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This study reports the use of deep‐eutectic‐solvent‐ (DES‐) assisted hydrothermal carbonization (HTC) to disrupt the floc structure of sewage sludge (SS) for deep carbonization, with the resulting hydrochars employed in the preparation of formaldehyde‐free plywood bioadhesives. Sewage‐sludge‐based bioadhesive exhibits an excellent wet shear strength, complying with the requirements of Chinese national standard GB/T 9846–2015 (≥0.7 MPa). The molecular weight of proteins and the formation of covalent bonds via dehydration have a notable role in improving adhesive performance (wet shear strength). The Maillard reaction is a key reaction during HTC to destroy the secondary structure of proteins, resulting in the release of more OH and NH2. The main reaction during hot‐press treatment is dehydration. High ash content in bioadhesives improves flame resistance potential, particularly on addition of DES. A plausible mechanism is proposed for this. This work provides a new method for the valorization of SS‐derived hydrochars and contributes to the development of greener formaldehyde‐free wood bioadhesives. [ABSTRACT FROM AUTHOR]

Abstract: Bio-oils obtained from liquefaction/pyrolysis of biomass have undesired properties such as high water content (15–25wt.%), high oxygen content (low heating value), high corrosiveness (acidity) and instability. Therefore, they cannot be directly adopted for fuel applications. Solubilizing bio-oil in diesel by microemulsion technology is one of the most convenient approaches for further upgrading bio-oil. In this work, a synthetic bio-oil was prepared to overcome the limitation posed by complex nature and instability of crude bio-oil. Effects of several microemulsion parameters on the solubilization capacity of bio-oil in diesel were evaluated, including initial bio-oil/diesel volume ratio (B/D ratio), surfactant concentration (Span80), cosurfactant type (n-butanol, n-pentanol, n-hexanol, n-heptanol and n-octanol) and the mass ratio of cosurfactant/surfactant (C/S ratio). The optimum bio-oil/diesel volume ratio was 5:5. The proper concentration of Span80 was 0.36M. N-octanol was certified as an ideal cosurfactant. A proper C/S ratio of 0.40 was suggested. Meanwhile, fuel properties of bio-oil/diesel microemulsion were examined, including heating value, density, kinematic viscosity, cloud point, pour point, water content, corrosivity and stability. Elemental analysis and thermogravimetric analysis of bio-oil/diesel microemulsion were conducted. Compared with the original synthetic bio-oil, the bio-oil/diesel microemulsion had more desirable fuel properties close to diesel. [Copyright &y& Elsevier]