The Effect of SGA Phase Structure on Adhesive Joint Strength and Physical Properties of Bulk Specimens

Abstract

Second-generation acrylic adhesives（SGA）exhibit cohesive failure during fracture testing, making them easy to design for bonding and suitable for use in a wide range of products. At the same time, because they undergo phase separation into a hard phase and a soft phase during curing, thereby exhibiting both strength and ductility, they serve as an excellent subject for research as a unique polymer. In this study, we investigated the tensile properties and adhesive properties of two types of second-generation acrylic adhesives（SGA）that share the same main components but differ in reaction rate. The slow-reacting SGA exhibited a higher elastic modulus and resin strength than the fast-reacting SGA, but its elongation at break was lower. Furthermore, in butt-joint adhesion tests, the slow-reacting SGA demonstrated higher adhesive strength. Observation of the fracture surface revealed that the slow-reacting SGA formed a phase structure containing larger acrylic aggregates, measuring tens of micrometers. Furthermore, TEM observations indicated that the slow-reacting SGA exhibited smaller acrylic phases within the matrix resin. Analysis of the elastic modulus distribution using AFM revealed that the fast-reacting SGA exhibited a large difference between low-modulus and high-modulus phases, making it prone to phase separation. A phase structure model that accounts for the curing process successfully explained the differences in mechanical properties.