Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The main aim of this study was to use poly (ethylene-co-vinyl alcohol) (EVOH) as vehicle to
incorporate nanofillers into low density polyethylene (LDPE). For this purpose, chitin and cellulose
nanowhiskers were prepared through a process of acid hydrolysis and then incorporated into
different EVOH copolymers with varying ethylene contents by means of two different experimental
methods, namely solution casting and electrospinning. The extremely small dimensions of
nanowhiskers make it difficult to observe the degree of dispersion in the electrospun fibers using
methods such as transmission electron microscopy (TEM) and scanning electron microscopy
(SEM). Fluorescence microscopy was therefore investigated as an alternative characterization
technique to obtain better results with regard to tracking the filler dispersion. TEM analysis proved
to be the most successful method for observing the dispersion of nanowhiskers for solution cast
EVOH nanocomposites as well as electrospun EVOH nanocomposites. Clear differences between
EVOH composites with low nanowhisker and high nanowhisker loading were observed in TEM
images for these nanocomposites. Thermal analysis of solution cast as well as electrospun fibers
were carried out using techniques such as differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA). These results revealed changes in crystallization behaviour as
well as changes in thermal stability of the EVOH nanocomposites compared to the pure polymer
matrix. The incorporation of cellulose and chitin nanowhiskers indicated a general increase in
percentage crystallization which probably resulted from the nanowhiskers acting as nucleating
agents and therefore increasing the crystallization of most EVOH nanocomposites. The thermal
stability is observed to increase as the cellulose nanowhisker loading is increased. This increase in
thermal stability proved to be partly attributed to the presence of sulphuric acid which were not
completely removed during dialysis of cellulose nanowhiskers. Neutralisation of cellulose
nanowhiskers and the treatment with a strong base was therefore further investigated to improve
degradation within the EVOH nanocomposites during thermal treatment. The last step in this study
involved the incorporation of electrospun EVOH nanofibers containing cellulose nanowhiskers into
LDPE in order to improve the mechanical properties. The tensile strength and Young’s modulus of these LDPE nanocomposites were seen to improve quite significantly while a decrease in
elongation at break was observed. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie studie was om poliëtileen (ko-viniel alkohol) (EVOH) as voertuig te
gebruik om nanofillers in lae digtheid poliëtileen (LDPE) te inkorporeer. Kitien en sellulose
nanokristalle is vir hierdie doel geproduseer deur middel van ʼn suurhidrolise proses en daarna in
verskillende EVOH-kopolimere met verskillende etileeninhoude geïnkorporeer met behulp van
twee verskillende eksperimentele metodes, naamlik ʼn drogings- en elektrospinproses. Die uiters
klein dimensies van die nanokristalle maak dit uitdagend om die mate van verspreiding van die
nanokristalle binne in die elekrogespinde vesels waar te neem m.b.v. metodes soos transmissieelektronmikroskopie
(TEM) en skandeerelektronmikroskopie (SEM). Fluoressensie is dus as ʼn
moontlike alternatiewe karakteriserings tegniek bestudeer om beter resultate rakende die
verspreiding van die nanokristalle te kan waarneem. In hierdie studie is gevind dat TEM-analise die
suksesvolste metode was om die verspreiding van nanokristalle te bestudeer en dit geld vir beide
die gedroogte en gespinde EVOH-nanosamestellings. Duidelike verskille is waargeneem vir
monsters wat hoër en laer nanokristalinhoude gehad het. Saambondeling van die nanokristalle
kom duideliker voor by dié wat ʼn hoër inhoud van nanokristalle bevat. Termiese analises van
gedroogte EVOH-nanosamestellings en ook die gespinde nanosaamgestelde vesels is uitgevoer
d.m.v. tegnieke soos differensieëlskandeerkalorometrie (DSC) en termiese-gravimetriese analise
(TGA). Die resultate wat verkry is vanaf die bogenoemde tegnieke het bewys dat daar verandering
in die kristallisasie, sowel as die degradasie temperatuur, van die EVOH-nanosamestelling is. Die
byvoeging van sellulose en kitien nanokristalle het ʼn algemene verhoging in die persentasie
kristallisasie van die EVOH-nanosamestelling te wee gebring. Die byvoeging van nanokristalle tree
waarskynlik gedeeltelik op as kernvormings agent vir die EVOH-molekules. TGA analises toon dat
die termiese stabiliteit van die EVOH-nanosamestelling verhoog met die byvoeging van
nanokristalle. Die teenwoordigheid van die sulfaatgroepe wat nie heeltemal verwyder is tydens die
wasproses nie, is bewys om gedeeltelik verantwoordelik te wees vir die verhoging in termiese
stabiliteit van die EVOH-nanosamestellings. Die neutralisasie en behandeling van die nanokristalle
met ʼn sterk basis is dus verder ondersoek om die degradasie van die EVOH-nanosamestellings
tydens verhitting te verbeter. Die laaste stap in hierdie studie het behels dat elektrogespinde EVOH
vesels wat verskillende hoeveelhede sellulose nanokristalle bevat, geïnkorporeer is in LDPE ten einde die meganiese eienskappe te verbeter. Die treksterkte en die Young’s modulus het met ʼn
beduidendende hoeveelheid verbeter terwyl die verlenging by breekpunt verlaag het. / National Research Foundation
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80312 |
| Date | 03 1900 |
| Creators | Du Toit, Madeleine Leonore |
| Contributors | Lutz, M., Van Reenen, Albert J., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xv, 124 p. : ill. (some col.) |
| Rights | Stellenbosch University |
Page generated in 0.0031 seconds