U.S. patent application number 14/441263 was filed with the patent office on 2015-10-29 for mixing drying of nanofibrillated polysaccharide.
The applicant listed for this patent is Stora Enso Oyj. Invention is credited to Lars Axrup, Kaj Backfolk, Isto Heiskanen, Veikko Jokela, Henri Kastinen, Anna Kauppi, Ari Kotilainen, Cecilia Land Hensdal, Esa Saukkonen, Heidi Saxell.
Application Number | 20150308017 14/441263 |
Document ID | / |
Family ID | 50684139 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150308017 |
Kind Code |
A1 |
Backfolk; Kaj ; et
al. |
October 29, 2015 |
MIXING DRYING OF NANOFIBRILLATED POLYSACCHARIDE
Abstract
A method for drying nanofibrillated polysaccharide to obtain a
substantially dry nanofibrillated polysaccharide product,
comprising the following steps: (i) providing an aqueous suspension
of nanofibrillated polysaccharide; (ii) increasing the solid
content of said suspension, thereby forming a high solid content
microfibrillated cellulose suspension; and (iii) drying said high
solid content microfibrillated cellulose suspension, through a
simultaneous heating and mixing operation.
Inventors: |
Backfolk; Kaj;
(Lappeenranta, FI) ; Saxell; Heidi; (Vantaa,
FI) ; Heiskanen; Isto; (Imatra, FI) ; Axrup;
Lars; (Hammaro, SE) ; Land Hensdal; Cecilia;
(Karlstad, SE) ; Jokela; Veikko; (Rauha, FI)
; Saukkonen; Esa; (Lappeenranta, FI) ; Kotilainen;
Ari; (Helsinki, FI) ; Kastinen; Henri;
(Helsinki, FI) ; Kauppi; Anna; (Helsinki,
FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Stora Enso Oyj |
Helsinki |
|
FI |
|
|
Family ID: |
50684139 |
Appl. No.: |
14/441263 |
Filed: |
October 30, 2013 |
PCT Filed: |
October 30, 2013 |
PCT NO: |
PCT/IB2013/059778 |
371 Date: |
May 7, 2015 |
Current U.S.
Class: |
536/56 |
Current CPC
Class: |
D21C 9/18 20130101; C08L
1/04 20130101; D21C 9/007 20130101; D01F 2/00 20130101; D21C 9/06
20130101; D21H 11/18 20130101; F26B 3/36 20130101 |
International
Class: |
D01F 2/00 20060101
D01F002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2012 |
SE |
1251280-2 |
Claims
1. A method for drying nanofibrillated polysaccharide to obtain a
substantially dry nanofibrillated polysaccharide product,
comprising the following steps: (i) providing an aqueous suspension
of nanofibrillated polysaccharide; (ii) increasing the solid
content of said suspension, thereby forming a high solid content
microfibrillated cellulose suspension; and (iii) drying said high
solid content microfibrillated cellulose suspension, through a
mixing operation, comprising a fibrillation or grinding
operation.
2. The method for drying as claimed in claim 1, wherein in step
(ii), the solid contents is increased to >15 wt %.
3. The method of drying as claimed in claim 1, wherein step (ii)
comprises any one of a centrifugal force operation, pressing
operation and dewatering operation.
4. The method as claimed in claim 3 wherein the dewatering
operation comprises an electro-osmosis operation.
5. The method as claimed in claim 3, wherein the pressing operation
comprises a wet pressing operation.
6. The method as claimed in claim 1, wherein at step (iii) the
temperature of the suspension is in the range of 75-99.degree.
C.
7. The method as claimed in claim 1, wherein at step (iii) the
suspension is heated from about room temperature to the range of
75-99.degree. C.
8. The method as claimed in claim 1, wherein at step (iii) the
temperature of the suspension is in the range of from 40 to
50.degree. C.
9. The method as claimed in claim 1, wherein in step (iii) there is
further provided a simultaneous heating and mixing operation.
10. The method of drying as claimed in claim 1, where step (iii) is
performed under vacuum.
11. The method as claimed in claim 1, wherein the nanofibrillated
polysaccharide is a nanofibrillated cellulose or a microfibrillated
cellulose.
