EP0701581A1

EP0701581A1 - Processing of polyesters

Info

Publication number: EP0701581A1
Application number: EP94917075A
Authority: EP
Inventors: John Jamieson Liggat; Gregory O'brien
Original assignee: Zeneca Ltd; Monsanto Co
Current assignee: Monsanto Co
Priority date: 1993-06-02
Filing date: 1994-06-01
Publication date: 1996-03-20
Also published as: CA2163443A1; GB9311401D0; AU6851494A; JPH09504808A; WO1994028048A1

Abstract

A process for improving mechanical properties of an aged polyester composition comprising at least one polyhydroxyalkanoate (PHA) and at least one plasticiser thereof, which comprises heating at a temperature whereby (i) the polyester is restored to its original non-aged properties, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age. The invention includes a polyester composition and shaped articles which have been subjected to the process and in which ageing is retarded.

Description

PROCESSING OF POLYESTERS

THIS INVENTION relates to a polyester composition and in particular to such a composition containing biodegradable polyester and capable of producing shaped articles resistant to embrittlement. It has been disclosed by de Koning et a in Polymer 1992, 33,

(1 5), 3295-3297 that whereas one such polyester poly[(R)-3- hydroxybutyrate] (PHB) when freshly moulded shows ductile behaviour, subsequent ageing seriously embrittles it and hampers its applicability. Within several weeks of storage at room temperature, the tensile modulus doubles, and the elongation at break drops below 10%. A typical feature of the ageing process is that it can be partly reversed by the employment of heat or mechanical strain. Using mild 'deageing' treatments, the improvement in toughness is only small and temporary. Such deageing appears to cause stability of physical properties of PHB homopolymer and of copolymers (PHBHA) having also hydroxyalkanoate (HA) other than hydroxybutyrate (HB) residue units. The effect on the copolymer, although important, is not as great as with PHB.

It has now been found that "deageing" treatment of hydroxyalkanoate copolymers is significantly more effective if a plasticiser is present and that "deaged" plasticised PHA homopolymer and copolymers have improved properties.

According to the present invention there is provided a polyester composition comprising at least one polyhydroxyalkanoate (PHA) and at least one plasticiser thereof, in which ageing has occurred, characterised

' in that (i) the polyester is restored to its original non-aged properties by a heat treatment, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age. Alternately the retardation of subsequent ageing may be indicated by substantial improvement of at least one measurement indicative of ageing compared to heat treated polyester of the same age without plasticiser.

According to a further aspect of the invention there is provided a shaped article at least partly made from a polyester composition comprising at least one polyhydroxyalkanoate (PHA) and at least one plasticiser thereof, in which ageing has occurred, characterised in that (i) the shaped article is restored to its original non-aged properties by heating, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age. Alternately the retardation of subsequent ageing may be indicated by substantial improvement of at least one measurement indicative of ageing compared to heat treated polyester of the same age without plasticiser.

"At least partly made" means having structural components made of PHA to such an extent that ageing of the PHA component ages the whole article. Thus for example, PHA may be homogeneously mixed with other biodegradable polymers such as polylactides or polycaprolactone. In such mixtures the minimum amount of PHBV is at least 30% ^w/w. Also articles having PHA components linked to other components such as razors and toothbrushes, and articles made of a matrix of some other biodegradable (e.g. starch) or non-biodegradable polymer (e.g. polypropylene) with PHA inclusions, are within the invention. In such mixtures the minimum amount of PHA is at least 30% ^w/w. Articles made of PHA alone, nucleated or otherwise, benefit most from the invention.

"Substantial improvement" means that the measurement indicative of ageing, for example, elongation to break, is improved by 50% or more, preferably 100% or more, compared to the heat treated aged polyester without plasticiser at the same age as the heat treated aged polyester with plasticiser, or alternately it can be compared to the non-heat treated polyester of the same age. The "same age" means the same period of ageing after the heat treatment i.e. one month after initial preparation of the polyester for the non heat treated polyester is the equivalent age to one month after heat treatment for the heat treated polyester.

By "restored to the original non-aged properties" is meant that the heat treatment restores at least 50% of the ductility of the polyester as measured by conventional methods e.g. elongation to break, impact testing (IZOD). Preferably the heat treatment restores at least 75 % of the ductility, especially at least 80%.

