Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1994-08-24
1995-12-26
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525309, 525 78, 525 79, 525 80, 525 92R, C08G 8102, C08L 6704, C08L 2302
Patent
active
054788927
DESCRIPTION:
BRIEF SUMMARY
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 criti
REFERENCES:
patent: 4880592 (1989-11-01), Martini
patent: 5135966 (1992-08-01), Chatterjee
patent: 5231148 (1993-07-01), Kleinke
Ballard Denis G. H.
Buckman Alfred J. P.
Schofer Joseph L.
Zemel I.
Zeneca Limited
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