Note: Descriptions are shown in the official language in which they were submitted.
2~2~7 1~
METHOD FOR THE RE:COVERY AND PROCESSING OF FIBERS
FROM HOLLOW STALK PLAN~S
The present invention relates to a method for the
recovery and processing of fibers from hollow stalk
plants and to the use of the fibers obtained by the
method. The invention particularly relates to fibers
of dicotyledonous plants and more particularly to fi-
bers of kenaf or hemp, their preparation, processing
and use.
Backqround of the Invention
1 5
The expression "hollow stalk plant" is intended
to encompass all plants which form a hollow, generally
rather long stem which is filled with a kind of woody
marrow. Examples of such plants are the dicotyledo-
nous plants such as kenaf and hemp, but also elder andsome reed species.
A dicotyledonous plant has two morphologically
distinct regions in its stem, namely the outer bark
fraction which contains the bast fibers, and the in-
ner, woody core. The ratio between the stalk compo-
nents varies according to the different species, the
nature of the soil and others, and the outer portion
comprises 40 to 10 ~ while the woody core comprises 60
to 90 % of the whole stalk.
In this document, kenaf fibers will be taken as a
basis for the following description of the invention.
However, it is emphasized that the invention is not
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limited thereto but can b~ practiced in using all di-
cotyledonous plants which have an analogous structure.
Kenaf (hibiscus cannabinus), an annual dicotyle-
donous plant, originates probably from Eastern CentralAfrica and is now cultivated all over the world. In
Europe, it grows in a height of until 5 meters and
produces a dry biomass substance of about 4 to 30 me-
tric tons per hectare, depending on the growth condi-
tions.
During the last decade, plants have been searchedfor on a worldwide scale which grow rapidly and form
cellulose since normal wood plants are growing too
slowly for covering the rising demand for paper and
paper-like materials. Due to this slow growth, cel-
lulose prices are going up. Furthermore, especially
conifers must be intensively chemically treated for
providing paper pulp since they contain a considerable
~0 amount of resin and hemicelluloses which cannot be to-
lerated in paper.
:~
It has already become known to prepare paper pulp
from kenaf. Thus, US-A-4,106,979 (Ruffini~ discloses
the preparation of paper pulp from kenaf and other
dicotyledonous plants. It appears that for kenaf raw
material to be acceptable as an economic papermaking
fiber, it will be necessary to first separate the two
said stem components which are greatly different in
physical, chemical and morphologigal characteristics;
only the fibrous components of the outer bark fraction
of the stem are suitable for papermaking or generally
sheet forming purposes; the core materials consist
mostly of fibers too but very special methods are ne-
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cessary to recover these fibers. In the cited docu-
ment, the field dried~ chopped kenaf stalks are stir-
red in a pulper at elevated temperature in an alkaline
aqueous medium, and the bast fibers are the separated
from the pulp on a slit screen fractionator. However,
in this known process, the separation efficiency is
relatively poor, 82 % according to Example 1, and the
separation step uses chemicals which present environ-
mental risks and render the method uneconomic.
It has also been tried to separate the bast
fibers from the core material by purely mechanical
means. Thus, for example, PCT/AU92/00027, published
under WO 92/12808, discloses a method and an apparatus
for grading fibrous material, exemplified by the
separation of kenaf stalk materials into the bark
fibers and the core materials. The apparatus com-
prises two or more hollow bodies rotating about in-
clined axes, the bodies having baffles for tumbling
the fibrous materials and slits for decharging the
fines. However, own tests have shown that the core
particles-of kenaf are partially opened in the appara-
tus, forming nest-like dims or tangles which catch
longer fibers; the separation efficiency of the method
is poor and does not even reach that of the first
cited document above, even when using more than three
hollow bodies. Furthermore, the starting fibrous ma-
terial must thoroughly be dried which raises the pro-
cess costs.
Poor separation efficiencies are also obtained by
using the apparatus disclosed in EP-A3-0,122,769.
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Therefore, and bearing in mind that hollow stalk
plants can only be used as a fiber material, for exam-
ple in the paper making industry, more generally in
the fiber sheet industry, without introducing additi-
onal, costly processing steps if the core materialshave been separated from the bark fibers with an ef-
ficiency of at least 90 %, it is the first and major
object of the present invention to provide a new
method and apparatus for the separation of fibers from
such plants which affords the required separation ef-
ficiency.