12. The method as claimed in claim 1, wherein in step (iii) there
is further provided a drying additive.
13. A substantially dry nanofibrillated polysaccharide product
obtainable by the method as claimed in claim 1.
14. Use of a dry nanofibrillated polysaccharide product as claimed
in claim 13 in, or for the production of composites.
15. Use of a dry nanofibrillated polysaccharide product as claimed
in claim 13, for any one of a rheology application, fixative agent,
strength enhancing agent, emulsifying agent, excipient, paper
applications, and in paper or paperboard of products thereof.
16. The method for drying as claimed in claim 1, wherein in step
(ii), the solid contents is increased to >20 wt-%.
17. The method for drying as claimed in claim 1, wherein in step
(ii), the solid contents is increased to >25 wt-%.
18. The method for drying as claimed in claim 1, wherein in step
(ii), the solid contents is increased to >30 wt-%.
19. The method for drying as claimed in claim 1, wherein at step
(iii) the temperature of the suspension is about 80.degree. C.
Description
TECHNICAL FIELD
[0001] The present document relates to a method of drying an
aqueous suspension of nanofibrillated polysaccharide to obtain an
substantially dry nanofibrillated polysaccharide product. More
particularly, the present disclosure relates to a nanofibrillated
polysaccharide product obtainable by such method and the uses
thereof.
BACKGROUND
[0002] Nanofibrillated polysaccharides, such as for instance
microfibrillated cellulose, have many end uses, such as in food,
composites, paper, paints, plastics, cosmetics, and medical
products, in which it would be good to be able to dosage
nanofibrillated polysaccharide in a dry form so that the original
properties of wet nanofibrillated polysaccharide would be
retained.
[0003] Microfibrillated cellulose which is added and used in
composites is typically in a dry form.
[0004] When microfibrillated cellulose is used in composites one
should ensure that micro fibrils are clearly separated from each
other and that micro fibrils are very well dispersed on the
matrix.
[0005] A low solid content dispersion of microfibrillated cellulose
in water is usually a gel having pseudoplastic or thixotropic
viscosity properties because the fibrils are very well dispersed in
the matrix (water). Upon drying, however, the properties of
microfibrillated cellulose are severely changed. It's
dispersibility, hydration and rheological properties are lost or at
least substantially reduced or changed, depending on the severity
of the drying. Typically after drying, micro and nano fibrils are
bound together and substantially less separate micro or nano
fibrils are present which hence affects the characteristic
property, for instance, as defined by a highly nanofibrillated
cellulose can be found via different analysis of the
nanofibrillated cellulose.
[0006] Conventional drying techniques for drying MFC or
nanofibrillated polysaccharides currently used today are e.g. spray
drying and freeze drying. Freeze drying produces the best quality
MFC in terms of preserving original properties and in
re-dispersability. However, both the operating and investment costs
are high and the process can be difficult to scale up to industrial
processing. Spray drying, which can rather easily be scaled up, has
high operation costs and during which process also hornification of
fibrils is prone to occur.
[0007] The term "hornification" refers to the stiffening of the
polymer structure that occurs in lignocellulosic materials when
they are dried or otherwise dewatered. Because of structural
changes in the wood pulp fibers upon drying the internal fiber
shrinks. Often the fibers needs to be rewetted, or re-suspended in
water for practical use and due to these structural changes the
original properties, i.e. being in a gel form having pseudoplastic
or thixotropic viscosity, is not regained. The effect of
hornification may be identified in those physical paper or wood
pulp properties that are related to hydration or swelling, such as
burst or tensile properties. (Hornification--its origin and
interpretation in wood pulps, J. M. B. Fernandes Diniz, M. H. Gil,
J. A. A. M. Castro, Wood Sci Technol 37 (2004) 489-494).
[0008] In articles (e.g. LeCompte T. R. (1931), Papier (34), p.
