Note: Descriptions are shown in the official language in which they were submitted.
WO 93/06169 2 1 1 8 5 7 7 pcr/us92/o7812
. ~
PLASTOMER COMPATIBILIZED
POLYETHYLENE/POLYPROPYLEN~ BLENDS
This Invention is a continuation in part of USSN 071760.623 filed September 16,
1991.
S Fleld of tbe Invention
This invention pertains to blends of polyethylene and polypropylene, and
particularly to such blends which are compatibilized with a low molecular weightplastomer so that they are suitable for use in applications such as, for example,
fibers used in nonwoven fabrics.
Back~rouDd of the Invention
There is a great demand for polyolefin fibers which can be used in
applications such as inner cover stock for disposable diapers and sanita~y napkins.
In such applications, the fibers are formed into nonwoven fabrics which have
specific property re4uirements, including soft hand (comfortable touch to the
skin~, light-weightness and high tensile strength. The fibers can be bonded
together to form a nonwoven fabric by several conventional techniques. The
needle punch method, for example, interlaces fibers to bond them into a fabric.
Piber binding has also been achîeved by depositing a solution of adhesive agent on ~-
w*s of the fibers. but this requires additional processing and energy to remove
the solvent from the adhesive agent. Another approach has been the use of binder ~;
fibers having a lower melting point than the primary bulk fibers in the fabric. The -
binder fibers are heated to fuse to the bulk fibers and produce the nonwoven
fabric.
Various attempts have been made in the prior art to employ polyethylene in
the manufacture of fibers. Fibers containing polyethylene and polypropylene havebeen used to manufacture nonwoven fabrics. Polypropylene fibers are known for
their high strength and good processability, but suffer from a lack of softness
(poor hand). Polyethvlene. on the other hand, is known for its good hand. but has
poor strength and processability. Blending the polyethvlene and polypropylene toform fibers having a ~ood balance of properties has been a long sought goal~ i.e. a
polyolefin with the hand of polyethylene, but having the strength and
processability characteristics of polypropylene. However~ problems have been
encountered in the manufacture of polyolefin fibers containing both polyethvlene
WO g3/06169 Pcr/vs92/07812
2118S~7 2
and polypropylene. Low density polyethylene (LDPE) and high density
polyethylene (HDPE) have been used as bicomponent fiber-forming polymers but
are not popular becal!se nonwoven fabrics produced using these polyethylenes have
unsatisfactory rigid hand and do not feel soft. Linear low densiq polyethylene
S (LLDPE) and polypropylene are generally immiscible and incompatible.
Biconstituent fibers containing them generally have a "bicomponent" morphology,
- i.e. the polyethylene and polypropylene are present in the fibers in co-continuous
phæs (side-by-side or sheath/core) rather than a dispersion of fibrils of one
constituent in a mat~Llc of the other. This has in turn led to various pr~cessing
problems which are generally addressed by the judicious selection of polyethylene -
- and polypropylene having a specific density and melt index or melt flow ratio.
U. S. Patent 4,874,666 teaches biconstituent fibers produced by melt
spinning a blend comprising more than 50 weight percent of a linear low density
polyethylene ~LLDPE) having a melt index (MI) of 25-100 dg/min and heat of
;~
fusion below 25 cal/g, and less than 50 weight percent of crystalline polypropylene
having a melt flow rate (MFR) below 20 dg/min. It is stated that these fibers can
be produced at relatively high spinning rates. However, it is taught that if the Ml
of the LLDPE is below 25, fibers cannot be made by high speed spinning, and if
the MI of the LLDPE is higher than lO0, its viscosity does not match the
polypropylene so that a uniform blend cannot be obtained during melt spinning
;
and a se~ious defect will take place in that the filaments being extruded will
`~
frequently break as they emerge from the spinnerette. It is similarly taught that
the LLDPE must have the low heat of fusion in order to obtain a uniform blend.
Similarly, it is taught that a crystalline polypropylene cannot have an MFR
exceeding 20 or uniform blending with the LLDPE cannot be obtained by any of
~-
the known commonly employed spinning apparatus, and as a result, great
difficulty is involved in spinning the blend at high speed. It is also taught that the
LLDPE in the spun fibers is a continuous phase and the polypropylene is a
-
dispersed phase, and that too great a difference in the melt viscosities between the
LLDPE and polypropylene results in the dispersed polypropylene particle size
being too large for smooth high-speed spinning.
