Note: Descriptions are shown in the official language in which they were submitted.
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SURFACE TREATED INORGANIC PARTICLE ADDITIVE FOR INCREASING THE
TOUGHNESS OF POLYMERS
The present invention relates to improvements in or relating to polymer
compositions. In
particular the invention relates to bioplastics systems which contain
biopolymer materials
that are biodegradable and or derived from renewable resources and have
sufficient
improved strength. The improved strength is manifest by a combination of
stiffness and
toughness. In one embodiment the improved strength allows the polymers to be
processed as films and used at economically attractive reduced thicknesses; it
also
allows the production of thermoformed articles such as food trays from thinner
materials.
Plastic films have many uses and the economics of film manufacture and use are
frequently governed by the thickness of the film that is required to provide
certain
mechanical properties. The thinner the film to provide the desired properties
the better.
The invention can also improve crystallisation kinetics of the biopolymer
which can
improve the processability of the polymer in techniques such as extrusion,
injection
moulding and blow moulding.
Disposal of plastics is increasingly of concern and biodegradability is
important to reduce
the amount of non-disposable plastic waste. Biodegradability can take various
forms
such as compostable perhaps with the aid of chemicals, films are also produced
from
polymers which have a natural biodegradation as can occur if a film, such as
an
agricultural mulching film, is dug into soil after use. Various polymers have
been
developed for their biodegradability, however the polymers tend to have poor
mechanical
strength rendering them unsuitable for certain uses or, for example requiring
an
undesirably thick film to achieve reelability and processing without fracture.
Impact
resistance, tear resistance and mode of failure are all important properties
of films,
thermoformed and injection moulded parts. In particular the biodegradable
polymers
with which this invention is concerned tend to be brittle due to an inherent
low toughness
as expressed as their ability to absorb energy before fracture; this
brittleness can lead to
fracture and splintering upon impact which can result in polymer fragments
from
packaging materials in products such as foods. In one embodiment the invention
provides bioplastics having a ductile failure mechanism useful as films, for
thermoforming and injection moulding applications.
Examples of biopolymers with which the present invention is concerned are
polylactic
acid sometimes known as polylactide (PIA), polyglyconate, poly (dioxanone),
polyhydroxy alkanoates (PHA), particularly polyhydroxybutyrates and
polyhydroxy
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vatarates, polymeric thermoplastic starches (amylose levels above 60%) and
combinations thereof, collectively known as biopolymers. Polylactides have
been
proposed as biodegradable replacements for polypropylene and polystyrene but
they
have not had sufficient strength. The present invention provides polylactides
with such
strength and also enables polylactides to compete as a biodegradable
replacement for
polycarbonates.
These polymers, particularly uncrystallised PLA have a low heat deflection
temperature
(HDT) which limits its use in high temperature applications. In addition they
may have a
slow crystallisation kinetics requiring lengthy moulding cycle times
particularly in injection
moulding.
An aim of the present invention is therefore to increase the strength of
bioplastics to
shorten moulding cycle times and to improve the crystallisation kinetics
without any
substantial decrease in biodegradability. It has previously been proposed to
include
rubbers with polyactides to improve their toughness, however although
toughness is
improved the stiffness of the polyactide is reduced and the conventional
rubbers are not
biodegradable. The biodegradable rubbers more recently available are
considerably
more expensive.
The inclusion of fillers in polymeric materials for various reasons is well
known. Fillers
are generally included to provide strength and/or reduce the cost of articles
made from
the polymeric material; fillers may be included in mouldings and extrusions of
all shapes
and sizes. Calcium carbonate is a well known filler for polymers and it is
known that the
size and morphology of the calcium carbonate can be tailored to impart certain
desirable
properties to the polymer in which it is included. It has, for example, been
proposed in
GB 2336366 A that calcium carbonate may be included in polyethylene, similarly
United
States Patent 6,911,522 describes the inclusion of calcium carbonate in e-
caprolactone
polymers. An article entitled 'The Reinforcement of Poly (Lactic Acid) using
High Aspect
Ratio Calcium Carbonate based Mineral Additive' by Zhiyong Xia, Dennis,
Prendes and
Patrick Wernett describes the inclusion of a calcium carbonate additive
EMforce. Bio with
polylactic acid in order to improve toughness and stiffness.
