Method for making blends of liquid crystalline and isotropic polymers

Blends of thermotropic liquid crystalline polymers and isotropic melt-processable polymers are made by extruding a molten stream of either a thermotropic liquid crystalline polymer or an isotropic polymer through a heated mixing zone and feeding the other of the two polymers into the stream of the first polymer in the mixing zone. The polymers are mixed under shearing conditions for a time sufficient to yield a uniform blend. Blends made according to this method exhibit improved properties in comparison with blends obtained by feeding the two polymers simultaneously into a heated mixing zone.

BACKGROUND OF THE INVENTION 
In an effort to optimize polymer properties for specific applications at 
the lowest cost, polymers are often blended together. Numerous blends 
comprising thermotropic liquid crystalline polymers (LCP's) and isotropic 
polymers have been reported in the literature. These include blends of 
LCP's with polyethylene terephthalate (U.S. Pat. No. 4,489,190), 
polyphenylene sulfide (U.S. Pat. No. 4,276,397), polycarbonate (U.S. Pat. 
No. 4,460,735), polysulfones (U.S. Pat. No. 4,460,736), and many other 
isotropic polymers (e.g., U.S. Pat. No. 4,386,174 and 4,792,587). These 
blends are generally made by mixing the polymers as solids, usually in the 
form of pellets, and feeding them together into an extruder, where they 
are melted and mixed together under shear to yield a uniform blend. 
Generally these polymers are not miscible, and the blends are composed of 
individual domains of one polymer in the second polymer. The properties of 
the resulting blends typically are the weighted average of the properties 
of the individual components of the blend (i.e., they follow the rule of 
mixtures). More often, the properties of the blends are less than 
predicted by the rule of mixtures. 
SUMMARY OF THE INVENTION 
A method has been found for making a blend of a thermotropic liquid 
crystalline polymer and a melt-processable isotropic polymer with improved 
properties compared with a blend of the same polymers made by the 
conventional method of simultaneously feeding the two polymers into an 
extruder. In this method, a stream of either the thermotropic liquid 
crystalline polymer or the isotropic polymer is extruded in a molten state 
through a heated zone under conditions in which the polymer is sheared. 
The other polymer component of the blend is then introduced into the 
stream of molten polymer that is being extruded through the heated mixing 
zone, and the two polymers are mixed under shearing conditions for a time 
that is sufficient to yield a uniform blend.

DETAILED DESCRIPTION OF THE INVENTION 
Preferably, the heated mixing zone is in an extruder comprising one or more 
screws rotating in a hollow barrel. The extruder is equipped with two 
ports for feeding the polymer into the barrel, with one polymer component 
being fed into each port. A first port for feeding polymer is generally at 
or near the beginning of the barrel, at the opposite end from the outlet, 
which is a heated die. The second port is downstream from the first port, 
preferably at a position between about 1/4 to about 3/4 of the length of 
the extruder from the feed port. Most preferably the second port is in 
about the middle of the length of the barrel of the extruder (about 40% to 
about 60% of the distance from the beginning of the extruder). 
If filled blends are desired, glass fibers and other fillers may be 
included. Preferably the glass fiber is added through the second port to 
minimize breakage of the fibers due to excessive mixing. Generally, 
blending can be carried out in a single screw or twin screw extruder. A 
twin screw extruder is preferred because of its higher shear, resulting in 
better mixing. 
Thermotropic liquid crystalline polymers that are utilized in making blends 
by the method described herein are well known in the art. The polymer 
chains are relatively rigid and linear, so that the polymers melt to form 
a liquid crystalline phase. Generally, the polymers useful in forming 
these blends melt to form liquid crystalline phases at temperatures less 
than about 400.degree. C. These polymers are generally condensation 
polymers, including aromatic polyesters, aliphatic-aromatic polyesters, 
aromatic poly(esteramides), aliphatic-aromatic poly(esteramides), aromatic 
poly(esteramides), aromatic poly(estercarbonates), aromatic polyamides, 
and aliphaticaromatic polyamides. The preferred thermotropic liquid 
crystalline polymers are aromatic polyesters and poly(esteramides) which 
form liquid crystalline melt phases at temperatures less than about 
350.degree. C. and include one or more monomer units derived from 
terephthalic acid, isophthalic acid, 1,4-hydroquinone, resorcinol, 
4,4'-dihydroxybiphenyl, 4,4'-biphenyldicarboxylic acid, 4-hydroxybenzoic 
acid, 6-hydroxy-2-naphthoic acid, 2,6-naphthalenedicarboxylic acid, 
2,6-dihydroxynaphthalene, 4-aminophenol, and 4-aminobenzoic acid. 
