The influence of low molecular weight additives containing polar groups and modified polyolefin-based compatibilisers on polypropylene (PP)-clay nanocomposites (PPCN) has been studied, in terms of intercalation and degree of exfoliation achievable by melt state mixing processes. PPCN were prepared by melt mixing of two commercial pp homopolymers with organically modified clay (OMMT) in the presence of maleic anhydride grafted pp (PP-MA). X-ray diffraction (XRD) analysis shows that the interlayer spacing of clay increases dramatically, whilst transmission electron microscopy (TEM) results show a significant improvement of clay dispersion in the PP matrix, when nanocomposites are prepared with commercial PP containing short chain organic additives with polar groups (amide-type slip and antistatic additives). Subsequent studies based upon customised PP formulations, with short chain amide molecules (AM), confirm the intercalation of this additive into clay galleries. The maximum interiayer spacing is achieved with low concentrations of this additive (0.5 wt. %). Contact angle measurements and low shear melt flow properties (MF!) further confirm the diffusion of this additive (AM) into the clay galleries rather than migrating away from the bulk of the PPCN. The interaction between the polar group (CONH2) of this additive and polar sites of the clay surface appears to be the driving force for the intercalation. Although this additive intercalates and allows the formation of an intercalated nanocomposite structure with non homogeneous dispersion of clay, an exfoliated PPCN structure is yet to be formed with this additive alone. A new preparation method for PPCN has therefore been developed by co-intercalation of AM and PP-MA. PPCN were prepared by this method with a significant reduction of overall PP-MA concentration in the nanocomposite structure, relative to conventional PPCN prepared with compatibiliser (PP-MA) only. XRD and TEM analysis showed that nanocomposite structures are formed with significantly improved clay dispersion, compared to PPCN prepared using the conventional method. Quantification of clay exfoliation, using image analysis software, showed that higher degrees of exfoliation can be achieved in PPCN from this new cointercalation method. Normalised melt flow index (n-MFI) data showed the relationship between low shear flow properties and clay structure and is an appropriate parameter to examine clay exfoliation and its interaction with pp in PPCN. Enhanced thennal stability of PPCN, in comparison to pure PP, further demonstrates the improved clay dispersion in nanocomposite structures prepared by the co-intercalation method. A possible mechanism for the co-intercalation of AM and PP-MA into clay galleries has been proposed, based upon hydrogen bonding between these additives and the silicate layers. Rheological characterisation of PPCN, using capillary rheometry experiments at high shear rates, shows a shear thinning, pseudoplastic behaviour similar to pure PP. However, a comparatively higher concentration of AM appears to reduce the shear viscosity of PPCN. Die swelling behaviour revealed a reduction in melt elasticity in PPCN melts in comparison to unmodified PP. Reduced die swell occurs as a result, together with a delay in the onset of melt fracture. Sheet extrusion was used to produce PPCN products with increasing clay loading levels that were evaluated for a range of mechanical properties. Significant enhancement of modulus in PPCN is achieved in comparison to pure PP whilst maintaining similar strength characteristics. However, impact resistance of extruded PPCN sheets is not improved in comparison to unmodified PP. Results have been interpreted with reference to the degree of exfoliation, additive content and differences in PP crystallinity.

