . 5i.9 110 7.0 51.8 : 130 8.7 47.6 i~

150 9.7 46.2 ~.; :

200 14.0 26.7 3~ The pulp darkening cculd be avoided and more '~ ~ -, : ':' ': .

ll_ i'''' :

f--~

105~35~9 ~
. . .
.
.
efficient ink removal obtalned if alkalis were dissolved in the digester liquor. Particularly bright pulps could be obtained if hydrogen peroxide was also added to the liquor. ;;~
Table 7B summarizes the results of practicing the method of the present invention with alkaline liquors. The cooking and pulp treatment techniques were identical to ~hose previously described in this example. ~i, ; TABLE 7B
DEINKING OF NEWSPRINT WITH ALKALINE LIQUORS ~`
j . ~.;,. , . ~
Applied digester pressure = 4.83 MPa r .'`,~'- '" ,, ~ ~ ~',''',' ', ' '. .
; Digester Maximum digester Elrepho green liquor contents temperature filter brightness ., (C) o~ pulp "'~
. , (~) '',''', ' . i^~,' '':
,~; 10 g/1 Na2SO3 110 53.7 - 10 g/l Na2SO3 150 54.5 ~ 50 g/l Na2SO3 150 57.4 j 20 ~ ,,-10 g/l NaOH 130 47.9 ~ ' 10 g/l NaOE~
5 g/l H2O2 130 60.1 1 ~ . ~ .

I' 1:~ . ' ' - ' ' ' '''' ~ ;. . .
,'~ ' ". ~ ' 1~ ' ' ~ ,''' ' " ",, i~3~0 - , . .

, -32-

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for defibrating waste-paper which comprises loading waste-paper into a digester vessel together with sufficient aqueous liquor to submerge the waste-paper;

pressurizing the digester vessel with a gas from an external source to achieve a rapid and uniform permeation of the aqueous liquor into the interstices of the waste-paper and thereby weaken the interfibre bonds between the cellulosic fibres of the waste paper; subjecting the weakened waste-paper to a turbulent discharge by rapidly opening a valve in an exit line of the digester vessel leading to a collector vessel of lower internal pressure than the digester vessel, said discharge being sufficiently turbulent to impose shear and tensile forces on the weakened waste-paper to thereby liberate the cellulosic fibres from the waste-paper, the said discharge being carried out while maintaining the gas pressure within the digester vessel at an elevated value; and separating the cellulosic fibre from the product collected in the collector vessel.

2. A method for defibrating waste-paper as claimed in claim 1 wherein the waste-paper submerged within the aqueous liquor is heated prior to or simultaneously with its subjection to the pressurized gas.

3. A method for defibrating waste-paper as claimed in claim 1 wherein the waste-paper submerged within the aqueous liquor is heated to a temperature not exceeding 180° C for a period not exceeding one hour.

4. A method for defibrating waste-paper as claimed in any one of claims 1, 2 or 3, wherein the digester vessel is pressurized for up to about five minutes prior to discharge of the weakened waste-paper.

5. A method for defibrating waste-paper as claimed in any one of claims 1, 2 or 3, wherein the aqueous liquor is water.

6. A method for defibrating waste-paper as claimed in claim 1 wherein the aqueous liquor contains one or more ingredients selected from the group consisting of:- alkalis, alkaline reacting salts, bleaching agents, and surface active agents.

7. A method for defibrating waste-paper as claimed in claim 6 wherein the alkalis and alkaline reacting salts are selected from the group consisting of:- sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium sulfite, hydrogen peroxide, sodium stearate, sodium oleate, sodium palmitate, potassium hydroxide, potassium sulfite, potassium carbonate and potassium bicarbonate.

8. A method for defibrating waste-paper as claimed in any one of claims 1, 2 or 3, wherein the gas used to pressurize the digester vessel is selected from the group consisting of:- nitrogen, carbon dioxide, halocarbons, hydrocarbons, halohydrocarbons, particulate-free low-oxygen flue gas, and air.

9. A method for defibrating waste-paper as claimed in any one of claims 1, 2 or 3, wherein the valve in the exit line of the digester vessel is opened in less than 0.1 seconds.

10. A method for defibrating waste-paper as claimed in any one of claims 1, 2 or 3, wherein turbulence inducing vanes and constrictions are fitted in the exit line of the digester vessel to promote flow turbulence during the discharge of the weakened waste-paper from the digester vessel.

11. A method for defibrating waste-paper as claimed in any one of claims 1, 2 or 3, wherein the waste-paper is pressurized with gas at 4.83 MPA for three minutes at ambient temperature prior to discharge through the exit line.

12. A method for defibrating high wet strength resin containing papers which comprises loading such paper into a digester vessel together with sufficient aqueous alkalis to submerge the paper; heating the submerged papers for a period of time to hydrolyse the resins; pressurizing the digester vessel with a gas from an external source to achieve a rapid and uniform permeation of the aqueous alkalis into the interstices of the paper and thereby weaken the interfibre bonds between the cellulosic fibres of the paper and complete hydrolysis of the resins; subjecting the weakened paper to a turbulent discharge by rapidly opening a valve in an exit line of the digester vessel leading to a collector vessel of lower internal pressure than the digester vessel, said discharge being sufficiently turbulent to impose shear and tensile forces on the weakened paper to thereby liberate the cellulosic fibres from the paper, the said discharge being carried out while maintaining the gas pressure with the digester vessel at an elevated value; and separating the cellulosic fibre from the product collected in the collector vessel.