Some of the aromatic groups may include substituents which do not react 
under the conditions of the polymerization, such as lower alkyl groups 
having 1-4 carbons, aromatic groups, F, Cl, Br and I. The synthesis and 
structure of some typical aromatic polyesters are taught in U.S. Pat. Nos. 
4,473,682; 4,522,974; 4,375,530; 4,318,841; 4,256,624; 4,161,470; 
4,219,461; 4,083,829; 4,184,996; 4,279,803; 4,337,190; 4,355,134; 
4,429,105; 4,393,191; and 4,421,908. The synthesis and structure of some 
typical aromatic poly(esteramides) are taught in U.S. Pat. Nos. 4,339,375; 
4,355,132; 4,351,917; 4,330,457; 4,351,918; and 5,204,443. Aromatic liquid 
crystalline polyesters and poly(esteramides) are available from Hoechst 
Celanese Corporation under the Vectra.RTM. trademark, as well as from 
other manufacturers. 
A particularly preferred liquid crystalline polyester comprises monomer 
repeat units derived from 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic 
acid, as taught in U.S. Pat. No. 4,161,470. Preferably, monomer units 
derived from 4-hydroxybenzoic acid comprise about 15% to about 85% of the 
polymer on a mole basis and monomer units derived from 
6-hydroxy-2-naphthoic acid comprise about 85% to about 15% of the polymer 
on a mole basis. Most preferably, the polymer comprises about 73% monomer 
units derived from 4-hydroxybenzoic acid and about 27% monomer units 
derived from 6-hydroxy-2-naphthoic acid, on a mole basis. 
Other preferred liquid crystalline polyesters or poly(esteramides) comprise 
the above recited monomer units derived from 6-hydroxy-2-naphthoic acid 
and 4-hydroxybenzoic acid, as well as monomer units derived from one or 
more of the following monomers: 4,4'-dihydroxybiphenyl, terephthalic acid 
and 4-aminophenol. A preferred polyester comprising these monomer units is 
derived from 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 
4,4'-biphenol and terephthalic acid, as taught in U.S. Pat. No. 4,473,682, 
with the polymer comprising these monomer units in a mole ratio of about 
60:4:18:18 being particularly preferred. 
A preferred poly(esteramide) comprises monomer units derived from 
4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, terephthalic acid, 
4,4'-biphenol and 4-aminophenol, as taught in U.S. Pat. No. 5,204,443; a 
highly preferred composition comprises these monomer units in a mole ratio 
of about 60:3.5:18.25:13.25:5. 
Another liquid crystalline poly(esteramide) that can be utilized in this 
invention is the polymer derived from 6-hydroxy-2-naphthoic acid, 
terephthalic acid, and 4-aminophenol, preferably in a ratio of about 
60:20:20. This poly(esteramide) is described in U.S. Pat. No. 4,330,457. 
The liquid crystalline polymers that are utilized in making the blends 
taught herein generally have a weight average molecular weight (M.sub.W) 
greater than about 5000 and preferably greater than about 10,000. The 
preferred LCP polyester comprising monomer units derived from about 73% 
4-hydroxybenzoic acid and 27% 6-hydroxy-2-naphthoic acid preferably has a 
molecular weight (M.sub.W) greater than about 20,000 and often in the 
range of about 30,000 to about 40,000. Molecular weights in the low end of 
the above range (i.e., M.sub.W starting as low as about 5,000) may also be 
utilized in the current invention. To achieve such low molecular weights, 
the addition of a small amount of an end-capping monomer unit or a slight 
imbalance in stoichiometry may be necessary. For example, a small amount 
of terephthalic acid may be included in polymers derived from 
6-hydroxy-2-naphthoic acid and 4-hydroxybenzoic acid to reduce the 
molecular weight. 
