Crystallisation behaviour of commercial polyethylenes: a fundamental study

dc.contributor.advisorVan Reenen, Alberten_ZA
dc.contributor.authorMatthews, Megan Esmeen_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.en_ZA
dc.descriptionThesis (PhD)--Stellenbosch University, 2018.en_ZA
dc.description.abstractENGLISH ABSTRACT: Commercial films are generally made of polyolefins, often using a blend of two different polyolefins. Specifically, low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are blended due to the mechanical strength of LLDPE and the processability of LDPE. However the behaviour of these blends is unpredictable due to the lack of understanding of the underlying processes which determine the final properties. This study focused on developing an understanding of the interactions between LDPE and LLDPE in the blended form through the crystallisation behaviour of the blends. The criteria for co-crystallisation are presented and systematically investigated in order to determine whether the blends meet the criteria. By analysing the blend miscibility in the melt, the crystal structure of the individual blend components as well as the crystallisation kinetics, conclusions can be made about the co-crystallisation potential of LDPE/LLDPE blends. Melt miscibility was investigated by using fluorescent labelling of both polymer components and tracking their movements after the blending process. No isolated domains could be detected with fluorescence microscopy indicating that phase separation did not occur during the melt blending process. However, differential scanning calorimetry (DSC) displayed a number of different crystalline environments which implied that phase separation occurred during the crystallisation process. DSC was also used to verify this through kinetics and showed that the LLDPE crystallised at a faster rate than the LDPE, making co-crystallisation unlikely. Solid state nuclear magnetic resonance (SS NMR) was used to probe the phase separation within the blends and was used to identify a number of different regions which had formed within the amorphous and interfacial areas which seemed to be the cause of the interactions. This disproved the hypothesis that the difference in rate and extent of crystallisation directly affected the ultimate blend properties but rather showed that the amorphous and interfacial regions determine blend behaviour.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Kommersiële films bestaan hoofsaaklik uit poliolefiene en meestal uit ‘n samestelling van twee verskillende poliolefiene. Spesifieke verwysing word gemaak na die samestelling van lae digtheid poliëtileen (LDPE) en liniêre lae digtheid poliëtileen (LLDPE) as gevolg van die meganiese sterkte van LLDPE en die verwerkbaarheid van LDPE. Die werkverrigtinge van hierdie samestellings is onvoorspelbaar as gevolg van ‘n gebrek aan begrip oor die onderliggende prosesse wat die finale eienskappe daarvan bepaal. Die fokus van hierdie studie is om begrip te ontwikkel van die interaksie tussen LDPE en LLDPE in ‘n samestellende vorm, deur die kristallisasie van die samestellings. Die kriteria vir ko-kristallisasie word voorgelệ en sistematies ondersoek om te bepaal of die samestellings aan die vereistes voldoen. ‘n Ontleding van die mengbaarheid van die samestelling in die smeltsel, die kristalstruktuur van die individuele komponente van die samestelling asook die kristallisasie kinetika kan lei tot bevindings oor die ko-kristallisasie potensiaal van die LDPE/LLDPE samestellings. Fluorosserende merkers van beide polimeer komponente word gebruik om die mengbaarheid van die smeltsel te ondersoek asook om die bewegings na die smeltingsproses te volg. Resultate toon dat fase skeiding nie gedurende die smeltingsproses voorgekom het nie. ‘n Bewys hiervan is die gebrek aan geÏsoleerde domeine wat waargeneem is deur die toepassing van fluoressensie mikroskopie. Differensieel skandering kalorimetrie (DSC) het wel bewys gelewer van ‘n aantal verskillende kristallyne areas wat impliseer dat fase skeiding plaasgevind het gedurende die kristallisasie proses. DSC was ook gebruik om fase skeiding deur kinetika te bewys. Dit het ook aangedui dat kristallisasie van LLDPE teen ‘n vinniger tempo as LDPE plaasvind, wat ko-kristallisasie onwaarskynlik maak. Soliede fase kern magnetiese resonansie (KMR) was gebruik om die fase skeiding binne die amorfe en skeidingsvlak areas te ondersoek wat die oorsaak van die interaksies blyk te wees. Die hipotese dat die verskille in die tempo en omvang van kristallisasie die mengsel eienskappe direk affekteer, is verkeerd bewys. Die resultate toon wel dat mengbaarheid bepaal word deur die amorfe en skeidingsvlak areas.en_ZA
dc.format.extent138 pages : illustrationsen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.titleCrystallisation behaviour of commercial polyethylenes: a fundamental studyen_ZA
dc.rights.holderStellenbosch Universityen_ZA

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