INDIVIDUALIZED CELLULOSE STRANDS NANO-DISPERSION IN POLYOLEFINS FOR PRODUCTION OF BIODEGRADABLE PLASTIC ARTICLES

DISPERSION NANOMETRIQUE DE FILAMENTS DE CELLULOSE DISTINCTS DANS DES POLYOLEFINES POUR LA PRODUCTION D'ARTICLES EN PLASTIQUE BIODEGRADABLE

English Abstract

The present invention describes: A cellulose-based composite where
individualized
strands are homogeneously nano-dispersed in a polyolefin (PO) matrix; a
process,
leading to the said nano-dispersion, using a hydrophilic ionic liquid as co-
solvent; a
method to prepare selected hydrophilic ionic liquid co-solvents; a process to
prepare
articles using conventional moulding techniques.

Claims

What we claim is:


1) The ionic liquid solvent used in step 1 is a salt for which the anion is a
bromide or a
chloride or a combination of bromide and chloride salts or a bromide, a
chloride or a
combination of bromide and chloride salts within a salt of a different anion.


2) The ionic liquid solvent according to claim 1 is a salt for which the
cation is a
quarternized aliphatic or aromatic amine or phosphine, with one or more
heteroatom-containing substituent as shown in figure 1.


3) The ionic liquid solvent as described in claim 2 where one or more
substituent have a
common oxypropyl (-CH2-CH2-CH2-OR) motif, where the R group is a methyl, an
ethyl, an hydroxyethyl, a methoxyethyl, a repeating unit of the general
formula:
(CH2-CH2-O)n-H, (CH2-CH2-O)n-C p H2p1, (CH2-CH2-O)n-C p H2p
Where: n = 2, 3, 4; p=1, 2, 3, 4.


4) The ionic liquid solvent according to claim 3 where the oxypropyl
substituent
(-CH2-CH2-CH2-OR) originates from the corresponding chloride:
Cl-CH2-CH2-CH2-OR and used for the quaternization of the corresponding amine
or
phosphine according to claim 2. Where the R group is a methyl, an ethyl, an
hydroxyethyl, a methoxyethyl, a repeating unit of the general formula:
(CH2-CH2-O)n-H, (CH2-CH2-O)n-C p H2p+1, (CH2-CH2-O)n-C p H2p
Where: n = 2, 3, 4; p=1, 2, 3, 4.


5) The oxypropylchloride compound according to claim 4 which for R= CH2-CH2-OH

is obtained by reacting 1 equivalent of 1-chloropropan-1-ol with 1 to 4
equivalent of
ethylene carbonate, but preferably 1 to 1.5 equivalent, in the presence of 0.1
to 0.5
equivalent of base such as, but not limited to: sodium of potassium hydroxide,

pyridine or triethylamine.


6) The oxypropylchloride compound according to claim 5 which for
R=(CH2-CH2-O)n-H is obtained by repeating n times, successively the procedure
according to claim 5.


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7) The oxypropylchloride compound according to claim 5 and 6 is isolated by
standard
work-up known to a person familiar with the art, followed by distillation.
Alkylation
by standard procedures known to a person familiar with the art provides the
remaining oxypropylchloride compound according to claim 4, where R=(CH2-CH2-
O)n-C p H2p+t, (CH2-CH2-O)n-C p H2p.


8) The cellulose solution, described in step 1 is an ionic liquid cellulose
solution of 1 to
25 % in weight concentration of cellulose and preferably 10 to 15 % in weight.


9) The process involved in dissolving the Cellulose as described in step 1,
may also
include:
a) Microwave irradiation of the solution, to facilitate dissolution.
b) Addition of a compatibilizer, such as but not limited to one or more fatty
acids
or one or more acid anhydrides, or a combination of one or more of the former
with one or more of the latter said compatibilizing agent.


10)The cellulose may be regenerated, microcrystalline, cotton fibres, paper or
wood
pulp, recycled paper or any other sources of cellulose, de-lignified prior to
use when
required.


11)The process involved in melting the polyolefin material (POM) as described
in step
2, may also include:
a) The use of an ionic liquid solvent as plasticizer to improve fluidity.
b) The use of an organic solvent as plasticizer to improve fluidity.


12) The process, according to claim 11 where the ionic liquid solvent can be:
the same
ionic liquid solvent used in step 1 and according to claims 1, 2 and 3; a
different
ionic liquid which may differ only by the cation, the anion or by both; a
combination
of one or more ionic liquids.


13) The process, according to claim 11 where the organic plasticizer is a
commercially
available solvent, varying in nature depending on POM used.


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14) The polyolefin material (POM), as described in step 2 and according to
claim 11
wherein the POM is composed of low density polyethylene (LDPE), linear low
density polyethylene (LLDPE), high density polyethylene (HDPE), any other type
of
polyethylene resin, polypropylene (PP) or polystyrene (PS).


15) The polyolefin material (POM), as described in step 2 and according to
claim 14
wherein the POM is composed of a mixture of one or more of the resins
described in
claim 14.