Aged polyester or shaped article in the present context means that it has the mechanical properties equivalent to the polyester or article having been stored for 24 hours or more at 20°C. Non-aged polyester or shaped article in the present context means that it has the mechanical properties equivalent to the polyester or shaped article having been freshly processed, i.e. mechanical properties equivalent to storage for up to 24 hours at 20°C, preferably storage for up to and including 1 hour at

20°C of having been processed.

According to a preferred aspect of the present invention there is provided a polyester composition comprising polyhydroxybutyrate (PHB) or copolymer of hydroxybutyrate units and hydroxyvalerate (PHBV) units and at least one plasticiser thereof, in which ageing has occurred, characterised in that (i) the polyester is restored to its original non-aged properties by a heat treatment, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age. Alternately the retardation of subsequent ageing may be indicated by substantial improvement of at least one measurement indicative of ageing compared to heat treated polyester of the same age without plasticiser.

The PHA is especially capable of a relatively high level of crystallinity, for example over 30%, especially 50-90%, in the absence of plasticiser. Suitably it is or includes at least one microbiologically produced polyester having units of formula I:

- O - C_m H_n - CO - I where m is in the range 1 -1 3 and n is 2m or (if m is at least 2) 2m-2. Typically C_m H_n contains 2-5 carbon atoms in the polymer chain and the remainder (if any) in a side chain. In very suitable polyesters n is 2m and especially there are units with m = 3 and m = 4 copolymerised together and with respectively a C* and C₂ side chain on the carbon next to oxygen in the chain. The polymer may be homopolymer, especially PHB, or a copolymer PHBV containing preferably 4-20 mol% of m = 4 units. Thus, particular polyesters contain a preponderance of m = 3 units, especially with 70 - 98 mol % of such units, the balance (if any) being units in which m = 4. The molecular weight of the PHA is preferably over 50000, especially over 100000, up to eg 2 x 10⁶.

The PHA is conveniently a blend of two or more copolymers differing in the value of m. A particular example contains (a) PHA consisting essentially of Formula I units in which 2-5 mol % of units have m = 4, the rest m = 3; and (b) PHA consisting essentially of Formula I units in which 5-30 mol% of units have m = 4, the rest m = 3.

In each such PHA there are side chains as above mentioned. The proportions in such a blend are preferably such as give an average m = 4 content in the range 4 - 20 mol %. In each such PHA having units with m = 3 and m = 4 there may be very small, typically fractional, percentages of units having higher values of m.

PHA comprising hydroxybutyrate units and hydroxyvalerate units includes PHBV copolymers containing up to 1 mol percent of other oxyalkanoate units whether introduced deliberately or not.

The PHA is preferably a fermentation product, especially of a microbiological process in which a microorganism lays down PHA during normal growth or is caused to do so by cultivation in the absence of one or more nutrients necessary for cell multiplication. The microorganism may be wild or mutated or may have had the necessary genetic material introduced into it. Alternatively the necessary genetic material may be harboured by a eukariote, to effect the microbiological process.

Examples of suitable microbiological processes are the following: for Formula I material with m = 3 or m = partly 3, partly 4 : EP-A-69497 (Alcaligenes eutrophus) for Formula I material with m = 3: US 4101 533 (A. eutrophus H-1 6), EP-

A-14401 7 (A. latus); for Formula I material with m = 7-1 3: EP-A-0392687 (various

Pseudomonas). The PHA can be extracted from the fermentation product cells by means of an organic solvent, or the cellular protein material may be decomposed leaving microscopic granules of polymer. For specialised end uses the cellular protein may be partly or wholly allowed to remain with the PHA, but preferably subjected to cell breakage.

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 (R)-3-hydroxy forms of PHB and PHBV. Typically the composition contains microbiologically produced PHA to the extent of over 50% w/w, especially over 80% w/w.

Alternately, the PHB or PHBV can be a product of synthetic chemistry (Bloembergen and Holden, Macromolecules 1 989, 22, p1 656- 1 663. Bloembergen, Holden, Bluhm, Hamer and Marchessault, Macromolecules 1 989, 22, p1 663-1 669).

