WO1994011173A1 - Process for producing polylactide molded bodies by extrusion or compression molding - Google Patents

Process for producing polylactide molded bodies by extrusion or compression molding Download PDF

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Publication number
WO1994011173A1
WO1994011173A1 PCT/EP1993/003225 EP9303225W WO9411173A1 WO 1994011173 A1 WO1994011173 A1 WO 1994011173A1 EP 9303225 W EP9303225 W EP 9303225W WO 9411173 A1 WO9411173 A1 WO 9411173A1
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WIPO (PCT)
Prior art keywords
polylactide
amorphous
extrusion
preform
molded bodies
Prior art date
Application number
PCT/EP1993/003225
Other languages
German (de)
French (fr)
Inventor
Hans-Josef Sterzel
Original Assignee
Basf Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Basf Aktiengesellschaft filed Critical Basf Aktiengesellschaft
Priority to EP94901813A priority Critical patent/EP0669866A1/en
Priority to JP6511731A priority patent/JPH08502935A/en
Publication of WO1994011173A1 publication Critical patent/WO1994011173A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B11/00—Making preforms
    • B29B11/06—Making preforms by moulding the material
    • B29B11/12—Compression moulding

Definitions

  • Poly-L-lactide, poly-D-lactide and their copolymers are known. They are compostable polymers, the decomposition of which does not result in non-natural degradation products, but only biomass and carbon dioxide. Because of this behavior, polylactide has great potential, especially in the packaging sector.
  • Polylactides can also be produced entirely from renewable raw materials: L-lactide, D-lactide, DL-lactide or mixtures thereof are obtained from lactic acid and ring-opening to high-molecular products and polymerized while maintaining the asymmetric carbon atom.
  • the homopolymeric D- and L-lactides have melting points around 175 ° C, the tensile modulus at room temperature is 3,000 N / mm 2 , the weight average molecular weights being 50,000 to 200,000 g / mol.
  • the glass transition temperature is 50 ° C.
  • polylactides have a disadvantage for conventional injection molding processing: they crystallize so slowly that cooling times of up to several minutes are required in order to obtain partially crystalline moldings with appropriate dimensional stability above the glass transition temperature. The long cooling time is also needed to avoid sticking in the mold.
  • polylactides can be made more tensile by one-dimensional orientation (DE 16 42 112, DE 16 42 111, DE 14 92 427). Fibers are extruded and stretched at temperatures from 60 to 150 ° C up to ten times their original length.
  • Such fibers are commonly used as surgical sutures.
  • the object is achieved by processing polylactides by compression molding or extrusion molding, the mass flowing and oriented in several directions in a temperature range from 60 to 150 ° C. and spontaneous crystallization occurring.
  • the crystallization therefore takes place in fractions of a second, while it takes place in the range of minutes without the presence of flow and orientation.
  • amorphous preforms or semi-finished amorphous products are produced by extrusion or injection molding when the melt is cooled to below 30 ° C.
  • This amorphous preforms or the amorphous semifinished product is at temperatures of 60 to 150 ° C within 1 to 3 min. heated.
  • the temperature conditions are set so that the material does not crystallize.
  • the heating can take place via electrical heat radiators as well as by contacting with a heating liquid such as water, ethylene glycol, glycerol or high-boiling petroleum ether or by means of a warm air stream.
  • the semi-finished product is then brought into a mold with a temperature of 60 to 150 ° C., preferably the same temperature as that of the semi-finished product, and the mold is then closed.
  • the mass of the semi-finished product is chosen so that the finished molded part just fills the mold.
  • the increase in density due to crystallization is taken into account.
  • the finished molded part can be removed from the mold within a few seconds. 5
  • the processing of polylactide according to the invention allows the production of complex objects with high heat resistance and high solvent resistance within economically short cycle times.
  • a poly-L-lactide with an inherent viscosity of 1.59 is used, measured as a 0.1% solution in chloroform at 25 ° C.
  • the amorphous density of the material, measured on a quenched injection molded part, mold temperature 20 ° C., is 1.25 g / cm 3 .
  • the material was pre-dried at 120 ° C for 15 to 20 hours at a pressure of less than 10 mbar.
  • the processing itself was carried out under argon coverage in order to avoid degradation of the molar mass by oxidation and / or hydrolysis.
  • the melt temperature was 25 205 ° C.
  • Poly-lactide is melted in the plasticizing unit of an injection molding machine and then injected into a mold for the production of cups, lower diameter 45 mm, upper diameter 58 mm, height 56 mm, wall thickness 1.5 mm.
  • the cup weighs 20.4 g.
  • the mold surface temperature is varied between 90 and 130 ° C.
  • the shortest demolding time is 4.1 min. at a mold surface temperature of 110 ° C.
  • a crystalline fraction of approximately 20% is measured as the quotient of the area of the crystalline X-ray peak to the total area.
  • the modulus of elasticity is 2,900 N / mm 7 .
  • polylactide is melted and then injected into a mold cooled to 20 ° C., after 20 seconds. Cycle time to obtain a disk-shaped amorphous preform with a diameter of 37.3 mm, a height of 15 mm and a weight of 20.5 g.
  • the preform is in boiling water within 30 seconds. heated to 100 ° C. It is then placed in the middle of a press die heated to 100 ° C. The stamp is then lowered, likewise at a temperature of 100 ° C., in order to obtain a molded part corresponding to the cup from Example 1.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Casting Or Compression Moulding Of Plastics Or The Like (AREA)

