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Formation and Properties of Epoxy Resins Containing PES Copolymer Modifiers

Man, Zakaria (2003) Formation and Properties of Epoxy Resins Containing PES Copolymer Modifiers. PhD thesis, University of Manchester Institute of Science and Technology.

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Two epoxy network-forming systems based either on a diglycidyl ether of bisphenol A (Epikote 828) or a triglycidyl p-amino phenol (MY051 0), were crosslinked using stoichiometric amounts of 4,4'-diaminodiphenyl sulfone (DDS). Both epoxy systems were modified with random copolymers, polyethersulfone-poly( ether-ethersulfone) (PES:PEES), with either amine- (NHz-) or chlorine- (CI-) end-groups, at I 0 and 20 wt %. The Epikote 828/DDS (ED) and MY051 0/DDS (MD) systems were reacted at 190 and 180 °C, respectively, and all the unmodified and modified epoxy systems were prepared without the use of solvent. Real-time analytical techniques were used to study network structure development through investigations of polymerisation kinetics using DSC and FTIR spectroscopy. and of gel times and power-law behaviour using rheometry. DSC has limitations for the measurement of chemical conversion, particularly as crosslinking reactions approached completion. As an alternative, FTIR spectroscopy in the near-infrared frequency region was refined and improved to provide more accurate conversiontime data. Overall, the reaction mechanisms were autocatalytic in nature independent of the PES:PEES concentration. Gel-point conversions, PgeJ, were determined from combined DSC and rheology data. Values of Pgei for unmodified ED and MD systems were 0.61 ± 0.01 and 0.50 ± 0.02, respectively, compared with 0.58 and 0.41, as predicted by Flory-Stockmayer statistics, for the corresponding ideal networkforming systems. The gel times, lgeJ, in the epoxy network-forn1ing systems were delayed by incorporating PES:PEES, which acts as a diluent. although gel conversions were unaffected. In addition, a posteriori characterisation of the fully-reacted network materials was carried out using TMDSC, DMA and tensile tests, SAXS. SEM and TEM to evaluate the thermal and mechanical properties in relation to morphological structures. The modified ED systems were miscible at the molecular level as shown by SAXS analysis. In contrast the modified MD systems were phase-separated. Co-continuous and phase-inverted morphologies were generated in MD systems containing. respectively, 20 wt % of amine-and chlorine-terminated PES:PEES. Differences in the morphologies between modified ED and MD systems were related to differences in crosslink densities of the epoxy networks. In the phase-separated systems, the Tg of PES:PEES-rich phases shifted to higher temperatures, and the Tg of the epoxy-rich phases shifted to lower temperatures, as shown by TMDSC and DMA. In the rubbery state, the presence of PES:PEES in the epoxy systems was shown to increase the molecular weight between crosslinks, Me. so decreasing the crosslink density. The increase in Me with increasing modifier content was attributed to a swelling effect in the epoxy network by molten PES:PEES. Incorporating PES:PEES in the epoxy network systems increased the ductility of the unmodified epoxy systems. This was shown by SEM on epoxy fracture surfaces carried out after tensile testing. Modified epoxy systems increased tensile properties such as strain at break, strength and toughness with only slight reductions in the Young's modulus. The tensile toughness of the modified ED and MD systems containing 20 wt% NH2-PES:PEES were increased by 130 and 300 %, respectively.

Item Type: Thesis (PhD)
Academic Subject : Academic Department - Chemical Engineering - Material Development
Subject: Q Science > QD Chemistry
Divisions: Sciences and Information Technology
Depositing User: Users 2053 not found.
Date Deposited: 26 Sep 2013 13:25
Last Modified: 25 Jan 2017 09:47
URI: http://utpedia.utp.edu.my/id/eprint/6840

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