The effect of chemical composition and morphology on the properties of polyolefin films

Barnard, Johannes Lodewiekus (2018-03)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: This thesis consists of three parts, in the first part a preliminary study was conducted pertaining to dunnage bags. Dunnage bags are large inflatable restraining devices used in containers to keep the cargo from toppling over when in transit. Dunnage bags currently in use consist of two materials; one of polyethylene (PE) for air permeability resistance and polypropylene (PP) for strength. In an attempt to create a single layer dunnage bag a material had to be selected having various properties such as high strength, puncture resistance and air permeability resistance. After preliminary testing it was found that high impact polypropylene (HIPP) or heterophasic ethylene-propylene copolymers (HEPCs) conformed to most of the required properties and were therefore selected as ideal candidate materials for further testing. HEPCs are readily available and widely used in various industries. The copolymer consists of an extremely complex composition consisting of PP and PE homopolymers as well as ethylene-propylene copolymers creating rubbery phases. Mechanical properties of this material are well known, but research into how polyethylene inclusion contribute to its permeability properties is still in its infancy. The concepts and problems introduced through answering this problem led to part two. Part two served as the main part of the study and dealt with observation of the finer material properties on a molecular level which related to the macroscopic properties of the final product. The gas permeability of a series of HEPCs with varying ethylene content (sampled by online time-dependent extraction) were investigated and attempts were made to relate this macroscopic property to how ethylene inclusion affects the morphology. This was done by using various analytical techniques such as permeability testing, differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS), X-ray diffraction spectroscopy (XRD) and polarizing optical microscopy (POM). Crystal morphology and crystallization kinetics as well as polymer composition turned out to have a contribution towards the final permeability properties. In part three these techniques were employed on a different sample set to substantiate the conclusions made in part two. A HDPE:LDPE blend with varying LDPE composition was studied. Interesting findings were made and substantiated by a PALS experiment. Part three agreed with the findings made in part two and a promising way of predicting the permeability of a polymeric film with varying chemical composition was achieved.

AFRIKAANSE OPSOMMING: Hierdie tesis bestaan uit drie dele, in die eerste deel was ‘n voorlopige studie gedoen met betrekking tot dunnage sakke. Dunnage sakke is groot opblaasbare sakke wat vragte in houers keer om te tuimel gedurende die vervoer daarvan. Dunnage sakke bestaan huidiglik uit twee materiale; een van poliëtileen (PE) vir weerstand teen lugdeurlaatbaarheid en polipropileen (PP) vir sterkte. In 'n poging om 'n enkele laag dunnage sak te skep, moes 'n materiaal gekies word wat bestaan uit verskeie parameters soos hoë sterkte, punksieweerstand en lugdeurlaatbaarheid. Na voorlopige toetsing is bevind dat hoë impak polypropyleen (HIPP) of heterofasiese etileen-propileen kopolimere (HEPKs) uit die gunstigste eienskappe bevat, en daarom as ideale kandidaat-materiaal gekies is vir verdere toetsing. HEPK's is maklik bekombaar en word in verskeie nywerhede gebruik. Die kopolimeer bestaan uit 'n uiters komplekse samestelling, wat PP en PE homopolimeer en asook etileen-propileen kopolimere bevat wat rubberagtige fases skep. Meganiese eienskappe van hierdie materiaal is welbekend, maar navorsing oor hoe poliëtileen-insluitingby dra tot die deurlaatbaarheidseienskappe, is nog in sy kinderskoene. Die konsepte en probleme wat gestel is deur die probleem te beantwoord, het tot deel twee gelei. Deel twee het gedien as die hoofdeel van die studie en het aandag gegee aan die waarneming van fyner materiaal eienskappe op molekulêre vlak wat verband hou met die makroskopiese eienskappe van die finale produk. Die gasdeurlaatbaarheid van 'n reeks HEPK's met wisselende etileeninhoud (ingesamel deur aanlyn tydafhanklike ekstraksie) is ondersoek. 'n Poging is aangewend om hierdie makroskopiese eienskap te vergelyk met hoe etileen-insluiting die morfologie beïnvloed. Dit is gedoen deur gebruik te maak van verskeie analitiese tegnieke soos deurlaatbaarheidstoetsing, differensiële skanderingskalorimetrie (DSK), positronvernietiging leeftyd spektroskopie (PVLS), X-straal diffraksie spektroskopie (XRD) sowel as gepolariserende optiese mikroskopie (POM). Kristal morfologie en kristallisasie kinetika sowel as polimeer samestelling blyk om 'n bydrae te lewer tot die finale deurlaatbaarheidseienskappe. In deel drie is die tegnieke wat in deel 2 ontwikkel is toegepas op 'n nuwe stel polimere om die gevolgtrekkings in deel twee te staaf. 'n HDPE:LDPE mengsel met verskillende LDPE samestelling is bestudeer. Interessante bevindinge is gemaak en gestaaf deur 'n PVLS-eksperiment. Deel drie het ooreengekom met die bevindinge wat in deel twee gemaak is en 'n belowende manier om die deurlaatbaarheid van 'n polimeerfilm met verskillende chemiese samestelling te voorspel, is behaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103683
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