The Role of the Blend Interface Type on Morphology in Cocontinuous Polymer Blends

Abstract

Three different categories of blend interfaces are examined systematically in order to isolate the role of the interface in the development of cocontinuous morphologies during melt mixing. They are Type I, compatible binary blends based on high-density polyethylene (HDPE)/styrene-ethylene-butylenestyrene (SEBS) and HDPE/styrene-ethylene-butylene (SEB); Type II, an incompatible binary system comprised of HDPE/polystyrene (PS); and Type III, compatible ternary systems comprised of HDPE/PS compatibilized by SEBS in one case and by SEB in another. The Type I and Type III systems represent conventional approaches to preparing blend systems of low interfacial tension. The cocontinuous morphology is analyzed using three techniques: microscopy/image analysis, solvent extraction/gravimetric analysis, and BET characterization of surface area and pore size. A mechanism for the formation of dualphase continuity based on droplet and fiber lifetimes during melt mixing has been proposed. For the Type I compatible binary systems continuity development and microstructural features are dominated by thread-thread coalescence. In the Type II incompatible HDPE/PS binary system and Type III compatibilized ternary systems, continuity development and microstructural features are controlled by droplet-droplet coalescence and reduced droplet-droplet coalescence, respectively. In the latter case, the generation of fresh interface during droplet deformation results in a system that is only partially emulsified. The relative presence of fibers or droplets during dynamic mixing is analyzed quantitatively using a matrix dissolution/image analysis technique. A thread frequency ratio (TFR) is proposed as a basic general parameter to classify the relative presence of fibers to droplets during mixing and hence the type of continuity development for a given system.

Continuity development in polymer blends of very low interfacial tension

“…This highly stable thread behavior occurs as a result of the very low interfacial tension between EPDM and PP and can be explained directly from Tomotika theory [44] as outlined in other work [33,[45][46][47][48]. This result is also a support for the observation of highly stable fibers that will be discussed later in this paper.…”

“…Both polymers are amorphous in nature and possess an interfacial tension of 0.6 mN/m. In that work it was shown that, because of the partial miscibility, the blend demonstrated significantly different morphological features as compared to that reported for fully immiscible blends of low interfacial tension by Li et al [33]. Marin et al found that these partially miscible blends exhibited very fine dispersed phase morphologies, artificially high percolation thresholds, and attained cocontinuity at higher than expected compositions of the minor phase.…”

Melt Blending with Thermoplastic Starch

“…Granular starches are compact particles, such as those observed in the PE2/TPS40 blends. Fiber-like particles observed in PE1/TPS40 blends could be responsible for a lower apparent percolation threshold in this system and, consequently, higher enzymatic degradation values (Li et al, 2005). Extent of enzymatic degradation of LDPE/TPS40 blends is very similar to that obtained by acid hydrolysis.…”

Nanomembrane Materials Based on Polymer Blends

“…Farhangi et al [120] pointed out that for gas separation, the membrane must have small enough porosity and pore size so as to increase the selectivity, and a thinner skin layer so as to improve gas permeation flux. The role of the interface on continuity development for PE/PS systems was investigated [121]. It was shown that the pore sizes in those systems could be controlled from 0.3 to 6.3 mm.…”