U.S. patent application number 15/976890 was filed with the patent office on 2018-09-13 for method for the preparation of nfc films on supports.
The applicant listed for this patent is Aalto University Foundation sr, Teknologian tutkimuskeskus VTT Oy. Invention is credited to Ulla Hippi, Arto Salminen, Tekla Tammelin.
Application Number | 20180258244 15/976890 |
Document ID | / |
Family ID | 44883713 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180258244 |
Kind Code |
A1 |
Tammelin; Tekla ; et
al. |
September 13, 2018 |
Method for the preparation of NFC films on supports
Abstract
The present invention concerns a method of preparing a film of
nanofibrillated cellulose (NFC) on at least one surface of a
support material, wherein the film is applied and spread directly
onto a surface of the plastic support material in the form of a
suspension of nanofibrillated cellulose, whereby the
nanofibrillated cellulose forms a film. Further, the invention
concerns a structure containing or consisting of a film of
nanofibrillated cellulose prepared using said method.
Inventors: |
Tammelin; Tekla; (Espoo,
FI) ; Hippi; Ulla; (Helsinki, FI) ; Salminen;
Arto; (Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Teknologian tutkimuskeskus VTT Oy
Aalto University Foundation sr |
Espoo
Aalto |
|
FI
FI |
|
|
Family ID: |
44883713 |
Appl. No.: |
15/976890 |
Filed: |
May 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14353775 |
Apr 24, 2014 |
10000614 |
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PCT/FI2012/051015 |
Oct 23, 2012 |
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15976890 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/31971 20150401;
C08J 2301/02 20130101; Y10T 428/269 20150115; B32B 2262/062
20130101; C08J 5/18 20130101; B32B 5/02 20130101; C09D 101/02
20130101 |
International
Class: |
C08J 5/18 20060101
C08J005/18 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2011 |
FI |
20116048 |
Claims
1. A method of preparing a detachable film of nanofibrillated
cellulose (NFC) on at least one surface of a support material, or
detached from the support, comprising applying and spreading a
suspension of nanofibrillated cellulose directly onto a surface of
a continuous plastic support material and a drying via controlled
evaporation at a temperature maintained below 60.degree. C.,
whereby the nanofibrillated cellulose forms a film on said support
material in a continuous process.
2. The method according to claim 1, wherein such a nanofibrillated
cellulose is used, which can be dispersed into water or another
compatible solvent, wherein it forms a gel.
3. The method according to claim 1, wherein fine nanofibrillated
cellulose is used.
4. The method according to claim 1, wherein the suspension of
nanofibrillated cellulose is formed using a solvent containing
water.
5. The method according to claim 1, wherein a suspension containing
less than 2 wt-% nanofibrillated cellulose is used.
6. The method according to claim 1, wherein the nanofibrillated
cellulose is applied on a support made of a plastic material.
7. The method according to claim 1, wherein the nanofibrillated
cellulose or the support material, or both, is chemically modified,
prior to formation of the film, by the addition of charged,
hydrophobic or polar functional groups, preferably selected from
functional groups containing one or more O, S or N atoms or one or
more double bonds.
8. The method according to claim 1, wherein the nanofibrillated
cellulose is applied onto the support by a rod, blade or roll
coating method.
9. The method according to claim 1, wherein the nanofibrillated
cellulose is applied onto the support to a thickness of 50 to 150
.mu.m.
10. The method according claim 1, wherein the film suspension is
dried, after applying onto the support, via controlled evaporation
at a temperature in the range of 25 to 60.degree. C., whereby the
film material solidifies in a controlled manner, forming an even
film.
11. The method according to claim 1, wherein the is detached from
the support.
12. The method according to claim 1, wherein the dried film is
pressed, preferably by hot pressing, to obtain a thinner film
structure, either after being detached from the support or while
attached to the support.
13.-17. (canceled)
18. The method according to claim 1, wherein the NFC is an
unmodified nanofibrillated cellulose.
19. The method according to claim 1, wherein the NFC is a
chemically modified nanofibrillated cellulose.
20. The method according to claim 1, wherein the NFC is silylated
nanofibrillated cellulose.
21. The method according to claim 3, wherein the fine
nanofibrillated cellulose has a fiber width from 5 nm to submicron
values and a fiber length up to 30 .mu.m.
