Crosslinkable poly(vinyl acetate) emulsions for wood adhesive

Abstract

Purpose

The purpose of this paper is to enhance the water resistance and the heat resistance of poly(vinyl acetate) (PVAc) emulsion adhesive, by providing the emulsion with controllable thermosetting capability.

Design/methodology/approach

Emulsion polymerisation was used to synthesise PVAc/VeoVa 10 copolymers with varying proportions of acetoacetoxyethyl methacrylate (AAEM) incorporated in the copolymer chains. The AAEM component provided sites for crosslinking the chains via reaction of diamines with AAEM. The emulsion copolymers formed crosslinked films on addition of a range of diamines, during drying at ambient temperature. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy were employed to characterise the copolymerisation and crosslinking reaction. Glass transition temperatures of the polymer films were measured using dynamic mechanical thermal analysis to quantify the effects of copolymer composition variation and crosslinker. The performance of the crosslinked emulsions as wood adhesives was evaluated in accordance with the ISO 6238 standard by measuring the maximum shear stress of wood joints.

Findings

The crosslinking reaction between acetoacetoxy groups in the copolymer chains and the added diamines gives enamine structures, and occurs rapidly at ambient temperature. Major changes in the ¹³C NMR spectrum include the appearance of an enamine signal at 82 ppm, and disappearance of the acetoacetoxy carbonyl signal at 202 ppm. The new vibrational band at 1,597‐1,606 cm⁻¹ in the FTIR spectrum is assigned to the vibrations of the enamine double bond. The experimental results showed substantial increases in T_g and viscosity as the AAEM proportion in the copolymer emulsion increased. The crosslinked adhesives showed superior wood adhesive performance to unmodified PVAc emulsion.

Research limitations/implications

It was necessary to adjust the pH of the emulsion for extended shelf life.

Practical implications

The method developed provides a simple and practical route to emulsions with improved water and heat resistance and bonding strength.

Originality/value

The method for enhanced water and heat resistance of PVAc wood adhesive was novel, straightforward and environmental friendly.

Citation

Lu, J., Easteal, A.J. and Edmonds, N.R. (2011), "Crosslinkable poly(vinyl acetate) emulsions for wood adhesive", Pigment & Resin Technology, Vol. 40 No. 3, pp. 161-168. https://doi.org/10.1108/03699421111130423