Browsing by Subject "polylactide"

Now showing 1 - 4 of 4
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    Impact of Architecture on High-Performance Sustainable Aliphatic Polyester Thermoplastic Elastomers
    (2022-11) Liffland, Stephanie
    Thermoplastic elastomers (TPEs) are a class of reprocessable materials that behave like chemically crosslinked elastomers at their usage temperatures but can be processed like thermoplastic materials. This reprocessability is a result of the physical rather than chemical crosslinks present in the materials. Commercial TPEs are typically linear ABA triblock polymers with hard polystyrene endblocks and a soft polydiene midblock and have varied applications from adhesives to personal care products depending on composition . Unfortunately, these petrochemical-derived materials last long beyond their functional lifetimes and contribute to the growing problem of plastic waste. Aliphatic polyester-based TPEs (APTPEs) present an alternative to these non-renewable materials that can be sustainably derived from renewable biomass with enhanced degradation capabilities through recycling or composting. The best performing APTPEs consist of poly(L-lactide) and poly(γ-methyl-ε-caprolactone) and have shown to be competitive with commercial styrenic materials. The work presented in this thesis is focused on continued improvements to the mechanical properties of these APTPEs through alterations to the ABA triblock architecture. Chapter 1 provides an analysis of the methods in which we assess sustainable materials and background on thermoplastic elastomers. Chapter 2 investigates the influence of composite (i.e. glassy and semicrystalline) hard domains in ABCBA pentablock terpolymers. Chapters 3 details systematic investigations into the impact of symmetric multiarm star architectures on the mechanical performance of APTPEs. Chapter 4 further expands on the enhancements observed in the materials reported in Chapter 3 through the introduction of stereoblock PDLA-PLLA hard domains to star APTPEs. Chapter 5 details a study into the potential for high-performing star block APTPEs to act as sustainable medical devices.
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    Modification of Poly(lactic acid) by Melt Blending
    (2017-12) Gu, Liangliang
    Poly(lactic acid) (PLA), a renewable, biodegradable, and biocompatible polyester, is one of the most successful solutions to revolutionize renewable plastic production. Nevertheless, application of pristine PLA is largely limited by its brittleness in solid state and low melt strength in melt state. Various strategies have been developed to improve the performance of PLA, among which melt processing is the most viable and economical for industrial use. This thesis covers several independent aspects of PLA modification and presents some new possibilities in melt processing of PLA and PLA-based blends. Chapter 2 and Chapter 3 focus on branching of PLA with multifunctional aziridine to improve melt strength. Multifunctional aziridine as a branching agent has its advantage in fast reaction kinetics that leads to stable final product properties. Extensional rheology was extensively used to clarify the correlation between melt strength and chain structure. Chapter 4 seeks to toughen PLA by blending with poly(ethylene oxide)-poly(propylene oxide )-poly (ethylene oxide) (PEO-PPO-PEO) triblock copolymers, which are commercially known as Pluronic® (by BASF). Pluronic copolymers with large PPO block size and low PEO content can increase the elongation of break from 5% to more than 100% at a low loading of 5 wt.%, along with the additional benefits of reduced blend viscosity and easy mold-release. Chapter 5 and chapter 6 are less property-oriented, focusing on cocontinuous immiscible polymer blends. In Chapter 5, carboxylic acid/oxazoline reaction is used to compatibilize cocontinuous PLA/polystyrene (PS) blend. Reactively formed interfacial graft copolymer reduced the phase domain size to submicron scale, which is hard to achieve in melt-processed cocontinuous blends. Hierarchically porous PLA, with primary pore size 5 – 20 µm and secondary pore size 0.5 – 2 µm, was further made from compatibilized PLA/PS/linear low density polyethylene (LLDPE) blend after selective extraction of PS and LLDPE. By studying the wetting behavior of ternary PLA/PS/PE blend, we confirmed that PLA/PE interfacial tension is much higher than PLA/PS interfacial tension. Chapter 6 uses branched PE and PLA to study the effect of extensional viscosity on cocontinuity formation in immiscible polymer blends. Blending with two branched polymers broadened the range of cocontinuity. This was attributed to the ability of a strain hardening matrix to promote elongation, and hence percolation, of the minor phase.
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    Rheological Design of Sustainable Block Copolymers
    (2016-08) Mannion, Alexander
    Block copolymers are extremely versatile materials that microphase separate to give rise to a rich array of complex behavior, making them the ideal platform for the development of rheologically sophisticated soft matter. In line with growing environmental concerns of conventional plastics from petroleum feedstocks, this work focuses on the rheological design of sustainable block copolymers - those derived from renewable sources and are degradable - based on poly(lactide). Although commercially viable, poly(lactide) has a number of inherent deficiencies that result in a host of challenges that require both creative and practical solutions that are cost-effective and amenable to large-scale production. Specifically, this dissertation looks at applications in which both shear and extensional rheology dictate performance attributes, namely chewing gum, pressure-sensitive adhesives, and polymers for blown film extrusion. Structure-property relationships in the context of block polymer architecture, polymer composition, morphology, and branching are explored in depth. The basic principles and fundamental findings presented in this thesis are applicable to a broader range of substances that incorporate block copolymers for which rheology plays a pivotal role.
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    Supporting data for Preparation and characterization of H-shaped polylactide
    (2024-05-16) Zografos, Aristotelis; Maines, Erin, M; Hassler, Joseph, F; Bates, Frank, S; Hillmyer, Marc, A; hillmyer@umn.edu; Hillmyer, Marc, A; University of Minnesota Department of Chemistry
    These files contain primary data along with associated output from instrumentation supporting all results reported in Zografos et al. Preparation and Characterization of H-Shaped Polylactide. In Zografos et al. we developed an efficient strategy for synthesizing H-polymers. An H-polymer has an architecture that consists of four branches symmetrically attached to the ends of a polymer backbone, similar in shape to the letter ‘H’. Here, a renewable H-polymer efficiently synthesized using only ring-opening transesterification is demonstrated for the first time. The strategy relies on a tetrafunctional poly(±-lactide) macroinitiator, from which four poly(±-lactide) branches are grown simultaneously. Proton nuclear magnetic resonance (1H-NMR) spectroscopy, size exclusion chromatography (SEC), and matrix assisted laser desorption/ionization (MALDI) spectrometry were used to verify the macroinitiator purity. Branch growth was probed using 1H-NMR spectroscopy and SEC to reveal unique transesterification phenomena that can be controlled to yield architecturally pure or more complex materials. H-shaped PLA was prepared at the grams scale with a weight average molar mass Mw > 100 kg/mol and narrow dispersity Ð < 1.15. Purification involved routine precipitations steps, which yielded products that were architecturally relatively pure (~93%). Small-amplitude oscillatory shear and extensional rheology measurements were used to demonstrate the unique viscoelastic behavior associated with the H-shaped architecture.