Note: Descriptions are shown in the official language in which they were submitted.
213~3~
BAC:KGRt:)l3ND OF THE IM/ENTlONi
ingruber et al., Pulp and Paper Manufacgure, Volume 4, TAPPI, CPPA, p. 160
(1985) define that convention conventional ultra-high-yield chernithermomechanical
5 or chemimechanical pulping is preferably conducted at a pH level between 4 and 9,
and involves either iiquid or vapor phase cooking with sodium sulphite-bisulphite
solutions for about 10 to 30 minu~es at a temperature between 60 and 175C. It i5
generally accepted that the chemical tr~atmsnt is mainly respGnsible for permanent
fibre softening, increase in long fiber content, fibre sp~cific surface and conformability,
10 as demonstrated by Heitner et al., Pulp and Paper Can., (84)11: T2s2- r2s7 (1983).
There is another so~tening approach which consists of a steam treatmant of
chips at high temp~ratur~s followed by explosiv~ decompresslon.
The production of pulp using high-pressure and high steam chip softening well
above glass transitlon temperatures of lignin should theoretically lead to lower energy
- 15 consump~ion in subsequent refining stages.
The inilial research in the ~ield of high-pressure staam cooking, followed by
defibration by explosion~ was made by Mason, U.S. Pat. 1 824 221; 2 645 623; 2 494
545; 2 379 8290. The masonite pulp obtained ~ccording to a two stage Sprout-
Waldron refining procedure showed weak physical strength, dark c~lor and yield loss
20 of 16% to 20%, and revealed itseff simply unsuitable for the production of paper
according Koran et al., Pulp and Paper Can., 79(3): T107-T-113 (19783. Mamers and
al., TAPPI, 64(7~: 93-96 (1981); APPITA, 29(5): 356-362 (1976~ invsstigated
explosion pulping of pinus elilotti wood chips with the help of high pressure carbon
dioxide solutions and bagasse of wheat straw explosion pulping under high pressure
25 of nitrogen. Paper propertias which were obtained were similar to that ot CTMP/CMP
pulps, but at the expense of brightness. The major problem to oY0rcome are
oxidation, as well as hydrolytic degradation of fibers leading to brlghtness and yield
loss.
It has been suggested by Vit et Kokta, VTt et al., Can. Pat. 1 212 505 (1986) that ~Z
30 the ultra-high-yield (90%+) pulp suitable for papermaking can be produced by vapor ~Ic~
2~'i3~
phase s~eam explosion cooking. The initial proper~ies of papers made from exploded
softwood chips were similar to those of TMP. However, refining energy was about
20% to 25% lower. Recentiy, a pulping process entitled "Process for Preparing Pulp
for Paper Making", Kokta B.V., Can. Pat. 1 230 208 (1987~; U.S. Pat. 4 798 ~51
(198g); Can. Pat. Appl. #542 643 (May 1937), referred to as "Steam Explosion
Pulping Process" or "S-pulping" has b~0n propos0d both ~or so~twoods and
haldwoods. In this process, impregnation and cooking conditions were aimed at
minimizing yield and brightness loss, maximizlng resulting paper properties and
decreasing specific refining en0rgy. The steam explosion pulping process consists o~
the chemical impregnation of chips, short duration saturated steam cooking at
temperatures varying from 1B0C to 2l0C, pressure release, refining and bleaching
(if necessary).
Kokta et al., Paperi Ja Puu ~ Paper and Timb~r, 9, 1044-105~ (1989), hava
shown that the specific refining energy of aspen explosion pulps is at least 50% lower
than that of CMP pulp of similar yield and ionic content level, while paper strength
increases by up to 50%. Compare at similar CSF levels, explosion hardwood pulps
(i.e. aspen, maple, hardwood mixtures, eucalyptus) at 90% yield provide similar or
higher paper properties then commercial low yield (_ 50%) bleached hardwood
pulps.
Nonwood fiber pulping which resulted in IQ~L~ of ~leachable ~rade as
a substitute of chemical pulp was also described in literature by Mamers et al., Appita,
33(3):201 (1979) and Mamers et al., Tappi, 64(7):93 (1981). They studied the effect of
pressure (3.4 MPa and 13.8 MPa) and temperatures (447K and 473K) with saturatsd
steam inlet pressure of 1.72 MPa on explosion pulp with bagasse and wheat straw
and compared their properties with conventional soda pulp. They racommended the
operation of explosion digester at pressure ~,~ in order to obtain suitable
strength pulp. Pulp quality suitable for newsprint prepared by CMP and CTMP
processes have been reported by Ramos, Pro~. Ta~i Conf., Orlando: 427-433 (nov.
1991).
3'~
OBJECTS
The object of this invontion is to provide a process in which improved paper
properties from annual plants are obtained when compared papers prepared by
5 conventional mechanical sulfites CTMP or CMP processes. The proposed process is
steam explosion pulping process using alcaline sulfites during impregnation and
cooking.
THE INVENTION
The major problems accompanying previous process~s using explosive
decompression are believed to have been the degradation due to the oxidation of
wood and acid hydrolysis leading to loss in brightness, deterioration of fiber and
paper properties and loss of yield. The approach adopted by this invention is
therefore to attempt to curtail hydrolytic and oxidative fiber degradation and thereby to
protect against loss of yield, brightness and fiber strength. The loss of fiber strength
will be particularly great if the degree of polymerization of the cellulose ~alls below the
critical value which is about 500-600. Hydrolytic degradation will also cause yieid
loss due mainly to degradation of hemi-cellulose.
