U.S. patent application number 15/242993 was filed with the patent office on 2016-12-08 for toughened polylactic acid polymers and copolymers.
The applicant listed for this patent is Tepha, Inc.. Invention is credited to Amit Ganatra, Kicherl Ho, David P. Martin, Said Rizk, Simon F. Williams.
Application Number | 20160355677 15/242993 |
Document ID | / |
Family ID | 38189011 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160355677 |
Kind Code |
A1 |
Rizk; Said ; et al. |
December 8, 2016 |
TOUGHENED POLYLACTIC ACID POLYMERS AND COPOLYMERS
Abstract
Toughened compositions of PLA and PLA copolymers are disclosed,
which also have low tensile modulus values and greater elongation
to break. These toughened compositions are prepared by blending PLA
and PLA copolymers with poly-4-hydroxybutyrate, and copolymers
thereof. Blending of poly-4-hydroxybutyrate with PLA and its
copolymers has been found to impart advantageous properties to the
resulting blend. These compositions, and objects formed from these
compositions, have improved toughness and lower stiffness than
polylactic acid polymers or copolymers alone.
Inventors: |
Rizk; Said; (Windham,
NH) ; Martin; David P.; (Arlington, MA) ; Ho;
Kicherl; (Groton, MA) ; Ganatra; Amit;
(Attleboro, MA) ; Williams; Simon F.; (Sherborn,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tepha, Inc. |
Lexington |
MA |
US |
|
|
Family ID: |
38189011 |
Appl. No.: |
15/242993 |
Filed: |
August 22, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11671544 |
Feb 6, 2007 |
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15242993 |
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60747144 |
May 12, 2006 |
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60765840 |
Feb 7, 2006 |
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60765808 |
Feb 7, 2006 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 31/06 20130101;
A61K 47/34 20130101; C08K 5/0083 20130101; A61L 15/26 20130101;
A61L 17/12 20130101; A61L 29/049 20130101; A61L 31/041 20130101;
A61L 17/105 20130101; A61L 29/06 20130101; A61L 27/18 20130101;
C08K 3/014 20180101; A61L 27/26 20130101; C08G 63/06 20130101; C08K
5/0016 20130101; A61L 29/049 20130101; A61L 31/10 20130101; C08L
67/04 20130101; A61L 31/041 20130101; A61L 31/18 20130101; C08K
5/005 20130101; A61L 31/148 20130101; C08L 67/04 20130101; A61L
27/26 20130101; A61L 31/10 20130101; C08L 2666/18 20130101; C08L
67/04 20130101; C08L 67/04 20130101; C08L 67/04 20130101; C08L
67/04 20130101 |
International
Class: |
C08L 67/04 20060101
C08L067/04; A61L 31/04 20060101 A61L031/04 |
Claims
1. A medical device comprising a toughened polymer composition
comprising poly-4-hydroxybutyrate homopolymer or copolymer thereof
wherein the composition further comprises at least one polylactic
acid homopolymer or copolymer, and the amount of
poly-4-hydroxybutyrate homopolymer or copolymer added is sufficient
to increase the elongation to break of the composition to greater
than the elongation to break of the polylactic acid homopolymer or
copolymer.
2. The medical device of claim 1 wherein the composition has been
oriented.
3. The medical device of claim 1 wherein the elongation to break of
the composition is greater than 3%.
4. The medical device of claim 3 wherein the elongation to break of
the composition is between 3% and 281%.
5. The medical device of claim 1 wherein the Young's modulus of the
composition is less than the Young's modulus of the polylactic acid
homopolymer or copolymer.
6. The medical device of claim 5 wherein the Young's modulus of the
composition is less than 700 kgf/mm.sup.2.
7. The medical device of claim 1 wherein the ratio of the
polylactic acid homopolymer or copolymer to the
poly-4-hydroxybutyrate homopolymer is between 9:1 and 1:9 by
weight.
8. The medical device of claim 1 wherein the polylactic acid
homopolymer is poly-L-lactic acid.