Abstract

A process for producing polylactide molded bodies is characterised in that an amorphous polylactide semi-finished product or a compact amorphous preform is heated up to a temperature between 60 and 150 °C. The preform remains amorphous and is then extruded in a tool which is equally heated up to a temperature between 60 and 150 °C. The polylactide thus flows along multiple axes, is oriented and crystallized.

Description

Verfahren zur Herstellung von Polylactid-Formkörpern durch Form¬ pressen oder FließpressenProcess for the production of polylactide moldings by compression molding or extrusion molding
Beschreibungdescription
Poly-L-Lactid, Poly-D-Lactid sowie deren Copolymere sind bekannt. Es sind kompostierbare Polymere, bei deren Verrottung keine naturfremden Abbauprodukte, sondern nur Biomasse sowie Kohlen- dioxid entstehen. Aufgrund dieses Verhaltens hat Polylactid ein großes Potential, besonders im Verpackungsbereich.Poly-L-lactide, poly-D-lactide and their copolymers are known. They are compostable polymers, the decomposition of which does not result in non-natural degradation products, but only biomass and carbon dioxide. Because of this behavior, polylactide has great potential, especially in the packaging sector.
Polylactide können außerdem vollständig aus nachwachsenden Roh¬ stoffen hergestellt werden: L-Lactid, D-Lactid, DL-Lactid oder Mischungen davon werden aus Milchsäure erhalten und zu hoch¬ molekularen Produkten ringöffnend und unter Erhalt des asym¬ metrischen Kohlenstoffatoms polymerisiert.Polylactides can also be produced entirely from renewable raw materials: L-lactide, D-lactide, DL-lactide or mixtures thereof are obtained from lactic acid and ring-opening to high-molecular products and polymerized while maintaining the asymmetric carbon atom.
Die homopolymeren D- und L-Lactide weisen Schmelzpunkte um 175°C auf, der Zug-E-Modul liegt bei Raumtemperatur bei 3.000 N/mm2, wobei die Gewichtsmittel der Molmassen 50.000 bis 200.000 g/Mol betragen. Die Glasübergangstemperatur liegt bei 50°C.The homopolymeric D- and L-lactides have melting points around 175 ° C, the tensile modulus at room temperature is 3,000 N / mm 2 , the weight average molecular weights being 50,000 to 200,000 g / mol. The glass transition temperature is 50 ° C.
Allerdings weisen Polylactide für die übliche Spritzgießver- arbeitung einen Nachteil auf: Sie kristallisieren so langsam, daß Kühlzeiten bis zu mehreren Minuten erforderlich sind, um teil¬ kristalline Formkörper mit entsprechender Formbeständigkeit ober¬ halb der Glasübergangstemperatur zu erhalten. Die lange Kühlzeit wird auch benötigt, um ein Kleben in der Form zu vermeiden.However, polylactides have a disadvantage for conventional injection molding processing: they crystallize so slowly that cooling times of up to several minutes are required in order to obtain partially crystalline moldings with appropriate dimensional stability above the glass transition temperature. The long cooling time is also needed to avoid sticking in the mold.
Polylactide können - wie die meisten Polymeren - durch ein¬ dimensionale Orientierung zugfester gemacht werden (DE 16 42 112, DE 16 42 111, DE 14 92 427) . Dabei werden Fasern extrudiert und bei Temperaturen von 60 bis 150°C bis zum zehnfachen der ursprüng- liehen Länge verstreckt.Like most polymers, polylactides can be made more tensile by one-dimensional orientation (DE 16 42 112, DE 16 42 111, DE 14 92 427). Fibers are extruded and stretched at temperatures from 60 to 150 ° C up to ten times their original length.