The process of this invention tries to achieve a positive improvement in the
strength of the paper that will be produced from the fibers by increasing the number of
hydrophilic groups on the fiber surfaces th~roby adding to the potential sites for
hydro~en bonding.
The conditions for the achievement of the foregoing objacts in accordance with
the process of this invention are as follows:
1~ Th~ annual plants ~ragments, having fibers suitable for papor making, such
-. as flax, bagasse, kenaf, bamboo, wheat straw, are in a form in which thorough
chemical impregnation can be achieved in a reasonable time.
2) There is an initial thorough impregnation of the plant fragments by an
alkaline aqu00us iiquor having a~ least one agent acting to produce hydrophilic
,~
2~ 'J 3~
groups and as an antioxidant which is capable of protecting the chips against
oxida~ion and develops hydrophilic groups during the cooking stage. Th0 same
chemical may act as both an agent to produce hydrophilic groups and as an
antioxidant or these functions may be performed by separate chemicals. In this
5 inven~ion sodium ascorbate is used as an powerfull antioxidant. At the end of cooking
the pl I should not be lower than about 6.0, so that acids released during cooking will
be neutralized. Preferably a swelling agent is also used in the case when the
strength of low yield chemical pulps is to obtained.
3) The impregnated fragments ar~s cooked using saturated steam in the
10 substantial absence of air at hi~h temperature and pressure.
~ ) After cooking, the fragments are subjected to explosive decompression
which results in its defibration.
5) The defibrated fragm~nts are pr0f~rably wash~d and then, without undue
delay, and preferably immediately, refined to provide pulp.
The steps of the process of this invention which will for convenience be
referred to as the steam explosion process, will now be considered in more delail.
The ~nnL~I pl~n~f~r~gm~nt~
The starting material will normaly be annual plant fragments in which the fibars20 are of a length suitable for paper making.
The fragments would also, as is well known, be suitable in the sense of being
free from foreigner matter.
It Is deslrable for th~ purposes of thls inv6ntion that too coars~ fragments be
avoided as otherwise the subsequent impregnation may deposit chemicals only on
25 the surface, unless impregnation is carried out for a very long time. Another problem
with coarse fragments is that cooking would not be complete. It is best to use
shredded or thin fragments of a 4-8 mm thickness and 10-20 mm of length. It has
been found that this process is applicable to flax, kenaf, bagasse, bamboo, straw, etc.
giving stronger papers at lower refining energy compared with conventional chemo-
30 thermo m~chanical or chami-m~chanical pulping.
~206rj~39
ImPr~gn~tlon.
The purposo of impregna~ion is to protect the fragments against oxidatlon
during cooking and during transfer from the cooking vessel to the refiner. It is also an
objective to provide a positive increase in strength by developing hydrophylic groups
5 on the fiber surface during steam treatment. This will then provide additional sites for
hycirogen bonding.
The preferred hydrophylic agent is sl3dium sulphite Na2SO3 which also act as
antioxidant, and which is available at a low cost. It is used to provide a concentration
of absorbed chemical of about 1 to 15%. Concantrations below 4% woulci be used
10 where brightness protection is unimportant and high strength is not required. Where,
however, brightness is important the sodium sulphite should be at least 6%. If
physical properties are important these will be improved by using a concentration of
at least 6% sodium sulphite and will be further improved as the concentration isfurther increased towards 16%. The concentration of the solution is preferably about
15 the same as percent of chemical to be absorbed where there are equal quantities of
chips and liquor. For example, a ton of tragments of 50% consistency mixed wi~h one
ton of 8% solution will result in about 8% absorbed on the fragments. Of importance
is thorough impregnation to distribute the antioxidant evenly rather than depositing it
just on the surface. Other ~ntioxidants that can be used are potassium sulphite or
20 magnesium sulphite. Ammonium sulphite could b~ used if cooking conditions are not
severe or with a buffer. Complexing agents such as ethylene diamine tetracetic acid
(EDTA), sodium diethylene triaminepentacetate (DTPA), sodium tripolyphospha~e
(TPF) and other complexing agents known in the art as being usable under alkaiine
conditions may be added to minimize the catalytic effect of metals such as iron on
25 oxidative degradation.
It is desirable also to use a swelling agent to assist the antioxidant or
hydrophilic agent in penetrating the fragments and this contributes also to their
softening. This is of particular value in the case of high density species. Suitable
swalling agents are sodium or potassium hydroxide or ammonium hydroxide or
30 sodium carbonate or sodium bicarbonate or magnesium carbonate which will
2 0 $ ~ ~ ~ 3
contribute also to providing hydrophilic group~s. Other swelliny agents that can be
used and which may be desirable as auxiliary swelling agents for high density wood
are zinc chloride, sodium chloride, sodium bromide, calcium isocyanate, Schweitzers
solution, cupriethylenecliamne (C.E.D.) tetraethylammonium hydroxide, dimethyl-
5 dibenzylammonium hydroxide. The concentration of swelling agent and conditions ofswelling must be controlled in such a way as to avoid any dissolution of the
hollocellulose. Thus the percentage of swelling agent in the impregnating solution
will be in the range of about 1 to 4% depending on the agent anc~ the contlitions.