1193, Jayme, G. (1944) Papier-Fabr (42), p. 187, Lyne, L. M.,
Gallay, W. (1954) Measurements of wet web strength, Tappi Journal
37(12):694-697, Higgins, H. G., Mckenzie, A. W. (1963) The
structure and properties of paper XIV: Effects of drying on
cellulose fibers and the problem of maintaining pulp strength)
concerning hornification phenomenon and pulp swelling after drying
and rewetting there are suggestions made that pulp could be less
hornificated if its dried in such a way that fibers do not stick
together during drying. According to Lyne and Gallay (1950)
rigorous agitation during boiling of pulp neutralizes the
dehydrating effect, and that mechanical effect prevents to a large
extent the loss in swelling which otherwise occurs.
[0009] It is however impractical for pulp and papermakers to dry
fibers under e.g. vigorous agitation.
[0010] Spray-drying of fibrillated cellulose is described e.g, in
WO 2011/139749 A2. An aqueous suspension of nanofibrils (NFC),
which are regarded as a category of MFC, is atomized in a drying
chamber of a drying apparatus. A drying gas, such as ambient air,
may be used as an aid to evaporate the water present in the
suspension, yielding dry NFC as the product. The teachings even
include coating the NFC particles with sodium silicate prior to the
atomizing step.
[0011] WO 2011/095335 A1 describes a process, in which MFC is
formed by defibrillation of a suspension of cellulose fibers and a
liquid, which is miscible with liquid CO.sub.2, and then replacing
said liquid in the suspension by liquid CO.sub.2, and finally
removing the CO.sub.2 by evaporation so as to yield dry MFC. The
process is claimed to overcome the MFC deterioration problems
afflicting ordinary oven-drying and freeze-drying processes.
[0012] Still there is room for an improved process of drying
nanofibrillated polysaccharide comprising composites, which is
simpler to carry out while yielding a dry MFC composite material,
without loss of important re-dispersibility properties, since, if
strong hornifiction or agglomeration occurs during drying the
beneficial properties of cellulosic fibrils or fibrillated
aggregates are not obtained. It it thus preferable that the dried
composite maintains its characteristics when dispersed in aqueous
systems, other solvents or e.g. polymeric matrices, It is also
necessary to find a solution that prevents hornification without
necessary use of chemical additives, which might affect the
properties of the final composition.
SUMMARY
[0013] It is an object of the present disclosure, to provide an
improved or alternative method of drying microfibrillated
cellulose, which eliminates or alleviates at least some of the
disadvantages of the prior art.
[0014] The invention is defined by the independent claims.
Embodiments are set forth in the appended dependent claims and in
the following description and drawings.
[0015] According to a first aspect, there is provided a method for
drying nanofibrillated polysaccharide to obtain a substantially dry
nanofibrillated polysaccharide product, comprising the following
steps:
[0016] (i) providing an aqueous suspension of nanofibrillated
polysaccharide;
[0017] (ii) increasing the solid contents said suspension, thereby
forming a high solid contents microfibrillated cellulose
suspension; and
[0018] (iii) drying said high solid contents microfibrillated
cellulose suspension, through a simultaneous heating and mixing
operation.
[0019] By "aqueous suspension of nanofibrillated polysaccharide"
(NFP) is meant that the solid contents of the suspension is in the
range of 0.01 wt-% to 25 wt-%. This suspensiom or dispersion in
water may be in a gel form. The said suspension might also contain
functional additives which assist in re-dispersability but they can
also have another function such as providing optical effects or
improved compoundability in polymers.
[0020] The term "nanofibrillated polysaccharide" includes
nanofibrous polysaccharides, micro or nano fibrillated cellulose
(MFC/NFC), micro or nano crystalline cellulose (MCC/NCC),
regenerated cellulose, cellulose whiskers, nanofibers spun from
polysacchardies such as starches, cellulose nanoparticles, porous
cellulose particles, starch fibrils, or mixtures thereof or
mixtures with normal pulp or fibers or with inorganic or organic
synthetic fibers. The nanofibrillated polymer can also be surface
modified with e.g. one or several polymer layers.
[0021] By "substantially dry NFP product" is meant that the water
content in the NFP product is reduced to a level where the product
may be in a powder form, but still being suitable for re-dispersion
in a solvent such as water. As such the solids content of the
product may be in the range of 50-99 wt-%.