9. The medical device of claim 1 wherein the device is a suture,
suture fastener, meniscus repair device, rivet, tack, staple,
screw, bone plate, bone plating system, biocompatible coating,
rotator cuff repair device, surgical mesh, medical textile, repair
patch, sling, cardiovascular patch, tissue engineering scaffold,
vascular graft, vascular closure device, catheter balloon,
anti-adhesion device, drug delivery device, embolization particle,
orthopedic pin, adhesion barrier, stent (including coronary stents,
peripheral stents, carotid stents, biliary stents, gastroenterology
stents, urology stents, and neurology stents), embolization coil,
guided tissue repair/regeneration device, articular cartilage
repair device, nerve guide, tendon repair device, intracardiac
septal defect repair device (including, but not limited to, atrial
septal defect repair devices and PFO closure devices and left
atrial appendage (LAA) closure devices), pericardial patch, bulking
and filling agent, vein valves, bone marrow scaffold, meniscus
regeneration device, ligament graft, tendon graft, ocular cell
implant, spinal fusion cage, imaging device, skin substitute, dural
substitute, bone graft substitute, bone dowel, would dressing, or a
hemostat.
10. A process for preparing the medical device of claim 1,
comprising blending poly-4-hydroxybutyrate homopolymer or copolymer
thereof with at least one polylactic acid homopolymer or copolymer,
wherein the poly-4-hydroxybutyrate homopolymer or copolymer thereof
and at least one polylactic acid homopolymer are mixed in the
molten state at a temperature between 110.degree. C. and
230.degree. C., and extruded.
11. The process of claim 8 further comprising extruding the
toughened composition, wherein the composition is dried to a water
content of less than 0.01% (w/w) prior to extrusion, and wherein
the composition is extruded at a temperature between 140.degree. C.
and 250.degree. C.
12. The process of claim 9 wherein the extrudate is oriented by
drawing it with stretch ratios of 1X to 11X.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. Ser. No.
11/671,544, filed Feb. 6, 2007, which claims priority to U.S. Ser.
No. 60/747,144 filed May 12, 2006, U.S. Ser. No. 60/765,840, filed
Feb. 7, 2006 and U.S. Ser. No. 60/765,808 filed Feb. 7, 2006.
FIELD OF THE INVENTION
[0002] The present invention generally relates to polymeric
compositions that can be processed into various extruded as well as
molded forms, including fibers, tubes, films, nonwovens, injection
molded or thermoformed components, which products have
substantially uniform physical properties, and physical and
thermo-mechanical integrity. The compositions comprise polylactic
acid polymers or copolymers and polymers or copolymers comprising
4-hydroxybutyrate.
BACKGROUND OF THE INVENTION
[0003] Polylactic acid (PLA) is an aliphatic polyester that can be
prepared, for example, by direct condensation of lactic acid,
azeotropic dehydrative condensation, and by ring-opening
polymerization of lactide. In the latter case, the product is
sometimes referred to as polylactide. The relative proportions of
the optically active enantiomers, D- and L-lactic acids, which are
incorporated into the polymer, determine the specific properties of
PLA. Varying the enantiomer proportions can result in polymer
compositions that are amorphous or up to about 40% crystalline,
with glass transition temperatures (Tg) ranging from about
50.degree. C. to 80.degree. C., and melting points (Tm) ranging
from about 130.degree. C. to 180.degree. C.
[0004] Elongation at break of poly-L-lactic acid (PLLA) is,
however, typically just several percent. The polymer has a glass
transition temperature well above room temperature, and therefore
shaped objects of PLLA tend to be brittle and glassy at room
temperature. Several methods have been used to increase the
elongation at break of PLLA. Melt processing of the polymer,
followed by orientation at temperatures above the glass transition
temperature, can result in shaped objects with somewhat improved
elongation to break. However, these objects are generally stiff due
to the relatively high tensile modulus of the polymer.
