|Title of Invention||
"A COMPOSITION HAVING IMPROVED TRIBOLOGICAL PROPERTIES"
|Abstract||Internally lubricated polymer compositions containing a styrene- and/or polyphenylene ether-containing polymer, an olefin-containing polymer, and a compatibilizer are provided. The olefin-containing polymer, which is present in the compositions in about 3 to about 30 weight percent, provides internal lubrication and improves the tribological properties of the compositions compared with the styrene or polyphenylene ether-containing polymer alone, as determined by wear measurements. Preferred compositions exhibit wear factors less than about 130 x 10-11 mm5/Pa-m. A preferred composition includes a blend of polystyrene/polyphenylene ether, linear low density polyethylene, and styreneethylene-butadiene-styrene. Methods are also provided for improving tribological properties of styrene- and/or polyphenylene ether-containing base polymers by incorporating into the base polymers at least one olefin-containing polymer and at least one compatibilizer, or by incorporating at least one substantially halogen-free internal lubricant.|
|Full Text||COMPOSITIONS CONTAINING POLYPHENYLENE ETHER AND/OR
POLYSTYRENE HAVING IMPROVED TRIBOLOGICAL PROPERTIES AND
METHODS FOR IMPROVING TRIBOLOGICAL PROPERTIES OF
POLYPHENYLENE ETHER AND/OR POLYSTYRENE COMPOSITIONS
BACKGROUND OF THE INVENTION
Traditionally, wear systems utilize external lubricants, such as oil or grease, to
increase the wear resistance and to reduce frictional losses between moving
contacting surfaces of components in tribological systems. However, such external
lubricants often must be replaced periodically and may be unevenly distributed over
the wear surface, resulting in increased cost and inefficiency of the wear system.
Additionally, in some areas, such as food processing and photocopying, in which
product contamination is a concern, traditional external lubricants,may be undesirable.
Therefore, in many wear systems, it may be desirable to replace or eliminate external
lubricants by using internal lubricants in polymeric components to improve the
tribological properties (such as wear resistance and friction resistance). Internal
lubricants can be used to reduce coefficients of friction between polymeric and
metallic surfaces, increase wear resistance, improve flow characteristics, and enhance
properties of the polymer, such as knitting and wetting. The use of an internal
lubricant can either eliminate the need for an external lubricant or provide improved
part life in an application mat cannot tolerate an external lubricant. Commonly used
internal lubricants include waxes, fatty acids, metal stearates, aramid, silicone,
graphite, and molybdenum disulfide. Additionally, certain fluoropolymers are known
to contribute low coefficients of friction in certain polymers. For example,
polytetrafluoroethylene (PTFE), which has a very low coefficient of friction and
exhibits favorable lubricant properties, is a commonly used internal lubricant for
many compounds and base polymers.
However, in some systems, it may be desirable to utilize a composition free of PTFE.
For example, some applications require materials which are non-halogenated, and
thus PTFE should be avoided. PTFE is also known to adversely affect the impact
properties of some polymer composites, which would preclude the use of such a
compound in such applications in which impact strength is of increased importance.
Finally, PTFE is generally more expensive than base polymers in which it is
compounded, in which case the level of benefit imparted by the PTFE may not justify
the added expense. However, since some level of internal lubrication may still be
desirable, alternatives to PTFE are needed.
Methods for using polyolefins as internal lubricants to improve the tribological
properties of Various types of polymer composites are known. Such composites
include polyamide/ polypropylene blends and polycarbonate compositions, including
polycarbonate/polyolefin blends. However, there remains a need in the art for a PTFE
replacement which will function as an internal lubricant for polyphenylene ether
and/or styrene-containing compositions and is demonstrated to improve the
tribological properties of such compositions, yet exhibits none of the disadvantages of
PTFE outlined above,
BRIEF SUMMARY OF THE INVENTION
The invention includes a composition comprising: (a) a base polymer selected from
the group consisting of a polymer comprising styrene and a polymer comprising
polyphenylene ether; (b) a polymer comprising olefin for providing internal
lubrication; and (c) a compatibilizer;
wherein the composition exhibits improved tribological properties in comparison with
the base polymer alone.
