Chemical grafting of waste polystyrene with acrylic acid and subsequent amine functionalization to enhance polystyrene modified bitumen characteristics

The rigid polystyrene (PS) waste could be an alternative bitumen modifier, which brings great economic and environmental efficiency. However, because of low polarity and high rigidity nature of PS, it sometimes poses some difficulties in compatibility, elasticity, and storage stability. To address these limitations, the present study proposed an alternative chemical modification method for waste polystyrene through grafting with acrylic acid followed by a reaction with diethylenetriamine to produce PS-g-AM. Functionalized groups of the polymer were confirmed by performing FT-IR and 1 H-NMR spectroscopy which approved that PS-g-AM was successfully synthesized and identified. The synthesized PS - g-AM was mixed with bitumen with percentages of 3, 5, 7 and 10wt% from total binder weight. A multi-scale correlation between microscopic mechanisms and macroscopic performance is integrated. The microscopic characterization including FTIR and AFM techniques were performed and successfully verified the good compatibility via hydrogen bonding interaction between PS-g-AM and bitumen. Also, the macroscopic characterization including storage stability, and elastic recovery test demonstrated that the prepared PS-g-AM modified binders (7wt%) showed significantly a high storage stability (≤ 0.3), and better elastic recovery (55%) compared to untreated PS modifier (2.5), and (25%) respectively. The dynamic mechanical properties are also studied and the results revealed a considerable improvement in rutting resistance (G/sin δ) PG degree increased from 70 to 76, tan δ reduction. In summary, results confirmed that chemical grafting turned PS from a hardening agent to an efficient elastic modifier into asphalt and provided great opportunity for a high-performance sustainable method of modifying the asphalt.