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