The isotropic polymers utilized in making blends by the method disclosed 
herein are also well known in the art. These polymers are melt 
processable, melting to form isotropic molten phases. They melt at 
temperatures of less than or about 350.degree. C. They can be 
semicrystalline or amorphous. Semicrystalline isotropic polymers that may 
be used in this invention include poly(alkylene terephthalate)s, 
poly(alkylene naphthalate)s, such as poly(ethylene naphthalate), 
poly(arylene sulfide)s, aliphatic polyamides, aliphatic-aromatic 
polyamides, and polyesters comprising monomer units derived from 
1,4-cyclohexanedimethanol and terephthalic acid. The preferred 
semicrystalline isotropic polymers include poly(ethylene terephthalate), 
poly(butylene terephthalate), and poly(phenylene sulfide). The most 
preferred isotropic polymer is poly(ethylene terephthalate). Amorphous 
polymers that can be used include polycarbonates and polyarylates, wherein 
the polyarylates are derived from bisphenol A, terephthalic acid and 
isophthalic acid. 
As stated previously, the blends are preferably made in a twin screw 
extruder having two ports for feeding polymers and other materials. One of 
the polymers (i.e., either a thermotropic liquid crystalline polymer or an 
isotropic polymer) is fed through the first port near the beginning of the 
barrel of the extruder. The other of the two polymers is fed through the 
downstream port, which is preferably approximately in the middle of the 
extruder. Preferably the isotropic polymers is fed through the first port 
and the thermotropic liquid crystalline polymer is fed through the 
downstream port. 
Blends of poly(ethylene terephthalate) and a liquid crystalline polymer are 
highly preferred. Their properties show the greatest improvement when the 
poly(ethylene terephthalate) is fed into the extruder first and the liquid 
crystalline polymer is fed into the stream of poly(ethylene terephthalate) 
through a second port. In this case, the liquid crystalline polymer 
preferably comprises monomer units derived from about 15% to about 85% on 
a mole basis of 4-hydroxybenzoic acid and about 85% to about 15% on a mole 
basis of 6-hydroxy-2-naphthoic acid, and most preferably comprises about 
73 mole % of monomer units derived from 4-hydroxybenzoic acid and about 27 
mole % of monomer units derived from 6-hydroxy-2-naphthoic acid. 
Blends made by the above method generally exhibit an improvement in one or 
more of the following physical properties: tensile strength, measured 
according to ASTM method D-638; tensile modulus, measured according to 
ASTM method D-638; or Notched Izod impact strength, measured according to 
ASTM method D-256, when compared with a blend of the same polymers made by 
the conventional method of melt blending, where the two polymers are 
introduced simultaneously into the mixing zone. Preferably, the 
improvement in one of these physical properties is by an amount of at 
least about 10%. 
Additives may also be included in the blends made by this method. Examples 
of such additives include reinforcing fibers, mineral fillers, nucleating 
agents, mold release agents, colorants, antioxidants, stabilizers, and 
lubricants. These can be fed into the extruder with either polymer. A 
preferred additive is glass fiber, which is generally fed into the 
extruder through the second port along with the second polymer. 
EXAMPLE 1 
A series of unfilled blends of a liquid crystalline polymer (LCP) and 
polyethylene terephthalate (PET) was made by conventional melt blending 
and by the sequential feed method. The PET was obtained from Hoechst 
Celanese Corp., Somerville, N.J., and had an intrinsic viscosity of 0.95 
when measured at 25.degree. C. in o-chlorophenol. The LCP was a polyester 
containing about 73% of 4-oxybenzoyl monomer units and about 27% of 
6-oxy-2-naphthoyl monomer units. Filled forms of this polymer are 
available from Hoechst Celanese Corp. under the Vectra.RTM. trademark as 
the A series of resins. The polymer can be synthesized by the methods 
taught in U.S. Pat. Nos. 4,161,470 and 4,429,105. The LCP resin exhibited 
a melting point by differential scanning calorimetry (DSC) of 282.degree. 
