Thermal and kinetic studies of epoxidized natural rubber in lithium salts-epoxidized natural rubber polymer electrolytes

摘要

The thermal and kinetic studies of epoxidized natural rubber (ENR) and its polymer electrolytes, LiX/ENR PEs, (where X = ClO_4~-, CF_3SO_3~-, COOCF_3~-, I~-, and BF_4~-) were carried out using thermogravimetric analysis at different heating rates. The thermal behaviors for LiX/ENRPEs are closely related to the morphology and interactions between the LiX and ENR chains. The LiCF_3SO_3, LiCOOCF_3, and LiI form pseudo-crosslinking within the ENR; their thermal behavior resembled purified ENR. The LiClO_4 tends to form aggregates within the ENR. This phenomenon has promoted a much earlier decomposition of epoxide in the ENR. The occurrence of ring-opening and complexation or cross-linking reactions in and between the ENR chains in the LiBF4/ENR has produced a thermally stable macrostructure. The activation energy for the thermal degradation (E_d) of purified ENR was 239.8 and 239.9 kJ mol~(-1) using Kissinger and FWO methods, respectively. According to the Coats–Redfern method, the degradation mechanism of purified ENR follows the F_1 type model, while the Criado method revealed that the degradation starts with F_1 followed by D_3 type models. The E_d for LiX/ENR (X = COOCF_3~-, CF_3SO_3~-, I~-, and BF_4~-) PE’s obtained via the Kissinger method are 258.5, 257.0, 251.0, and 198.9 kJ mol~(-1), respectively, and the corresponding Ed values obtained by FWO are 236.0, 223.6, 349.7, and 206.6 kJ mol~(-1), respectively. The degradation of ENR in these PEs followed the D_3 type model. However, for LiClO_4/ENR, the presence of two distinct degradations of ENR gave two E_d values. These are 174.5 and 234.7 kJ mol~(-1) using Kissinger and 117.8 and 293.6 kJ mol~(-1) using FWO method. The degradation mechanism of ENR in the LiClO_4/ENR PE was similar to purified ENR that is F_1 followed by D_3 type models.