Polymer blends and compatibilizers

Blends of biodegradable polymers of hydroxybutyric acid and polyolefines of improved properties are produced by incorporating a compatibilising agent which comprises a block copolymer in which at least half of the mass of one block is represented by alkyl side chains and at least half of the mass of another block is represented by side chains which comprise hydroxy acid residues.

POLYMER BLENDS AND COMPATIBILISERS 
It is known to blend polymers of different types in order for example to 
obtain plastics compositions possessing a combination of their properties. 
However, when the polymers are of dissimilar chemical composition they may 
be incompatible and such blends may possess poor mechanical properties due 
to localised segregation of the polymers and weak bonding at the 
interfaces between regions of different polymer composition. The problem 
is particularly acute when films are to be formed by a process which 
comprises stretching a sheet or film to reduce its thickness. This may be 
carried out in one, or in two substantially perpendicular directions in 
order for example to achieve axial or biaxial orientation of the film. 
Blends of polyolefins and polyesters are prone to such problems. 
It is desirable to achieve films which are readily biodegradable, as these 
can be used for example as components of disposable diapers, ostomy bags 
and even as ordinary wrappings with a reduction in problems of disposal 
after use. 
Very satisfactory biodegradable polymers comprise hydroxybutyrate groups 
(PHB polymers) especially those PHB polymers which also comprise 
hydroxyvalerate groups (PHB/PHV copolymers). Polymers of this type are 
described in for example our European Patents 52,459 and 69,497. However, 
although they can be formed into satisfactory films with care, when used 
alone there is a tendency with such polymers to produce a proportion of 
off-specification material and the manufacturing process is subject to 
considerable constraints. It is desirable therefore to devise improved 
polymer compositions of this type. 
We have found that blends of such polymers with polyolefins possess 
favourable properties provided that the components are rendered 
compatible. Polypropylene is particularly favourable and has the advantage 
that it degrades more readily than polyethylene especially if no 
antioxidants are present. It is however difficult to render these 
materials compatible with PHB polymers. 
We have found that such blends can be made with unexpectedly good 
properties by incorporating into them a compatibilising agent which 
comprises a block copolymer in which in at least one block (Block A) at 
least half of the mass of the block is represented by alkylene or 
preferably alkyl side chains, which preferably have straight chains and 
which are suitably at least five and preferably at most 20, for example 
six to twelve carbon atoms long, and in which in at least one other block 
(Block B) at least half and preferably at least 70% of the mass of the 
block is represented by side chains which comprise hydroxybutyric acid 
residues and optionally also other hydroxyalkanoate residues which are 
preferably hydroxyvalerate residues. 
Preferably at least half of the units of the side chains are hydroxybutyric 
acid residues and any remaining units of said side chains consist 
essentially of hydroxyvalerate units. These side chains are suitably of 
average molecular weight 100-80,000 and preferably 200-10,000. The mass 
ratio of Block A to Block B is preferably 1:5 to 5:1. 
This invention comprises said compatibilising agents and also polymer 
blends compatibilised with them. These agents are believed to be useful as 
compatibilisers in polyolefin/polyester blends generally. 
Block A may derived from a polymerisable olefinically unsaturated monomer 
(preferably a methacrylic or acrylic monomer) having a moiety linked to 
the polymerisable olefinically unsaturated bond which is or includes a 
hydrocarbyl group of at least 5 carbon atoms (preferably at least 7). The 
alkyl or alkenyl groups of Block A are usually part of a larger grouping 
such as alkyl (or alkenyl) ester or alkyl (or alkenyl) ether groups, and 
will be spaced from the polymerisable olefinically unsaturated double bond 
by an intermediate chemical species; typical spacer groups are ester 
groups and ether groups. With regard to the olefinically unsaturated 
monomer providing block A, the upper limit for the number of carbon atoms 
in the hydrocarbyl group is not critical but for practical purposes will 
usually be about 22 (more usually about 15). The use of less than 5 carbon 
atoms in the hydrocarbyl group tends to result in poor compatibilisation. 