The polyester composition can contain the usual additional polymer processing additives such as particulate or fibrous or platy filler or reinforcer, fibres, nucleating agents (for example boron nitride, talc or ammonium chloride), and pigments. The nucleant is preferably present in 0.1 to 10phr, especially 1 to 5phr. The composition can be in the form of mouldings, extrudates, coatings, films or fibres, including multilayer coatings, films or fibres.

The plasticiser is any material capable of plasticising polyester, i.e. capable of improving the ductility of the polyester and especially any material capable of plasticising PHB or PHBV. There may be one or more plasticisers present. The ratio of such plasticiser to PHA is in the range up to and including 40 phr w/w which includes most of the likely uses, particularly 1 to 40 phr w/w, and for making effectively rigid but not brittle articles the range 5-20 phr especially 6-1 2 phr w/w is generally suitable.

Examples of suitable plasticisers are:

(a) high-boiling esters of polybasic acids, such as phthalates, isophthalates, citrates, fumarates, glutamates, phosphates or phosphites. The esterified radicals may be for example C- - C₁₂ alkyl, aryl, aralkyl or aralkyl. Particular examples are dioctyl-, dibaptyl- and dirindecyl- phthalates and dialkylalkylene oxide glutamate (Plasthall 7050);

(b) high-boiling esters and part- of polyhydric alcohols, especially glycols, polyglycols and glycerol. The acid-derived radical of the ester typically contains 2-10 carbon atoms. Examples are triacetin, diacetin and glycerol dibenzoate;

(c) aromatic sulphonamides such as paratoluenesulphonamide Particular examples of such plasticisers are esters of polyhydric alcohols, for example glyceryl esters of C, - C . carboxylic acids.

Generally it is preferred that the plasticiser should be biodegradable.

A particularly preferred plasticiser is a doubly esterified hydroxycarboxylic acid having at least 3 ester groups in its molecule. "Doubly esterified" means that at least some of the hydroxy groups of the hydroxycarboxylic acid are esterified with a carboxylic acid and at least some of the carboxy groups thereof are esterified with an alcohol or phenol. Preferably at least the hydroxycarboxylic acid from which the ester is derived is aliphatic or cycloaliphatic. Its backbone structure (that is, apart from carboxy groups) preferably contains 2-6 carbon atoms. It contains preferably 2-4 carboxy groups and 1 -3 hydroxy groups; and preferably the number of carboxy groups exceeds the number of hydroxy groups.

The groups with which the carboxy groups are esterified contain preferably 1 -7, especially 2-5 carbon atoms. In the ester molecule they can be the same or different. Preferably they are aliphatic. For thermal stability but biodegradability such aliphatic groups preferably have straight chains. If desired, a small portion of these groups are divalent, so as to give an oligomer suitably containing up to 3 repeating units. The groups with which the hydroxy groups are esterified preferably contain 2-7, especially up to 4, carbon atoms, including the carbon atom of the carboxy of such groups. In the ester molecule such groups can be the same or different. Preferably they are aliphatic and, for thermal stability and biodegradability, have straight chains. If desired, a small proportion of these groups are divalent, so as to give an oligomer suitably containing up to 3 repeating units.

Other polyhydroxyalkanoates may act as plasticisers in this system, for example polycapralactone.

This list is not exhaustive and any plasticiser of polyester which is not listed above or which becomes available after the date of this application would be suitable for use in this invention.

The invention also provides a process for improving mechanical properties of an aged polyester comprising at least one polyhydroxyalkanoate and at least one plasticiser thereof, which comprises heating at a temperature whereby (i) the polyester is restored to its original non-aged properties, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age. Alternately the retardation of subsequent ageing may be indicated by substantial improvement of at least one measurement indicative of ageing compared to heat treated polyester of the same age without plasticiser.

The properties of the polyester or article of the present invention can be assessed using the following measurements : stress-strain curve including calculations of elongation to break, Youngs modulus, and tensile strength; impact testing, for example IZOD; and dynamic mechanical thermal analysis (DMTA). These are all standard methods for testing mechanical properties.

Any one or more of the above-mentioned characterising properties can be used to monitor the progress of the heat treatment. In practice it is often sufficient to test the article by taking a sample from a batch, cooling it to room temperature and subjecting it to manual flexing. In established manufacturing it is often possible to fix the heating temperature and then adopt a time that is fully adequate and affords a small margin to cover accidental variations.