The impregnating solution must be alkaline and have enough free hydroxyl to
10 be able to neutralize the liberated wood acids such as formic acid ancl acetic acid
Normally the starting pH is about 7 5 or hlgher and the final pH after stearn cooking
should be at least 6 or higher The optimum pH of impregnating solution is from 9 to
10.8.
The time of impregnation at atmospheric pressure in holding tanks typically
15 ranges from about 12 hours to 24 hours at a temperature of about 30C to 60C.
Approxima~ely equal weights of fragments and of aqu~ous Impregnating solution can
be used. For industrial purposes, however, the time may be shortened to minutes by
impregnating with steam under pressure and at a higher temperature. The pressureshould be up to about 1 atmospheric extra pressur~ at a temperature of about 100C
20 to 110C. To improve impregnation the fragments should be comprassed in advance
of impregnation in cooi solutions ot chemicals. Under these conditions, penetration
will be achieved in a shorter time, but penetration is wha~ predominanlly occurs.
There is no significant cooking.
25 Steam ço~klng
The impregnated fragments are s~eam cooked at a high temperature and
pressure.
Equipment and methods that can be used for preliminary compacting of the
impregnated fragments, for cooking the fragments with steam and for the discharge of
30 the fibers under conditions of ~xplosiv0 decompression and describad in Canadian
Patent 1 070 537 dated January 29, 1 980;1 070 B46 dated January 29, 1980;1 1 19033 dated March 2, 1982 and 1 138 708 dated January 4, 1983, all of which were
granted to Stake Technology Ltd. The equipment used in the examples was acquiredfrom that compagny.
The temperature of cooi(ing shoulcJ be within the range of about 180C to
210C and preferably within the range 1g0-Z00C, which is in excess of the
temperatures considered possible according to the publications of Asplund and
Higgins previously referred to. These temperatures correspond with a pressure of 1
MPa for 180C and 1.5 MPa for ~00C the pressures being considerably lower than
that reported by Mamer. It is these high pressures which mak~ a very important
contribution to ensuring excellent penetration of th0 fragments by the cooking liquor.
The cooking may be preceded by steam flushing under low pressure steam at
100C for a short period such as one minute. This is a matler of convenience, in that
with a batch reactor the cooking vessel is initially open to the atmosphere, to eliminate
air. This air would be disadvantageous in that it would rasult in oxidation if it were
trapped in the cookir)g vessel. Additional antioxidant may if desir~d be added at this
s~age. S~eam flushing is desirable with a batch reactor but would not be necessary
for a ContinuQus reactor.
This prsliminary treatment is then followed by cooking for about 30 seconds to
6 minutes and preferably about I to 4 minutes.
~x,~loslvl3 d~ompreS$1Qn
After cooking the pressure is Instantaneously released and the plant fragments
are exploded into a release vessel. If there is to be a delay between release of th~
fragments and refining it is imporlant to cool tha fibers down by washing them.
VVashing may also be desirable for ~he purpose of chemical recovery.
It is desirable immediately to refins the fibers after explosive decompression.
Otherwise, if the fibers are stored, some oxidation will occur with resultant loss of
brightness. The rapidity with which this wil7 ococur depends on how rnuch residual
antivxidant is present at that tim0 and on the temperature o~ the fibers anci the extent
r~ 3 9
of exposure to oxygen. Preferably, there~ore, refining is immediate so that it is
unnecessary to incur the cost of excess antioxidant. In any event, unclue delay should
be avoided. Such delay is regarded as being undue if oxidation takes place to anextent that will materially af~ect brightness.
The fragments resulting from the explosive decompression are softened and
are partially or fully defibrated.
~(AMPLE 11.
Mat~l~l~
Bagasse used in this study was supplied in dry (90/O dryness) and cutting form,The bagasse also seems ~o be depithed. Average cut size, as received, was as
tollows: length 1.0 cm to 4.25 cm with mostly 2 cm; width 0.4 to 5 mm; thickeness .3 to
1 rnm.
15 Chemlçal P~-tr~tment of B~g~sso
100 g of bagasse cu~tings at about 50% of moisture contsnt were mixed in
plastic bags with different amount of solution ranging from 150 to 250 g (liquor/cutting
ratio = 4 to 6). Solutions were made either of 8% Na2SO3 or 16% Na2SO3 or 8%
Na2SO3 and 1% NaOH. The ~im~ of impr~gnation was 48 hours a~ 60C.
Levels of sulfonation and carboxylation obtainod are presented in Tables 1, 2
and 3 determined by method described by Katz et al.
S~am Ç~kln~
Cooking was done in a laboratory batch reactor designed and manufactured
25 by Stake Technology Limited. The ternperature was 190C and the processing time
(cookingj varied from 2 to 4 minutes. Cooking was preceded by one minute steam
flushing at atmosph~ric prassure. After cooking, the pressura was instantan00usly
released and chips which explod~d into ths release vassel ware washed and cooledwith one liter of tap water and subsequently refined after being stored in a cold room.
30 Cooking conditions were chosen on the basis of previous studies. In the case of
2~r~
"CTMP", cooking temperature was 128C and cooking time was 10 minutes and in th~case of CMP, cooking temperature was 150C and cooking time 30 minutes. Cooking
yield was measured after exploded fibers were defibrated for 3 minutes in laboratory
domestic blender Osterizer B-86 14 at a consistency level of 2%. The oven dry weight
of thoroughly washed and dried pulp was related to initial oven dry bagasse cuttin~
weight.