It is also known that calcium carbonate may be coated to improve its
compatibility with
the polymers with which it is used. For example GB 2336366 fills polyethylene
with
calcium carbonate coated with stearic acid to avoid die lip build up when the
polymer is
extruded and United States Patent 6,815,479 discloses the use of calcium
carbonate
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coated with from, 2.50 to 4.00 wt % stearic acid as a filler for the polymer
Capron nylon
to improve the impact strength of the polymer.
It has been found that the use of certain fillers in bioplastics enables an
increase in
strength to be obtained without impairing the biodegradability of the
bioplastics and in
particular improves impact resistance and ductability without impairing the
stiffness of the
polymer. Ductability is indicated by the shape of the stress strain curve and
an indication
that the bioplastic is ductile if the area under the curve up to the maximum
peak is
greater than 35% of the total area under the curve the material can generally
be
regarded as having a ductile failure mode. This has been found to be
particularly useful
when the biopolymer containing the filler is used to produce films as it
enables the
production of thinner films having desirable mechanical properties without
impairing their
biodegradability. It is especially useful for the production of agricultural
films and refuse
sacks which may be dug into the soil and composted after use. It is also
useful in
thermoforming and injection moulding applications where the ductability and
reduced
brittleness reduces splintering of the bioplastic.
One embodiment the present invention therefore provides a bioplastic
containing from
10-40 wt % of a coated filler, said coated filler containing less than 1 wt %
water as
measured by the weight loss when heated at 200 C to constant weight.
In a further embodiment the invention provides a bioplastic containing from 10
- 40 wt%
of an inorganic particle coated with about 2.3 wt% or more of a fatty acid,
fatty acid
derivative, rosin, rosinate, polyolefin based waxed, oligomers and minerals
oils and
combinations thereof.
In a further embodiment the invention provides the use of an inorganic
particle coated
with one or more of a fatty acid, fatty acid derivative, rosin, rosinate,
polyolefin based
wax, oligomers and mineral oils to improve the impact resistance of a
bioplastic without
sacrificing the stiffness of the bioplastic.
In a further embodiment the invention provides the use of an inorganic
particle coated
with one or more of a fatty acid, fatty acid derivative, rosin, rosinate,
polyolefin based
wax, oligomers and mineral oils to accelerate the crystallisation kinetics of
a biopolymer
from the melt.
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It has been found that the combination of the coating on the filler and the
low water
content is important in enabling the production of high strength biodegradable
materials
and also to accelerate crystallisation from the melt, one function of the
coating is to operate as a dispersant and it is preferably a molecule with a
polar head
that will attach to the filler particle so that the coating is not removed by
the biopolymer
when it is in the molten state, preferably it is also provided with
substantially non polar
tail that will integrate with the polymer structure to aid the dispersion of
the filler within
the polymer. Examples of suitable dispersants are fatty acids and their
derivatives (such
as fatty acid amides and fatty acid esters) and also their alkali metal salts.
For example,
C10 to C22 saturated and unsaturated carboxylic acids and their alkali metal
salts such as
stearic, palmitic, myristic, oleic, linoleic, linolenic acids and their sodium
salts are
particularly useful. Rosins and rosinates and materials based on abietic acid
are other
suitable materials that may be used. Other less preferred coating materials
that can be
used include polyolefin based waxes, oligomers and mineral oils and
combinations
thereof.
It has been found that the amount of the coating used is important to obtain
the
improvement in the properties of the bioplastic. The amount required will
depend upon
the nature of the biopolymer and the particular property or properties with
which the
bioplastic user is concerned. We have found that with polylactides preferably
the coating
should be present in an amount of at least 2.3 wt % of the filler material and
up to 10.0
wt% may be used. I-polylactides can typically be up to about 40 wt %
crystalline material
with the remainder being amorphous. The coated filler used in the present
invention is
believed to serve two functions particularly in polylactic acid, firstly it
will nucleate the
crystallisation of the polymer speeding up crystallisation rate and producing
more
uniform crystallites and secondly it will debond from the amorphous phase of
the polymer
when subject to impact thus absorbing energy so increasing the strength of the
material
whilst reducing crack propagation and rendering the polymer less brittle. If
the polymer
is poly-3-hydroxy butyrate which has a higher crystallinity, a lower amount of
the
dispersant may be required.
The preferred filler is calcium carbonate which may be precipitated calcium
carbonate
(PCC) or ground calcium carbonate (GCC). Precipitated calcium carbonate is
preferred
and it is preferred that the calcium carbonate have an acicular morphology
with an
aspect ratio (length : width) greater than 4, preferably greater than 5. The
aspect ratio of
GCC is typically about 1. The aspect ratio of the filler particles were
determined by using
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a injection moulded polymer-mineral composite piece. The polymer was plasma
etched
revealing the mineral particles which were removed from the surface using 2-
propanol.