The invention also includes a molded article prepared from a composition comprising
(a) a base polymer selected from the group consisting of a polymer comprising
styrene and a polymer comprising polyphenylene ether; (b) a polymer comprising
olefin for providing internal lubrication; and (c) a compatibilizer; wherein the
composition exhibits improved tribological properties in comparison with the base
A flame retardant article is also provided by the invention. The article is prepared
from a composition comprising (a) a base polymer selected from the group consisting
of a polymer comprising styrene and a polymer comprising polyphenylene ether; (b) a
polymer comprising olefin for providing internal lubrication; (c) a compatibilizer; and
(d) a flame retardant; wherein the composition exhibits improved tribological
properties in comparison with the base polymer alone.
A method of improving a tribological property of a base polymer wherein the base
polymer is selected from the group consisting of a polymer comprising styrene and a
polymer comprising polyphenylene ether is also included in the invention. The
method comprises providing at least one polymer comprising olefin and at least one
compatibilizer to the base polymer to form a composition.
A further method of improving a tribological property of a base polymer selected
from the group consisting of a polymer comprising styrene and a polymer comprising
polyphenylene ether is also provided herein. The method comprises providing at least
one substantially halogen-free internal lubricant to the base polymer to form a
The invention also provides a method of improving the wear resistance of a base
polymer in a dry, smooth contact sliding tribological wear system, wherein a surface
of the base polymer bears against another surface causing friction. The method
comprises: (a) providing a base polymer selected from the group consisting of a
polymer comprising styrene and a polymer comprising polyphenylene ether; (b)
providing a polymer comprising olefin to the base polymer; (c) providing a
compatibilizer to the base polymer; and (d) melt mixing the base polymer, the
polymer comprising olefin, and the compatibilizer to form a composition. The
composition has an increased wear resistance compound to the base polymer and a
wear factor of less than about 130 x 105 mm5/Pa-m in a tribological system.
Finally, the invention includes a method of providing an internal lubricant to a base
polymer wherein the base polymer is selected from the group consisting of a polymer
comprising styrene and a polymer comprising polyphenylene ether. The method
comprises providing at least one polymer comprising olefin and at least one
compatibilizer to the base polymer to form a composition.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The foregoing summary, as well as the following detailed description of preferred
embodiments of the invention, will be better understood when read in conjunction
with the appended drawings. For the purpose of illustrating the invention, there are
shown in the drawings embodiments which are presently preferred. It should be
understood, however, that the invention is not limited to the precise arrangements and
In the drawings:
Fig. 1 is a graphical representation of the wear rate of several compositions of the
invention measured in real time; and
Fig. 2 is a graphical representation of the wear rate of several additional compositions
of the invention measured in real time.
DETAILED DESCRIPTION OF THE INVENTION
An internally lubricated polymer composition is provided which may be used in
tribological wear systems, particularly those in which the tribological system includes
a component comprising styrene or based on a styrene monomer and/or a component
comprising polyphenylene ether (PPE). The use of such compositions reduces or
eliminates the need for an external lubricant, while providing a halogen-free,
relatively inexpensive alternative to PTFE-lubricated styrene compositions and
reducing frictional losses. The internally lubricated compositions exhibit reduced
coefficients of friction and lower wear factors (better wear resistance) in
polymeric/metallic tribological systems.
The compositions may be used to fabricate contacting components for tribological
systems, such as those typically found in machinery or household appliances. The
term "tribological" may be understood to relate to wear and friction, which may be
measured as described in more detail below.
In a typical tribological wear system, the surface of a polymeric composite is brought
to bear against a dry or unlubricated surface, including metallic surfaces, such as steel.
For friction and wear testing of the present invention, 1141 cold rolled steel was used
as the metallic surface. While components formed from the polymeric compositions
of the present invention are preferably used under dry conditions, the components
may also be used under wet conditions or in contact with a wide variety of materials
such as other polymers, etc.
The primary wear mechanism of polymeric components in dry, smooth-contact
tribological wear systems under moderate load conditions is adhesive wear. As the
polymeric and metal components are brought into loaded moving (e.g., sliding)
contact, the surface of the polymeric composite shears and spreads to form a
polymeric film which becomes chemically attached to the surface of the metal
component, i.e., a transfer film is formed on the surface of the metal component. The
adhesive wear is influenced by two factors, namely the amount of work being done in
the polymeric surface and the intrinsic durability of the sliding interface. The wear
factor K, or rate of decay of the polymeric material surface, is determined by the rate
of attrition and subsequent replacement of the transfer film as new layers of the
surface of the polymeric material are abraded by sliding contact with the metal
component. However, wear properties of materials in tribological systems are
generally unpredictable based on other mechanical properties of the polymers.
