U.S. patent application number 10/372069 was filed with the patent office on 2003-07-03 for ultrasound assisted continuous process for making polymer blends and copolymers.
Invention is credited to Hong, Chang Kook, Isayev, Avraam.
Application Number | 20030124211 10/372069 |
Document ID | / |
Family ID | 25132264 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030124211 |
Kind Code |
A1 |
Isayev, Avraam ; et
al. |
July 3, 2003 |
Ultrasound assisted continuous process for making polymer blends
and copolymers
Abstract
This invention relates to a process for making polymer blends
and copolymers by ultrasonic treatment during or after mixing the
polymers. In the process of the present invention, an unexpected
phenomenon occurs. The process brings about enhancement of the
mechanical properties when compared with identical blends not
subjected to ultrasonic treatment. The ultrasonic treatment of the
blends is believed to enhance intermolecular interaction and
improve adhesion between dissimilar polymers and make chemical
bonds between polymers that otherwise are incompatible or
immiscible with each other.
Inventors: |
Isayev, Avraam; (Akron,
OH) ; Hong, Chang Kook; (Akron, OH) |
Correspondence
Address: |
RENNER, KENNER, GREIVE, BOBAK, TAYLOR & WEBER
FOURTH FLOOR
FIRST NATIONAL TOWER
AKRON
OH
44308
US
|
Family ID: |
25132264 |
Appl. No.: |
10/372069 |
Filed: |
February 21, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10372069 |
Feb 21, 2003 |
|
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09784374 |
Feb 15, 2001 |
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6528554 |
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Current U.S.
Class: |
425/174.2 |
Current CPC
Class: |
B29C 48/40 20190201;
B29B 7/421 20130101; Y10T 428/2424 20150115; B29C 35/0261 20130101;
Y10T 428/24248 20150115; B29K 2021/00 20130101; B29B 7/36 20130101;
B29B 7/48 20130101; B29B 7/42 20130101; Y10T 442/608 20150401; B29C
48/14 20190201; B29B 7/08 20130101; B29C 48/67 20190201; B29C 48/03
20190201; B29C 48/535 20190201 |
Class at
Publication: |
425/174.2 |
International
Class: |
B29C 047/38 |
Claims
What is claimed is:
1. An apparatus for the production of polymer blends and copolymers
comprising: a continuous mixer having a mixing section selected
from the group consisting dispersive mixers and/or distributive
mixers; and an ultrasonic horn communicating with said continuous
mixer.
2. An apparatus as in claim 1, wherein said continuous mixer is
selected from the group consisting of single-screw extruders
twin-screw extruders, and modular twin screw extruders.
3. An apparatus as in claim 2, wherein said ultrasonic horn
communicates with said continuous mixer at the exit of said
continuous mixer.
4. An apparatus as in claim 2, wherein said continuous mixer
includes a die attachment and said ultrasonic horn communicates
with said die attachment.
5. An apparatus for the production of polymer blends and copolymers
comprising: a twin-screw extruder; a pressurized treatment zone;
and an ultrasonic horn communicating with said pressurized
treatment zone.
6. An apparatus as in claim 5, wherein said pressurized treatment
zone is provided at the exit of said twin-screw extruder, said
ultrasonic horn being positioned proximate said exit.
7. An apparatus as in claim 5, further comprising a die attachment,
said pressurized treatment zone being within said die attachment,
and said ultrasonic horn communicating with said die
attachment.
8. An apparatus as in claim 6, wherein said twin screw extruder is
a modular twin screw extruder.
9. An apparatus for the production of polymer blends and copolymers
comprising: a batch mixer having at least one wall defining an
interior of said batch mixer; an ultrasonic horn communicating with
said interior through said at least one wall; rotors within said
batch mixer and providing, upon the operation thereof, a
pressurized zone proximate said ultrasonic horn.
10. An apparatus as in claim 9, wherein said batch mixer is
selected from the group consisting of Banbury mixers, Farrel
mixers, and Haake mixers.
Description
[0001] The present invention gains priority from U.S. patent
application No. 09/784,374, filed on Feb. 15, 2001.
TECHNICAL FIELD
[0002] The present invention relates to an ultrasonic assisted
process for bringing about in situ chemical interaction between at
least a small portion of the individual polymer components within a
blend of at least two polymers. More particularly, the present
invention relates to a process creating chemical interactions
between at least two polymers by ultrasonic treatment of a mixture
of such polymers during or after mixing using continuous or batch
mixers. In the process of the present invention, an unexpected
chemical phenomenon occurs that enhances or improves the mechanical
properties of these polymer blends when compared with identical
polymer blends not subjected to the ultrasonic treatment.
BACKGROUND OF THE INVENTION
[0003] Blending polymers is a useful approach for the preparation
of new materials with specially tailored or improved properties
that are often absent in the single component polymers. Enhanced
properties of polymeric materials are achieved by developing
multi-component systems in the form of polymer blends composed of
two or more homopolymers. However, many polymer pairs are
incompatible or immiscible with each other and exhibit either very
low or no interfacial adhesion and phase separate on blending. The
mechanical properties of polymer blends are strongly influenced by
the strength of the interfaces between the different phases, as
well as the dispersion and interaction between them.