~::
There is a further object of this invention to
provide an effective separation method as pointed out
above which does not use hazardous chemical reagents ~ .
and which produces pure fibers in an economical man- : ~:
ner. ~
SummarY of the Invention - -.:
~ :~
The objects set forth above are attained by the
present invention which achieves the required high ef-
ficient separation in a wet method using a new and
useful separation device, namely a hydrocyclone which
will be described later on in more detail. The method
of the invention comprises pulping a fiber material
previously obtained by field drying, chopping, and
coarse comminution of the plant stalks and subsequent
summary removal of core particles, in warm or hot wa-
ter, preferably water of at least 50 C, more prefer-
ably of 80 to 85 C, to a solids concentration of from ~ .
4 to 20 % by weight during about 5 to 40 minutes, then
separating fine, lightweight fibers, other fines and
residual core particles from this pulp, and recovering
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a fibrous pulp wherein the fibers contain less than 10
% by weight of non-fibrous materials. This separation
is preferably achieved in passing the pulp into a
hydrocyclone having circumferential, central and in-
termediate collecting volumes, and recovering the fi-
brous pulp from said intermediate volume of the
hydrocyclone situated between said circumferential and
central collecting volumes.
This method, using said hydrocyclone, affords a
separation efficiency of at least 95 %, i.e. that the
fibrous pulp flowing out of the new hydrocyclone of
the invention contains solids comprising at least 95 %
by weight of fibers.
According to preferred embodiments, the overall
yield of fibrous materials can be improved as well as
the overall separation efficiency when the fibrous
pulp discharged from the intermediate volume of the
hydrocyclone is fed into a classifying device where
fibre bundles not yet opened in the pulping step, and
any residual core particles are separated from the
fibers and returned to pulping after a milling treat-
ment.
The material in the circumferential volume of the
hydrocyclone, i. e. a layer adjacent to the inner
hydrocyclone wall, comprises compact core particles.
This material may be collected, separated from the
suspending aqueous phase, then milled and returned in-
to the pulper. During milling, the core particles are
opened in yielding fine fibers which will, during the
procedure described above, accumulate in the central
volume of the hydrocyclone. The central volume in the
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hydrocyclone, comprising fine fibers and other light-
weight fines, is discharged therefrom and may be used
for papermakinq or other purposes, thus improving the
overall economics of the method.
The object of the invention is also met by a dry
separation technique, comprising feeding a dry fiber
material previously obtained by field and/or air dry-
ing, chopping, and coarse comminution of the plant
stalks and subsequent summary removal of the core par-
ticles, into a multistage zigzag wind sifter. The
overhead output of this device is an air suspension of
fibers which have been separated from the core parti-
cles with an efficiency of at least 90 %. The fibers
thus separated from the core particles can easily be
recovered from the supporting air by screens well
known to the one skilled in the art. For a number of
uses, this purity of the fibers is already sufficient
but if not, the fibers may be subject~d to the wet ~-
separation procedure already described above.
Brief Description of the Drawinas
~ ' '
The invention will now be described in further
~5 detail with reference to the drawing wherein:
Fig. 1 is a process flowsheet showing sche-
matically the overall process of the invention,
Fig. 2 is a vertical cross-sectional view of
the hydrocyclone used in the process of the invention,
and
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Fig. 3 is a horizontal cross~sectional view
of the hydrocyclone in the line III-III of Fig. 2.
Detailed Description of the Invention
Referring now to Fig. 1 which shows in a schema-
tical manner a general flowsheet of an installation 10
for the separation of kenaf fibers from core material,
the reference numeral 12 denotes the kenaf feed charg-
ed into a pulper vessel 14.
The kenaf feed is obtained in the following way:The kenaf plants are preferably harvested by means of
a modified corn chaffcutter machine and pre-dried on
the field. The leaves are separated from the stalks
and left on the field as a natural fertilizer. The
stalks are then coarsely comminuted in a suitable
shredder or a corn chaffcutter into lengths of about
10 to 20 mm. The stalk shreds are then dried to a wa-
ter content of about 13 to 15 %, either naturally onthe field or in grass drying facilities.
The dried kenaf shreds are further processed in a
central installation, comprising chopping the shreds
or opening same on torsion spring drums, and these ma-
terials are then separated in a sieving device such as
a turbulence classifier. This step results in an
about 70 to 80 % separation of the bast fibers from
the core materials which are discarded or separati~ly
processed.
The fibers which still contain from about 2 to 40
by weight of core particles constitute the feed 12
(Fig. 1). These fiber materials also contain fiber
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bundles which were left unopened in the chopping step
mentioned above.
The pulper vessel 14 is equipped with a stirrer
16, driven through a shaft by the stirrer motor 18.