C., and the PET melted at 252.degree. C. by DSC analysis. Both polymers 
were dried for at least 12 hours at 130.degree. C. in a convection oven 
prior to blending. 
The blending experiments were carried out in a 30 mm ZSK twin screw 
extruder manufactured by Werner Pfleiderer Corp. The screw length was 
about 890 mm long. The barrel in which the screws turned contained two 
ports. The first port was at the beginning of the extruder. The second was 
about in the middle of the extruder (about 40-50% of the distance from the 
beginning to the exit). There was also a vent to which vacuum could be 
applied near the exit end of the barrel. The polymer was extruded through 
a die at the end of the barrel. For convenience, the port at the beginning 
of the barrel is referred to as Port No. 1, and the port near the middle 
of the barrel is referred to as Port No. 2. The barrel was heated by 5 
heaters in sequence, so that there were 5 heated zones, with the first 
heated zone being near Port No. 1, the third heated zone being near Port 
No. 2, and the fifth heated zone being near the vent. The die was also 
heated. The blending conditions for the three polymer blends that were 
made are shown in Table 1. 
For purposes of comparison, blends of LCP: PET in weight ratios of 70:30, 
50:50 and 15:85 were made by two methods, the conventional method 
(simultaneous feed) and sequential feed, which are described below. 
Conventional. A mixture of dried pellets of LCP and PET in the desired 
ratio was placed into a feed hopper above Port No. 1. These were fed into 
the extruder. The feed rate of polymer pellets was controlled to maintain 
a rate of production of the blend of about 30 lbs/hr. The polymer melt was 
cooled in water as it exited from the extruder and was pelletized on line. 
Sequential Feed. The extruder was set up with feed hoppers above both Port 
No. 1 and Port No. 2. One of the polymers (in the form of dried pellets) 
was fed into Port No. 1 at the beginning of the shaft, and the other (also 
dried pellets) was fed at Port No. 2, somewhat before the middle of the 
shaft. At the beginning of the experiment, the polymer at Port No. 1 was 
fed first, and once conditions stabilized, the other polymer was fed into 
Port No. 2. The feed rates of the two polymers were controlled to give 
blends of LCP:PET of 70:30, 50:50, and 15:85. Separate batches were made 
in which (1) PET was fed at Port No. 1 and LCP at Port No. 2, so that LCP 
was fed into a stream of molten PET as it was being extruded, and (2) LCP 
was fed at Port No. 1 and PET at Port No. 2, so that PET was fed into a 
stream of molten LCP. These are referred to respectively as "PET First" 
and "LCP First" in Table 3. The compositions of the blends were confirmed 
by extracting PET from samples of the blends with hexafluoroisopropanol 
and weighing the undissolved LCP polymer. Physical Testing. The pelletized 
blends described above were injection molded into test bars required for 
testing of tensile properties, notched Izod impact strength, and heat 
distortion temperature according to ASTM test methods. The molding 
conditions for the three polymer blend compositions are shown in Table 2. 
The physical properties were then measured according to standard test 
methods. These are shown in Table 3. The tensile modulus, tensile strength 
and elongation were measured using ASTM D-638. The Notched Izod impact 
strength was measured using ASTM D-256. The heat distortion temperature 
(distortion temperature under load) at 264 psi was measured by ASTM D-648. 
It can be seen in Table 3 that the tensile properties and notched Izod 
impact strength measurements are usually higher for the blends made by 
sequential feeding than for the same blends made by simultaneous feeding. 
EXAMPLE 2 
Glass filled compounds of LCP and PET were made using the sequential feed 
method described in Example 1, with the PET being fed first and the LCP 
and glass fiber being fed into the molten PET stream. A 30 mm ZSK twin 
screw extruder with two ports for feeding was again used. Dried PET 
pellets were fed into Port No. 1, at the beginning of the shaft, through a 
feed hopper. A mixture of glass fiber and dried LCP pellets was introduced 
into Port No. 2, at about the middle of the barrel, through a feed hopper. 