[0004] In most cases, mixing of two dissimilar polymers results in
blends that are weak and brittle. It is commonly known that, in
order to achieve compatibilization, a third component, typically a
block copolymer, may be added to the system. The addition of a
pre-made block copolymer to an otherwise immiscible or incompatible
polymer blend can lead to a reduction of interfacial tension. Such
block copolymers are selected to contain blocks chemically
identical to the components within the polymer blend, thereby
assuring miscibility between the copolymer segments and the
corresponding blend components at the interface.
[0005] Alternatively, forming blends of two or more dissimilar
polymers may be achieved through an in situ chemical reaction using
specifically selected or specifically tailored chemicals. This is
generally known as reactive blending. Reactive blending typically
relies on either the in situ formation of copolymers or the surface
interaction of polymers using specifically selected or specifically
tailored chemicals. The blend components themselves are chosen or
modified so that reaction occurs during melt blending. Also,
existing technologies for making plastic/rubber blends involve
compounding components with the aid of chemicals (compatibilizers
or coupling agents) or dynamic vulcanization of rubber phase
components with the aid of curatives. These generally known
processes, briefly introduced above, lead to modification of the
polymer interfaces in multi-phase blends, and thereby to tailoring
of the phase structure, and hence properties. However, these
methods are restrictive in that different, specifically tailored
chemicals or copolymers are required for different polymer
mixtures.
[0006] Notably, economic factors play an important part in deciding
how to prepare polymer blends. Those of ordinary skill in the art
appreciate that existing technologies, employing specifically
tailored or specially selected block copolymers and/or
compatibilizers, coupling agents, or curatives, are neither
optimally time effective nor cost effective.
[0007] Thus, the ability to make virtually any two or more polymers
compatible with each other to produce polymer blends and copolymers
exhibiting desirable mechanical properties is the focus of the
present invention. The ultimate goal of polymer blending according
to the present invention is a practical one of achieving
commercially viable products exhibiting desirable properties at low
cost. Additionally, through practice of the present invention, the
recycling of various polymers and/or polymer products may also be
greatly enhanced in that used polymers can be combined to achieve
desirable chemical and physical properties.
SUMMARY OF THE INVENTION
[0008] In general, the present invention provides an efficient
process for the production of novel polymer blends and copolymers.
The process includes feeding at least two polymers to a pressurized
treatment zone and treating the at least two polymers with
ultrasonic waves in the pressurized treatment zone. The at least
two polymers are selected from the group consisting of
thermoplastics, thermosets, rubbers, and liquid crystalline
polymers (LCP's).
[0009] Advantageously, the present invention overcomes the problems
associated with the prior art of chemical compatibilization of
polymer blends by treating blends of polymers, with ultrasound
either during or after mixing using continuous-type or batch-type
mixers. It is known that the mechanical properties of such blends
depend upon the adhesion between components as well as the
dispersion and interaction between them. After the ultrasonic
treatment of such blends during extrusion, an unexpected phenomenon
is found, namely, significant enhancement of mechanical properties,
such as tensile strength, modulus, elongation at break and
toughness, in comparison with blends not subjected to
ultrasound.
[0010] Experimental data supports a conclusion that new copolymers
or graft polymers are created from the blended polymers at the
interface and at the vicinity of the interface between the polymers
after only a very short time (in the order of a few seconds) of
ultrasonic treatment under high pressures and temperatures above
the melting point or glass transition temperature of the polymers,
because the enhancement of mechanical properties realized for such
blends after ultrasonic treatment thereof indicates that more than
a simple mix of polymers is being produced. Surprisingly, these
copolymers are obtained for pairs of polymers that otherwise cannot
be polymerized into copolymers since they are incompatible or
immiscible with each other. Thus, it is believed that this
invention makes it possible to create new copolymers or graft
polymers from practically any pairs of existing polymers, and such
copolymers or graft polymers may be created with desirable
resultant physical properties.
[0011] In the present invention, novel polymer blends are prepared
through an in situ chemical interaction resulting from ultrasonic
treatment. By "in situ chemical interaction" it is meant any
chemical (i.e. non-physical or mechanical) interaction wherein at
least a portion of the polymers blended are chemically linked via a
chemical reaction. In particular, experimental evidence supports
the conclusion that this in situ chemical interaction forms
copolymers or grafted polymers at least a portion of the interface
between the blended polymers. Generally, only a fraction of the at
least two polymers blended undergo this in situ chemical
interaction.
[0012] Unexpectedly, the ultrasonic treatment of polymer blends,
during or after mixing, is found to greatly improve their
mechanical properties. The present invention also proposes
continuous and batch processes for carrying out in situ chemical
interactions without adding chemicals. It is believed that
ultrasonic treatment of the blends enhances intermolecular
interaction and makes chemical bonds between dissimilar polymers
creating a small but effective amount of copolymer or graft
copolymer without the use of any chemicals.
