Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Patent
1996-04-17
1997-12-02
Acquah, Samuel A.
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
525 544, 525450, 528361, 2641761, 264212, 264239, 264291, 264299, 26433111, 264540, 428 357, B29D 2200, B28B 320, C08G 6348
Patent
active
056933894
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/GB94/01095, filed May 20, 1994.
This invention relates to a polyester composition and to modified polyesters useful as components thereof.
Poly-3-hydroxybutyrate (PHB) has the disadvantage of being brittle especially when melt cast. The apparent reason for this brittleness is the presence of large spherulites in the polymer. Such large spherulites frequently have cracks which open up under little extra strain and produce brittle failure of the sample (Barham P. J., Keller, A., Journal of Polymer Science Vol 24, p69-77 1986). One way of increasing the ductility of PHB is to nucleate the melt with small particles which reduces the spherulite size thereby producing major benefits in the mechanical properties of the polymer. Another benefit from nucleation is faster crystallisation and thus reduced processing times. A commonly used nucleant is boron nitride but is an expensive material and is not biodegradable. Alternative less expensive sources of nucleant and biodegradable nucleants are therefore desirable.
Thus, according to the invention in its first aspect there is provided a polyester composition comprising at least one first semi-crystalline or crystallisable polyhydroxyalkanoate (PHA-X) and at least one second polyhydroxyalkanoate (PHA-Y) in semi-crystalline or crystalline form and having a higher crystalline melting point than said PHA-X.
In the present context the terms crystalline, semi-crystalline and crystallisable have the following meanings: has a crystalline content but is not 100% crystalline, and crystallisable means polymer which is capable of crystallising including polymer materials in the amorphous state.
The polyester composition may comprise at least one microbiologically produced polyester or at least one synthetically produced polyester.
In one form of the composition the crystalline melting point of PHA-Y is higher by at least 5.degree. C., especially 10.degree. to 50.degree. C., than that of the PHA-X. Typically the amount of PHA-Y contained in the PHA-X is sufficient to nucleate the PHA-X in melt processing, that is, to decrease its crystallisation time.
The invention particularly includes a two-phase composition when at a temperature at or above the crystalline melting point of the molten PHA-X but below that of the solid PHA-Y.
The PHA-X and PHA-Y are polymers capable of a relatively high level of crystallinity, for example over 30%, especially 50-90%, in the absence of plasticiser. Suitably the composition may include polyester having units of formula I: Typically C.sub.m H.sub.n contains 2-5 carbon atoms in the polymer chain and the remainder (if any) in a side chain. In very suitable polyesters m is 3 or 4, n is 2 m and especially there are units with m=3 and m=4 copolymerised together and with respectively a C.sub.1 and C.sub.2 side chain on the carbon next to oxygen in the chain. Particular polyesters contain a preponderance of m=3 units, especially with at least 70 mol % of such units, the remainder being units in which m =4.
In the following description the crystalline melting point T.sub.m and heat of fusion H.sub.f are determined by Differential Scanning Calorimetry (DSC). T.sub.m is the peak of the curve of dH/dt against temperature. H.sub.f is the area under that curve.
The molecular weight (Mw) of PHA-X is preferably over 200000, up to for example, 2.times.10.sup.6. The Mw of the PHA-Y can be of the same order as that of the PHA-X.
The polyhydroxyalkanoate is preferably polyhydroxy-butyrate (PHB) or polyhydroxybutyrate-co-valerate (PHBV), which may be 3-hydroxy or 4-hydroxy or a mixture of both. Especially preferred are the 3-hydroxy forms of PHB and PHBV.
The PHA-X may be PHB homopolymer or PHBV co-polymer as demonstrated by (a) below, or a blend of two or more polymers differing in the value of m, for example, a blend of homopolymer and copolymer or a blend of two copolymers. An example of a blend of two copolymers contains units have m=4, the rest m=3; and units have m=4, the rest m=3. In each such PH
REFERENCES:
ORGAN, et al: "Phase separation in a blend of poly (hydroxybutyrate) with poly (hydroxybutyrate-co-hydroxyvalerate)", POLYMER, vol. 34, No. 3, Feb. 1993, pp. 459-467, see figures 10,13C,13E.
Acquah Samuel A.
Zeneca Limited
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