Thermally stimulated creep spectroscopy for the study of DGEBA-DDM networks

Abstract

During the past two decades, Thermally Stimulated Creep Recovery (TSCR) has been used successfully to study molecular mobility in polymers. The main feature of this technique is its quite good sensitiveness: the sample undergoes a shear stress, so that the subsequent strain is linear in a range larger than in elongation or compression experiments. Furthermore, the low equivalent frequency of TSCR permits the resolution of normally overlapping peaks.In this study, the TSCR technique has been used to investigate a series of DGEBA-DDM networks differing from the value of the amine-to-epoxy ratio which was systematically varied below stoichiometric composition. The magnitude of the fl-mode (glassy region) is seen to decrease unexpectedly as the network gets looser, while its peak-temperature decreases. This result is interpreted in terms of 'internal antiplasticization'. Moreover, we show that the important shift of the a-peak associated with the glass transition has an essentially entropic origin.

Structure and properties of amine‐hardened epoxy/benzoxazine hybrids: Effect of epoxy resin functionality

“…The inverse dependence of modulus on the degree of polymerization has been described as an indicator for internal antiplasticization, as well 26, 28, 42. Similar antiplasticizing effect (shift of β‐transition peak towards lower temperatures and lowering its intensity by an excess of epoxy prepolymer) has been attributed to the intermolecular hydrogen bonds between the unreacted epoxy groups and the relaxing units 30. One can conclude that all above‐mentioned effects are linked with changes in the network structure.…”

“…This is because of many factors that should be taken into account during interpretation. For example, size of relaxing groups,28 size and position of substituents, stereochemical microstructures, stoichiometry,29–31 curing procedure,32 hydrothermal and physical ageing,33, 34 additives (either plasticizers or antiplasticizers),25–27, 35 etc. can influence the position and intensity of β‐relaxation.…”