Satoshi Anzai

Most research on Nanobubble Water (NBW) for lignocellulose conversion has focused on anaerobic digestion, with relatively few studies examining direct pretreatment methods such as liquefaction. In this study, we explored the potential of NBW as a pretreatment method for bagasse meal liquefaction. Bagasse meal was treated with oxygen, nitrogen, and carbon dioxide NBW. Changes in component composition ratio, crystallinity, total crystallinity index (TCI), lateral order index (LOI), pyrolysis peak temperature (T_max), and apparent activation energy (E_a′) were investigated. For the liquefaction process, changes in residue content, apparent liquefaction reaction rate constant (k′), average molecular weight, hydroxyl value, functional group information, and T_max of the liquefied residue were examined. Results showed a 2.0–3.0% decrease in cellulose and a 1.0–4.0% decrease in lignin. Crystallinity increased by 5.8–12%, TCI decreased by 6.7–13%, and LOI increased by 4.7–9.8%. T_max decreased by 1.6–3.5 °C, and E_a′ decreased by 1.9–2.8%, both reaching their lowest values with carbon dioxide NBW. At this time, the residue content decreased by 6.3–19%, and k′ increased by 50%. These findings indicate that NBW pretreatment is a promising approach for liquefying bagasse meal under laboratory conditions. Future investigations will be directed towards its scalability and economic viability.

Recycled carbon fibres frequently exhibit degraded surface functionality owing to prior matrix removal processes, limiting their compatibility with contemporary epoxy resin systems. This study proposes a nanobubble-based surface treatment route designed to restore and enhance the surface characteristics of recycled carbon fibres without aggressive chemical oxidation. The study generated ozone and carbon dioxide nanobubbles in aqueous media and experimentally investigated the effects of nanobubble treatment on the surface properties and adhesive behaviour of recycled carbon fibres. Surface chemical changes were examined using X-ray photoelectron spectroscopy, which revealed an increase in oxygen-containing functional groups due to the nanobubble treatment, indicating improved surface polarity and potential for chemical interaction with epoxy networks. The practical effectiveness of the treatment was assessed via a pinhole pull-out test that served as an indirect measure of interfacial adhesion with epoxy resin, especially the combination of ozone nanobubbles and recycled carbon fibres. Notably, the nanobubble-treated recycled carbon fibres exhibited an increase in the adhesion compared with untreated recycled carbon fibres, rising from 84.5 ± 11.5 MPa to 138.5 ± 14.8 MPa, reflecting enhanced wetting behaviour and stronger fibre–matrix interfacial bonding. Overall, the proposed nanobubble processing route offers a mild, scalable, and environmentally favourable method for restoring surface reactivity in recycled carbon fibres, supporting their reintegration into high-performance composite applications.