Full-Component Valorization of Corncob by Enzymatic Production of Fermentable Sugars and Synthesis of Lignin-Based Phenolic Formaldehyde Adhesives

Corncob, a common agricultural waste, is often directly burned for heating, leading to environmental concerns. In this study, corncobs were used as a raw material to produce fermentable sugars for biofuel production. Moreover, a green valorization route was established to convert enzymatic hydrolysis lignin (EHL), the solid byproduct of hydrolysis, into lignin-based phenol-formaldehyde adhesives (LPFA). Specifically, the corncob was pretreated with diluted acid and subsequently subjected to enzymatic hydrolysis at 50 °C for 72 h, yielding fermentable sugars and EHL. The enzymatic hydrolysis achieved an efficiency of 75% at a cellulase loading of 10 FPU/g. To enhance its reactivity, the EHL was modified via phenolation. The resulting LPFA, synthesized using phenolated EHL as the raw material, exhibited a maximum bond strength of 3.0 MPa, well above the standard requirement of 0.7 MPa (following ASTM D5868-01). Additionally, the contents of free phenol content and free formaldehyde in the LPFA were 0.19 and 0.15%, respectively, both of which comply with industrial safety limits (<1.0 and <0.3%). This work demonstrates the comprehensive valorization of the corncob by integrating enzymatic saccharification and adhesive synthesis, providing a sustainable strategy for the utilization of agricultural waste.