16) The polyolefin material (POM), as described in step 2 and according to
claim 14
wherein the POM is composed of one or more resins according to claim 14 molten

separately.


17) The polyolefin material (POM), as described in step 2 and according to
claim 14, 15
and 16 wherein the source of one or more of the resins present in the POM may
be
virgin, pre-consumer, industrial or municipal post-consumer, reprocessed, in
the
form of pellets, powder, fibres or otherwise or from any other source and in
any
other form.


18) The polyolefin material (POM), according to claim 15 and 16 wherein the
POM may
be also composed of one or more compatibilizers.


19) The process involved in mixing the Cellulose and polyolefin material (POM)
as
described in step 3, may be achieved, but is not limited to the use of a co-
rotating
twin-screw extruder of a mixing tank.


20) The process, according to claim 18 and according to claim 11, 12,13 and 19
wherein
the mixing temperature is ~50°C about the melting temperature of the
said POM.

21) The process according to claim 19 and 20 where one or more compatibilizers
may be
added at one or more stages of the said extrusion.

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22) The process, according to claim 19 and 20 where one or more of the molten
resins
according to claim 16 and 18 may be added at one or more stages of the said
extrusion.


23) The process as described in step 4, wherein the solvent for setting of the
CIS/PO
nano-dispersion is a Cellulose and PO non-solvent such as, but not limited to:
water,
methanol, ethanol, isopropanol, ethylene glycol or acetone.


24) The process as described in step 4 and according to claim 23, wherein
retrieving of
the said ionic liquid is achieved by evaporation with or without prior nano-
filtration
of the solution.


25) The process according to claim 23 and 24, wherein the said evaporation may

involve, but is not limited to rotatory evaporation, under vacuum or not,
spray-
drying, or a combination of these techniques.


26) The process as described in step 5 wherein moulding of CIS/PO material is
achieved
by standard methods, known to a person familiar with the art. The moulding
methods
include, but are not limited to: pressure moulding, low pressure moulding,
injection
moulding, blown moulding and die casting.


27) The process according to claim 26 wherein one or more plasticizers may be
used.

28) The process according to claim 27 wherein the plasticizer may be one or
more
hydrophilic ionic liquid as defined according to claims 1 to 7 inclusively.


29) The process according to claim 28 wherein the plasticizer is removed by
water
washings or by washings with a suitable organic solvent as described according
to
claim 23.


30) The process according to claim 29 wherein the plasticizer is retrieved
using methods
according to claims 23, 24 and 25.


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31) The process according to claim 19 to 22, inclusively and 26 to 28
inclusively,
wherein at any of these stages, a dye or a combination of dyes may be added.


32) The process according to claim 19 to 22, inclusively, 26 to 28 inclusively
and claim
31, wherein at any of these stages, an antioxidant or a combination of
antioxidants
may be added.


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Description

CA 02541259 2006-03-15
BACKGROUND AND PRIOR ART

With the increasing importance of green technology to society, the interest
generated by
materials such as biodegradable plastics comes as little surprise. Voluminous
reports and
patents have appeared in the last two decades; a tribute to the continuing
search to answer
the problem of plastic wastes. Specifically: polyethylenes (LDPE, HDPE);
polypropylene
(PP) and polystyrene (PS); polyolefms (PO) that compose the majority of
municipal and
industrial end-of-use plastics.
Biodegradable or degradable plastics may be categorized in two distinct
classes that we
will define as follow for the purpose of the present document:

Polymer Blends containing a degrading agent. [1] The former may be made of
one or more resins while the latter may be one ore a combination of chemical
additives, capable of degrading the blend usually under specific conditions:
photochemical, chemical or biochemical (although examples of combination
exist).

Polymeric Composites: These may be formed by one or more polymers,
containing at least one biodegradable component. [2] In the vast majority of
cases
the biodegradable component is a polysaccharide such as Cellulose or Starch,
with or without compatibilizers.

The main advantage of Polymer Blends is their superior mechanical properties
(relative
to composites. Moreover, their protagonists argue that with Polymer Blends
there is no
need for large-scale, damaging agriculture to provide Starch or Cellulose
sources.
However, additives-based degradability of polymer blends often raises concerns
about the
degradation process itself. For instance photodegradation occurs only in the
presence of
light; if the material is buried, it looses its degradability properties.
Other concerns
include the need to establish the benign nature of these additives, and their
spent form.
Certainly, if fertilizers may be harmful to the environment, accumulation of
these
additives may just as well be.