[0005] Incorporation of D-lactic acid in combination with
orientation can yield further improvement. For example,
incorporation of D-lactic acid at a level of 2% in an oriented film
increases the elongation at break to 5-10%. The latter may be
further increased to 78-97% with incorporation of about 6% D-lactic
acid. Orientation and incorporation of D-lactic acid has also been
used to improve the toughness of fibers of PLA. Melt extruded
fibers of PLA with elongation to break of 50-60% are commercially
available under the trade name of Ingeo.TM. PLA (Cargill, Minn.).
The modulus of these objects is however still relatively high.
[0006] Polymer scientists have also investigated blends of PLA with
other polymers and additives to improve PLA properties, for
example, to improve toughness and decrease the stiffness. For
example, blends of PLA with other PLAs and copolymers,
polycaprolactone, poly-3-hydroxybutyrate-co-3-hydroxyvalerate
(PHBV), poly-R-3-hydroxybutyrate (PHB), poly-R,S-3-hydroxybutyrate,
poly-3-hydroxyoctanoate, poly(hexamethylenesuccinate),
poly(butylene succinate), poly(ethylene/butylene succinate),
poly(ethylene oxide), poly(phosphazene), poly(sebacic anhydride),
poly(vinyl alcohol), and poly(vinyl acetate) have all been reported
(Tsuji, H., Polyesters, III, 4:129-177 (2002)). Blends of PLA
comprising multiple components have also been reported. For
example, U.S. Pat. No. 5,939,467 to Wnuk et al. discloses blends
comprising PLA, polyhydroxyalkanoates, and polyurethane or
polycaprolactone. These approaches have met with varying levels of
success because many polymers are immiscible when blended, creating
undesirable phase separation during processing, and/or such blends
exhibit poor mechanical properties. These difficulties are
exacerbated in the processing of fibers and films, where processing
time is often much shorter.
[0007] It would therefore be desirable to identify polymers that
could be blended with PLA and its copolymers, which provide a blend
with improved toughness and lower stiffness.
[0008] It is therefore an object of this invention to provide
toughened blends of PLA and its copolymers.
[0009] It is another object of this invention to provide blends of
PLA and its copolymers with lower stiffness values.
[0010] It is still yet another object of this invention to provide
blends of PLA and its copolymers with increased elongation to
break.
[0011] It is yet another object of this invention to provide blends
of PLA and its copolymers that can be processed into shaped
objects, such as fibers, films, molded items, and nonwovens.
SUMMARY OF THE INVENTION
[0012] Toughened compositions of PLA and PLA copolymers are
disclosed, which also have low tensile modulus values and greater
elongation to break. These toughened compositions are prepared by
blending PLA and PLA copolymers with poly-4-hydroxybutyrate, and
copolymers thereof. Blending of poly-4-hydroxybutyrate with PLA and
its copolymers has been found to impart advantageous properties to
the resulting blend. These compositions, and objects formed from
these compositions, have improved toughness and lower stiffness
than polylactic acid polymers or copolymers alone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is the chemical structure of poly-4-hydroxybutyrate
(P4HB, TephaFLEX.RTM. biomaterial).
[0014] FIG. 2 shows some of the known biosynthetic pathways for the
production of P4HB. Pathway enzymes are: 1. Succinic semialdehyde
dehydrogenase; 2. 4-hydroxybutyrate dehydrogenase; 3. diol
oxidoreductase; 4. aldehyde dehydrogenase; 5. Coenzyme A
transferase and 6. PHA synthetase.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Toughened blends comprising PLA and its copolymers have been
developed that have improved properties.
[0016] I. Definitions
[0017] "Poly-4-hydroxybutyrate" as generally used herein means a
homopolymer comprising 4-hydroxybutyrate units. It may be referred
to herein as P4HB or TephaFLEX.RTM. biomaterial (manufactured by
Tepha, Inc., Cambridge, Mass.).
[0018] "Copolymers of poly-4-hydroxybutyrate" as generally used
herein means any polymer comprising 4-hydroxybutyrate with one or
more different hydroxy acid units.
