Orientadores: Liliane Maria Ferrareso Lona, Paula Forte de Magalhães Pinheiro Bonassi Machado / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T16:56:26Z (GMT). No. of bitstreams: 1 Moraes_SamaraBoaventurade_M.pdf: 2271450 bytes, checksum: 53f3a25eef4f92dd7e80b68fe8945abd (MD5) Previous issue date: 2013 / Resumo: O interesse pelos nanocompósitos de matriz polimérica tem crescido acentuadamente nos últimos anos, pois estes materiais apresentam melhores propriedades mecânicas, térmicas, entre outras, quando comparados aos materiais convencionais. Entre os diferentes tipos de nanocompósitos de matriz polimérica, aqueles reforçados com compostos lamelares têm sido amplamente estudados. Os hidroxissais lamelares (HSLs) são exemplos de compostos lamelares e o estudo sobre estes materiais é um assunto novo. Trabalhos na literatura que envolvem os HSLs são relativamente escassos e a maioria está relacionada à sua síntese e caracterização estrutural. Neste trabalho foram sintetizados nanocompósitos de poliestireno utilizando hidroxissais lamelares como agente de reforço. Os nanocompósitos foram produzidos via polimerização in situ utilizando a polimerização em massa e diferentes frações mássicas de HSL. Foram produzidos HSLs intercalados com o ânion dodecilsulfato e o ânion laurato. O polímero puro foi caracterizado pelas análises de cromatografia de permeação em gel, análise gravimétrica, difração de raios-x, espectroscopia no infravermelho por transformada de Fourier, calorimetria exploratória diferencial, termogravimetria e teste de inflamabilidade. Os hidroxissais lamelares foram caracterizados pelas técnicas de inchamento de Foster, difração de raios-x e espectroscopia no infravermelho por transformada de Fourier. Os nanocompósitos poliméricos sintetizados foram caracterizados pelas técnicas de difração de raios-x, espectroscopia no infravermelho por transformada de Fourier, calorimetria exploratória diferencial, termogravimetria e teste de inflamabilidade. Foi escolhido um dos nanocompósitos sintetizados e foi realizada análise gravimétrica para avaliar a influência do HSL na conversão do polímero. Dentre as propriedades do material, os resultados obtidos mostram que os nanocompósitos sintetizados tendem a apresentar melhoras na inflamabilidade quando comparados ao polímero puro e, também apresentam temperatura final de degradação superior ao do poliestireno, além de não influenciarem significativamente na temperatura de transição vítrea do polímero / Abstract: Interest in the nanocomposite polymeric matrix has grown dramatically in recent years because these materials exhibit better mechanical and thermal properties, among others, when compared to conventional materials. Among the different types of nanocomposite polymeric matrix, those reinforced with layered compounds has been widely studied. The layered hydroxides salts (LHSs) are examples of layered compounds and the study of layered hydroxides salts is a new subject. Studies in the literature involving the LHSs are relatively scarce and most of them are related to their synthesis and structural characterization. In this work nanocomposites of polystyrene using layered hydroxides salts as a reinforcing agent were synthesized. The nanocomposites were produced via in situ bulk polymerization. Polymer nanocomposites were synthesized with different mass fractions of LHS. LHSs intercalated with dodecyl sulfate anion and laurate anion was produced. The pure polymer was characterized by analysis of gel permeation chromatography, gravimetric analysis, x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric and flammability test. The layered hydroxides salts were characterized by swelling of Foster techniques, x-ray diffraction and Fourier transform infrared spectroscopy. The synthesized polymer nanocomposites were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric and flammability test. One of the synthesized nanocomposites was chosen and gravimetric analysis was performed to assess the influence of LHS on the conversion of the polymer. Among the material properties, the results obtained show that the nanocompósito synthesized tend to have improved flammability compared to the pure polymer, and also present final temperature higher than the degradation of polystyrene, and do not significantly influence the glass transition temperature of the polymer / Mestrado / Desenvolvimento de Processos Químicos / Mestra em Engenharia Química

Multifunctional nanocomposites are promising for a variety of applications ranging from microwave devices to biomedicine. High demand exists for magnetically tunable nanocomposite materials. My thesis focuses on synthesis and characterization of novel nanomaterials such as polymer nanocomposites (PNCs) and multi-walled carbon nanotubes (MWCNTs) with magnetic nanoparticle (NP) fillers. Magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) NPs with controlled shape, size, and crystallinity were successfully synthesized and used as PNC fillers in a commercial polymer provided by the Rogers Corporation and poly(vinylidene fluoride). Magnetic and microwave experiments were conducted under frequencies of 1-6 GHz in the presence of transverse external magnetic fields of up to 4.5 kOe. Experiments confirm strong magnetic field dependence across all samples. When incorporated in to a cavity resonator device, tangent losses were reduced, quality factor increased by 5.6 times, and tunability of the resonance frequency was demonstrated, regardless of NP-loading. Work on PNC materials revealed the importance of NP interactions in confined spaces and motivated the study of confinement effects of magnetic NPs in more controlled environments, such as MWCNTs with varying diameters. MWCNTs were synthesized with diameters of 60 nm, 100 nm, 250 nm, and 450 nm to contain magnetic NP fillers (~10 nm) consisting of ferrites of the form MFe2O4, where M = Co2+, Ni2+, or Fe2+. All confined samples exhibit superparamagnetic-like behavior with stronger magnetic response with respect to increasing MWCNT diameter up to 250 nm due to the enhancement of interparticle interactions. This thesis provides the first systematic study of this class of nanocomposites, which paves the way to inclusion of novel nanostructured materials in real-world applications.