The collected mineral particles were analyzed by transmission electron
microscopy
(TEM) using a JOEL LTD. JEM 1200 EXIT instrument. Digital images were
collected with
an Advanced Microscopy Techniques, Incorporated digital camera system and the
filler
dimensions were measured using ImagePro Plus software. Twenty-four TEM images
were collected and analyzed for each sample. The average aspect ratio value
was then
derived by curve fitting the long versus short dimensions of the particles
(aspect ratio)
distribution data.
It is also preferred that the calcium carbonate whether it be PCC or GCC has a
95%
particle size as measured by a micrometrics 5001 sedigraph and it is
particularly
preferred that 90% of all particles are no more than 20 microns in size as
measured by
the sedigraph, more preferably no more than 18 microns and most preferably no
more
than 2 microns. The particle size measurement is performed using 2g of the
uncoated
calcium carbonate in 50 ml of a 0.2% DAXAD solution and sonicating the slurry
at a 3.5
(out of 5) power setting for 5 minutes prior to introduction into the
Sedigraph instrument..
It is important that the water content of the filler be no greater than 1 wt %
based on the
weight of the filler, more preferably the water content is below 0.5 wt % at
the processing
temperature of the biopolymer, the water content is measured by Karl Fischer
titration of
a sample when heated to 200 C. The biopolymers with which the present
invention is
concerned are biodegradable and compostable and tend to decompose in the
presence
of moisture and the decomposition tends to be accelerated at the elevated
temperatures
that are typically used for processing the biopolymers. For example,
polylactic acid is
typically processed at temperatures between 180 C to 210 C and the presence of
water
can cause rapid degradation of the polymer at these temperatures.
According to a preferred embodiment of this invention therefore, inorganic
additives such
as calcium carbonate (CaCO3) particles coated with a fatty acid greatly
improve the
mechanical properties such as toughness of polymers and particularly
biopolymers such
as biodegradable or compostable polylactide (PLA) polymers without hindering
the
polymer's compostability. Toughness is a material's ability to absorb energy
during
fracture and biodegradable polymers such as PLA are brittle because of their
inherent
low toughness. This property of biopolymers has limited their use but when
enhanced
with inorganic additives according to the present disclosure, the biopolymers'
toughness
is substantially improved and the usefulness of the biopolymers enhanced. The
fatty
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acid coated inorganic additives such as fatty acid coated calcium carbonate
can be used
for enhancing the toughness or impact resistance of biopolymers such as PLA,
polyglyconate, poly(dioxanone), polyhydroxyalkanoates (PHA) particularly
polyhydroxbutyrates and thermoplastic polymeric starches such as those
containing
more than 60% amylose, and combinations thereof.
Biopolymers as referred to herein includes polymers derived from natural
renewable
resources and/or those that are generally compostable or generally
biodegradable
polymers. Bioplastic materials contain these biopolymers. According to this
invention
the toughness of bioplastics is improved by incorporating an additive
comprising
inorganic particles that are coated with a coating material such as one of
fatty acids, fatty
acid derivatives (such as fatty acid amides and fatty acid esters), rosins,
rosinates,
oligomers, polyolefin based waxes and mineral oils. The inorganic particles
are
preferably coated with the coating material at a coating level of about 2.3 wt
% or more
per weight of the inorganic particles. Bioplastics according to the present
invention have
improved physical properties (including toughness, ductility, and/or
stiffness) and may be
incorporated into various products, including automotive, electronics and
appliance
components (e.g., bumpers, dashboards, computer/cell phone housings, etc.),
consumer
goods (e.g., credit card stock, eating utensils, cups, food trays, fast food
containers,
plateware, etc.), and packaging products (e.g., food containers, bottles and
films such as
agricultural films and refuse sacks, etc.).
It has also been found that the incorporation of the coated filler into the
bioplastics
according to the present invention improves the crystallisation kinetics of
the biopolymer.
The faster crystallisation enables shorter moulding cycles in operations such
as injection
moulding and thermoforming where the time required particularly for moulding
PLA has
been considerably long.
The filler is typically inorganic particles and can be one of a carbonate,
silica, kaolin, talc,
fine metal particles, wollastonite and glass microspheres, and combinations
thereof.