Derartige Fasern werden gewöhnlich als chirurgisches Nahtmaterial verwendet.Such fibers are commonly used as surgical sutures.
Es ist auch bekannt, extrudierte Profile (DE 39 39 363) bei 105 bis 160°C zu strecken. Auch die Herstellung von Schrauben, Stiften und Rohren höherer Längsfestigket durch Verstrecken von Poly- lactiden ist beschrieben (EP 321 176) . Derart hergestellte Teile werden als biologisch abbaubare Prothesenteile eingesetzt. Anders als bei eindimensional verstreckten und belasteten Teilen treten beim Herstellen mehrdimensional zu belastender Teile wie Folien oder Hohlkörpern ernste Probleme dadurch auf, daß die Festigkeit senkrecht zur Verstreckrichtung infolge der mole- kularen Orientierung leidet, so daß die Teile bei Belastung senk¬ recht zur Verstreckrichtung auseinanderbrechen oder aufspleißen. Dieser Nachteil wird durch die erfindungsgemäßen mehrdimensio¬ nalen Fließorientierungen in vorteilhafter Weise behoben.It is also known to stretch extruded profiles (DE 39 39 363) at 105 to 160 ° C. The production of screws, pins and tubes of higher longitudinal strength by stretching polylactides is also described (EP 321 176). Parts manufactured in this way are used as biodegradable prosthesis parts. In contrast to one-dimensionally stretched and loaded parts, serious problems arise in the manufacture of multi-dimensionally loaded parts such as foils or hollow bodies in that the strength suffers perpendicular to the stretching direction due to the molecular orientation, so that the parts break apart perpendicularly to the stretching direction when loaded or unplug it. This disadvantage is eliminated in an advantageous manner by the multi-dimensional flow orientations according to the invention.
Es ist Aufgabe der Erfindung, ein Verfahren zur Herstellung von komplexen Formkörpern zu finden, das Polylactid-Formteile oder Halbzeug herzustellen erlaubt mit einer Formbeständigkeit von über 50°C und unter kurzen Kühlzeiten in der Form.It is an object of the invention to find a process for the production of complex moldings which allows polylactide moldings or semi-finished products to be produced with a dimensional stability of over 50 ° C. and with short cooling times in the mold.
Die Aufgabe wird gelöst, indem man Polylactide durch Formpressen oder Fließpressen verarbeitet, wobei die Masse in einem Temperaturbereich von 60 bis 150°C in mehreren Richtungen fließt und orientiert wird und spontane Kristallisation eintritt. Die Kristallisation findet also in Bruchteilen von Sekunden statt, während sie ohne Anwesenheit von Fließen und Orientierung im Bereich von Minuten stattfindet.The object is achieved by processing polylactides by compression molding or extrusion molding, the mass flowing and oriented in several directions in a temperature range from 60 to 150 ° C. and spontaneous crystallization occurring. The crystallization therefore takes place in fractions of a second, while it takes place in the range of minutes without the presence of flow and orientation.
Damit werden die erwünschten kurzen Zykluszeiten sowie die er¬ höhten Wärmeformbeständigkeiten erhalten. Zusätzlich findet man erhöhte Steifigkeiten in Richtung von Vorzugsorientierungen sowie erhöhte Lösemittelbeständigkeiten.The desired short cycle times and the increased heat resistance are thus obtained. In addition, there are increased stiffnesses in the direction of preferred orientations as well as increased solvent resistance.