In this dissertation, algorithms for creating estimated potentials for metals and modeling of nano composites are developed. The efficacy of the algorithms for estimated potentials were examined. The algorithm was found to allow molecular dynamic and Monte Carlo modeling to be included in the potential building process. Additionally, the spline based equations caused issues with the elastic constants and Young’s modulus due to extra local minima. Two algorithms were developed for improved modeling of nano composites: one was a random number generation algorithm for initializing polymer, second was a bonding algorithm for controlling bonds between polymer and nano particle. Both algorithms were effective in their tasks. Additionally, the algorithms for improved nano composite modeling were used for preliminary material design of PMMA metal oxide nano composite systems. The results from the molecular dynamic simulations show the bonding between polymer matrix and nanoparticle has a large effect on the Young’s modulus and if this bonding could be controlled, the tensile properties of PMMA-metal oxide nano composites could be tailored to the applications’ requirements. The simulations also showed bonding had caused changes in the density of the material which than effected the energy on the polymer chain and the Young’s modulus. A model was than developed showing the relationship between density and the chain energy, and density and the Young’s modulus. This model can be used for a better understanding and further improvement of PMMA-metal oxide nano composites.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Novel silicone nanocomposites were prepared using poly(acrylonitrile) (PAN) based reinforcing fibres as well as multi-walled carbon nanotubes (MWCNTs). Compatibility of the fibre fillers with the silicone matrix required the synthesis of novel amphiphilic, organic–inorganic graft copolymers of PAN and poly(dimethylsiloxane) (PAN-g-PDMS). These fibre precursor materials were synthesised via the “grafting through” technique using conventional free radical copolymerisation. The PDMS macromonomer content in the feed was varied from 5 wt% to 25 wt% and the molecular weights of the macromonomer were 1000 g.mol-1 and 5000 g.mol-1. The solvent medium of the precipitation reaction was optimised at a volume ratio of 98% benzene to 2% dimethylformamide (DMF). Successful incorporation of PDMS yielded graft copolymer blend materials of PAN-g-PDMS, blended with PAN homopolymer and unreacted PDMS macromonomer. A gradient elution profile was developed to track the successful removal of the PDMS macromonomer via hexane extraction. The gradient profile showed that as the PDMS content in the feed increased, the number of graft molecules in the blend increased relative to the number of PAN homopolymer molecules. The crystallisability of the PAN segments was shown to decrease as the PDMS content increased. The synthesised polymer was used as precursor material for the electrospinning of fibre fillers. The electrospinning of the precursor material was successfully achieved using 100% DMF as electrospinning solution medium. The amphiphilic nature of the precursor material in DMF resulted in self-assembled aggregate structures in the electrospinning solution. An increasing PDMS content was shown to affect the aggregation of the precursor material, and resulted in an increase in the solution viscosity. The “gel-like” solutions limited the achievable fibre morphological control when altering conventional electrospinning parameters such as voltage, tip-to-collector distance, and solution concentrations. The rapid evaporation and stretching of the solution during electrospinning, combined with the phase segregated amphiphilic molecules in solution and the crystallisation of the PAN segments resulted in (non-equilibrium morphology) fully porous fibres. The crystallinity was shown to decrease after electrospinning of the fibre precursor materials. Successful incorporation of surface oxidised MWCNTs into the electrospun fibres was achieved. The content of nanotubes was varied from 2 wt% to 32 wt%. The MWCNTs reduced the mean fibre diameters by acting as cross-linkers between the PAN segments and increasing the solution conductivity. The nanotubes dispersed well throughout the porous structure of the fibres and aligned in the direction of the fibre axis. Fabrication of silicone composites containing nonwoven and aligned fibre mats (with 8 wt% MWCNTs in the fibres, and without) was successfully achieved. The compatibilisation of the PDMS surface segregated domains allowed excellent dispersion and interaction of the PAN based fibre fillers with the silicone matrix. Mechanical analysis