Note: Descriptions are shown in the official language in which they were submitted.
1~89305
This invention relates to a method for increasing
strength properties and refinability of high yield chemical
wood pulp by oxygen and alkali treatment. The enhanced
properties of the pulp are advantageous for the manufacture
of linerboard paper.
Sulfate pulp with a lignin content corresponding
to a Kappa number of from about 60 to about 120 is
conventionally used for the production of unbleached
linerboard. Linerboard pulp manufactured in this way has
good strength properties at relatively high yields (55-
60%). The dry weight of washed fibers which are recovered
after pulping is generally reported as a percentage of the
weight of dry lignocellulosic material which was charged to
the digestion process. This percentage is termed "yield".
Any decrease in yield caused by loss of lignocellulosic
materials is undesirable in papermaking. Two of the more
important strength properties of linerboard are burst and
edgewise compressive strength. To obtain the desired burst
and compressive strength, pulp is refined before the
linerboard is formed. The action of refining fibrillates
and collapses the pulp fibers, allowing them to form a more
strongly bonded and dense board. Linerboard density is
strongly correlated with burst and compressive strength
levels. However, the pulp cannot be refined too severely
since this will cause the pulp to drain poorly on the
linerboard machine, resulting in low production rates.
Broad density is therefore achieved by a combination of
refining and wet pressing on the paper machine.
It is known generally that delignification of
pulp with oxygen and alkali is a commercially acceptable
process. The process is usually applied to low yield
chemical pulps as a pre-bleaching stage, before final
bleaching with chlorine-containing chemicals. The Kappa
number of the pulp is usually reduced from 30-35 to 15-20,
signifying a reduction in lignin content of 40-50%.
- Reduction in lignin content to such a degree would result
in paper of insufficient strength properties for linerboard
manufacture.
, ~
t~05
Kleppe et al ("Delignifying highyield pulps with
oxygen and alkali," TAPPI, vol. 68, no. 7, p. 71, 1985)
teach that sulfate pulp having a Xappa number within the
range of 140-150 can be delignified with oxygen and alkali
to pulp with a Kappa number of 110. In both of these
treatments, however, oxygen, alkali, and pulp are reacted
at a temperature (105C) and pressure (0.5 mPa, 58 psig)
which were optimized for the removal of lignin from the
pulp. Delignification rates and strength levels of
highyield soda pulps are strongly influenced by temperature
during oxygen and alkali treatment. Thus, reaction
temperatures above 100C increase the extent and rate of
delignification and promote oxidative degradation of wood
carbohydrates.
Because of the relatively severe conditions of
the above treatments, the pulps are stabilized against
carbohydrate degradation by treatment with magnesium salts
(0.05-0.15%, based on o.d. (oven dried) pulp) . These
salts, however, reduce the yield loss associated with the
carbohydrate fraction of the pulp allowing for further
delignification.
It is an object of this invention, therefore, to
provide an improved method of producing high strength kraft
linerboard while reducing the refining energy required for
its manufacture.
Accordingly, the invention provides a method for
producing linerboard paper from high yield chemical wood
pulp by treating the pulp with oxygen and alkali at a
temperature of from about 50C to about 100C and a
pressure of up to about 150 psig in the absence of
protectors to increase the refinability of the pulp and the
strength properties of the paper by limiting the reduction
in lignin and carbohydrate content in the pulp as
determined by a Kappa number reduction of no greater than
25% in the treated pulp.
Thus, the instant invention achieves the above
objective by an improved linerboard manufacture method
which uses oxygen and alkali as a means to chemically
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L~
,5
modify residual lignin present in high yield sulfate pulp
without a substantial decrease in pulp yield. Hence, the
process conditions utilized in this invention are much less
severe (preferably, 74~C, 0.13 mPa, and 15 psig) than those
used in prior art oxygen and alkali delignification
processes resulting in minimized lignin and carbohydrate
loss.
Embodiments of the invention will now be
described, by way of example, with reference to the
accompanying drawings, in which:
Figure 1 shows graphically the relationship
between the oxygen and alkali treatment of pulp and
Williams Slowness at different beating times;
Figure 2 show graphically the relationship
between the oxygen and alkali treatment of pulp and
linerboard compressive strength at different beating times;
Figure 3 shows graphically the relationship
between the oxygen and alkali treatment of pulp and
linerboard burst factor at different beating times; and
Figure 4 shows graphically the relationship
between the oxygen and alkali treatment of pulp and
linerboard tensile breaking lengths at different beating
levels.
The figures thus present graphs which illustrate
the ability to control linerboard pulp properties by
regulating the beating time of pulps treated according to
embodiments of the present invention.