[0013] In general, the present invention provides a process for the
in situ chemical interaction of polymer blends, including the steps
of feeding to a pressurized treatment zone at least two polymers
selected from the group consisting of thermoplastics, thermosets,
rubbers, and liquid crystalline polymers, and ultrasonically
treating the polymer mixture in the pressurized treatment zone with
an ultrasonic wave.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic of a cross-sectional view of an
ultrasonic reactor based on a single screw extruder with one
ultrasonic horn placed at the extruder die parallel to the screw
axis.
[0015] FIG. 2 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a single screw extruder and a die with
two ultrasonic horns placed before the die in the extruder
perpendicular to the screw axis.
[0016] FIG. 3 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a single screw extruder an ultrasonic
die attachment with two ultrasonic horns placed in the die
perpendicular to its axis.
[0017] FIG. 4 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a single screw extruder having a mixing
section and an ultrasonic die attachment with two ultrasonic horns
placed in the die perpendicular to its axis.
[0018] FIG. 5 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a single screw extruder having a mixing
section and two ultrasonic horns placed before the die in the
extruder after the mixing section perpendicular to the screw
axis.
[0019] FIG. 6 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a single screw extruder with a static
mixer followed by an ultrasonic die attachment with two ultrasonic
horns placed in the die perpendicular to its axis.
[0020] FIG. 7 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a twin screw extruder with ultrasonic
die attachment having one ultrasonic horn placed at the die exit
parallel to the die axis.
[0021] FIG. 8 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a twin screw extruder with ultrasonic
die attachment having two ultrasonic horns placed in the die
perpendicular to its axis.
[0022] FIG. 9 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a twin screw extruder wherein an
ultrasonic horn cross-head die assembly is employed.
[0023] FIG. 10 is a schematic of a cross-sectional view of the
ultrasonic reactor based on a batch mixer.
[0024] FIG. 11 is a graph showing the molecular weight
distributions for treated and non-treated polymer blends of natural
rubber with styrene-butadiene rubber.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
[0025] It has been discovered that through the application of
certain levels of ultrasonic amplitudes, in the presence of
pressure and heat, an unexpected enhancement of the mechanical
properties of polymer blends can be achieved. The process of the
present invention generally entails feeding a mix of polymers
selected from thermoplastics, thermosets, rubbers and LCP's into a
pressurized treatment zone, and subjecting these mixtures, in the
molten state, to treatment with an ultrasonic wave within this
pressurized treatment zone.
[0026] Polymers designated as either rubbers, thermoplastics,
thermosets, or LCP's are generally known in the art and at least
two of any such polymers may be employed to practice the present
invention. Non-limiting examples of useful rubbers include natural
rubbers, isoprene rubbers, styrene-butadiene rubbers (SBR), butyl
rubbers, nitrile rubbers, polyurethane rubbers, fluoroelastomer
rubbers, silicone rubbers, ethylene propylene diene rubbers (EPDM),
butadiene rubbers and chloroprene rubbers. Non-limiting examples of
useful thermoplastics include polyethylenes (HDPE, LDPE, LLDPE),
polypropylenes, polyvinylchlorides (PVC), polystyrene, polyesters,
copolyesters, polyamides, polyimides, polyetheretherketones,
polysulfones, acetals, polyarylates and polyacrylates. Non-limiting
examples of useful thermosets include polyesters, polyurethanes,
and epoxy resins. Non-limiting examples of useful LCP's include
wholly aromatic polyesters.
[0027] Some non-limiting examples of particularly desirable polymer
blends that can be enhanced through practice of the present
invention include blends of polyethylene/polypropylene, HDPE/LDPE,
HDPE/LLDPE, LDPE/LLDPE, polystyrene/polypropylene,
polystyrene/polyethylene, polypropylene/EPDM, polyamide/EPDM,
natural rubber/SBR, PVC/polyurethane wholly aromatic
polyester/polyester blends, wholly aromatic polyester/rubber
blends, and blends of wholly aromatic polyesters. As is generally
known, these blends are difficult to produce because their
respective polymer components typically are immiscible.
[0028] Despite the discussion immediately hereinabove regarding
examples of useful rubbers, thermoplastics, thermosets, and LCP's,
it is to be understood that the process herein is believed to be
operable for a mixture of virtually any polymers. Thus, as stated
above, the present invention is not to be limited to any particular
mixture of polymers.
[0029] The pressurized treatment zone is preferably provided by a
continuous-type mixer that ensures that the polymer blends being
compounded and treated are adequately mixed using distributive
and/or dispersive mixing devices so as to increase the interfacial
area between the various polymers employed. Non-limiting examples
of useful continuous-type mixers include single screw extruders,
pin barrel extruders, twin screw extruders, single screw extruders
with attached static mixers, single screw extruders with mixing
sections, twin screw extruders with attached mixing sections, Buss
Ko-Kneader extruders, modular twin screw extruders, and the like.
Non-limiting examples of useful batch-type mixers include internal
mixers such as Banbury mixers, Farrel mixers, Haake mixers, and the
like.
[0030] Referring now to the drawings wherein the showings are for
purposes of illustrating the preferred embodiment of the invention
only and not for purpose of limiting the same, the Figures show the
application of ultrasonic treatment to polymer blending.