22. The method according to claim 4, wherein the solvent consists
of water.
23. The method according to claim 1, wherein a suspension
containing less than 0.25 to 2 wt-% nanofibrillated cellulose is
used.
24. The method according to claim 1, wherein the nanofibrillated
cellulose is applied on a support made of a plastic material
selected from polyethylene, polystyrene and a cellulose ester.
Description
FIELD OF THE INVENTION
[0001] The present invention concerns a method for the preparation
of large scale films of nanofibrillated cellulose on tailored
support materials. Further, the invention concerns the film
structures obtained with such a method.
DESCRIPTION OF RELATED ART
[0002] Nanofibrillated cellulose is a material, which can be
prepared from macroscale cellulosic fibres by a combination of
enzymatic or chemical and mechanical treatments (Paakko M. et al.
Biomacromolecules 27 (2007) 1934-1941). Due to the high aspect
ratio, nanoscale fine structure, strong self-association tendency
and swelling ability, NFC forms gel-like structures already at very
low solids contents (<2 wt-%).
[0003] Upon drying, the NFC has an ability to form films also on
supports through the strong interactions between the surface
hydroxyl groups. Previously it has been reported that strong film
and membrane structures can be prepared using NFC by solvent
casting (Aulin C. et al. Cellulose 17 (2010) 559-574) and by the
filtration procedure also at moderately large scale (Henriksson M.
et al. Biomacromolecules 9 (2009) 1579-1585; and Sehaqui H. et al.
Biomacromolecules 11 (2010) 2195-2198).
[0004] However, the challenge related to the slow dewatering of the
films due to strong water binding ability has limited the real
large scale manufacturing process.
[0005] In addition, the strong attractive interactions between the
surface hydroxyl groups on the fibril surface leads to remarkable
shrinkage of the formed films during drying. This leads to the
partial loss of, among others, the strength properties of the NFC
films.
[0006] The advantageous properties of structures including
nanocellulose films, such as their barrier properties, are known,
and there is a lot of research relating to this technology.
Industrial applications include, among others, flat screens and
food packaging.
[0007] JP 2010260317 concerns a method of manufacturing a layered
structure, wherein an organic layer is first provided on a
substrate, whereafter a nanofiber layer is applied onto the organic
layer. This structure is said to provide excellent adhesion.
[0008] WO 2007/088974 concerns a method of imparting water
repellency and oil resistance with the use of cellulose nanofiber,
wherein a cellulose-nanofiber-containing liquid is used to
impregnate or apply onto a base material, most suitably being
paper. However, when coating paper, the nanofiber layer will not be
smooth.
[0009] Further, although the above described advantageous
properties of the obtained films can be obtained using the prior
art processes, the processes have disadvantages, such as failing to
provide smooth films, slow dewatering and causing shrinkage.
[0010] Thus, there remains a need for a method of preparing films
of nanofibrillated cellulose having smooth surfaces and being
suitable for large scale production, while avoiding the slow
dewatering and the shrinkage normally related to such methods.
SUMMARY OF THE INVENTION
[0011] It is an aim of the present invention to provide films of
nanofibrillated cellulose having smooth surfaces, and being
essentially translucent or transparent, at least without added
colorant, and a method for preparing such films.
[0012] Particularly, it is an aim of the present invention to
provide a method of preparing films of nanofibrillated cellulose or
supports coated with such films, which method avoids slow
dewatering and shrinkage of the film.
[0013] These and other objects, together with the advantages
thereof over known films, coated supports and methods, are achieved
by the present invention, as hereinafter described and claimed.
[0014] The invention describes a method of preparing smooth and
even films of nanofibrillated cellulose (NFC) in large scale. The
films are prepared on film supports, such as supports made of
plastic, by controlling the adhesion and the spreading of the NFC
on the support material. Detachable and removable films can be
prepared, or films of double layer structures (NFC+support). An NFC
suspension can be applied onto the plastic by rod, blade or roll
coating methods. A combination of the suitable support, controlled
drying and hot pressing enables controlling the porosity of the NFC
films and, thus, transparent and strong films with thicknesses of
50 to 150 .mu.m, among others having good oxygen barrier
properties, can be manufactured.