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CA 02541259 2006-03-15

The main advantage of Polymer Composites is their obvious biodegradability.
Without
requiring specific conditions or treatment, polysaccharides (whether Starch or
Cellulose)
will naturally degrade in benign components.
But Biodegradability comes at a price with Cellulose/Starch based Polymer
Composites,
as mechanical properties are adversely affected by Starch or Cellulose
content. [3]
Although this problem may partially be resolved with the use of
compatibilizers,
presently existing Starch/PO and Cellulose/PO composites suffer from
inefficient
interface with the plastic matrix and low contact area.
On one hand, Starch is chiefly made of amylopectin, a dendriform (branched)
polysaccharide, with and essentially spherical geometry. Even though Strarch
may be
homogeneously dispersed within a PO matrix, its architecture precludes
effective
Starch-PO interaction creating mechanically weakening microdefects.
On the other hand, Cellulose is an entirely filiform (threadlike)
architecture, also found in
PO, such as PE for instance. However Cellulose-based plastic composites
presently use
exclusively Cellulose fibres, such as wood, pineapple and others. This
translates in a
limited, bulk (macroscopic) homogeneity of the composite, while clearly-defmed
separated PO and Cellulose domains exist at a microscopic scale.
The use of Cellulose Individualized Strands (CIS) would allow unprecedented,
microscopic homogeneity, hence providing a biodegradable material with
superior
properties, as both contact surface and dispersion efficiency are
significantly increased.
The obstacle for CIS/PO composites has been the lack of low operating
temperature
solveiits of adequate capacity to dissolve cellulose.
To this day, the only industrial cellulose solvent, used in Lyocell process
is
N-methyl morpholine oxide (NMMO). NMMO's operating temperature is 130 C. This
temperature is too high when considering mixing a PO resin with Cellulose and
the
consequent thermal damage to both polymeric materials. In addition, the
operating
temperature of NMMO is too close to its explosion temperature of 150 C to be
considered a safe process. [4]

Recently, we and others have focused our attention on room-temperature (r.t.)
ionic
liquids (IL) as safe and efficient, low operating temperature solvent (LOTS)
for cellulose.
Ionic liquids are non-flammable, thermally stable and have negligible vapour
pressure.
For those IL with a chloride anion, they possess a significant capacity to
dissolve
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CA 02541259 2006-03-15

cellulose at low temperature (from r.t. to 100 C). Although these solvents
have been
available, at least for experimentation, if not industrially, the interest of
dissolving
cellulose by the use of IL as LOTS has mostly been driven by the interests of
the paper
and fabric industries in spinning or modifying cellulose towards improved
fibres. [5]
However, the use of ionic liquids as LOTS solvent or co-solvent for cellulose,
towards
the preparation of superior cellulose-based composites has never been
explored.
The present invention describes such CIS/PO composites, of unprecedented
homogeneity
obtained by the use ionic liquids as LOTS to achieve this goal. The effect of
the
unprecedented homogeneity of CIS/PO is particularly apparent with regards to
tensile
strength and elongation at break.
Moreover, the biodegradability properties of CIS/PO composites are improved
compared
to its equivalent composites.
The present invention also describes the process to achieve the preparation of
CIS/PO
composites.

REFERENCES
1) For example: a) Jin, H.; Zeng, X.; Liu, J. US Patent Appl. 2004/0152802 Al.
b)
Downie, R. H. US Patent 6,482,872 B2, November 19, 2002.

2) For example: Schiltz, D. C. US Patent 5,449,708, September 12, 1995.

3) a) Pedroso, A.G. Rosa, D.S. Carbohydrate Polymers 59 2005 1- 9.
b) Arvanitoyannisa, I. Carbohydrate Polymers 36 1998 89- 104. c) George, J. et
al.
Composites Science and Technology 58, 1998, 1471-1485.

4) Cuculo et al., US Patent 6,827,773, December 7, 2004.

5) a) Swatloski, R. P. et al. U. S. Patent 6,824,599 November 30, 2004. b)
Graenacher, C.
U.S. Patent 1,943,176, 1934.

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CA 02541259 2006-03-15
DESCRIPTION OF THE INVENTION

Preparation of CIS/PO composites

The process involves the following steps:
1. The preparation of a Cellulose solution of 1 to 50 wt% concentration,
within an
hydrophilic ionic liquid solvent, at a temperature ranging from 0 C to 185 C,
but
preferably, at a temperature of 65 C to 85 C. The solution is stirred until
completely homogeneous.
2. The melting of a polyolefin material (POM) to reach a state fluid enough to
allow rapid mixing with the above-mentioned Cellulose solution.
3. The mixing of the Cellulose solution with the POM melt, within a mixing
tank
until completely homogeneous. The mixing occurs at a temperature 10 C to 50 C
above the melting point of the POM but preferably, 10 C to 25 C. The process
is
simple for someone familiar with the art.
4. The setting of the cooled nano-dispersed CIS within the PO matrix by
washing
of the dispersion with a ionic liquid solvent, in sufficient quantity to
ensure
complete elimination of the ionic liquid. The CIS/PO composite powder is then
collected and dried. The solution of the ionic liquid is collected to retrieve
the
ionic liquid co-solvent.
5. The moulding of the CIS/PO composite is achieved by standard moulding
procedures. Additives may be incorporated in the moulding process to further
improve the resulting composite articles or facilitate the moulding process
itself.
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Representative Drawing