R~flnln~
Defibration and re~ining of exploded fibers were don0 using a domastic
blender Osterizer B 8614 at a consist~ncy level of 2%. Total refining and blending
energy were measured using a tilOKI model 3181-01 powermeter. Specific refining
energy was calculated by substracting the blending energy of water-beated fiber
suspension from total refining energy.
Prop~r~y~ EvaluatlQn
Paper sheels wer~ prepar~d and tested according to CPPA standard methods.
The brightness (Elrepho) was measured on 1.3 g or 3 g sh~ets prepared using
demineralized water. Bleaching conditions used are described in Tables 4.
~Su!~ ~d dlscusslQns
C:omparlson of explosion ~lp. C~MP ~nd MP
For the sake of a reliable comparison of different ultra-high yield processes, the
following methodology was adopted:
i) same bagasse cuttings were used;
2s ii) same impregnation procedure was followed in all cases;
iii~ vapour phase steam cooking was varied out in the same reac~or;
iv) yield was evaluated in th0 sam~ way;
v) laboratory refining was done using the same blenders and specific
refinin~ energy was evaluated in the same manner. The results, even
though relative ones, correlate reasonabiy well in the case of explosion
2 ~ 3~3
pulps with that obtained on semi-Tndustrial r~iners both as far as
properties and specific refining energy i~ concerned. In the case of
CTMP and CMP pulps refining energies found in semi-industrial trials
were about 25% higher than that found in laboratory;
vi) pulp and paper properties were evaluated using the same techniques as
well as the same testing equipments;
vii) all work was done by tha same personnel. The only diiference was in
cooking time and temperature
...128C for 10 mlnutes In the case of simulated (:;TMP (refining done at
atmospheric pressure)
...150C for 30 rninutes in the case of CMP and
...190C for 2, 3 or 4 minutes in the case of explosion S-pulping.
Detailed results are graphically evaluated in Figur~s 1 to 12. The following
conclusions can be drawn from Figures:
... Explosion pulp is offering strongest papers for all measured range followed by CMP and CTMP.
... Absolute values of braking length of 6 km for CSF-100 ara comparable to
that of bagasse low yield chemical pulps and substantial,y higher than ~hat of
bagasso kraft pulp of breaking longth 3 km,
... Breaking leng~h of explosion pulp increases from 5 to 6.3 km with the
increase of cooking time from 2 to 4 minutes. This corresponds a decrease in
pulp yield from B0.47 to 8û%.
... both explosion pulp and CMP require very low specKic rQfiing energy (i9SS
than 0.5 MJtkg to arive at CSF-100) and CTMP requires nearly 2 MJ/kg at the
similar CSF level when th~ impregnation solution contains 1% NaOH in
addition to 8% Na2SO3.
Tear ver~ ~r~akln~ gth
- Correlation between tear index and breaking length shows that explosion pulp
30 is sup~riQr ~Q CMP~nd CI~/IP~ ~s brsa~in~ l~ngth is conc~rned.
2 0 ~
Sp~lfl~ reflnln~L~n~r~y v~rs~s br~klng long~h
CMP requires less than 0.5 MJ/kg of specific refining energy to arrive at
breaking length of nearly 1.5 km at lhe level of CSF 100. The explosion pulp requires
about 2.7 MJ/kg of specific refining energies to arive at breaking length of about 4 km
at 100 CSF level. CTMP requires nearly 4 M~l/kg of re~ining energy to arrive at
breaking length of only 2 km at 1û0 CSF- level. In all the above cases, only 8%
Na2SO3 was used in impragnation solution (Table 1 and Figure 15).
When the impregnation solution contains 1% NaOH in addition to 8% Na2SO3,
the ex~losion ~ul~L,$ mor~ kenefile~thal (,l~nd.~TMP. Both explosion pulp and
CMP consume less than 0.5 MJ/kg of reiining to arrive at 100 CSF level, but the
breaking length of th~ ~xplosiQn ~ul~ i~s ne~ 1 km high~r than th~t~CMP. CTMP
requires about 1.8 MJlkg of refining energy to obtain a br~aking length of about2.5 km corresponding to 100 ml CSF.
Comp~r_ ~
The properties of unbleached bagasse explosion pulp obtained with 1% NaOH
in impregnation solution can be compared ~ven wilh bl~ached low yield bagasse
chemical pulp'P. The unbleached bagasse explosion pulp gives breaking length of
5.8 km, tear index of 7.7 mN.m2/g and burst indQx o~ 3.5 kPa.m2/g at 100 CSF level,
whereas bleached bagasse chemical pulp gives breaking length of about 6.6 km, tear
index of 5.1 mN.m2/g and burst index 3.4 kPa.m2/g at 447 CSF level. It is well known
that chemical pulp shows best physical propertiss in ~he CSF ranye of 300 to 500 ml,
whereas the high yield / ultra-high yield pulp shows best physical properties around
at 10U ml CSF level. Again, the bleaching process can increase the physical
properties of the pulp frorn 15 to 20%. In that case, the bagasss explosion pulp will
be even better than the chemical pulp. The brightness of blaached bagasse
explosion pulp (brightness 73.8% with yellowing of 11.6%) and that of bleached
bagasse explosion pulp (brightness 62.1% after colour reversion) is also comparable.
