Structure-property relationship of polyolefins used as packages and adhesives

Polyolefins are among the most abundantly used polymeric materials in the world. The structure-property relationship of polyolefins, especially for package and adhesive applications, is the primary focus of this dissertation.;In part I, structure-property relationship of biaxially oriented polypropylene (BOPP) films for package application was investigated. The clarity of BOPP films was strongly dependent on the thermal history during processing. The clearest film was obtained by orienting a quenched unoriented sheet at the lowest temperature. Oxygen permeability was reduced by biaxial orientation processing. The decrease in permeability was attributed to reduced mobility of amorphous tie molecules. A single one-to-one correlation between the oxygen permeability and the intensity of the dynamic mechanical beta-relaxation was demonstrated for all the films used in the study. In order to further decrease the oxygen permeability of BOPP films, the layer-multiplying coextrusion with a subsequent biaxial orientation was used to generate the nanoparticles in situ by transforming a spherulitic polymer into impermeable, high aspect ratio lamellae that resemble polymer single crystals. The platelet-like single lamellae were homogeneously dispersed and highly oriented in BOPP films. Very substantial increases in gas barrier and gas selectivity were imparted to BOPP films while also increasing tear strength without sacrificing clarity.;In Part II, some polyolefin elastomers used as adhesives or compatibilizers for polypropylene (PP) and high density polyethylene (HDPE) were studied. The compatibilizer was preferentially located at the interface between the PP matrix and the dispersed HDPE particles. The blend compatibilized with an olefin block copolymer (OBC) had the best combination of low brittle-to-ductile temperature and high toughness. This improved mechanical performance was attributed to the sufficient interfacial adhesion provided by the compatibilizer. The interfacial adhesion was measured in terms of the delamination toughness by peeling PP/compatibilizer/HDPE microlayered tapes. By treating the delamination damage zone as an Irwin plastic zone, it was demonstrated that a critical delamination stress controlled the delamination toughness. A quantitative correlation was established between the adhesion strength and mechanical performance.