According to one preferred embodiment, the inorganic particles are calcium
carbonate
particles coated with a C10 to C22 fatty acid or its derivatives to the
coating level of
between about 2.3 - 10 wt % per weight of calcium carbonate. The calcium
carbonate
can be any type of calcium carbonate such as precipitated calcium carbonate
("PCC"),
ground calcium carbonate ("GCC"), and blends thereof.
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In one preferred embodiment for enhancing the toughness of PLA polymers, the
inorganic additive can be calcium carbonate additive material in particle-like
form such
as PCC, GCC, or blends thereof. Some examples of calcium carbonate additives
in
which the present disclosure can be implemented are Omyacarb UFT product
available
from OMYA Inc. North America, and Superfil product available from Specialty
Minerals
Inc. The calcium carbonate particles can be coated with a fatty acid such as
stearic acid,
which is one of the useful types of saturated fatty acids that comes from many
animal
and vegetable fats and oils.
The enhanced polymers described above can be prepared by compounding the
coated
calcium carbonate particles into the polymer resin precursor for the
bioplastic material
and forming the composite material into a desired form. The coated calcium
carbonate
particles can be compounded into the polymer resin precursor by melt
compounding
using a twin screw extruder or similar equipment. An example of such an
extruder is a
twin screw extruder manufactured by the Leistritz Corporation. As an additive
to
enhance the toughness of a PLA polymer, the calcium carbonate particles coated
with
about 2.3 wt % up to about 10.0 wt % preferably up to about 6.0 wt%, more
preferably up
to about 4.0 wt% of fatty acid can be compounded into PLA at a loading level
between
15 to 30 wt % per weight of PLA polymer.
Coating the mineral particles according to the method of the present
disclosure has
resulted in unexpectedly significant increase in the toughness of the
bioplastic system. It
is generally known that surface treatment of mineral filler particles in
polymer systems
improve mechanical properties of the polymer somewhat by reducing absorbed
moisture
on the particles and lowering the surface energy of the mineral particles.
This results in
better dispersion of the mineral particles in the polymer system. But, with
previously
known surface treatments to the mineral filler particles, only minor increase
in toughness
of the polymer systems were observed.
With the coating of the mineral particles according to the present disclosure,
substantial
enhancement of the bioplastic composite's toughness is achieved. This appears
to be
attributed to the coated mineral particles in the resulting polymer composite
matrix
absorbing energy through debonding at the particle-to-polymer interface more
efficiently
than in conventional surface treated mineral fillers in other polymer systems.
The
debonding at the particle-to-biopolymer interface absorbs energy of a crack
propagating
through the polymer composite. It is believed that this is particularly the
case with
polymers such as PLA which contain substantial amounts of amorphous regions.
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The bioplastic containing the coated filler may be processed to produce a wide
range of
articles traditionally made from plastics. They may be injection moulded,
extruded,
thermoformed or blow moulded according to the nature of the articles to be
produced.
For injection moulding we prefer that the composition contain from 10 to 40 wt
% of the
coated filler, more preferred from 15 to 30 wt %, particularly 20.to 30 wt %.
For extruded
materials up to 40 wt % of the coated filler should be used. The materials may
be used
to produce moulded components for the transportation industry, household
goods,
packaging materials, construction materials and the like. One particular use
is in the
production of films particularly films that are compostable and may be used as
agricultural films and refuse bags. Here we have found that the use of the
additive of
this invention allows the production of thinner films with the desirable
mechanical
properties. For example, compostable agricultural films of polylactic acid may
be
obtained that have the required mechanical properties such as impact strength,
tear
resistance and ductile failure at a thickness below 50% of comparable film
without filler,
in some instances the properties may be obtained at a thickness of 30% or even
25% of
the thickness of one unfilled film. These films may be produced by the bubble
expansion
process' or a stenter process. The polymers may also be thermoformed to
produce
biodegradable food trays.
In the processing of other polymer systems it is usually necessary to include
various
additives into the polymer to aid processing. Examples are slip agents,
antistatic agents,
viscosity modifiers and the like. An additional benefit of the present
invention is that the
biopolymers with which the invention is concerned may be processed without the
need
for any additional additives. Accordingly in a further embodiment the present
invention
provides a bioplastic composition of the invention substantially free from
additional
additives.
The invention is illustrated by reference to the following examples:
Example I
In a laboratory experiment, the inventor was able to demonstrate the
beneficial effect of
a fatty acid coated calcium carbonate additive in improving the toughness of
PLA
polymer. Specifically, the improvement in room and low temperature impact
toughness
as well as improvement in the stiffness of PLA was demonstrated.
