Adhesion between polyethylenes and different types of polypropylenes

Abstract

To understand the effect of processing and co-monomer content on interfacial adhesion, we quantified adhesion levels of bilayers of a polyethylene (PE) with various polypropylenes (PPs) prepared using bilayer co-extrusion and lamination processes. We tested adhesion between a medium-density PE (MDPE) with different types of PPs, including impact-modified PP (with various amount of ethylene), isotactic PP and ethylene-propylene random copolymers. Increasing the concentration of ethylene or ethylene-propylene rubber gave rise to increased adhesion. The impact-modified PP with 20 wt% ethylene content exhibited adhesion with MDPE almost two orders of magnitude higher compared with other PPs. Although lamination and co-extrusion processes showed good agreement in these trends with ethylene content, the operation parameters are critical for adhesion control. For lamination, ice-water cooling generated a stronger adhesion than that with air cooling. Faster cooling rates in co-extrusion also gave rise to stronger adhesion. Increasing draw down ratio and varying flow rate to put the interface near the wall resulted in stronger adhesion. Fast quenching rate and increased crystallinity induced by drawing down are believed to be the causes. Both atomic force microscopy and transmission electron microscopic images exhibited roughened interfaces for samples with strong adhesion. Keywords: adhesion; crystallization; extrusion; interface; polyethylene; polypropylene INTRODUCTION Polyethylene (PE) and isotactic polypropylene (iPP) are the first and second highest-volume thermoplastics based on worldwide consumption. 1 The advent of catalysis chemistry, new applications and an expanded user base are projected to fuel the growth of these polyolefins. PE and iPP are low-cost materials providing good mechanical properties for moderate temperature applications.Melt blending is frequently used to extend the property range of polymers. It is also an attractive approach for recycling mixed polymer waste streams. Despite the fact that PP and PE are similar, these two polymers are thermodynamically immiscible. The incompatibility of PP and PE results in blends that have extremely low fracture strain and poor toughness. For instance, when PP and PE blends are cooled from their molten state, each phase 'solidifies by chain-folding into extended crystalline lamellae sandwiched between amorphous regions composed of disorganized looping sections of polymer' . 2 To improve the compatibility of these two polymers, compatibilizers are usually required. To be effective, the

Development of Inorganic Particle-Filled Polypropylene/High Density Polyethylene Membranes via Multilayer Co-Extrusion and Stretching

“…Co-extrusion may offer a significant degree of adhesion between intermediate and outer layers in multilayer films, as layers are joined in a molten state at high temperature, when using faster cooling and high drawing ratios [ 35 , 36 ]. In addition, in some non-compatible polymer systems, tie layers or adhesive layers can strongly bind structures together [ 35 ].…”

Reactive coupling between immiscible polymer chains: Acceleration by compressive flow

“…Although pressure changes the capture volume around a reactive group and accelerates reaction, the pressure dependence of the rate constant for typical liquid‐phase reactions is much too weak to alter the rate for the range of pressures encountered here . Crystallinity is known to affect interfacial adhesion, and this could increase adhesion even with constant copolymer reaction rate. We compared the crystallinity and crystal structures near the interface for coextrusion with different dies.…”

“…Coextrusion is widely used to produce multilayer sheets . It is a process in which two or more polymer layers are combined and extruded simultaneously.…”

Review on modification strategies of polyethylene/polypropylene immiscible thermoplastic polymer blends for enhancing their mechanical behavior

“…A significant amount of scientific work has been carried out on the nonreactive compatibilization of PE/PP polymer blends. 13,[50][51][52][53][54][55][56][57][58][59] Among the non-in situ coupling agents, ethylene-propylene rubber (EPR) has been one of the most used thermoplastic elastomers in the case of PE/PP blends, because it is widely available, cheap, and easy to process. When introducing EPR to the PE/PP binary system, the propylene repeating units of EPR are inserted within the PP.…”

“…The PE/PP binary system has been gaining a great interest since decades ago, due to good availability, low cost, good performance, and great processability. 13 However, for this blend to be used in advanced applications, there is the need for enhancing the synergy between PE and PP, leading to superior physicochemical and mechanical properties. Different and effective methods of PE/PP compatibilization have been widely explored in the past decades, giving a better understanding of how specific coupling agents can act as emulsifiers at the blend interface, reducing the energy gap that keeps the two polymers separated from each other, hence increasing the interfacial adhesion.…”