The present polymeric compositions may be used to form tribological wear
components having high wear resistance (low wear factor) and low coefficient of
friction for use in a wide variety of sliding components.
In one preferred embodiment, the present composition preferably comprises at least
three primary components: a base polymer comprising styrene and/or polyphenylene
ether, a polymer comprising olefin, which provides internal lubrication, and a
compatibilizer. The resulting internally lubricated composition exhibits improved
tribological properties compared with the base polymer alone.
The composition preferably contains a base polymer comprising polyphenylene ether,
and in an alternate embodiment may comprise a styrene-containing polymer in
addition to or instead of polyphenylene ether. The styrene-containing polymer may
be any homopolymer or copolymer based on a styrene monomer and derivatives
thereof, including, but not limited to, polystyrene, polyacrylonitrile-butadiene-styrene
(ABS), polystyfene-acrylonitrile (SAN), or blends of any of the foregoing materials
with other polymers such as preferably polyphenylene ether. The most preferred base
polymer is a polyphenylene ether/polystyrene blend, such as those commercially
available as Noryl® from General Electric. Such blends are preferred due to high
temperature performance, chemical resistance, and strength. However, depending on
the particular application, an alternative base polymer or blend of polymers may be
The olefin-based component which provides internal lubrication for the
polyphenylene ether and/or styrene-containing base polymer may be any polymer
which would be considered a polyolefin by those skilled in the art. Preferred olefinbased
polymers include, but are not limited to high density polyethylene (HDPE), low
density polyethylene (LDPE), linear low density polyethylene (LLDPE),
polypropylene, and ethylene-propylene copolymers. Other olefin-based polymers
within the scope of the invention include ethylene-vinyl acetate, ethylene-vinyl
alcohol, ethylene-acrylic acid, ethylene-cycloolefiri copolymers, and polybutylenes,
such as polyisobutylene and polybut-1-ene. The most preferred olefin-comprising
polymer is LLDPE because it has been shown to result in compositions with
particularly low wear factors. However, depending on the particular application, an
alternative olefin-based polymer may be more desirable.
Finally, one or more compatibilizers for use in the compositions are preferably
copolymers formed from both styrene and olefin monomers, such as polystyreneethyl
ene-butadiene-styrene (SEES), styrene-ethylene interpolymers, polystyreneethylene-
propylene (SEP), and styrene-butadiene rubber. However, other
compatibilizers known to those in the art or to be developed would also function
within the scope of the invention. The compatibilizer functions to make the
compositions more moldable, and also allows them to retain a higher proportion of the
styrene- or polyphenylene ether-containing base polymer's properties, such as impact
strength. The preferred compatibilizer is SEBS, but depending on the particular
application, an alternative compatibilizer may be more desirable.
The polymer comprising olefin is preferably present in the compositions in an amount
of about 3 to about 30 weight percent based on the total weight of the compositions,
and about 5 to about 15 weight percent in a more preferred embodiment. If the
amount of olefin-containing polymer becomes too low, the wear factor of the
compositions may be undesirably high, and thus the compositions may not be
appropriate for use in some wear applications. Alternatively, higher percentages of
polymer containing olefin may result in compositions which exhibit properties more
like the olefin-containing polymer than the polyphenylene ether or styrene-containing
base polymer, which may not be more desirable for wear applications than the
preferred compositions, and may result in undesirable mechanical properties.
The compatibilizer is preferably present in the compositions in an amount of about 1
to about 20 weight percent, and more preferably about 3 to about 10 weight percent of
the total weight of the compositions, depending on the amount of olefin-containing
polymer in the compositions and on the particular base polymer or polymers used in
the compositions. The incorporation of higher amounts of compatibilizer tends to
increase the viscosity of the compositions, which may be desirable or undesirable
depending on the particular application. The ratio of olefin-containing polymer to
compatibilizer is preferably about 0.5:1 to about 10:1, and more preferably about 1:1
In addition to these three components, the compositions may further include standard
additives. Typical performance enhancements obtained by these additives include but
are not limited to reinforcement, flame retardance, thermal and/or electrical
conductivity, dimensional stability, flow, and impact modification. It is preferred that
such additives do not materially affect the tribological properties of the compositions.
