Compatibilisers

Blends constitute about a third of all the world s polymer consumption. They offer a good balance of technical properties or the motive may be economic, as when a cheap commodity polymer is added to a more expensive engineering polymer to reduce costs. Incorporating an impact modifier in a brittle polymer also creates a blend. Finally, recycled post-consmner waste often consists of a blend of one polymer contaminated and weakened by another. 

Some pairs of polymers are readily miscible in an extruder, but others are incompatible and they form two phases, one being dispersed in another. The mechanical properties of an incompatible mix are poor because of the weak interfaces between the two phases. 

The term compatibiliser refers to an additive used to improve the miscibility and properties of a polymer blend. It is sometimes more specifically used to mean an additive used to promote adhesion between a polymer and an inorganic smface such as a mineral, or glass fibres. In this report, the coupling agents used to promote adhesion between polymer and inorganic additives are discussed imder the heading of Fillers, and this section concentrates almost entirely on the compatibilisers used to promote the compatibility of two organic polymers. 

Compatibilisers are normally copolymers (block or graft, but not random). Block copolymers have long chain molecules in which a sequence of several identical structural units, PPPPPP, is followed by a sequence of several different structural units, QQQQQ, all in the same chain in the case of graft copolymers, one sequence is a branch attached to the main chain in a T-shaped structure, and is not part of the trunk. The compatibiliser is usually of a higher molecular weight than the polymers being mixed. 

Whether the copolymer is a block or a graft, one sequence, P, is chosen to be compatible with polymer A, and the other, Q, with polymer B. The sequence P may even be identical with the polymer repeat unit A, or not. If polymer A and polymer B are incompatible and are being mixed, the simplest arrangement would be to use a block copolymer of A and B as compatibiliser, but this is not the only possibility. 

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More extensive roughening of an interface between incompatible polymers can be obtained by use of various types of copolymer, introduced at the interface as putative compatibilisers. The interface may be strengthened, as a result of interdiffusion and roughening on a nanoscale. Many elegant experiments have been done in this area. 

Recycling of glass fibre-reinforced plastics is reviewed, with special emphasis on remelting of thermoplastic composites, mechanical recycling of thermoset composites, depolymerisation and dissolution of thermosets and thermoplastics, closed loop recycling of glass, and the use of glass as a mechanical compatibiliser. 32 refs. 

Papke N. and Kargar-Kocsis J., Thermoplastic elastomer based on compatibilised poly(ethyleneterphtha-late) blend Effect of rubber type and dynamic curing. Polymer, 42, 1109, 2001. 

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity,... 

Usually polymeric substances of appropriate chemical structure and morphology which promote the miscibility of incompatible materials. Block copolymers are especially useful surfactants at the polymer/polymer interface because the two blocks can be made up from molecules of the individual polymers to be mixed. Typical compatibilisers in polymer blends are LDPE-g-PS in PE/PS CPE in PE/PVC acrylic- -PE, -PP, -EPDM in polyolefin/PA and maleic-g-PE, -PP, -EPDM, -SEBS in polyolefin/polyesters. 

Another important class of copolymers synthesized by chain polymerisation are block (or sequenced) copolymers diblock and triblock copolymers being the most important ones. They are very useful as compatibilisers (emulsifiers) in immiscible polymer blends. Another major use is as thermoplastic elastomers. Both uses are best explained through the example of butadiene-styrene block copolymers. 

Copolymers (graft or block) made of immiscible sequences give rise to biphasic morphologies depending on the ratio of immiscible sequences (or of their lengths). Such possible microstructures are reported in Figure 33. A minor phase can be dispersed as nodules (spheres) or filaments (cylinders) while, when concentrations of both phases get similar, lamellar (interpenetrated) structures can appear. It should be noted that rather similar morphologies could also be found in (compatibilised) polymer blends. 

Single- and twin-screw extruders with customised screw profiles are used to produce low density PETP-PP foams in the presence of reactive compatibiliser and coagents. Low density PETP foam is also produced from... 

Blends of poly (ethylene terephthalate) (PETP) and polypropylene (PP) with different rheological properties were dry blended or compounded, and extrusion foamed using both physical blowing and chemical agents, and the foam properties compared with those of foam produced from the individual components in the absence of compatibilisers and rheology modifiers. The foams were characterised by measurement of density, cell size and thermal properties. Low density foam with a fine cell size was obtained by addition of a compatibiliser and a co-agent, and foamed using carbon dioxide. The presence of PP or a polyolefin-based compatibiliser did not effect... 

New Orleans, La., August 1999, p.752-3 POLYSTYRENE/POLYPROPYLENE POLYMER BLEND COMPATIBILISATION WITHOUT ADDITION OF PREMADE BLOCK OR GRAFT COPOLYMERS OR FUNCTIONALISATION Furgiuele N Khait K Torkelson J M (ACS,Div.of Polymer Chemistry)... 

A novel approach is used to compatibilise a blend without addition of premade copolymers or functionalisation of polymers lacking functional groups. Solid-state shear pulverisation (S3P) processes polymers at temperatures below the melt transition (for semicrystalline polymers) or the glass transition (for amorphous polymers). The polymer, introduced as pellets or flakes into the pulveriser. 

