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Structure-property relationship of bimodal high density polyethylene: Effect on rheology
Thesis (MSc)--Stellenbosch University, 2021.
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| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867613782993272832 |
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| access_status_str | Open Access |
| author | Lamola, Hellen |
| author2 | Van Reenen, Albert |
| author_browse | Lamola, Hellen Van Reenen, Albert |
| author_facet | Van Reenen, Albert Lamola, Hellen |
| author_sort | Lamola, Hellen |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/123753 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:41:37.777Z |
| 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:10019.1/123753 Structure-property relationship of bimodal high density polyethylene: Effect on rheology Lamola, Hellen Van Reenen, Albert Pasch, Harald Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. Bimodal HDPE Molar mass distribution Chemical composition distribution Fractionation UCTD Polyethylene Thesis (MSc)--Stellenbosch University, 2021. ENGLISH ABSTRACT: Bimodal polyethylene is a version of HDPE that is tailor-made to possess better processability and mechanical strength. Polymerisation is carried out in a low-pressure dual reactor system in the presence of a catalyst. Hydrogen and ethylene are fed to the first reactor to produce a polyethylene homopolymer of very low molar mass. In the second reactor, comonomer of 1- alpha olefins is introduced to create short chain branching. A homogenous distribution of comonomer along the polyolefin chain is important in determining final resin performance. The present work looks at three bHDPE resins with almost similar microstructural properties but different rheological behaviour during the film blowing process. A benchmark industrial resin (Reference) was compared to two similar resins (Resin 1 and Resin 2) where Resin 2 exhibited poor processability regarding bubble instability and melt strength. In the first part of this work, bulk resins are analysed using various analytical techniques. Carbon-thirteen nuclear magnetic resonance (13C NMR) was used to determine the type and quantity of the comonomer in all samples. Other techniques used included high-temperature size exclusion chromatography (HT-SEC), differential scanning calorimetry (DSC), crystallisation analysis fractionation (CRYSTAF), high-temperature interaction chromatography (HT-IC), high-temperature liquid chromatography (2D-LC), dynamic mechanical analysis (DMA) and tensile strength. Results showed that the Reference had a different comonomer to Resin 1 and Resin 2. Also, Resin 2 had a slightly higher comonomer content but overall, comonomer content was very low (<0.8 %) for all samples. Fractionation was performed on a preparative scale and collected fractions were further analysed using 13C NMR, HT-SEC, and DSC. Firstly, preparative temperature rising elution fractionation (pTREF) was performed followed by preparative molar mass fractionation (pMMF). Analyses of the fractions showed that the comonomer in Resin 2 was concentrated in certain fractions and not broadly distributed along the polyolefin chain. As a result, Resin 2 had certain fractions of significantly higher crystallinity to those of the Reference and Resin 1. It was also shown that Resin 2 had high molar mass in the lower TREF temperature fractions where it is expected to be of low molar mass. The Reference conversely had an even distribution of very low and very high molar mass chains as well as an evenly distributed comonomer throughout the polymer chains. Overall observed differences in chemical composition distribution (CCD) and molar mass distribution (MMD) do have an effect on the rheology and processability of bHDPE resins. More specifically, the narrow distribution of iv comonomer in Resin 2 could justify the observed differences in rheological behaviour during processing. AFRIKAANSE OPSOMMING: Bimodale poliëtileen is 'n weergawe van HDPE wat pasgemaak is om beter verwerkbaarheid en meganiese sterkte te besit. Polimerisasie word uitgevoer in 'n laedruk dubbele reaktorsisteem in die teenwoordigheid van 'n katalisator. Waterstof en etileen word na die eerste reaktor gevoer wat 'n poliëtileen homopolimeer met 'n baie lae molêre massa lewer. In die tweede reaktor word komonomeer van 1-alfa-olefiene bygevoeg om kort ketting vertakkings vorm. 