Typical additives include fillers, reinforcing agents, additional lubricants, coloring
agents such as tints, processing aids, impact modifiers, plasticizers, slip agents,
ultraviolet absorbers or stabilizers, flame retardants, mold release agents, flow
modifiers and/or heat stabilizers. Specific examples of such additives include carbon
fiber, carbon powder, glass fiber, glass powder, glass beads, aramid fiber,
polyethylene terephthalate fiber, stainless steel fiber, ceramic fiber, ceramic powder,
wollastonite, talc clay, mica, pigments, stearates, waxes, molybdenum disulfide and
various oils, including silicone oil. Preferably, additives are minimized, particularly
those which may have any significant detrimental effect on wear and/or frictional
properties of the compositions.
A preferred composition according to the invention comprises a flame retardant, and
such a composition may be used to prepare a flame retardant article. The flame
retardant for inclusion in the composition may be a halogen-containing flame
retardant, such as -decabromodiphenylether, tetrabromobisphenol A, or a brominated
oligomer or polymer; a phosphorus-containing flame retardant, such as red
phosphorus, a phosphate, a phosphonate, or, a phosphoric acid ester such as resorcinol
diphosphate; a nitrogen-containing flame retardant such as melamine cyanurate; or a
combination of one or more of these types of flame retardants, such as melamine
polyphosphate. These specific flame retardants are only exemplary and .other flame
retardants known in the art or to be developed would also be appropriate for use in the
compositions according to the invention. Preferred flame retardants are
nonhaloganted flame retardants, such as resorcinol diphosphate and bisphenol A
diphosphate. The flame retardant is preferably included in the composition in an
amount of about 3 to 30% by weight, and more preferably about 5 to 15% by weight
of the total weight of the composition.
In order to form the compositions having improved tribological properties, the
components may be blended or melt mixed in any suitable manner known to those in
the art, such as by melt-mixing using any appropriate thermoplastic processing
apparatus, blender, mixer and the like, or by melt processing. Alternatively, blending
may be accomplished using static or screw/auger-type mixing, for example.
Preferably, the components are combined in a twin-screw compounding extruder,
such as are commercially available from Werner Pfleiderer or a Buss kneader from
Buss (America) Inc. of Elk Grove Village, HI.
The compositions according to the invention may also be formed into molded articles
using any suitable method known to those in the art including extrusion molding,
compression molding, injection molding, co-extrusion, extrusion/compression, and
the like, either in raw or pelletized form. The components may also be blended with
other molding pellets or powders of other thermoplastics.
The tribological properties of the polymer compositions according to the invention
may be assessed by evaluating the dynamic friction and wear values as follows.
Typically, the friction and wear testing are determined according to a standard thrust
washer dry sliding wear test method similar to that described in ASTM D3702.
Briefly, a polymeric sample is mated against a steel thrust washer in an LRI-la
Automated Tribometer (Lewis Research, Inc.), which collects continuous data and
observes the wear, friction, and temperature of the tribological system. The value
obtained for the friction coefficient will depend on both the load (pressure or
perpendicular force) and the velocity, which correspond to a certain pressure-velocity
(PV) value. This value contributes to the wear factor, also known as a K factor. The
test can be of varying length, but typically runs for longer than 24 hours, and can run
for seven days or more.
To analyze the tribological properties of the compositions according to the present
invention, wear tests were conducted at a contact pressure of 275.8 kPa and a test
speed of 0.254 m/s at room temperature (approximately 23 °C) against a mating metal
surface of 1141 cold rolled steel. Each sample was run for 75 hours and the relevant
measurements recorded. Wear factors (represented by K, in units of mm5/Pa-m) for
each composition were based on overall wear rates and represent the system wear
rather than the wear of either individual component.
The wear values for the compositions according to the present invention as
determined by the above described test are less than about 130 x 105 mm5/Pa-m, and
more preferably less than about 65 x 105 mm-YPa-m. The dynamic coefficient of
friction of the compositions is typically less than about 0.5. In comparison,
unlubricated 100% polystyrene and 1:1 polystyrene/polyphenylene ether blend both
exhibit a wear value of approximately 3000 x 10"11 mm5/Pa-m under the same
conditions, and dynamic coefficients of friction of 0.73 and 0.88, respectively.
