Mechanical properties of acid‐cured epoxide resins with different network structures

Abstract

Static and dynamic mechanical properties of cured epoxide resins based on ester bonds, ether bonds, or a mixture of ester and ether bonds were investigated. Their network structures were estimated from the results of gel content before and after saponification, and conversion of functional groups. It was found that cured epoxide resins based on a mixture of ester and ether bonds indicate intermediate properties between the resins based on ester bonds and the resins based on ether bonds. Both dynamic and static mechanical properties were strongly affected by their network density and their segmental structures suggested in this paper.

Development of completely bio‐based epoxy networks derived from epoxidized linseed and castor oil cured with citric acid

“…The narrow α ‐relaxation peak of epoxy is noticed at higher temperature (95°C) confirming higher degree of crosslinking and restricted mobility of the chains. Similar relaxation peak was observed in case of DGEBA cured with adipic acid due to presence of larger amount of ether bonds . The broader peak of the tan δ curve and larger area signifies better damping material, which is observed in case of ELO and ECO‐based network.…”

“…On the other hand, both the increase in intensity of the damping peak and a lower T g (38°C) confirm the flexibility of ECO, which may be attributed to the increase in polymer segmental motion due to lower crosslink density and presence of flexible polyol group. Same T g was observed for BPH cured ECO through thermomechanical analysis by Park et al The reduced T g of bio‐based ELO and ECO may be attributed to the presence of mixture of ester and ether bonds during curing . Further, the difference in T g of these bioresins can be explained due to the inherent character of the aliphatic fatty acids, their length, functionalities, backbone, and distribution .…”

“…In addition to this, etherification may take place by the reaction of the hydroxyl groups formed in ring‐opening of epoxy (III). Carboxylic acid‐cured epoxy resins without any catalyst act as a system being composed of a mixture of ether and ester bonds . Crosslinked polyesters may have also been formed by the reaction of a hydroxyl group of CO and carboxylic group of CA through bulk polycondensation process …”

“…Thus, it is of great importance to utilize eco‐friendly curing agent preferably derived from renewable‐based resources to substitute petro‐based resources for producing next‐generation bio‐based epoxy networks . In this context, different bio‐derived carboxylic acids have been used, by several researchers in the past, as curing agents to develop both petro‐based and bio‐based epoxy products, with and without use of catalyst …”

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

“…The epoxy system based on the reaction of the difunctional epoxy monomer diglycidyl ether of bisphenol-A, DGEBA, with aliphatic amines is such an example. The properties of this and other epoxy systems can be varied as a function of the molecular weight of the hardener molecule [7][8][9][10] , by variations in processing conditions [11][12][13] or by the use of different hardener to monomer ratios 8,11,[13][14][15][16][17][18][19][20][21] . This last variable introduces boundary condition (i.e., when a variable like temperature or the amount of monomers is changed).…”