U.S. Patent 4,839,228 discloses a two-part blend of polypropylene with 20
to 45 wt. % LLDPE or alternatively LDPE or HDPE for the producdon of fibers.
U. S. Patent 4,748,206 discloses a four-part blend of 20 to 70 weight
percent crystaUine polypropylene, 10 to 50 weight percent amorphous copolymer
(EPR), S to 50 weight percent ethylene/alphalpha-olefin copolymer, typically
WO 93/06169 2 1 1 8 S 7 'rcr/us92/o7
ULDPE and S to 30 weight percent LLDPE or HDPE to be used for molded
articles.
U.S. Patent 4,634,735 discloses a three part blend of 50 to 97 wt. %
isotactic polypropylene, 2 to 49% elastomer (EPR) and 1 to 30 wt. % LLDPE
5 with a density of up to 0.935 for production of molded articles.
JP 9043 043-A discloses a three part blend of 100 parts by weight
polypropylene, 3 to 10 parts by weight LLDPE, and S to 15 parts by weight of
elastomer, typically EPR for production of film.
U.S. Patent 4,833,195 discloses a three-part blend of an oligomer or
10 degraded polyolefin, typically polypropylene, blended with an olefinic elastomer,
typicaUy EPR, and thermoplastic olefin with functional group which is typically
LLDPE for the production of films and fabrics. ~
The latter four references all disclose blends containing elastomer rather ; -
than plastomer. As will be discussed below plastomers have significant
- 15 differences from elastomers. Briefly, the plastomers of this invendon have higher
crystallinity than elastomas which translates to unexpectedly greater strength and
abrasion resistance properties, among othas.
Blief Descriptioo of the Dra-lvings
- Figure 1 is a graph correlating Mw with Mooney viscosity.
20 S~ of the Inveotion
In accordance with the present invention a polyethylene/polypropylene
blend is provided especially useful for the producdon of fibers and nonwovens.
By using a low mo!ecular weight plastomer as a compatibilizer, it has been
discovered that linear low density polyethylene (LLDPE) can be dispersed in a
25 generally condnuous matrLl~ of polypropylene. The dispersion results in reladvely
smaU particles of the LLDPE dispersed through the polypropylene matrix phase
which facilitate processability of the Uend into melt spun or melt blown
biconstituent fibers having a good balance of strength and hand.
Broadly, in accordance with the present invention the present invention
30 polyethylene/polypropylene blend of crystalline polypropylene, L~DPE and a
plastomer is provided. The polypropylene preferably comprises more than about
50 pe~cent by weight of the blend. The LLDPE preferably comprises at least
about 10 but less than about S0 percent by weight ~f the blend. The LLDPE is
dispersed in a matrix of the polypropylene. The plastomer acts as a
Wo 93/~6169 Pcr~uss2/o78l2
rl rl ,
compatibilizer, thus a compatibilizing amount of the plastomer is present. The
plastomer is an ethylene/alpha-olefin copolymer having a weight average
molecular weight between about 5000 and about 50,000, a density between about
0.865 g/cm3 and about 0.90 g/cm3, and a melt index of at generally above 50
dg/min.
In another aspect, the present invention provides fibers made from the
plastomer-compatibilized polyethylene/polypropylene blend. Melt spun fibers are
preferably prepared from the blend wherein the polypropylene has a melt flow rate
from about 20 to about 50 dg/min, preferably at least about 35 dg/min. Melt
blown fibers are preferably prepared from the blend wherein the polypropylene
has a melt flow rate of from about 40D to about 1000 dg/min. ln either case, thepolypropylene is preferably of controlled rheology having MW/Mn less than about
4, especially from about l.5 to about 2.5. The LLDPE preferably comprises a
copolymer of ethylene and at least one C4-C12 alpha-olefin, has a density from
about 0.915 to about 0.94 g/cm3, and a melt index from about 10 to about 100
dg/min.
In a further aspect of the invention, there is provided a nonwoven fabric
made from a melt spun or melt blown blend of the compatibilized
- polyethylene/polypropylene.