However, the same PPE/PS blend containing a traditional internal lubricant, PTFE,
would exhibit a wear factor of approximately 130 x 10"11 mm5/Pa-m, comparable to
the wear factors of the compositions according to the invention. It can thus be seen
" that the present compositions function as an excellent, nori-halogenated alternative to
PTFE as an internal lubricant for styrene- and/or polyphenylene ether-containing
In addition to the compositions, the invention also provides a method of improving a
tribological property of a base polymer comprising polyphenylene ether and/or
styrene. The method comprises providing at least one polymer comprising olefin and
at least one compatibilizer to the base polymer to form a composition. The nature and
relative amounts of the polyphenylene ether- and/or styrene-containing polymer, the
olefin-containing polymer, and the compatibilizer may be any as previously
described. By incorporating the olefin-containing polymer and the compatibilizer, the
resulting composition exhibits a wear factor less than about 130 x 10"11 mm5/Pa-m
and more preferably less than about 65 x 105 mm5/Pa-m. Additional components
may also incorporated into the composition, such as the additives previously
described, provided it is preferred that for wear applications the tribological properties
are not adversely affected. The composition may be prepared by any known method,
such as those previously described.
A second method of improving a tribological property of a base polymer comprising
styrene and/or polyphenylene ether according to the invention comprises providing at
least one substantially halogen-free internal lubricant to the base polymer to form a
composition. The substantially halogen-free internal lubricant is preferably, but not
limited to an olefin-containing polymer as previously described, and preferably is
incorporated into the composition in an amount of about 3 to about 30 weight percent,
and more preferably about 5 to about 15 weight percent of the composition based on
the total weight of the composition. In a preferred embodiment, the method further
comprises providing a compatibilizer, such as those described previously, into the
composition. The preferred amount of compatibilizer is about 1 to 20 weight percent,
and more preferably about 3 to about 10 weight percent based on the total weight of
the composition, and the ratio of olefiri-containing compound to compatibilizer is
preferably about 0.5:1 to about 10:1. The resulting composition preferably exhibits a
wear factor as previously described.
The invention also provides a method of improving the wear resistance of a base
polymer in a dry, smooth contact sliding tribological wear system, wherein a surface
of the base polymer bears against another surface causing friction and wear. The
method comprises: (a) providing a base polymer comprising polyphenylene ether
and/or styrene; (b) providing a polymer comprising olefin to the base polymer; (c)
providing a compatibilizer to the base polymer; and (d) melt mixing the base polymer
comprising polyphenylene ether and/or styrene, the polymer comprising olefin, and
the compatibilizer to form a composition. The composition has an increased wear
resistance and a wear factor of less than about 130 x 105 mm5/Pa-m in a tribological
system. The components of the composition and their preferred weight percentages in
the composition are as previously described. The tribological systems intended herein
are also described above. Wear resistance is improved in the method and the
tribological properties of the composition are improved over the base polymer alone
(lower K factor and lower coefficients of friction).
Finally, the invention relates to a method of providing an internal lubricant to a
styrene-and/or polyphenylene ether-containing base polymer. The method comprises
providing at least one polymer comprising olefin and at least one compatibilizer to the
base polymer. The styrene- and/or polyphenylene ether-containing polymer, olefincontaining
polymer, and compatibilizer and their preferred amounts and ratios are as
previously described. The resulting wear factor is preferably less than about 130 x 10"
5mm5Pa-m, and more preferably less than about 65 x lO5mm5Pa-m.
The invention will now be described in further detail with respect to the following
Eight compositions were prepared by blending a base polymer containing a blend of
1:1 polyphenylene ether/styrene, a polyolefin, and a compatibilizer. The base
polymer was Noryl®731 or Noryl®EN185 (commercially available from General
Electric), in which the "EN 185" blend contains a flame retardant. As a
compatibilizer, polystyrene-ethylene-butadiene-styrene (SEES) grade Kraton™
G2705 or G1651 (commercially available from Kraton Polymer) was included.
Finally, the polyolefin was either a linear low density polyethylene (LLDPE)
(Petrothene GAS 18-07, commercially available from Equistar) or a
polyethylene/polypropylene (PE/PP) copolymer (Cl 05-02, commercially available
from Dow Chemical). Each composition contained 7.5% or 15% by weight of total
polyolefin and compatibilizer and a 2:1 ratio of polyolefin to compatibilizer. The
relative amounts of the components of each composition, denoted A-H, are shown in
The compositions were prepared by hand blending and were extruded using a Werner
Pfleiderer ZSK-40™ twin screw-extruder and subsequently pelletized. The extruded
compositions were injection molded into 3.175 mm thick plaques from which pails
were machined for testing. The machined parts were approximately 28.6 mm outer
diameter, with an outer annular region having an inner diameter of approximately
22.9 mm which was the contact surface for testing. The friction and wear testing of
each specimen was determined .according to the thrust washer dry sliding wear test
method using the parameters described previously. The results of the friction and
wear loss testing, as well as other physical properties of the compositions, are set forth
in Table 1.