The glass fiber was included in an amount that would give a 30% 
glass-filled blend. As in Example 1, the PET feed was started first. Once 
that stabilized, the feed of LCP/glass fiber was started and gradually 
increased until the desired ratio was obtained. Blends of 70:30 and 50:50 
LCP:PET filled with 30% glass fiber were made by this method. These were 
then injection molded under the same conditions as in Example 1 to produce 
test specimens for measuring physical properties. Tensile properties 
(modulus, strength and elongation), the Notched Izod impact strength, and 
heat distortion temperature at 264 psi were measured by the same test 
methods as in Example 1. These data are presented in Table 4. 
It is to be understood that the above described embodiments of the 
invention are illustrative only and that modification throughout may occur 
to one skilled in the art. Accordingly, this invention is not to be 
regarded as limited to the embodiments disclosed herein. 
TABLE 1 
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Blending Conditions 
LCP/PET Ratio 
70/30 50/50 15/85 
______________________________________ 
Zone 1 Temperature (.degree.F.) 
542 541 543 
Zone 2 Temperature (.degree.F.) 
540 553 579 
Zone 3 Temperature (.degree.F.) 
562 570 577 
Zone 4 Temperature (.degree.F.) 
562 562 565 
Zone 5 Temperature (.degree.F.) 
560 564 572 
Die Temperature (.degree.F.) 
562 561 567 
Melt Temperature (.degree.F.) 
600 602 589 
Screw RPM 175 175 200 
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TABLE 2 
______________________________________ 
Injection Molding Conditions 
LCP/PET Ratio 
70/30 50/50 15/85 
______________________________________ 
Temperature, Rear (.degree.F.) 
545 570 555 
Temperature, Middle (.degree.F.) 
545 570 555 
Temperature, Front (.degree.F.) 
545 570 555 
Nozzle Temperature (.degree.F.) 
550 575 565 
Mold Temperature (.degree.F.) 
170 125 200 
Cycle Time, High Injecter Pressure 
3 3 3 
(Sec.) 
Cycle Time, Low Injector Pressure 
15 15 15 
(Sec.) 
Cooling (Sec.) 20 20 20 
Total Cycle Time (Sec.) 
38 38 38 
High Injector Pressure (psi) 
9200 9700 12,300 
Low Injector Pressure (psi) 
8700 8500 12,000 
Screw RPM 95 95 95 
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TABLE 3 
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Properties of LCP/PET Blends 
Tensile 
Tensile Notched 
Modulus 
Strength 
Elongation 
Izod HDT 
Order of Feed 
LCP/PET 
(Mpsi) 
(kpsi) 
(%) (ft-lb./in.) 
at 264 psi 
__________________________________________________________________________ 
-- 0/100 0.33 4.08 216 0.57 67.degree. C. 
Simultaneous 
15/85 0.36 8.3 3.6 0.51 -- 
PET first 
15/85 0.47 9.8 3.5 0.52 69.degree. C. 
LCP first 
15/85 0.46 10.4 3.3 0.58 -- 
Simultaneous 
50/50 0.96 16.5 2.6 0.87 -- 
PET first 
50/50 1.39 22.9 2.3 2.37 83.degree. C. 
LCP first 
50/50 0.84 12.9 1.9 0.76 -- 
Simultaneous 
70/30 1.26 15.2 1.6 1.68 -- 
PET first 
70/30 1.62 23.5 2.0 6.84 156.degree. C. 
LCP first 
70/30 1.42 20.3 2.0 5.88 -- 
-- 100/0 1.69 28.9 3.7 10 180.degree. C. 
__________________________________________________________________________ 
TABLE 4 
______________________________________ 
Properties of 30% Glass-filled LCP/PET Blends 
LCP/PET.sup.(1) 
50/50.sup.(2) 
70/30.sup.(2) 
100/0 
______________________________________ 
Tensile Modulus (Mpsi) 
2.13 2.18 2.4 
Tensile Strength (kpsi) 
27.7 20.5 30 
Elongation (%) 1.82 1.24 2.2 
Notched Izod (ft.-lb/in.) 
2.99 4.32 2.8 
HDT at 264 psi 219.degree. C. 
225.degree. C. 
230.degree. C. 
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.sup.(1) Composition by weight of polymer blend. Also includes 30% glass 
fiber. 
.sup.(2) Blends were made by introducing LCP and glass fiber downstream 
from PET in a twin screw extruder.