[0015] Thus, the present invention concerns a method of preparing a
film of nanofibrillated cellulose (NFC) on at least one surface of
a support material.
[0016] More specifically, the method of the present invention is
characterized by what is stated in the characterizing part of claim
1.
[0017] Further, the film structure of the present invention is
characterized by what is stated in claim 13.
[0018] The basic idea of the invention is to prepare large scale,
thin and dense films of nanofibrillated cellulose on the support
material with a tailored surface energy in order to control the
adhesion and the spreading of NFC on the support material. The
formed NFC films can either be removed from the support (to provide
thin films of only NFC) or they can be retained attached to the
support (to provide structures of two or more layers).
[0019] Considerable advantages are obtained by means of the
invention. Thus, the present invention provides a method for
preparing even, dense, strong and uniform films from widely
selectable NFC materials, the method being suitable for use in
large scale roll-to-roll production of NFC films and membranes. All
the operations described here can be up-scaled and transformed into
on-line solutions.
[0020] The films can be used as effective barriers for oxygen and
grease, and they can act as strong starting materials and templates
for, e.g., nanocomposites and thermosets.
[0021] Further, the film manufacturing method described here
overcomes both of the above mentioned challenges of slow dewatering
and shrinkage.
[0022] Next, the invention will be described more closely with
reference to a detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0023] The present invention concerns a method of preparing a film
of nanofibrillated cellulose (NFC) on at least one surface of a
support material. The film is applied and spread out directly onto
a surface of the support material as a suspension of
nanofibrillated cellulose, whereby the NFC forms a film.
[0024] Further, the invention concerns a structure containing a
film of nanofibrillated cellulose, or consisting of such a film,
the structure having been prepared using said method. A structure
containing said film can, for example, be a structure formed from
several layers, such as one or more film layers on a support layer,
further optionally including other layers, while a structure
consisting of said film is formed of a mere film layer in the
absence of the support.
[0025] The basic idea of the invention is to prepare large scale,
thin and dense films of nanofibrillated cellulose on a support
material with a tailored surface energy. Such tailored support
materials can be manufactured from, for example, polyethylene,
polypropylene, polyamide, polyvinyl chloride (PVC) and polyethylene
terephthalate (PET). The tailoring can be carried out, for example,
via activation of the surface using a plasma or corona
treatment.
[0026] Thus, the invention describes a method of preparing smooth
and even films of nanofibrillated cellulose (NFC) in large scale.
The films are prepared on film supports by controlling the adhesion
and the spreading of the NFC on the support material. Detachable
and removable films can be prepared, or films of layered structures
(NFC+support).
[0027] The adhesion (and the spreading) is generally controlled by
selecting the type of NFC and the type of support material in a
manner providing them with compatible surface energies. Either one
or both of the NFC and the support may, for example, be modified to
improve the adhesion. Thus, the method of the present invention can
include a step of treating the surface of the support (using e.g.
plasma or corona treatments) or a step of modifying at least the
surface of the NFC (using e.g. silylation), or both these
steps.
[0028] Since the attachment of the NFC onto the support takes place
via the reactive groups on the surfaces of both the NFC and the
support, such as the hydroxyl groups on the cellulose surface, the
addition of further reactive groups on both the NFC and the support
will naturally increase the adhesion, as will increasing the
hydrophilic nature of the support (hydrophilized e.g. using plasma
or corona treatments) when used together with hydrophilic NFC, or
adding hydrophobic groups on the support surface when used together
with hydrophobic NFC.
[0029] Compatible combinations of NFC and support include the
following preferred options: [0030] 1) Selecting support layers
with surface energies which allow sufficient spreading and adhesion
of NFC. Examples of these are: hydrophobic support and
hydrophobized NFC (e.g. polystyrene/PE/PP+silylated NFC) as well as
hydrophilic support and hydrophilic NFC (e.g. cellulose derivative
supports+unmodified NFC). [0031] 2) Selecting support layers with
surface energies that can be tailored using, e.g., corona/plasma
treatments in order to enhance the compatibility with the NFC (e.g.
plasma/corona treated PE+unmodified NFC).
[0032] A combination of a suitable support, controlled drying and
an optional hot pressing enables controlling the porosity of the
NFC films and, thus, transparent and strong films with advantageous
thicknesses, among others having good oxygen barrier properties,
can be manufactured.