_
Rao, M.V.G., Rao, hl.R.M., Sarker, P.K., Satyanorayana, T.V.V. and Dorairajan, V., "Our s~ar~ up
Experiences in Newsprint Mill Based on 13agasse~, p. 121-127, TAPPI Proceedi~g$, 1986 Pulping
Conference, Toronto, ocl. 26-30.
11
' ~ fi~ ~
~s~n~LQn
S-pulping of bagasse results in pulp of ~xcell0nt paper properti0s. Strength of
S-pulp when 1% NaOH used is similar to tha~ of low yield bagasse chemical pulp.
Bagasse explosion pulp givas paper of higher breaking length than that of CMP and
5 Cl MP. Both bagasse explosion pulp and (`,MP requires similar low refining energy to
arrive 100 ml CSF leYel, but the breaking length of explosion pulp is at least 1 km
higher than that of corresponding CMP. Resulting yield range from 70 to 80% is
expected to increase further by 3 to 4% in indusSrial production where higher
temperature (195 to 200C) and shorter cooking times (60 seconds to ~5 seconds)
10 are going to be used.
It is also expected that obtained unblaached brightness of 33% would increase
in industrial production to nearly 41% and bleached brightness to 66% level with 4 to
10% H22 applied.
Specific refining energy is also expected to be iow for S-pulp produced
15 industrially.
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Mat3rl~1s
Kenaf Everglades # 41, grown at Muskogee, Oklahoma, lJSA and harv~sted
on Nov. 25, 19a8 was supplied by Kenaf of North America Inc. of Tulsa, O.K.
The provided samples of Kenaf stalk base, lower middle; upper middle; upper
middle; lower top and top were manually chopped to 2.5 cm 7ength. All samples ware
characterized by moderate to high discoloration. In order to get representative
sample for pulping, samples were mixed ~o get composition of that of whole stalk(sections of whole stallc were provided lor comparison).
~h~mlcal ~re-tr~atm~nt
110 ~ of chips (50% dryness) were mixocl in plastic bags along with 110 ml of
solution containing either 8% Na2SO3 or 16% Na2SO3 or 8% Na2SO3 and 1%
NaOH. The time of impregnation was 24 hours at 60C.
NQte: Only 110 g chips were used instead of usual 150 g because of lower
density of Kenaf when compared to wsod sp~cies. Cooking iiquor was absorb~d
completely by the chips after impregnation.
Levels of sul~onation and carboxylation obtained afler cooking and defibration
were determined by m~thod described by Katz and al.
~t~m ~ n~
Cooking was done in a laboratory batch reactor designed and manufaotured
by Stake Technology Limited. The temperatura was 190C and processing time
~cooking) was 240 seconds. Cooking was preceded by one minuta steam flushing at
atmospheric pressure. After cooking, ths pressure was instantaneously raleased and
chips which exploded into the retease vessel ware washed and cooled with one liter
of top wat~r and subsequently refined after being stored in a cold room. Cookingconditions, i.e. temperature 190C and time 4 minutes were chosen based on
previous studies. In the case of "CTMP", cooking temperatures was 128C and
30 cooking time was ~0 minutes and in the case of CMP, cooking temperature was
28
2 0 ~
l50C and cool<ing time 30 minutes. Cooking yield was measured after exploded
fibers were defibrated for 3 minutes in laboratory domes~ic blender Osterizer B-8614
at a consistency levei of 2%. The O.D. weight of thoroughly washed and dried pulp
was related to initiai O.D. chip weight.
R~t3nlng
Defibration and refining of axplocled fibers was done using a domestic blender
Osterizer B 8614 at a consistency level of 2%. Total refinin~ and blending energy
were measured using a HIOKI model 3181-()1 powerm~t0r. Specific refining ~n~rgy
was calculatod by subs~racting the blendin~ energy of water-beated fiber suspension
from total refining energy. It was shown prc\/iously that paper properties obtained by
blender refining of mechanical and explosion pulps corresponds well to that obtaineti
on pulps refined industrially or semi-industrially.
Prop~rty ~v~ atI~n
Paper sheets were prepared and tested according to CPPA testing methods
and the properties were evaluated under dry conditions.
The brightness ~EIrepho) was measured on 1.2 g or 3 g: sheets made ~Ising
demineralized water. Bleaching conditions using one stage hydrogen peroxide
brightening have been as follows: ~H2O2): 4%; (MgSO4): 0.05%; (NaOH~: 3%;
(Na2SiO3): 3%, consistency of pulp: 20%; time: 2 hours; temperature: 80C.