[0031] With reference to FIG. 1, a single horn embodiment of an
apparatus for carrying out the process of the present invention is
generally represented by the numeral 10. Apparatus 10 includes a
single screw extruder 12 with one ultrasonic horn 14 placed at the
extruder exit 16 parallel to the screw axis. As shown, single screw
extruder 12 includes a barrel 18, which is fed through hopper 20.
Screw 22, within barrel 18, mixes polymers fed through hopper 20
and advances the polymer mixture toward a die portion 24 and exit
16, through which the polymer mixture is extruded. A gap 26 is
provided between die portion 24 and ultrasonic horn 14.
[0032] Polymer mixtures are extruded through gap 26, between horn
14 and die portion 24, by operating extruder 12 as is generally
known in the art. As the polymer mixture is forced through gap 26,
it is subjected to significant pressure due to the narrowing of the
path through which the mixture is advanced. Additionally, as should
be generally understood from the placement of horn 14, the polymer
mixture is subjected to ultrasonic treatment proximate gap 26.
Thus, for purposes of the present invention, it is to be generally
understood that the polymer mixture is advanced through a
pressurized treatment zone and is subjected to treatment with an
ultrasonic wave within this pressurized treatment zone.
[0033] It should be noted that, while it is possible to add the
individual polymers to the hopper as separate, individual
components, the polymers to be treated may be premixed and
pelletized before addition to an ultrasonic apparatus according to
the present invention. Thus, as will be clearly appreciated in the
experimental examples hereinbelow, the polymers may be premixed in
an extruder absent any ultrasonic treatment, cooled, and thereafter
pelletized such that non-treated, pelletized polymer mixtures are
fed to the apparatus wherein the mixture is to be ultrasonically
treated.
[0034] Pressure effects the process of the present invention by
introducing volumetric compression in the molten blend, leading to
more efficient propagation of the ultrasonic waves. Thus,
generally, an increase in pressure exerted on the polymer blend
during ultrasonic treatment will tend to increase the effect of the
ultrasonic waves, while a decrease in the pressure exerted on the
polymer blend during ultrasonic treatment will tend to decrease the
effect of the ultrasonic waves. In a preferred embodiment of the
present invention, the pressure at the entrance to the treatment
zone is between about 0.6 to about 35 MPa, but lower and larger
pressures are also envisioned. Additionally, as the pressure
proximate gap 26 is dependant at least in part upon the size of gap
26, between exit 16 and horn 14, the size of gap 26 may be
optimized. In a preferred embodiment of the present invention, gap
26 is between about 0.2 to about 10 mm. Notably, the optimal size
of gap 26 may depend on such variables as amplitude, frequency,
temperature, flow rate and the nature of the specific blend, and,
therefore, the selection of an optimal size for gap 26 most likely
will need to be determined experimentally for a given process. Such
a determination through experimentation is within the ordinary
skill in the art.
[0035] As the polymer blend approaches the tip of horn 14, the
blend flows into the path of the ultrasonic waves generated by the
horn. The arrangement of the horn allows the ultrasonic treatment
to proceed in an environment not exposed to atmospheric oxygen,
thereby minimizing the amount of product degradation that might
otherwise occur. As discussed previously, gap 26 is preferably
between about 0.2 and about 10 mm, but larger and smaller gaps are
envisioned. In this condition, the polymer blend is required to
pass through the treatment zone under sufficient pressure and in
the ultrasonic wave path to ensure in situ compatibilization.
[0036] While the figures and ensuing discussion have focused in
particular on the application of an extruder to advance the
original polymer materials to a pressurized treatment zone, there
is no reason to limit the invention to such. In fact, the only
requirements essential for apparatus according to the present
invention is that they be capable of advancing material, under
pressure, toward a zone ultrasonic treatment.
[0037] Optionally, the extruder should be capable of being heated.
The heating of the extruder tends to decrease the internal pressure
and reduction of power consumption of the motor.
[0038] The addition of heat to the polymer mixture advancing
through apparatus 10 may also be necessary in some processes.
Particularly, it should be noted that the polymer mixture is to be
ultrasonically treated while in the molten state. Thus, when
necessary, heat may be added to the system to properly carry out
the invention. More particularly, the process of the present
invention is carried out at a temperature that is above the melting
temperature or glass transition temperature of the individual
polymers within the mixture. Again, various polymer mixtures will
require processes carried out at various temperatures, and operable
temperatures may need to be determined experimentally for a given
polymer mixture. Generally, the temperature at which the present
process is carried out is preferably between about 20.degree. C.
and 400.degree. C., although the process should not be limited
thereto or thereby.
[0039] The energy imparted by the ultrasonic waves and imposed on
the polymer mixture, in the presence of pressure and heat, is
believed responsible for bringing about an in situ chemical
interaction at the interface between the polymeric components,
resulting in the improvement of mechanical properties of the
polymer blends. Thus, both ultrasonic wave frequency and amplitude
are notable processing parameters.