'n Homogene verspreiding van komonomeer in die poliolefin-ketting bepaal die finale produk prestasie. Die huidige werk kyk na drie bHDPE produkte met byna soortgelyke mikrostruktuur- eienskappe, maar verskillende reologiese gedrag tydens die film blaas proses. 'n Standaard industriële hars (verwysing) is vergelyk met twee soortgelyke harse (hars 1 en hars 2), waar hars 2 swak verwerkbaarheid ten opsigte van film stabiliteit en smelt sterkte vertoon het. In die eerste gedeelte van hierdie werk word grootmaat harse geanaliseer met behulp van verskillende analitiese tegnieke. Koolstof-dertien kernmagnetiese resonansie (13C NMR) is gebruik om die tipe en hoeveelheid van die samekundige in alle monsters te bepaal. Ander tegnieke wat gebruik word, sluit in hoë-temperatuurgrootte-uitsluitingschromatografie (HT- SEC), differensiële skanderingskalorimetrie (DSC), kristallisasie-analise fraksionering (CRYSTAF), interaktiewe chromatografie met hoë temperatuur (HT-IC), vloeistofchromatografie met hoë temperatuur (2D-LC). ), dinamiese meganiese analise (DMA) en treksterkte. Resultate het getoon dat die verwysing 'n ander comonomeer het as Resin 1 en Resin 2. Resin 2 het ook 'n effens hoër comonomer-inhoud, maar oor die algemeen was die comonomer-inhoud baie laag (<0,8%) vir alle monsters. Fraksionering is op voorbereidende skaal uitgevoer en versamelde breuke is verder geanaliseer met behulp van 13C NMR, HT-SEC en DSC. Eerstens is voorbereidende temperatuurstygende eluerings fraksionering (pTREF) uitgevoer, gevolg deur voorbereidende molêre massa fraksionering (pMMF). Analises van die breuke het getoon dat die komonomeer in Hars 2 in sekere fraksies gekonsentreer is en nie breed versprei is langs die poli- olefineketting nie. As gevolg hiervan het Hars 2 sekere fraksies met 'n beduidend hoër kristalliniteit as dié van die Verwysing en Hars 1. Daar is ook aangetoon dat Hars 2 'n hoë molêre massa in die laer TREF-temperatuurfraksies het, waar dit na verwagting 'n lae molêre massa het. Die verwysing het omgekeerd 'n eweredige verspreiding van baie lae en baie hoë molêre massakettings sowel as 'n eweredig verspreide komonomeer deur die polimeerkettings. Algehele waargenome verskille in chemiese samestellingsverspreiding (CCD) en molêre massadistribusie (MMD) het 'n effek op die reologie en verwerkbaarheid van bHDPE-harse. Meer spesifiek, kan die smal verspreiding van komonomeer in Hars 2 die waargenome verskille in reologiese gedrag tydens verwerking regverdig. Masters 2021-11-11T03:47:04Z 2021-12-22T14:19:29Z 2021-11-11T03:47:04Z 2021-12-22T14:19:29Z 2021-12 Thesis http://hdl.handle.net/10019.1/123753 en_ZA Stellenbosch University 96 Pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Bimodal HDPE Molar mass distribution Chemical composition distribution Fractionation UCTD Polyethylene Lamola, Hellen Structure-property relationship of bimodal high density polyethylene: Effect on rheology |
| title | Structure-property relationship of bimodal high density polyethylene: Effect on rheology |
| title_full | Structure-property relationship of bimodal high density polyethylene: Effect on rheology |
| title_fullStr | Structure-property relationship of bimodal high density polyethylene: Effect on rheology |
| title_full_unstemmed | Structure-property relationship of bimodal high density polyethylene: Effect on rheology |
| title_short | Structure-property relationship of bimodal high density polyethylene: Effect on rheology |
| title_sort | structure property relationship of bimodal high density polyethylene effect on rheology |
| topic | Bimodal HDPE Molar mass distribution Chemical composition distribution Fractionation UCTD Polyethylene |
| url | http://hdl.handle.net/10019.1/123753 |
| work_keys_str_mv | AT lamolahellen structurepropertyrelationshipofbimodalhighdensitypolyethyleneeffectonrheology |