showed improved properties as the PDMS content in the fibre increased. The highest PDMS content fibres did, however, exhibit decreased properties. This was ascribed to increased PDMS (soft and weak) content, decreased crystallinity and increased fibre diameter (lower interfacial area). Dramatic improvements in strength, stiffness, strain and toughness were achieved. The most significant result was an increase in strain of 470%. The mechanical results correlated with results of SEM analysis of the fracture surfaces. The dramatic improvements in properties were a result of the fibre strength and ductility, as well as the mechanism of composite failure. / AFRIKAANSE OPSOMMING: Nuwe silikonnanosamestellings is berei deur gebruik te maak van poli(akrilonitriel) (PAN) gebaseerde versterkende vesels wat multi-ommuurde koolstof nanobuisies bevat het. Versoenbaarheid van die vesels met die silikonmatriks het die sintese van nuwe amfifiliese, organies–anorganiese ent-kopolimere van PAN en poli(dimetielsiloksaan) (PAN-g-PDMS) benodig. Die vesel voorlopermateriaal is deur middel van ‘n “ent-deur” vryeradikaalkopolimerisasie gesintetiseer. Die inhoud van die PDMS makromonomeer in die reaksie het gewissel vanaf 5% tot 25%. Die gebruik van twee verskillende molekulêre massas makromonomere is bestudeer (1000 en 5000 g.mol-1). Die optimale oplosmiddelmengsel vir die neerslagreaksie was 'n volume verhouding van 98% benseen tot 2% dimetielformamied (DMF). Suksesvolle insluiting van PDMS het versnitmateriale van PAN-g-PDMS kopolimere gemeng met PAN homopolimere en ongereageerde PDMS makromonomere gelewer. 'n Gradiënteluering- chromatografiese profiel is ontwikkel om die suksesvolle verwydering van die PDMS makromonomere via heksaanekstraksie te bepaal. Die gradiëntprofiel het aangetoon dat indien die PDMS inhoud in die reagense verhoog is, die aantal entmolekules relatief tot PAN homopolimeermolekules ook verhoog het. 'n Toename in PDMS inhoud het egter 'n afname in kristallisasie van die PAN segmente tot gevolg gehad. Die gesintetiseerde polimeer is gebruik as die beginmateriaal vir die elektrospin van veselvullers. Die elektrospin van die beginmateriaal was suksesvol wanneer 100% DMF as elektrospinoplosmiddel gebruik is. Die amfifiliese aard van die beginmateriaal in DMF lei tot outokonstruksie van aggregaatstrukture in die elektrospinoplossing. Toenemende PDMS inhoud beïnvloed die outokonstruksie van die molekules in oplossing en het gelei tot 'n toename in die oplossings se viskositeit. Die "gelagtige" oplossings beperk die haalbare vesel se morfologiese beheerbaarheid wanneer konvensionele elektrospin parameters soos elektriese spanning, punt-tot-versamelaar afstand, en oplossingkonsentrasies gewysig word. Die vinnige verdamping en strek van die oplossing tydens elektrospin, gekombineer met die fase-geskeide amfifiliese molekules in oplossing en die kristallisasie van die PAN segmente, het gelei tot (nie-ewewig morfologie) volledige poreuse vesels. Die kristalliniteit van die veselbeginmaterial het afgeneem nadat elektrospin toegepas is. Die insluiting van die oppervlak-geoksideerde multi-ommuurde koolstof nanobuisies in die elektrogespinde vesels was suksesvol. Die inhoud van die nanobuisies het gewissel van 2 wt% tot 32 wt%. Die MWCNTs het die gemiddelde veseldeursnit verminder deur op te tree as kruisbinders tussen die PAN segmente van die molekules. Die nanobuisies was goed versprei deur die poreuse struktuur van die vesels en dit was gerig in die rigting van die vesel-as. Bereiding van die silikonsamestellings bestaande uit nie-geweefde en gerigte veseloppervlakke (met en sonder 8 wt% multi-ommuurde koolstof nanobuisies in die vesel) was suksesvol. Die versoenbaarheid tussen die oppervlak van die PDMS-geskeide gebiede en die silikonmatriks laat uitstekende verspreiding en interaksie van die PAN-gebaseerde veselvullers met die silikonmatriks toe. Meganiese analise het aangetoon dat die fisiese eienskappe verbeter het namate die PDMS inhoud in die vesel vermeerder het. Die vesels met die hoogste PDMS inhoud het egter verswakte eienskappe getoon. Dit is toegeskryf aan ‘n verhoogde PDMS inhoud (sag en swak), ‘n afname in kristalliniteit en ‘n verhoogde veseldeursnit (laer grensoppervlakke). Dramatiese verbeterings in sterkte, styfheid, verlengbaarheid, vervorming en taaiheid is bereik. Die mees betekenisvolle gevolg was 'n toename in die verrekking van 470%. Die meganiese resultate is gekorreleer met SEM ontleding van die brekingsoppervlakke. Die veselkrag en vervormbaarheid, sowel as die meganisme van die splyting van die samestellings, het tot die dramatiese verbeterings in die meganiese eienskappe gelei.