Polyester composition

A polymer composition comprises (a) a stereospecific, preferably fermentation derived, polyester of molecular weight Mw over 100000 consisting of repeating units of formula --O--C.sub.m H.sub.n --CO-- in which n=2m and units with m=3 and m=4 with respectively a C.sub.1 and C.sub.2 side group on the carbon atom next to oxygen in the polymer chain are copolymerised together, m being 3 in 70-95 mol percent of such units; and (b) at least one alkyl phenol in which the alkyl group preferably contains at least one tertiary carbon atom adjacent to or within 4 carbon atoms of the phenol nucleus. The alkyl phenol may be hindered and may contain a C.sub.1-6 alkoxy group para to the phenolic hydroxy group. Suitable alkyl phenols include 2-tert-butyl-4-hydroxy-anisole and alpha- or delta- tocopherol and others usable as antioxidants in foods, oils and polymer systems. The polyester and alkyl phenol and relative proportions thereof are preferably chosen to provide inhibition of crystallisation of the polyester corresponding to an Avrami `k` parameter less than 0.03.

POLYESTER COMPOSITION 
THIS INVENTION relates to a polyester composition and in particular to a 
composition comprising an aliphatic polyester and a plasticiser. 
Examples of such polyesters have become available commercially as the 
result of developing microbiological processes for making them. The 
earliest example, PHB, was difficult to melt-process owing to low thermal 
stability at its melting temperature. Corresponding copolymers melt at a 
lower temperature. When such polyester is used for making plastics shaped 
articles, it may be necessary to formulate it with a plasticiser in order 
to obtain desired mechanical properties. Many plasticising compounds have 
been proposed for this duty, but there is room for improvement in the 
mechanical properties obtained and their permanence. 
It has now been found that compositions comprising such polyesters (which 
term is herein to include homopolyesters, copolyesters and mixtures 
thereof) and one or more phenolic compounds of a defined class show 
substantial advantages. 
ACCORDING TO THE INVENTION in its first aspect a polymer composition 
comprises 
(a) a stereospecific polyester of molecular weight Mw over 100000 
consisting of repeating units of formula --O--C.sub.m H.sub.n --CO-- in 
which n=2m and units with m=3 and m=4 with respectively a C.sub.1 and 
C.sub.2 side group on the carbon atom next to oxygen in the polymer chain 
are copolymerised together, m being 3 in 70-95 mol percent of such units; 
and 
(b) at least one alkyl phenol. 
In the alkyl phenol there is preferably at least one alkyl group containing 
a chain of at least 2 and suitably up to 20 carbon atoms. Preferably at 
least one such alkyl group contains at least one tertiary carbon atom, for 
example linked to 2 side substituents other than hydrogen, at least one of 
which atoms is carbon. The chain preferably carries at least 2 and 
suitably up to 6 hydrocarbon side substituents, and these are preferably 
C.sub.1-6, especially methyl. A or the tertiary carbon atom is preferably 
adjacent to or within 4 carbon atoms of the phenol nucleus. On any of the 
tertiary carbon atoms, any side substituent atom that is not carbon is 
preferably oxygen. 
The alkyl phenol is preferably "hindered", that is, rotation of the alkyl 
group is inhibited by collision with a nuclear substituent (especially OH 
or O-alkyl) ortho to the alkyl group or is prevented by a ring-forming 
linkage of the alkyl group to the phenolic nucleus. 
The alkyl phenol preferably contains also at least one hydrocarbonoxy 
group, preferably para to the phenolic OH group. Suitably the 
hydrocarbonoxy group is C.sub.1-6 alkoxy. 
Particular examples of suitable alkyl phenols are: 
2-tert-butyl-4-hydroxyanisole) mixture `BHA` 
3-tert-butyl-4-hydroxyanisole) 
3,5-di-tert-butyl-4-hydroxytoluene `BHT` 
.alpha.-tocopherol `.alpha.-T` 
.delta.-tocopherol `.delta.-T`. 
Instead of the free alkyl phenol, an ester thereof may be present, for 
example a C.sub.1-6 carboxylic ester. It is believed that such ester is an 
example of a precursor decomposable to the alkyl phenol during processing 
and/or ageing of the polyester. Likewise, a thermal and/or oxidative 
reaction product of the alkyl phenol, such as may result from processing 
and/or ageing, may be added instead of free alkyl phenol. A particular 
example is 2,2'-dihydroxy-5,5'-dimethoxy-3,3'-di-tert-butylbiphenyl, an 
oxidation product of 3-tert-butyl-4-hydroxyanisole. 