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The properties of PLA polymer can be controlled by controlling the ratio of
the
stereoisomers comprising the PLA. For example, the polymerization of
predominately
the L-form with greater than about 15 mole % of either the D or meso lactide
will
generate an amorphous PLA random copolymer. Whereas, the polymerization of the
L-
form of lactic acid will lead to poly-L-lactide (PLLA) which is a
semicrystalline polymer
with the crystallinity of up to 40 % or more.
The inventor used a number of different calcium carbonate based additives and
coated
them with stearic acid and compounded into PLLA polymer samples to confirm the
beneficial effects of stearic acid coated calcium carbonate on the mechanical
properties
of PLA. The particular calcium carbonate additive samples utilized as the
starting
materials were Specialty Minerals Inc.'s EMforce Bio, Superfil , OMYA's
Omyacarb
UFT, and a 50:50 blend of EMforce Bio and Superfil . Specialty Minerals
Inc.'s
EMforce Bio is an engineered calcium carbonate filler additive that is coated
with
greater than 2.7 wt % of fatty acid as-manufactured and is intended for
reinforcing
biopolymers. The samples of the other calcium carbonate additives were coated
using a
laboratory Henschel mixer to each coating level concentration (0.0 to 4.0 wt
%). Each
calcium carbonate additive material was compounded into PLLA resin at a target
concentration of about 25 wt % level.
The compounding of calcium carbonate additive into PLLA can be carried out by
melt
compounding using a twin screw extruder. In this example, a Leistritz twin
screw
extruder was used having an LID ratio of 40, a diameter of 27mm and 10
independent
heating zones was used to compound all formulations. The extruder was operated
in a
co-rotating mode to ensure good dispersion of calcium carbonate in the PLLA.
The
PLLA resin was introduced into the feed throat of the extruder (at ambient
temperature)
using a K-TRON hopper-fed loss on weight feeder. All fillers were side-fed via
a K-
TRON loss-on-weight feeder into zone 5 of the extruder.
The EMforce Bio material was produced at a Specialty Minerals Inc.'s
manufacturing
facility and has an as-manufactured coating level of 3.3 wt % and a water
content below
0.5 wt %. The other calcium carbonate additive samples were prepared in the
laboratory
to a total coating level of 3.3 wt %. EMforce Bio produced the greatest
impact/stiffness
balance compared to the other fillers but at the 3.3 wt % coating level, all
of the fillers
increase the PLLA toughness similarly (including the OMYA UFT product). A
50:50
blend of EMforce Bio and Superfil produced properties that were intermediate
between the two pure components and is a viable option as a "next generation"
EMforce
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Bio product as a potential reduced cost product. The addition of 3.3 wt %
fatty acid to
the PLLA resin without a calcium carbonate additive showed no improvement in
the
mechanical properties compared to the unfilled resin.
The calcium carbonate additives were melt compounded in PLLA (Natureworks
4042D)
on a Leistritz 27-mm twin screw extruder operating in co-rotating mode at
target
concentrations of 20, 25 and 30 wt %. 3.3 wt % fatty acid was also compounded
with
PLLA to determine if the fatty acid alone could improve PLLA toughness.
Composite
samples were dusted with an aluminium stearate antiblocking agent prior to
injection
moulding on an Argburg 88-ton Allrounder machine. Test specimens were
conditioned
in a controlled temperature and humidity environment (23 C and 50% R.H.) for 3
days
prior to mechanical testing.
The particle size distribution of the calcium carbonates used in this study is
presented in
Table I and the plot shown in Figure 1. Samples plotted are Superfil calcium
carbonate coated with stearic acid to 3.3 wt % level 11; UFT calcium carbonate
coated
with stearic acid to 3.3 wt % level 12; EMforce Bio (Pallet #12) having as-
manufactured
3.3 wt % coating level 13; and a 50/50 blend of EMforce Bio/Superfil 14. The
Superfil 11 had the largest topsize and median particle size while EMforce
Bio 13 had
the lowest topsize and median particle size.
Table 1. Particle Size Distribution of the Calcium Carbonate Additives (pm).