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The properties of polymer nanocomposites depend greatly on the chemistry of the polymer matrices, the nature of the nanofillers, and the way in which they are prepared. Understanding the synthesis–structure–property relationship of nanocomposites is vital for the development of advanced polymer nanocomposites with enhanced mechanical strength, stiffness and toughness for structural engineering applications. To this end, the primary aim of this study was to determine the impact that the preparation methods have on the properties of PP/filler nanocomposites, with specific focus on the in situ polymerization of propylene via the methylaluminoxane (MAO) activated metallocene catalyst technique. Two different fillers (Silica and Calcium carbonate) were used as support for the metallocene catalysts. Different supporting methodologies for the synthesis of the supported catalyst were examined. A C2 symmetric metallocene catalyst ansa dimethylsilylbis(2-methyl benzoindenyl) zirconium dichloride (MBI) was used in this study. The catalyst systems were then evaluated for propylene polymerization. The early observation shows that a direct adsorption of the metallocene onto the filler has a diminishing effect on the catalyst productivity and the fillers had to be treated with MAO in order to avoid catalyst deactivation by the filler surface. Due to the low productivity of the supported active species, the presence of soluble catalyst active species, besides the supported active species is required in the synthesis of PP nanocomposites via in situ polymerizations. The syntheses of PP nanocomposites were carried out via in situ polymerization in which different quantities of MAO treated fillers were reacted with pre-activated catalyst solution. The effect of the addition of MAO-filler on the polymerization kinetics and consequently on PP matrix microstructure was investigated. Changes in the in situ polymerization kinetics, compared to kinetics of homogeneous polymerization, were observed. Therefore, the microstructure of the polymer matrix was also influenced by the presence of nanofillers in the polymerization media. The influence of the different synthesis methods on the performance of the nanocomposites was investigated using melt-mixed PP/filler nanocomposites obtained using PP homopolymer. The dispersed phase morphologies of the different nanocomposites were investigated by transmission electron microscopy (TEM). Results show that PP nanocomposites with improved filler dispersion were achieved by in situ polymerization compared to melt-mixed nanocomposites. The influence of the synthesis method on the crystallization behaviour of PP nanocomposites was also investigated. It was found that, for the in situ prepared nanocomposites the tacticity of the PP matrix plays the major role in determining the degree of crystallinity. Results also show that when nanocomposites with comparable PP matrices are compared, the overall crystallization rate of the in situ polymerized nanocomposites is higher than that of the melt mixed nanocomposites. The mechanical properties of in situ polymerized PP and melt mixed PP nanocomposite were also investigated and compared. Due to improved nanoparticle dispersion in the PP matrix, in situ polymerized nanocomposites show enhanced mechanical properties, especially tensile and impact properties, compared to pure PP and melt mixed prepared nanocomposites when a PP matrix of equivalent microstructure was used. Finally, the melt compounding method was further investigated using different fillers and commercial PP as a matrix. The effect of filler type, size and applied surface coating on the flow and mechanical properties of PP nanocomposites was studied. The aim of this part of this study is to obtain a good trade-off between the processability and the mechanical properties and to gain insight into the cause of the emergence of different properties for nanocomposites prepared by melt compounding. / AFRIKAANSE OPSOMMING: Die eienskappe van polimeer nanokomposiete hang grotendeels af van die chemie van die polimeer matriks, die wese van die nano-vullers, en die manier waarop hierdie materiale berei word. Om die sintese-struktuureienskap verwantskap te verstaan is noodsaaklik vir die ontwikkeling van gevorderde nanokomposiete met beter meganiese eienskappe, styfheid en taaiheid vir strukturele ingenieurstoepassings Die primêre doelstelling van hierdie studie was dus om die impak van voorbereidingsmetodes op die eienskappe van PP/vuller nanokomposiete te bestudeer, met spesifieke fokus op die in-situ polimerisasie van propileen met metiel alumoksaan-geativeerde metalloseen kataliste. Twee verskillende vullers (silika en kalsium karbonaat) is gebruik as ondersteuning vir