The defined class of alkyl phenols includes compounds effective as 
anti-oxidants, for example in foods, oils and polymer systems. These may 
be used and are believed to be preferable, especially if they are harmless 
to life and/or are biodegradable. 
The invention includes: 
(a) the composition as freshly prepared; 
(b) the composition after processing steps short of conversion to finished 
article; 
(c) finished article: in which there is present the defined alkyl phenol 
and/or whatever conversion product has been formed from it. 
The polyester is preferably capable of a relatively high level of 
crystallinity, eg over 30%, especially 50-90%, in the absence of 
additives. 
The molecular weight Mw of the PHA is for example up to eg 
2.times.10.sup.6. 
In PHAs having m=3 and m=4 there may be very small, typically fractional, 
percentages of units having higher values of m. PHA consisting essentially 
of m=3 units is poly-3-R-hydroxybutyrate (PHB), and PHA consisting of m=3 
and 4 units is polyhydroxybutyrate-co-valerate (PHBV). 
The PHA can be a product of fermentation, especially a process in which a 
microorganism lays down PHA during normal growth or is caused to do so by 
starvation of one or more cell nutrients necessary for cell 
multiplication. The microorganism may be wild or mutated or may have the 
necessary genetic material introduced into it. Alternatively the necessary 
genetic material may be harboured by an eukariote. PHA so made is 
R-stereospecific. Examples of suitable microbiological processes are 
disclosed in EP-A-69497 (Alcaligenes eutrophus). 
The PHA can be extracted from the fermentation product cells by decomposing 
non-PHA cellular material leaving microscopic granules of PHA, or by means 
of an organic solvent applied to the fermentation product or to such 
product after one or more steps such as cell breakage or 
part-decomposition of cellular material. For specialised end-uses cellular 
material may be partly or wholly allowed to remain with the PHA, but 
preferably subjected to cell breakage. 
Alternatively the PHA can be synthetic, produced for example as described 
by Bloembergen et al. in Macromolecules 1989, 33. 1656-1663 (PHB) and 
1663-1669 (PHBV). 
The polyester component of the composition may contain more than one 
polyester, for example: 
(a) polyesters having the same repeating units but differing in molecular 
weight; part of the polyester component may be of too low a molecular 
weight to be usable alone as structural material; 
(b) polyesters having different combinations of repeating units; 
(c) polyesters of a different class--e.g. synthetic with 
microbiological--but mutually miscible; 
(d) polyester of a different class but not mutually miscible; 
(e) polyester, whether or not differing as (a) to (d), having a different 
history, for example a different manufacturer or extraction procedure or 
different previous processing such as re-work or recycle or end-group 
modification. 
The alkyl phenol is present in a plasticising proportion, that is, a 
proportion sufficient in itself to provide, or with other plasticiser(s) 
to enhance, a plasticising effect. The proportion of alkyl phenol to 
polyester depends on the intended use of the composition. The range 2-40 
phr w/w includes more of the likely uses. For making effectively rigid but 
not brittle articles the range 5-20, especially 6-12, phr w/w is generally 
suitable. 
The polyester, alkyl phenol and relative proportions thereof are preferably 
chosen to provide at least 30, especially at least 50, percent inhibition 
of crystallisation of the polyester. Such a composition preferably has an 
Avrami `k` parameter less than 0.03, especially less than 0.01. Further, 
its DSC crystallisation peak preferably has an area less than 20, 
especially less than 5, percent of that of the same polyester free of 
plasticiser. 
Such preferred compositions exemplify a new polyester composition defined 
in terms only of those parameters, and constituting a second aspect of the 
invention. 
The composition may contain components in common use in plastics 
processing, for example: 
(a) one or more other plasticisers other than the defined alkyl phenol; 
(b) one or more stabilisers against thermal or oxidative decomposition; 
(c) inorganic filler, for example glass fibre, carbon fibre platy or foil 
particle, silica, clay, magnesium silicate; 
(d) organic filler, for example, cellulose fibre or particulate, protein 
fibre, synthetic polymer particle or fibre, wood flour; 
(e) polymer other than polyester; 
(f) pigment; 
(g) nucleant, especially boron nitride, talc, ammonium chloride or DZB/Zn 
stearate, at preferably 0.2 to 2.0 phr; 
(h) volatile solvent for the polyester and alkyl phenol. 