(The monomer may of course also possess a hydrocarbyl group(s) of less 
than 5 carbon atoms in addition to the hydrocarbyl group of &gt;5 carbon 
atoms). The olefinically unsaturated monomer is preferably a methacrylic 
or acrylic monomeric species, the polymerisable unsaturated bond being 
provided by the double bond of a methacrylic group CH.sub.2 
.uparw.C(CH.sub.3)-- or the double bond of an acrylic group CH.sub.2 
.uparw.CH--. More preferably the monomer providing block A is an ester of 
methacrylic acid or acrylic acid of formula CH.sub.2 .uparw.CR.sup.1 
CO.sub.2 R.sup.2 where R.sup.1 is methyl or H and R.sup.2 is an alkyl, 
cycloaolkyl or aryl group of at least 5 carbon atoms, more preferably at 
least 7 carbon atoms (usual ranges being 5 to 20 and 7 to 15 carbon 
atoms). Examples of such monomers include n-octyl methacrylate, 
2-ethylhexyl methacrylate, n-decyl methacrylate, lauryl methacrylate, 
cyclohexyl methacrylate, and docosanyl methacrylate (and the corresponding 
acrylate compounds). n-Octyl methacrylate and 2-ethylhexyl methacrylate 
are particularly preferred. 
The compatibilising agent may comprise a copolymer comprising at least one 
block of poly alkyl acrylate or poly alkyl methacrylate units (suitably of 
molecular weight 10,000-200,000 and preferably 20,000-200,000) and at 
least one block which comprises acrylate or methacrylate units of which a 
substantial proportion for example 20 to 100% are esterified to 
hydroxyacid chains as aforesaid. The compatibilising agent may be made by 
reacting a copolymer reactant comprising at least one block which 
comprises a poly primary alkyl acrylate or methacrylate and at least one 
block which comprises tertiary alkyl acrylate or methacrylate or acrylic 
or methacrylic acid units with a polymer comprising hydroxyacid units as 
aforesaid, for example a PHB polymer. This may be carried out by heating 
the two polymers together optionally in the presence of a catalyst, for 
example an acid catalyst and optionally in the presence of a solvent. On 
heating, an olefin or alcohol corresponding to the tertiary alkyl group is 
also formed. The block containing the tertiary alkyl group acrylate or 
methacrylate units may also comprise other more stable acrylate or 
methacrylate ester units for example those of lower alkyl groups for 
example C to C.sub.3 primary or secondary alkyl groups, if desired. 
The copolymer reactant may be made according to the procedures of our 
European Patent Application No 434,316 and UK Patent Application 8929024.1 
from which the said European Patent Application claims priority the 
disclosures of which are incorporated herein by reference. 
The polymer blend may be made by contacting the polyolefine, PHB polymer 
and a copolymer reactant at an elevated temperature sufficient to form the 
compatibilising agent and to melt the components under mixing conditions, 
for example at a temperature of 190.degree. C. optionally in an extruding 
process. 
It may also be made by preforming the compatibiliser or optionally a 
mixture of the compatibiliser with a PHB polymer by reacting the copolymer 
reactant with PHB polymer, and contacting the product with the polyolefin. 
The polymer blend is preferably conditioned by holding it for at least 10 
seconds and suitably 20 seconds to 1 minute at a temperature of 40.degree. 
to 70.degree. C. after formation at a higher temperature. 
The polyolefin is preferably blended as a high surface area polypropylene 
powder made by a gas phase process.

EXPERIMENT 
A three necked 500 ml flask, equipped with mechanical stirrer and pressure 
equalised dropping funnel and a rubber septum is flame dried under vacuum 
to remove all air and moisture. The flask is filled with dry nitrogen and 
cooled in an ice/salt bath to 0.degree. C. 120 ml toluene (distilled over 
sodium) is syringed into the flask. While stirring at 0.degree. C. 1.8 ml 
triisobutyl aluminum solution (molar in toluene) and 0.35 ml of tButyl 
lithium (1.7 molar in hexane) is syringed into the flask, thus 
constituting an initiator solution. 
20 ml toluene and 1.2ml of the above triisobutyl aluminum solution and 30 
ml octylmethacrylate (dried on silica column) are premixed in the dropping 
funnel and then slowly added to the flask containing the initiator 
solution. The temperature is kept at 0.degree. C. and the polymerisation 
is allowed to go to completion over a period of three hours. 
Then 20 ml toluene and 6 ml t-butylmethacrylate and 6 ml 
methyl-methacrylate and 0.6 ml of the above triisobutyl aluminum solution 
are premixed and added to the flask which contains the octylmethacrylate 
polymer. The flask is stirred for another 3 hours and then the 
polymerisation is terminated by adding 0.2 ml water, thus forming a 
copolymer comprising an poly octyl methacrylate block and a random 
t-butyl/methyl methacrylate block. 
