Fig. 1
From: High enthalpy storage thermoset network with giant stress and energy output in rubbery state
The stress and energy storage and recovery behavior. a The fully constrained stress recovery profile in rubbery state (recovered at 170 °C for 8 h; the glass transition zone is between 140 and 160 °C; see Supplementary Fig. 3) for a sample compression programmed with 45% pre-strain at a strain rate of 0.5 mm/mm/min and temperature of 170 °C. Detailed compression programming and fully constrained shape recovery test can be found in Supplementary Methods. The recovery stress in the rubbery state is about 17.87 MPa at 1.0 h, 17.0 MPa at 1.5 h, and 16.07 MPa at 8 h. b The relationship between the recovery stress and recovery strain (the recovery stress was taken at 1.5 h). The test procedure is given in Supplementary Methods. The free shape recovery ratio was 99.9%. The energy output, which is calculated based on the area of the recovery stress–strain curve, is about 2.12 MJ/m3. c The stepwise iso-strain programming profile. In order to elucidate the different modes for energy storage, step-wise iso-strain compression programming was conducted. In each step of loading, the strain increases; the stress then relaxes while holding the strain constant, which completes the one loading-relaxation cycle. In each step, the sample was compressed to 2% strain and then let it relax for 4 min. The detailed test procedure is shown in Supplementary Fig. 16 and the strain rate effect is illustrated in Supplementary Fig. 13. d The change of programming stress after relaxation, or stored stress, with programming strain. The stored stress increases as the programming strain increases, which suggests that more energy input leads to more energy storage, and thus higher recovery strain and higher recovery stress. The stored energy is calculated by the area of this relaxation stress–strain curve, which is 4.10 MJ/m3
