Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Patent
1996-04-05
1998-08-04
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
528481, 528502, 2641761, 26421112, 264319, 26433111, 264346, 264901, 264904, C08F 600, C08J 500
Patent
active
057895368
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/GB94/01181, filed Jun. 1, 1994.
THIS INVENTION relates to processing of polyesters and in particular to producing shaped articles less liable to embrittlement.
It has been disclosed by de Koning et al in Polymer 92, 33, (15), 3295-3297 that whereas one such polyester poly(R)-3-hydroxybutyrate when freshly moulded shows ductile behaviour, within several weeks at room temperature the tensile modulus doubles and elongation at break drops below 10%. A typical feature of such ageing is that it can be partly reversed by heat or mechanical strain. Using mild `deageing` treatment, the improvement in ductility is only small and temporary, but heating at above 100.degree. C. restores the original mechanical properties and prevents or at least retards ageing to a large extent.
It has now been found that such age-embrittlement can be prevented or slowed by applying the heat treatment to shaped articles made substantially of polyhydroxybutyrate (PHB), polyhydroxybutyrate co-valerate (PHBV) and/or other polyhydroxyalkanoates before they have undergone significant ageing.
Thus according to the invention there is provided a polyester composition comprising polyhydroxyalkanoate (PHA) in which ageing of the polyester is retarded characterised in that after preparation the polyester is cooled to below 90.degree. C. and then heat treated at 90.degree. C. to 160.degree. C. within 24 hours of preparation, and in that subsequent ageing is substantially retarded compared to the non-heat treated polyester.
In a further aspect of the invention there is provided a shaped article at least partly made of polyhydroxyalkanoate (PHA) in which ageing of the polyester is substantially retarded characterised in that after preparation the article is allowed to cool to below 90.degree. C. is heat treated at 90.degree. C. to 160.degree. C. within 24 hours of preparation, and in that subsequent ageing is substantially retarded compared to the non-heat treated polyester.
"Ageing" means deterioration of the mechanical properties of polymer with time, for example, ductility and tensile strength. Loss of mechanical properties can be measured by measurements indicative of ageing, for example, elongation to break and impact resistance (Izod).
In the present context "substantially retarded" means that for practical purposes the polyester or article is not defective for brittleness or ductility for at least one month after the heat treatment. Preferably the polyester or article shows at least 40%, especially 60%, improvement in brittleness or ductility compared to the non-heat treated polyester or article. This can be measured using any measurement indicative of ageing, for example, by elongation to break measurements or impact strength measurements (Izod).
By "within 24 hours" is meant up to 24 hours, preferably within 12 hours of preparation, particularly 60 minutes or less from preparation.
"At least partly made" means having structural components made of PHA, for example PHB or PHBV, to such an extent that embrittlement of the PHA components embrittles the whole article. Thus for example articles having PHB components linked to other components, and articles made of a matrix of some other polymer with PHB inclusions, are within the invention. Articles made of PHB alone benefit most from the invention.
The heat treatment can be any that does not involve a step effecting substantial crystallisation of the polyester in the article presented to the heat treatment at 100.degree. C. to 140.degree. C.
If shaping has been by melting or sintering, the heat treatment may follow immediately upon shaping, for example by holding an article in its mould for a suitable time; the mould temperature may be deliberately adjusted or may be arrived at as the resultant of the molten polymer temperature and the initial mould temperature. If desired, the article may be held at a temperature appropriate for crystallisation before the heat treatment according to the invention. If shaping has been continuous, f
REFERENCES:
De Koning, et al: Ageing phenomena in bacterial poly
Saiki, et al: "Stretching of poly (beta-hydroxybutyric acid) molding", Chemical Abstracts, vol. 105, No. 14, Oct. 6, 1986, abstract No. 116100 & JP,A,61 069 431, Apr. 10, 1986.
De Koning, et al: "Crystallization phenomena in bacterial nol 34, No. 19, 1993, pp. 4089-4094.
Liggat John Jamieson
O'Brien Gregory
Acquah Samuel A.
Bond Gary M.
Monsanto Company
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