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Title:Development of aromatic polyesters for high performance applications and use of interchain transesterification reactions as a solid-state fabrication tool
Author(s):Meyer, Jacob Lee
Advisor(s):Economy, James
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
stock shape
high temperature
Abstract:Deposition and cure of aromatic thermosetting copolyester (ATSP) oligomers is explored across several potential schemes: plasma spray, solvent-borne, and as an electrostatic powder coating. It is generally found that all methods are potentially viable as low friction, low wear coatings but that ATSP as an electrostatic powder coating is the simplest and highest performing deposition mechanism in terms of wear rate and provides the highest glass transition temperatures in an electrostatically-deposited polymeric powder coating known in literature or commercially. Low production of wear debris coupled with stable and high mechanical property films transferred to the tribopair counterface (as seen via energy-dispersive X-ray spectroscopy) lends evidence that during tribological experiments that produce contact temperatures of up to 320°C that interchain transesterifications (ITR - a class of solid state chemical reactions available to aromatic polyesters) are responsible in part for low wear rates via ATSP reincorporating its own wear debris and development of a stable transfer film. Additionally, it is found that a mixed liquid crystalline/amorphous oligomer set will phase segregate and produce surface texture corresponding to the phase segregated ordered region. This surface texture and the high glass transition temperature of ATSP enables the in-situ formation of micro-reservoirs of lubricant during lubricated tribotesting. Micromechanical experiments were used to assess the contribution of cohesive wear to ATSP resins as well as several neat polymer and commercially deposited coatings. In instrumented scratch experiments ramped up to 80mN in applied force with a 4.3 μm conispherical indenter tip, it is found that ATSP exhibits a uniquely high tendency towards what is termed “elastic recovery” wherein the scratched region of the coating surface recovers most of the deformed depth during retrace experiments. As well, the wear mode of amorphous ATSP coatings maintains this performance at applied loads significantly in excess of any other observed coating. It is hypothesized that the crosslinked structure and potential for the aromatic polyester chains to deform via crankshaft motion about the ester bond may be responsible for this interesting mechanical feature. Vacuum assisted resin transfer molding is demonstrated as a potential fabrication technique for continuous fiber ATSP composites. The potential for ATSP to be the first weldable thermoset material is also explored. Fully cured laminae of ATSP/carbon fiber are fused into a single workpiece via solid-state interchain transesterification reactions. Resin-dominated mechanical properties of the composite such as interlaminar shear strength and the Mode I fracture toughness of the composite at the bondline adhered via ITR. Results indicate interlaminar properties beyond that of traditional epoxy and polyimide resins. Additionally, cryogenic thermal cycling experiments are used to assess the composite’s resistance to microcracking which indicates excellent resistance to microcracking as well as potential repair schemes for ATSP composites. Single fiber fragmentation testing was used to determine the interfacial shear strength of the fiber/matrix bond. The high strength here and observation via scanning electron microscopy of all fibers entirely coated in resin suggest that cracking in ATSP composites predominantly occurs within the resin phase. The lack of low energy surfaces at fiber/matrix interface to propagate suggests a rationale to the high Mode I fracture toughness observed for ATSP composites. Mechanical and thermal performance of ATSP foams and fully dense structures recycled from the foams via interchain transesterification reactions are described. Tribological results of the fully dense structures when filled with PTFE lubricating additives suggest application as a low-friction and low wear material. Several novel additive fabrication schemes and a process to weld aromatic polyester composites are also suggested as future areas of research.
Issue Date:2015-12-11
Rights Information:Copyright 2015 Jacob Lee Meyer
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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