Crucial Aspects of Phase Morphology Generation and Stabilization in Two- and Three- Phase Polymer Blends. Physical, Reactive and Combined Routes of Compatibilization

CRUCIAL ASPECTS OF PHASE MORPHOLOGY GENERATION AND STABILIZATION IN TWO- AND THREE-PHASE POLYMER BLENDSPhysical, Reactive and Combined Routes of Compatibilization.In this thesis the relationship between the phase morphology and properties of in situ polymerized, and melt-processed uncompatibilized and reactively compatibilized selected polymer blends has been thoroughly investigated. A fundamental understanding of this relationship is required for an effective control of the ultimate properties of immiscible polymer blends.Three binary blends, namely polyamide 6/ethylene-butylene elastomer (PA6/EB elastomer), polypropylene/polycyclohexylmethacrylate (PP/PCHMA) andpolypropylene/polystyrene (PP/PS) as well as a ternary polyamide 6/polypropylene/polystyrene (PA6/PP/PS) blend were considered. Different strategies of compatibilization have been applied to these binary and ternaryblend systems. The focus was put on specific aspects of formation and stabilization of the phase morphology.Blend system 1: PA6/EB elastomer blends.The polymerization of caprolactam monomer in the presence of low molecular weight hydroxyl (–OH) or isocyanate (–NCO) end-capped EB elastomers as a new concept for the development of a sub-micron phase morphology incompatibilized PA6/EB elastomer blends is considered. The blends were compatibilized using a pre-made triblock copolymer PA6-b-EB-b-PA6, or a diblock copolymer PA6-b-EB, reactively generated during melt-blending (extrusion-prepared blends), or built-up via anionic polymerization of -caprolactam initiated by –NCO groups attached to EB chain ends (polymerization-prepared blends). The phase morphology and viscoelastic behavior ofthe polymerization-designed blends were compared to those of similar blends prepared via melt-extrusion of PA6 and the EB elastomer. In situ polymerized/physically compatibilized and in situ polymerized/in situ compatibilized blends show a significant particle size reduction (0.14 and 1.1 μm, respectively) compared to uncompatibilized blends of PA6/EB elastomer (12 μm). The notched Izod impact strength of the physically compatibilized blend with premade PA6-b-EB-b-PA6 triblock copolymer having a sub-micron particle-in-matrix morphology is found to be more than twice higher (16 kJ/m2) than that of pure PA6 (6 kJ/m2), non-compatibilized, or in situ polymerized/compatibilized blends (7 kJ/m2).Blend system 2 (chapter 3): Binary PP/PCHMA blends.The strategy of reactive compatibilization, where the compatibilizer isformed in situ by chemical reactions during melt-mixing of the blend, has been applied to binary PP/PCHMA blends using maleic anhydride graftedpolypropylene (PP-g-MA) and amine end-capped polystyrene (PS-NH2) as reactive precursors. PP-g-MA is highly compatible with the parent PP phase, while PS-NH2 is fully miscible with PCHMA. The PP-g-PS graft copolymeris reactively generated at the interface during melt-blending. PP/PCHMAblends covering the whole range of compositions were prepared. The composition window at which the blends exhibit a droplet/matrix phase morphology and that where the two phases are co-continuous were determined using selective solvent extraction (SE) in combination with scanning electron microscopy (SEM). Solvent extraction results showed that the onset and offset (threshold) of phase co-continuity take place over a composition window from 10 to 20 wt% PP and from 80 to 90 wt% PP, respectively. Inbetween these compositions, a co-continuous two-phase morphology prevails. Significant differences in phase morphology of PP/PCHMA/((PP-MA)/(PS-NH2)) compatibilized blends were found in relation to the MA content (1or 8 wt% MA) of the PP-g-MA reactive compatibilizer precursor with the same precursor PSNH2. In the blends having a droplet/matrix type of morphology, the particle size was largely reduced (by a factor of more than 10). A fully co-continuous phase morphology, observed at an onset and offset of co-continuity, is significantly altered upon in situ generation of PP-g-PS compatibilizer; the phase morphology becomes mixed, partiallycontinuous and partially dispersed in a matrix phase.Blend