[0022] By this method there is achieved a way of drying NFP without
causing hornification problems of the micro fibrils and pulp
swelling after drying and rewetting. There is further provided a
way of drying the NFP in a energy efficient manner.
[0023] By the mixing operation removal of water may be affected by
evaporation or using co-solvents, such as ethanol or isopropanol.
The co-solvents may be recycled during the mixing and heating
operation.
[0024] The mixing operation also provides for micro fibrils that
are clearly separated from each other and that micro fibrils are
very well dispersed in the matrix, which is normally achieved by a
refining or homogenizing step a the process for producing e.g.
MFC.
[0025] According to one alternative of the first aspect the solid
contents may, in step (ii), be increased to >15 wt-%, or to
>20 wt-%, or to >25 wt-% , or to >30 wt-%.
[0026] This solids content is based on the NFP-water ratio, but it
may in certain cases contain other substances in which case the
solids content may be even higher.
[0027] According to another embodiment step (iii) may comprise a
grinding operation.
[0028] The grinding operation may be performed in a PVC mixer or by
any similar method, such as a high speed mixer, where the
mechanical energy is converted into heat in the suspension whereby
water is caused to evaporate. Alternativley part of the energy may
be used to provide for a fibrillation or to cut fibers. Since the
solid content, or the dry contents, of the suspension is relativley
high at the onset of mixing the shear forces, and friction evolved
in the suspension becomes greater thus resulting in an increased
temperature. At a solids content of >15-20 wt-% the NFP solution
is viscous, thus causing greater friction.
[0029] Step (ii) may further comprise any one of a centrifugal
force operation, pressing operation and dewatering operation.
[0030] The dewatering operation may comprise an electro-osmosis
operation or electric field induced dewatering, electric field flow
fractionation and the pressing operation may comprise a wet
pressing operation.
[0031] According to one alternative of the first aspect, the
temperature of the suspension, at step (iii) may be in the range of
75-99.degree. C., preferably about 80-85.degree. C.
[0032] The temperature is thus kept relativley low, which is
advantageous not only in that less energy is consumed, but also in
that the effect on hornification of the micro fibrils may be
reduced, as hornification is prone to occur at a higher
temperature. It may be that the temperature towards the end of the
drying process is more important to control, or to keep at a low
level in order to prevent hornification of the fibrils, and that
the temperature at the beginning of the process, i.e. when the
solids content is still relativley low may be higher than the
preferred temperature range. This increase in temperature may
mainly be created through the mechanical energy provided to the
suspension by the mixing operation.
[0033] According to an alternative embodiment the suspension may
further be heated from about room temperature to the range of
75-99.degree. C.
[0034] According to one alternative embodiment, the temperature of
the suspension in or at step (iii) may be in the range of from 40
to 50.degree. C., which is a sufficient temperature for the drying
to occur. This means that the heat evolved from the mixing
operation it self may be sufficient for the drying.
[0035] According to one embodiment of the method according to the
first aspect there may further be provided a simultaneous heating
and mixing operation in step (iii). This means that the suspension
may, in step (iii) be actively heated in addition to the heat
evolved during the mixing operation. This "active heating" may for
instance be used at the onset of the mixing operation to achieve a
higher starting temperature and thus a more efficient drying.
According to another embodiment this heating operation may be
combined with a subsequent cooling operation to ensure the optimal
temperature of the suspension as the solid content is increased,
i.e. towards the end of the drying operation, in order to prevent
any hornification or other harmful structural changes from
occuring.
[0036] According to another embodiment of the first aspect step
(iii) may be performed under vacuum.
[0037] By introducing a vacuum, or performing the drying step under
vacuum it is further possible to reduce both the energy needed and
the drying temperature, which may lead to a further reduction in
the hornification of the micro fibrils. If vacuum is introduced the
heat developed trough the mechanical energy provided to the
suspension may be lower than under normal pressure.
[0038] The nanofibrillated polysaccharide may, according to onel
alternative of the first aspect of the invention, be a
nanofibrillated cellulose or a microfibrillated cellulose.
