Non-reactive blending

Amorphous PA (20) / S-IPO (1% IPO) (80) internal mixer at 200°C / torque rheometry / selective solvent extraction / SEM study of morphology development in reactive and in non-reactive blends Scott and Macosko, 1995... 

For either reactive or non-reactive blends in an extruder, internal mixer, or a miniature cup-and-rotor mixer, similar morphological features were observed. Initially, during melting, the polymers were stretched into sheets and ribbons, which broke into fibers, then in turn into drops. One reason that may explain the reported differences in morphology is the concentration of the dispersed phase — 5 vol% was used by the first authors, whereas > 20 wt% by the latter. More detailed information of this, as well as on the topic discussed in the following part, will be found in Chapter 9 Compounding Polymer Blends. 

Other types of morphological changes during blending in TSE were also observed [Sundararaj et al., 1992, 1995]. The authors reported that both reactive and non-reactive blends in an extruder, internal mixer, or a miniamre cup-and-rotor mixer, show similar morphological features. Initially, during the melting, the polymers stretch into sheets and ribbons that first broke into fibers then into drops. 

PE/PB non-reactive blends Leistritz TSE Impact modification of PE Sato, 1995... 

HDPE/LDPE non-reactive blends TSE Improved low-T properties Bohm et al., 1994... 

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. 

The shear viscosity in polymer melts and solutions has been investigated for more than a half century. The blending process of polymers is generally performed in the molten state, particularly in shear flow. It is thus necessary to understand the flow (or better rheological) characteristics of polymer melts [66-70]. In both reactive and non-reactive blends, the shear viscosity of each polymer, and thus viscosity ratio, and bulk viscosity of polymer blend system needs to be understood. 

EL67 Bisphenol-A/Bisphenol-F Reactive/Non reactive blend 1.13 0.1 -0.5... 

An important part of the present chapter discusses the interrelation between reactive compatibilization and the blend phase morphology generation, as well as the crystallization behavior of reactively compatibilized blends containing crystallizable components. The phase morphology development in reactive blending is discussed in conjunction with the non-reactive blending approach. 

In order to understand the influence of reactive blending on phase morphology development, it is important to review briefly the morphology development in non-reactive blending. The latter was a subject matter of many investigations [49-56]. 

Similarly to non-reactive blends, Scott and Sundararaj showed that the major reduction of the particle size of reactive blends, e.g., polyamide/polystyrene and polypropylene/ polystyrene prepared in batch mixer or in twin-screw extruder, occurred during the softening/melting step of the blend components with, however, a clear influence of the chemical reaction at the interface [63, 46]. 

Nevertheless, there are many similarities in morphology development of reactive and non-reactive blends. Indeed, much of our knowledge concerning reactive blends has been obtained through comparison with or extension fi om knowledge of non-reactive blends. The discussion, which follows thus, generally applies to both types of blends, with special emphasis on the effects of the interfacial chemical reaction. 

Suppression of domain coalescence in the melt flow regime is one of the most important effects of the interfacial reaction on morphology and morphology development. Simdararaj and Macosko [33] have conducted a careful study of morphology as a function of dispersed phase voliune fraction in reactive and non-reactive blends to discern the influence of the reaction. Figure 5.9 illustrates the dependence of the dispersed phase domain size on the dispersed phase concentration for typical uncompatibilized blends. At dispersed phase concentrations less than about 0.5 wt.% the system is dilute enough that coalescence is insignificant due to the very low frequency of dispersed phase domain... 

Figure 5.17 [5] compares the torque as a function of time in a batch intensive mixer for non-reactive and reactive blends of polystyrene/ethylene-propylene rubber. These results are typical for a relatively slow interfacial reaction. As the room temperature pellets of the blend are added to the hot mixer, the mixing torque rises rapidly in the melting regime. The torque for both blends then begins to fall as the temperature increases and the polymers soften. In the case of the non-reactive blend, the torque continues to fall and levels out to a reasonably constant value. However, in the case of the reactive blend there is a second peak in the torque due to the chemical reaction. The interfacial chemical reaction builds molecular weight, and in some cases may result in local crosslinking. This increases the viscosity of the blend relative to a non-reactive blend. 

Rheological behavior of reactive blends is complex due to the presence of copolymer with poorly understood chain structure and spatial distribution. Rheological differences between reactive and non-reactive blends are substantial. Key microstructural issues needed for a detailed understanding of the rheology such as the copolymer composition, chain structure, and spatial distribution within the blend are yet to be explored carefully. 

Figure 6.8 (a) Morphology development of a PS/PMMA (60/40) non-reactive blend and a (PS+PS-OH)/ (PMMA + PMMA-r-NCO) reactive blend as a function of mixing time in an internal batch mixer (b) Copolymer formation kinetics in the reactive blend. After Hu and Kadri [31]... 

Figure 6.18 (a) Dispersed phase particle size as a function of the distance from the feed point for the PA6/SAN (75/25) non-reactive blend at 25, 50, 100 and 200 rpm screw speed (b) Dispersed phase particle size as a function of the distance from the feed point for the PA6/SAN/IA (75/25/5) reactive blend at 50, 100 and 200 rpm screw speed (c) Fraction of reacted amine end groups as a function of the distance from the feed point for the PA6/SAN/1A (75/25/5) reactive blend at 50, 100 and 200 rpm screw speed. After Majumdar et al. [45]... 

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