Dispersive Mixing Applied to Polymer Blending

The question immediately raised is would this technique portray an opposite or negative adhesion response if applied to a polymer blended system where no interfacial bonding could be present Such a system would be cis-polybutadiene and high molecular weight polyisobutylene restricted to that portion of the blend system where polyisobutylene is the minor dispersed phase in cis-polybutadiene. A high molecular weight polyisobutylene [L-300 Vistanex (Enjay Chemical Co.)] was compounded with zinc oxide, sulfur, and TMTDS and then dissolved in hexane. cis-Polybutadiene (Phillips Chemical Co.) was also mixed with... 

Several implications can be drawn directly from Eq. (2-39). First, A // is always positive. Thus, the rule like attracts like, inferred from Eq. (2-30) for molecular mixtures, should also hold at the continuum level. Second, when dispersion forces are dominant, the Hamaker constant is small when ha= b—that is when the dispersed phase (A) has an index of refraction close to that of the medium (B), These rules also apply to molecular mixtures. Nevertheless, small molecules with a significant difference in index of refraction often mix because of the large entropy thereby gained. But particles lose too little entropy on coagulation to resist doing so when there is an attractive van der Waals interaction, and so particle-particle clumping is the norm in suspensions, unless countermeasures are taken to stop it (see Section 7.1). Analogous considerations explain the prevalence of phase separation in polymer blends (see Section 2.3.1.2). 

These considerations apply both to mixing of the components of a polymer blend and to dispersion of particulate fillers. For blends the obtained size of the... 

In non-reactive blending, a two- (or multi-)phase mixture is formed when the immiscible polymers are physically mixed with each other. The minor phase, rich in B, is dispersed as droplets into a major phase rich in A. Apart from low interfadal tension, high shear rates and similar viscosities of both polymers are important for the size of the dipersed phase and therefore for the product quality. The reactive route follows the synthesis of a minor component via polymerization into a major component that acts as a host polymer. An alternative route for reactive blending is in situ formation of block co-polymers during the mixing process to decrease the interfacial tension. An extruder is the most commonly applied apparatus for the continuous production of polymer blends. 

Phase contrast light microscopy has been applied extensively to the analyses of unfilled binary elastomer combinations. Ihis method is based on differences in the refractive indices of the polymers and has been reviewed by Kruse [27a]. Callan et al. [27b-d] have shown the versatility of the method for a wide range of binary blends containing NR, SBR, BR, CR, NBR, EPDM, HR, and CIIR. The results of these experiments are shown in Table III, which lists the measured areas of the disperse phase in more than 50 combinations of Banbury-mixed 75/25 binary blends containing eight different elastomers. Blends of IIR-CIIR and SBR-BR are excluded since the contrast was low. It can be seen that NBR produced the greatest heterogeneity in all blends except those with CR. 

The word mixing is applied to both the processes of compounding and blending, and describes the process of intimate intermingling of polymers with fiUers/additives or two polymers without any specific restrictions. It covers a broad spectrum of dispersion of various ingredients to form a homogeneous mixture on some definable small scale. 

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