Seawater pretreatment of hemp fibres using microwave-assisted chemical-free methods: An eco-friendly and cost-effective approach

The traditional pretreatment methods for lignocellulosic biomasses are often harsh, prolonged, energy-intensive, and environmentally unfriendly. This study investigated the effectiveness and mechanism of microwave-assisted seawater pretreatment without using any chemicals. The proposed pretreatment method significantly removed lignin (77.0 % similar to 77.3 %) and hemicellulose (47.3 % similar to 48.9 %) in hemp fibres even after five cycles of seawater. This process yielded cellulose fibres with remarkable fineness (4.8 dtex) and enhanced tenacity (4.0 cN/dtex), which meet the requirement for textile application. Additionally, the pretreatment led to an impressive 44.2 % increase in glucose yield after enzymatic saccharification. The HSQC NMR analysis indicated that the pretreatment induced structural changes in lignin, facilitating its efficient removal. Further investigation into the effects of individual seawater salts on the pretreatment process revealed that certain salts, particularly FeCl3, NaCl, and KBr, exhibited exceptional lignin removal capabilities. Moreover, NaCl and FeCl3 demonstrated impressive hemicellulose removal rates. The findings highlight the potential of seawater as a highly efficacious, eco-friendly, time-efficient, energy-efficient, and cost-effective alternative to conventional pretreatment methods.