Abstract
Polyetheretherketone (PEEK)/polyethersulfone (PES) blends are initially not miscible, except when the blends are prepared by solvent mixing. We propose a route to elaborate PEEK/PES blends with partial miscibility by melt mixing at 375 °C with phenolphthalein. The miscibility of blends has been examined using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMTA). When adding phenolphthalein to PEEK/PES blends, the glass transitions are shifted inward as an indication of miscibility. We suggest that phenolphthalein acts as a compatibilizer by creating cardo side groups on PEEK and PES chains by nucleophilic substitution in the melted state, although this condensation reaction was reported only in the solvent until now. In addition, phenolphthalein acts as a plasticizer for PES by decreasing its glass transition. As a consequence, the PEEK phase is softened which favors the crystallization as the increase of crystalline rate. Due to aromatic moieties in phenolphthalein, the storage modulus of blends in the glassy region is kept identical to pure PEEK. The morphological analysis by SEM pictures displays nano- to microsized PES spherical domains in the PEEK matrix with improved PEEK/PES interfacial adhesion.
Highlights
Polymer blends play a central part in the development of new materials with tailored properties
It can assume that a blend with the polymer of longer chains would give an immiscible blend or partially miscible, but with high mechanical rigidity, while a blend with shorter chains would result in a material with better miscibility but lower rigidity
Each polymer was processed separately according to the same extrusion conditions
Summary
Polymer blends play a central part in the development of new materials with tailored properties. Blending two polymers may be the easiest option to design such materials with controlled morphology. Thermoplastics are not miscible, and the resulting blends display nice structures such as droplets dispersed in a main continuous phase, from spherical to elongated domains up to co-continuous phases when the phase ratio is close to 1. Such structures constitute beautiful and refined images to entertain scientists, these polymer blends are typically described as unstable phase morphologies. Compatibilization makes the system more stable and better-blended phase morphology by creating interactions between the two previously immiscible polymers. The compatibilization enhances the mechanical properties of the blend, and yields properties that are generally not attainable in a single pure component
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