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Four different approaches were taken to improve the water resistance of poly(vinyl acetate) (PVAc) emulsion adhesives. The improved wood adhesives were tested according to the ISO 9020 standard. Tensile storage modulus (E’) and glass transition temperature of the polymer films were measured using dynamic mechanical thermal analysis to quantify the influence of different approaches on those variables. Gel fraction and swelling ratio of the polymer film were measured to evaluate internal crosslink density. The experimental results showed that blending melamine/urea/formaldehyde (MUF) resin with PVAc emulsions modified the water resistance considerably and the film had a high E’ since an interpenetrating network‐type structure was formed in the polymer. The advantages and limitations of each modification were assessed on the basis of comparison of the results.

Fillers with different chemical properties were used to study their effects on poly(vinyl acetate) (PVAc) emulsion wood adhesives. The elastoplastic behaviour of the filler treated PVAc emulsions was studied using differential scanning calorimetry and dynamic mechanical thermal analysis. The results show that the glass transition temperature (T_g) of the polymer is not changed significantly by the addition of the fillers, while the tensile modulus is changed together with the hardness and stiffness. The viscosity of the emulsions and their performance on wood surfaces are greatly affected by fillers. Fillers with high oil‐absorption capacity increase viscosity to a greater extent. The acidity of the fillers influences the setting time for bonding of the emulsions to wood, and the water resistance, since some chemical reactions can take place during curing.

Poly (vinyl acetate)‐based emulsion polymer/isocyanates (EPI) structural wood adhesives were prepared and their performance benchmark tested according to the specifications of the Japanese JAS‐111 standard. The changes of the glass transition temperature of the cured emulsions relative to unmodified poly(vinyl acetate) emulsion, measured using differential scanning calorimetry, indicated the chemical structure changes resulting from modification of poly(vinyl acetate) emulsion. The EPI adhesives showed excellent water resistance and near‐colourless gluelines in wood joints, ease of application and additional significant advantages over other types of wood adhesives. The performance test results are interpreted on the basis of the viscoelastic behaviour of free‐standing adhesive films. Other types of crosslinkers were used in the study to compare with the isocyanate hardeners.