Zum Formpressen oder Fließpressen werden über Extrudieren oder Spritzgießen bei Abkühlung der Schmelze auf unter 30°C amorphe Vorformlinge oder amorphes Halbzeug hergestellt.For compression molding or extrusion molding, amorphous preforms or semi-finished amorphous products are produced by extrusion or injection molding when the melt is cooled to below 30 ° C.
Diese amorphen Vorformlinge oder das amorphe Halbzeug wird auf Temperaturen von 60 bis 150°C innerhalb von 1 bis 3 min. erhitzt. Die Temperierbedingungen werden so eingestellt, daß das Material gerade nicht kristallisiert. Die Erwärmung kann über elektrische Wärmestrahler wie auch durch Kontaktierung mit einer Heizflüssig¬ keit wie Wasser, Ethylenglykol, Glycerin oder hochsiedendem Petroleumbenzin oder durch einen Warmluftström erfolgen.This amorphous preforms or the amorphous semifinished product is at temperatures of 60 to 150 ° C within 1 to 3 min. heated. The temperature conditions are set so that the material does not crystallize. The heating can take place via electrical heat radiators as well as by contacting with a heating liquid such as water, ethylene glycol, glycerol or high-boiling petroleum ether or by means of a warm air stream.
Sodann wird das Halbzeug in eine Form mit einer Temperatur von 60 bis 150°C, vorzugsweise der gleichen Temperatur wie der des Halb¬ zeugs gebracht und die Form danach geschlossen. Dabei wird die Masse des Halbzeugs gerade so gewählt, daß das fertige Formteil die Form gerade ausfüllt. Dabei wird die Erhöhung der Dichte in- folge Kristallisation berücksichtigt. Während der Verformung des Halbzeugs fließt dieses in verschie¬ dene Richtungen, wobei es entsprechend orientiert wird und bis zu Anteilen um 80 % kristallisiert. Das fertige Formteil kann der Form innerhalb weniger Sekunden entnommen werden. 5The semi-finished product is then brought into a mold with a temperature of 60 to 150 ° C., preferably the same temperature as that of the semi-finished product, and the mold is then closed. The mass of the semi-finished product is chosen so that the finished molded part just fills the mold. The increase in density due to crystallization is taken into account. During the deformation of the semi-finished product, it flows in different directions, whereby it is oriented accordingly and crystallizes up to 80%. The finished molded part can be removed from the mold within a few seconds. 5
Die erfindungsgemäße Verarbeitung von Polylactid erlaubt die Her¬ stellung komplexer Gegenstände mit hoher Wärmeformbeständigkeit sowie hoher Lösemittelbeständigkeit innerhalb wirtschaftlicher kurzer Taktzeiten.The processing of polylactide according to the invention allows the production of complex objects with high heat resistance and high solvent resistance within economically short cycle times.
1010
BeispieleExamples
In den nachstehenden Beispielen wird ein Poly-L-Lactid mit einer inhärenten Viskosität von 1,59 eingesetzt, gemessen als 0,1 %ige 15 Lösung in Chloroform bei 25°C. Die amorphe Dichte des Materials, gemessen an einem abgeschreckten Spritzgießteil, Formtemperatur 20°C, beträgt 1,25 g/cm3.In the examples below, a poly-L-lactide with an inherent viscosity of 1.59 is used, measured as a 0.1% solution in chloroform at 25 ° C. The amorphous density of the material, measured on a quenched injection molded part, mold temperature 20 ° C., is 1.25 g / cm 3 .
