Liquefied wheat straw as phenols for bio-based phenolic resins: Reaction parameters optimization and chemical routes

The value-added conversion of biomass materials is accepted as a promising approach to alleviate the energy crisis and promote green chemistry. This work aims to investigate the conversion process and chemical routes from liquefied wheat straw (LWS) to bio-based phenolic resins (BPFRs) and their potential opportunity as an alternative to petroleum-based asphalt binders. Response surface methodology (RSM) was introduced for the optimization of synthesis conditions, while the Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) were used to explore the chemical reactions during the conversion process and the morphological characteristics of resins. The feasibility of BPFRs application in asphalt binders was investigated based on rheological tests. The results demonstrate that the LWS is rich in phenolic compounds with reactive sites in para or ortho positions, which can replace petroleum-based phenol in the reaction with formaldehyde. Further, the produced intermediates, methylolphenols and bisphenol F, are subject to the condensation reaction to form BPFR molecules with about five phenolic nuclei. The connection between phenolic nuclei is dominated by para-methylene bridges (about 70%). The synthesis is suggested to be carried out at a molar ratio of phenol-to-formaldehyde of 0.75 without additional sulfuric acid , and the preferred polymerization temperature and time are 95 °C and 120 min. It should be noted that the reactivity of LWS is lower than that of petroleum-based phenol and may be accompanied by self-curing effects. Noticeable folds are observed on the surface of BPFRs. Encouragingly, acceptable compatibility and rutting resistance in the BPFR-asphalt system are identified. • Liquefied wheat straw can replace phenol in the synthesis of BPFRs. • The impact of F/P ratio, H 2 SO 4 dosage, temperature, and time is investigated. • Reaction parameters are optimized by response surface methodology. • The phenolic nuclei in BPFRs are mainly connected by para-methylene bridges. • The BPFR-asphalt system shows acceptable compatibility and rutting resistance.