Bonding of wood with high strength and excellent water resistant cellulose colloidal adhesives

Development of a high-strength bio-based adhesive using simple, environment-friendly method is of great significance, as an alternative to petroleum-based adhesives. In this paper, Cellulose colloidal adhesives (CCA) with high stability and good reactivity were prepared by selective activation of microcrystalline cellulose (MCC) using sodium periodate under acidic conditions, with colloidal sizes ranging from nanometers to micrometers. CCA was applied to different types of veneer (poplar/beech/pine) to prepare 3-ply plywood. Compared to conventional activated cellulose adhesives, the CCA plywood showed excellent water resistance, dry/wet tensile shear strength of 3.7 MPa/1.6 MPa, met the requirements of Chinese national standards (GB/T 9846–2015). The excellent water resistance of CCA plywood was attributed to several factors. The colloidal particles filled the cell lumina of the wood, creating a mechanical interlocking effect. Additionally, CCA self-crosslinked to form stable intermolecular forces, the formation of cellulose nanocrystals by selective activation has an enhancing effect for CCA, while covalent and non-covalent bonds were established between CCA and the wood. Meanwhile, CCA has been shown to be universally applicable to cellulose extracted from various types of wood. This study realized the virtuous cycle of “from wood to wood”.