[0019] "Blend" as generally used herein means a physical
combination of different polymers, as opposed to a copolymer
comprised of two or more different monomers which are linked by
polymerization.
[0020] "Toughness" means a property of a material by virtue of
which it can absorb energy; the actual work per unit volume or unit
mass of material that is required to rupture it. Toughness is
usually proportional to the area under the load-elongation curve
such as the tensile stress-strain curve. (Rosato's Plastics
Encyclopedia and Dictionary, Oxford Univ. Press, 1993.)
[0021] "Stiffness" means a property of the material to resist a
change in shape. For fibers, this is typically measured as the
tensile modulus or Young's modulus and is the initial slope of the
stress strain curve. For other shaped articles, like molded goods,
the stiffness could relate to the ability of the material to resist
bending.
[0022] "Elongation" or extensibility of a material means the amount
of increase in length resulting from, as an example, the tension to
break a specimen. It is expressed usually as a percentage of the
original length. (Rosato's Plastics Encyclopedia and Dictionary,
Oxford Univ. Press, 1993.)
[0023] "PLA" as used herein refers to a polymer comprising a lactic
acid monomer unit. The polymer may be referred to as polylactic
acid or polylactide. It may be a homopolymer or copolymer. The
lactic acid repeating units can be L-lactic acid, D-lactic acid, or
D,L-lactic acid. Copolymers may also comprise monomeric units other
than lactic acid, such as, but not limited to, glycolic acid.
[0024] "Molecular weight" as used herein, unless otherwise
specified, refers to the weight average molecular weight (Mw) as
opposed to the number average molecular weight (Mn).
[0025] "Absorbable" as generally used herein means the material is
broken down in the body and eventually eliminated from the
body.
[0026] "Biocompatible" as generally used herein means the
biological response to the material or device being appropriate for
the device's intended application in vivo. Any metabolites of these
materials should also be biocompatible.
[0027] "Compostable" as generally used herein means the ability of
the material to undergo physical, chemical, thermal, and/or
biological degradation in a municipal solid waste composting
facility such that the material will break down into, or otherwise
become part of, usable finished compost.
[0028] II. Polymeric Compositions
[0029] A. PLA Polymers
[0030] The polylactic acid or polylactide polymers (together
referred to as "PLA") comprise a lactic acid monomeric unit, which
may be L-lactic acid, D-lactic acid, or a mixture of D,L-lactic
acid. Examples of commercially available PLA polymers include
polylactic acid sold by Natureworks.RTM. (Cargill, Minn.),
Lacea.RTM. sold by Mitsui Chemical (Tokyo, Japan), and Resomer sold
by Boehringer Ingelheim (Ingelheim Am Rhein, Germany). In a
preferred embodiment, the PLA is in a semi-crystalline form with at
least 80 mole percent of the repeating unit being either L-lactide
or D-lactide, and even more preferably 95 mole percent. If desired
more than one PLA composition may be used. For example, two PLA
polymers with different molecular weights or melting temperatures
may be used. PLA copolymers may also comprise monomeric units other
than lactic acid. A preferred PLA copolymer comprises glycolic
acid, and is available commercially, for example, under the
Vicryl.RTM. trade name.
[0031] B. Polymers Comprising 4-Hydroxybutyrate
[0032] Tepha, Inc. of Cambridge, Mass. produces
poly-4-hydroxybutyrate (P4HB) and copolymers thereof using
transgenic fermentation methods. Poly-4-hydroxybutyrate is a
strong, pliable thermoplastic polyester that is produced by a
fermentation process, as described in U.S. Pat. No. 6,548,569 to
Williams et al. Despite its biosynthetic route, the structure of
the polyester is relatively simple (FIG. 1). The polymer belongs to
a larger class of materials called polyhydroxyalkanoates (PHAs)
that are produced by numerous microorganisms (see: Steinbuchel A.,
et al. Diversity of Bacterial Polyhydroxyalkanoic Acids, FEMS
Microbial. Lett. 128:219-228 (1995)). In nature these polyesters
are produced as storage granules inside cells, and serve to
regulate energy metabolism. They are also of commercial interest
because of their thermoplastic properties, and relative ease of
production. Several biosynthetic routes are currently known to
produce P4HB, as shown in FIG. 2. Chemical synthesis of P4HB has
been attempted, but it has been impossible to produce the polymer
with a sufficiently high molecular weight necessary for most
applications (Hori, Y., et al., Polymer 36:4703-4705 (1995)).