Vor der Verarbeitung wurde das Material jeweils bei 120°C 15 bis 20 20 h bei einem Druck kleiner als 10 mbar vorgetrocknet.Before processing, the material was pre-dried at 120 ° C for 15 to 20 hours at a pressure of less than 10 mbar.
Die Verarbeitung selbst erfolgte jeweils unter Argon-Abdeckung, um einen Molmassenabbau durch Oxidation und/oder Hydrolyse zu vermeiden. In allen Beispielen betrug die Schmelzetemperatur 25 205°C.The processing itself was carried out under argon coverage in order to avoid degradation of the molar mass by oxidation and / or hydrolysis. In all examples, the melt temperature was 25 205 ° C.
Beispiel 1 (Vergleichsbeispiel)Example 1 (comparative example)
In der Plastifiziereinheit einer Spritzgießmaschine wird Poly- 30 lactid aufgeschmolzen und danach in eine Form zur Herstellung von Bechern, unterer Durchmesser 45 mm, oberer Durchmesser 58 mm, Höhe 56 mm, Wanddicke 1,5 mm gespritzt. Der Becher wiegt 20,4 g. Die Formoberflächentemperatur wird zwischen 90 und 130°C variiert. Die kürzeste Entformungszeit beträgt 4,1 min. bei einer Form- 35 oberflächentemperatur von 110°C. In mittlerer Höhe wird ein kristalliner Anteil von ca. 20 % gemessen als Quotient der Fläche des kristallinen Röntgenpeaks zur Gesamtfläche. Der E-Modul be¬ trägt 2.900 N/mm7.Poly-lactide is melted in the plasticizing unit of an injection molding machine and then injected into a mold for the production of cups, lower diameter 45 mm, upper diameter 58 mm, height 56 mm, wall thickness 1.5 mm. The cup weighs 20.4 g. The mold surface temperature is varied between 90 and 130 ° C. The shortest demolding time is 4.1 min. at a mold surface temperature of 110 ° C. At medium height, a crystalline fraction of approximately 20% is measured as the quotient of the area of the crystalline X-ray peak to the total area. The modulus of elasticity is 2,900 N / mm 7 .
40 Beispiel 240 Example 2
In der Plastifiziereinheit einer Spritzgießmaschine wird Polylac¬ tid aufgeschmolzen und danach in eine auf 20°C gekühlte Form ges¬ pritzt, um nach 20 see. Zykluszeit einen scheibenförmigen amor- 45 phen Vorformling mit 37,3 mm Durchmesser, 15 mm Höhe und 20,5 g Gewicht zu erhalten. Der Vorformling wird in siedendem Wasser innerhalb von 30 see. auf 100°C erhitzt. Sodann wird er in der Mitte eines auf 100°C temperierten Gesenks einer Presse plaziert. Anschließend wird der Stempel, ebenfalls auf 100°C temperiert, heruntergefahren, um ein Formteil entsprechend dem Becher aus Beispiel 1 zu erhalten.In the plasticizing unit of an injection molding machine, polylactide is melted and then injected into a mold cooled to 20 ° C., after 20 seconds. Cycle time to obtain a disk-shaped amorphous preform with a diameter of 37.3 mm, a height of 15 mm and a weight of 20.5 g. The preform is in boiling water within 30 seconds. heated to 100 ° C. It is then placed in the middle of a press die heated to 100 ° C. The stamp is then lowered, likewise at a temperature of 100 ° C., in order to obtain a molded part corresponding to the cup from Example 1.
Nach 5 see. wird die Presse geöffnet und der Becher ohne Kleben entnommen. Der kristalline Anteil in mittlerer Becherhöhe als Verhältnis der Fläche des kristallinen Peaks der Röntgenbeugung zur Gesamtfläche beträgt ca. 45 %, der E-Modul an dieser Stelle beträgt ca. 3.900 N/mm?. After 5 see. the press is opened and the cup removed without gluing. The crystalline fraction in the middle cup height as the ratio of the area of the crystalline peak of the X-ray diffraction to the total area is approximately 45%, the modulus of elasticity at this point is approximately 3,900 N / mm ? ,