20 DetaUed Description of the lnvention
The blend of the present invention includes crystalline polypropylene, ;linear low density polyethylene (LLDPE), and a plas~omer as the essential -~
constituents. The primary constituent is polypropylene, preferably in an amount at
least about 50 weight percent by weight of the blend, more preferably from about50 to about 85 weight percent, more preferably about 55 to about 80 weight
percent, even more preferably about 60 to about 75 weight percent. If insufficient
polypropylene is employed, the strength charaGteristics of the blend are adversely
affected. If too much polypropylene is employed, the blend properties imparted
by the prese~ce of the compatibilized polyethylene, i.e. improved hand, are not
achieved. -
The polypropylene is generally crystalline, for example, isotactic. The
polypropylene is generally prepared by conventional controlled rheological
treatment of a high molecular weight polypropylene (which is made by
polymerizing propylene in the presence of a Ziegler Natta catalyst under
temperatures/conditions well known in the art) with peroxide or another free-
WO 93~06169 Pcr/vs92/07812
5 2118~77
radical initiator to provide a polypropylene having a lower molecular weight and a
narrow molecular weight distribution. The polypropylene preferably has MW/Mn
less than about 4, and especially from about 1.5 to about 2.5. The MFR of the
polypropylene depends on the intended application of the blend. For example,
S where the blend is to be melt spun into fiber, the MFR of the polypropylene
should be at least 20 dg/min, preferably at least about 3S dg/min. For melt blown
fiber which generally roquires a lower melt viscosity, the polypropylene should
have an MFR in the range from about 400 to about 1000 dg/min. As used herein,
polypropylene MPR is determined in accordance with ASTM D-1238, condition
L. Such polypropylene is well hlown in the art and is comme~cially available.
The LLDPE which is used in the blend and fiber of the present invention is
a copolymer of e~hylene and at least one alpha~lefin having from 3 to about 12
carbon atoms, preferably 4 to 8 carbon atoms. The alpha~lefin comonomer(s)
generally comprises from about I to about 15 weight percent of the LLDPE. The
LLDPE gen~ally has a density in the range from about 0.915 to about 0.94
g/cm3, and a melt index from about 10 to about 100 dg/min. As used herein, the
MI of LLDPE is determined in accordance with ASTM D-1238, condition E.
The LLDPE constituent should be present in the blend in an amount
sufficient to obtain the desired properties, for example, improved hand, withoutsedously detracting from the desirable properties of the polypropylene, for
example, strength and processability. The LLDPE preferably comprises from
about 10 to about 50 percent by weight of the blend, more preferably from about
15 to about 40 percent by weight, even more preferably about 20 to about 30
weight percent.
The plastomer is a low molecular weight ethylene/alpha-olefin copolymer
which has properlies generally intermediate to those of thermop!a~ic materials and
ela~ic materials, hence the term "plastomer. " The plastomers used in the
blend and fiber of this invendon comprise ethylene and at least one C3-C20 alpha-
olefin, preferably a C4-Cg alpha-olefin, polymerized in a linear fashion using asingle site metallocene catalyst such as the catalysts disclosed in European Patent
to Welborn, EP 29,368, U. S. Patent to Turner, 4,752,597, U. S. Patents to
Welborn, 4,808,561 and 4,897,455, which are herein incorporated by reference.
The alpha-olefin comonomer may be present at about 5 to 25 mole percent,
preferably about 7 to about 22 mole percent, more preferebly between about 9 to
18 mole percent. In gene al the plastomer has a density in the range of about
0.865 g/cm3 to about 0.90 g/cm3. The phstomer generally hæ Mw in the range
WO 93~06169 Pcr/us92/07812
s~'l
of from about 5000 to about 50,000, preferably from about 20,000 to about
30,000. The melt index of the plastomer is generally above about 50 dg/min, ;
preferably from about 50 to about 200 dg/min, as determined in accordance with
ASTM ~1238, condition E. The plastomer is used in an amount sufficient to ~
S compatibilize the LIDPElpolypropylene blend, i.e. to facilitate dispersion of the ~-
11 npE in the polypropylene. An excessive amount of the plastomer is preferably
avoided sv ~at ~e desirable strength properties of the polymer are not advers~ly -;
affected thereby. Preferably, the plastomer is used in an amount of from about 2to about 15 weight percent, more preferably about 5 to about 12 weight percent.
