Note: Descriptions are shown in the official language in which they were submitted.
CA 02437616 2003-08-04
Specific Area of Invention
This invention pertains to the development of a process for production of
cellulose nano fibrils
from Root crops like Rutabaga, Natural fibres like I-hemp, Flax Bast fibres,
Kenaf; l~gro based
fibres like Soy, Wheat, Corn, and Bagasse and Wood fibres as thermo mechanical
pulp and
Kraft pulp. This invention describes the various steps used in manufacturing
process of nano
fibrils.
7..
f
'v
CA 02437616 2003-08-04
aCkgr~urid
Natural cellulose fibres have advantages over glass fibre as they are less
expensive, Iow bulls
density, good moldability, biodegradable, abundantly availahle from renewable
resources and
have a high specific strength. Like synthetic fibres, natural fibres in the
form of woven or
nonwoven mats present outstanding opportunity to develop a new class of
advanced
lightweight composites.
Much work has been done on the elongated fibres from plants such as Hemp, Flax
and Jute as
in the research work by Batra S.K. Long vegetable fibres, Handbook of fibre
science and
technology, Vol. 4, Fibre chemistry, New York: Marcel Dekl~er, 1985.p.727-807,
Hornsby PIZ,
Hinrichsen E, Tarverdi K. "Preparation and properties of polypropylene
composites reinforced
with wheat and flax straw fibres" . Part II Analysis of composite
microstructure and mechanical
properties, Journal of Material Science 1997; 32:1009-i5 and Simonsen John,
Utilizing straw
as a filler in thermoplastic building materials, Construction a:r~d Building
Materials, 1996 vol
10, no. 6 ,pp 435-440.
These fibres are few microns in diameter and 3-4 millimetres long as shown by
Fengel D,
Wegener G, Wood, chemistry, ultra structure, reactions, pp 268-269. However
there is
tremendous potential of utilizing the natural fibres, agro base; fibres & root
crops sources
(which are found in abundance) with non-elongated nano-si:aed microfibrils for
making
thermoplastic nano-composites. These are fibres on much smaller scale and
having 5-50 nm
diameter and are thousands of nanometer length as illustrated by D.G.Hepworth,
&
D.M.Bruce, "The mechanical properties of a composite manufactured from non
fibrous
vegetable tissue and PVA", Composites Part A: Applied Scic°nce and
Manufacturing Issue
31(2000) pp 283-285 . These nano-sized microfibrils demonstrate high strength
properties
comparable to synthetic fibres.
Nano-sized microfibrils are cellulose chains aggregating to form a fibril, a
long thread like
bundles of molecules stabilized laterally by hydrogen bonds between hydroxyl
groups of
adj acent molecules. The molecular arrangement of these fibx~llar bundles is
called microfibrils.
These nano-sized microfibrils (also referred as cellulose nano-fibrils) are
around 10 nm
diameter and 30-100 cellulose molecules in extended chains as mentioned by
A.Stamboulis,
C.A.Baillie, T.Peijs, "Effects of environmental conditions on. mechanical and
physical
properties of flax fibers" Composites Part A: Applied Science and
Manufacturing Issue
CA 02437616 2003-08-04
32(2001), pp 1105-1115. These nano-sized microfibrils are embedded in the
matrix of
hemicelluloses and pectins. Fibre cell wall is consists of primary cell wall
and three secondary
cell walls. Each cell wall contains a complex matrix of lignin, hemicelluloses
and pectins
surrounded by these nano-sized microfibrils.
The challenge of this work is to isolate nano-sized microfibrils from the
secondary cell wall by
chemical and mechanical treatments and then evaluate their strength in terms
of aspect ratio of
the individualized nano-fibrils.
brief Description of Invention
This invention is focussed on the nan-fibrils, which are embedded in the
secondary cell wall.
These cellulose nano-fibrils have diameter in the range of 5-ti0 nm and the
length in thousands
of nanometre. A method has been developed to manufacture these nano-fibrils at
a high yield
from natural fibres.
A process for obtaining cellulose nano fibrils from natural fil7res involves
heating a pulp
suspension to 80-90 °C, extracting the cellulosic material with an acid
(dilute HCl of 1M cone.)
followed by the extraction of pulp with base (cone. less than. 3%, by wt/wt),
and then pouring
liquid nitrogen into the pulp and keeping the sample in liquid nitrogen for S-
10 minutes to
freeze the cell wall water and then applying high impact for hreaking the cell
walls and hence
liberating the microfibrils from the secondary cell wall. This step is then
followed by high
pressure defibrillation by passing the 2% w/w suspension of the LNZ crushed
sample through
high pressure defibrillator using PANDA 2K by NIRO SOAVI ~ unit subjecting the
treated
suspension to a high pressure. The resultant suspension after 30 min contains
nano-fibrils in the
range of 25-60 nm diameters. The resultant suspension has .above 18% yield of
nano-fibrils
entangled together. The invention includes a process to disperse the
nanofibrils and prevent
them from further agglomeration .