~SUIl~ ~n~ dl~u~lQrl~
Comp~risoll of exploslon ~JIp. ~:TMP ~n~C:MP
In order to achieve a credible comparison of different ultra-high yield
process~sj the following methodology was adopted:
i) same chips were usad;
ii) same impregnation proc0dure was followed in all cases;
iii) vapour phase steam cooking was carried out in the same reactor;
iv~ yield was evaluated in the same way;
29
20~nS~
v) laboratory refining was done using the same blenders, and specific
energy was evaluated in the same manner; obtainecJ results, eventhough
relative ones7 correlate reasonably well in the case of explosion pulps
with that obtained on semi-industrial refiners both as far as properties
and specific refining energy is concerned. In the case of "CTMP" and
CMP pulps re~ining energies found in semi-industrial triais were about
25% higher than that found in laboratory;
vi3 pulp and paper properties were evaluated using the same techniques as
well as the same testing equipments;
vii) all work was done by the same personnel. The only difference was in
cooking time and temperature:
...128C for 10 minules in the case of simulated "CTMP" (refining done at
atmospheric pressure)
...150C for 30 minutes in the case of CMP and
15 \ ... 190C for 4 minutes in the case of explosion S-Pulping
Detailed results are graphically presented in figures 13-22. The following
conclusions can be drawn:
...Kenaf pulp with excellent paper proper~ies can be pr~pared using steam
explosion pulping process
... Different chemical contents during impregnation result in different sulfonation
levels and in consequence in differerlt paper properties
...16% Na2SO3 used during impregnation lead to best papre properties closely
followed by that of 8% Na2SO3 + 1 ~/o NaOH and 8% Na2SO3. This correlation
can be explained by sulfonation levels being 85.5 mmol/kg (16% Na2SO3); 81
mmol/kg (8% Na2SO3 ~1% NaOH~ and 47 mmol/k~ (8% Na2SO3)
.. Absoluta values of paper properties are ven higher to that found ~or S-Aspen
pulp (i.e. Breaking length amost 9 km for CSF 100 comparing to BL 8 km for
Aspen). At the same time, tear index is 7.7 mN m2/g comparing to that o~ S-
Aspen pulp being 6.2 mN m2/g.
~; 30
2 ~
...Combination of very high breaking length with high tear is characteristic of
that lound in spruce S-pulp wh~re breaking leng~h of 7 km is combined with
tear 10.Z mN m2/g. These values are identical to that found for S-pulp of Kenaf
...On the negative side, yield values for S-pulp of Kenaf are considerably lowerthan that found in case of S-pulps of Aspen or Spruce.
Yield values, being function of sulfonate content, varies from 72.7% l8%
Na2SO3) to 66% (16% Na2SO3) or 66.2% (8% Na2SO3 ~ 1% NaOi-l). In the
case of Aspen, yield values were substantially higher varying from 94% (8%
Na2SO3) to 91% (8% Na2SO3 ~ 0.5% NaOH). In case of S-pulp of spruce,
obtained yield was 91.8% (8% Na2SO3).
...Vptical properties of S-Kenaf pulp are very good and similar than that of S-
Aspon pulp. Brightness varied from 62.5% (8% Na2SO3) to 60.4% (16%
Na2SO3) or 57.6% (8% Na2SO3 ~1% NaOI-i). Comparable values of S-Aspen
pulp were brightness 69.5% (8% Na2SO3) or 60% (8% Na2SC)3 + 0.5%
NaOH).
...On the other han~, opacity valu~s of S-Kenaf pulp, b~ing 94.6% (8%
Na2SO3) or B8.4% (16% Na2SO3) or 87.3% (8% Na2SO3 + 1% NaOH) were
better than that S-Aspen pulp being 86.4% (8% Na2SO3) and B2.7% (8%
NazSO3 + 0.5% NaOH~. In case of SwSpruce pulp, tho optical properties wer~
inferlor wilh brightness 51.8% and opacity 92.7% all for 8% Na2SO3.
l~ is clear, that S~Kenaf refines extremely well and takes very low amount
refining energy (i.e. BL = 5 km, Energy = 0.4 M~/kg) at 8% Na2SO3. This amount is
comparable to that of S-Aspen pulp with 8% Na2SO3 and 0.5% NaOH. In case of
higher sulfonation level (81-85 mmol/kg), corresponding a%Na2SO3 ~1% NaOH or
16% Na2SO3 impregnation concentration, specific refining energies are ~Imost
rLeg~ ai~l~ (breaking length of 8 km obtained 0.4 MJ/kg comparing to 3.2 MJ/kg in
case of S-Aspen pulp~.
31
...Specific refining energy eventhough slightly higher for 16% Na2SO3 (BL
8 km; energy 0.65 MJ/kg) than that of B% Na2SO3 + 1% NaOH (BL 8 km; energy
0.4 MJ/kg) is still extremely low.
...Specific refining energies for S-spruce pulp are higher (i.e. BL - 5 km; energy
5 =4.7MK/kg).
C:~mp~rlson QfQ~ploslPn~ rNllP" ~n~ C:MP ~Iping
The following conclusion can be drawn:
10 1 ) ~oncqntr~tlon ~% N~2,.SQ3 l~ading to 47 m~nol/kg,,sulf~c~t~ ~ont~n~
...S-pulping results at the best~n~çhanical propertLQ~BL - 6 krn;~c~lQ,2
m~!m~
At thè same breaking 10ngth of 3.~ km, S-pulp leads to almost ~kLe tear
values:
CMP or"CTMP", Tear= 5.5 mNm2tg
EXPLOSION, Tear = 10.9 mNm2/g
(E~plQ~ion pulp has ~8~ r ~ than 1~aP or.~I~
...At the same breaking length of 3.5 km, steam explosion Kenaf pulp has the
Iowest refining energy.