[0039] The nano- och microfibrillated cellulose may be obtained
through conventional methos such as mechanical liberation of
fibrils or by acid hydrolysis of cellulosic materials, e.g.
disclosed in WO 2009021687 A1, or MFC suspension produced by
enzymatic hydrolysis of Kraft pulp cellulose, e.g. disclosed in
W02011004300 A1 acid hydrolysis followed by high pressure
homogenization, e.g. disclosed in US20100279019, or by any other
means known to the skilled person. One method of producing
nanofibrils is by spinning or e-spinning cellulose or
polysaccharides or mixtures thereof.
[0040] The concentration of MFC is usually about 1-6% and the
remaining part is water or components used to promote e.g.
runnability or used for grafting of fibrillated cellulose such as
Na-CMC.
[0041] According to yet an alternative of the first aspeact there
may further be provided a drying additive in step (iii).
[0042] By introducing a drying additive the drying process may be
event further improved. Such additives are disclosed in CA1208631.
A drying additive may also be a solvent.
[0043] According to a second aspect there is provided a
substantially dry nanofibrillated polysaccharide product obtainable
by the method according to the first aspect.
[0044] By "substantially dry NFP product" is meant that the water
content in the NFP product is reduced to a level where the product
may be in a powder form, but still being suitable for
re-dispersion, in a solvent such as water or solid phase.
[0045] As such the solids content of the product may be in the
range of 50-99 wt-%. In a preferred embodiment the solids content
is in the range of 75-90 wt-%.
[0046] The dry NFP or MFC product obtained through the method
described above may have very good and well separated straight
individual micro fibrils when re-dispersed in water, i.e. the
hornification problems normally associated with drying of NFP has
been greatly reduced. The applicability of this dried NFP product
may therefore be greatly increased for applications such as
composites, paints, food and pharmaceutical uses.
[0047] According to a third aspect there is provided a use of a dry
nanofibrillated polysaccharide product according to the second
aspect in, or for the production of composites.
[0048] According to a fourth aspect there is provided a use of a
dry nanofibrillated polysaccharide product according to the second
aspect, for any one of a rheology application, fixative agent,
strength enhancing agent, emulsifying agent, excipient, paper
applications, film forming agent, moisture control agent, and in
paper or paperboard of products thereof.
[0049] The dry product may thus be used in, for instance, textiles,
food, pharmaceuticals, paints, concrete, asphalt, rubber,
plastic-wood composites, inks, etc.
DESCRIPTION OF EMBODIMENTS
[0050] In the below, a method of drying a nanofibrillated
polysaccharide, or as it may be a microfibrillated cellulose is
disclosed. These definintions may be used alternately in the below,
but is not intended to exclude one or the other. The definitions
for nanofibrillated polysaccharide and microfibrillated cellulose
may also be found in the below description.
[0051] In a preferred embodiment, however, the method is applied to
the drying of microfibrillated cellulose or nanofibrillated
cellulose, in a pure form or alternativley including additives.
[0052] According to one embodiment the method of drying
nanofibrillated polysaccharide (NFP), is provided through a process
in which an aqueous suspension of NFP is provided. The solid
contents of this suspension may be in the range of 0.01 wt-% to 25
wt-%, according to one embodiment the solids content is the range
of 0.01 wt-% to 15 wt-% (can be 20-25%).
[0053] The solids content or the consistency of this aqueous
suspension is then increased to at least 15% by weight. According
to one embodiment the solids content of the suspension is raised to
30-35%.
[0054] This increase may be performed by a mechanical dewatering.
According to one embodiment this dewatering is performed by
centrifugation. According to another embodiment it is performed
through pressing, such as wet pressing in a paper making machine.
According to yet an alternative embodiment the dewatering is
performed through electro-osmosis combined with mechanical
pressure. Other alternative ways to provide for an increase in the
solids content of the suspension may include, but is not limited to
any one of a decanter centrifuge, wire press, belt press,extended
dewatering nips, and magnetically induced dewatering. The
dewatering may also be performed by heating to a suitable
temperature, evaporation, or adsorption e.g. into felt or using
radiation such as IR, NIR or microwave. When selecting the suitable
manner to increase the solids content care must however be taken
that the chosen method does not, in a negative way, influence the
occurrence of hornification, which the skilled person would readily
be able to determine.
