Abstract
Tri-block copolymer styrene–butadiene (SBS) is extensively applied in bituminous highway construction due to its high elasticity and excellent weather resistance. With the extension of time, tri-block structural SBS automatically degrades into bi-block structural SB- with some terminal oxygen-containing groups under the comprehensive effects of light, heat, oxygen, etc. In this paper, the effects of aging temperature, aging time and oxygen concentration on the molecular structure of thermo-oxidative aged SBS were mainly investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and the correlation between oxygen-containing groups and thermal properties (TG–DTG) was further discussed. The FTIR and XPS results show that rapid decomposition of SBS will occur with increments of aging temperature, aging time and oxygen concentration, and a large number of oxygen-containing groups such as –OH, C=O, –COOH, etc. will be formed during thermo-oxidative aging. In short-term aging, changes in aging temperature and oxygen concentration have a significant impact on the structural damage of SBS. However, in long-term aging, it has no further effect on the molecular structure of SBS or on increasing oxygen concentration. The TG and DTG results indicate that the concentration of substances with low molecular weight gradually increases with the improvement of the degree of aging of the SBS, while the initial decomposition rate increases at the beginning of thermal weightlessness and the decomposition rate slows down in comparison with neat SBS. From the relation between the XPS and TG results, it can be seen that the initial thermal stability of SBS rapidly reduces as the relative concentration of the oxygen-containing groups accumulates around 3%, while the maximum decomposition temperature slowly decreases when the relative concentration of the oxygen-containing groups is more than 3%, due to the difficult damage to strong bonds on the molecular structure of aged SBS.
Highlights
Tri-block copolymer poly (SBS) has been widely applied in modified bitumen materials due to its excellent physical and mechanical properties [1,2,3,4,5,6]
Despite all this, the molecular structure will still suffer from the destruction from the outside environment no matter whether SBS exists in bitumen or not, as temperature, ultraviolet radiation and oxygen are major determinants leading to its structural failure [9,10,11,12,13]
SBS-modified bitumen will be increasingly produced to the performance failure
Summary
Tri-block copolymer poly (styrene-b-butadiene-b-styrene) (SBS) has been widely applied in modified bitumen materials due to its excellent physical and mechanical properties [1,2,3,4,5,6]. It plays a vital role in improving the high and low temperatures of modified bitumen because of its unique molecular structure [7,8]. Amounts of waste SBS-modified bitumen will be due increasingly produced deterioration of SBS after a long period of use [14,15,16,17,18,19,20,21].
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