Synthesis and characterization of starch stabilized polyvinyl acetate-acrylic acid copolymer-based wood adhesive.

Exploitation of fossil fuels has resulted in the declination of petrochemicals, which catalysed chemical industries to search for substitute raw material sources. The major raw materials used in wood adhesives, such as hydrocarbons like vinyl acetate (VAc) and polyvinyl alcohol (PVA), would be gradually replaced by renewable natural polymers. Starch, being a naturally abundant polymer, has been explored in wood adhesives. However, starch grafted polyvinyl acetate (PVAc) emulsion-based adhesive has inferior properties, such as poor water resistance, weak adhesion. Hence, to mitigate the issues, emulsion polymerization of acrylic acid (AA) as a co-monomer in starch stabilized PVAc-based wood adhesives has been investigated. Further, the sample is formulated with PVA, plasticizer, and preservatives. It was observed that AA provided sites for cross-linking the chains via reaction of the acid group at acidic conditions. Various analyses were further carried to study the effects of addition of AA and aluminium nitrate on stability and water-resistance of starch stabilized emulsion. Differential scanning calorimetry result showed a substantial increase in glass transition temperature, with the addition of starch in the copolymer emulsion, which is also confirmed in film hardness testing. Reaction between acid group in the copolymer chains, the free hydroxyls of starch and PVA, and the added aluminium nitrate resulted in a cross-linked network structure. The adhesion properties were evaluated by measuring the tensile shear strength of wood joints in dry and wet conditions. The cross-linked adhesive with starch showed improved water resistance, mechanical properties, and stability, unlike PVA stabilized cross-linked wood adhesives. [ABSTRACT FROM AUTHOR]