Grafting Compatibilisation

The grafting reactions with MA are important not only for better compatibility, but also because new types of materials with improved properties can be produced. Furthermore, the range of optimal processing parameters may also be widened. On 

Using the grafting reaction not only MA, but other compounds may also couple to the polymer chain. For the sake of better compatibility, the most commonly prepared structures are the following PP-g-MA, FfDPE-g-MA, HDPE-g-MA, ethylene propylene diene monomer (EPDM)-g-MA, PS-g-MA, PP-g-PS or PC-g-PMMA [64, 65]. 

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Researchers at Michigan State University have patented the use of aliphatic polyester-grafted starch as a compatibiliser between starch and aliphatic polyesters such as PCL [86]. These grafted compatibilisers provide enhanced interfacial adhesion between the starch and polyester phases. Compositions with two phases can be generated with a variety of morphologies that affect the properties of the blend. Interfacial adhesion is one factor... 

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. 

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)... 

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]. 

Scheme 5.3 Mechanism of compatibilisation between PE grafted onto DBM (PEgDBM) and PVC through hydrogen bonding and dipole-dipole interaction...

Reactive blending of thermoplastic starch/polymer blends has been examined recently and aims to increase properties and performance via control of blend morphologies. Mani [58, 59] examined different techniques for compatibilising starch-polyester blends. They examined development of maleic anhydride grafted polyester/starch blends and starch-g-polycaprolactone... 

There are a number of polymeric compatibilisers, e.g., block/graft copolymers like tri-block copolymers of SBS used mostly in styrenic blend compatibilisation, and functionalised polymers with certain functional groups (epoxidised or maleated), which can act like a surfactant . 

Figure 12.5 shows some of the possible types of compatibiliser, which are all forms of block or graft copolymers. The basic principle is that the... 

Fig. 12.5 Possible types of compatibiliser (a) diblock, (b) triblock, (c) multigraft and (d) single-graft copolymers at the interface of a heterogeneous polymer blend. A and B represent the two components of the blend O and represent the monomers of the blocks C and D, respectively, of the compatibilising molecules. (Adapted with permission of Elsevier Science.)...

Due to its non-polar chemical structure, PP interacts poorly with the typically pwlar fillers such as CaC03, and optimum dispersion is normally difficult to achieve. Compatibilisers are frequently used to improve the interfacial adhesion between CaC03 and PP, in order to gain the envisaged enhancement in mechanical properties (Fuad et al, 2010). Bi-functional molecules such as maleic-anhydride grafted PP (PP-g-MAH) are commonly used as compatibilisers for PP and CaC03 (Roberts Constable, 2003). 

PET-LDPE compatibilised with diethylmaleate grafted polyethylene (120), and... 

Blends of polyethylene terephthalate and linear low-density polyethylene were compatibilised using diethylmaleate grafted polyethylene, and characterised using Fourier transform infra-red spectroscopy, thermogravimetric analysis and scanning electron microscopy. Interactions between the components in the blends were observed, which affected the glycol sequences of the polyester and also improved the thermal oxidative stability of the blends. The introduction of the compatibiliser resulted in a particle size reduction of the dispersed phase and better adhesion between the phase and the matrix. 15 refs. 

These samples, simultaneous PU/PS IPNs, were synthesised by a one-short route. The IPN topology appears to restrict phase separation, which results in materials with broad transition regions. By variation of the crosslink level in either or both polymer networks, the controlled introduction of internetwork grafting or the incorporation of compatibilisers into the PS network, the compatibility of the two polymer networks can be increased. For simultaneous IPNs, it has been found [129] that the network which is first formed... 

Copolymerisation of these macromonomers with norbomene or norbomene acetate has yielded a series of poly(norbomene)-graft-poly-(e-caprolactone) copolymers of well-defined structures. Furthermore, PCL macromonomers were also homopolymerised in high yield into high molecular weight comb chains of narrow molecular weight distribution MJM =1.10). Such copolymers have potential applications as surface modifiers, polymeric surfactants, compatibilisers in polymer blends, and dispersion stabilisers. 

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. 

Silane coupling agents such as gamma-methacryloxypropyl trimethoxysilane have also been tried, by grafting them onto nanosilica particles. Compatibilisation can sometimes be further enhanced by functionalising the polymer as well, e.g., polypropylene may have to be treated with maleic anhydride in order to insert it between the layer planes of the clay. 

Polystyrene and polypropylene are normally immiscible, but they have been successfully compatibilised by PP grafted with an aromatic vinyl polymer. 

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