[0040] Considerable latitude is permissible in selection the wave
frequency and amplitude of the ultrasonic treatment, and, as
suggested in the preceding, optimum conditions for particular
polymer mixtures are best determined by experimental trials
conducted on the mixtures of interest. Within such considerations,
however, it has been found that the frequency of the waves should
be in the ultrasound region, i.e., at least 15 kHz. The amplitude
of the wave can be varied from at least about 1 micron to about 100
microns, again, the exact amplitude and frequency best suited for a
particular application being readily determined by
experimentation.
[0041] While an ultrasonic reactor has been generally described so
far containing mainly a single screw extruder with a single horn,
there is no reason to limit the invention to such. As seen in FIGS.
2-8, multiple extruder combinations, mixing devices, horn
configurations, horn positioning, horn numbers, and die/horn
combinations are envisioned. There is no limit on the number of
horns and die/horn combinations other than that which is a natural
ramification of available space considerations. Additionally,
although not necessarily preferred, it should be noted that the at
least two polymers fed to any apparatus according to the present
invention may be premixed before being fed. Such a premixing step
is clearly set forth in the experimental examples provided
hereinbelow.
[0042] As seen in FIG. 2, a double-horn embodiment of an apparatus
for carrying out the process of the present invention is generally
represented by the numeral 30. Apparatus 30 includes a single screw
extruder 32, having a barrel 34 that is fed through hopper 36.
Single screw extruder 32 is equipped with two ultrasonic horns 38,
40 placed before the die 42, which is perpendicular to the axis of
screw 44. As with the previous arrangement of FIG. 1, the gaps 46,
48 between screw 44 and ultrasonic horns 38, 40, respectively, is
between about 0.2 to about 10 mm and the pressure at the entrance
to the treatment zone is between about 0.6 to about 35 MPa. As
apparatus 30 of FIG. 2. begins to make clear, there is no limit on
the position and number of horns (such as horns 38,40) in the
extruder 32.
[0043] FIG. 3 illustrates a double-horn embodiment of an apparatus
for carrying out the process of the present invention that is
generally represented by the numeral 50. Apparatus 50 includes a
single screw extruder 52, having a barrel 54 that is fed through
hopper 56, and the materials being fed are advanced by screw 58.
Apparatus 50 displays the ability to incorporate an ultrasonic die
attachment 60 with two ultrasonic horns 62, 64 positioned in die
60, perpendicular to the axis of die 60. Two ultrasonic horns 62,
64 are positioned along parallel planes to the longitudinal axis of
die 60. Ultrasonic horns 62, 64 are separated by a single gap 66,
which is defined between the opposed surfaces of horns 62, 64.
Notably, because gap 66 is between two horns 62, 64, the preferred
dimension for gap 66 is generally twice the value for the gap in
FIG. 1. Thus, a gap such as gap 66, between two opposed horns such
as horns 62, 64, is preferably between about 0.4 to about 20 mm,
although the present invention is not to be limited thereto or
thereby inasmuch as the selection of an optimal size for gap 66
most likely will need to be determined experimentally for a given
process.
[0044] In the embodiment employing single screw extruders it should
be appreciated that Buss Ko-Kneader extruders or pin barrel
extruders could alternatively be employed. Such extruders will
typically achieve a better mixing of the polymers being fed,
creating more interface between the polymers and thereby more
efficient in situ chemical interaction upon ultrasonic treatment.
Thus, single screw extruders are to be understood as including pin
barrel extruders, Buss Ko-Kneader extruders, and other extruders
containing one screw and providing efficient mixing as known in the
art.
[0045] Referring now to FIG. 4, it can be seen that extruders
employed in carrying out the present invention may optionally be
configured with a mixing section, generally represented in FIG. 4
at numeral 70. Particularly, FIG. 4 shows a double-horn embodiment
of an apparatus for carrying out the process of the present
invention that is generally represented by the numeral 50B.
Apparatus 50B is substantially identical to apparatus 50 of FIG. 3,
with like elements receiving identical numeral designations.
However, apparatus 50B includes mixing section 70, within barrel
54, around screw 58. Mixing section 70 may be a dispersive and/or
distributive mixing section, as are generally known and employed in
the art to increase the degree of mixing of the components fed to
an extruder such as extruder 52. Notably, such a mixing section 70
may be employed with any extruder previously described or
hereinafter described.
[0046] FIG. 5 illustrates a double-horn embodiment of an apparatus
for carrying out the process of the present invention that is
generally represented by the numeral 80. Apparatus 80 includes a
single screw extruder 82, having a barrel 84 that is fed through
hopper 86. The materials being fed are advanced by screw 88.
Particularly, FIG. 5 illustrates a combination of single screw
extruder 82 with mixing section 90 and two ultrasonic horns 92, 94
placed after the mixing section 90 in the extruder perpendicular to
the axis of screw 88. Gaps 96, 98 exist between screw 88 and horns
92, 94, respectively. Thus, the pressurized treatment zone wherein
the polymer mix fed to extruder 82 is subjected to ultrasonic
treatment lies within barrel 84, within and proximate gaps 96,98.
After such treatment, the polymer blend is extruded through die
100.
