Continuity development in polymer blends of very low interfacial tension

Abstract

Continuity development in polymer blends of very low interfacial tension AbstractPhase continuity development and co-continuous morphologies are highly influenced by the nature of the interface in immiscible polymer blends. Blends of ethylene-propylene-diene terpolymer (EPDM) and polypropylene (PP) possess an interfacial tension of about 0.3 mN/m and provide an interesting model system to study the detailed morphology development in a very low interfacial tension binary system. A variety of blends with viscosity ratios of 0.2-5.0 and shear stresses of 11.7-231.4 kPa were considered. Using a variety of sophisticated morphology protocols it is shown that at low blend compositions, the dispersed phase actually exists as stable fibers of extremely small diameter of 50-200 nm and the continuity develops by fiber-fiber coalescence. An analysis using break-up times from Tomotika theory also supports the notion of highly stable dispersed fiber formation. These results challenge the current view of the dispersed phase as small spherical droplets. It is shown, under these conditions, that a seven-fold variation in the viscosity ratio has virtually no influence on % continuity or morphology, while a large change in the matrix shear stress from 11.7 to 90.9 kPa has an important effect on pore diameter. Both sides of the continuity diagram are studied and highly symmetrical continuity behavior is observed with composition. In fact a single master continuity curve is observed for these blends varying in viscosity ratio from 0.7-5.0 and with shear stresses from 11.7-90.9 kPa. Although the glass transition temperatures indicate that these materials are completely immiscible after melt mixing and cooling, it is shown that the blends demonstrate the morphological features of a partially miscible system. These results support a concept that the blend was partially miscible during melt blending, at which time the gross morphological features of the blend were developed, but becomes fully phase separated upon cooling. It appears that the quenching of the EPDM/PP blend from the melt is rapid enough to preserve the imprint of that partial miscibility on the gross blend morphology. q

Effect of dynamic vulcanization on co‐continuous morphology

“…The EPDM is evident as a red phase corresponding to a topographical valley of 30 nm. Note that although the EPDM appears to be dispersed in this 2-D micrograph, it is in fact fully co-continuous as confirmed by solvent gravimetry data in our previous article, 3 and also as shown later in Figure 7. For the purpose of further discussion, this co-continuous, noncrosslinked, 50 EPDM/50 PP morphology will be referred to as the "␣-network".…”

“…The capability of combined FIB/AFM is clearly able to resolve the presence of very small EP domains. In an earlier publication, 3 using SEM analysis, we demonstrated that these dispersed domains are actually very fine diameter stable fibers. There is a good correlation between the phase size observed here and in that previous article.…”

“…There is a good correlation between the phase size observed here and in that previous article. 3 The typical surface profile across a particle is shown below the micrograph. It is evident that EPDM is being etched more than PP and that a height difference of 12 nm exists between the phases.…”

“…Our two previous articles 3,4 examined the detailed morphology, continuity development and co-continuity in noncrosslinked ethylene-propylene-diene terpolymer (EPDM)/ polypropylene (PP) blends. Despite the major commercial significance of EPDM/PP TPVs, many fundamental questions related to the effect of dynamic crosslinking on the microstructure of these blends have remained unanswered.…”

Polyamide blend-based nanocomposites: A review

“…Due to the high specific surface area of nanoparticles, the anchoring of the polymer components on the solid nanoparticles is believed to thermodynamically stabilize nano-filled polymer blend systems [54]. Phase continuity development and co-continuous morphologies are highly affected by the nature of the interface in immiscible polymer blends [55]. In general, the mechanical and optical properties of immiscible polymers depend on the disperse phase morphology.…”