The plastomer is also characterized by an X-ray crystallinity of at least 10%,
preferably at least 15 to about 25%.
Plastomers differ from elastomers in some significant ways. An elastomer ~ -
typically has a density from 0.86 to 0.875, a high molecular weight ~-
(lOO,OOO+Mw) and is typicaUy used to make molded articles such as tires, car
bumpers, etc. the instant plastomer has a density of 0.88 to 0.90 and a Mw of
5,000 to 50,000. ~-
In addition, plastomers and elastomers differ in specific properties.
Plastomers have higher crystallinity than elastomas, which contributes to
increased tensile strength and greater abrasion resistance. Less a ystalline
elastomers typically do not have nearly the same abrasion resistance and tensilestrength. As a consequence, plastomers unlike elastomers, can be utilized "neat,"
without the need for fiUing and/or crosslinking. Data that evidence the propertydifferences between plastomers and elastomers are shown in Table I.
2~18S77
TABLE I: ~NALYIICAL AND P}~O.PERTY/PERFORMANCE
DD~RENC~
BEIWEEN ETHYLENE/ALPHA-OLE~IN ELASTOMEl~S~)
PLASTOMERS
PLASTOMER ELASTOME~ ELASTOMER
EXXON EXACT DUPONT NORDEL MITSUI
3017C 27æ TA~MER P-0480
Mw (wt. avg.) 42,000 97,000 100,000
COMPOSITION C2=/B~E-l EPDM EP
(MOLE % 7.7 MOLE% C4= 19 MOLE % C3-- 24 MOLE % C3--
COMONOMER)
DENSITY (g/cm3) 0.901 0.872 Q.8666
X-RAY > 20 7 < 5
CRYSTALLINITY
(%)
TENSILE 1250 730 300
Sll~ENGTH AT (8.61 MPa) . (5.03 MPa) 2.07 MPa)
BREAK (psi)
(ASTM D-638)
TENSILE IMPACT 105 210 90
Sll~ENCiTH (7.2 x 105NIM2) (1.5 x 106NIM2) (6.2 x 105N/M2)
(ftlb/in2)
~ASTh~ D-1822)
SHORE "A" > 80 71 66
HARI)NESS
(ASTM D-2240)
1. Physical prope~ties measured on compression molded pads of neat base
polymer.
2. X-ray crystallinity determined by X-ray dif~rac~on techniques (see I,.E.
Alexander *-rav Di~rac~on Methods in Polymer Science, Wiley (Interscience),
New York, 1969).
The data in Table 1 show that even though the molecular weight of
applicants' claimed plastomer is less than half that for the elastomer products, the
"neat" plastomer offers a better balance of physical properties, i.e. tensile strength
at break > 1000 psi (6.895 MPa); tensile impact strength > 100 ft.lb~in2~6.9 x
105N/M2), shore "A" hardness > 80, as opposed to the elastomer products.
Table I shows the plastomers to have better tensile strength, good impact
strength and better abrasion resistance( through the higher hardness value) than the
elastomer products. Further is achieved with a lower molecular weight produc~, in
.
SU~S;TITUTE SHEET
WO 93/06169 Pcr/us~2/078t2 ~
5~ 8
direct contradiction to the expected norm, i.e. that as Mw falls, the strength
properties fall.
In more technical parlance, key analytical differentiating features of a
plastomer vis-a-vis an ethylenetalpha-olefin elastomer are its lower molecular
weight and its higher crystallinity (or density). The majority of ethylenetalpha-
olefin elastomers are >20 Mooney viscosity (at 125C), a typically used unit to
characterize molecular weight. A Mooney viscosity > 20 (at 125C) translates to
a molecular weight (Mw~ the weight average) > 100,000 (see Pigure 2 for a
correlation of Mooney viscosity with Mw). By contrast, our defined plastomers
boxcomprisespolymers< 100,000MW. Oncrystallinity,ethylene/alpha-olefin
elastomers are generally substantially amo~phous, having x-ray crystallinity levels
generally < 7% (densities < 0.875 g/cm3). Bycontrast, ourplastomers
comprises polymers for the most part > 0.875 g/cm3. Specifically, the
plastomers with 0.89 g/cm3, or about 20% crystallinity and 20,000 to 30,000 Mw
are dearly outside the generally accepted definition of ethylene/alpha-olefin
elastomers and could not be made by standard manufacturing unitslprocedures
used generally to produce ethylenelalpha-olefin elastomers.
