Blend compatibility

DMPPO and polystyrene form compatible blends. The two components are miscible in all proportions (59). Reported dynamic—mechanical results that indicate the presence of two phases in some blends apparendy are caused by incomplete mixing (60). Transition behavior of thoroughly mixed blends indicates that the polymers are truly compatible on a segmental level (61). CompatibiUty may be attributed to a %— % interaction between the aromatic rings of the two polymers sufficient to produce a negative heat of mixing. However, the forces are very small, ie, = ca40 J/mol (9.6 cal/g), and any... 

One of the important attributes of alkyds is their good compatibiUty with a wide variety of other coating polymers. This good compatibiUty comes from the relatively low molecular weight of the alkyds, and the fact that the resin stmcture contains, on the one hand, a relatively polar and aromatic backbone, and, on the other hand, many aUphatic side chains with low polarity. An alkyd resin in a blend with another coating polymer may serve as a modifier for the other film-former, or it may be the principal film-former and the other polymer may serve as the modifier for the alkyd to enhance certain properties. Examples of compatible blends foUow. 

Poly(ethyl methacrylate) (PEMA) yields truly compatible blends with poly(vinyl acetate) up to 20% PEMA concentration (133). Synergistic improvement in material properties was observed. Poly(ethylene oxide) forms compatible homogeneous blends with poly(vinyl acetate) (134). The T of the blends and the crystaUizabiUty of the PEO depend on the composition. The miscibility window of poly(vinyl acetate) and its copolymers with alkyl acrylates can be broadened through the incorporation of acryUc acid as a third component (135). A description of compatible and incompatible blends of poly(vinyl acetate) and other copolymers has been compiled (136). Blends of poly(vinyl acetate) copolymers with urethanes can provide improved heat resistance to the product providing reduced creep rates in adhesives used for vinyl laminating (137). 

A compatible blend should have good processing properties along with a smooth surface and cross-section. If needed, further tests on mechanical properties should be carried out on testing samples made from 2-mm films produced by compression molding. 

It is possible to distinguish between SBR and butyl rubber (BR), NR and isoprene rubber (IR) in a vulcan-izate by enthalpy determination. In plastic-elastomer blends, the existence of high Tg and low Tg components eases the problems of experimental differentiation by different types of thermal methods. For a compatible blend, even though the component polymers have different Tg values, sometimes a single Tg is observed, which may be verified with the help of the following equation ... 

Heterogeneous compatible blends of preformed elastomers and brittle plastics are also an important route for the development of blends of enhanced performance with respect to crack or impact resistance. Polycarbonate blends with preformed rubber particles of different sizes have been used to provide an insight into the impact properties and the fracture modes of these toughened materials. Izod impact strength of the blends having 5-7.5 wt% of rubber particles exhibits best overall product performance over a wide range temperature (RT to -40°C) [151-154]. 

FIG. 16 Mucus membrane compatibility blends of DLSS and SLES. 

P-plastomers, even more than the E-plastomers, have been blended with a number of substrates [23]. The most-important one is blend with iPP which forms compatible blends with P-plastomer for a wide range of relative weights fractions of P-plastomer and iPP as well as a wide range of molecular weights for both of the components. The formation of the blends with iPP leads to changes in the elastic and tensile response with elongation modulus, monotonicaUy increasing with the amount of iPP. 

Based on the extensive work, Ghosh and De have concluded that fluoroelastomer and silicone mbber form technologically compatible blends of micro-heterogeneous stmcture with thermal stability between those for the blend components. The blend could be used as a replacement for fluorosilicone mbber. 

For making compatible blends, the polymers should have comparable polarities and viscosities. The oil needs to be selected properly so that its solubility parameter is close to those for blend components. The cure system should be efficient for all constituent rubbers and the filler system needs to be appropriate. Finally, cost consideration should be taken into account to provide a commercially viable product. 

We have recently initiated our investigation of blends by examining the compatibility between our modified polymer sample 4 and poly(methyl methacrylate). Mixtures with a composition of between 10% and 30% of sample 4 yield compatible blends which are transparent under a polarized light microscope, and are characterized by a single Tg. Mixtures richer than 60% of 4 undergo complete phase separation. 