A further advantage of the present invention is that after treatment the rate of ageing appears to get slower over a period of a few weeks indicating that substantial stability of measurements indicative of ageing occurs faster in the heat treated polyester than the non heat treated polyester. As a consequence, substantial stability occurs at a level significantly above that for the non heat treated polyester, preferably 50%, especially 100% above that for the non heat treated polyester, i.e. the mechanical properties stabilise at a level substantially improved compared to the non heat treated polyester.

The invention also extends to shaped articles of the polyester subjected to the above process.

The heating temperature is preferably in the range from 80°C to 1 50°C, especially in the range from 100°C to 140°C. The heating time is typically at least 0.5 min after the article has reached the intended temperature. Since times up to a few hours appear to have no detrimental effect, the time can be chosen to suit the characteristics of the processing plant and economic requirements.

Heating can be effected in air or oxygen-depleted or inert gas or in yacuo, or in water or a fluid which does not interfere with the integrity of the polyester, or in a mould.

Heat transfer can be by conduction, radiation, convection or resistive heating. Heat transfer methods may include ovens, water baths and hot rollers. A preferred form of heat transfer is by infra red radiation, for example, black body and quartz tubes. The shaped article is generally subjected to infra red radiation for 30 seconds to 1 5 minutes, preferably 30 seconds to 10 minutes.

The shaped articles may be run through the oven or other heating method on a continuous belt at a speed which is optimal to enable the shaped article to reach the correct temperature. A preferred method is to

^' have a multi-zone system, preferably a 2 zone heat system in which the first zone gives a rapid rate of heating (i.e. the actual temperature in the zone may higher than that to be achieved by the shaped article) to bring it to the actual temperature required and then in the second zone the shaped article is maintained at the actual temperature to be achieved for the desired time period.

The composition can contain the usual polymer processing additives such as fillers, fibres, nucleants and pigments. It can be in the form of mouldings, extrudates, coatings, films or fibres, including multilayer coatings, films or fibres.

The invention provides methods of making the composition by mixing its components. If desired, this may be effected in a solvent, such as a halogenated hydrocarbon or alkylene carbonate. Such a method is convenient for coating or for centrifugal spinning of fibres.

More conveniently the plasticiser is mixed with powdered dry polymer and the mixture is treated in conditions of shear, such as in a plastic mill or extruder. The product is then granulated and used as feed for a shaping operation such as extrusion, injection moulding, injection blow- moulding or compression moulding.

The composition is especially useful for making the following shaped articles: films, especially for packaging, fibres, non-woven fabrics, extruded nets, personal hygiene products, bottles and drinking vessels, agricultural and horticultural films and vessels, ostomy bags, coated products (such as paper, paperboard, non-woven fabrics), agricultural and horticultural films and vessels, slow-release devices. Alternatively, the polymer composition with suitable additives can be used as an adhesive.

The invention is now further described, but is not limited by, the following examples. In the following examples the tests were conducted with PHBV of the (R)-3-hydroxy form.

Formulation and Test Procedures

Compositions were prepared by mixing copolymer (500 g) with 1 phr boron nitride acid (if required) plasticiser, and extruding the mixture in a Betol 2520 extruder in these conditions: Zone 1 130°C

Zone 2 140°C

Zone 3 1 50°C

Die 1 50°C

Screw Speed 100 rpm The extrudate, a single 4mm lace, was crystallised at 50-60°C in a water bath, dried in a current of air and cut into granules.

The granules were then injection moulded (Boy 1 5S) into tensile bars, dumbbell-shaped according to ISO R 537/2, their prismatic part measuring 40 x 5 x 2 mm. The bars were numbered as they came out of the mould, then allowed to cool at ambient temperature. Injection moulding conditions were:-

Barrel Zone 1 130°C

Barrel Zone 2 130°C

Nozzle 1 30°C

Mould heater temperature 74-77°C

Mould temperature 60°C

Pressure hold on time 1 2 sec

Cooling time 30 sec

Injection pressure 45 bar

Screw speed 250 rpm

Tensile testing was carried out using an Instron 1 1 22 fitted with a Nene data analysis system. The jaw separation used was 50 mm and crosshead speed was 10 mm/min^"1. Example 1

The following formulations were compared: A Copolymer 90B/10V, 1 phr BN, no plasticiser