die metalloseen kataliste. Verskillende metodiek is gebruik om die ondersteunde kataliste te berei. ‘n C2 simmetriese metalloseen katalis ansa-dimetielsiliel(2-metiel bensoindeniel) sirkonium dichloride (MBI) is in die studie gebruik. Die katalissisteme is daarna evalueer vir propileen polimerisasie. Daar is oorspronklik vasgestel dat direkte adsorpsie van die metalloseen op die vuller ‘n negatiewe effek op die katalis aktiwiteit gehad het, en dat die vuller oppervlak eers met MAO behandel moes word om deaktivering van die katalis deur die vuller-oppervlak te vermy. As gevolg van die lae aktiwiteit van die ondersteunde aktiwe katalisspesies, is die teenwoordigheid van opgeloste aktiewe katalis nodig vir die voorbereiding van PP nanokomposiete via in situ polimerisasie-reaksies. Die sintese van PP nanokomposiete is uitgevoer deur in –situ polimersiasie waartydens verskillende hoeveelhede MAO-behandelde vullers gereageer is met vooraf-geaktiveerde katalis oplossings. Die effek van die byvoeging van MAO-vuller op die polimerisasie-kinetika en gevolglik op die PP matriks mikrostruktuur is ondersoek. Dit is gevind dat die mikrostruktuur van die polimeer-matriks beinvloed word deur die teenwoordigheid van nanovullers in die polimerisasie-medium. Die invloed van verskillende bereidingsmetodes op die eienskappe van die nanokomposiete is ondersoek deur smelt-vermengde PP/vuller nanokomposiete te maak. Die dispersie-fase morfologie van verskillende nanokomposiete is ondersoek deur transmissie elektron mikroskopie (TEM). Resultate wys dat PP nanokomposiete met verbeterde vuller-dispersie berkry is deur in situ polimerisasie in vergelyking met die smelt-vermengde materiale. Die effek van die sintese-metode op die kristallisasie van die PP nanokomposiete is ook ondersoek. Daar is gevind dat, vir die in situ bereide nanokomposiete, die taktisiteit van die PP matriks die grootste rol speel in die bepaling van die persentasie kristalliniteit. Resultate het ook gewys dat, wanneer nanokomposiete met soortgelyke PP matrikse vergelyk word met die in situ nanokomposiete, die laasgenoemde se tempo van kristallisasie hoer is as vir die smelt-vermengde nanokomposiete. Die meganiese eienskappe van die in situ bereide en smelt-vermengde PP nanokomposiete is ook ondersoek en vergelyk. As gevolg van verbeterde nano-partikel dispersie in die PP matriks, het die in situ bereide nanokomposiete beter meganiese eienskappe openbaar, in vergelyking met die smelt-vermenge nanokomposiete, veral trek- en slagsterkte. . Laastens is die smelt-vermengings metode verder ondersoek deur gebruik te maak van verskillende vullers en kommersiële PP as matriks. Die effek van die tipe vuller, die grootte en die oppervlakbedekking van die vullerpartikels op die vloei en meganiese eienskappe van die PP nanokomposiete is ondersoek. Die doel van hierdie studie was om ‘n balans te kry tussen prosesseerbaarheid en meganiese eienskappe en om insig te verkry oor die verskille in eienskappe wat openbaar word wanneer smeltvermengde nanokomposiete bereie word.

The need for efficient, lightweight armour solutions has never been so great as it is today. Increasing numbers of personnel, both military and civilian are being placed in an expanding variety of life-threatening situations, and we must recognise the responsibility to maximise their combat survivability. One way to help protect these people is to provide them with some form of armour. Advanced polymeric materials are finding an increasing range of industrial and defence applications. These materials have the potential to improve the performance of current armour systems, whilst also reducing their cost and weight. Polymers may be reinforced with the addition of nanofillers such as carbon nanotubes or graphene, to produce nanocomposites, an exciting emerging polymer technology. Nanomaterials have been shown to exhibit extraordinary strength, far higher than that of traditional armour materials. Nanocomposites have the possibility of being remarkable materials, with high strength and light weight. The work detailed in this report is an investigation into the mechanical properties of nanocomposites along with some novel blended polymer composites. Two compressive testing techniques have been used to carry out this investigation. The intermediate strain-rate Optical Drop-Weight, and the high strain-rate Split-Hopkinson Pressure Bar. The latter required some significant modifications in order to optimise it for use with low-density polymers. Ultimately, nanocomposites were found to behave virtually indistinguishably from the monolithic polymer matrices. Yield strengths and energy absorption characteristics remained inside the ordinary experimental scatter. Blended composites, in which a long chain length polymer is combined with a chemically similar polymer with a shorter chain length, proved to be more interesting. Yield strengths of these novel materials were increased over that of either constituent material, although energy absorption remained low.