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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.

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.

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.

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.

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

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

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

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.

Modifications of poly(vinyl alcohol) (PVA) can improve the properties and performance of poly(vinyl acetate) (PVAc) emulsions stabilized with these modified colloids. Water resistance and toughness of the emulsions as wood adhesives can be achieved through chemical reactions of the hydroxy groups of the colloid with various modifiers. The chemical changes can be carried out either in the preparation of PVA through hydrolysis of copolymers of vinyl acetate and other monomers, or by the reaction of modifiers with PVA aqueous solutions. The modified PVAc emulsions show better properties than those of the conventional emulsions in performance tests and applications. The modified colloids are becoming increasingly used in the manufacture of PVAc emulsions in the adhesive industry, because of their advantages over emulsions made using conventional (unmodified) PVA. The trend of current research is to introduce more functionality into the colloid, so that the traditional protective colloids can be modified to function as crosslinkers and chain transfer agents.

Various modifications of polyvinyl acetate emulsion wood adhesive were made and their performance evaluated in standard tests. The results are interpreted in the context of adhesion theories and the chemical structures of the polymers and wood. The adhesion of the polymers to wood and the cohesive strength of the polymers are the two predominant factors determining the performance of the adhesives. Adhesive strength in thermosetting resins is enhanced by irreversible chemical reactions that create extensive networks within the adhesive layer and strong bonds to the wood substrate, leading to strong and durable joints that passed all of the performance evaluation tests. Most of the PVAc emulsions exhibited good adhesive performance in the dry state, but failed in water soak and boiling water immersion tests since their adhesion and cohesion are mainly based on weaker physical interactions. Emulsions with (hard) core‐(soft) shell morphology and correspondingly high glass transition temperatures gave poor performance under all conditions.