It has been discovered that a high strength kraft
linerboard can be accomplished by subjecting industrially
prepared kraft pulp to a mild oxygen and alkali treatment.
The oxygen and alkali treatment of a high yield (55-60%)
pulp produced from wood chips cooked in an alkaline cooking
liquor allows production of a linerboard grade of paper
with higher densities and physical strength levels than
conventionally prepared linerboard. Upon refining, the
oxygen and alkali treated pulp reach a given Williams
Slowness and strength level more quickly than untreated
pulp, indicating the treated pulp is easier to refine than
.5
conventional linerboard pulp. (The Williams Slowness is
the amount of time in seconds for one liter of water to
drain through a three-gram sample of pulp~. The oxygen and
alkali treatment is carried out on a pulp of medium
consistency (8-20%, preferably 12%) at lower temperatures
and pressures than those used in conventional oxygen
delignification processes and in the absence of cellulose
protectors. Employment of the pulp produced by this
process in linerboard results in linerboard strength
properties (burst, density, compressive strength)
significantly higher than that measured in linerboard
employing conventional kraft pulp of the same Kappa number.
The process has the effect of modifying the residual lignin
present in high yield kraft pulp rather than substantially
reducing pulp yield through lignin dissolution as is
conventionally practiced with oxygen and alkali processes.
Embodiments of the invention are described in
more detail with reference to the following Examples which
summarize laboratory experiments in which industrial and
laboratory prepared linerboard pulps were treated with
oxygen and alkali.
Control ExamPle A
This pulp was an industrially produced kraft
southern pine pulp with a Kappa number of 96.5. The pulp
was washed in the laboratory which reduced the Kappa number
to 87.7. The pulp was then beaten in a Valley Beater to
various Williams Slowness levels and test handsheets were
made.
Control ExamPle B
The same pulp as in Control Example A was treated
in a laboratory oxygen reactor for one hour at 78C in the
absence of oxygen. The pulp consistency was 12% and the
initial pH was 10.9. After the treatment the pulp was
washed and the Kappa number determined. The pulp was then
beaten in a Valley Beater to various Williams Slowness
levels, and test handsheets were made.
Example 1
The same pulp as in Control Example A was mixed
with sodium hydroxide solution and sufficient water to
bring the pulp consistency to ]2%. The sodium hydroxide
charge was 1~ based on the o.d. weight of the pulp. The
initial pH of the pulp was 12.1. The pulp was then treated
in a laboratory oxygen reactor for one hour at 78C with an
oxygen pressure of 15 psig. After the treatment, the pulp
was washed, and the Kappa number was determined to be 81.1.
The pulp was then beaten in a Valley Beater to various
Williams Slowness levels and test handsheets were made.
The pH of the pulp after the treatment was 10.3.
:~,
..~ ,,~
:
05
Ca~e 'Po~ket 110. ~IIR 85-l~
Exam~ 2
The same p~lp as in Control ExaInple A was mix~d wi~h
sodium hy~ro,ci~1e solution and suf~icien~ wat~r to bring the pulp
consisteney to 12%. The ,sodium hydro~ide charge was 2% based ~n
o.d. pulp welght. Tbe initial pl~ of the pulp was 12.2, The pulp
was then tre~ted in a la'boratory oY~ygen reac~or for one ho~r at
78~C with an oxygen pres~s~re ~f 15 psig. A~ter treat~ent the
pulp was washed al1d the Kappa number de~er~lned to be 77.l. The
pulp t~as then beaten ln a Valley Bcater ~o various Williams
Slowness levels, and test handsheets ~7ere made~ The pH o~ the
pulp af~er ~he treat~ent was lO,9.
.Y~ample 3
The same pulp as in Cont~ol E~ample A was ~ixed with
sodium h~dro:~ide solu~ion al~d s-~fficien~ wate~ to bri~g the pulp
conslstency ~o 12%. The sodium hydroxi~e ~har~e was 5~. ~ased on
o,d. pulp wci~h~. The lnitial pll o~ the pulp was 13,0. The pulp
was then ~rea~ed in a labora~ory oxygen reactor ~or one hour at
7~C and ~n oxy~cn prcssure o~ 15 p.si~. Ater tre~tment the p~lp
was washed and the K~ppa num~cr determined ~o be ~8.2. The pulp
was then beaten in a Valley Benter to various Williams Slo-~ness
levcls, ~nd ~es~ handsheet,s ~e~e made.
The be~ting ti~es, Williams Slo~mess, handsheet
densitles, ~nd pulp strength propertie~ ~r~ shown in Table I.
