Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-04-12
2002-12-17
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S187000
Reexamination Certificate
active
06495631
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to melt-processable lactide polymer compositions and processes for manufacturing such compositions from lactide.
BACKGROUND OF THE INVENTION
The present disclosure concerns ongoing efforts in developing lactide polymers useable in preferred manners. U.S. Pat. No. 5,142,023 issued to Gruber et al. on Aug. 25, 1992, discloses, generally, a continuous process for the manufacture of lactide polymers with controlled optical purity from lactic acid having certain desired physical properties. A related process for generating purified lactide and creating polymers therefrom is disclosed in U.S. Pat. No. 5,338,822 issued to Gruber et al. on Aug. 16, 1994.
Generally, manufacturers of polymers utilizing processes such as those disclosed by Gruber et al. in the '023 and '822 patents will convert raw material monomers into polymer beads, resins or other pelletized or powdered products. The polymer in this form is typically sold to end users who extrude, blow-mold, cast films, blow films, foam, thermoform, injection-mold or fiber-spin the polymer at elevated temperatures to form useful articles. The above processes are collectively referred to herein as melt-processing. Polymers produced by processes such as those disclosed by Gruber et al. in the '023 and '822 patents, which are to be sold commercially as beads, resins, powders or other non-finished solid forms, are herein generally referred to collectively as polymer resins.
It is generally known that lactide polymers or poly(lactide)s are unstable. The concept of instability has both negative and positive aspects. A positive aspect is the biodegradation or other forms of degradation that occur when lactide polymers or articles manufactured from lactide polymers are discarded or composted after completing their useful life. A negative aspect of such instability is the degradation of lactide polymers during processing at elevated temperatures as, for example, during melt-processing by end-user purchases of polymer resins. Thus, the same properties that make lactide polymers desirable as replacements for non-degradable petrochemical polymers also create undesirable effects during production of lactide polymer resins and processing of these resins.
There are a number of technical problems which have heretofore inhibited development of commercially viable lactide polymer-based replacement resins for existing conventional resins. Lactide polymers are subject to unwanted degradation during melt processing via a number of pathways. These pathways include hydrolysis and other side reactions, which, for example, result in molecular weight decline and/or lactide formation. Furthermore, at high processing temperatures (especially to above about 230° C.), lactide polymer degradation is accelerated.
Some of polylactide's physical properties make it difficult to use for particular types of applications. In general, polylactide is a relatively brittle polymer with a low impact resistance. Because polylactide is a relatively brittle polymer, articles made of polylactide may be brittle and prone to shatter under use conditions. For example, if polylactide is used to make articles such as razor holders, shampoo bottles and plastic caps, these articles may be prone to undesirable shatter in use.
There exists a need for polylactide polymers with modified physical properties, such as impact resistance, and methods for making these types of polylactide polymers preferably without unduly compromising other physical properties, such as tensile modulus, yield strength, and blocking resistance (i.e. tendency to stick).
SUMMARY OF THE INVENTION
The invention is directed toward melt-processable polymer compositions having at least two phases. These two phases include: (a) a first phase having polylactide-based polymer; and (b) a second phase having elastomer. Each phase may be a mixture of materials. As used herein, the term “melt-processable” refers to a polymer composition capable of withstanding melt-processing techniques, such as extruding, blow molding, injection molding, film casting, film blowing, foam making, thermal forming, fiber spinning, or other means used to convert the polymer at elevated temperatures to form useful articles. Preferably, the elastomer, if it is a polylactide-based polymer, is a non-thermoplastic elastomer. Herein, the term “non-thermoplastic-polylactide-based polymer” is sometimes used to refer to this characteristic. If a thermoplastic elastomer is used, it can be either a polylactide-based or non-polylactide-based polymer. In many preferred applications, the elastomer is a non-polylactide-copolymerized elastomer. As used herein, the term “nonpolylactide-copolymerized elastomer” refers to an elastomer that does not comprise the product of a copolymerization with lactide or lactide oligomer.
The elastomer forming in second phase is preferably present in an amount effective to provide the melt-processable polymer composition with an impact resistance of at least about 0.7 ft-lb/in., when the melt-processable polymer composition has been injected molded into bars and tested according to ASTM D256 (1993) method C. Preferably, the compositions of the invention are provided with sufficient elastomer to provide an impact resistance of at least about 1 ft-lb/in. and more preferably of at least about 2 ft-lb/in., when the melt-processable polymer composition has been injected molded into bars and tested according to ASTM D256 (1993) method C. Most preferably, the elastomer is present in an amount effective to provide the melt-processable polymer composition with an impact resistance of at least about 6 ft-lb/in, when the polymer composition is tested pursuant to the Izod impact test. It is noted that, typically, most preferred compositions of the invention have an impact resistance of at least about 10 ft-lb/in when the polymer composition is tested pursuant to the notched Izod impact test.
Selected polymer compositions according to the present invention can be provided with an elongation at break of at least about 10%, a tensile modulus of at least about 200,000 psi, and a yield strength of at least about 3,000 psi, when the polymer composition has been injection molded into bars and tested according to ASTM D638-91, as described below. As discussed more fully below, in many applications, the second phase will comprise discrete domains within the first continuous phase. In others, especially those including relatively high elastomer content (i.e. about 20 wt %), the second phase may be co-continuous instead of comprising discrete domains within a continuous phase. In a composition with co-continuous phases, the first and second phases are each continuous in space and each is distributed relatively uniformly throughout the composition. Co-continuous phases are more fully disclosed in
Encyclopedia of Polymer Science and Engineering,
2nd Edition, Vol. 9 at pp. 776-778 (Wiley-Intersciences, 1987). In the compositions, preferably, the first phase is the continuous phase and the second phase comprises a phase distinct from the first phase.
In a most preferred embodiment, the melt-processable composition includes a polylactide-based polymer in the first phase, and epoxidized rubber in the second phase, and a reactive compatibilizing agent. Preferably, the epoxidized rubber is present in an amount of about 1% by weight of the composition to about 40% by weight. As used herein, the weight percentages stated are the percent of the melt-processable polymer composition without regard to fillers, unless otherwise stated. More preferably, the epoxidized rubber is present in an amount of about 5% by weight of the composition to about 30% by weight. Most preferably, the epoxidized rubber is epoxidized natural rubber, present in an amount of at least about 10% by weight of the composition. Most preferably, the reactive compatibilizing agent is present in an amount of about 0.3% by weight to about 3% by weight of the composition. In another most preferred embodiment, natural rubb
Hall Eric Stanley
Hartman Mark Henry
Kolstad Jeffrey John
Lunt James
Randall Jed Richard
Cargill Incorporated
Merchant & Gould P.C.
Woodward Ana
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