Cumulative Mass Superfil UFT Emforce 50/50 Blend
Finer % Pallet #12 Emforce /Superfil
98 7.596 4.118 2.078 6.399
90 4.957 2.150 0.997 3.777
84 4.209 1.770 0.809 2.930
50 2.110 0.867 0.447 0.826
20 0.933 0.424 0.280 0.388
16 0.776 0.370 0.253 0.345
10 0.521 0.28 0.199 0.273
Figure 2 shows the flexural modulus of the various polymer samples measured at
23 C
(room temperature). As discussed above PLLA resin samples were compounded with
calcium carbonate to target concentrations of 20, 25 and 30 wt % . The
respective line
plots shown are PLLA filled with Superfil (3.3 wt % coating level) 21; PLLA
filled with
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UFT (3.3 wt % coating level) 22; PLLA filled with EMforce Bio (3.3 wt %
coating level)
23; PLLA filled with 50/50 EMforce Bio/Superfil blend (3.3 wt % coating
level) 24. In
addition, control samples of an unfilled PLLA control 25 and PLLA with just
3.3 wt %
(based on total weight of the polymer composite) of stearic acid 26 were also
prepared
and measured. Because the two control samples are not filled with calcium
carbonate
their additive concentration levels are 0.0 wt %. All calcium carbonate
additives
significantly increased the flexural modulus compared to the unfilled PLLA 25
and stearic
acid-PLLA resin mix 26. EMforce Bio filled PLLA 23 produced the greatest
increase in
flexural modulus'. Superfil filled PLLA 21 produced the lowest increase in
flexural
modulus of all the calcium carbonate containing composites and the 50/50
EMforce
Bio/Superfil blend 24 yielded intermediate results as expected.
Figure 3 shows the results of the Dynatup multi-axial impact energies at 23 C
(room
temperature). The EMforce Bio filled PLLA composite 33 produced the greatest
room
temperature toughness compared to the other calcium carbonate filled PLLA
composites
31 and 34 with the exception of the UFT filled PLLA 32 at 30 wt % loading
which had a
comparable toughness. Previous studies have shown that a minimum of 20 wt %
EMforce Bio is required to substantially increase the PLLA composite
toughness
compared to the unfilled control PLLA 35. A maximum toughness is achieved
around 25
wt % loading of EMforce Bio and the toughness begins to decrease above 30
wt.%.
This is the same trend observed for the Superfil filled PLLA 31 and the
EMforce
Bio/Superfil blend 34.
Figure 4 shows the results of the Dynatup multi-axial impact energies at 0 C.
All of the
PLLA composites failed in a brittle mode (or nearly all brittle failures, see
Table 2). In
this case, the Superfil filled PLLA 41 produced the greatest toughness to
which the
UFT filled PLLA 42 matched at the 30 wt % concentration. This is likely due to
a surface
area-coating level effect, Superfil having the lowest surface area. The lower
surface
area of Superfil product would require less stearic acid molecules to
encapsulate the
particle compared to the higher surface area particles. This would be expected
to
produce a thicker coating level around the Superfil particles. Previous
studies in
Natureworks 4032D PLLA indicated that EMforce Bio can greatly increase 0 C
impact
energy of PLLA and provide a ductile failure mechanism at coating level
concentrations
of about 3.5 wt % or greater.
Table 2 also includes the heat deflection temperature ("HDT") data. All of the
mineral
fillers at every concentration examined in this study had no effect on
increasing the HDT
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of the PLLA. The addition of stearic acid in the absence of a mineral filler
showed a
significant decrease in the HDT of the PLLA.
Table 2. Multi-Axial Impact Failure Mechanisms and the Heat Deflection
Temperature of
PLA and PLA Composites
Sample Mineral % Ductility Heat Deflection
Concentration 23 C 0 C Temperature
(%) ( C)
PLA Control 0 0 0 54.2
20 50 10 54.2
Superfil 25 90 10 53.9
30 100 10 54.2
20 0 0 54.1
U FT 25 80 0 53.9
30 100 10 54.1
20 100 0 54.3
EMforce Bio 25 100 0 54.2
30 100 0 53.7
EMforce Bio 20 50 0 53.6
Superfil 25 100 0 53.6
Blend 30 90 10 53.7
(50:50)
PLA+3.3% 0 0 0 49.7
Stearic
Figure 5 shows the room temperature notched Izod impact test results performed
on the
polymer samples. All of the stearic-coated calcium carbonate filled PLLA
composites
were slightly better than the unfilled and stearic acid-PLLA controls and
similar to one
another. The plot lines shown are Superfil filled PLLA 51, UFT filled PLLA
52,
EMforce Bio filled PLLA 53, 50/50 EMforce Bio/Superfil blend filled PLLA
54,
unfilled PLLA control 55 and PLLA with stearic acid control 56.