If such other plasticiser is present, it may be selected from those already 
known for these polyesters and/or from any found to plasticise them 
subsequent to this invention. Examples are: 
(a) high boiling esters of polybasic acids, such as phthalates, 
isophthalates, citrates, fumarates, glutarate, phosphates or phosphites. 
The esterified radicals may be for example C.sub.1 -C.sub.12 alkyl, aryl 
or aralkyl. Particular examples are dioctyl-, diheptyl- and diundecyl- 
phthalates and dialkylalkylene oxide glutarate (Plasthall 7050); 
(b) high boiling esters and part-esters of polyhydric alcohols, especially 
glycols, polyglycols and glycerol. Examples are triacetin, diacetin and 
glyceryl dibenzoate; 
(c) aromatic sulphonamides such as paratoluene-sulphonamide. 
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 
hydroxy-carboxylic 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. An example of such a plasticiser is Estaflex* (acetyltri-n-butyl 
citrate). *Trade mark of AKZO. 
According to a further aspect of the invention a method of making the 
composition comprises blending the polyester with the alkyl phenol. This 
may be effected by for example: 
(i) mixing the alkyl phenol with the polyester in particulate form, for 
example in particles smaller than 1000, especially smaller than 100, 
microns. Preferably the particles are in the size range 0.1 to 50 microns. 
The particles are especially those obtained by enzymatic removal of 
non-polyester cell material such as protein from a microbiologically 
produced biomass. The alkyl phenol can be introduced at any convenient 
stage, including stages before the particles are isolated from the aqueous 
medium. 
(ii) melting a mixture of polyester with alkyl phenol. The mixture is 
preferably as made by method (i). Other components, for example as in (a) 
to (d) above, especially those that assist melting, may be present; 
(iii) bringing the polyester and alkyl phenol together in a volatile 
solvent for the polyester. The solvent may have been introduced as a means 
of extracting the polyester from a microbiologically produced biomass or 
an intermediate product from which microbiological cell material has been 
partly removed. Solvent can then be removed or not, according to the 
requirements of further processing. Suitable solvents include cyclic 
carbonate esters and halogenated hydrocarbons such as dichloromethane, 
chloroform and 1,2-dichloroethane. A particular process comprises: 
(i) forming a biomass of cells containing PHA granules and non-PHA cell 
material by fermentation; 
(ii) treating the biomass to solubilise non-PHA cell material; 
(iii) separating the PHA granules from the liquid phase; and is 
characterised by introducing at least one alkyl phenol as hereinbefore 
defined. 
The process may include treating the granules with a peroxide whereby to 
solubilise non-PHA cell material additional to what has been solubilised 
in step (ii), and separating the granules from the resulting liquid phase. 
In a yet further aspect the invention provides a process of making a shaped 
article by confining, eg in a mould or on a surface or through a die, a 
composition as defined above. 
Particular methods include injection moulding, compression moulding, 
extrusion of fibre or film, extrusion of profile, gas-current spinning, 
tack spinning, coating on to substrate, any of these being carried out, as 
appropriate, using the composition in the form of melt, particulate or 
solution in volatile solvent. Examples of shaped articles made by such 
methods include films especially for packaging, coated products (such as 
paper, paperboard and non-woven fabrics), fibres, non-woven fabrics, 
extruded nets, personal hygiene products, bottles and drinking vessels, 
agricultural and horticultural films and vessels, slow-release devices and 
ostomy bags. Alternatively the composition can be used as an adhesive. 
The drawings accompanying this specification are as follows: 
FIG. 1 : a family of DSC heating curves for control, reference and 
invention compositions; 
FIG. 2 : DSC heating curves (a) and cooling curves (b) for pure polyester 
and composition containing 20phr of BHA.

The following further data relate to the curves shown in FIG. 2. 
______________________________________ 
No Additives 
(a) Heating 
Peak from : 108.73.degree. C. 
Peak 159.48.degree. C. 
to : 172.00 
Onset 133.72 
J/g 65.14 
(b) Cooling 
Peak from : 23.23.degree. C. 
Peak 52.97.degree. C. 
to : 82.15 
Onset 66.36 
J/g 31.04 
20 ph v BHA 
(a) Heating 
Peak from : 82.10.degree. C. 