The analytical differences highlighted above translate to property and performance
differences. For example, because ethylenelalpha-olefin elastomers are
substantially amorphous, they have poor intrinsic tensile properties, low abrasion `
resistance (e.g. low hardness) and low modulus. As a consequence they are
seldom, if ever, used without being filled andlor cross linked. Alternately, they
are blended with other polymers to derive useful strength properties. By contrast,
plastomers offer adequate inherent tensile and impact properties etc., such thatthey can be utiliæd "neatn, without the need for filling andlor
cross linking. Examples showing this practical differentiation are provided in
Table I.
Yet another means of differentiating plastomers from elastomers is
in their application in blends. An important commercial application for
ethylenelalpha-olefin elastomers is in blends with other polymers (e.g. blends with
polypropylene for impact strength enhancement). It is well known in the art thatthe closer the viscosity match of the blend partners, the better the dispersion and
the smaller the size of the dispersed particles, for imisicible systems. It is also
well known that smaller particle sizes (generally 1-2 microns or smaller) provide
good mechanical properties (e.g. impact strength). Plastomers offer a different
response, versus ethylene/alpha-olefin elastomers, in this area. Their lower
WO 93/06169 PCl'~US92/078t2
9 2118577
molecular weights allow easy blending utilizing standard mixing techniques,
yielding well dispersed blends of favorably small particle size. In contrast, the
blend viscosity match-up with ethylene/alpha-olefin elastomers (higher molecularweight) is poorer. To achieve good dispersions and favorably small particle siæs,
S special mixing equipment/mixing procedures are generally required. The lower
molecular weight of the plastomers means that there is a better dispersion. Thiscontributes to faster and easier processing. Thus, these blends can be processed on
standard machinery witnout having to make expensive adjustments, unlike the highMw elastomers of the references.
The Uend of the present invention may also contain relatively minor
amounts of conventional polyolefin additives such as colorants, pigments, UV
stabilizers, andoxidants, heat stabilizers and the like which do not significantly
impair the desirable features of the blend. However, the blend should be
essentially free of additives which adversely affect the compatibility of the blend
15 components, and panicularly such components which adversely affect the ability to
form the blend into fiber.
The blend constituents may be blended together in any order using
conventional blending equipment, such as, for example, roll mills, Banbury mixer,
Brabender, extruder and the like. A mixing extruder is preferably used in order to
20 achieve good dispersion of the compatibilized LLDPE particles in a continuouspolypropylene matrix. In an unoriented state, i.e. before fiber formation or other
mechanical drawing, the blend is characterized by a dispersion of relatively fine
particles of LLDPE suspended in the polypropylene. Of course, when the blend is
oriented as in fiber formadon, or other mechanical drawing techniques, the
25 pardcles become more ellipsoid and/or fibrile than spherical. The spherical
LLDPE pardcles generally have a particle size less than about 30 microns,
prefe~ably from about 1 to about 5 microns. This is in sharp contrast to the prior
art blends prepared without the plastomer compatibilizer which result in relatively
large particles of the dispersed phæ, and in extreme cases, even cocondnuous
30 phases, which adversely affect fiber formation.
The blend of the present invention may be formed into fiber using
conventional fiber formation equipment, such as, for example, equipment
commonly employed for melt spinning or to form melt blown fiber, or the like.
In melt spinning, either monofilaments or fine denier fibers, a higher melt strength
35 is generally required, and the polypropylene preferably has an MFR of from about
20 to about 50 dg/min. A target MFR for the polypropylene of about 35 dg/min
. . ' '",
WO93/06169 PCI/US92/0781~
2~s~ 7 10
is usually suitable. Typical melt spinning equipment includes a mixing extruder
which feeds a spinning pump which supplies polymer to mechanical filters and a
spinnerette with a plurality of extrusion holes therein. The filament or filaments
formed from the spinnerette are taken up on a take up roll after the polyolefin has
S solidified to form fibers. If desired, the fiber may be subjected to further drawing
or stretching, either heated or cold, and also to textudzing, such as, for example,
air jet texturing, steam jet texturing, stuffing box treatment, cutting or crimping
into staples, and the like.
