Gelation and Crystallization Phenomena in Polyethylene Plastomers Modified with Waxes

Abstract

Polyethylene (PE) plastomers, single-site catalyst-based homogeneous linear low-density PEs (LLDPEs), combine low crystallinity, softness, and elasticity, making them ideal candidates for numerous applications such as hot-melt adhesives (HMA). As plastomers crystallize rather slowly, a number of possible low molecular weight polyolefin components were tested to accelerate solidification. An ideal modifier should accelerate solidification while maintaining transparency and softness of the base polymer. A Queo plastomer type was modified with different PE and PP waxes at concentrations of 5 to 25 wt.-%. Next to conventional calorimetry, a rheological technique was applied to study solidification. The resulting morphology was studied by atomic force microscopy, and the final compositions were investigated regarding their mechanical and optical performance. Accelerated solidification was observed in all cases, but a quite different course of structure formation could be concluded. PE waxes dissolve in the melt state, forming a lamellar network during cooling, whereas PP waxes form a heterogeneous blend in the melt for which the wax droplets solidify before the matrix. The particulate-type modification by the PP wax also affects stiffness less while retaining transparency better.