Filler-surface modifier dispersant

As shown for the synthesis of PS [291], the monomer may be localized in the vicinity of the filler surface by previously grafting a polymer capable of swelling in the base monomer. Copolymeric latex of polychloroprenemethacrylic acid was added to the aqueous dispersion of chalk. The acid groups reacted with chalk and the latex particles became chemically grafted to chalk. When further portions of styrene were added they were completely absorbed by modified chalk. 

Filler surface chemistry is clearly important, although the effects vary widely according to the exact nature of the filler, polymer and surface modifier. Some of the factors that can influence toughness and are, at least in part, controlled by filler surface chemistry include the level of filler polymer interaction [40], the structure of heterophasic polymers [41], the amount of polymer degradation during compounding [42], filler dispersion [43] and polymer crystallinity arising from altered nucleation processes [44]. 

This investigation of silicone-modified hybrid composites demonstrates that compatibilized, segmented liquid rubbers can be tailored to promote the formation of colloidal rubber dispersions, which enhance the toughness of the epoxy matrix. Furthermore, such segmented liquid rubbers can in situ-modify filler surfaces to form core-shell particles with a hard filler core and a thin... 

This is a very common method for the preparation of graphene/conjugated polymer nanocomposites. In a typical synthetic procedure, surface-modified graphene or GO can be dispersed in acidic water and /or surfactant solution followed by the addition of monomer. It was then stirred obeying a certain conditions to disperse filler in the solvent and monomer homogeneously. Finally, the initiator (generally peroxides are used as initiator) is added to initiate the polymerization reaction at a certain temperature. Aniline, pyrrole, thiophene, 3,4-ethylenedioxythiophene, etc. can be polymerized by this method [73-80]. 

Theories that describe the reduction of the size of the dispersed phase in the presence of nanoparticles vary, depending on whether the filler is located in the continuous phase, in the dispersed phase, or at the interphase between the two blend components. Compatibilizing effects due to polymer adsorption on the filler surface, as well as reduction in the interfacial tension between the two phases in the presence of the filler, are the generally accepted mechanisms when the fillers are located at the interface [11,13,26]. Ray et al. [11] showed that upon addition of only 0.5 wt% of organically modified clay, the interfacial tension decreased from 5.1 to 3.4 mN/m for a PS/PP blend and from 4.8 to 1.1 mN/m for PS/PP-g-MA, suggesting a possible interfacial activity of the clay that is localized at the interface in similar fashion to classical compatibilizers. 

Surface treatment is another value-added step that can improve the performance of kaolin. Since the filler is naturally very hydrophilic due to its hydroxyl groups, a treatment can be applied to render its surface hydrophobic or organophilic. These surface-modified kaolins are useful especially in plastics and rubber industries, where they improve adhesion and dispersion and hence act more effectively as functional fillers. Silanes, titanates, and fatty adds as discussed in Chapters 4-6, respectively, may be used to modify the surface charaderistics of either hydrous or calcined kaolins, promoting dea lomeration, often lower viscosities, and improved mechanical and eledrical properties. 

In recent years, lamellar nanofiUers have been established as the most important filler type for barrier and mechanical reinforcement. Dal Point et al. reported a novel nanocomposite series based on styrene-butadiene rubber (SBR latex) and alpha-zirconium phosphate (a-ZrP) lamellar nanofiUers. The use of surface modified nanofiUers improvement the mechanical properties. However, no modification of the gas barrier properties is observed. The addition of bis(triethoxysilylpropyl) tetrasulfide (TESPT) as coupUng agent in the system is discussed on the nanofiUer dispersion state and on the fiUer-matrix inteifacial bonding. Simultaneous use of modified nanofillers and TESPT coupling agent is found out with extraordinary reinforcing effects on both mechanical and gas barrier properties [123]. 

The probe compounds may be chosen as model acids (for example, carboxylic acids or chloroform) and bases (for example, pyridine or ether), with which to measure the acid-base character of the filler surface. However, the probes may be actual interfacial modifiers used in the composite system under investigation, for example an organosilane coupling agent or fatty acid dispersant. Furthermore other interesting interactions have been studied by the authors and include stabiliser - filler interactions during evaluation of controlled release/displacement effects. 

Studies have been carried out using combinations of acrylic acid and isostearic acid in an attempt to produce surface modifier systems that combine effective coupling with good dispersant characterisics [13]. In this study sequential adsorption of isostearic acid and acrylic acid on to magnesium and aluminium hydroxides in the FMC cell indicated that acrylic acid will displace isostearic acid from both fillers, however, isostearic acid will adsorb onto a layer of adsorbed acrylic acid producing a hybrid layer. 

With the notable exception of carbon blacks, the natural surfaces of most particulate fillers are less than optimum for dispersion into, and interaction with, polymers. Surface modifiers can frequently improve this, and other filler properties. Sometimes materials which are effective surface modifiers will be found to have been added for filler manufacturing reasons. The main reasons for finding surface modifiers present are ... 

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