Improving performance of polyvinyl acetate (PVA) as a binder for wood by combination with melamine based adhesives

Abstract

In this study blending PVA with MUF and MF was evaluated as an approach to enhance the performance of PVA towards water and elevated temperatures. MF and MUF were added to PVA at different proportions: 15%, 30%, 50%, 70% and 100%. Blends of PVA with MF and MUF were used as adhesives to bond wood joints. The shear strength of wood joints was measured at dry and wet states, and elevated temperatures. Thermogravimetric analysis was used to study thermal stability of PVA and its blends with MF and MUF. The structural changes caused by the inclusions were characterized by Fourier transforms infrared spectroscopy (FT-IR). The results showed that shear strength of wood joints were improved by the addition of MF and MUF to PVA in all conditions. Adding small amounts of MUF or MF (as low as 15%) enhanced the performance of wood joints towards water and elevated temperatures. The extent of improvement was sometimes so high that the strength of glue line surpassed strength of wood in wet conditions leading to wood failure rather than glue failure. MF had more effectiveness in improving shear strength of wood joints than MUF in all conditions. Thermal stability of PVA was increased by MF but the effect of MUF on thermal stability of PVA was dependent on MUF proportions and temperatures. FT-IR analyses showed that there are some chemical bonds between PVA and MF. Considering costs, effectiveness and formaldehyde emission, adding 15% MF to PVA seems the optimal proportion of MF in the PVA blends.