The experiment discussed above show that at 3.3 wt % coating level, no further
improvement on the mechanical properties of the PLLA, such as the impact
toughness,
is observed over the performance achieved with 2.7 wt % coating level.
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Example 2
Figure 6 shows the results of a coating level study on an uncoated EMforce
Bio
calcium carbonate precursor particle to determine the optimal coating level.
Falling
weight impact energy was measured for PLA polymer samples prepared from
polymer
resin compounded with calcium carbonate particles at various coating levels.
The
calcium carbonate precursor samples were dry-coated using a laboratory
Henschel
mixer to each coating level concentration (0.0 to 4.0 weight %). However, the
coating
process is not limited to a dry-coating process. A wet-coating process can
also be used.
Each calcium carbonate material was compounded into PLLA at a target
concentration
of 25 wt %. The measurement of toughness in this test is a falling weight. The
resulting
plot of Figure 6 shows a classic "S-shaped" curve 60 demonstrating a minimum
coating
level required to improve impact toughness of the PLLA. From the steep part 62
of the
"S-curve," a minimum coating of about 2.3 wt % is estimated to be required to
greatly
improve the impact toughness of a PLLA composite to about 25 ft. lbs. or
better. Tables
3A-3C show the underlying data for the plot of Figure 6.
Table 3A
Project #2007-5 EMforce Bio coating level study in PLA 4032D
Sample Coating NatureWorks Flexural Modulus
ID level PLA
Filler type % stearic Filler 4032D ASTM-D790
acid Level
(%) (%) (PSI) S.D.+/-
4962- None None 0 100 498,979 5,784
194-1
4962- EMforce Bio 0.0 25 75 813,764 1,537
194-8
4962- EMforce Bio 1.5 25 75 763,734 8,973
194-2
4962- EMforce Bio 2.0 25 75 754,623 1,313
194-3
4962- EMforce Bio 2.5 25 75 740,978 2,890
194-4
4962- EMforce Bio 3.0 25 75 757,026 5,261
194-5
4962- EMforce Bio 3.5 25 75 766,653 5,411
13
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194-6
4962- EMforce Bio 4.0 25 75 743,614 4,367
194-7
Table 3B
Project#2007-5 EMforce Bio coating level study in PLA 4032D (Continued)
DYNATUP IMPACT (drop ht. = 8.0 in.)
23 C 0 C
Sample ID Initiation %D Initiation E DI Total E Total E Total E
(ft.lbs) STD. (ft.lbs) STD STD
(ft.lbs) (ft.lbs)
4962-194- 1.8 0 0.7 11.7 2.1 0.7 0.7
1
4962-194- 1.4 0 0.4 17.7 1.7 0.5 0.5
8
4962-194- 2.2 0 1.2 15.1 2.7 1.4 0.5
2
4962-194- 5.5 0 2.6 10.4 6.3 3.5 0.6
3
4962-194- 16.7 100 0.8 53.2 35.7 2.6 2.5
4
4962-194- 17.5 100 0.6 53.7 37.7 1.1 3.4
4962-194- 17.1 100 0.3 53.7 37.0 1.0 4.5
6
4962-194- 17.8 100 0.8 54.6 39.2 0.9 2.7
7
Table 3C
Project#2007-5 EMforce Bio coating level study in PLA 4032D (Continued)
Notched Izod impact Tensile Strength ASTM-D6381(2 IN. / MIN.)
@RT
ASTM-D256 Strain Stress @ peak strain @
@peak break
Sample ID (ft. S.D. (%) (PSI) S.D. (%)
lbs/in.)
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4962-194-1 0.72 0.08 2.7 11,171 75 2.9
4962-194-8 0.52 0.08 1.5 9,865 347 1.5
4962-194-2 0.79 0.11 1.6 9,161 332 1.9
4962-194-3 1.09 0.14 2 8,579 80.0 2.1
4962-194-4 1.58 0.13 2.2 8,325 102.0 2.4
4962-194-5 1.96 0.08 2.2 8,124 23.0 2.4
4962-194-6 2.25 0.16 2.1 7,941 89 2.3
4962-194-7 3.25 0.15 2 7,855 45.2 2.2
Note: All samples were evaluated unannealed in 5 lb batches.