Peak 126.46.degree. C. 
to : 150.71 
Onset : 110.17 
J/g : 35.93 
(b) Cooling 
(No further data) 
______________________________________ 
The invention is illustrated by the following experimental data by way of 
example. TEST PROCEDURES : SERIES A PROPERTIES OF FRESH COMPOSITION 
Differential scanning Calorimetry (DSC) Specimen Preparation 
Polyester and plasticiser (if used) (together totalling 1.0 g) were 
dissolved in chloroform (60 ml), warmed at 50.degree. C. for 10 min, then 
cast in a stainless steel tray (inside diameter 76.2 mm) and dried under 
vacuum. The resulting film was 0.2 to 0.28 mm thick. A specimen (ca 4 mg) 
was cut from the film, placed in each aluminium pan of the DSC instrument 
and sealed. 
DSC Examination 
This technique measures the energy flow towards or from a specimen in 
comparison with an inert reference as a function of time and temperature. 
A DSC instrument typically includes two isolated insulated holders on each 
of which a pan containing respectively the test specimen or the reference 
is mounted. The heat flow is measured and compensated for, to maintain the 
temperature with respect to the reference. The instrument can be operated 
in dynamic mode under a preset temperature program or in isothermal mode. 
(i) A Perkin Elmer DSC-2 instrument equipped with a Thermal Analysis Data 
Station was used in dynamic mode: 
Run 1: heat at 20.degree. C. min.sup.-1 from 20.degree. C. to 200.degree. 
C.; hold at 200.degree. C. for 1 min to ensure sample fully melted; cool 
at minus 200.degree. C. min.sup.-1 to minus 80.degree. C.; hold at minus 
80.degree. C. for 10 min to preserve amorphous state. 
Run 2: Finally heat at 20.degree. C. min.sup.-1 from minus 80.degree. to 
200.degree. C. 
From the measured heat flows the following parameters were derived: 
T.sub.g glass transition temperature (run 2); 
T.sub.p (1) and T.sub.p (2)peak temperature of melting for the 2 peaks 
seen; 
.DELTA.H melting enthalpy. 
(ii) The DSC-2 instrument was operated in isothermal mode as follows: 
heat at 20.degree. C. min.sup.-1 from 20.degree. C. to 200.degree. C.; 
hold for 10 min at 200.degree. C. to melt; 
cool to 57.degree. C. rapidly; 
hold at 57.degree. C., recording crystallisation peak(s). 
The results were analysed by computer loaded with a DSC-2C/4 isothermal 
program, and then further in terms of the Avrami equation 
.theta.=exp (-kt.sup.n) 
where .theta. is the fraction of uncrystallised material remaining after 
time t; 
k is a rate constant; and 
n is the Avrami exponent, which is usually considered to be characteristic 
of the mode of nucleation. 
Tensile Test 
Following Japanese Industry Standard K6301, film 0.2 mm thick as made for 
DSC (see above) was cut into No 3 dumbbell pieces of central dimensions 
5.times.20.times.0.2 mm. These were tested at 0.2 mm sec.sup.-1 on a 
TA-XT2 machine from Stable Micro Systems, Haslemere, UK. 
EXAMPLES 
Polyester compositions were prepared from a PHB of this specification: 
structure: PHBV 90:10 copolymer (formula 1, m=3.1 average); 
molecular weight M.sub.w 477000; 
origin: fermentation of glucose+propionic acid by Alcaligenes eutrophus; 
extraction: enzymatic cell-debris removal. 
The compositions tested were as follows: 
Control--no additive 
Reference--known plasticiser triacetin TA 
Invention--BHA 
Invention--BHT 
Invention--.alpha.-T 
Invention--.delta.-T 
Each additive was used at 10, 20 and 30% w/w, i.e. 11.11, 25 and 42.86 phr. 
Results were as follows: 
DSC second run dynamic mode results are set out in Table 1. (Note: the AH 
values have been recalculated to give energies relative to the amount of 
polymer present: the 30% compositions for example contain only 70% of 
polymer). 
TABLE 1 
______________________________________ 
.DELTA. H (cal/g 
Additive T.sub.g 
T.sub.p 2 T.sub.p 2 
polyester) 
______________________________________ 
None -14.3 152.5 161.0 
15.1 
10% : BHA -18.6 142.2 152.9 
11.88 
BHT -18.1 144.8 155.3 
13.64 
.alpha.-T 
-15.2 152.7 158.1 
15.4 
.delta.-T 
-17.5 146.6 155.1 
14.3 
(TA -23.1 143.1 157.7 
15.07) 
20% : BHA -26.3 130.7 138.7 
6.84 
BHT -28.1 134.6 147.5 
12.00 
.alpha.-T 
-23.6 142.1 153.4 
12.48 
.delta.-T 
-25.8 137.9 151.1 
12.48 
(TA -40.2 126.2 146.2 
12.84) 
30% : BHA -29.9 125.0 0.0 1.56 
BHT -33.3 129.3 143.3 
13.39 
.alpha.-T 
-36.3 138.6 151.3 
13.39 
.delta.-T 
-41.2 135.2 149.8 
13.52 
(TA -47.9 118.5 140.4 
15.21 
______________________________________ 
The following effects are observable: 
T.sub.g : each invention additive lowers T.sub.g, but less strongly than 
triacetin. The tocopherols appear to give a stronger effect per unit 
weight of phenolic OH. 