Steam and, if necessary, water can be introduced into
the pulper vessel 14 through the conduit 20 and 21,
respectively, so that the liquid level will be kept
constant. The pulping water in the vessel 14 is main-
tained at a temperature of from about 50 to about 90C, preferably about 80 to about 85 C. The amount of
charged kenaf fibers is such that their concentration
in the pulper is maintained between 4 and 20 % by
weight, preferably at about 14 i~ by weight. The dwell
time of the kenaf fibers in the pulper is about 10 to
20 minutes.
The contents of the vessel 14 is then discharged
by line 22 i.nto the storage vessel 24. During pulp-
ing, the kenaf fibers are hydrated and softened, mostof the fiber bundles are opened, and also a substan-
tial portion of the core particles are opened to yield
additional, fine fibers. The pulp in vessel 24 is
then pumped into the tangentially ending input pipe 30
of the hydrocyclone 28 for classification; the opera-
tion of the hydrocyclone will be explained below. The
fiber suspension entering the hydrocyslone 28 is clas-
sified into a fiber fraction which leaves the cyclone
through line 32, a heavy core fraction consisting
principally of unopened core material in the form of
dims or tangles discharged through the line 34, and
lightweight, fine fibers and other fines, leaving the
hydrocyclone by the line 36. The hydrocyclone 28 thus
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achieves a separation of the charged suspension into
three fractions.
The fiber fraction is passed into the vertical
separator 38, equipped for example with hole or slot
sieves, where remaining fiber bundles are separated
from the kenaf fibers. This separator 38 is an op-
tional device sin~e it need not be used if fiber bund-
les can be tolerated in the final sheet made from the
fibers, such as a mulching sheet or low-quality pa-
pers. The proportion of fibers in the suspension
flowing through line 32 is more than 99 %, about 2 to
3 % thereof being residual fiber bundles. These fiber
bundles, separated from the fibers in the separator
38, are fed to a vibration sieve 40 through line 42.
The fiber suspension which is free from bundles and
any other impurity is passed through line 44 into a
deflaker 46, and the deflaked mass is discharged into
a reaction vessel 50 through line 48.
If desired, the fines in line 36 from hydro-
cyclone 28 can be used together with the finally sepa-
rated kenaf fibers in paper pulp, particularly if
mulch sheets are to be produced. Therefore, they can
be charged through line 54 into the reaction vessel
50. When this is not desired, the fines are passed
through line 56 to other processing facilities or to
disposal.
The fiber suspension leaving the separator 38
through line 44 is a suspension of non-classified
fibers stemming from the bark portion of the plant.
These fibers have a length of about 2 to 13 mm or
more. For some special uses of the fibers, it has
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been found advantageous to further separate these
fibers, namely for example into a first, short fiber
fraction wherein the fibers have a length of about 2
to 8 mm, which can be used as normal binder fibers in
papermaking, and a second, long fiber fraction where
the fibers have a length of more than 8 mm; these
fibers can be used as so-called armouring fibers.
When such a fiber separation is desired, a second
hole-and-slit sieve separator (not shown) having a
construction similar to separator 38 will be disposed
between the first separator 38, shown in Fig. 1, and
the deflaker 46. Like separator 38, this second sepa-
rator has one inlet and two outlets. One outlet is
connected to deflaker 46, and the other outlet pro-
vides a suspension of either the short fibers or thelong fibers, as desired.
As shown in Fig. 1, the core particles separated
from the fibers in hydrocyclone 28 are charged through
line 34 on the vibration sieve 40 together with the
fiber bundles (and, if any, residual core particles~
coming through line 42 from separator 38. On the vi-
bration sieve 40, the solids are separated from the
aqueous pulping liquor which is collected in vessel 58
and then returned through line 60 into storage vessel
24. The solids remaining on the sieve 40 are fed to a
milling device 62, for example an attrition mill sold
by Alpine, Austria, wherein the fiber bundles are
opened and the core particles are further comminuted;
this comminution yields fine fibers since the core
particles are mostly tangles of very fine fibers hav-
ing a length of about 0.1 to 3 mm. The outlet of the
attrition mill 62 is returned through line 64 back to
the pulper 14.
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In the reaction vessel 50, the fibers coming from
deflaker 46 and, optionally, the .ines from the hydro-
cyclone 28 (line 54) are further optionally treated to
provide bleached fibers. It has surprisingly been
found that, probably due to the aforesaid aqueous
treatment and separation steps of the fibers, unusual
mild conditions are suffficient for this bleaching
treatment, and the same bleaching effect is obtained
as a bleaching under more severe conditions of fibers
which have not undergone the processing method of this
invention.