According to the above data, at room temperature, the brittle-ductile
transition occurs
above 2.0 wt % coating level. The falling weight failures remain ductile at
all values
above 2.5 wt % and the beneficial effect appears to flatten out somewhat above
3.0 wt %
in room temperature applications. This transition point will most likely
change if the test
conditions are changed. Thus at least for room temperature applications, in
PLA
polymer systems, the coating level can be controlled to between about 2.3 -
4.0 wt % to
minimize the amount of coating. As shown in the curve of FIG. 6, the Dynatup
drop
energy has just begun to improve above 2.0 wt % coating level, in another
preferred
embodiment, the coating level can be controlled to between about 2.5 - 4.0 wt
%. A
higher impact velocity, or lower temperature, should require a higher coating
level to
produce a ductile failure. It appears that a coating level greater than 3.5 wt
% coating is
required to produce ductility at a test temperature of zero degrees
centigrade.
The notched Izod impact strength increased linearly with coating level.
Flexural modulus
was not affected by coating level while tensile modulus decreased as coating
level
increased. This is because the coating decreases the bond strength between the
filler
and the polymer. It is easier for the filler particles to "pull out" of the
polymer when a
tensile stress is applied. Note that the tensile strength also decreases with
an increase
in coating level. The "pull out" forces are lower in flexural testing and
therefore the
flexural modulus is not affected.
It appears that a coating level of about 3.0 - 4.0 wt % would be a preferred
coating range
to ensure improvement in the impact toughness of the PLLA resin. The impact
toughness balance improves with an increase in coating level but there is a
trade-off with
tensile strength and tensile modulus.
CA 02709269 2010-06-14
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By using the coated calcium carbonate filler of the present disclosure, the
toughness of
the PLA resin can be improved by as much as 10x that of the unfilled resin.
Stearic acid
as the coating material for the calcium carbonate filler is an example only
and other fatty
acid coatings would be expected to provide similar improvement in the resin's
toughness.
Example 3
Test strips of PLA of variable thickness and containing variable amounts of
coated
calcium carbonate were produced on a Brabender Intellitorque using a single
screw
extruder with a variable gap die and a variable speed strip puller. The
mechanical
properties were measured using a Gardner impact test at 23 C, and an Elmendorf
Tear
test. The results are shown in Figures 8 and 9 and shows that the filler has a
significant
increase on Gardner Impact resistance. Figure 8 shows the average drop height
required for failure of samples of PLA containing varying amounts of coated
filler.
Figure 9 shows the force required to propagate a tear according to the
Elmendorf tear
test of the various samples of PLA containing the coated filler and shows a
significant
increase in tear strength in the filled samples.
The aspect ratio distribution of the material was measured by TEM micrographs
as
explained earlier in the text and is shown in Figure 7.
Example 4
PLA containing the coated additive were prepared as in Example 1. Test strips
were
produced as in Example 3 with target thickness of 4 mil (0.102 mm); 9 mil
(0.229 mm)
and 15 mil (0.381 mm).
The Gardner impact strength of the strips is shown in Figure 10 and the
Elmendorf Tear
strength in Figure 11. The figures show that the additive increases toughness
with
increasing sheet thickness as opposed to the decrease in toughness that is
experienced
in the absence of the additive. The increase in Gardner Impact strength allows
a 3 to 4
times reduction in thickness to achieve comparable mechanical properties.
Example 5
The compounds obtained according to the process set out in Example 1
containing
various amounts of filler were injection moulded in an Arburg Allrounder 370c
Injection
Moulder to produce samples conforming to ASTM.
16
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The Flexural modulus of the samples is shown in Figure 12, the room
temperature
multiaxial impact total fracture energy as measured by an Instron Corporation
Dyanatup
9250 HV instrumented multiaxial impact tester is shown in Figure 13 showing
the
improvement in ductability and impact energy required for fraction achieved
when from
15 wt% to 35 wt% of the coated filler is used.
The Figures show that the additive significantly improves the toughness and
stiffness of
polylactides and, furthermore the addition of the additive converts a brittle
failure to a
ductile failure.
Example 6
The crystallisation kinetics of a sample of PLA containing 30 wt% EMforce Bio
at
various temperatures were compared with an unfilled PLA sample.
The crystallisation half time from the melt was measured by differential
scanning
calorimetry and the results are shown in Figure 14 which shows that a
significant
reduction of the crystallisation half time from the melt can be achieved
according to the
present invention.
Example 7
The melt viscosity of PLA containing 0, 10, 15, 20, 25, 30 and 40 wt% of
EMforce Bio
were measured using a Dynisco Incorpoated LCR 7001 capillary rheometer and the
results are shown in Figure 15 showing that the additive significantly reduces
melt
viscosity.
17