[0033] Preferably, such a nanofibrillated cellulose is used, which
can be dispersed into water or another solvent wherein the NFC
forms a gel, particularly selected from unmodified, hydrophobized
or otherwise chemically modified NFC, such as NFC modified by
introducing reactive groups. For example, the NFC can be modified
by oxidizing or silylating. However, a particularly preferred type
of NFC for use in the present invention is fine, unmodified
nanofibrillated cellulose, most suitably having a fiber width from
5 nm to submicron values and a fiber length up to several
micrometers, particularly up to 30 .mu.m.
[0034] Most suitably, the NFC is selected from those types having a
film forming ability. In case of hydrophobic NFC types, it is also
preferred to select the NFC from those types providing the film
with a contact angel of water of larger than 90 degrees.
[0035] The suspension of nanofibrillated cellulose is generally
formed using a solvent or a solvent mixture, whereby the solvent,
when used alone, preferably is water, and the solvent mixture
preferably contains water, more preferably consisting of a mixture
of water and an organic solvent, more preferably a 1:5 to 5:1
mixture of water and an organic solvent. The organic solvent is
selected based on its hydrophobicity/polarity, i.e. by providing a
solvent or a solvent mixture having a polarity that essentially
matches that of the NFC or the modified NFC. As stated above, a
particularly preferred solvent is water. Other similarly preferred
options are organic solvents that are compatible with regular
unmodified NFC, such as dimethylacetamide and methanol. According
to another option, the suspension is formed using a solvent mixture
consisting of water and a polar organic solvent.
[0036] Conventional organic solvents may be used. However, the
suitable solvent is preferably selected according to its
hydrophobicity. Thus, the solvents can be divided into groups,
based on their polarity and ability to form hydrogen bonds: [0037]
Solvents considered to be non-polar include hexane, benzene,
toluene, diethyl ether, chloroform and 1,4-dioxane. [0038] Solvents
considered to be polar, while aprotic, include ethyl acetate,
tetrahydrofuran, dichloromethane, acetone, acetonitrile, dimethyl
formamide and dimethyl sulfoxide. [0039] Solvents considered to be
polar and protic include acetic acid, n-butanol, isopropanol,
n-propanol, ethanol, methanol and formic acid.
[0040] Also water is considered to be polar and protic.
[0041] An exemplary suitable solvent mixture is a 1:1 mixture of
water and methanol.
[0042] Controlling the solids content of the suspension is not
essential. It is sufficient to use a suspension that forms a film
without forming aggregates.
[0043] However, according to a preferred embodiment, the used
suspension contains less than 2 wt-% nanofibrillated cellulose,
preferably 0.25 to 2 wt-% nanofibrillated cellulose.
[0044] The film formation can optionally be assisted by the
addition of plasticizers, such as glycerol or sorbitol, or a
mixture thereof. The use of plasticizers is not necessary, since
the used NFC is capable of forming a film, as such, but the
plasticizer can further improve the mechanical properties of the
resulting film.
[0045] According to an embodiment of the invention, the
nanofibrillated cellulose is applied on a support made of a plastic
material, preferably selected from polyethylene, polystyrene and a
cellulose ester. The support is selected from materials of low
porosity to prevent the filtration of the NFC suspension.
Procedures utilizing filtration are less suitable for use in
manufacturing large uniform structures, particularly in continuous
processes. On the contrary, the materials used in the present
invention are suitable for use in roll-to-roll type continuous
processes.
[0046] The hydrophobicity of the support can be selected or
modified to provide a suitable adhesion to the NFC. This adhesion
should be strong enough to provide the needed attachment during
drying to prevent shrinkage, but not so strong as to prevent
detachment of the dried film from the support in cases where the
structure to be prepared consists of only said NFC film.
[0047] Both the nanofibrillated cellulose and the support material
may be chemically modified, prior to formation of the film, by the
addition of charged, hydrophobic or polar functional groups,
preferably selected from functional groups containing one or more
O, S or N atoms or one or more double bonds, most suitably selected
from hydroxyl and carboxyl groups.
[0048] The application onto the support may be carried out, for
example by a rod, blade or roll coating method.