Claims

Patentansprüche Claims
1. Verfahren zur Herstellung von Polylactid-Formkörpern, dadurch gekennzeichnet, daß man ein amorphes Polylactid-Halbzeug oder einen kompakten amorphen Vorformling auf 60 bis 150°C er¬ wärmt, wobei der Vorformling amorph bleibt, gefolgt von einem Fließpreßvorgang in einem ebenfalls auf 60 bis 150°C tempe¬ rierten Werkzeug, wobei das Polylactid mehrachsig fließt und dadurch orientiert und kristallisiert wird.1. A process for the production of polylactide moldings, characterized in that an amorphous polylactide semi-finished product or a compact amorphous preform is heated to 60 to 150 ° C, the preform remaining amorphous, followed by an extrusion process in a likewise to 60 Tool tempered up to 150 ° C, the polylactide flowing in multiple axes and thereby being oriented and crystallized.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß Vor¬ formling oder Halbzeug und Werkzeug die gleiche Temperatur aufweisen. 2. The method according to claim 1, characterized in that preform or semifinished product and tool have the same temperature.
PCT/EP1993/003225 1992-11-19 1993-11-18 Process for producing polylactide molded bodies by extrusion or compression molding WO1994011173A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP94901813A EP0669866A1 (en) 1992-11-19 1993-11-18 Process for producing polylactide molded bodies by extrusion or compression molding
JP6511731A JPH08502935A (en) 1992-11-19 1993-11-18 Method for producing polylactide molded body by compression molding or flow molding

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DEP4238997.6 1992-11-19
DE19924238997 DE4238997A1 (en) 1992-11-19 1992-11-19 Process for the production of polylactide moldings by compression molding or extrusion

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WO1994011173A1 true WO1994011173A1 (en) 1994-05-26

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EP (1) EP0669866A1 (en)
JP (1) JPH08502935A (en)
DE (1) DE4238997A1 (en)
WO (1) WO1994011173A1 (en)

Cited By (1)

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Publication number Priority date Publication date Assignee Title
US9732184B2 (en) 2014-07-29 2017-08-15 W. L. Gore & Associates, Inc. Process for producing articles formed from polylactic acid and articles made therefrom

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006131973A1 (en) * 2005-06-09 2006-12-14 Sumitomo Heavy Industries, Ltd. Molding apparatus for injection-molded articles and molding method

Citations (4)

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Publication number Priority date Publication date Assignee Title
EP0238076A2 (en) * 1986-03-18 1987-09-23 Asahi Kasei Kogyo Kabushiki Kaisha A shaped article of an oriented tetrafluoroethylene polymer
WO1990011060A1 (en) * 1989-03-17 1990-10-04 Zachariades Anagnostis E A process for producing uhmwpe product
US5007939A (en) * 1987-11-19 1991-04-16 Solvay & Cie (Societe Anonyme) Article made of lactic acid polymer capable of being employed particularly as a biodegradable prosthesis and process for its manufacture
EP0321176B1 (en) * 1987-12-14 1995-02-08 JOHNSON & JOHNSON ORTHOPAEDICS INC. Molecularly oriented thermoplastic member and process of forming same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0238076A2 (en) * 1986-03-18 1987-09-23 Asahi Kasei Kogyo Kabushiki Kaisha A shaped article of an oriented tetrafluoroethylene polymer
US5007939A (en) * 1987-11-19 1991-04-16 Solvay & Cie (Societe Anonyme) Article made of lactic acid polymer capable of being employed particularly as a biodegradable prosthesis and process for its manufacture
EP0321176B1 (en) * 1987-12-14 1995-02-08 JOHNSON & JOHNSON ORTHOPAEDICS INC. Molecularly oriented thermoplastic member and process of forming same
WO1990011060A1 (en) * 1989-03-17 1990-10-04 Zachariades Anagnostis E A process for producing uhmwpe product

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9732184B2 (en) 2014-07-29 2017-08-15 W. L. Gore & Associates, Inc. Process for producing articles formed from polylactic acid and articles made therefrom
US9987773B2 (en) 2014-07-29 2018-06-05 W.L. Gore & Associates, Inc. Process for producing articles formed from polylactic acid and articles made therefrom
US10150232B2 (en) 2014-07-29 2018-12-11 W. L. Gore & Associates, Inc. Process for producing articles formed from polylactic acid and articles made therefrom

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EP0669866A1 (en) 1995-09-06
JPH08502935A (en) 1996-04-02

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