Microgels blending

The treatment of blends as a two phase system opened up an interesting field of modifying the composite properties by the use of a (third component within the interface boundaries, which is termed as compatibilizers [1]. Such modifications are still being extended to the formation of microgel out of the interaction between the two blend partners having a reactive for functionalities. This type of interchain crosslinking does not require any compatibilizer to enhance the blend properties and also allows the blends to be reprocessed by further addition of a curative to achieve still further improved properties [3,4]. Such interchain crosslinking is believed to reduce the viscoelastic mismatch between the blend partners and, thus, facilitates smooth extrusion [5,6]. 

Improvement in the processing and vulcanized qualities of a range of systems have been reported over the past decades. Modification of natural rubber, due to work in the British Rubber Producers Research Association, yields some of the most striking applications of microgel. A detailed study at the MV Lomonosov Institute of Fine Chemical Technology, in Moscow, on the effect of microgels on mechanical properties of cis-polyisoprene and butadiene-styrene rubbers extensively illustrates the properties of blends from latex combination of microgel and conventional or linear systems.(31)... 

When liquid-liquid phase separation occurs, resulting in water-in-water emulsions where the different biopolymers are concentrated in the different phases, and when one or both phases can gel, these systems can be used to produce anisotropic microgel particles and/or gel composites with anisotropic inclusions, resulting in a variety of interesting microstructures and morphologies. An interesting concept to generate alternative gel structures with basis on phase separated biopolymer blends... 

Figure 14.14 shows the SEM micrograph of dynamically vulcanized EPDM/PP (75/25) blend fracture surfaces etched by hot xylene vapor. The microdomains of EPDM have the shape of dumbbell-like microgel of about 0.8-1.0 pm in size, where the dark portions represent the PP phase extracted out by hot xylene vapor. The morphology of the microgel domain of EPDM reveals the reason why the dynamically vulcanized blend can be processed and the dynamic vulcanization prevents the cross-linking of EPDM phase from tmly continuous network (24). 

The resinous thickeners above are thermoplastic and all ultimately soluble in one solvent blend or another. As we have seen, their low shear effects can be destroyed by solvent additions. If, however, the polymers are made as latexes or non-aqueous dispersions by emulsion or dispersion polymerization (Chapter 11) and a small amount of cross-linking is introduced via polyfunc-tional monomer, then insoluble colloidal resin particles are produced. These are called microgels. 

ThFFF, SEC, and light scattering have been used to determine the MWD of anionically polymerised p-methoxystyrene, p-methylstyrene, p-chlorostyrene, and p-cyano-styrene. ThFFF and SEC/multiangle laser light scattering have been used to study the thermal diffusion coefficients of PS, poly( er -butylstyrene) (PtBS) and PS/PtBS copolymer microgels [138]. The retention behaviour of poly(styrene-co-methyl-methacrylate) and poly(styrene-f -iosprene) in ThFFF and SEC have been studied [139]. SEC fractions of blends and copolymers of PS and polyethylene oxide were cross fractionated by ThFFF [140]. 

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