[0055] According to the method, after the solids content has been
increased the suspension is dried. This drying operation is
performed through a simultaneous grinding and heating of the
suspension, for instance in a mixing apparatus, and thereby
effecting removal of water by evaporation.
[0056] Alternatively the drying operation is performed under
vacuum, i.e. the suspension is treated under vacuum.
[0057] According to one alternative the drying is performed through
a grinding drying operation, e.g. by PVC mixer similar method where
heat and mechanical energy is introduced at the same time as water
is allowed to evaporate.
[0058] According to one embodiment, at the drying operation, the
temperature of the suspension is in the range of 75-99.degree. C.,
preferably about 80.degree. C. For instance the mixing apparatus
may heat the dispersion from about room temperature to the range of
75-99.degree. C.
[0059] The effect of the temperature in drying step of the process
is critical, which was found here. An optimal temperture,
particularly at the end of drying, prevents hornification of the
fibers. By optimal temperature is thus meant a temperature which is
low enough to prevent the hornification process.
[0060] According to one alternative a temperature range of from 40
to 50.degree. C. is a low enough temperature.
[0061] According to one embodiment the drying step can be done in
presence of different additives, such as those disclosed in
CA1208631.
[0062] According to one embodiment the suspension may be cooled or
kept at a constant temperature by cooling or heating the
suspension. The cooling or heating may be performed by conventional
means known to the skilled person.
[0063] According to one alternative embodiment the temperature of
the suspension may be further increased, for instance in the mixing
appartus after the NFP suspension has been dried to a water content
of at most 10 wt-%.
[0064] The total drying time at the drying operation step may be in
the range of 15-40 min, preferably about 30 min, thus allowing for
a fast and drying operation which may be incorporated into a
industrial process. The drying time may be dependent on the initial
solids content of the suspension, the energy input, any additives
and the batch size.
Definition of Nanofibrillated Polysaccharide
[0065] This definition includes bacterial cellulose or
nanocellulose spun with either traditional spinning techniques or
membrane technique or then with electrostatic spinning. In these
cases, the material is preferably a polysaccharide but not limited
to solely a polysaccharide.
[0066] Also whiskers, microcrystalline cellulose (MCC) and
nanocellulose Crystals (NCC) regenerated cellulose particles or
fibers is included in this definition. It can also be a mixture of
e.g. MCC and MFC.
Definition of Microfibrillated Cellulose
[0067] The microfibrillated cellulose (MFC) is also known as
nanocellulose. It is a material typically made from wood cellulose
fibers, both from hardwood or softwood fibers. It can also be made
from microbial sources, agricultural fibers such as wheat straw
pulp, bamboo or other non-wood fiber sources. In microfibrillated
cellulose the individual microfibrils have been partly or totally
detached from each other. A microfibrillated cellulose nanofiber is
normally very thin (.about.20 nm) and the length is often between
100 nm to 10 .mu.m. However, the microfibrils may also be longer,
for example between 10-200 .mu.m, but lengths even 2000 .mu.m can
be found due to wide length distribution. Fibers that has been
fibrillated and which have microfibrils on the surface and
microfibrils that are separated and located in a water phase of a
slurry are included in the definition MFC. Furthermore, whiskers
are also included in the definition MFC.
EXAMPLE
[0068] Microfibrillated fibers were dewatered in paper machine type
of wire section and subsequent wet pressing to a solids content of
about 30-35% by weight. The high solids MFC was dosaged into a PVC
mixer and mixed so that the temperature was increased to about
80.degree. C., until the MFC was substantially dry, after which the
temperature was further incrased to about 95.degree. C. In this
example a PVC mixer having a size of was 200/100 liters was used.
The motor was of 50 kW.
[0069] The total drying time was about 30 min and the batch size
was 25 kg wet MFC dispersion, which gave about 9 kg dry MFC.
[0070] After rewetting of micro fibrillated cellulose it was
studied under microscope; and very good and well separated straight
individual micro fibrils could be seen. This in turn implies that
little or no hornification of the micro fibrils has taken place,
which was confirmed with water retention value measurements. This
type of micro fibrills are very well suitable for composites and
other applications where dry micro fibrillated cellulose is
preferred instead of wet.
* * * * *