Dynamic properties of NR/EVA polymer blends: Model calculations and blend morphology

Polymer researchers have had a long-standing interest in understanding the evolution of blend morphology when two (or more) incompatible homopolymers or copolymers are melt blended in mixing equipment. In industry, melt blending is conducted using either an internal (batch) mixer (e.g., a Banbury mixer or a Brabender mixer) or a continuous mixer (e.g., a twin-screw extruder or a Buss kneader). There are many factors that control the evolution of blend morphology during compounding, the five primary ones being (1) blend composition, (2) rheological properties (e.g., viscosity ratio) of the constituent components, (3) mixing temperature, which in turn affects the rheological properties of the constituent components, (4) the duration of mixing in a batch mixer or residence time in a continuous mixer, and (5) rotor speed in a batch mixer or screw speed in a continuous mixer (i.e., local shear rate or shear stress). When two immiscible polymers are compounded in mixing equipment, two types of blend morphology are often observed: dispersed morphology and co-continuous morphology. Numerous investigators have reported on blend morphology of immiscible polymers, and there are too many papers to cite them all here. Some investigators (Han 1976, 1981; Han and Kim 1975; Han and Yu 1972; Nelson et al. 1977; van Oene 1978) examined blend morphology to explain the seemingly very complicated rheological behavior of two-phase polymer blends, and others (Favis and Therrien 1991; He et al. 1997; Ho et al. 1990; Miles and Zurek 1988; Scott and Macosko 1995; Shih 1995; Sundararaj et al. 1992, 1996) investigated blend morphology as affected by processing conditions. Today, it is fairly well understood from experimental studies under what conditions a dispersed morphology or a co-continuous morphology may be formed, and whether a co-continuous morphology is stable, giving rise to an equilibrium morphology, or whether it is an unstable intermediate morphology that eventually is transformed into a dispersed morphology (Lee and Han 1999a, 1999b, 2000). Let us consider the morphology evolution in an immiscible blend consisting of two semicrystalline polymers, A and B, in a compounding machine, and let us assume that the melting point (Tm,A) of polymer A is lower than the melting point (Tm,B) of polymer B.

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Rheology of Immiscible Polymer Blends

Rheology and Processing of Polymeric Materials: Volume 1: Polymer Rheology ◽

10.1093/oso/9780195187823.003.0017 ◽

2007 ◽

Author(s):

Chang Dae Han

Keyword(s):

Mechanical Properties ◽

Polymer Blends ◽

Experimental Studies ◽

Polymeric Materials ◽

Random Copolymer ◽

Random Copolymers ◽

Immiscible Polymer Blends ◽

Blend Morphology ◽

Immiscible Polymer ◽

New Findings

The polymer industry has been challenged to produce new polymeric materials by blending two or more homopolymers or random copolymers or by synthesizing graft copolymers. To meet the challenge, various methods have been explored, namely, (1) by synthesizing a new monomer, polymerizing it, and then blending it with an existing homopolymer or random copolymer, (2) by copolymerizing existing monomers and then blending it with an existing homopolymer or random copolymer, (3) by chemically modifying an existing homopolymer or random copolymer and then blending it with other homopolymers or copolymers already available, or (4) by synthesizing new compatibilizer(s) to improve the mechanical properties of two immiscible homopolymers or random copolymers that otherwise have unacceptable mechanical properties. There are numerous monographs (Cooper and Estes 1979; Han 1984; Paul and Newman 1978; Platzer 1971, 1975; Sperling 1974; Utracki 1990) describing various aspects of polymer blends. In the 1970s, Han and coworkers (Han 1971, 1974; Han and Kim 1975; Han and Yu 1971a, 1971b, 1972; Han et al. 1973, 1975; Kim and Han 1976) conducted seminal experimental studies on the rheology of immiscible polymer blends and related the observed rheological behavior to blend morphology. Independently, in the same period, Vinogradov and coworkers (Ablazova et al. 1975; Brizitsky et al. 1978; Tsebrenko et al. 1974, 1976; Vinogradov et al. 1975) conducted a series of experimental studies relating the blend rheology to blend morphology. Van Oene (1972, 1978) also pursued, independently, experimental studies for a better understanding of rheology–morphology relationships in immiscible polymer blends. Since then, using different polymer pairs, numerous researchers have conducted experimental studies, which were essentially the same as, or very similar to, the previous experimental studies of Han and coworkers, Vinogradov and coworkers, and van Oene in the 1970s. It is fair to state that those studies in the 1980s and 1990s have not revealed any significant new findings.

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