Browsing by Subject "Blends"

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    Compatibilization of polyolefin blends
    (2015-08) Thurber, Christopher
    Polymer blends are used to access unique combinations of properties beyond those of neat homopolymers. Blends confer flexibility in tailoring a specific material to a given application, and in some cases, they can lend improved properties compared to their constituent materials. Some examples of blend-synergistic properties in the literature include toughness enhancement, increased chemical resistance, increased modulus, and improved processability. Given the breadth of properties that can be improved by blends, they are employed extensively in commercial products, with more than a third of all polymer resins used in blends (Utracki, 2003). Most polymer pairs are immiscible, thus their blends require compatibilization to aid dispersion in the melt state and to transfer stress across interfaces in the solid state. Block copolymers have proven to be successful compatibilizers, in both premade and reactively formed systems. This thesis focuses mainly on reactive systems. The reaction at immiscible polymer interfaces is kinetically limited and most reactions are too slow for applications, so general methods of increasing interfacial reaction rate have been investigated. This work also seeks to find new tools for measuring localization and conversion in polymer blends, with the ultimate goal of making useful, economical materials, and understanding the resulting structures. This thesis attempts to further our knowledge of compatibilization of polyolefin blends in particular. Chapter 2 attempts to create facile reactive compatibilization schemes for polyolefins with poly(methyl methacrylate). Chapters 3 and 4 examine the use of catalysts to increase interfacial reaction rate between functional polyethylene and polylactide. Chapter 3 demonstrates stannous octoate catalyst is localized at the interface, and blends show better compatibilization than those with a more active but non-localized tin chloride dihydrate catalyst. Chapter 4 uses cobalt octoate catalyst to increase interfacial reaction rate by ~90-fold and the extension at break of polylactide majority blends to ~200%. Structural dependence of copolymers on compatibilization efficiency in polypropylene/polyethylene blends is investigated in Chapter 5. Finally, a small scale coextruder is created using a dual-bore capillary rheometer, with the potential to examine the effect of flow on copolymer localization, catalyst localization, and interfacial reaction rate (Chapter 6).
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    Component terminal dynamics in weakly and strongly interacting blends.
    (2009-12) Ozair, Sehban N.
    Miscible blend dynamics have been long been a subject of interest and are not as well understood as dynamics of homopolymer melts. Their anomalous behavior, such as time-temperature superposition failure, broadening of calorimetric glass transition, etc., makes these systems very intriguing and challenges our understanding of miscible blend dynamics. In this work we investigated temperature and composition dependence of two different, dynamically heterogeneous blend systems using rheology and forced Rayleigh scattering (FRS). The first blend investigated was a weakly interacting one comprising poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA). Monomeric friction factors of PEO and PMMA were reported for a wide range of temperature and composition. PEO terminal dynamics were found to have strong composition dependence unlike that of PEO segmental dynamics previously reported. Also, PEO maintained its rapid relaxation mechanisms even in stiffer surroundings. The PEO hydroxyl end groups were found to have no significant impact on component chain dynamics. The FRS and rheology results agreed remarkably well for this system. The Lodge-McLeish model failed to describe the experimental results. In order to understand the role of hydrogen bonding on chain dynamics, a strongly interacting system of PEO/poly(vinyl phenol) (PVPh) was investigated using rheology. The blends consisted of a high molecular polymer tracer dispersed in low molecular weight matrix to extract relevant dynamic information from tracer contribution to material properties. Monomeric friction factors were reported for a wide temperature and composition range. Time-temperature superposition failure was observed in PEO tracer blends at high PVPh concentration. The shape of tracer relaxation spectra for PVPh tracer blends had a strong composition dependence while those for PEO tracer blends were independent of composition. The tracer contribution to blend viscosity had a strong temperature dependence at high PVPh composition. Across the composition range, single and narrow glass transitions were observed for these blends. PVPh chain conformations were investigated using SANS and contradictory conclusions were reached. Therefore, no conclusive remarks can be made regarding PVPh chain conformations in dilute solution.