Work Up 
The copolymer is precipitated from its solution in toluene by addition to a 
solution of 10% by weight HCl in methanol. The polymer is filtered off and 
dried in a vacuum oven at 80.degree. C. for 4 hours. The yield of 
copolymer is 98% of the monomers fed. 
The calculated number average molecular weight is 175000. The number 
average molecular weight determined by gell permeation chromatography 
(GPC) is 40000. The number average (Mn) to mass average (Mw) molecular 
weight Mn/MW was 1.3. Polyoctylmeth-acrylate is known to come out of GPC 
showing much lower Mn than real Mn. This is because the GPC was calibrated 
for polymethyl methacrylate only. 
Grafting of PHB/PHV Copolymer 
Method 1 
Dissolve octymethacrylate methylmethacrylate/tbutylmethacrylate block 
copolymer as produced above (20 g) in 250 ml toluene and add 2.5 g 
paratoluenesulphonic acid monohydrate. Also add 20 g PHB/PHV copolymer 
(88% PHB/12% PHV molar) powder. Reflux this mixture in a flask fitted with 
a reflux condenser at atmospheric pressure for 70 hours under nitrogen. 
Precipitate with methanol to give a white polymer powder. (Residual 
degraded PHB/PHV copolymer is soluble in methanol). 
Method 2 
As an alternative to the previous method of grafting mix the PHB/PHV 
copolymer with the 
octylmethacrylate/methylmethacrylate/t-butylmethacrylate block copolymer 
(1 to 5% by weight based on the PHB/PHV copolymer). Extrude this mixture 
at 190.degree. C. in a single screw extruder. The extrusion cleaves the 
tbutyleeter to give butene and free acid groups, which can react with the 
thermally degrading PHB/PHV copolymer to give the required graft 
copolymer. 
Preparation of Polypropylene/PHB/PHV Copolymer Composites with 
Compatibiliser 
The required amount of compatibiliser was dissolved in 100 ml of toluene 
and added to the polypropylene powder. This was stirred for 2 hours to 
allow the compatibiliser to absorb onto the polypropylene. (The toluene 
helps by swelling the polypropylene amorphous regions). The toluene is 
then removed on a rotary evaporator and the polypropylene is dried in a 
vacuum oven for 2 hours at 80.degree. C. PHB/PHV copolymer powder is added 
to the polypropylene. All blends were prepared on a total weight of 1 kg 
after addition of all components. The blends were then extruded into 
pellets using a single screw extruder at 190.degree. C. 
The following table shows test results of the composites. 
TABLE 1 
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Blends of PHB/PHV Copolymer and Polypropylene (equal 
weight) with different amounts of compatibiliser 
Stress at 
Compat- Unnotched Break 
ibiliser Izod Impact 
MPa Young's 
% by test (mega Modulus 
weight J/mm.sup.2 .times. 10.sup.3 
pascals) MPa .ident. N/mm.sup.2 
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PP#/BP** 
0 2.67 17.6 1414 
PP#/BP** 
2 6.52 24.4 1393 
PP#/BP** 
3 5.05 21.0 1321 
PP# * 37.6 1301 
BP** 5.35 23.2 2219 
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* out of range; ** PHB/PHV Copolymer; # Polypropylene. 
Tests on Films 
A compression moulded plaque of composite is drawn to approximately 8 times 
its original length and width at about 50.degree. C. Films were made of a 
75% Polypropylene 25% PHB/PHV copolymer by weight composition containing 
1% of the compatibiliser. The samples were very easily drawn into films, 
compared with pure PHB/PHV copolymer. 
The tensile properties of this sample were tested in both orientation 
directions and compared to pure PHB/PHV copolymer 25 film (Table 2). The 
film felt very strong. 
TABLE 2 
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Tensile Properties of 75/25 Composite compared to 
Biaxially oriented PHB/PHV Copolymer 
PHB/PHV 
Copolymer 
Composite 
Composite biaxially 
Horizontal 
Vertical oriented 
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Stress at peak MPa 
65 72 34 
Stress at break MPa 
65 72 33 
Young modulus MPa 
1170 1270 249 
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