Multiscale Creep Compliance of Epoxy Networks at Elevated Temperatures

Abstract

Epoxy networks are thermoset polymers for which an important structural length scale, molecular weight between crosslinks (M c ), influences physical and mechanical properties. In the present work, creep compliance was measured for three aliphatic epoxy networks of differing M c using both macroscale torsion and microscale depth-sensing indentation at temperatures of 25 and 55-C. Analytical relations were used to compute creep compliance (J(t)) for each approach; similar results were observed for the two techniques at 25-C, but not at 55-C. Although creep compliance measurement differed at elevated temperatures, there were clear correlations between M c , glass transition temperature, T g , and the observed time-dependent mechanical behavior via both techniques at 55-C, but these correlations could not be seen at 25-C. This work demonstrates the capacity of depth-sensing indentation to differentiate among epoxy networks of differing structural configurations via J(t) for small material volumes at elevated temperatures.

Creep Mechanics of Epoxy Vitrimer Materials

“…This regime is stress-controlled and is clearly seen in all samples, regardless of the catalyst concentration and temperature for T > T g ; however, primary creep is seen to last longer and is more readily discernible for samples at T ≪ T v . Similar power law dependencies between creep strain and time have been previously reported for the creep response of epoxy adhesives and other polymers. ,,,,,,,, …”

“…For example, at a temperature of 100 °C ( T ≪ T v ), the material’s creep response is almost identical, regardless of the catalyst concentration, and merely behaves like a traditional epoxy (cf. Figure b). ,,− ,, This behavior indicates a lack of transesterification reactions taking place on the time scale of the experiment. In contrast, at 200 °C ( T ∼ T v for a 5 mol % sample), the creep response is directly related to the catalyst concentration (cf.…”

“…Figure 3b). 4,6,[37][38][39][40]44,47 This behavior indicates a lack of transesterification reactions taking place on the time scale of the experiment. In contrast, at 200 °C (T ∼ T v for a 5 mol % sample), 24 the creep response is directly related to the catalyst concentration (cf.…”

“…Similar power law dependencies between creep strain and time have been previously reported for the creep response of epoxy adhesives and other polymers. 2,4,22,32,37,39,40,44,45 Primary creep depends on the slack of the polymer chains when all samples are tested at T > T g . We postulate that the primary creep regime corresponds to the conformational freedom of the polymer chains relative to each other before a percolated path of loaded crosslinks emerges.…”

Connection between dynamic mechanical properties and sliding wear resistance of polymers

“…Another useful technique of surface evaluation is the nanoindentation creep which can be connected to glass transition temperatures of polymers. [32][33][34][35] …”