Blends semicompatible

This study (3) was done to produce an ABS type resin by dry and melt blending SAN and a nitrile rubber in a motionless mixer. In polyblends of two semicompatible polymers, the particle size of the dispersed phase is an important factor concerning final properties, particularly if a rubber is dispersed to improve impact strength. Motionless mixers should give precise control over the final particle size since for laminar flow the number of fluid layers and the striation thickness can be predicted mathematically. The hypothesis that the impact strength should peak out at a precise number of mixing elements was thus investigated. 

The trend of Tm and G versus composition for the iPP/PiB and iPP/EPDM blends suggests that the polymers are semicompatible at the investigated T. This hypothesis is in agreement with the finding that the solubility parameters 6, calculated using Hoy s tables for the molar atraction constans and literatura data ... 

While detailed descriptions of relevant terms are placed as appropriate throughout the text, brief definitions are in order at the outset. After blending together, polymer pairs may be qualitatively considered incompatible, semicompatible, or compatible, depending on whether two distinct or immiscible phases remain, partial mixing of the two polymers takes place... 

Figure 3.9. Electron micrograph of a thin section of a PVC/NBR-20 blend the NBR contains 20 % acrylonitrile. The rubber phase in this semicompatible mixture appears to form a network structure extending throughout the PVC matrix. (Matsuo, 1968.)...

Similarly, in the blends of PVC and NBR-20 (Figures 3.13), the presence of an E" peak corresponding to the Tg of NBR-20 at — 40°C is evident however, its upper tail overlaps with that of the PVC transition. This could indicate that although the rubber phase exists independently in this semicompatible system, the interaction between the two phases is marked. The values of E do not exhibit two transitions instead the glass transition is broadened and shifted lower in temperature. 

Figure 3.13. Temperature dependence of dynamic modulus E and dynamic loss modulus E for PVC/ NBR-20 blends (a semicompatible system) (—) 100/0 (---) 100/15 ...

Figure 3.28. EfTect of AN content in NBR on Charpy impact strength of PVC/NBR blends. Impact resistance reaches a maximum in the semicompatible region. Room temperature, 25°C PVC/NBR = 100/15. (Matsuo, 1968.)...

A second important type of biconstituent fiber is a semicompatible blend on nylon 66 with nylon 61 (I referring to isophthalic acid), with nylon 61... 

The characteristic damping behavior of a semicompatible mechanical blend (Mizumachi, 1969, 1970) is illustrated in Figure 13.12. This behavior may be compared with the behavior of the semicompatible latex IPN already discussed in Section 8.8.2. 

For technological purposes, one can define blends as compatible when they show a synergistic behavior in some valuable properties, incompatible when they show a minimum in some property-composition curves, and semicompatible when the properties are intermediate between those of the two polymer parents and are. 

By blending with semicompatible materials that have Tg well below the expected service temperature range (e.g., HIPS). 

Figure 2.12. Morphology of a PVC/P(B-co-AN) blend, containing 20% AN. This semicompatible morphology corresponds to the data in Figure...

Due to their technological importance, polymer blends have attracted considerable attention during the past decade. For thermodynamic reasons, most polymer pairs are immiscible and their degree of compatibility is of underlying importance to the microphase structure and consequently, to the mechanical properties of the blend. The Floiy Huggins % interaction parameter for the polymer pair plays a dominant role in explaining critical phase behavior of a compatible pair and in estimating interfacial tension and interfacial thickness for semicompatible or incompatible pairs. Direct measurement of this parameter is not always possible, thus the obtained information, in conjunction with suitable theoretical models of polymer solutions may lead to an assessment of the interaction parameters for the actual polymeric case. 

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