"CTMP" ... 5.6 MJ/kg
CMP ..... 3.6 MJ/l<g
EXPLOSION . . 0.5 MJ/l<g
2) ~Aa9~6~_~Q3, le~çl3ng to ~5 mmol/kg sulfona~
25 c~nt~nt
...S-pulp gives the best paper properties, followed by CMP and "CTMP".
Combination of breaking length of ~m with T0ar Z~Lm~ is even higher than
that found in case of S-Aspen pulp.
32
2 ~
When the paper properties are compared at breaklng length ot 7 krrl (Explosion
and CMP; "CTMP" is too weak) pulp has ayain ç~nsi~erablo advantage in tear
value:
CMP: Tear= 6.3 mNm2/g
EXPLOSION: Tear = 10.2 mNm2/g
(Explosi~n pu!~ as ~,Lç~mparablQBL = 7_m 62% higher Tear valu~ ~han
equivalent CMP!
At the same breaking length of 7 km, S-pulp has the lowest specific refining
energy.
CMP: 1.5 MJ/kg
"CTMP": 5 MJ/kg
EXPLOSION: 0.4 MJ/kg
~Speçi~c r~finin~ energy of S-puip ~ only abo~t 27% or ~% of th~t gf
equivalent CMP or"~T~YlP~)
33 ~Qnçen~tr~ation of ~% Na~ 1% ~H l~sling t~ 81 mmol/k~
~ul~on~te, ço,ntçnl
S-Kenaf pulp gives the best proporties again followod by CMP and "CTMP"
pulps.
~0 ... Combination of Breaking Length of 9 km and Tear B.8 mNm2/g is excQllent,
high2r than that found in S-Aspen pulp.
When the paper properties are compared at Breakiny length of 7 km
(Explosion versus CMP), explosion pulp show again considerable advanta~e in
Tear valuo:
CMP: Taar = 6.6 mNm2/g
EXPLOSION: Tear= 8.9 mNm2/g
~ExplQs~on pulp has ~smpa!able ~:L = 7 km. ~5% hi~her Tear valuç th~
e~uivalent CMP~
...At the sama value level of Breaking l~ngth of 7 km, S-pulp has again the
30 lowest specific r~fining ener~y eventhough .all l2UlD~ has tha a~sol~t~ valu~ low:
33
2 ~ 3
CMP: 0.23 MJ/kg
"CTMP": 0.88 MJ/kg
EXPLOSION: 0.17 MJ/kg
Specific refining energy of SEP (Steam Explosion pulp or S-pulp) is about
74% of 20% of that of equivalent CMP or "CTMP".
Brlghtness ~nd bri~htn~ss stablll~y
Brightness level of 78.4% obtained with 4/O i-i2O2 applied (or 3% H2O2
consum0d), case of 8% Na2SO3 could be increase to 80%~ level with 4% H22
consumed or 5-6% H2O2 applied. Brightness stability is very good (1.4% brightness
lost only at 105C; 60 minutes).
Brightness levels of higher sulfonation content, it means 76.6% (16% Na2SO3)
or 77.4% (8% Na2SO3 + 1% NaOi-i) could be also bleached to 80% level but with
higher H2O2 concentration (= 4.5% consumed) if bleached in one stage. YVe believe
that this percentage of H2O2 can be decrease in industrial 2 stage brightening.
~onc~us!Qn
Steam explosion pulping process leads te excellent pulp and paper properties
from Kenaf.
Comparing to convontional CMP or CTMP proc~ss, S-puiping process results
in superior pulp and paper properties and lower specific refining enargy. The usual
trade-off strength for brightness is also observed for Stearn Explosion Kenaf pulp.
34
2 ~ 6 .~ 9
E2~AMPLE ~
T~stlrL~ QthQdolog~L
Ma~l~
Flax samples were provided by Crown Managernent i30ard of Saskatchewan.
5 Sample flax # 1 was a white sample with fiber cut and outer layer removed. Samples
flax ~ 2 had to be manually cut to length of ai~out 2 inches.
Ch~ml~als Pr~-tre~tm~t-~f~l!~x
150 g of flax at about 50% of moisture content were rnixed in plastic bags either
lo with 150 g of solution (liquor/chip ratio = 3) or with 300 g of solution ~liquor/chip ratio =
5). Solutions were made either of 8~/o Na2SO3 or 8% Na2SO3 and 1% NaOH. The
time of impregnation was 24 hours at 60C.
Levels of sulfonation and carboxylation obtained are presented in Tables
were determined by method described by Katz et al.
S~e~m ~ooklng
Cooking was done in a laboratory batch reactor designed and manufactured
by Stake Technology Limited. The temperature was 190C and processing time
(cooking) was 240 seconds. Cookin~ was preceded by one minuto steam flushing at
20 atmospheric pressure. After cooking, the pressure was instantaneously released and
chips which expioded into the release vessel were washed and cooled with one liter
of top water and subsequently refined after being stored in a cold room. Cookingconditions, i.e. ~emperature 190C and time 4 minutes were chosen based on
previous studies. In the case of "CTMP" of flax, cooking temperature was 130C and
25 cooking time was 10 minutes. Cooking yield was measured a~ter exploded fiberswere defibratad for 3 minutes in laboratory domestic biender Osterizer B-8614 at a
consistency level of 2%. The O.D. weight of thoroughly washed and dried pulp wasrelated to initial O.D. chip weight. RMP was prepared by refining of original flax which
was not chemically pre-treated.
