Rheology of Polymer Blends

Abstract

The first polymer blend was patented in 1846 and since then blends have became ubiquitous. Blending may provide a full set of material properties, improving processability and/or specific properties. With the advancement of technology there is the notorious growth of complexity -while in the beginning blending involved two polymers, initially without a compatibilizer, more recent commercial alloys have up to five polymers, three compatibilizers, and frequently are reinforced with macro-or nanoparticles [1].Blends are classified as either thermodynamically miscible or immiscible, with the latter dominating. However, imposition of a flow affects the thermodynamic equi librium and it may enhance the miscibility of immiscible blends or vice-versa -there is an interrelation between rheology and thermodynamics. Similarly, flow affects the degree of deformation of the dispersed phase, thus in immiscible blends there are other interrelations between rheology and morphology, which affect the blend performance. To the complexity of polymer alloys and blends (PAB) behavior one must add the incorporation of solids, either in the form of filler and nanofiller particles or by simple fact of blending two components with widely different transition temperatures.Since the flow of PAB is complex, it is useful to revert to simple models, for example, for miscible blends to solutions or mixtures of polymer fractions, for immiscible blends to emulsions or suspensions, and for compatibilized blends to block copolymers (Table 2.1). It is also advisable to study flow behavior of multiphase systems at constant stress (not at constant deformation rate) [2,3].For miscible blends, the free volume theory predicts a positive deviation from the log-additivity rule (PDB, positively deviating blend). However, depending on the system and method of preparation, these blends may show a positive deviation, negative deviation, or additivity [4]. Upon mixing, the presence of specific interac tions may change the free volume and degree of entanglement, which in turn affect the flow behavior [5,6]. For immiscible blends the flow is similarly affected, but in addition there are at least three contributing phases: of the polymeric matrix, of the First Edition. Edited by Avraam I. Isayev.

Phase structure evolution during mixing and processing of poly(lactic acid)/polycaprolactone (PLA/PCL) blends

“…It seems that PLA and PCL do not show perfect adhesion at the interface, which is the condition for validity of the Kerner equation. This imperfect adhesion is apparently interrelated to the slip at the interface, which is commonly accepted explanation to the negative deviation of the viscosity dependence of many immiscible polymer blends on their composition from additivity [44]. Due to this discrepancy, Palierne's theory cannot be utilized for determination of r in our system.…”

Structural characterization and mechanical properties of dextrin-graft-poly(butyl acrylate-co-styrene) copolymers

“…Observation of two glass transitions is an indication of a phase separation. According to Utracki [30], distinct glass transitions may be observed as soon as the domain size exceeds 30 nm. Observations by transmission electron microscopy were carried out on dextrin-graft-poly(butyl acrylate) and dextrin-graftpolystyrene samples and images are reported on Figure 6c and Figure 6d.…”

Influence of aspect ratio of fillers on the properties of acrylonitrile butadiene styrene composites

“…During injection molding, the morphology at the surface (skin) differed from the morphology of the interior (core) for the ABS composites. This effect is known as the skin‐core effect, where the filler particles are oriented in the direction of flow at the surface and randomly oriented at the core . This is due to the fact that melt is subjected to different flow rates as well as cooling rates at the surface and inside (core).…”

“…The orientation takes place during the fountain flow by stretching the flow elements and then depositing them on the cold mold surface. As cooling is slower in the core, the orientation is weak or random . It is more evident in case of anisometric fillers like talc, mica, due to their shape.…”