Extrusion coating performances of PP/LDPE blends

Abstract

The performance of PP/LDPE blends in extrusion coating process was investigated in the terms of neck-in and draw-down ability. It is well known that PP alone is not proper because of lower draw-down ability with severe draw resonance in elongational flow. In order to obtain high draw-down ability, PP was blended with LDPE. Strain hardening behaviors was found to be a crucial condition in good extrusion coating performance by blending with LDPE which has long chain branches in our studies. First, PPs having different molecular weight distribution (MWD) were used in this study in order to find out the effect of MWD of PP on neck-in and draw-down ability. To obtain different MWD PP, controlled rheology technique using peroxide was used. It was observed that PP/LDPE blend with narrower MWD exhibits higher draw-down ability with a comparable neck-in value in high draw down ratio. Neck-in and draw-down ability were correlated with shear and elongational properties obtained by several rheological measurements. It is supposed that neck-in is affected mainly by elasticity and shear viscosity in low frequency, and high draw-down ability is affected by low melt strength and strong strain hardening behavior. It is believed that high molecular weight chains of PP in PP/LDPE blend mainly affect to the different result of extrusion coating performance with different MWD. Second, the effect of type of PP on extrusion coating performances was also investigated. Two types of homo PP and two types of random PP having different composition and crystallinity were used as a base PP. They were also treated with same degree of degradation by peroxide to fit the proper MFR for extrusion coating process. PP/LDPE blend incorporated with high comonomer shows high draw-down ability. Neck-in values of four different PP/LDPE blends does not exhibit the dependency on type of PP. From our investigation with several measurements, it is supposed that incorporation with high comonomer affects...