Orientador: Eliana Aparecida de Rezende Duek / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-27T23:48:09Z (GMT). No. of bitstreams: 1 Leal_ClaudeneteVieira_D.pdf: 6830750 bytes, checksum: e1a33a17e1e2276d0b1b5bace3231cb6 (MD5) Previous issue date: 2015 / Resumo: Nanocompósitos poliméricos exibem potencial para aplicações como biomateriais, pois podem melhorar as propriedades dos polímeros por meio da associação com nanoestruturas, resultando em um material com propriedades estruturais e funcionais superiores. O objetivo desse trabalho foi o desenvolvimento e posterior caracterização de nanocompósitos de poli (L-ácido lático) (PLLA) e nanotubos de carbono (NTC). Os NTC têm sido pesquisados para aplicações biomédicas devido às suas excelentes propriedades, entretanto, os NTC possuem características estruturais que podem causar toxicidade em ambiente biológico. Nesse trabalho, primeiramente foi aplicado um método para purificar os NTC por modificação química com objetivo de melhorar a dispersibilidade e diminuir os efeitos tóxicos. Posteriormente foram preparados os nanocompósitos na forma de membranas de PLLA com NTC em diferentes concentrações, utilizando o método de evaporação de solvente. Foram realizadas caracterizações morfológicas com microscopia eletrônica de varredura e microscopia de força atômica, estudo do comportamento térmico por calorimetria exploratória diferencial e microscopia ótica com luz polarizada, e ensaios mecânicos sob módulo de tração, análise dinâmico-mecânica e nanoindentação. Na última etapa foi realizado teste in vitro de cultura de células. Resultados indicaram aumento da rugosidade das amostras após a adição de NTC, o estudo do comportamento térmico revelou que o NTC atua como agente nucleante nos nanocompósitos, promovendo a formação de maior quantidade de núcleos cristalinos na matriz polimérica. As propriedades mecânicas indicaram aumento no módulo de elasticidade, alongamento e dureza nos nanocompósitos. Na análise biológica, os resultados obtidos comprovaram que, após a adição de NTC, as células foram capazes de aderir e sustentar a proliferação celular sobre as membranas, apresentando favorável citocompatibilidade / Abstract: Polymer nanocomposites exhibit potential for applications as biomaterials because they can improve the properties of polymers by combination with nanostructures, resulting in a material with superior structural and functional properties. The purpose of this work was the development and further characterization of poly (L-lactic acid) (PLLA) and carbon nanotubes (CNT) nanocomposites. CNTs have been investigated for biomedical applications due to their excellent properties, however, pristine NTC have structural characteristics that may cause toxicity in biological environment. In this work, a method to purify the NTC by chemical modification in order to improve the dispersibility and to reduce the toxic effects was firstly applied. Subsequently, PLLA/NTC nanocomposite membranes were prepared at different concentrations by solvent casting. Samples were characterized by scanning electron microscopy, atomic force microscopy, polarized optical microscopy, differential scanning calorimetry, dynamic mechanical analysis, tensile test, nanoindentation and X ray diffraction. In the last step, in vitro cell culture assay was performed. The results indicated an increase of the roughness of the samples after the addition of NTC. Thermal behavior study showed that the NTC act as a nucleation agent in nanocomposites, promoting the formation of a larger amount of crystal nucleous in the polymer matrix. Mechanical properties indicated an increase in elastic modulus, elongation and hardness in the nanocomposites. In biological testing, the results showed that, after addition of NTC, cells were able to adhere and sustain cellular proliferation on membranes and showed a favorable cytocompatibility / Doutorado / Materiais e Processos de Fabricação / Doutora em Engenharia Mecânica

The effect of incorporation of montmorillonite layered silicate (MLS) on poly (ethylene terephthalate) (PET) matrix was investigated. MLS was added in varying concentration of 1 to 5 weight percent in the PET matrix. DSC and polarized optical microscopy were used to determine the crystallization effects of MLS addition. Non isothermal crystallization kinetics showed that the melting temperature and crystallization temperature decrease as the MLS percent increases. This delayed crystallization along with the irregular spherulitic shape indicates hindered crystallization in the presence of MLS platelets. The influence of this morphology was related with the fracture toughness of PET nanocomposites using essential work of fracture coupled with the infra red (IR) thermography. Both the essential as well as non essential work of fracture decreased on addition of MLS with nanocomposite showing reduced toughness.