[0047] With reference to FIG. 6, another double-horn embodiment of
an apparatus for carrying out the process of the present invention
is designated generally by the numeral 110. FIG. 6 shows a single
screw extruder 112, having a barrel 114 that is fed through hopper
116. The materials being fed are advanced by screw 118 through die
120 and into a static mixer 122, which serves to more adequately
mix the various polymer components fed into extruder 112 before the
polymer mix is treated with ultrasonic waves. Upon exiting static
mixer 122, the polymer mix is advanced through die 124, which is
substantially like die 60 of FIG. 3, having horns 126, 128 and a
single gap 130.
[0048] FIG. 7 is a schematic representation of a twin screw
extruder embodiment of an apparatus for carrying out the process of
the present invention generally represented by the numeral 140.
Apparatus 140 includes a twin screw extruder 142, having a barrel
144 that is fed through hopper 146. The polymers being fed are
advanced by twin screws 148 through die 150 and, more particularly,
extruded through exit 152 toward gap 154 and horn 156. Notably, die
150, exit 152, gap 154, and horn 156 are interrelated substantially
as like parts in FIG. 1. Twin screw extruder 142 is desirable
because, as is generally known in the art, it provides a more
efficient mixing of the polymer components fed to hopper 146 than
does a single screw extruder.
[0049] FIG. 8 illustrates a twin screw extruder embodiment of an
apparatus for carrying out the process of the present invention
generally represented by the numeral 160. Apparatus 160 includes a
twin screw extruder 162, having a barrel 164 that is fed through
hopper 166. The polymers being fed are advanced by twin screws 168
through die 170, which is substantially identical to die 60 of FIG.
3, and includes horns 172, 174 and gap 176.
[0050] FIG. 9 illustrates a twin screw extruder reactor having a
die assembly attached thereto, the combination being generally
represented by the numeral 180. The combination extruder and die
assembly 180 includes a twin screw extruder 182 having a barrel 184
that is fed through hopper 186. The polymers being fed are advanced
by twin screws 188 toward die assembly 190 having ultrasonic horn
192 retained therein. As can be seen, the polymers enter die
assembly 190 perpendicular to the longitudinal axis of horn 192.
The polymers fill die assembly 190 to be forced, under a pressure
preferably in the range of from about 0.6 to about 35 MPa, through
gap 194, preferably having dimensions in the range of from about
0.2 mm about 10 mm, and out exit 196.
[0051] In the embodiment employing twin screw extruders it should
be appreciated that modular twin screw extruders should preferably
be employed. Modular twin screw extruders will typically achieve a
better mixing of the polymers being fed, creating more interface
between the polymers and thereby more efficient in situ chemical
interaction upon ultrasonic treatment.
[0052] In its simplest mode of operation, the reactor is fitted at
its exit bore with a die having one inlet bore and one exit bore.
However, there is no reason to limit the invention to such. It is
also within the scope of the invention that the die and/or reactor
exit bore be of constant dimensions, or varying dimensions. The
shape of the pressurized treatment zone can also be varied. It can
be a straight, angular, or helical channel. The important
consideration is that the polymers are forced to pass through the
channel or channels and are subjected to the ultrasonic
treatment.
[0053] Polymers may also be treated in batch mixers according to
the present invention, and the design considerations with respect
to such an embodiment will be readily appreciated by those of
ordinary skill in the art. To generally disclose this embodiment,
reference is now made to FIG. 10, wherein a batch mixer according
to the present invention is represented by the numeral 200.
Generally, at least one area of the wall 202 of batch mixer 200 is
adapted to receive an ultrasonic horn 204, similar, for example, to
the manner in which the barrel of the extruder is adapted to
receive an ultrasonic horn in FIG. 5. However, to provide the
pressurized treatment zone for treatment of the polymer mix within
batch mixer 200, batch mixer 200 is equipped with rotors 206, which
are distanced from the ultrasonic horn 202 so as to provide a gap
208 of from about 0.2 mm to about 10 mm, and is further equipped
with ram 210 which serves to pressurize the mixing chamber 212 as
is generally known in the art. As the polymer mix is forced through
the area proximate gap 208, the polymer is necessarily subjected to
increased pressure, preferably in the range of from about 0.6 to
about 35 MPa. It is in this pressurized treatment zone, proximate
the ultrasonic horn 204 and gap 208, that the in situ
compatibilization occurs, as within the continuous extruders
discussed above. Ultrasonic horn 204 is operated at a frequency
within the ultrasonic region, namely, at about at least 15 kHz.
[0054] In order to demonstrate the practice of the present
invention, the following examples have been prepared and tested as
described in the General Experimentation section hereinbelow. The
examples should not, however, be viewed as limiting the scope of
the invention. The claims will serve to define the invention.
GENERAL EXPERIMENTATION
Example 1
[0055] Polymer blends according to the present invention were
prepared. Polyolefins (high-density polyethylene (HDPE) or
polypropylene (PP)) and uncured rubbers (natural rubber (NR),
styrene-butadiene rubber (SBR) or ethylene-propylene-diene rubber
(EPDM)) were first mixed using a modular twin screw extruder (JSW
Labotex30) before ultrasonic treatment. The composition of each of
these polymer blends, based on weight percent, was 50:50. The feed
rate was 60 g/min. Screw speed was set at 150 rpm and zone
temperatures were set to 140.degree. C./140.degree. C./145.degree.