[0033] Copolymers of P4HB include 4-hydroxybutyrate copolymerized
with 3-hydroxybutyrate or glycolic acid (U.S. Patent Publication
No. 20030211131 by Martin & Skraly, U.S. Pat. No. 6,316,262 to
Huisman et al., and U.S. Pat. No. 6,323,010 to Skraly et al.).
Methods to control molecular weight of PHA polymers are disclosed
by U.S. Pat. No. 5,811,272 to Snell et al.
[0034] PHAs with degradation rates in vivo of less than one year
are disclosed by U.S. Pat. No. 6,548,569 to Williams et al. and WO
99/32536 by Martin et al. Applications of P4HB have been reviewed
in Williams, S. F., et al., Polyesters, III, 4:91-127 (2002), and
by Martin, D. et al. Medical Applications of
Poly-4-hydroxybutyrate: A Strong Flexible Absorbable Biomaterial,
Biochem. Eng. J. 16:97-105 (2003). Medical devices and applications
of P4HB have also been disclosed by WO 00/56376 by Williams et
al.
[0035] C. Other Components
[0036] The toughened PLA compositions may comprise other materials
in addition to the polymers described above, including
plasticizers, nucleants, and compatibilizers. Non-limiting examples
of plasticizers are disclosed by U.S. Pat. No. 6,905,987 to Noda et
al. In addition, other components may be added to impart benefits
such as, but not limited to, the following: stability including
oxidative stability, brightness, color, flexibility, resiliency,
workability, processibility (by addition of processing aids),
viscosity modifiers, and odor control. Therapeutically,
prophylactically or diagnostic agents may be added. Active
components, such as drugs, and other biologically active substances
may be incorporated, for example, for controlled release of the
drugs or other substances. It may also be advantageous to
incorporate contrast agents, radiopaque markers, or radioactive
substances. For certain applications it may also be desirable to
incorporate fillers, including materials such as titanium dioxide,
calcium carbonate, hydroxyapatite, and tricalcium phosphate.
[0037] III. Methods of Making Toughened Compositions of PLA and PLA
Copolymers
[0038] In a preferred method, a toughened composition of a PLA
polymer or PLA copolymer is prepared as follows. A PLA polymer or
PLA copolymer is selected and compounded in a predetermined ratio
with a P4HB polymer or copolymer using a twin screw extruder. If
desired, other additives, such as plasticizers, nucleants, and
compatibilizers may be added. Typically, the PLA polymer or
copolymer will be present from 1% to 99%, by weight. The exact
ratio of PLA to P4HB will be determined by the desired toughness
and stiffness of the composition. Increasing the quantity of P4HB
in the blend will generally decrease the tensile modulus
(stiffness) and increase the elongation to break of the composition
(and also any shaped object derived from the composition). The
extrudate is cooled, and then cut into granules in a pelletizer.
The granules obtained may then be subsequently processed by melt or
solvent processing techniques.
[0039] PLA compositions toughened with P4HB polymers or copolymers
are characterized by increased elongation to break, and decreased
stiffness.
[0040] IV. Fabrication with Toughened PLA Compositions
[0041] The compositions possess properties that are desirable in
both processing and the final product. For example, the properties
would be desirable in processing by extrusion,
injection/compression/blow molding, coating, spinning, blowing,
thermoforming, laser cutting, thermal welding and calendaring
processes. A person skilled in the art would recognize that the
compositions are useful in any application where increased
toughness, elongation and/or decreased stiffness is desired. The
compositions may also provide other desired properties such as
increased melt strength, impact and aging characteristics, and be
useful in any application where these properties are desired.
