Peel adhesion and viscoelasticity of poly(ethylene-co-vinyl acetate)-based hot melt adhesives .1. 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. (C) 1997 John Wiley & Sons, Inc.