system 3: Binary PP/PS blends.The reactive compatibilization concept using PP-g-MA (1 and 8 wt% MA) and PS-NH2 as reactive precursors to compatibilize their parent PP and PShomopolymers, was studied in detail. The phase morphology of the blendswas investigated using a selective solvent extraction technique for a 3D-volume characterization, combined with 2D direct microscopic (SEM) observations on cryo-fractured and cryo-smoothed surfaces in the perpendicular and longitudinal directions to the flow. Differences in phase morphology of the blends are discussed based on the viscoelastic properties ofthe components, the blend composition, and the type and content of the compatibilizer precursors employed. The phase morphology developed was found to exhibit a highly elongated anisotropic structure upon melt flow through the die of the extruder. When the blends were thermally annealed, a 50/50 PS/PP co-continuous blend exhibits a substantial phase coarsening from micro- to millimeter scale without alteration of the phase co-continuity. The reactive compatibilization of the PP/PS blends by means of a 5 wt% reactively in situ generated PP-g-PS copolymer was able to significantly retard the phase coarsening process. In dispersed/matrix and co-continuous phase morphologies, the in situ formed compatibilizer based on PP-MA8 was much more efficient in stabilizing the formed phase morphology than that generated based on PP-MA1.With the same PP/PS blend, the part of the thesis focused on the comparison of the characterization tools for co-continuous phase morphologies.Melt- and solid-state mechanical properties using dynamic stress rheometry (DSR) and dynamic mechanical thermal analysis (DMTA) were used to detect co-continuity in addition to classic methods, like solvent extraction and SEM. Solvent extraction allowed to estimate quantitatively the window of co-continuity for the several PP/PS blend systems studied, whichis within the range of 70/30 - 10/90 wt%, depending on the viscosity ratio of the constituents used. Melt-state rheological measurements showeda clear difference between the dispersed/matrix and co-continuous structures. The local maxima in the composition dependence of the shear storage modulus of the blends at 60/40 and 10/90 wt% PP/PS were attributed tothe higher amount of the interface present in these blends, and described as boundaries of co-continuity. DMTA measurements allowed to detect precisely the phase inversion composition for the three different groups of PP/PS blends, which was 56, 61 and 67 vol%, for the viscosity ratios of 0.3, 1.0 and 3.3, respectively. Based on the experimental results, anequation has been proposed to predict the PI point in immiscible polymer blends. Dynamic scanning calorimetry (DSC) has been applied as a new technique to detect phase continuity based on the heterogeneous and homogeneous nucleation behavior of the crystallizable phase of the blend.Blend system 4: Ternary PA6/PP/PS blends.The focus was put on the phase morphology development in ternary uncompatibilized and reactively compatibilized blends of PA6, PP and PS. Reactive compatibilization was ensured using two reactive precursors, PP-g-MA(with 2 or 8 wt% MA), and styrene-maleic anhydride copolymer (SMA) with2 wt% MA, for the PA6/PP and PA6/PS pairs in ternary PA6/PP/PS blends, respectively. The phase morphology investigated using SEM and selective solvent extraction tests revealed that the PA6/PP/PS blend having a composition of 70/15/15 is constituted of a PA6 matrix in which composite droplets of a PP core encapsulated by the PS phase are dispersed. This behavior of the phase morphology was in disagreement with the prediction ofHarkin‘s spreading coefficient and free interfacial energy concept. This failure was ascribed to the substantial differences in viscosity between the dispersed components. A co-continuous three-phase morphology was formed in the uncompatibilized blends having a 40/30/30 composition. This morphology has been significantly affected in reactively compatibilized PA6/(PP/PPMA)/(PS/SMA) blends. The PA6 phase was no more continuous but became finely dispersed in the PS continuous phase. However, the PP phase showed a continuous bulk structure, which was confirmed by SEM and DSC measurements.status: publishe