[0042] The compositions may be used in commodity, industrial and
medical applications. In the latter case, the compositions may be
used to make partially or fully absorbable biocompatible medical
devices. Such devices include sutures, suture fasteners, meniscus
repair devices, rivets, tacks, staples, screws, bone plates and
bone plating systems, biocompatible coatings, rotator cuff repair
devices, surgical mesh, medical textiles and drapes, repair
patches, slings, cardiovascular patches, tissue engineering
scaffolds, vascular grafts, vascular closure devices, catheter
balloons, anti-adhesion devices, drug delivery devices,
embolization particles, orthopedic pins, adhesion barriers, stents
(including coronary stents, peripheral stents, carotid stents,
biliary stents, gastroenterology stents, urology stents, and
neurology stents), embolization coils, guided tissue
repair/regeneration devices, articular cartilage repair devices,
nerve guides, tendon repair devices, intracardiac septal defect
repair devices (including, but not limited to, atrial septal defect
repair devices and PFO closure devices, and left atrial appendage
(LAA) closure devices), pericardial patches, bulking and filling
agents, vein valves, bone marrow scaffolds, meniscus regeneration
devices, ligament and tendon grafts, ocular cell implants, spinal
fusion cages, imaging devices, skin substitutes, dural substitutes,
bone graft substitutes, bone dowels, wound dressings, and
hemostats.
[0043] The devices can also be a shaped object used as or in
packaging, personal hygiene products, bags, utensils, disposable
and/or compostable articles, garments, surgical drapes, and gloves.
The shaped object can be a disposable article, compostable article,
packaging, personal hygiene product, textile, fiber, film, molded
object, bag, utensil, garment, surgical drape, or glove.
[0044] The present invention will be further understood by
reference to the following non-limiting examples.
EXAMPLES
Example 1
Preparation of a Blend of PLA Polymer and P4HB Polymer
[0045] PLLA polymer (Resomer L 214 lot #1012474, Boehringer
Ingelheim, Germany) with a viscosity of 5.9 dl/g (IV) was
compounded with P4HB (poly-4-hydroxybutyrate, Mw 178,000, 2.3 dl/g
(IV) (Tepha, Inc., Cambridge, Mass.) using a Leistritz 18 mm twin
screw extruder (24:1 L/D). Compounding was undertaken at a
temperature of 110.degree. C. at the feed, and 230.degree. C. at
the die. The polymers were mixed in the molten state, extruded into
large diameter filament, quenched into a water bath set at
5-20.degree. C., and cut into 2-5 mm length pellets. The PLLA and
P4HB were compounded in the following three different ratios by
weight: PLLA (90%):P4HB (10%); PLLA (77.5%):P4HB (22.5%); and PLLA
(10%):P4HB (90%).
Example 2
Preparation of a Blend of PLA Polymer and P4HB Polymer
[0046] PLLA polymer (Resomer L 214 lot #1002260, Boehringer
Ingelheim, Germany) with a high intrinsic viscosity of 7.0 dl/g
(IV) was dry mixed with P4HB (poly-4-hydroxybutyrate, Mw 170,000,
2.1 dl/g (IV) Tepha, Inc., Cambridge, Mass.) by tumble mixing at
room temperature. The PLLA and P4HB were compounded in the
following three different ratios by weight:
PLLA (90%):P4HB (10%); PLLA (77.5%):P4HB (22.5%); and
PLLA (10%):P4HB (90%).
Example 3
Fiber Extrusion of PLA/P4HB Blends
[0047] The blends prepared in Example 1 were extruded into
monofilament fiber using the following method. The blends were
dried under vacuum overnight to less than 0.01% (w/w) water. Dried
pellets of the blended polymers were fed into an extruder barrel of
an AJA (Alex James Associates, Greer, S.C.) 3/4'' single screw
extruder (24:1 L:D, 3:1 compression) equipped with a Zenith type
metering pump (0.16 cc/rev) and a die with a single hole spinneret
(0.026'', 2:1 L:D) under a blanket of nitrogen. The 4 heating zones
of the extruder were set at 140.degree., 190.degree., 200.degree.
and 205.degree. C. The block, metering pump and the die were
maintained at a constant temperature, preferably 180-250.degree. C.