In the reaction vessel 50, the fiber suspension
is slightly diluted to a solids content of about 2.5
to 3.5 % by weight. Sodium hydroxide is added until a
concentration of about 1.5 % by weight. The mixture is
heated, and after about 20 minutes at 80 to 90 C,
about 3 g of hydrogen peroxide having a concentration
of about 25 % are added per kg of the suspension. The
warm suspension is kept under stirring a further 15 to
25 minutes in the temperature range mentioned above.
The suspension is then neutralized by means of a weak
acid, particularly acetic acid, to a pH of about 6.5.
The fibers are separated by centrifuging and optional-
ly dried. They can be used, as already mentioned, asreinforcing fibers in paper pulps, optionally further
containing recycled waste paper, or for replacing cel-
lulose and recycled paper in paper pulps.
It can be seen that the above described method
fundamentally differs from separation, pulping and
bleaching methods hitherto disclosed for wood and also
for dicotyledonous plants. The sole liquid wastes are
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water and a weak sodium acetate liquor which is fully
biodegradable.
The fines leaving the hydrocyclone 28 alternati-
vely through line 56 can easily be separated from the
pulping water and can advantageously be used, as such
or together with the compact core particles leaving
the hydrocyclone through line 34, as organic, biologi-
cally degradable and food allowable filler.
1 0
Referring now to Fig. 2 which shows a vertical
sectional view of the hydrocyclone 28 used in the me-
thod of this invention, reference numerals 30, 32, 34
and 36 denote the same ports or lines, respectively,
as in Fig. 1. The pipe 30 ends, in a known manner,
tangentially in the upper portion of the cyclone. The
upper and lower outlets 32 and 34, respectively, are
known from conventional cyclones. However, th~ cyclone
of Fig. 2 further comprises an inner, central pipe 37
which extends to about the half of the height of the
cyclone 28 and serves for evacuating by means of a
pump (not shown) the fines fraction of the fibrous ma-
terial pulp fed into the cyclone through pipe 30.
,:
Fig. 3 shows a horizontal cross-sectional view of
the cyclone of Fig. 2 in a plane according to line
III-III of Fig. 2. This Figure represents the
separating condition of the fiber suspension 66 fed
into the cyclone through pipe 30. Due to the centri-
ugal forces of the helical flow of the suspension, the
relatively heavy, unopened core particles 68 accumu-
late near to the inner wall of the cyclone 28 and are
transported by inertial forces downward to the outlet
opening 34. The central region of the cyclone 28 is
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subjected to nearly no turbulence and centriugal for-
ces; the lightest fibres and other fines 70, stemming
from opened core tangles, accumulate in this central
space and are evacuated through pipe 37. Finally, the
most interesting main fibers having a length of about
2 to 13 mm or more, as described above, will occupy
the intermediate region between the inner wall of the
cyclone and the central region and are discharged from
the hydrocyclone 28 through the pipe 32 together with
the main stream of the liquid fed into the cyclone.
The installation described above operates as a
continuous process starting from storage vessel 24.
The pulping of the kenaf raw material in vessel 14 is
discontinuous, but it would be possible to replace the
pulping vessel 14 by a continuous pulper.
The ob~ect of the invention, namely the separa-
tion of the compact core particles from a fiber mate-
rial previously obtained by field drying, chopping,and coarse comminution of hollow stem plant stalks, is
also attained in a dry process by passing the com-
minuted stalks through a vertical zigzag wind sifter
or air classifier, known per se in the art and sold by
the Alpine Company, Austria. In a known manner, air
is passed from below into the wind sifter, and the fi-
brous mass to be separated is charged from above into
the device. A separation is obtained at all the edges
of every angle of the wind sifter tube sections which
are disposed according to a zigzag configuration. The
fibers are lighter than the core particles and are
carried away by and together with the air flow through
the separator; they can be collected by suitable
screening means known per se from this air flow. The
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heavier core particles fall down against the air
stream and can be collected at the bottom of the air
separator. The use of air as a separating medium
avoids the still repeating entanglement of core tang-
les and free fibers which, in the known methods, hasimpaired the desired separation.
Separation efficiencies around 90 % have been ob-
tained, that is, the fiber fraction is contaminated by
less than about 10 % of core particles.
If desired, a complete and total separation from
the remainin~ about 10 % of core particles can be ob-
tained in feeding the fiber fraction, obtained from
the wind sifter, into the wet separation installation
described above. The overall separation efficiency
will be at least 99,5 %. ~
It follows from the foregoing description that -
not only the efficiency of separation, as defined
above, is dramatically increased, but that the overall
yield of usable fibers is increased too since the me-
thod of the invention provides an opening of fiber
bundles and of core particles which, in the known
techniques, are either not separated, thus limiting
the uses of the product, or in part separated and dis-
carded.