The invention demonstrates a much higher aspect ratio of the nano fibrils than
the long fibres.
Further the invention relates the use of natural fibres in cornl~ination with
the plastic polymers
and bioplastics to produce composite with high strength andl stiffness and
still having ultra
lightweight.
The natural fibres used in this invention to isolate nano fibrils are:
CA 02437616 2003-08-04
~sHemp
Flax
Soy
~ Kenaf
Wood
fibres
~ Wheat
straw
~sCorn
~sBagasse
~sRutabaga
~ Turnip
Descripti~n of Drawings
Figure 1: Mechanism of Acid Hydrolysis in polysaccharides
Figure 2: SEM of Flax Bast fibres after chemical treatment with low pressure
defibrillation
Figure 3: Optical microscope of low pressure defibrillated flax bast fibres
e4verage diameter of nano-fibrils:
Figure 4: Flax nano fibrils after 30 min , average diameter 54 nm
Figure 5: AFM picture of Flax fibre after 30 min at a pressure above 500 MPa
for
defibrillation, average diameter. 30-60 nm
Figure 6: Flax nano-fibrils after high pressure defibrillation [20 min above
500 bars]
Figure 7: Rutabaga nano-fibrils after high pressure defibrillation [5 min
above 500 bars,
average diameter 35 nm
Figure 8: Wheat straw nano-fibrils after high pressure defibrillation [~0 min
above 500
bars] average diameter 30 nm
Figure 9: Hemp nano-fibrils after high pressure defibrillation [20 min above
500 bars]
average diameter 60 nm
Comparison of extent of defibrilliaation after ~rarious passes
Figure 10: Flax bast fibres
Figure 11: Rutabaga
Figure 12: Wheat straw
Figure 13: Hemp fibres
CA 02437616 2003-08-04
Figure 14: Chart for diameter and aspect ratio for Flax
Figure 15: Chart for diameter and aspect ratio for Rutabaga
Figure 16: Chart for diameter and aspect ratio for Wheat
Figure 17: Chart for diameter and aspect ratio for hemp
Figure 18: ATR Chart showing the removal of pectins and hemicelluloses after
chemical
treatments
Figure 19: Comparison charts for untreated, acid treated and acid & all~ali
treated samples
showing the percentages of hemicelluloses, cellulose, lignin and pectin
contents
Figure 20: Flax nano-fibrils diameter distribution curve
Detailed description of the Invention
As previously mentioned, this invention is based on developing a technique of
the production
of cellulose nano fibrils from natural fibres like hemp, flax, from root crops
and also from agro
based fibres.
,Swellihg of'Fabres:
Swelling agents primarily strong electrolyte solvents have been employed to
pre-treat
cellulose. Two types of swelling agents have been known: one is
intercrystalline and the other
intracrystalline. For example water can penetrate and loosen only the
amorphous region of
cellulose; this is considered as an intercrystalline swelling agent. Gn the
other hand swelling
agents such as certain salts and alkali solutions affect both amorphous and
crystalline regions
of cellulose. They are called intracrystalline swelling agents. In other words
intracrystalline
swelling agents are effective in loosening the crystalline region of
cellulose.
The expanded capillary structure of swollen fibres may cause a significant
increase in surface
area of the cellulose fibre, and the total area of the swollen material may be
as much as 100-
fold greater than the area that results after drying the material. This
enlarges the fine structure
so that the substrate is more accessible to cellulose and also it facilitates
the diffusion as
explained by L.T.Fan, M.M.Gharpuray 8z Y.H.Lee Cellulose; Hydrolysis 1987]
CA 02437616 2003-08-04
Fibres [except root crop fibres] were soaked in 17.5% w/w sodium hydroxide
solution
overnight to swell the cell wall to enable large chemical molecules to
penetrate through the
crystalline region of the cellulose.
Sample preparation:
Fibres were made into pulps with water in l0:lwater to fibre ratio then the
sample was vacuum
filtered for further chemical treatment.
