Binary blend systems

A binary blend system can be used as an example to discuss the Flory—Huggins theory, from which several important parameters will be introduced. Fig. 7.1 is a schematic plot showing two polymer molecules, A and B in a mixed state. Both of the polymer chains are assumed to stay in their natural coiled form/conformation. 

However, it is most likely that the intermolecular CTC mainly contributes to the fluorescence in the solid state of wholly aromatic Pis, from the fact that the fluorescence intensity of the PI film prepared at 400°C for 1 h (rapid cure) was approximately 10 times higher than that cured upon the mildest condition (200°C/5 h), as shown in Fig. 12. In other words, the intramolecular CT fluorescence is much weaker than the intermolecular one. This may be rationalized in terms of a model compound result in which the benzimide-phenyl coplanarization leads to an essentially non-fluorescent character as will be shown later. The intermolecular CTC fluorescence hypothesis is also supported from the miscibility-sensitive CT fluorescence intensity in a PI binary blend system composed of non-fluorescent and fluorescent PI, as discussed later. 

Figure 7.8 [17] shows the relationship between the viscosity ratio of a polyamide-rubber binary blending system and the size of domain particles obtained by mixing and kneading with a twin screw extruder [16-18]. Generally, it is easier to obtain the fine domain size under conditions where the two melt viscosities are close. Furthermore, the domain size reduction easily occurs when the surface tension tt between each polymer particle is low, even if there exists a considerable melt-viscosity difference. This means that both the addition of a compatibilizer or interfacial copolymerization reactions result in lower surface tension and, consequently, the domain size reduction is effectively accelerated. To analyze the domain size in polyblending, the Weber Number Wg or the following modified... 

Figure 7.25 Morphology change in a twin screw extruder (mPP-PA binary blend system)...

Miscibility in polymer blends is controlled by thermodynamic factors such as the polymer-polymer interaction parameter [8,9], the combinatorial entropy [10,11], polymer-solvent interactions [12,13] and the "free volume effect [14,15] in addition to kinetic factors such as the blending protocol, including the evaporation rate of the solvent and the drying conditions of the samples. If the blends appear to be miscible under the given preparation conditions, as is the ca.se for the blends dcscibcd here, it is important to investigate the reversibility of phase separation since the apparent one-phase state may be only metastable. To obtain reliable information about miscibility in these blends, the miscibility behavior was studied in the presence and absence of solvents under conditions which included a reversibility of pha.se separation. An equilibrium phase boundary was then obtained for the binary blend systems by extrapolating to zero solvent concentration. 

Quatemized P4VP core PS shell/poly(methacrylic acid) (PMA) core/PS shell type microsphere binary blend systems have a common PS sequence in the shell. Material with three-phase separated microdomains, such as both dispersed P4VP (positively charged region) and PMA (negatively charged region) spheres in a PS matrix, was obtained in this blend film [51]. 

The thermal, mechanical, and morphological behaviors of two binary blends, HDPE-E-plastomer (Engage 8200) and iPP-E-plastomer (Engage 8200) have been investigated to compare the compatibility and molecular mechanistic properties of the blends. Both systems are thermodynamically immiscible but mechanically compatible. Thermal studies indicate that both blends exhibit two distinct melting peaks and there is depression of the HDPE melting peak in the blend with high... 

With the discussion above in mind, it is now possible to provide a similar semi quantitative framework in which to view the results obtained on ternary systems (homopolymer A, homopolymer B, diblock AB) and on binary blends of one homopolymer and a diblock copolymer. Of particular importance is the need for an explanation of the fact that the diblock copolymer may serve either as an emulsifying agent (9,25) or as a homogenizing agent (1, 4 ) in ternary blends. 

BICARBONATE, 105 135 BICYCLE, 167 BINARY BLEND, 5 BINARY SYSTEM, 134 BIREFRINGENCE, 218 BLENDING, 11 28 368 BLISTER PACKAGING, 454 BLOCK COPOLYMER, 31 101 107 178 252 368 BLOW EXTRUSION, 19 74 79 BLOW MOULDING, 34 35 95 140 193 263 312 420... 

For both linear and star polymers, the above-described theories assume the motion of a single molecule in a frozen system. In polymers melts, it has been shown, essentially from the study of binary blends, that a self-consistent treatment of the relaxation is required. This leads to the concepts of "constraint release" whereby a loss of segmental orientation is permitted by the motion of surrounding species. Retraction (for linear and star polymers) as well as reptation may induce constraint release [16,17,18]. In the homopol5mier case, the main effect is to decrease the relaxation times by roughly a factor of 1.5 (xb) or 2 (xq). In the case of star polymers, the factor v is also decreased [15]. These effects are extensively discussed in other chapters of this book especially for binary mixtures. In our work, we have assumed that their influence would be of second order compared to the relaxation processes themselves. However, they may contribute to an unexpected relaxation of parts of macromolecules which are assumed not to be reached by relaxation motions (central parts of linear chains or branch point in star polymers). 

Rg is the polymer radius of gyration, Xs is the value of the x parameter (see Section 2.3.1) at the spinodal point, and D is the mutual diffusion coefficient of the two polymer components. Bates and Wiltzius (1989) have confirmed the predictions of Eqs. (9-4) and (9-5) for early-time SD of binary blends of perdeuterated and protonated 1,4-polybutadiene. Neutron-scattering studies of SD on a similar system by Jiimai et al. (1993a, 1993b) also confirm the Cahn theory at early times, but the spinodal growth rates deviate somewhat from Eq. (9-5). 

The simulation result for the time evolution of structure factors as a function of the scattering vector q for an A/B 75/25 (v/v) binary blend is shown in Fig. 9 where time elapses in order of Fig. 9c to 9a. The structure factor S(q,t) develops a peak shortly after the onset of phase separation, and thereafter the intensity of the peak Smax increases with time while the peak position qmax shifts toward smaller values with the phase-separation time. This behavior suggests that the phase separation proceeds with evolution of periodic concentration fluctuation due to the spinodal decomposition and its coarsening processes occurring in the later stage of phase separation. These results, consistent with those observed in real polymer mixtures, indicate that the simulation model can reasonably describe the phase separation process of real systems. 

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