A new approach to estimate the curing mode of thermosetting polymer films with regard to physical aging and slow chemical processesстатья
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Дата последнего поиска статьи во внешних источниках: 17 июня 2020 г.
Аннотация:We propose an original method to determine the temperature and time required for additional curing of physically aged partially cured glass-shaped systems, based on the example of epoxy amine systems. The approach consists of the plotting of temperature–time–transformation (TTT) diagrams, sup- plemented with lines, which illustrate the shift in glass transition temperature (Tg) as a result of the processes of physical aging (enthalpy relaxation) and with isoconversion curves. Then we should determine Tg of partially cured and aged sample at a certain temperature. Having known this Tg value, the posi- tion of the isoconversion curve at a given point and Tg,∞ as well, we can deter- mine the postcuring time at T = Tg,∞ + 5 K. Thus, the method provides information about the temperatures and the duration of these two consecutive steps. The TTT diagrams are based on experimental results obtained by differ- ential scanning calorimetry in dynamic mode with preliminary heated samples in an external thermostat. The proposed approach based on epoxy amine sys- tems allows the prediction of the optimal curing mode for thermosetting sys- tems to provide the highest degree of cure. Our method is applicable to a wide range of thermosetting polymer systems that complete transition to a glassy state before full conversion is achieved.