Polymer filler interactions

The interactions between the polymer and ceramic phases of a composite are paramount if the material is to be used in any practical device. This is particularly important in 0-3 composites, where the polymer-filler interface within the system is considerable. Inadequate bonding between the components due to physical and chemical incompatibility, contaminants and defects on either surface can have profound effects on the ultimate integrity and performance of the composite. Careful selection of compatible components and the optimization of processing conditions are therefore of prime importance. 

The degree of polymer wetting on the particle surface is determined primarily by the relative surface tensions and free energies of the components. The adhesion work W associated with a drop of liquid at equilibrium on a solid surface may be generally described by the Young-Dupre equation 

The coefficients of thermal expansion for the components should be similar if adequate coupling of the surfaces is to be maintained. When the thermal expansion characteristics of the two phases are not matched, interphase stresses and decoupling can arise with thermal cycling of the material during both the fabrication processes and any subsequent use of the composite that involves considerable changes in temperature. 

If a polar solvent enters the composite, it will tend to cancel out stress-induced charges and lower the sample sensitivity. The filler-polymer interface adhesion may also be reduced, producing the following effects  

The crack-pinning mechanism provided by the ceramic particles is impaired. 

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The processing methods for siHcone mbber are similar to those used in the natural mbber industry (59,369—371). Polymer gum stock and fillers are compounded in a dough or Banbury-type mixer. Catalysts are added and additional compounding is completed on water-cooled roU mills. For small batches, the entire process can be carried out on a two-roU mill. Heat-cured siHcone mbber is commercially available as gum stock, reinforced gum, partially filled gum, uncatalyzed compounds, dispersions, and catalyzed compounds. The latter is ready for use without additional processing. Before being used, sihcone mbber is often freshened, ie, the compound is freshly worked on a mbber mill until it is a smooth continuous sheet. The freshening process eliminates the stmcturing problems associated with polymer—filler interactions. 

Based on this variety of properties, amorphous polybutadiene has found a niche in the mbber industry. Moreover, it appears that the anionicaHy prepared polymer is the only polymer that can be functionalized by polar groups. The functionalization is done by using aromatic substituted aldehydes and ketones or esters. Functionalization has been reported to dramatically improve polymer-filler interaction and reduce tread hysteresis (70—73). 

The authors of [99] proposed a calorimetric method for determining the degree of the polymer-filler interaction the exothermal effect manifests itself in the high energy of the polymer-filler adhesion, the endothermal effect is indicative of a poor, if any, adhesion. The method was used to assess the strength of the PVC-Aerosil interaction with Aerosil surface subjected to different pre-treatments... 

Depending on the nature of the polymer-filler interaction and the fracture surface status (smooth or rough), Eq. (34) predicts either a rather smooth variation of the elongation with increasing filler concentration or a sharp drop at some small filler content. 

The formation of PPD groups on the polymer backbone provides a mechanism to improve the polymer-filler interactions. The nitrogen-hydrogen bonds are capable of hydrogen bonding with polar groups on the surface of the filler. This enhanced interaction provides for somewhat unique dynamic mechanical properties. Under ideal conditions rolling resistance improves when QDI is used in the mix. Also, abrasion characteristics are maintained and in some cases even modest improvements occur. 

In addition to increases in high-strain loss modulus, reductions in low-strain loss modulus are also observed. This may be attributed to the improvements in polymer-filler interactions which may reduce the amount of filler networking occurring in the compound. The low-strain losses are dominated by disruptions in the filler-filler network, the Payne effect. 

Quinone diimines are capable of reacting rapidly with radicals formed during intensive mixing. The product, a polymer-bound PPD moiety, provides a polar functionality which is capable of improving polymer-filler interactions. In general the improvements can result in modest reductions in tangent delta (rolling resistance) and modest improvements in abrasion resistance. 

Polymer-filler interaction of carbon black surface... 

It has been well established that wear resistance of filled rubber is essentially determined by filler loading, filler morphology, and polymer-filler interaction. For fillers having similar morphologies, an increase in polymer-filler interaction, either through enhancement of physical adsorption of polymer chains on the filler surface, or via creation of chemical linkages between filler and polymer, is crucial to the enhancement of wear resistance. In addition, filler dispersion is also essential as it is directly related to the contact area of polymer with filler, hence polymer-filler interaction. 