~'hemical Treatment
The structure of lignocelluloses in the cell wall resembles that of a
reinforced concrete pillar
with cellulose fibres being the metal rods and lignin the natural cement. Nigh
order molecular
packing of cellulose in its crystalline regions hinders the heterogeneous
chemical reactions on
the external surface of crystallities. Chemical treatments have been
extensively used for the
removal of lignin/pectins surrounding cellulose and destroying its crystalline
structure.
Although cellulose possesses excellent strength and good stability, yet it can
be degraded by
resorting to a variety of chemical and physical processes under certain
conditions. The most
common manifestation of its deterioration is a decrease in DP. This decrease
is accompanied
by a chemical modification of cellulose molecule such as an increase in its
reducing power or
development of reactive groups along the chains.
Acid Treatment - Extraction of Pectin
Acids serve primarily as catalysts for hydrolysis of cellulose than as
reagents for pre-treatment.
When cellulose is hydrolyzed in an acidic medium to glucose, the ? -1-4.
glucosidic bonds of
cellulose chains molecules are split by the addition of the water molecules,
this addition yields
fragments of shorter chain lengths while preserving the basic; structure. ~ne
of the new-formed
end groups of chain molecules is a potential aldehyde group possessing
reducing power. The
objective of the acid treatment is to remove the pectin, extractives and
hemicellulose since
cellulose fibres are embedded in the matrix of hemicellulose and pectin. Acid
treatment will
hydrolyse these impurities and will liberate the cellulose fibres.
CA 02437616 2003-08-04
Hydrolysis of cellulose with acid proceeds through the formation of
hydrocellulose to soluble
polysaccharides and then to simple sugars. This occurs only after the
crystalline structure of the
cellulose is destroyed by its dissolution or swelling in hot dilute acid.
Native Cellulose -.Stable Cellulose-~--Soluble Polysaccharides --P Calucose
The extracted pulp was treated with dilute hydrochloric acid [1 ti~I) at 80
°C+/-5 for two hours.
Acid hydrolysis proceeds in three steps [Figure 1). In the fir<.;t step the
proton ofthe catalyzing
acid interacts with the glycosidic oxygen linking two sugar units of
polysaccharide [I], forming
a conjugate acid [II). This step is followed by a slow cleavage of C-O bond
forming an
intermediate carbo canon [III). The carbo canon finally reacts with a water
molecule, resulting
in a stable end product and release of proton. [Fengel I7, Wegener G, Wood,
chemistry, ultra
structure, reactions, pp268-269)
After acid treatment, the sample is removed from the hot water bath, cooled
and washed with
distilled water abundantly until the filtrate becomes neutral, ohen the sample
was vacuum
filtered for further treatment.
r~lkalf Treatment
Alkali treatment of lignocellulosic material causes swelling leading to an
increase in surface
area, decrease in the DP, decrease in cryastallinity, and separation of
structural linl~ages
between lignin and carbohydrate and disruption of lignin structure. Therefore
to remove the
remaining hemicelluloses and pectin from the sample, alkali treatment is done.
At elevated
temperatures, polysaccharides are attacked by alkali and dissolution of
undegraded
polysaccharides takes place. Pectins are naturally soluble in aqueous medium.
This alkali
treatment results in solubilization ofpectins and hemicellulose.
Cell-OH + NaOH ~ Cell-ONa -~ + HZO+ surface impurities
The samples were weighed and 2% w/w sodium hydroxide solution is added to the
sample.
The sample with NaOH solution is placed over a hot water bath maintained at 80
°C+ 5 °C for
two hours with constant stirring for better impregnation of alkali into the
fibres. After 2 hrs
sample was removed from the bath and cooled and then washed with abundant
distilled water
until becomes neutral, then the sample was vacuum filtered .and residue was
frozen.
CA 02437616 2003-08-04
It is noteworthy that until this stage nano-sized microfibrils are still
associated with the call
wall. Therefore, mechanical treatment is necessary to shear them apart from
the cell wall.
Liquid Nit~ogeh Gushing:
The chemically treated residue was frozen and then frozen pulp was crushed
with liquid
nitrogen. Liquid nitrogen is a cryogenic gas at 77 K temperature at standard
atmospheric
pressure. The objective of the cryocrushing is to form ice cystals within the
cells. When we
apply high impact on the frozen pulp, ice crystals exert pressure on the cell
wall and when we
apply high mechanical impact, the cell wall ruptures and liberates the
microfibrils.
Then the pulp, pulp is washed abundantly with distilled water and a 2% w/w
suspension is
which
Disintegration:
Above liquid nitrogen treatcd sample is made to 2% w/w suspension in distilled
water and
fibres were dispersed evenly in a disintegrator for 10 minutes at 2000 RPM
speed.