[0049] The thickness of the film of nanofibrillated cellulose
applied onto the support is preferably in the range of 50 to 150
.mu.m. The thickness of the support is not an essential parameter.
However, generally the thickness of the used support ranges between
150 .mu.m and 2000 .mu.m.
[0050] Generally, the film suspension is dried, after applying onto
the support, via controlled evaporation, preferably at a high
temperature, optimized to a point where hydroxyl groups are able to
interact at an advantageous rate through self-association, which
leads to even film formation. Particularly, the film suspension is
dried at a temperature that is .ltoreq.60.degree. C., more
preferably at a temperature in the range of 25 to 60.degree. C.
most suitably at room temperature, whereby the film material
solidifies at an advantageous rate. Thus, slow dewatering via
filtration is avoided. Concomitantly, the sufficient adhesion with
the support material prevents the shrinkage of the NFC film upon
drying.
[0051] The film may either be detached from the support prior to
use or prior to further processing or the film may be used or
further processed as a layered structure, while still attached to
the support. The detaching may be carried out, e.g. by re-wetting
the film using a solvent or a solvent mixture, most suitably using
methanol.
[0052] The dried film may further be pressed, preferably by hot
pressing, preferably at a temperature of 60 to 95.degree. C., most
suitably at a temperature of 80.degree. C., to obtain a thinner and
more dense film structure with a controlled porosity. The pressing
can be carried out either on the film, as such, or with the film
still attached to the support.
[0053] This procedure to prepare even, dense and uniform films can
be regarded as a route to large scale roll-to-roll production of
NFC films and membranes. The films can be used as effective barrier
films for oxygen and grease, and they can act as a strong starting
material for, e.g. nanocomposites and thermosets.
[0054] As stated above, the film of the obtained structure
containing or consisting of a film of nanofibrillated cellulose
preferably has a thickness of 50 to 150 .mu.m.
[0055] The film may be present as a coating on at least one surface
of the support, which preferably is made of a plastic material,
more preferably from polyethylene, polystyrene or a cellulose
ester, or the film may be used as such, i.e. without the presence
of the support.
[0056] The basic idea of the invention is to prepare large scale,
thin and dense films of nanofibrillated cellulose on the support
material with a tailored surface energy in order to control the
adhesion and the spreading of NFC on the support materials. The
formed NFC films can either be removed from the support (to provide
thin films of only NFC) or they can be retained attached to the
support (to provide structures of two or more layers).
[0057] The products formed using the present invention can be
further applied in the production of larger structures, such as
laminated (nano)composite materials, food packaging materials and
medical bandages or wound treatments, or as supports for
functionalities, e.g. printed intelligence. Examples of suitable
structures to be prepared using the film structures of the present
invention are layered structures containing resin between two or
more structures according to the present invention.
[0058] The following examples are intended to illustrate the
preferred embodiments of the invention without limiting the scope
of the invention.
Examples
[0059] Examples of compatible combinations of the NFC and support
materials, providing suitable film structures include the
following, wherein the NFC has been applied on the support by
direct casting (see Example 1) or by roll coating and dried at a
temperature of less than 60.degree. C.:
Example 1
Using Supports with Strong Adhesion and High Compatibility with
NFC
[0060] An NFC film was cast on cellulose ester by applying a dilute
dispersion of NFC on the cellulose ester film and drying at room
temperature.
[0061] Double layer film structures are achieved, with the NFC film
still attached to the support.
Example 2
Using Supports with Moderate Adhesion and Tailored Compatibility
with NFC
[0062] The used support is made of a film of polyethylene, which is
first hydrophilized by plasma or corona treatments prior to the NFC
application.
[0063] Large and uniform NFC films are achieved that can either be
detached/removed from the support or left on the support, thus
forming a layered structure.
Example 3
Using Hydrophobic Plastic Films as Supports for Treated NFC with
Strong Adhesion
[0064] Several structures were manufactured. The used supports were
made of films of polyethylene and polystyrene, and the NFC was
hydrophobized by silylation prior to application onto the
support.
[0065] Double layer film structures are achieved, whereby the film
can either be detached/removed from the support by re-wetting the
film with methanol, or left on the support, thus forming a layered
structure.
* * * * *