Peel adhesion and viscoelasticity of poly(ethylene-co-vinyl acetate)-based hot melt adhesives. I. The effect of tackifier compatibility

A series of poly(ethylene-co-vinyl acetate) (EVA)-based hot melt adhesives containing either a rosin or a hydrocarbon (C5–C9) tackifier have been prepared to investigate viscoelastic properties and peel adhesion. Fracture energies were determined by the use of a T-Peel geometry (two polypropylene films bonded with model EVA adhesives). The rosin has only one glass transition temperature, but the C5–C9 resin has two glass transition temperatures, indicating phase separation. The rosin has better compatibility with EVA than does the C5–C9 resin. The bond strength of tackified EVA to polypropylene depends not only on compatibility, but also on viscoelastic properties. A higher storage modulus results in a higher T-Peel strength. Under certain test conditions, glassy C5–C9-rich domains act as reinforcing filler, resulting in a higher storage modulus. Here, a C5–C9-tackified EVA adhesive has higher T-Peel strength than does one containing rosin.