Using graphene oxide as a compatibilizer in immiscible polymer blends

Abstract

In this thesis, normally highly immiscible blends of low-density polyethylene and polyamide 66 were created and studied. Blends, which are based on engineering thermoplastic, like polyamide, and on commodity plastic, like polyethylene, are an interesting research target because it would be possible to create blends, with many desired properties and low cost. These blends could be then exploited in many applications in different fields. The usual problem of polymer blending is related to the different chemical structures of blend’s components. This leads to phase separation in the blend, which leads to poor properties. To tackle this problem, a third component can be added to the blend. These components are called compatibilizers and they are usually block or graft copolymers but using them in blends has many challenges. That is why in this work, graphene oxide was used as a compatibilizer to research its potential to enhance blends properties. The theoretical part of the thesis presents information about low-density polyethylene, polyamide66, polymer blending and graphene. The basic properties, structural information and typical uses of low-density polyethylene and polyamide 66 are discussed first. Followed by this, is a section of polymer blending. Polymer blending is introduced by providing information about extruders, mixing processes and thermodynamics. Also, compatibilizers are introduced. Finally, graphene is presented. The focus is mainly on graphene oxide and reduced graphene oxide, providing information about their structures, properties and ways to produce them. The functionalization of graphene oxide is also presented. The experimental part included modified Hummers’ method to produce graphene oxide and preparation of suitable masterbatches for processing. Melt compounding with twin-screw extruder was performed to mix the blends and to potentially partially reduce and functionalize the graphene oxide. Various characterization methods were used in this work with suitable programs to analyze the samples and to see if there were any indications about successful blending. Several characterization methods indicate, that the dispersion of polyamide 66 in low-density polyethylene matrix was enhanced with the use of partially reduced and non-covalently functionalized graphene oxide as a compatibilizer. This is a key thing in blending and in enhancing blends properties. Also, positive results on enhanced thermal properties and chemical interactions between components are witnessed.