| Series of poly(ethylene-co-vinylacetate) based hot melt adhesives containing either a rosin or a C5-C9 resin tackifier have been prepared to investigate the relationship of composition and viscoelastic properties to T-Peel strength. The rosin is fully compatible with the EVA at concentrations lower than 30 wt%, while the C5-C9 resin appears to be fully compatible only at very low concentrations. EVA/rosin blends have higher melt viscosities than EVA/resin blends. Complex melt viscosities can be shifted to form a mastercurve, indicating homogeneous melts are formed. Melts of lower viscosity require a shorter time to reach equilibrium T-Peel strength. The bond strength of tackified EVA to polypropylene depends not only on compatibility but also the viscoelastic properties of the blends. Higher storage moduli give higher T-Peel strength. Wax has little effect on the Tg of EVA-tackifier blends; moreover, wax increases the concentration of the EVA-rich phase in the heterogeneous blends. T-Peel fracture energies of EVA/tackifier/wax blends bonded to PP film are controlled by two factors: (i) a wax weak boundary layer that has a deleterious effect on bonding, and (ii) on the other hand, an increased rubbery response in the stick-slip region that strengthens joints. |