A considerable amount of work has already been successfully carried out in HASETRI with naturally occurring oils as eco-friendly process oils in conventional tire recipes [31,32]. These naturally occurring oils were found to be suitable on the basis of low PCA content. Some of the naturally occurring oils showed better processing properties, polymer-filler interaction, and dispersion properties in NR-based truck tire tread cap compound and hence better mechanical and dynamic mechanical properties. As the presently available low PCA oil in the market in the form of MES TDAE and naphthenic oil are comparatively costly, these natural oils can act as the best alternative processing aids for the elastomer industry, especially in developing and underdeveloped countries. 

Aid in the uniform dispersion of additives. Make powdered solids (e.g. particulate fillers with high energy and hydrophilic surface) more compatible with polymers by coating their surfaces with an adsorbed layer of surfactant in the form of a dispersant. Surface coating reduces the surface energy of fillers, reduces polymer/filler interaction and assists dispersion. Filler coatings increase compound cost. Fatty acids, metal soaps, waxes and fatty alcohols are used as dispersants commonly in concentrations from 2 to 5 wt %. 

A silicone oil plasticiser is desirable to facilitate dispersion and to prevent undesirable polymer-filler interaction prior to vulcanisation. 

Adsorption-desorption techniques are often used for the study of surface treatment or modeUng of polymer/filler interaction. Gravimetric techniques or. 

In order to calculate polymer/filler interaction, or more exactly the reversible work of adhesion characterizing it, the surface tension of the polymer must also be known. This quantity is usually determined by contact angle measurements or occasionally the pendant drop method is used. The former method is based on the Young, Dupre and Eowkes equations (Eqs. 21,8, and 10), but the result is influenced by the surface quality of the substrate. Moreover, the surface (structure, orientation, density) of polymers usually differs from the bulk, which might bias the results. Accuracy of the technique maybe increased by using two or more liquids for the measurements. The use of the pendant drop method is limited due to technical problems (long time to reach equilibrium, stability of the polymer, evaluation problems etc.). Occasionally IGC is also used for the characterization of polymers [30]. 

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

In addition, Maiti and Bhowmick [93] also used fluoroelastomers having different microstructure and viscosity (Viton B-50, Viton B-600, Viton A-200, and VTR-8550). Viton is a terpolymer of vinylidene fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). Even with the addition of only 4 phr of clay in Viton B-50, the tensile strength and modulus improved by 30-96% and 80-134%, respectively, depending on the nature of the nanoclays. The better polymer-filler interaction in the case of NA clay and the fluoroelastomers has... 

Choudhury et al. [86] have studied the effect of polymer-solvent and clay-solvent interaction on the mechanical properties of the HNBR/sepiolite nanocomposites. They chose nine different sets of solvent composition and found that chloroform/methyl ethyl ketone (Qi/MEK) (i.e., HNBR dissolved in Ch and sepio-lite dissolved in MEK) is the best solvent combination for improvement in mechanical properties. XRD, AFM, , and UV-vis spectroscopy studies show that the dispersion of clay is best in the Ch/MEK solvent combination and hence polymer-filler interaction is also the highest. images shown in Fig. 14a, b clearly elucidate the aforementioned phenomena. Consequently, the tensile strength and modulus are found to be higher (5.89 MPa and 1.50 MPa, respectively) for the Ch/MEK system due to the minimum difference in interaction parameter of HNBR-solvent (xab) and sepiolite-solvent (Xcd)- Choudhury et al. have also studied the effect of different nanoclays [NA, , 15A, and sepiolite (SP)] and nanosilica (Aerosil 300) on the mechanical properties of HNBR [36]. The tensile... 

Compatibility of NA with organic polymer is much inferior to the compatibility of , 15A, and SP. Thus, Sl-NA-4 has inferior thermal stability as compared to the other three clays. Moreover, the intergallery spacing of NA is very small (only 1.22 nm, obtained from XRD results, Fig. 26a). Only a few chains of HNBR (with 34% acrylonitrile content), being bulky in nature, can find their way into such a small gallery space, which results in poor polymer-filler interaction. This is confirmed by both XRD and (Fig. 26a, b). 

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