It can be seen from the data that the overall wear factor for each composition ranged
from 41 to 157 x lO5mn5/Pa-m, and the dynamic coefficient of friction ranged from
0.309 to 0.443. Lower wear factors were obtained using LLDPE (41 to 56 x 105
mm-VPa-m) rather than polyethylene/polypropylene (PE/PP) copolymer as the
polyolefin. For comparison, the wear factor of pure Noryl® 731 is 3900 x 105
mm5/Pa-m, demonstrating the effectiveness of the polyolefin internal lubricant
according to the invention.
The LRI-la Automated Tribometer is additionally capable of plotting the wear
performance of a composition in real time. The slope of the line is used to calculate
the wear factor, such as those cited previously. The resulting wear data are shown
graphically in Fig. 1.
The composition was prepared by the method described above using 100%
polystyrene as the base polymer, 15% SEES (Kraton G1651) as the compatibilizer,
and 10% LLDPE as the polyolefin. The wear data for the resulting composition are
shown in Table 1 and Fig. 1. The wear factor for composition I was 59 x 105
mm5/Pa-m, compared with 3900 x 10"11 mms/Pa-m for pure polystyrene. This
demonstrates that tribological properties of pure polystyrene can be improved by
incorporating an appropriate polyolefin and compatibilizer.
Eight additional compositions were prepared by the method described above using a
1:1 polyphenylene ether/styrene blend as the base polymer (Noryl®731), SEBS
(Kraton™ G1651) as the compatibilizer, and LLDPE (Petrothene GAS 18-07) as the
polyolefin. Each composition contained between 2 and 30% by weight of polyolefin,
0 to 6% by weight compatibilizer, and a ratio of polyolefin to compatibilizer which
ranged from 30:0 to 2:1. The relative amounts of .the components of each
composition are shown in Table 2. The properties were assessed as previously
described and are tabulated in Table 2 and shown graphically in Fig. 2.
Samples J, L, M, and N, which all contain 10% polyolefin and increasing
concentrations of compatibilizers from 0 to 5 weight %, all exhibit favorable wear
factors between 16 and 105 x 10"^ mm5/Pa-m. These samples also demonstrate that
an increase in the concentration of compatibilizer improves the impact strength, as
evidenced by the increase in Notched Izod values. Specifically, the Notched Izod
impact value of Noryl®731 is 215 J/ra. In comparison, sample J, which contains no
compatibilizer, has a notched Izod impact value of 106.8 J/m. However, as the
concentration of compatibilizer increases, the notched Izod impact value increases as
well, such that sample N, which contains 5% compatibilizer, exhibits an impact value
of 184.2 J/m, approaching that of the base polymer. Accordingly, the presence of the
compatibilizer in the composition helps to retain the properties of the base polymer.
A flame retardant composition "R" was prepared by the method described above
using Noryl®PPE (containing no styrene) as the base polymer, SEBS (Kraton™
O1651) as the compatibilizer, and LLDPE (Petrothene GAS 18-07) as the polyolefm.
The Noryl material contains a flame retardant (resorcinol diphosphate (RDP),
commercially available from Akzo Nobel as Fyrolflex). The weight percentages of
each of the components are shown in Table 2. The properties were assessed as
previously described and are included in Table 2: It can be seen that a favorable wear
factor of 29 x 10"^ mm^/Pa-m was obtained, demonstrating that polyolefin is
effective at providing internal lubrication to polymer compositions based solely on
polyphenylene ether. Further, this example demonstrates that in some situations, it
may be desirable to include more compatibilizer than olefin-containing polymer in the
composition. This example further demonstrates that incorporation of additives such
as a flame retardant may achieve additional properties without reducing the
effectiveness of the olefin lubricant.
COMPARATIVE EXAMPLE 1
As a comparison, a sample of a polypropylene/polyphenylene ether blend, in which
polypropylene is the predominant component (commercially available as Noryl®PPX
7110 from General Electric) was evaluated and was found to exhibit a wear factor of
234 x 10"^ mm5/Pa-m and a dynamic coefficient of friction of 0.599 under the same
conditions. It can also be graphically observed in Figure 2 that the slope for the
polypropylene/ polyphenylene ether blend is higher than the examples of the
invention, indicating a higher wear factor.
