Polymer Melt-Blend Glasses

A novel approach is used to compatibilise a blend without addition of premade copolymers or functionalisation of polymers lacking functional groups. Solid-state shear pulverisation (S3P) processes polymers at temperatures below the melt transition (for semicrystalline polymers) or the glass transition (for amorphous polymers). The polymer, introduced as pellets or flakes into the pulveriser. 

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. 

The decomposition temperature of the CBA should be higher than the melting point (Tm) or glass transition temperature (Tg) of the polymer. The blending operation of CBA and the polymer should be conducted at a temperature sufficiently above (close to the order-disorder temperature Toa = or Tg + 55°C) but preferably below the decomposition temperature of the CBA. 

Many properties of pure polymers (and of polymer solutions) can be estimated with group contributions (GC). Examples of properties for which (GC) methods have been developed are the density, the solubility parameter, the melting and glass transition temperatures, as well as the surface tension. Phase equilibria for polymer solutions and blends can also be estimated with GC methods, as we discuss in Section 16.4 and 16.5. Here we review the GC principle, and in the following sections we discuss estimation methods for the density and the solubility parameter. These two properties are relevant for many thermodynamic models used for polymers, e.g., the Hansen and Flory-Hug-gins models discussed in Section 16.3 and the free-volume activity coefficient models discussed in Section 16.4. 

There are a number of important factors governing the change of the crystallization rate and semicrystalline stracture of a polymer in blend systems. Those include the degree of miscibility of the constituent polymers, their concentration, their glass-transition and melting temperamre, the phase morphology and the interface structure in the case of immiscible blends, etc. 

These are a relatively new development. They are low-melting-point glasses which can be blended with certain organic polymers and injection moulded to give products with superior thermal and dimensional stability. They include alkali/zincpyrophosphate/sulphate compositions (Table 12.26) [62]. 

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