- In the case of melt blown fiber, the blend is generally fed to an extrusion
10 die along with a high pressure source of air or other inert gas in such a fashion as
to cause the melt to fragment at the die orifice and to be drawn by the passage of
the air into short fiber which solidifies before it is deposited and taken up as a mat
or web on a screen or roll which may be optionally heated. Melt blown fiber
formation generally requires low melt viscosity material, and for this reason, it is
15 desirable to use a polypropylene in melt blown fiber formation which has an MPR
in the range from about 400 to about 1000 dgimin.
In a preferred embodiment, the blend of the present invention may be used
to form nonwoven fabric. The fiber can be bonded using conventional techni~ues,
such as, for example, needle punch. adhesive binder, binder fibers, hot embossed20 roll calendaring and the like. In a p~rticularly preferred embodiment, the fiber of
the present invention can be ussd to form a fabric having opposite outer layers of
melt spun fiber bonded to an inner layer of melt blown fiber disposed between the
outer melt spun layers. Typically, each outer layer is from about S to about 10
times thicker than the inner layer. The melt spun fiber pre~ared from the present
25 invention is preferably ussd as one or both outer layers, and the melt blown fiber
of the present invention for the inner melt blown fiber layer, although it is
possible, if desired, to use a different material for one or both of the spun bonded
layers or a different melt blown fiber for the inner melt blown fiber layer.
Conventional heated calendaring equipment can be ussd, for example, to bond the
30 outer melt spun fiber layers to the intermediate melt blown fibsr layer by heating
the composite layersd stnucture sufficiently to at least partially melt the inner layer
which melts more easily than the outer layers. As is known, insufficient heatingmay not adequately bond the fibers, whereas excessive heating may result in
complete melting of the inner and/or outer layers and void forrnation. Upon
35 cooling, the inner melt blown layer fuses to the fiber in the adjacent outer layers
and bonds the outer layers together.
211~77 .
11
It is also contemplated that the blend of the present invention can be used
as one component of a bicomponent fiber wherein the fiber includes a second
component in a side-by-side or sheath-core configuration. For example, the
polypropylene/LLDPE blend and polyethylene terephthalat~ (PET) can be formed
into a side-by-side or sheath-core bicomponent fiber by using equipment and
techniques known for formation of polypropylene/PE~T bicomponent.
The present invention is illustrated by the examples which foltow.
E~ample 1
Polypropylene, I LDPE and plastomer in a weight ratio of 70t20/10 were
blended together and formed into pressed film and monofilament for evaluation.
The polypropylene was prepared from a l.0 MFR polypropylene by peroxide
treatment to obtain a controlled rheology polypropylene of 35 MFR. The LLDPE
was a copolymer of ethylene and 4 weight percent 1 butene, having a density of
0.924 g/cm3 ~nd a 22 MI. The plastomer was an ethylene-butene copolymer with
a 120 MI and a 0. 89 g/cm3 density. The blend was mixed in a Brabender mixer
at 170-200C for 5-lO minutes with a mixing head speed of about 60-80 rpm.
The blend was pressed into films using a Carver press at about 100 psi at 170-
200C for about 14 minutes. The composition of Example 1 is summarized in
Table 2 below. Low voltage scanning electron micrographs of the pressed film
revealed a dispersed morphology wherein the LLDPE was dispersed in a
continuous phase of the polypropylene. The LLDPE partic!es were in the 1-2
micron size range. The film had a stress at break of 4110 psi(28.3 MPa), a strain
at brea~ of 10 percent, a modulus of 104,000 psi(717. 1 MPa) and impact strengthof 5 lbs/in. The physical properties are summarized in Table 3 below. The blend
was also formed into a fiber using a special one-hole die apparatus in which the- polymer blend was melted at 180-250C in a device similar to a melt indexer and
drawn from the die hole by a take up spool at faster and faster speeds untit thefiber breaks away from the die. The fiber exhibited a compliance of 2.4, co~lld be
spun at a rate of 440 feet/min(134.2 m/min)~ and had a melt strength of 3.2 g.
The fiber formation and morphology are summarized in Table 4 below.