EXAMPLES S and T
Two samples were prepared as previously described which contained Nory5Sl as
the styrene polymer, LLDPE (Petrothene GA818-07), and SEES (Kraton™ G1651).
In these comparative examples, only 2% of the polyolefin was included. The
resulting compositions exhibited higher wear factors of 1239 and 1386 x 10"11
mm5/Pa-m, demonstrating that the relatively low concentration of polyolefin did not
improve the tribological properties as well as did greater amounts. However, the
properties still compare favorably with 3900 x 10"11 mm5/Pa-m for pure polystyrine.
From all of the examples, it can be seen that the choice of olefin-containing polymer
significantly affects the wear properties of the compositions. Though these samples
vary in wear properties, it is clear that there is a difference in performance between
the compositions containing PE/PP copolymer and those including LLDPE.
Interestingly, in other blends, particularly nylon composites, it has been observed that
the PE/PP copolymer provides excellent performance, with wear factors lower than
those observed with the samples according to the present invention. However, as
shown by these examples, LLDPE is a superior internal lubricant for systems
containing polyphenylene ether and/or styrene.
It may also be observed that an increase in additive level does not necessarily result in
a performance improvement. For example, in samples A and C, a total additive
loading of 7.5% achieves the same wear factor as a sample containing 15% additive,
and also gives a lower dynamic coefficient of friction. In considering Fig. 1, although
it might be assumed at first glance that sample A is superior, it is the slope of the
curve, rather than the position, which is used to determine the wear factor, and sample
C performs equally well after an initial break-in period, which is common in many
materials. Additionally, sample R, which contains only 7.5% additive, performs as
well as those examples with higher additive loadings, even with the presence of a
It will be appreciated by those skilled in the art that changes could be made to the
embodiments described above without departing from the broad inventive concept
thereof. It is understood, therefore, that this invention is not limited to the particular
embodiments disclosed, but it is intended to cover modifications within the spirit and
scope of the present invention as defined by the appended claims.
1. A composition having improved tribological properties, comprising:
(a) a base polymer selected from the group consisting of a polymer comprising styrene and a polymer comprising polyphenylene ether;
(b) a polymer for providing internal lubrication; and
(c) a compatibilizer;
characterized in that the polymer for providing internal lubrication is linear low density polyethylene, wherein the composition has a wear factor of less than 65 x 10"11 mm5/Pa-m.
2. The composition as claimed in claim 1, wherein the polymer consisting essentially of linear low density polyethylene comprises 5 to 30 weight percent of the composition based on a total weight of the composition.
3. The composition as claimed in claim 2, wherein the polymer consisting essentially of linear low density polyethylene comprises 5 to 25 weight percent of the composition based on the total weight of the composition.
4. The composition as claimed in claim 1, wherein the base polymer is a blend of the styrene polymer and the polyphenylene ether.
5. The composition as claimed in claim 1, wherein the compatibilizer comprises a styrene/olefin copolymer preferably selected from the group consisting of polystyrene-ethylene-butadiene-styrene, styrene-ethylene interpolymer, styrene-butadiene rubber, and polystyrene-ethylene-propylene.
6. The composition as claimed in claim 1, wherein the base polymer is a blend of polyphenylene ether and polystyrene, and the compatibilizer is polystyrene-ethylene-butadiene-styrene or a copolymer of polystyrene and propylene.
7. The composition as claimed in claim 1, optionally comprising:
at least one additive selected from the group consisting of a filler, a reinforcing agent, an additional lubricant, a coloring agent, a processing aid, an impact modifier, a plasticizer, a
slip agent, an ultraviolet absorber, an ultraviolet stabilizer, a flame retardant, a mold release agent, a flow modifier, and a heat stabilizer.
8. A composition as claimed in any preceding claim as and when used as a molded article such as a flame retardant article.
|Indian Patent Application Number||3473/DELNP/2005|
|PG Journal Number||40/2011|
|Date of Filing||04-Aug-2005|
|Name of Patentee||SABIC INNOVATIVE PLASTICS IP B.V.|
|Applicant Address||PLASTICSLAAN 1,4612 PX BERGEN OP ZOOM THE NETHERLANDS|
|PCT International Classification Number||C08L 25/04|
|PCT International Application Number||PCT/US2004/000513|
|PCT International Filing date||2004-01-09|