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Since the discovery of carbon nanotubes (CNTs), a large interest has developed around the incorporation of these into polymeric matrices in order to introduce the excellent mechanical, thermal and electrical properties of CNTs into the resultant composites. Nanocomposites of polymer/CNT composition allow for the favourable combination of the physical properties of the polymeric matrix and of the CNT filler. The biggest existing challenge of producing such nanocomposites is presented by the tendency of CNTs to occur in bundles or aggregates which are difficult to break up and to disperse in solution which leads to non-uniform distributions within the polymeric matrix. This problem has been combated through the use of CNT surface functionalization. However, a disadvantage exists with this solution. Since covalent functionalization of the CNT surface disrupts the electronic π-electron cloud which is responsible for the excellent electronic properties which CNTs are often desired for, an alternative method of functionalization must be employed in order to maintain the excellent intrinsic properties of CNTs yet create uniform dispersion of the nanotubes upon compatibilization with the polymeric matrix. Two alternative methods for the production of noncovalent compatibilization of multi-walled carbon nanotubes (MWNTs) with polystyrene were investigated and compared. These two methods involved the synthesis of a pyrene-functional macroinitiators for reversible addition fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP). Both of these methods allow for the controlled polymerisation of pyrene functional polystyrene chains. For comparison, the direct covalently functional MWNTs were also synthesised first by oxidation of the MWNT surface and conversion of the MWNT into the multifunctional RAFT and ATRP macroinitiator in which the styrene chains were controllably directly grafted from the surface of the MWNTs. The interaction of the pyrene chains with MWCNTs was monitored by using NMR, TGA and fluorescence spectroscopy. The NMR results showed the broadening and weakening of the pyrene protons as well as the polystyrene (PS) protons. TGA showed the loss of the pyrene-functional PS portion throughout the heating process. Fluorescence provided the conclusive result that the noncovalent compatibilization had occurred through the quenching of the emission and excitation signals as a result of electron transfer being facilitated by the π-stacking interactions. Finally, the MWNT nanocomposite polymer nanofibres are produced via the electrospinning technique with the various covalent and non-covalent compatibilized MWNT. The fibre morphology for the different compatibilization methodologies is compared as a function of the MWNT content. Distinct differences are observed for the different composites. / AFRIKAANSE OPSOMMING: Sedert die ontdekking van koolstof-nanobuisies (KNBs), het ʼn groot belangstelling ontwikkel rondom die betrekking van KNBs in polimeriese matrikse om samestellings met uitstekende meganiese, termiese en elektriese eienskappe te vervaardig. Nanosamestellings van polimeer/KNB komposisie laat toe dat gunstige kombinasies van fisiese eienskappe van die polimeer en die KNB vuller gerealiseer kan word. Die grootste uitdaging van die vervaardiging van sulke nanosamestellings is die neiging van KNBs om gebondelde formasie te vorm wat baie moeilik is om op te breek. Dit maak hulle verspreiding in oplossings en in polimeer matrikse oneweredig. Hierdie probleem word deur funksionalisering opgelos. Nogtans, ʼn nadeel van hierdie oplossing is dat kovalente funksionalisering verander die elektroniese struktuur van die KNB oppervlakte deur die ontwrigting van die π-elektron wolk wat vir die uitstekende elektroniese eienskappe verantwoordelik is. Dus moet ʼn alternatiewe funksionalisering metode gebruik word om die inherente eienskappe van die KNBs te behou en terselfde tyd ʼn uniforme verspreiding te bewerkstellig gedurende die vermenging met die polimeer matriks. Twee alternatiewe metodes vir die vervaardiging van nie-kovalente gefunksionaliserde multiommuurde koolstof-nanobuisies (Eng: MWNTs) met polistireen (PS) was ondersoek en vergelyk. Hierdie twee metodes was uitgevoer deur die sintese van ʼn pyreen-funksionele omkeerbare addisie-fragmentasie-kettingoordrag (OAFO) en atoomorrdragradikaaladdisie (AORA) makromiddel. Al twee van