C./150.degree. C./150.degree. C./155.degree. C./160.degree.
C./160.degree. C. for HDPE/rubber blends and 165.degree.
C./165.degree. C./175.degree. C./180.degree. C./180.degree.
C./185.degree. C./190.degree. C./190.degree. C. for PP/rubber
blends. After the mixtures were extruded from the twin screw
extruder, the extrudates were cooled, pelletized and then dried in
a vacuum oven for 24 hours at a temperature of 60.degree. C.
[0056] After drying, the blends were ultrasonically treated using a
1.5 inch single screw extruder with ultrasonic attachment (shown in
FIG. 2). A 3 KW ultrasonic power supply was used. Two ultrasonic
horns vibrate longitudinally with a frequency of 20 kHz at
amplitude 6 and 10 .mu.m. The temperature of the extruder barrel
was 150.degree. C. for HDPE/rubber blends and 190.degree. C. for
PP/rubber blends. The feed rate was 0.63 g/sec. Screw speed was 20
rpm. The gap between the horn and screw shaft was set at 2 mm.
[0057] The compression molding of sheets (127.times.127.times.2
mm.sup.3) was performed using an electrically heated compression
molding press (Wabash). The mold was at a temperature of
160.degree. C. for HDPE/rubber blends and 180.degree. C. for
PP/rubber blends and under a pressure of 13.8 MPa that was
maintained for 5 minutes. The samples were kept under compression
and cooled in water to maintain the overall dimensional stability
and flatness of the sheets.
[0058] An Instron tensile tester (model 5567) was used for the
tensile property measurements. All tests were performed at room
temperature with a crosshead speed of 500 mm/min. Young's modulus
was measured at 3% strain.
[0059] Results for the various blends produced through the above
experimentation are displayed in Tables 1 through 5.
Example 2
[0060] An NR/SBR blend was prepared by ultrasonic treatment. The
NR/SBR blend was first prepared on a two-roll mill (Dependable
Rubber Machinery Co.) at 50.degree. C. The rubbers were added to
the nip in the rolls and masticated for 5 minutes. The composition
of NR/SBR blend was 50/50 wt. %.
[0061] The blend was then ultrasonically treated in a 1.5 inch
single screw extruder with an ultrasonic die attachment with one
horn (shown in FIG. 1). The temperature of the extruder barrel was
set at 120.degree. C. The gap between the die and horn was set at
2.54 mm. The flow rate was 0.63 g/s. The ultrasonic treatment was
carried out at a frequency of 20 kHz and at amplitudes of 5 and 7.5
.mu.m.
[0062] The untreated and ultrasonically treated NR/SBR blends were
compounded on a two-roll mill (Dependable Rubber Machinery Co.) at
50.degree. C. with 2phr of sulfur, 5phr of zinc oxide, 1phr of
stearic acid, and 1.1phr of CBS
(N-cyclohexylbenzothiazole-2-sulfenamide). The blends were added to
the nip in the rolls and masticated for 1 minute. The ingredients
were then slowly added to the rolling bank followed by alternating
cuts for 6 minutes to achieve a homogenization of the rubber
constitution.
[0063] The compression molding of slabs (127.times.127.times.2
mm.sup.3) was performed using an electrically heated compression
molding press (Wabash) at 160.degree. C. The cure time was
determined based on the time to achieve the maximum torque on the
cure curve measured by a Monsanto oscillating disc rheometer
according to ASTM D2084. The torque-time curve was measured at
160.degree. C.
[0064] An Instron tensile tester (model 5567) was used for the
tensile property measurement according to ASTM D412 (type C). All
tests were performed at room temperature with a crosshead speed of
500 mm/min.
[0065] The results for the NR/SBR blend herein under study are
displayed in Table 6.
Discussion
[0066] As is evident from Tables 1-5, ultrasonic treatment of
polymer (plastic/rubber) blends greatly enhanced their mechanical
properties. Ultrasonic treatment significantly increased tensile
stress, elongation at break, Young's modulus and toughness of each
blend as compared to the untreated blend. In Table 6, tensile
stress, elongation at break, and toughness of the rubber/rubber
blend were improved by ultrasonic treatment.
[0067] Without wishing to be bound by any theory, the improved
mechanical properties typically observed, as shown experimentally
hereinabove, are believed to result from an in situ chemical
interaction at the interface between dissimilar polymers and the
vicinity thereto during a very short time (in the order of few
seconds) of ultrasonic treatment under high pressures and
temperatures. This chemical interaction is experimentally supported
as being a chemical (i.e. non-physical or mechanical) interaction
wherein at least a portion of the polymers blended are chemically
linked via a chemical reaction that is not hydrogen bonding. In
particular, experimental evidence supports the conclusion that this
in situ chemical interaction forms copolymers or grafted polymers
at a portion of the interface between the blended polymers. This
chemical interaction occurs rapidly, in a very short time, on the
order of seconds. Generally, only a fraction of the at least two
polymers blended undergo this in situ chemical interaction. It is
believed that these copolymers or grafted polymers, created at the
interface and the vicinity thereto lead to the improved adhesion
between two dissimilar polymers and also dispersion of polymers in
the blends.
