Interphase interactions, compatibilizing effect

Enhanced interphase interactions, deduced from thermal and dynamic mechanical properties and morphology observed by SEM, demonstrate the efficient compatibilizing effect of iPS-fo-iPP copolymer on iPS-iPP blends. Each sequence of the iPS-fc-iPP diblock copolymer can probably penetrate or easily anchor its homopolymer phase and provide important entanglements, improving the miscibility and interaction between the iPS and iPP phases. This is in good agreement with what is inferred from the mechanical properties of the iPS-fo-iPP-iPS-iPP polyblends. 

The effect of compatibilization of grafted or block copolymers as controllers of interphase interaction has been well known (1,28). Marosi and Bertlan (29), for example, described the compatibUizing effect of polybutylene terephthalate-polytetramethylene oxide block copolymers on PA6/HDPE blends. The addition of a block copolymer prevents separation in the blends during processing and increases the impact strength of the material several times. 

Miscibility between the individual polymers is the most important factor to determine the performance characteristics of a polymer blend. Mutual solubility of the phases, the thickness and properties of the interphase formed during blending and the structure of the blend are mainly dependent on the miscibility of individual polymers within a polymer. As a result, a quantitative estimation of interactions is very much important for the prediction of blend properties. Comparison of solubility parameters of individual polymers is an effective method to predict the extent of miscibility within a blend. According to the Hildebrand solubility theory, a large difference in solubility parameters (6p) of individual matrices results in immiscibility between them in the absence of any interfacial compatibil-izer [222]. Jandas et al. have reported that PLA and PHB have Hildebrand solubility parameters (6p) of 23.5 J /cm and 19.8 J Vcm which can turn out to be partially miscibile blends in between them [35]. In case of partially miscible blends, the miscibility can be controlled by compatibili-zation using proper interactables. 

Compatibilization enhances dispersion, increases the total apparent volume of the dispersed phase, rigidities the interface, and increases interactions not only between the two phases but also between the dispersed drops. These changes usually increase the blend s viscosity, elasticity, and the yield stress. The compatibihzer effects are especially evident at low frequencies. There are two mechanisms that may further affect these behaviors (i) the copolymer may form micelles inside one or both polymeric phases instead of migrating to the interphase and (ii) an addition of compatibihzer may increase the free volume resulting in decreased viscosity. 

Compatibilization of polymer blends aims to improve the interaction between phases, ascertaining the appropriate, stable morphology and improved performance. Blends have been compatibilized mainly by addition of a compatibilizer, a co-solvent, or in a reactive process, where the compatibilizing molecules are formed within the interphase [1, 73, 302]. About 20 years ago a note in a USSR technological journal reported that the addition of a small amount of PMMA to a PE/PS blend reduced the PS drop diameter by a factor of ten. The effect was later explained by a balance of the three interfacial tension coefficients in the blends, inter-related by Neuman s triangle equation [1,352,353]. In simple terms, the PMMA, immiscible in PE and PS, formed a layer around PS drops, preventing coalescence. In a sense, addition of nanoparticles to polymer blends acts similarly. 

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