Valorizing cashew nutshell residue for sustainable lignocellulosic panels using a bio-based phenolic resin as a circular economy solution

The motivation for this study stems from the significant annual amount of cashew nutshells produced worldwide, which has raised growing concerns about proper environmental disposal. One alternative is to utilize the nutshells to produce particleboards and eco-friendly resin, thereby contributing to the circular economy. The present study proposes an innovation by providing the first insights into particleboard production, utilizing pressed cashew nutshell and a phenolic resin derived from the reaction of cashew nutshell liquid (CNSL) with formaldehyde. The mass proportions of CNSL to formaldehyde were varied at 1:0.25, 1:0.5, and 1:0.75 (w/w) without the necessity for isolating chemical compounds at 105 C. The resin was characterized using rheology, DSC, FTIR, HPLC, and NMR techniques. The mechanical properties of the particleboard were evaluated through density, tensile, flexural, water absorption, and thickness swelling tests. The formaldehyde emission and biodegradability content of the particleboards were also evaluated. Eco-friendly phenol -formaldehyde resin promoted the modulus of elasticity (MOE) from 707 to 1866 MPa and the modulus of rupture (MOR) from 6.4 to 14.3 MPa. In addition, using adhesive with CNSL to formaldehyde mass ratios of 1:0.25 and 1:0.50 resulted in particleboards of class E1 in terms of formaldehyde emissions. The biodegradability of panels PB25, PB50 and PB75 was 30%, 21% and 20%, respectively, in 30 days. These findings demonstrate the potential of cashew nutshell biomass and eco-friendly resin as an adhesive in the particleboard industry.