2~5Jf~
~g
Defibration and refining of exploded fibers was done using a domestic blender
Osterizer B-8614 at a consistency ievel of 2%. It was shown, that paper properties
obtained by blender refining of mechanical ancl explosion pulps corresponds well to
5 that obtained on pulps refined industrially or semi-industrially.
Property Ev~lu~tiQn
Paper sheets were prepared and tested according to CPPA testing methods
and the properties were evaluated under dry conditions. Considering different
10 behavior of flax paper sheet under stress, breaking length was evaluated using Peak
load.
The brightness (Elrepho) was measured on 1.2 g.~ sh~ets made using
demineralized water.
15 R~lt~ and dl~ sslon
F~esults summarized in the Tables 4-7 and in the Figures 23-27 are
selfexplanatory. The following conclusisns can be drawn:
- The adhesion properties of Flax S-pulp such as burst and breaking length are
considerably stronger than that of equivalent RMP (refiner mechanical pulp) and
20 "CTMP" flax pulps when 8% Na2SO3 and 1% NaOH were used during impregnation
stage.
- Flax # 1 samples (without outer sh~ll present) gives stronger and brighter
pulp than that of flax # 2.
- Absolute strength of flax # 1 pulp Is similar to ~hat of FIMP and TMP of spruce
25 pulps but flax # 1 h~: is, i.e. for peak breaking length ~ km e~al tv ~ mN~m~compared to that 5 mN.m2/g of RMP or 8.5 mN.m2/g of TMP or 11 mN.m2/g for CTMP.
- The brightness of flax # 1 pulp (51% to 54%) was higher than that of flax # 2
(45% to 48%), was increased to the 70% level (flax tt 1) or 65%~ level (flax # 2) by
single stage bleaching with 4% H2O2.
46
2 ~ ', 9
- Paper prop~rties ware further improved by bleaching. Bleaching of exploded
flax # 1 (8% Na2SO3, 1% NaOH) increase breaking length by 247%, peak breaking
length by 32% and burst by 38%.
- Yield of S-puiped of flax is in 75% ~ level.
- Refining times of flax samples were very shor~ indicating low specific refining
energies levels (estimated between 1 MJ/kg and 2 MJ/kg).
- Commercial use of steam explosion flax pulps will be in end uses where tear
is of critical concern. These pulps could be used to increase the tear in Kraft pulp
based furnishes and could also apply to the specialty paper mark~t ~i.e. cigarett~
paper) where tear is important.
- S-Pulp equal SEP equal EXP equal Explosion pulp.
TAEILE 4
Explosion, "C:rMP" and RMP pulplng of flax ~t 1
PULP RMP "CTMP" EXPI OSICIN
Liquor/chip - 3 3
Na2SO3 ~%) 8 8 8
NaOH ~%) - 0 1 0
Temperature (C) - 130 130 190 1g0
Time ~Min) ~ 10 10 4 4
Yield ~%) 96 80.3 79.1 75.1 75.3
Brightness (%) 39.4 53 50.5 51 50.5
Opacity (%) 91 ~8.8 88.7 90 90.5
lonic content (mmoVk~) - 230 296 202 230.5
47
TABLE 5
Exploslon, "CTMP" and RMP pulplng of flax # 1
~--~
PULP RMP EXPL0510N "CTMP"
Liquor/chip - 5
Na2SO3 (%) -
NaOH (%)
T~mp~ratur~ (C) - 190 190
Time (Min) - 4 4
Yield (%) 96 76.9 81.3
Brightness (%) 39.4 54 52.8
Opacity (%) 91 ~9 87.5
lonic cont~nt (mmol/kg) - 264.6 270.3
- TABLE 6
EJ~ploslon pulplng of flax # 2
PUI LP EXPLOSION
Liquor/chip 3 3
NazSO3 (%) 8 ~ 8
NaOH ~%) 0 1 0
Temperature (C) 190 190 190
Time (Min) 4 4 4
Yield (%) 76 75.2 75.6
Brightn~ss (/0) 45.3 45.3 48.5
Opacity (%) 93 92 91
lonic content (mmol/kg) - ~ -
'.~
48
2 ~
TAB LE 7
Bleachln~ of Stake 5team Exploded Flax # 1
Proc~s$in~ ~r~ Qn~
Chemical Impregnation 8% Na2SO3 8% Na2~O3
0% NaOH 1% NaOH
(UC = 5) (UC = 3)
Steam i-xplosion (~atch) 190(:; 1 90C
4 mirlutes 4 minutes
Bleaching 4% H202 4% H202
PulLprop~d~s lln~l~b~ ~h~ Unbl~ach~d ~l~j~
CSF (ml) 225 225 346 346
Yield (% on drychips) 76.7 72.4 75.367.B
Breaking Length (km3 0.46 1.60 0.341.18
Peak Breaking Length (km) 2.35 3.38 2.563.37
Burst Index (kPa.m2/g) 1.74 2.35 1 652.28
Tear Index (mN.m2/g) 19.6 16.5 23.522.9
Bulk (cm3/g3 4.56 2.88 4.372.91
Brightness (%) 54.1 73.6 50.7 61
Opacity (%) 89.1 70 3 90.8 77
Light Scattering Coef. (cm2/g) 337 227 357 273
,
;
49