Journal of Vinyl and Additive Technology 2,No.3, Sept. 1996, p.258-62 COMPATIBILISER SYSTEM FOR EXTRUDED PE FOAM AND FILM... 

Antec 96. Volume II. Conference proceedings. Indianapolis, 5th-10th May 1996, p. 1948-54. 012 COMPATIBILISER SYSTEM FOR EXTRUDED... 

A stndy was made of the effects of foam formulation and process conditions and liner composition on the adhesion of HCFC-141b blown rigid PU foam thermal insulation to refrigerator liner protective layers made of ABS, high-impact PS (HIPS), PE and blends of HIPS and PE containing a compatibiliser and adhesion promoter. A tensile test was used to quantify the level of adhesion before and after thermal cycling, and the Brett mould was used for laboratory simulations of foam adhesion within... 

As pointed out above, PVAc is frequently not used as a hompolymer but rather as the major component of a copolymer (VAE, terpolymers, vinylacrylics, etc.). Additionally, in the applications mentioned above PVAc and the related polymers are usually not used alone but as a part of a more or less complex mixture with other components. These components can be, for example, fillers, plasticisers, impact modifiers, compatibilisers, or other polymers. These components need to be taken into account when discussing biodegradabUity. They influence the biodegradability of the mixture as a whole but they may in particular influence the biodegradability of the PVAc moiety by altering the physical circumstances under which degradation reactions can take place. 

J. Pospfsil, I. Forteln, D. Micheilkovei, Z. Kruli , and M. Slouf, Mechanism of reactive compatibilisation of a blend of recycled LDPE/HIPS using an EPDM/SB/aromatic diamine co-additive system, Polym. Degrad. Stab., 90(2) 244-249, November 2005. 

Diblock copolymers, especially those containing a block chemically identical to one of the blend components, are more effective than triblocks or graft copolymers. Thermodynamic calculations indicate that efficient compat-ibilisation can be achieved with multiblock copolymers [47], potentially for heterogeneous mixed blends. Miscibility of particular segments of the copolymer in one of the phases of the bend is required. Compatibilisers for blends consisting of mixtures of polyolefins are of major interest for recyclates. Random poly(ethylene-co-propylene) is an effective compatibiliser for LDPE-PP, HDPE-PP or LLDPE-PP blends. The impact performance of PE-PP was improved by the addition of very low density PE or elastomeric poly(styrene-block-(ethylene-co-butylene-l)-block styrene) triblock copolymers (SEBS) [52]. 

Inmiscible blends of HDPE or LDPE with PS have been compatibilised with various graft copolymers, such as PS-graft-PE, PS-graft-EPDM or block copolymers such as SBS triblocks, SEBS, PS-block-polybutadiene [53, 54]. The same block copolymers are suitable for PP-PS blends [55]. 

Compatibility of PE with PVC is improved by poly(ethylene-graft-vinyl chloride) or partial chlorinated PE. To compatibilise blends of PE with PET, common for the scrap of beverage bottles, EPDM or SEBS are effective additives [56]. 

Styrene-butadiene or styrene-(ethylene-co-propylene) block copolymers are common compatibilisers for the commingled recyclate from PCW [27]. Improvement of the mechanical properties of heterogeneous PCR (33% PE+39% PVC+28% PET) or (44% PE+1% PP+28% PET+9% PS+2% PVC+16% other plastics) was performed with EPDM or hydrogenated SBS triblocks [52]. 

Scheme 3.2 Probable mechanism of compatibilisation between EPDMgDBM and PCP.

It is concluded that IR spectroscopy provides information on qualitative as well quantitative analyses of rubbery materials, apart from their microstructures (that is, whether cis or trans, syndiotactic, atactic or isotactic). Different types of rubber blends (compatibilised or self-crosslinked) can be identified by the infrared spectroscopy. Synthesis, and degradation of polymers can also be followed by IR spectra. Mechanism of interaction between rubbers and fillers, can also be studied by IR-spectra. Different types of chemical reactions like the milling behaviour of rubbers, mechanism of adhesion and degradation can also be studied with the help of IR spectroscopy. The technique plays a great role in the product analysis under reverse engineering. 

The ionic aggregates present in an ionomer act as physical crosslinks and drastically change the polymer properties. The blending of two ionomers enhances the compatibility via ion-ion interaction. The compatibilisation of polymer blends by specific ion-dipole and ion-ion interactions has recently received wide attention [93-96]. FT-IR spectroscopy is a powerful technique for investigating such specific interactions [97-99] in an ionic blend made from the acid form of sulfonated polystyrene and poly[(ethyl acrylate - CO (4, vinyl pyridine)]. Datta and co-workers [98] characterised blends of zinc oxide-neutralised maleated EPDM (m-EPDM) and zinc salt of an ethylene-methacrylic acid copolymer (Zn-EMA), wherein Zn-EMA content does not exceed 50% by weight. The blend behaves as an ionic thermoplastic elastomer (ITPE). Blends (Z0, Z5 and Z10) were prepared according to the following formulations [98] ... 

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