Exam~le 2
The equipment and procedures of Exampte 1 were used to prepare a simitar
blend of 60 weight percent polypropylene, 30 weight percent LLDPE and 10
weight percent plastomer. The polypropylene was a controlled rheology
SU8~TITUTE SHEET
2118~77
polypropylene of 400 MFR prepared from a 1.0 MFR polypropylene by peroxide
treatment. The LLDPE was a copolymer of ethylene and 2.8 mole percent 1-
octene having a density of about 0.92 g/cm3 and 117 MI. The same plastomer as
in Example 1 was used. The composition of Example 2 is summarized in Table 2
below. A low voltage scanning electron micrograph of the blend revealed i
dispersed morphology wherein the LLDPE was dispersed in a continuous phase of
the polypropylene. The LLDPE particles where in the 1-30 micron size range.
The MFR of the polypropylene was too high to make a film for mechanical testing
or fiber from the one-hole die apparatus. The blend is made into melt blown fiber
with acceptable properties.
Comparative Example A
The procedures and techniques of Example 1 were used to prepare a blend
of 60 weight percent polypropylene, 40 weight percent LLDPE and no plastomer.
In contrast to the compadbilized polypropylene/LLDPE blends of Example 1,
Comparative Example A had a high compliance (5.1), could only be spun at low
speeds (240 feetlmin(73.2 m/min)) and exhibited a low melt strength and a
cocontinuous morphology with some dispersed LLDPE particles in the
polypropylene cocontinuous phase. The composition, physical properties and
spinning and morphological characteristics are summarized in Tables 2, 3 and 4
below.
Comparative Example B
The procedures an~ techniques of Example 1 were used to prepare a blend
of 47.5 weight percent polypropylene, 47.5 weight percent LLDPE and 5 weight
percent plastomer. In contrast to the compatibilized polypropylenelLLDPE blends
of Examplei, Comparative Example B could not be spun even at low speeds
(below 25 feet/min(7.6 m/min)) and exhibited a cocon~nuous mo~phology. The
composidon, physical proper~es and spinning and morphological charactenstics
are summanzed in Tables 2, 3 and 4 below;
SUBSflTUTE SHEET
211~577
13
- - TABLE 2
.
. . _ .
COMPOS~TION (WT %)
1 70 20 10
COMP A 60 40 - 0
.COMP. B 47.5 47.5 5
~ ._
2 604 305 10
1. 35 MFR; 2.5 MW/Mn
2. 22 MI; 0.924 g/cm3; 4 wt % butene
3. 120 MI; 0.89 g/cm3; butene-l copolymer.
4. 400 MFR; 3.? MWlMn
5. 117 MI; 0.92 g/cm3; 2.8 mole % l-octene.
TABLE 3
_
EXAMPLE STRESS (psi) S~N (%) MODULUS IMPACT
(}cpsi) SIRENGTH
_ ~Ib/in.) ~-
_ _ :~
_ 1 ~ 10 104 (717. lMPa) S
. . ~ ..
COMP. A 2430 (16.9MPa) 5 85 (586.1 MPa) < I ~--
COMP. B 2520 (17.4 10 67 (462.0 MPa) < 1
MPa)
TABLE 4
EXAMPLE COMPLIANCE SPEED TO ,MELT MORPHOLOGY
- (~o) BREAK Sll~ENGT~I (p~rtiicle size, mm).
_ (ft/min) (~)
I 2.4 440 (134.2 3.2 Dispe~sed (1-2) . ,,, m/min) .
_
COMP. A 5.1 240 (73.2 1.4 Cocontinuous/
m/min) DisDersed (> > 10)
. .. .
COMP. B 2.9 Could Not NIA CocontinuousSpin (> >20) -
2 - N/A N/A N/A Dispersed (1-30)
N/A = Data not ~vailable.
SUBS~ITU~E SHET
.
WO 93/06169 PCr/US92/0781
From the foregoing, it is seen that compatibilized blends of polypropylene
and LLDP~ wherein polypropylene is the primary constituent can be prepared by
employing a plastomer compatibilizer. In contrast, blends prepared without the
compatibilizer do not have the necessary properties for easy fiber formation, and
5 have inferior mechanical properties. However, the foregoing teachings are
intended only to illustrate and explain the invention and the best mode
contemplated, and are not intended to limit the invention. Variations and
modifications will occur to those skilled in the art in view of the foregoing. lt is
intended that all such variations and modifications which fall within the scope or
10 spirit of appended claims be embraced thereby.
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