Research on epoxy resin decomposition under microwave heating by using ReaxFF molecular dynamics simulations

Abstract

To investigate the effects of microwave heating on decomposing epoxy resin, ReaxFF molecular dynamics simulations are performed. As one of its special effects, the thermal runaway phenomenon is studied and compared under microwave heating and under conventional heating. This study shows that this phenomenon results from the enhancement of system absorption of microwave energy, which is caused by the increasing number of small size polar species generated during the pyrolysis of epoxy resin under microwave heating. Meanwhile, non-thermal effects are investigated under microwave heating.Simulations indicate that, at the early stage of decomposition, average generating rates of H 2 O and H 2 obtained under microwave heating are always, or partly, lower than that obtained under conventional heating. To analyze the influence of microwave heating on reaction rates, collision theory is introduced.Further, several simplified collision models are constructed and formulated to study the effectiveness of collision orientations under microwave heating. Analyses illustrate that external microwave heating reduces the effectiveness of collision orientations between polar hydric fragments as well as hydroxyl radicals and polar hydric fragments, thus, decreasing relevant reaction rates.

Theoretical Study on Decomposition Mechanism of Insulating Epoxy Resin Cured by Anhydride

“…The first gas product was found to be CH 2 O, and other main small-molecule products include H 2 O, CO, and H 2 [ 29 ]. Zhang et al simulated the decomposition process of epoxy resin heated by microwave by using ReaxFF, and they investigated the factors influencing the H 2 O and H 2 production rates [ 30 ].…”

High Temperature Pyrolysis of Toluene under Electromagnetic Fields at Different Frequencies

“…As mentioned above, the higher phase lag between the rotation of dipole moment and external E -field would result in less control of microwave to the rotation performance of the dipole . It is logical to deduce that the influence of EM field on pyrolysis of toluene would have an upper limit at a certain frequency, at this case of 100 GHz.…”

“…Notice that the higher phase lag between the rotation of dipole moment and external E-fields would lead to less control of microwave to the rotation performance of the dipole. 60 Since the phase lag rises along with the increasing of EM field frequency shown in Table 3, it should be reasonable that the heating ability of microwaves at a very high frequency on a toluene system would reach the ceiling. Arrhenius Analysis.…”

“…It is concluded that lower frequency brings smaller intrinsic friction, at least for the frequency range of 50–200 GHz, finally leading to less energy absorbed from EM fields within a same irradiation time. Notice that the higher phase lag between the rotation of dipole moment and external E -fields would lead to less control of microwave to the rotation performance of the dipole . Since the phase lag rises along with the increasing of EM field frequency shown in Table , it should be reasonable that the heating ability of microwaves at a very high frequency on a toluene system would reach the ceiling.…”

“…As studied in ref , during the pyrolysis of epoxy resin, introducing the microwave would affect the orientation performance of hydrogenous polar fragments, leading to decline the collision orientation factor on the process of forming hydrogen gas based on collision models. Consequently, based on the collision models in ref , it can be concluded that external EM field reduces the collision orientation factor of toluene decayed and hydrogen gas formed, resulting in a decline of the pre-exponential factor, and also leading to the promotion of relevant activation energy as shown in Figure a and c. As for the pre-exponential factor, it is mainly constrained by the collision frequency and collision orientation. Research on the influence of microwave heating on the hydrothermal treatment indicated that external microwave could increase the collision cross-section between polar fragments, due to the interactive collision caused by the rotation of dipoles under microwave irradiation.…”