Pump discharge pressure was kept below 1500 psi by controlling the
temperatures and the speed of the metering pump. The fiber spinning
system was set up with a drop zone, air quench zone, a guide roll,
three winders and a pickup. The fiber was oriented in-line with
extrusion by drawing it in a multi-stage process to provide
improved physical properties with stretch ratios of 1 to 11X. The
resulting spun extrudate filament was free from all melt
irregularities. To provide optimal physical properties to fiber,
the extrudate filament was then drawn through multistage
orientation in a heated tube or heated oven or hot water, which was
maintained at a temperature above the softening temperature of the
extrudate filament and then quenched in a cold water bath without
the filament touching any surface until it is sufficiently
cooled.
[0048] Oriented monofilament fiber produced according to the
procedure of Example 3 was tested on a MTS Mechanical Analyzer. The
results are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Properties of PLLA:P4HB Blends at different
ratios versus PLLA Elon- Diam- Break Break gation Young's Knot
Sample (% eter Load Stress at Break Modulus Load by weight) (mm)
(kgf) (kgf/mm.sup.2) (%) (kgf/mm.sup.2) (kgf) P4HB (90%): 0.309
5.05 67.4 24.3 170.9 3.01 PLLA (10%) P4HB (22.5%): 0.312 2.92 36.9
17.0 270.4 2.07 PLLA (77.5%) P4HB (10%): 0.382 4.02 35.2 16.7 302.1
2.89 PLLA (90%) Reference: 0.106 0.6 66.0 3.0 700.0 Nd PLLA
(100%)
[0049] It is evident from Table 1 that blending P4HB with PLLA
increases the toughness of the PLLA (elongation at break
increases), and decreases Young's modulus. The extent of these
changes increases with increasing weight percentage of P4HB in the
blend.
[0050] Note: The fibers in Table 1 have been oriented to increase
the tensile strength of the fiber. Much of the elongation to break
is reduced during the orientation process. (Higher elongation to
break (>200%) for partially oriented tubes is disclosed in
Example 4.)
Example 4
Tube Extrusion of PLA/P4HB Blends
[0051] The blends prepared in Example 1 and Example 2 were dried as
described in Example 3 and extruded into tubes with internal
diameters (ID) of 1-1.4 mm, and outer diameters (OD) of 1.3-1.7 mm
using the following equipment, 1.25'' 3 heat zone, 24:1 L/D, 3:1
compression horizontal extruder connected to conventional tubing
die with an air inlet port to control the ID of tubes. A water
trough for tube quenching, dual-plane laser gauge to measure OD in
two planes and a puller were also used. Extruder temperatures were
controlled at 120.degree. C. for the first zone, 240.degree. C. for
the second zone, 265.degree. C. for the third zone and 248.degree.
C. for the die. Screw speed was controlled between 10-40 rpm and
the die pressure was maintained at 1500 psi. During the extrusion
the quench trough was maintained at 10.degree. C. and process air
at 10-30 inch H.sub.2O pressure was used to obtain the intended
tubing ID.
[0052] The extruded tubes were tested on a MTS Mechanical Analyzer,
the Mw's of the tubes were analyzed by Gel Permeation
Chromatography (GPC) and the results are shown in Table 2.
TABLE-US-00002 TABLE 2 Properties of tubing melt extruded from
P4HB:PLLA blends (22.5:77.5% by weight). Elongation Tensile Mixing
Mw by GPC OD ID To Break Strength Method g/mol (mm) (mm) (%) (MPa)
Twin 285,000 1.547 .+-. 0.042 1.097 281 .+-. 69 33.5 Screw Dry
Blend 344,000 1.613 .+-. 0.029 1.363 206 .+-. 92 47.0
* * * * *