(aged for 1 week before heating, at 1 20°C for 1 h); B Copolymer 90B/10V, 1 phr BN, 20 phr dioctylphthalate (Jayflex

DIOP) (RTM)

(aged for 3 weeks, heated at 1 10°C for 1 h) C PHB homopolymer, 1 phr BN, 20phr Reoplas 39

(aged 1 week, heated at 140°C for 30 mins) Results are shown in Tables 1 A and 1 B. Table 1 A compares the treated polymers with a control sample which was measured for elongation to break prior to administering the heat treatment to the samples. Table 1A

Control: Period after Heating

Before 0.5h 7 days

Heating 28 days

% Extension A 8.85 256 29.35 23.3 to break B 23.2 453 358.5 321 The results show that the plasticised polymer is 3 times as ductile as the non plasticised polymer prior to heat treatment. After heat treatment this is initially reduced to 2 times as ductile, but after 7 days and a month after heat treatment the ductility of the plasticised polymer is well over 1 0 times that of the non plasticised polymer. The rate of ageing of the non plasticised material after the heat treatment is much greater in the first week after treatment than for the plasticised material leading to a much longer life. Thus the heat treatment has synergised the effect of the plasticiser. Table 1 B

sample days C

0 1 7 10 28 84 1 99 control 55.2 20.5 10.5 - 7.4 6.3 5.9 treated 60.7 43.7 - 42.9 - 35.6 26.4

The extension to break of the plasticised homopolymer is higher than that of A or B before the heat treatment. It is not greatly increased by the heat treatment but after only 1 day ageing it can be seen that the extension to break is over 100% better than the untreated control. This trend is maintained over a period of over 6 months as indicated by the 600% and 500% improvements in extension to break compared to the untreated control for the 84 day and 1 99 day periods respectively. Example 2

Compositions each consisting of copolymer 90B 10V, 1 phr of boron nitride and 20 phr of plasticisers were mixed, moulded and tested as described. The bars were aged at room temperature for 56 days, deaged at 1 10°C for 1 h and tested.

The plasticisers were D diundecyl phthalate (Jayflex DIUP) (RTM)

E di-isoheptyl phthalate (Jayflex 77) (RTM)

F acetyl tributyl citrate (Estaflex ATBC) (RTM)

Results are shown in Table 2. Table 2

Control Period after Heating before 0 1 day heating ^• 1 wk 1 mth

% B 8.58 256 - 29.4 23.3

Extension D 12.9 286 157 108 56 to break E 1 6.3 463 452 381 267

F 1 2.1 412 - 213 134

Conclusion

It is evident that using plasticisers D, E and F the decrease in extension is relatively slower in the period of one week from the heat treatment compared to the non plasticised polymer. Thus, at one month after treatment the elongation to break values are significantly higher for the plasticised polymer than those for the non plasticised polymer.

Example 3

Compositions each consisting of copolymer having 8% HV units, 1 phr of boron nitride and 10 phr of plasticisers were mixed, moulded as

380ml (1 2 fl oz) bottles. The bottles were aged at room temperature for at least one week, and then heated treated at approximately 130°C

(surface temperature of the bottles) for the period given in Table 3 and then aged for 21 days. The bottles (10 replicates) were filled with water and dropped from a height of 60 inches onto a 1 .3cm (14 inch) steel plate angled at 5°. Untreated bottles were dropped in the same test as a comparison. The results are given in Table 2 The plasticisers were

F acetyl tributyl citrate (Estaflex^" ATBC) (RTM) G triacetin (glycerol triacetate)

The results are shown in Table 3. Table 3

IR TIME (SECONDS) OVEN TEMP C %BOTTLE SURVIVAL

F 0 - 10

F 180 250 100

F 300 245 100

F 75 300 100

F 90 300 100

G 0 - 12

G 180 180 100

G 90 300 100

Conclusion

All the heat treatments caused highly significant improvement in the impact properties of the bottles compared to the untreated bottles. Example 4

The elongation to break (%E) was measured on bottles prepared as described in Example 3. The heat treated bottles were given 4 minutes in an infra red oven with a heater temperature of 250°C. This gave a bottle surface temperature of approximately 1 25 °C-1 30°C. The bottles were aged for several months prior to deaging and testing. Two bottle formulations were tested:

H 5phr Estaflex^* and 5phr epoxidised soya bean oil (Paraplex G62);