[0068] Experimental results support the belief that copolymers or
grafted polymers are created through the process of the present
invention. Particularly, Table 7 shows the results of an extraction
experiment in which samples of ultrasonically treated
polypropylene/natural rubber mixtures (the test mixtures) were
compared with a non-treated polypropylene/natural rubber mix (the
control mixture). In the extraction experiment, three mixtures of
50% polypropylene (PP) and 50% natural rubber (NR) were tested. The
control mixture was not ultrasonically treated, while one test
mixture was treated with ultrasonic waves with amplitude of 6
.mu.m, and the second test mixture was treated with ultrasonic
waves of 10 .mu.m. After treatment (or non-treatment in the case of
the control mixture), each mixture was subjected to soxhlet
extraction, using benzene as a solvent to dissolve any natural
rubber present in the mixture.
[0069] As table 7 shows, 49.8% (approx. 50%) of the control mixture
was not extracted, showing that the natural rubber content was
unchanged as was expected inasmuch as the control mixture was not
treated. However, 56.1% of the test mixture treated at 6 .mu.m was
not extracted, and 54.1% of the test mixture treated at 10 .mu.m
was not extracted, supporting the conclusion that a fraction of the
polypropylene and natural rubber polymers within the 50/50 PP/NR
chemically interacted such that the benzene could not extract that
fraction. These results, coupled with the increase in mechanical
properties shown in Table 1 for ultrasonically treated PP/NR
mixtures, supports the conclusion that copolymers or grafted
polymers were created through the process of the present invention,
although the present invention is not limited to or by this theory.
Additionally, as seen in FIG. 11, natural rubber and
styrene-butadiene rubber mixtures exhibit a broadening of molecular
weight distributions when treated with ultrasonic waves. The
increase in the high molecular weight tail also supports the
conclusion that copolymers or grafted polymers are formed between
the natural rubber and styrene butadiene rubber within the mix,
although, again, the present invention is not to be limited to or
by this theory.
1TABLE 1 PP/NR (50/50 wt. %) blends Tensile Stress, Elongation at
Young's Toughness, MPa break, % Modulus, MPa MPa Untreated 8.39
38.9 191.0 2.99 Treated (6 .mu.m) 11.27 111.7 250.0 12.19 Treated
(10 .mu.m) 10.60 126.8 215.0 13.19
[0070]
2TABLE 2 PP/EPDM (50/50 wt. %) blends Tensile Elongation Stress, at
Young's Modulus, Toughness, MPa break, % MPa MPa Untreated 9.87
29.1 229.0 2.68 Treated (6 .mu.m) 10.51 87.6 261.0 9.00 Treated
10.48 121.2 278.0 12.53 (10 .mu.m)
[0071]
3TABLE 3 HDPE/NR (50/50 wt. %) blends Tensile Stress, Elongation at
Young's Toughness, MPa break, % Modulus, MPa MPa Untreated 4.92
189.0 75.1 8.17 Treated (6 .mu.m) 5.71 300.6 126.5 16.00 Treated
5.78 299.1 127.0 16.35 (10 .mu.m)
[0072]
4TABLE 4 HDPE/EPDM (50/50 wt. %) blends Tensile Stress, Elongation
at Young's Toughness, MPa break, % Modulus, MPa MPa Untreated 4.74
88.2 103.0 4.24 Treated 4.78 116.0 109.0 5.76 (6 .mu.m) Treated
4.84 147.8 125.0 7.62 (10 .mu.m)
[0073]
5TABLE 5 HDPE/SBR (50/50 wt. %) blends Tensile Stress, Elongation
at Young's Toughness, MPa break, % Modulus, MPa MPa Untreated 5.33
15.4 59.0 0.59 Treated 5.46 28.7 101.0 1.32 Treated 5.58 32.5 129.0
1.61 (10 .mu.m)
[0074]
6TABLE 6 NR/SBR (50/50 wt. %) blends Tensile Elongation at Modulus
at 100% Toughness, Stress, MPa break, % strain, MPa MPa Untreated
2.89 378.4 0.89 5.20 Treated 4.41 522.1 0.70 8.37 (6 .mu.m) Treated
7.82 601.7 0.67 12.73 (10 .mu.m)
[0075]
7TABLE 7 PP/NR Extraction Experiment Ultrasound Amplitude 0 .mu.m 6
.mu.m 10 .mu.m Unextracted Fraction 49.8 56.1 54.1 (wt. %)
[0076] While the best mode and preferred embodiment of the
invention has been set forth in accord with the patent statues, the
scope of this invention is not limited thereto, but rather is
defined by the attached claims. Thus, the scope of the invention
includes all modifications and variations that may fall within the
scope of the claims.
* * * * *