Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-10-27
2001-02-20
Yoon, Tae (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S308000, C525S437000, C525S444000, C525S450000, C528S354000, C528S361000
Reexamination Certificate
active
06191203
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to biodegradable polymers. More particularly, it concerns biodegradable polymer blends containing oligomeric esters and use of such blends in the production of shaped polymeric objects having improved properties which do not diminish over time.
There has been considerable interest in recent years in the use of biodegradable polymers to address concerns over plastic waste accumulation. The potential worldwide market for biodegradable polymers is enormous (>10B lbs/yr). Some of the markets and applications most amenable to the use of such biopolymers range from single use applications, which can include packaging, personal hygiene, garbage bags, and others where the biopolymers become soiled and are ideally suited for biodegradation through composting, to markets and applications in which the biopolymers can be recovered as clean materials, such as garment bags, shopping bags, grocery bags, etc. and are suitable for recycling, as well as composting, or biodegradation in landfills.
Polyhydroxyalkanoate (PHA) biopolymers are thermoplastic polyesters, many of which can be produced by microorganisms in response to nutrient limitation. The commercial potential for PHA's spans many industries, and is derived primarily from certain advantageous properties which distinguish PHA polymers from petrochemical-derived polymers, namely excellent biodegradability and natural renewability.
Widespread use and acceptance of PHA's, however, has been hindered by certain undesirable chemical and physical properties of these polymers. For example, PHA's are among the most thermosensitive of all commercially available polymers. As such, the rate of polymer degradation, as measured by a decrease in molecular weight, increases sharply with increasing temperatures in the range typically required for conventional melt-processing of PHA's into end-products such as films, coatings, fibers etc. An additional limitation of the potential utility of PHA polymers relates to the observation that some polymer characteristics, for example ductility, elongation, impact resistance, and flexibility, diminish over time. This rapid “aging” of certain PHA-derived products is unacceptable for most commercial applications. Thus, the success of PHA as a viable alternative to both petrochemical-derived polymers and to non-PHA biodegradable polymers, will depend upon novel approaches to overcome the unique difficulties associated with PHA polymers and with products derived therefrom.
The blending of two or more polymers has become an increasingly important approach for improving the cost performance of commercial plastics. For example, blending may be used to reduce the cost of an expensive engineering thermoplastic, to improve the processability of a high-temperature or heat sensitive thermoplastic, to improve impact resistance, etc. Therefore, blending is one approach which has the potential to provide new classes of biodegradable PHA-containing polymers having unique and improved properties. In this way, it may be possible to overcome the limitations of PHA compositions that have limited their widespread industrial utilization while retaining their desirable features. Unfortunately, many polymers are immiscible when blended, and result in undesirable phase separation during processing. Generally, such blends of incompatible or thermodynamically immiscible polymers exhibit poor mechanical properties and processing difficulties.
Compatibilizing compounds have been identified and developed for numerous polymer systems. These compounds can reduce interfacial tension and thereby promote miscibility of otherwise poorly miscible polymers. The availability of compatibilizers provides an effective means by which polymeric compositions can be produced. However, with PHAs, very little has been achieved in this regard, and there is a need for the identification of compounds providing effective compatibilization of blends containing different PHA polymers or blends containing PHA and non-PHA polymers.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there are provided polymer compositions comprising a first biodegradable polymer comprising a polyhydroxyalkanoate (PHA), a second biodegradable polymer different from said first polymer, and one or more oligomeric esters. It has been found that the presence of oligomeric esters as described herein provide advantageous properties to blends of two or more biodegradable polymers. As a result, blends containing the oligomeric esters exhibit ductility, impact strength and aging characteristics improved to an unexpected and unpredictable extent.
Most oligomeric esters useful in the blend compositions of this invention can be represented by following structural formula:
H—(M
1
—N
1
)
a
—(M
2
—N
2
)
b
—O—R
where:
X is C
6
H
4
or (CH
2
)
f
a and b are independently an integer from 1 to 200;
c and f are independently integers from 1 to 30;
R is H or C
1
-C
12
alkyl or branched alkyl; and
R
d
and R
e
are H, or C
1
-C
12
alkyl or branched alkyl and can vary independently with each (C)
c
.
In a preferred class of oligomeric esters, f is 2 to 10. Most preferably, the compounds are oligomeric adipic esters, i.e., f is 4.
The oligomeric ester generally will be present in the blend at a level from 1 to 20 wt. %, preferably 2 to 15 wt. % of the blend. The molecular weights of the oligomeric esters are typically in the range of 200 to 20,000, preferably 500 to 15,000, and most preferably from about 1500 to 7500.
At least one of the polymers in the blend is a PHA, preferably having the structural formula:
where a=1-4, b=0-15, Y is H, and n is an integer. In a most preferred composition, one of the polymers in the blend is polyhydroxybutyrate (PHB) or polyhydroxybutyrate-co-valerate (PHBV).
A second polymer in the blend can be a PHA structurally distinct from the first PHA, or can be a non-PHA biodegradable polymer. The non-PHAs can be, for example, aliphatic polyesters or copolyesters derived from aliphatic dicarboxylic acids or anhydrides, aliphatic dicarboxylic acid chlorides, aliphatic dicarboxylic acid esters, and aliphatic diols or epoxides; polyurethanes made from said polyesters and copolyesters by reaction with a diisocyanate; aliphatic polycarbonates; polyanhydrides; polyester amides; polyester carbonates; polyester ethers; or polyether carbonates. Preferred non-PHA polymers for use in the invention include aliphatic polyesters and copolyesters, and polyester urethanes. More preferred non-PHA polymers include polycaprolactone (PCL, e.g. Tone 187P PCL, Union Carbide) and polybutylenesuccinate-adipate (PBSUA, e.g. Bionolle 3001 PBSUA, Showa High Polymer Co.).
In a most preferred composition of this invention, blends are provided which comprise a PHA, polycaprolactone, and an oligomeric ester. The oligomeric ester is preferably an oligomeric adipic ester, such as poly(1,3-butylene glycol-co-1,2-propylene glycol adipic acid) terminated with 2-ethylhexanol (Santicizer*S409A; Mw=3700, available from Solutia Inc.), poly(neopentyl glycol-co-1,4-butylene glycol adipic acid) terminated with 2-ethylhexanol (Santicizer*S433; Mw=3500, available from Solutia Inc.), poly(1,3-butylene glycol adipic acid) unterminated (Santicizer*S430; Mw=2500, available from Solutia Inc.), poly(1,3-butylene glycol adipic acid) unterminated (Santicizer*S421; Mw=1250, available from Solutia Inc.), poly(1,2-propylene glycol adipic acid-co-phthalic acid) terminated with 2-ethylhexanol (Santicizer*S438; Mw=1900, available from Solutia Inc.), poly(neopentyl glycol adipic acid) terminated with 2-ethylhexanol (Santicizer *S435; Mw=2500; available from Solutia Inc.), poly(1,2-propylene glycol adipic acid-co-phthalic acid) terminated with 2-ethylhexanol (Santicizer *431; Mw=1200; available from Solutia Inc.), poly(1,2-propylene glycol-co-1,4-butylene glycol adipic acid) terminated with 2 ethylhexanol (Santicizer *S4212; Mw=950; available from
Asrar Jawed
Pierre Jean R.
Beusen Jon
Howrey Simon Arnold & White , LLP
Monsanto Company
Yoon Tae
LandOfFree
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