High-Strength Binder-less Moldings Prepared by Reassembling Lignocellulosic Biomass Using Formic Acid

Lignocellulose is the most abundant renewable bioresource. We developed moldable lignocellulosic biomaterials without utilizing petroleum-derived polymeric resins and adhesives. Meals of Japanese cedar (Cryptomeria japonica), Eucalyptus globulus, and cotton linter were disintegrated by stirring in aqueous formic acid at a mild temperature (50 °C) for 1 week without any catalyst. Thereafter, distilled water was added to the obtained biomass mixture, and the resulting precipitates were collected, washed, and hot-pressed to obtain biomass moldings. The Fourier transform infrared spectra and composition analysis results of the moldings confirmed their formylation. The hydrophobicity test revealed that the contact angles of the water droplets on all of the moldings decreased owing to saponification-induced deformylation, and marked differences were observed in the hydrophobicities of the hardwood and softwood moldings. Further, the contact angle of the hardwood molding decreased much more slowly than those of the softwood moldings with and without saponification. Moreover, the saponification treatment revealed that the formylation of the biomass moldings increased the dimensional stability. Notably, the biomass moldings prepared from E. globulus without deformylation displayed the highest tensile and flexural strengths (43.19 and 86.43 MPa, respectively) as well as a flexural Young’s modulus (6.28 GPa), which was comparable to those of glass fiber-reinforced plastics.