I 10phr polycaprolactone (Tone 787^*, Union Carbide), 5phr

Estaflex^* and 3phr talc. The results are given in Table 4. Table 4

untreated treated

H 9.9 1 8.3

I 7.9 22.3

Conclusion

The heat treatment restored the bottles to a significantly increased level of ductility compared to the untreated bottles. Example 5 Dart drop impact performance testing was carried out on bottle walls. The bottles were prepared as described in Example 3, a piece of the bottle wall is cut out and flattened and subjected to the dart drop test which involves dropping an instrumented dart on to the bottle wall held horizontally and measuring the energy absorbed in the impact. The drop conditions were 12% relative humidity, 23.4°C temperature, weight

3.4kg (7.5lbs), height of drop 107cm (42 inches), the ring was 3.8cm (1.5 inches). The measurement is energy/thickness given in Jm^"1. Bottles were also subjected to the bottle drop test as previously described in Example 4. The bottles were aged for 3 weeks prior to heat treatment and then aged for 4 weeks and 8 week at 40°C after heat treatment and were tested 2-3 hours after the heat treatment. The infra red heat treatment gave 3 to 6 minutes in the IR oven providing a temperature at the bottle surface of 130 to 135°C.

Two formulations as follows were tested : J 6.5phr Estaflex^*, 1 phr boron nitride, O.δphr titanium dioxide and

0.1 5 silicon dioxide K 8.5phr Estaflex^*, 1 phr boron nitride, O.δphr titanium dioxide, 2phr talc and 10phr polycaprolactone. The results are given in Table δ and Table 6. Table 5: Dart drop impact performance (Jm ¹ )

Not treated IR (3mn) IR (4mn) IR (6mn)

J

0 days 229.7 NT 61 5.8 NT

1 day 177.7 NT NT NT

4 weeks NT 274 341 .3 392.7

8 weeks NT NT 348.9 NT

K

0 days 208.4 NT 654.2 NT

1 day 212.8 NT NT NT

4 weeks NT 438 404.3 66δ.7

8 weeks NT NT 445.4 NT

Table 6: Percentage of bottles surviving impact from 48 or 60 inches

Not treated IR treated

48 60 48 60

J

1 day 60 NT 100 87 4 weeks 60 NT 85 85 8 weeks 40 NT 100 NT

K

1 day 100 100 100 100 4 weeks 100 60 100 100 8 weeks 40 NT 100 NT

Conclusion

The results given in Table 5 indicate that the infra red heat treatment gave a very large increase in the energy to break of the bottles after the heat treatment even after a period of 8 weeks. These observations are backed up by visual inspection of the broken samples which showed that the bottles which had not been subjected to heat treatment gave a brittle fracture whereas the bottles which were given the heat treatment gave a ductile fracture. With a brittle fracture there is a punctured hole with radiating cracks or a flap with radiating cracks. This indicates that the polymer has become brittle. The ductile fracture indicates that the polymer is still ductile. These results and observations are further backed up by the results given in Table 6 which indicate that the infra red heat treatment gives a large increase in the impact resistance of the bottles even after the bottles have been aged for 2 months. Example 6

A further bottle impact test was conducted using bottles prepared from the following compositions: L 8% HV, 10phr Estaflex^'

M 12% HV, 10phr Estaflex^*

N 8% HV, 10phr Tone^* 700

O 8% HV, 10phr Tone^* 100

The bottles were aged for at least one weak prior to heat treatment. The bottle size was 300ml and the bottles were heat treated in an air oven pre-heated to 130°C. The temperature dropped to 108°C whilst treating the bottles and the oven took 20 minutes to re-equilibrate at 130°C. The bottles were held at 120 to 130°C for 20 minutes (or 30 minutes at 1 20°C). The bottles were drop tested from 1 22cm (48 inches) and 1 62cm (60 inches) at 1 week and 1 month after heat treatment. The percentage of bottles surviving the drop test results are given in Table 7. Table 7

Treatment Age at drop 122 cm 1 62 cm

L none 1 month 78 -

L 130°C 1 week - 100

L 1 30°C 1 month - 100

M none 1 month - 40 M 1 30°C 1 week - 100

M 130°C 1 month - 100

N none 1 month 70 -

N 120°C 1 week - 100

N 1 20°C 1 month - 100

0 none 1 month 70 -

0 125°C 1 week - 100

O 1 25°C 1 month - 100 ey : - means not tested Conclusion

In all cases the heat treated bottles at one month post heat treatment were significantly more impact resistant than the non-heat treated bottles at one month post moulding.

