Incorporation of polysaccharide nanowhiskers into a poly(ethylene-co-vinyl alcohol) matrix

Du Toit, Madeleine Leonore (2013-03)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/80312
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