T.sub.p : similarly a decrease in melting temperature was seen. This is 
again characteristic of plasticised systems. 
.DELTA.H: the melting enthalpy is indicative of the level of crystallinity 
achieved by the polymer during the DSC. The compositions containing BHA 
consistently give lower .DELTA.H values suggesting that crystallisation 
was being inhibited. 
The DSC second run results for compositions containing 30% additive are 
shown also in FIG. 1. It is evident that a strong crystallisation exotherm 
occurs in the unplasticised polyester and in the triacetin composition. 
However, this exotherm is weak in the composition containing .alpha.T 
acetate, very weak in the compositions containing BHT and .delta.T, and 
substantially absent in those containing BHA and .alpha.T. It is concluded 
that plasticisation in the invention compositions is by a mechanism 
distinct from that effective in the triacetin composition. 
This is borne out by the Avrami parameters: the following were calculated: 
______________________________________ 
n k 
______________________________________ 
control 2.3 0.368 
(triacetin 20% 2.2 0.055) 
BHA 20% 1.8 0.001 
.alpha.-T 20% 2.0 0.004 
______________________________________ 
The k values imply that the rate of recrystallisation of PHBV has been 
decreased drastically, but the n values show that the mechanism of 
recrystallisation is unchanged. 
DSC heating (a) and cooling (b) curves for unplasticised polyester and 
composition containing 20 phr BHA are shown in FIG. 2. From the heating 
curves it is evident that the area under the melting peak is halved by the 
plasticiser. The cooling curves shown a strong exotherm for unplasticised 
polyester, but no sign of crystallisation in the composition. 
Tensile Test 
The effect on elongation-to-break (ETB) is shown in Table 2: 
TABLE 2 
______________________________________ 
Additive % w/w ETB 
% 
______________________________________ 
None 0 15.9 
(TA 10 23.0 
20 28.0 
30 47.0) 
BHA 10 31.0 
20 40.0 
30 56.0 
.alpha.-T 10 25.0 
20 55 
30 80.0 
______________________________________ 
TEST PROCEDURES : SERIES B CHANGE OF PROPERTIES WITH TIME 
The following properties were determined by standard procedures at 90 days 
after preparation of the compositions: 
Young's modulus (YM) MPa 
Stress at break (SAB) MPa 
Displacement at break (DAB) % 
IZOD impact strength (IZOD) Jm.sup.-1. 
The composition tested consisted of: 
PHBV copolymer having a B:V molar ratio 93:7 but otherwise similar to the 
polymer used in the series A tests; 
20phr w.w plasticiser (if used); 
1 phr w/w boron nitride nucleant. 
The plasticisers used were: 
none (control); 
Acetyl-tri-n-butyl-citrate (ATBC) (control) BHA 
BHA+ATBC 10 phr w/w each .alpha.-T 
Results are shown in Table 3. 
TABLE 3 
______________________________________ 
Plasticiser 
None ATBC BHA BHA.ATBC 
.alpha.-T 
______________________________________ 
YM 1010.0 356.3 280.6 391.1 522.4 
SAB 24.4 15.0 14.7 16.0 17.2 
DAB 12.3 25.9 28.8 25.5 25.5 
IZOD 69.0 224.8 265.8 223.8 125.8 
______________________________________ 
The following conclusions can be drawn: 
From YM: the plasticised compositions are distinctly less stiff than the 
unplasticised composition; since the BHA/ATBC mixture is less effective 
than an equal proportion of either plasticiser used alone, it appears that 
these act by different mechanisms; 
.alpha.-T is less effective than BHA, but this may be due to its higher 
molecular weight per phenolic OH (.alpha.-T 430, BHA 180). 
From SAB and DAB: the invention plasticisers are at least equal to the 
known ATBC; 
From IZOD: BHA and BHA/ATBC are approximately equal but inferior to BHA 
alone. The lower impact strength using .alpha.-T may correlate with its 
higher molecular weight per phenolic OH.