hierdie metodes lei tot ʼn gekontrollerde polimerisasie van pyreen-gefunksionaliserde stireen. Vir vergelyking was ʼn kovalente- gefunksionaliserde MWNT vervaardig deur die oksidasie van die MWNT oppervlakte en die daaropvolgende immobilisasie van dieselfde AORA en OAFO middel aan hierde aktiewe punte. Daarvan af was stireen gekontroleerd gepolimeriseer deur middel van die AORA en OAFO middel. Die interaksie was gekarakteriseer deur TGO, KMR en fluoressensie spektroskopie. Die KMR resultate het seine gewys van die verspreiding en verswakking van die pyreen en PS protone. TGO het die verlies van die pyreen-funksionele PS deel van die nie-kovalente produk gewys. Fluoressensie het beslissende bewyse gelewer dat die nie-kovalente funksionalisiering plaas gevind het deur die onderdrukking van die stralende en opwekkings seine as ʼn gevolg van die elektron oordrag wat deur die π-stapel interaksies gefasiliteer word. Uiteindelik was die nanosamestellings vermeng met PS en geelektrospin. Die vesel morfologie vir die verskillende gefunksionaliserde MWNT nanosamestellings metodes was vergelyk as ʼn funksie van MWNT inhoud. Duidelike verskille is waargeneem vir die verskillende samestellings.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Polymer composites have been gaining more importance in our daily lives because of the favorable properties that can be provided by these types of material. A polymer composite consists of improved properties when compared to the individual polymers that it is compiled of. The reason that composites are better than the individual polymers is mainly because composites are a combination of all the bene cial properties from the individual materials that was used to make the polymer composite. High impact polypropylene (HiPP) is a complex copolymer that was developed to overcome the restrictions of polypropylene (PP). Although PP have excellent properties at lower temperatures, it loses these advantages at elevated temperatures. High impact polypropylene has a much better impact strength and is processable at high temperatures. High impact polypropylene has been studied in depth for its applications and its superior properties such as an improved impact strength. The tensile properties, after the incorporation of a nano ller, have however not been investigated to our knowledge. Nano llers have reinforcing abilities due to the nano-scale diameters. Particles that have sizes on a nanometer range are mostly devoid of defects. Nano llers that are biopolymers have additional advantages such that can consist of antimicrobial abilities, renewability, biocompatibility and biodegradability. Composites reinforced with chitin nanowhiskers (chnw) have shown to have valuable applications in the latest medical, industrial and environmental developments. Di erent loadings of chnw were incorporated into a HiPP matrix in order to investigate the e ects that this nano ller will have on the tensile properties of HiPP. There were two challenges that required attention during the incorporation of chnw into HiPP. The rst major challenge was the poor interaction that exist between chnw and HiPP due to the hydrophobic nature of the HiPP matrix and the hydrophilic nature of chnw. The second problem was the agglomeration that can occur because of the hydrogen bonding between the chnw that is caused by the structure of the chnw chains. In order to gain the best dispersion of chnw within the HiPP matrix it was necessary to use compatibilizers and di erent methods of incorporation. The two types of compatibilizers that were chosen to improve the compatibility between the HiPP matrix and chnw were polypropylenegraft- maleic anhydride (PPgMA) and poly(ethylene-co-vinyl alcohol)(EVOH). Injection molding is typically used to process HiPP and was chosen as one of the methods for incorporating chnw into the HiPP matrix. A second method of incorporation was used speci cally for the nancomposites containing EVOH known as electrospinning combined with meltpressing. Tensile testing, DSC, TGA and FTIR were used to investigate the changes in the mechanical and thermal properties of the nanocomposites. SEM and TEM were employed to investigate the morphology of the electrospun ber mats and to characterize the chnw. FTIR as well as TGA were used to characterize the chitin nanowhiskers and to identify the individual components within the nanocomposites after incorporation took place. The incorporation of chnw along with the compatibilizer did show improvement in some mechanical properties of the polymer matrix. However, the in uence that each type of compatiblizer had on this e ect varied depending on the content of the chnw and compatibilizer with regards to the polymer matrix.

