Modification and incorporation of chitosan nanoparticles into different polymer matrices

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: Chitosan is an abundantly found polysaccharide with known antimicrobial, biodegradable and nontoxic properties. Chitosan has been used in drug delivery systems and as partial components in food packaging materials. The main aim of this study was to incorporate functionalised chitosan nanoparticles into polymer matrices, which are used for packaging purposes, for investigation of their structure-property relationship. Therefore, poly(vinyl alcohol-co-ethylene) (EVOH) and low-density polyethylene (LDPE) were used as the matrices of interest. Chitosan was functionalised to N,O-carboxymethyl chitosan, for hydrophilic functionality, and a quaternary ammonium chitosan derivative, for hydrophobic functionality, before being crosslinked with sodium tripolyphosphate to produce three chitosan nanoparticle variants with different hydrophilic nature. The modified and unmodified chitosan nanoparticles were added to LDPE and three grades of EVOH copolymer, with varying ethylene content, to form composite films which were produced by solution casting and melt-pressing to create nanocomposite films. Furthermore, all three nanoparticles were added to the different EVOH copolymers by electrospinning to produce nanocomposite fibre mats. The nanoparticles were characterised by scanning electron microscopy and their thermal stability was evaluated by thermogravimetric analysis. The nanocomposite films and fibres were subjected to confocal fluorescence microscopy to investigate the nanoparticle distribution throughout the matrices. It was found that the electrospinning process improved the nanoparticle distributions when compared to solvent casting. Differential scanning calorimetry of the nanocomposites showed that a nanoparticle content of up to 8 wt% had an insignificant influence on the melting and crystallisation temperatures of the films and fibres but tended to decrease the melting and crystallisation enthalpies. Water uptake studies and static contact angle measurements showed, in general, that the addition of any of the three types of chitosan nanoparticles increased the wettability of the LDPE and EVOH films and fibres. It was also noted that the wettability of the EVOH fibres was more sensitive to the nanoparticle content. Antimicrobial studies were performed by using Staphylococcus aureus (S. aureus). The nanocomposite films all showed inhibition of S. aureus, irrespective of nanoparticle content. This inhibition was attributed to the hydrophobicity of the polymer films and the inability of S. aureus to attach onto the samples. The increased wettability of the nanocomposite fibres allowed the S. aureus to attach successfully and as a result no growth inhibition was observed. It was therefore concluded that a nanoparticle content of up to 8 wt% did not provide sufficient interaction with S.aureus.
AFRIKAANSE OPSOMMING: Die gebruik van chitosan is reeds bekend weens sy antimikrobiese, bioafbreekbare en nie-giftige eienskappe. Chitosan is al gebruik as deel van verpakkingsmateriale en word gebruik as nanopartikels om te dien as ‘n vervoermiddel vir sekere medikasies. Die hoof doel van hierdie studie is om chitosan te funksionaliseer, nanopartikels daarvan te maak en dit in matrikse te voeg wat gebruik kan word in die verpakkingsindustrie. Die matrikse wat ondersoek was was poli(viniel alkohol-ko-etileen) (EVOH) en lae digtheid poliëtileen (LDPE). Chitosan was gefunksionaliseer na karboksiemetiel chitosan, vir addisionele hidrofiliese funksionaliteit, en na ‘n kwaternêre ammonium chitosan, vir addisionele hidrofibisiteit. Nanopartikels was vervaardig vanaf die oorspronkilike chitosan en gefunksionaliseerde weergawes. Die drie tipes chitosan nanopartikels was in LDPE en EVOH matrikse gevoeg deur gebruik te maak van drogings- en elektrospinprosesse. Drie tipes EVOH, met verskillende etileeninhoude, was gebruik. Hierdie prosesse het nanosaamgestelde materiale van twee verskillende formate geskep wat geanaliseer kon word. Die vervaardiging van chitosan nanopartikels was bevestig deur skanderingelektronmikroskopie en termiese-gravimetriese analise was gebruik om die termiese stabiliteit van die nanopartikels te vergelyk met die oorspronklike chitosan. Die nanosaamgestelde- films en vesels was geanaliseer deur konfokale fluoressensiemikroskopie en het gewys dat die elektrospinproses ‘n meer homogene verspreiding van chitosan nanopartikels veroorsaak het, in vergelyking met die drogingsproses. Differensieëlskanderingskalorometrie van die nanosaamgestelde materiale het gewys dat daar geen noemenswaardige verandering plaasgevind het in die vesels en films se smeltings- en kristallisasie temperatuur nie. Daar was wel ‘n algemene afname in die smeltings- en kristallisasie entalpie tot en met 8% gewigsinhoud van die verskillende nanopartikels. Die wateropname en statiese kontakhoek lesings het gewys dat die teenwoordigheid van enige van die drie soorte chitosan nanopartikels die hidrofibisiteit van die EVOH en LDPE films en vesels verlaag. Dit was ook duidelik dat die vesels se hidrofibisiteit die meeste beinvloed was deur die chitosan nanopartikels. Staphylococcus aureus (S. aureus) was gebruik vir die antimikrobiese studies en het gewys dat geen mikrobiese groei plaasgevind het op die nanosaamgestelde films nie. Hierdie bevinding was onafhanklik van die nanopartikel inhoud. Hierdie inhibisie is toegeskryf aan die hidrofibisiteit van die polimeer films en die onvermoë van S. aureus om te heg aan die film monsters. Die verlaagde hidrofibisiteit van die nanosaamgestelde vesels het toegelaat dat S. aureus suksesvol kon aanheg en as ‘n gevolg was geen inhibisie van groei waargeneem nie. Dit was dus bepaal dat die nanopartikels teen 8% van die nanosaamgestelde gewig nie voldoende interaksie met S. aureus verskaf het nie.
Thesis (MSc)--Stellenbosch University, 2020.
Chitosan, UCTD, Polymer -- Matrices, EVOH, Low-density polyethylene, Nanoparticles