93SKM10S MS - 26 May 1 994

Claims

1 Polyester composition comprising at least one polyhydroxyalkanoate (PHA) and at least one plasticiser thereof, in which ageing has occurred, characterised in that (i) the polyester is restored to its original non-aged properties by a heat treatment, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age.

2 Polyester composition according to Claim 1 wherein the retardation of subsequent ageing is indicated by substantial improvement of at least one measurement indicative of ageing compared to the heat treated polyester of the same age without plasticiser. Polyester composition according to Claims 1 or 2 wherein the composition contains up to and including 40 parts per hundred of one or more plasticisers. Polyester composition according to Claims 1 to 3 wherein the heat treatment is carried out in the range from 80°C to 1 50°C. Polyester composition according to any of Claims 1 to 4 wherein the heat treatment is carried out in the range from 100°C to 140°C. Polyester composition according to any of Claims 1 to δ wherein the polyester is restored to at least 50% of the ductility of the original non-aged polyester. Polyester composition according to any of the preceding claims wherein the substantial improvement means that the measurement indicative of ageing is improved by 50% or more. Polyester composition according to any of the preceding claims wherein the PHA comprises polyhydroxybutyrate or copolymer of hydroxybutyrate units and hydroxyvalerate units. Polyester composition according to Claim 8 wherein the copolymer of hydroxybutyrate units and hydroxyvalerate units is in the (R)-3- hydroxy form. 10 Polyester composition according to any of the preceding claims wherein the copolymer of hydroxybutyrate units and hydroxyvalerate units contains at least 70 mol% of hydroxyvalerate units.

1 1 Shaped article at least partly made from a polyester composition comprising at least one polyhydroxyalkanoate (PHA) and at least one plasticiser thereof, in which ageing has occurred, characterised in that (i) the shaped article is restored to its original non-aged properties by heating, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age.

1 2 Shaped article according to Claim 1 1 wherein the retardation of subsequent ageing is indicated by substantial improvement of at least one measurement indicative of ageing compared to the heat treated polyester of the same age without plasticiser.

1 3 Process for improving mechanical properties of an aged polyester composition comprising at least one polyhydroxyalkanoate (PHA) and at least one plasticiser thereof, which comprises heating at a temperature whereby (i) the polyester is restored to its original non-aged properties, and (ii) subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to non heat treated polyester of the same age.

14 Process according to Claim 1 3 wherein subsequent ageing of the polyester is retarded as indicated by substantial improvement of at least one measurement indicative of ageing compared to heat treated polyester of the same age without plasticiser.

1 5 Process according to Claim 1 3 or 14 wherein the heat treatment is carried out at a temperature from 80°C to 1 50°C.

1 6 Process according to Claim 1 6 wherein the heat treatment is carried out at a temperature from 100°C to 140°C.

1 7 Process according to any of Claims 1 3 to 1 6 wherein the polyester composition is heat treated for a period from 5 seconds to 20 hours. Process according to any of Claims 13 to 17 wherein transfer of heat is by conduction or radiation. Process according to Claim 18 wherein transfer of heat is by infra red radiation. Process according to any of Claims 1 3 to 1 9 wherein the polyester is restored to at least 50% of the ductility of the original non-aged polyester. Process according to Claim 20 wherein the substantial improvement means that the measurement indicative of ageing is improved by 50% or more. Process according to any of Claims 13 to 21 wherein the PHA comprises polyhydroxybutyrate or copolymer of hydroxybutyrate units and hydroxyvalerate units. Process according to any Claims 13 to 22 wherein the polyhydroxybutyrate or copolymer of hydroxybutyrate units and hydroxyvalerate units is in the (R)-3-hydroxy form. Process according to any of Claims 13 to 23 wherein the mechanical properties of the heat treated polyester stabilise at a level substantially improved compared to the non heat treated polyester. Process according to Claim 24 wherein the mechanical properties of the heat treated polyester stabilise at a level at least 50% improved compared to non heat treated polyester of the same age.