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Structure property relationships in bimodal HDPEs
Thesis (MSc)--Stellenbosch University, 2021.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867614074649444352 |
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| access_status_str | Open Access |
| author | Wessels, Arina |
| author2 | Van Reenen, Albert J. |
| author_browse | Van Reenen, Albert J. Wessels, Arina |
| author_facet | Van Reenen, Albert J. Wessels, Arina |
| author_sort | Wessels, Arina |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/123903 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:46:15.146Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/123903 Structure property relationships in bimodal HDPEs Wessels, Arina Van Reenen, Albert J. Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. Bimodal HDPE UCTD Microstructure -- Polymer Polyethylene Polymer melting Polymer crystals Thesis (MSc)--Stellenbosch University, 2021. ENGLISH ABSTRACT: By explicitly tailoring the microstructure of a polymer, it is possible to obtain more desirable properties for the intended product application, in addition to ensuring suitability for the required processing operations. This concept of optimisation led to the development of bimodal high density polyethylenes (biHDPEs), which now account for more than 50% of HDPE demand growth. The chemical and physical properties of any polyethylene are primarily determined by molecular weight and branching on the polymer backbone, as well as the respective distributions thereof. BiHDPEs are comprised of a blend of low molecular weight (LMW) homopolymer and high molecular weight (HMW) copolymer. The subsequent bimodal molar mass distribution results in improved processability without loss of mechanical strength. In this study, the structure-property relationships in four commercially available biHDPEs were investigated. This was done by analysing the microstructures of the resins and relating the structural information to the mechanical and rheological properties. To reduce the complexity of the bulk samples and allow for more comprehensive analyses, the resins were fractionated with respect to crystallisation via preparative temperature rising elution fractionation (p-TREF) and with respect to molar mass via preparative molar mass fractionation (pMMF). The bulk samples, as well as the resulting fractions, were characterised by numerous advanced analytical techniques. The molecular weight and molecular weight distributions were determined using high-temperature size exclusion chromatography (HT-SEC). The chemical compositions were analysed via high-temperature high- performance liquid chromatography (HT-HPLC). High-temperature two-dimensional liquid chromatography (HT-2D-LC) was used further to elucidate the chemical composition distribution of the resins. Fourier transform infrared (FTIR) and carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy provided information regarding comonomer incorporation. Differential scanning calorimetry (DSC) and crystallisation analysis fractionation (CRYSTAF) were used to determine the crystallisation behaviours of the different samples. Tensile properties and melt flow indices (MFIs) of each of the bulk samples were determined and used as indicators of the mechanical performance and processability of the resins. Several conclusions were drawn regarding the structure-property relationships in the biHDPE resins. Additionally, comparisons between the two film grade and two blow moulding grade biHDPEs highlighted favourable microstructural features required for more successful biHDPEs resins. AFRIKAANSE OPSOMMING: Deur die mikrostruktuur van 'n polimeer uitdruklik aan te pas, is dit moontlik om meer gewenste eienskappe vir die beoogde produktoepassing te verkry, benewens die geskiktheid vir die vereiste verwerkingsoperasies. Hierdie konsep van optimalisering het gelei tot die ontwikkeling van bimodale hoëdigtheid poli-etileen (biHDPE), wat nou meer as 50% van die vraag na groei in HDPE uitmaak. Die chemiese en fisiese eienskappe van enige poli-etileen word hoofsaaklik bepaal deur molekulêre gewig en vertakking op die polimeer-ruggraat, asook die onderskeie verdelings daarvan. BiHDPEs bestaan uit 'n mengsel van lae molekulêre gewig (LMG) homo-polimeer en hoë molekulêre gewig (HMG) ko-polimeer. Die daaropvolgende bimodale molêre massaverspreiding lei tot verbeterde verwerkbaarheid sonder verlies aan meganiese sterkte. In hierdie studie is die struktuur-eienskap-verhoudings in vier kommersieel beskikbare biHDPEs ondersoek. Dit is gedoen deur die mikrostrukture van die harse te ontleed en die strukturele inligting te herlei na die meganiese en reologiese eienskappe. Om die kompleksiteit van die grootmaat- monsters te verminder en om meer omvattende ontledings moontlik te maak, is die harse gefraksioneer ten opsigte van kristallisasie deur middel van voorbereidende temperatuur stygende elueringsfraksionering (p-TREF) en ten opsigte van molêre massa deur middle van voorbereidende molêre massa fraksionering (pMMF). Die grootmaat-monsters, sowel as die gevolglike fraksies, is gekenmerk deur talle gevorderde analitiese tegnieke. Die molekulêre gewig en molekulêre gewigsverdelings is bepaal deur gebruik te maak van hoë temperatuur-uitsluitingschromatografie (HT-SEC). Die chemiese samestellings is geanaliseer deur middel van hoë temperatuur hoë- prestasie vloeistofchromatografie (HT-HPLC). Hoë temperatuur tweedimensionele vloeistofchromatografie (HT-2D-LC) is gebruik om die verspreiding van die harse verder te verduidelik. Fourier transformasie infrarooi (FTIR) en koolstof-13 kernmagnetiese resonansie (13C- KMR) spektroskopie het inligting verskaf oor die inkorporering van ko-monomeer. Differensiële skanderingskalorimetrie (DSC) en kristallisasie analise fraksioneering (CRYSTAF) is gebruik om die kristallisasiegedrag van die verskillende monsters te bepaal. Trek-eienskappe en smeltvloei- indekse (MFI's) van elk van die grootmaat-monsters is bepaal en gebruik as aanduidings van die meganiese prestasie en verwerkbaarheid van die harse. Verskeie gevolgtrekkings is gemaak rakende die struktuur-eienskapverhoudings in die biHDPE- harse. Boonop het vergelykings tussen die twee filmgraad en twee blaasvormgraad biHDPEs gunstige mikrostruktuur kenmerke beklemtoon wat nodig is vir meer suksesvolle biHDPEs-harse. Masters 2021-11-30T16:54:58Z 2021-12-22T14:28:08Z 2021-11-30T16:54:58Z 2021-12-22T14:28:08Z 2021-12 Thesis http://hdl.handle.net/10019.1/123903 en_ZA Stellenbosch University 142 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Bimodal HDPE UCTD Microstructure -- Polymer Polyethylene Polymer melting Polymer crystals Wessels, Arina Structure property relationships in bimodal HDPEs |
| title | Structure property relationships in bimodal HDPEs |
| title_full | Structure property relationships in bimodal HDPEs |
| title_fullStr | Structure property relationships in bimodal HDPEs |
| title_full_unstemmed | Structure property relationships in bimodal HDPEs |
| title_short | Structure property relationships in bimodal HDPEs |
| title_sort | structure property relationships in bimodal hdpes |
| topic | Bimodal HDPE UCTD Microstructure -- Polymer Polyethylene Polymer melting Polymer crystals |
| url | http://hdl.handle.net/10019.1/123903 |
| work_keys_str_mv | AT wesselsarina structurepropertyrelationshipsinbimodalhdpes |