The fiber materials processed and obtained by the
methods of the invention from hollow stem plants, more
particulary dicotyledonous plants such as kenaf and
hemp, may be used in a multitude of fields. These
uses have especially become possible through the me-
thod of the invention which guarantees an at least
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90 % separation of the compact core particles and, in
some cases, of the finest fibers, said separation ty-
pically yielding even a nearly 100 % separation ef-
ficiency. Examples for such uses which are by far not
exhaustive, are the following:
1. Use as a mulching sheet according to EP-A1-
0,556,150
The outflow of deflaker 46 is combined with the
outflow in line 54 coming from hydrocyclone 28. The
combined suspensions are processed in the conventional
pulp processing units and then on a Fourdrinier machi-
ne of a paper mill, and a mulch sheet is obtained hav-
ing a dark brown colour. Additives may be added to
the paper pulp from kenaf in the size press and/or the
head box which are evenly distributed in the obtained
mulch sheet web.
2. Use in filter sheets
For the manufacture of biologically fully degrad-
able filter sheets, the outflow of the deflaker 46
(line 48) is processed according to point 1. above and
passed on a mould machine. Optionally, the outflow of
deflaker 46 can be bleached before the other process-
ing steps, as described above.
In an analoguous manner, vleeces may be produced
on needle vleece machines or on other non-woven manu-
facturing facilities where binders such as starch are
used.
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3. Use in batch papers
satch papers are papers which contain such a pro-
portion of the fibers obtained in the present inven-
tion that their mechanical resistance values are im-
proved or at least held constant in spite of a reduced
proportion of cellulose fibers.
A short fiber fraction obtained, as described
above, in a vertical slot or hole sieve separator, may
be used. If desired, the fibers may be subjected to a
hot washing step wherein steam is introduced into the
pulper together with the solvent.
The fiber mash thus obtained is brought by means
of a deflaker and refiner to a freeness value which
corresponds to the product to be manufactured and
which is normally pre-established. Then, the mash can
be pumped into a storage vessel and further, in a con-
tinuous or batch-wise manner, into the machine chest
where it is blended with the conventional paper mash.
Alternatively, there is also the possibility to
pass the paper mash over the machine and to recover a
product as a vleece which can be transported and sold
like cellulose. These vleeces can be opened at the
end user and worked up like cellulose or rolls of re-
cycled waste paper. The advantage of this application
is to make the fiber material available to a circle of
users which can now use kenaf without having neither
the necessary detail knowledge nor the kenaf plant
themselves.
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~. Use in art stock and document papers
A mixture is prepared which can be processed on
the paper making machine according to points 1 or 3
above, and the mixture is blended with pH neutral
fibers to form a mash. A very high homogeneity is ob-
tained by parallel deflaking and refining and dispers-
ing. In this way, a specific volume is produced which
gives the final produet most desired speeial proper-
ties as to eoating, pigmenting, ealendering and espe-
eially resistance to ageing.
5. Use in food paekaging
Papers filled or reinforced with kenaf fibers may
be used as an alternative to known celluloses in the
field of food packaging. These raw fibers fulfil the
requirements of foodstuff regulations. No environmen-
tally hazardous substanees are formed during manufac-
ture, and they are not only economically but also eco-
logieally advantageous.
A possible applieation eomprises for example the
production of a sheet on a multiple wire maehine whose
uppermost layer consists of short kenaf fibers whieh
are prepared and proeessed as deseribed above~ see
point 3.
The second and following layers may eonsist of
waste paper or reeyeled papers, reinforeed by kenaf
fibers.
This proeedure ensures that no toxie or harmful
substanees will eome into eontaet with foodstuffs.
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6. Use in construction materials
A mixture of fibers and fines (combined outflow
of lines 48 and 54, Fig. 1) is made up to a mash ac-
cording to the technique of point 3 above and process-
ed to boards on a paperboard machine. These boards or
panels may be used as heat insulation, construction or
sound insulation boards in the field of construction.
7. Use in fiber moulding articles
The fibers of the long and short fiber fractions
can be used, separately or without separation, for
making a fiber pulp by the techniques of points 1 or 3
above which can be processed, for example, into press-
ed bodies such as egg package boxes, other shaped bo-
dies, or may be used as fillers and insulating materi-
als.
The invention and especially the possibilities of
use are not limited to the description given above.
The man skilled in the art will be aware of variants,
modifications and other changes in the frame of the
appended claims without departing from the scope of
the present invention.
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