- 6 -
~ase ~o~ke~ No. CH~ ~5-18
TABLE I
EFFECT OF OXYGEII-AIi~ALI ON SlRE~IGTII PROPERTIES O~ FT Pl~iE PULPS
STFI ~ns~le
Be~ting l~ ms Handshee~ Compressive Breakin~
Time Slown~ss Densi~y Strength ~urst Len~th
(~n.) ~sec.) (k~Lm ) (lb,/1n.~ _Factor (10~ ~)
C~ntrol 0 ~.3 40~ 11.5 24,0 39.1
Exa~ple A10 5.~ 483 15.8 36.0 5~,4
6.0 510 16.9 41.7 67.9
6.3 $4g 17.5 44.2 67.2
8.~ 610 19.2 57.0 75.3
10.9 64S 1~.5 58.5 73.3
Control 0 4.6 444 12,9 22,7 44.8
Exa~ple ~10 5.~ 500 17.8 3R,8 61.~
6.4 541 1~.~ 43.3 70.3
7.2 571 19,~ ~4.7 72.5
1~.1 602 1~.9 54.0 79.G
11.6 G45 20.~ 5~.7 7~.4
Example 1 0 5.5 4~5 14.4 ~.7 44.6
1~ 6.8 552 lg.3 46,~ 72.8
- ~5 7.8 5~5 l9.S 50.4 72.1
~.~ G06 19.9 55.2 77.7
1~.7 ~67 22,3 64.3 86.5
33.0 6~5 2~.6 ~6.7 91.8
E~m~le 2 0 5.1 467 1~.2 ~8.7 48.7
1~ 6.5 S49 1~ 4.5 69.~
7.5 592 20.Z 4~.3 74.3
9.9 ~21 20.3 54.Z ~3.5
19.3 G76 2~.3 64.6 g~.S
33.4 699 2Z.2 ~8.0 86.8
Example 3 0 5.0 505 15.9 33.g 50.7
7.9 ~33 Z0.0 55.3 70.1
13.~ 6g9 21,~3 ~3.8 ~4.0
27 1 733 22.9 6~.8 8G.0
57 0 769 23.2 71.G 95.3
As s~en from the examples, ~e~tments of p~lp with oxy~en and
- alkali prod~ed pulps wi~h highe~ shee~ densities and strcngth
prope~tle~ in ~he unbe~n state (O minu~es beat~ng time) ~h~r.
untrc~ted pulp~, Figure 1 shows the ~eating ~i~es plotted
~gain~t Williams glown~ess. Upon a s~udy of Fi~ure 1 i~ becomes
.
:
Case ~oc~et No. ~tlR ~5-ld
eviden~ ~ha~ t~)e ~,y~en and alkali ~re~t~ent allo~s the p~lp to
rc~ch a ~iven slowness with ~ lo~er amo~nt of beAt~ng, ~n an
ind~stri~l scale, this result translates into decreased refinin~
en~r~y for equivalent pulp ~lowness levels. Con~rol E~A~P1e B
show~ ~h~t sorn~ o~ the stren~h increases are due to mechanical
treatment ~eceivcd ~y thc pulp in the l~or~ory oxygen reactor.
~lowever, ~he.~e inereases are signi~icantly lower than those foun~
after thc additic)n o oxy~en and alkali.
In~rc~sc~ in ~he sodium hydroxide char~e in the
pxesence of oxy~en i.mproved p~lp strcngth properties and 10~7ered
~he ~ea~ing ~m~s required tn ac~lieve c~ ~iven stren&th and
slowness levcl. l'his ~an be deLermined fro~ a study of
- Fi~ures 2, 3, and 4. Thc ~os~ ~ignificant improvements were
~bseLvecl ~iLh ~I caustic application of 5% based on ~h~ o.d.
~eight o~ p~lp.
Another rcsult o the oxy~en-alkali tre~cnt was a
reduc~ion in p~llp happa nuMber. As shown in the ~ollowing
examples, the ~c~ree of ]~appa number reduc~ion ~ direc~l~
relatèd to tlle so~lium hydroxide char~e.
A comparison of the s~ren~h properties of oxygen and
~lk~li tre~ted l~b~ratory pulp with the sa~le pulp cooked ~o a
Kappa nu~ber similar ~o that o~ the o~ygen and ~lkali treated
pulp is 6hown in Table I~.