The Tg of a rubber or polymer depends on the structure and cooperative mobility of the chain segments. In the case of partially compatible blends, the Tg values of the blend components are expected to be shifted toward each other as compared with the pure components. The Tg values remain largely unaltered for a completely incompatible blend. Fig. 44b shows the tan 5 dependencies on the temperature for... 

In addition to the necessary protection of the contents of the emulsion droplets, effective encapsulation technology requires that the release of the active matter be controlled at a specified rate. Benichou et aL (2004) have demonstrated that a mixture of whey protein isolate (WPI) and xanthan gum can be successfully used for the controlled release of vitamin Bi entrapped within the inner aqueous phase of a multiple emulsion. The release profile, as a function of the pH of the external aqueous phase, is plotted in Figure 7.25. We can observe that the external interface appears more effectively sealed against release of the entrapped vitamin at pH = 2 than at pH = 4 or 7. It was reported that an increase in the protein-to-potysaccharide ratio reduced the release rate at pH = 3.5 (Benichou et aL, 2004). More broadly, the authors suggest that compatible blends of biopolymers (hydrocolloids and proteins) should be considered excellent amphiphilic candidates to serve as release controllers and stability7 enhancers in future formulations of double emulsions. So perhaps mixed compatible biopolymers wall at last allow researchers to... 

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

Mixtures of poly(vinylidene fluoride) with poly (methyl methacrylate) and with poly (ethyl methacrylate) form compatible blends. As evidence of compatibility, single glass transition temperatures are observed for the mixtures, and transparency is observed over a broad range of composition. These criteria, in combination, are acceptable evidence for true molecular intermixing (1, 19). These systems are particularly interesting in view of Bohns (1) review, in which he concludes that a compatible mixture of one crystalline polymer with any other polymer is unlikely except in the remotely possible case of mixed crystal formation. In the present case, the crystalline PVdF is effectively dissolved into the amorphous methacrylate polymer melt, and the dissolved, now amorphous, PVdF behaves as a plasticizer for the glassy methacrylate polymers. 

In order to investigate the molecular motions involved in this transition and, in particular, the nature of the associated cooperativity, it is interesting to consider not only BPA-PC, but also tetramethyl bisphenol A polycarbonate, TMBPA-PC, (Fig. 25) as well as copolymers of BPA and TMBPA carbonates, and compatible blends of BPA-PC and TMBPA-PC. 

Fig. 26 Temperature dependence of the dielectric loss, s", at 10 Hz, for BPA-PC, TMBPA-PC and their compatible blends. The TMBPA-PC volume fraction in the samples is Q 0, 0.22, x 0.38, A 0.53 and <> 0.82 (from [19])...

To analyse the occurrence of an intermolecular cooperativity, the compatible blends of BPA-PC and TMBPA-PC offer quite a useful opportunity [17,26, 28]. The dynamic mechanical results [28] are shown in Fig. 32. At first, two peaks are observed. They are located in the temperature range of each component. However, a more precise examination of the peak positions shows that the blend composition affects the two peaks differently (Fig. 33). Indeed, the TMBPA-PC peak is unchanged, whereas a downward temperature shift is observed for the BPA-PC peak with increasing TMBPA-PC content. Actually, the temperature shift of the maximum does not correspond to a shift of the whole low-temperature peak, but it results from the disappearance of the high-temperature peak when increasing the TMBPA-PC content, as clearly shown in Fig. 34. 

Various experimental techniques (dielectric relaxation, dynamic mechanical analysis, 1H, 2H and 13C solid-state NMR) have been used for investigating the secondary transitions of BPA-PC, and the block copolymers of BPA and TMBPA carbonates as well as compatible blends of BPA-PC and TMBPA-PC. They have provided lots of information on the motions of methyl, phenyl ring and carbonate units in bulk BPA-PC. The effect of intermolecular packing has also been clearly evidenced. 

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