In the present study, the thermal stability of non-oxidized polymer-modified binders in inert and oxidizing environments has been first systematically investigated using thermogravimetric and differential thermogravimetric analysis, including a quantitative assessment of kinetic and thermodynamic degradation parameters. The introduction of a 5 wt % SBS block copolymer has been found to significantly raise the degradation barrier of the binder: the activation energy of degradation increases from 142.8 to 172.6 kJ/mol. However, the process intensity increases and is accompanied by an increase in the frequency factor from 1.02 × 108 to 9.61 × 109 s–1 and activation entropy from –107.0 to –69.3 J mol–1 K–1, which is attributed to the formation of a spatial polymer matrix immobilizing low-molecular-weight components. Conversely, a plasticizer (vacuum gas oil) added in an amount of 10 wt.%, reduces the activation energy of degradation to 147.0 kJ/mol; however, the intensity of the process also falls; the frequency factor decreases to 1.44 × 108 s–1, and the activation entropy drops to –104.2 J mol–1 K–1 resulting in a decreased thermal stability due to the weakening of intermolecular interactions. A higher asphaltene content (by 1.5 wt %) contributes to a decrease in PMB (polymer-modified bitumen) thermal stability due to a limited compatibility with SBS: the activation energy is 170.1 kJ/mol, the frequency factor is 9.26 × 109 s–1, and the activation entropy is –69.6 J mol–1 K–1. In an oxidizing medium, degradation is a two-stage process: the first stage (370–490°C) proceeds with relatively low activation barriers (105–121 kJ/mol) and highly negative activation entropy (down to –159 J mol–1 K–1) due to orientation constraints of bimolecular oxidation reactions. The second stage (520–580°C) is oxidative gasification of high-carbon products and is characterized by sharply increased barriers (240–284 kJ/mol) and positive activation entropy (up to 43.7 J mol–1 K–1), ensuring high combustion intensity. The results of the study form a quantitative basis for the targeted management of the thermal stability and durability of unoxidized polymer-modified binders.
Akhmetzyanov et al. (Wed,) studied this question.