Miscible polymer blends with partial miscibility

Nishio, Y., Koide, T., Miyashita, Y., Kimura, N., Suzuki, H.J. Water-Soluble Polymer Blends with Partially Deacetylated Chitin A Miscibility Characterization. Appl. Polym. Sci. 37, 1533-1538 (1999)... 

Because the components must initially form miscible solutions or swollen networks a degree of affinity between the reacting components is needed. Therefore, most of the investigations into epoxy IPNs have involved the use of partially miscible components such as thermoplastic urethanes (TPU) with polystyrenes [57], acrylates [58-61] or esters which form loose hydrogen-bound mixtures during fabrication [62-71 ]. Epoxy has also been modified with polyetherketones [72],polyether sulfones [5] and even polyetherimides [66] to help improve fracture behavior. These systems, due to immiscibility, tend to be polymer blends with distinct macromolecular phase morphologies and not molecularly mixed compounds. 

Thus most of the time one obtains phase-separated systems in which the macromolecules of component A are not at all or only to a limited extent miscible with the macromolecules of component B, i.e., polymer A is incompatible or only partially compatible with polymer B. The synonymical terms polymer blend , polymer alloy , or polymer mixture denote miscible (homogeneous) as well as immiscible (heterogeneous) systems consisting of two or more different polymers. 

Figure 9.4c and 9.4d represent intermediate cases, 9.4c indicates partial miscibility we see a two-phase system of AB blends with different A/B ratios. This might be the result of segregation into the binodals. Figure 9.4d is called an interphase or a multiphase blend. The system is quasi-homogeneous, but it contains all A/B ratios between cpi = 0 and concentration gradients as a result of non-completed diffusion in a combination of well-compatible polymers. 

What is necessary with a polymer blend in order to achieve the desired breadth of transition is partial miscibility. Complete immiscibility leads to two Tgs unshifted with respect to the Tgs of the components, and complete miscibility leads to the same relatively narrow transitions observed for homopolymers. Of course, with immiscible blends, it is possible to mix two or more polymers with relatively close Tgs and achieve broad damping transitions in that way. Hourston and Hughes (33) have reported broad transitions for polyether ester-polyvinyl chloride (PVC) blends where specific interactions occur between the ether oxygens and the chlorines in the PVC leading to partial miscibility. 

The problems and challenges Inherent to developing useful materials with optimal morphologies and properties from an Immiscible or partially miscible polymer blend are not trivial and have spawned considerable Industrial and academic research. Work on polymer miscibility, compatibilizing agents, reactive systems, and the Influence of flow on the structure and properties of blends Is described in later chapters. 

The most basic question when considering a polymer blend concerns the thermodynamic miscibility. Many polymer pairs are now known to be miscible or partially miscible, and many have become commercially Important. Considerable attention has been focussed on the origins of miscibility and binary polymer/polymer phase diagrams. In the latter case, it has usually been observed that high molar mass polymer pairs showing partial miscibility usually exhibit phase diagrams with lower critical solution temperatures (LCST). 

This simple relationship turns out to be useful in a surprising variety of situations, provided the intensity is determined in absolute units so that the invariant Q can also be evaluated in absolute units. If the scattering length densities of the two phases are known, for example, from knowledge of their chemical compositions, the experimental value of Q can be used to provide the relative amounts of the two phases. If, on the other hand, the relative amounts are known beforehand, for example, when the sample is prepared by mixing known quantities of two substances, the invariant can be used to determine the difference pi — P2. An instance in which such information could be useful is with a polymer blend in which a partial miscibility is suspected. When known quantities of two polymers are mixed together, any decrease in p — p2... 

Figure 17.1. Generalized mechanical loss (tan 5) and modulus-temperature behavior for various types of polymer blends. Case 1 (dashed-dotted line), miscible Case 2 (dashed line), partially miscible Case 3 (dotted line), microheterogenous Case 4 (solid line) phase separated. Reproduced with permission from O. Olabisi, L. M. Robeson, and M. T. Shaw, Polymer-Polymer Miscibility , Academic Press, New York, 1979.

Cellulose blends with synthetic polymers also constitute an example of biodegradable polymer blends. Miscibility of cellulose with polyvinylpyrrolidone [Masson and Manley, 1991a], poly(4-vinyl pyridine) [Mason and Manley, 1991b], PAN [Nishio et al, 1987], PVAL [Nishio and Manley, 1988], and polyethyleneoxide (PEG) [Nishio et al., 1989] have been reported. Starch blends with commodity polymers have been commercialized as a low cost method to promote partial environmental degradability. While a defi-... 

A key paper involving the experimental interfacial aspects of polymer blends discussed the blends of more than two components wherein a polymeric constituent will concentrate at the interface between two of the blend constituents [Hobbs et al., 1988]. Employing the concepts of interfacial relationships, it was shown that a ternary component can concentrate at the interface between the other constituents and allow for compatibilization of dissimilar and incompatible components. As an example, it was shown that in the ternary blend of PMMA/PC/PBT, PC encapsulates PMMA as a dispersed phase in a matrix of PBT. PC, which exhibits partial miscibility with PMMA and PBT thus compatibil-izes PMMA/PBT blends. 

Poly(8-caprolactone) (PCL), on the other hand, is a semi-ciystaUine biodegradable polymer. This material is commonly used as plasticizer. The P(3HB)/ PCL blend exhibited partial miscibility, however, the elongation at break was increased about 81 % in comparison with pure P(3HB) [43]. 

Polymer blending is to combine two or more components and has superior mechanical, optical, or thermal properties than these individual polymers. From the practical and economical points of view, polymer blending from existing polymers is the most effective and convenient route to create new and useful materials with greater versatility and flexibility than the development of new polymers. Basically, three different types of blends can be distinguished completely miscible, immiscible, and partially miscible blends [1,2] as shown in Figure 2.1. 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

A series of composites of polystyrene (PS) and block poly(styrene-butadiene) (SBS) prepared by extrusion blending in the injection screw and injection moulding were studied by Fourier transform infrared (FTIR) analysis. Moulded samples were then dissolved and cast as a film and again studied using FTIR, with higher levels of miscibility noted than on the original moulding. SBS content of the samples was between 20 and 80 percent, with studies also completed on the pure polymers. Differences observed from simulated spectra of the polymer composites were explained by interactions between the two polymers due to partial miscibility. Corroboration of results was provided by calorimetry studies. 16 refs. 

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