: Control ~xam~le C
Thi~ pulp is a la~oratory prepared kra$t southern pine
pulp with a waslle~ l~appa nurnber o~ 98.1. The pulp ~s then
beaten ill ~ Vallcy Beater to v~rious Williams Slowness level~ and
te~t hsndsheets wcre made.
i
0.5
C~se ~o~l~et l~l~. C~t~ U5-18
Control Example ~
This p~lp ls a labvratory prepared kr~ft southern pine
pulp wlth a ~ashed K~ppa nu~er o~ 6~.6. ~'he pulp was then
beaten in a V~lle~ ~eater co various Williams Slo~mess lcvels and
~est handsheet.s wcre made.
Ex;3mple 4
The same pulp a3 in Control Example C was mixed wi~h
sodium l~ydroxide solution an~ su~icient ~ater to brin~ ~he pulp
consistency to 12%. The sodium hydroxide ch~rge was 5% based on
o.d. pulp weight. The ini~lal pll of the p~lp was 13Ø The pulp
was then ~reated in ~ laboratory reactor for one hour at 78C
wi~l ~n oxy~en p~ssure of 15 psig. Af~r the treatmen~ thc pulp
as washed ~tld the K~ppa number was de~e~min~d to bç 75.5, The
p~lp was then be~ten in a Valley Beater ~o vnriou3 Williams
Slo~mess levels, and tes~ handshee~s werc rnade. he pl~ o~ the
p~lp after treatmen~ was 11.5.
_ 9 _
.. . .
3.~0S ~e Do~ket ~lo. C11R ~5-1~
TA~LE II
CQ,IP~RISON OF OXYGEN AND ALKALI TREATE~ PIN~ P~LPS ~ H
KRAFT PULPS OF Sl~lILAR AND DIFFERENT KAPPA NU~BER~
Treatment Cond~tlons;
Labor~tt~ry Plne Pulp Prepared fr~m Charleston Pine ~hips
12~ Consistency
78C
One Hour Rcaction Time
5% NaOH ~pplied to Oxygen-Alkal~ Treated Pu1p
15,psig Oxygen
..
~TFl Tens~le
Beating Williams Sheet Compres~ive Breaking
~re~tmentTim~ Slowlles~ Penslty Strength Len~h Burst Tear
Uescription~In7n.) (sec.) (g/cc) (lb./in.) (lO ) Factor Factor
Control Example C 0 5.l 0,3~ lO.l 32.1 17.3 214.3
(KappA No. 9B.1) 10 5.7 0.485 14.6 57.1 37.~ 262.~
5.90.516 l~.Z 63.3 41.5 263.4
2~ 6.g0.558 17.3 7~.2 47.5 236.9
~ 37 20.1 86.~ ~8.3 2Z0.
l~.Z~.66S 20.5 86.5 G3. 5 20~.~
Control E~ample D 0 5.3 0.445 ll.7 3~.4 21.9 272.0
(Kappa l~o. 68.6) 10 5.6 0.550 l6.2 ~5.~ 41,3 30q.7
6.60.610 7~.4 73.1 50.1 272.3
7.90.64~ 19.9 80.2 58.6 259.Z
14.10.7l3 21.5 g2.2 69,9 2Z4.3
~5 24.80,~32 ~2.4 98.6 73.0 Z15.8
Oxygen-Alkali O ~.10.492 14.5 40.5 32.0 Z94.6
Treated ~x~mple 4 lO 6.6 O.S99 18,~ 69.0 51.0 250.4
(Kappa No. 75.5) 15 7.8 0.65~ 19.7 77.3 59.9 Z30.7
~0 9.70.680 20.8 ~2.1 ~3.5 210,5
23,50.743 22.6 94,7 69.8 196.1
3~ 40.50.77g 23.7 99.6 75.0 1e5.5
,
As ~een from Ta~le Il, t.he oxygen and alkali tr~.ted
pulp~was significan~ly higher in compressive stren~h, burst
factor, brcaking lcngth, and handshee~ density when compar~d ~o
~he two ~raft pulps at constant beating ti~e. It is evident,
~he~efo~e, that stren~h propertie~ are more f~vorably enhanced
by oxygen and alkali trea~ment than by an equlvalent red~ction in
pulp Kappa number achieved ~hrough k~aft p~lping ~hanges.
- 10 - '
1~ 05
Case ~ocket No, ~HK ~5-1~
l~hile this invention l--~s been described arld illustrated
herein by re~erence ~o various fipecific m~terials, proced~res and .
cxamples, it is understood that the inVenti.OTI is ~ot restricted
to ~he particular materi~ls, combina~ions of materlalsl and
procedures selected for tlla~ purpose. ~lumerous variations of
such details can be ~mployed, as will be appreciated by those
skilled in ~he ar~.
.