As a preliminary starting point for the present study, physical and mechanical properties of polypropylene nanocomposites (PPNCs) for samples received from Queen's University Belfast have been evaluated. Subsequently, polymer/clay nanocomposite material has been produced at Bradford. Mixing and processing routes have been explored, and mechanical properties for the different compounded samples have been studied. Clay intercalation structure has received particular attention to support the ultimate objective of optimising tensile and fracture behaviour of isotropic and die-drawn PPNCs. Solid-state molecular orientation has been introduced to PPNCs by the die-drawing process. Tensile stress-strain measurements with video-extensometry and tensile fracture of double edge-notched tensile specimens have been used to evaluate the Young's modulus at three different strain rates and the total work of fracture toughness at three different notch lengths. The polymer composite was analyzed by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, wide angle x-ray diffraction, and transmission electron microscopy. 3% and 5% clay systems at various compatibilizer (PPMA) loadings were prepared by three different mixing routes for the isotropic sheets, produced by compression moulding, and tensile bars, produced by injection moulding process. Die-drawn oriented tensile bars were drawn to draw ratio of 2, 3 and 4. The results from the Queen's University Belfast samples showed a decrement in tensile strength at yield. This might be explained by poor bonding, which refers to poor dispersion. Voids that can be supported by intercalated PP/clay phases might be responsible for improvement of elongation at break. The use of PPMA and an intensive mixing regime with a two-step master batch process overcame the compatibility issue and achieved around 40% and 50% increase in modulus for 3% and 5% clay systems respectively. This improvement of the two systems was reduced after drawing to around 15% and 25% compared with drawn PP. The work of fracture is increased either by adding nanoclay or by drawing to low draw ratio, or both. At moderate and high draw ratios, PPNCs may undergo either an increase in the size of microvoids at low clay loading or coalescence of microvoids at high clay loading, eventually leading to an earlier failure than with neat PP. The adoption of PPMA loading using an appropriate mixing route and clay loading can create a balance between the PPMA stiffness effect and the degree of bonding between clay particles and isotropic or oriented polymer molecules. Spherulites size, d-spacing of silicate layers, and nanoparticles distribution of intercalated microtactoids with possible semi-exfoliated particles have been suggested to optimize the final PPNCs property.

The dynamic relaxation characteristics of Matrimid® (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (ƴ and β transitions), and the glass-rubber (α) transition. For Matrimid, the low-temperature ƴ transition is purely non-cooperative, while the β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the ƴ transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The β relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (α) transition, dynamic mechanical studies reveal a strong shift in Tα to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement. The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or immobilized at the particle-polymer interface. Dielectric measurements, which were used to probe the time-temperature response across the local sub-glass relaxations, indicate no variation in relaxation characteristics with particle loading. Nanocomposite studies were also conducted on rubbery poly(ethylene oxide) networks crosslinked in the presence of MgO or SiO2 nanoparticles. The inclusion of nanoparticles led to a systematic increase in rubbery modulus and a modest positive offset in the measured glass transition temperature (Tα) for both systems. The sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in these crosslinked networks.

Les copolymères diblocs poly(styrène)-b-poly(acide acrylique) présentent une microséparation de phase et s'ordonnent en phase sphérique, hexagonale ou lamellaire dans leur état solide. Dans l'eau, ces nanostructures gonflent sélectivement en conservant leur ordre à grande distance car l'eau pénètre dans les domaines de PAA sans affecter les coeurs de PS, hydrophobes et vitreux. La période des phases lamellaires et hexagonales dispersées dépend alors du degré d'ionisation des brosses de PAA, contrôlable via le pH. Le gonflement de ces structures est étudié par diffusion des rayons X aux petits angles (DXPA) et par cryofracture et microscopie électronique à transmission (FF-TEM). Nous utilisons ces propriétés de gonflement contrôlé pour préparer des nanocomposites ordonnés de copolymères et de nanoparticules minérales. Cette approche consiste en une incorporation sélective des nanoparticules dans les domaines de PAA des phases ordonnées en utilisant l'eau comme vecteur. Un modèle simple nous permet d'estimer l'équilibre des effets d'interactions et de confinement lors de l'incorporation des nanoparticules en fonction des paramètres (pH, morphologie, taille des particules). Nous vérifions expérimentalement ces résultats en utilisant des nanoparticules de silice et d'oxyde de cérium et par des analyses effectuées en DXPA et en FF-TEM sur la structure interne des systèmes hybrides dispersés ainsi que sur les nanocomposites finaux obtenus après séchage. Nous obtenons en particulier des structures lamellaires contenant jusqu'à 12% en volume de nanoparticules d'oxyde bien ordonnées. De tels composites sont prometteurs pour des applications en matériaux fonctionnels.