High P~essua~e De~b~illatio~a
The suspension was then subjected to high shear defibrillation and cell wall
rupture process by
exposing the fibre to very cold temperature under water saturation condition
and high pressure
shearing with and without exposing them to a high pressure defibrillation done
with PANDA
2K by NIRO SOAVI S.p.A? . The passage of the suspension through this flow
passages
under high pressure and controlled flow action subjects the fluid to a
condition of high
turbulence and shear that creates the efficient mechanism of reduction in size
[to submicron
level]. The sample was repeated exposed to chemical treatment, freeze drying
followed by this
defibrillation at 0-150 MPa pressure.
The samples were analysed using transmission electron microscopy, which showed
that high-
pressure defibrillation led to the individualization of the nanc~-sized
rnicro.fibrils.
IiAaterials
Flax fast fibres and hemp fibres were used as a source for natural fibres.
Rutabaga and Turnip
were used as a source of Root crops, Wheat straw and bagaa.se are used as agro
based natural
CA 02437616 2003-08-04
fibres and thermo mechanical pulp and Draft pulp were used as wood fibres
source. All these
fibres were treated and then defibrillated to produce cellulose nano-fibrils.
The average
diameter range obtained from was in the range of 5-60 nm.
Examples
Experiments were undertaken to demonstrate the production of cellulose nano
fibrils from
different raw materials under dLifferent conditions.
Defibrillation vio~thout chemical treatments
Natural fibres have length in the range of 5-25 mm and they exist in the form
of fibre bundles.
Fibres are tightly attached to each other with pectin, which a.ct as cement to
bind them together
as a bundle of fibres. Without removing the pectic substancfa it is very
difficult to
individualise fibres for defibrillation. Moreover the opening of the nozzle in
the defibrillator
equipment is approximately 1-2 mm and when we pass the suspension of fibres of
length 2-25
mm, it chokes the nozzle opening and no circulation is possiible for
defibrillation.
Defibrillation vrrith chemical treatments and an~ithout high pressure
In one experiment, chemical treatment of the fibres was done but high pressure
was not applied
for the defibrillation of the fibrils. Then the samples were an;~lyzed in
optical microscope and
also using Scanning electron rr~icroscopy.
SEM in figure 2 and optical microscope in figure 3 show the fibrils after
defibrillation without
high pressure and it is clear that still the fibrils are attached to each
other and are in the form of
bundles. Therefore it is essential to apply a high pressure to iisolate theses
fibrils from each
other.
Impact of various che~rtical treatments
~Iarious chemical treatments are done to minimise the content of impurities
like
hemicelluloses, lignin, pectins and minerals in the sample used for isolation
of nano-fibrils.
Figure 13 shows the decline in hemicelluloses and lignin conaent and constant
increase of ?
cellulose. Higher content of cellulose will lead to a better stiffness and
strength of the fibrils.?
CA 02437616 2003-08-04
Impact of number of passes
Flax, Hemp and Wheat straw fibres, when examined under TEM and AFM
demonstrated better
extent of defibrillation after 2Q passes but Rutabaga root crop showed a
deterioration nn
fibrillation with increased number of passes (figure 9). At lower number of
passed, TEM
pictures showed that nano fibrils are still entangled to each other and these
fibrils diameter is in
the range of microns. Increasing the number of passes shows the better
isolation of nano fibrils
and better yield.
Conclusions
,mss Cellulose nano-fibrils have much higher aspect ratio than the long
fibres; hence they have
better strength properties.
~s By performing chemical and mechanical treatments we c;an isolate nano-sized
microfibrils.
,mss Different stages of chemical treatments lead to increase in cellulose
content in the sample
and hence increasing the yield of nano fibrils.
.mss Liquid nitrogen crushing before the high-pressure defibrillization plays
an important role in
rupturing the cell wall and in liberating the microfibrils from cell wall.
,mss Cell rupture technique is better suited for isolation the nano-fabrils
than only the shear
action.
,e~s T'EM and AFM techniques are used to identify the nano-fibrils and in
determining the
diameter and length of the nano-fibrils.
Potential Applications
The invention process will be ~:csed widely as a ultra light weight composite
in automobiles
interior and exterior parts.
Due to its lightweight and high strength its potentials application will be in
aerospace industry.
Since these nano-composites will be biodegradable with tremendous stiffness
and strength ,
they find application in the medical field such as blood bags, cardiac
devices, valves as a
reinforcing biomaterial.
