Synergistic reinforcement of foamed polyvinyl acetate with cellulose nanofibrils: mechanical and digital strain insights for plywood panel production

Abstract

The aim of this paper was to increase the interactions between wood layers by foaming polyvinyl acetate (PVA) and, thus, to obtain plywood panels with enhanced mechanical properties. Cellulose nanofibrils (CNFs) were also added to the PVA to improve the bonding quality. Woven glass fiber fabrics were laid between the wood layers to increase the flexibility of the resulting boards. Firstly, the morphological, thermal, and structural properties of CNFs and the foamed/un-foamed PVA reinforced with CNFs, and later, the bonding strength, flexural strength, flexural modulus, and strain analysis with digital correlation analysis (DIC) that occurred under tensile stress in the panels were conducted. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that the diameter of CNFs was changed from 25 nm to 35 nm. The foaming process and the adding CNFs improved the bonding strength of the plywood; however, both flexural strength and modulus generally decreased with the adding CNFs and foaming process, and the adding GF provided an improvement in the elongation in tensile and the deflection in the flexure. Digital image correlation (DIC) analysis revealed more strain distribution in the samples with foamed PVA with CNFs under mechanical loading.