Preparation and Improvement of Shear Strength of a Water-Redispersible Waterborne Acrylic Adhesive for Making Cellulose Joints

 In recent years, many attempts have been devoted to industrial usage of bio-based adhesives, as a result of fossil resources shortage and unusual increase in oil-based products prices. Adhesion strength of this category of adhesives, however, needs improvement. In the current study, lap-shear strength of joints made of a natural polymer, Persian gum (PG), exuded from wild almond tree, and three various substrates, glass, poly(ethylene terephthalate), and cellulose fabric, was investigated. Furthermore, in order to prepare powder acrylic adhesive and evaluate its adhesion to aforementioned substrates, the gum dispersion was blended with synthesized poly(methyl methacrylate-co-butyl acrylate) random copolymer containing 30 wt.% methyl methacrylate (MBC30). Molecular interactions in PG, MBC30, and 50 wt. % PG-containing blend were characterized by Fourier transform infrared spectroscopy. Moreover, morphology of blends containing various amounts of PG was evaluated using scanning electron microscopy of their fractured cross sections.
Main The textile joint made with PG dispersion in water showed high shear strength of about 340 kPa. However, PG could not form a suitable joint with glass and polyester substrates, as a consequence of its inability to form a homogeneous film, excessive brittleness, and its inability to diffuse and mechanically interlock with the substrates. Results showed that using an adhesive system containing 50/50 PG/MBC30, besides enabling preparation of powder adhesive, shear strength increased to 20, 11, and 14-fold with respect to pristine MBC30 on glass, poly(ethylene terephthalate), and textile substrates, respectively. In other words, shear strength of an adhesive could be improved by promoting the adhesive constituents interactions and subsequent increase in the blend cohesiveness, on the one hand, and increment of its adhesion to substrate, on the other hand. In the current research, Persian gum was introduced as a water-redispersing agent for acrylic pressure-sensitive adhesives and new adhesive systems were invented with usability in cellulose industry.