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Today, nanotechnology has added a new dimension to materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials and even though they show tremendous promise for dielectric/electrical insulation applications (“nanodielectrics” being the buzzword), the understanding related to these systems is very premature. Considering the desired research needs with respect to some of the dielectric properties of polymer nanocomposites, this study attempts to generate an understanding on some of the existing issues through a systematic and detailed experimental investigation coupled with a critical analysis of the data. An epoxy based nanocomposite system is chosen for this study along with four different choices of nano-fillers, viz. TiO2, Al2O3, ZnO and SiO2. The focus of this study is on the properties of nanocomposites at low filler loadings in the range of 0.1 - 5% by weight and the properties under investigation are the permittivity/tan delta behaviors, DC volume resistivity, AC dielectric strength and electrical discharge resistant characteristics. Significant efforts have also been directed towards addressing the interface interaction phenomena in epoxy nanocomposites and their subsequent influence on the dielectric properties of the material. The accurate characterization of the dielectric properties for polymer nanocomposites depends on the dispersion of nanoparticles in the polymer matrix and to achieve a good dispersion of nanoparticles in the epoxy matrix for the present study, a systematic design of experiments (DOE) is carried out involving two different processing methods. Consequently, a laboratory based epoxy nanocomposite processing methodology is proposed in this thesis and this process is found to be successful in dispersing nanoparticles effectively in the epoxy matrix, especially at filler concentrations lower than 5% by weight. Nanocomposite samples for the study are prepared using this method and a rigorous conditioning is performed before the dielectric measurements. The dielectric properties of epoxy nanocomposites obtained in the present study show interesting and intriguing characteristics when compared to those of unfilled epoxy and microcomposite systems and few of the results are unique and advantageous. In an unexpected observation, the addition of nanoparticles to epoxy is found to reduce the value of nanocomposite real permittivity below that of unfilled epoxy over a wide range of frequencies. Similarly, it has been observed that irrespective of the filler type, tan delta values in the case of nanocomposites are either same or lower than the value of unfilled epoxy up to a filler loading of 5% by weight, depending on the frequency and filler concentration. In fact, the nanocomposite real permittivities and tan delta values are also observed to be lower as compared to the corresponding microcomposites of the same constituent materials at the same filler loading. In another significant result, enhancements in the electrical discharge resistant characteristics of epoxy nanocomposites (with SiO2/Al2O3 nanoparticles) are observed when compared to unfilled epoxy, especially at longer durations of discharge exposures. Contrary to these encouragements observed for few of the dielectric properties, the trends of DC volume resistivity and AC dielectric breakdown strength characteristics in epoxy nanocomposites are found to be different. Irrespective of the type of filler in the epoxy matrix, it has been observed that the values of both AC dielectric strengths and DC volume resistivities are lower than that of unfilled epoxy for the filler loadings investigated. The results mentioned above seem to suggest that there has to be an interaction between the nanoparticles and the epoxy chains in the nanocomposite and therefore, glass transition temperature (Tg) measurements are performed to characterize the interaction phenomena, if any. The results of Tg for all the investigated nanocomposites also show interesting trends and they are observed to be lower than that of unfilled epoxy up to certain nanoparticle loadings. This lowering of the Tg in epoxy nanocomposites was not observed in the case of unfilled and microcomposite systems thereby strongly confirming the fact that there exists an interaction between the epoxy chains and nanoparticles in the nanocomposite. Considering the variations obtained for the nanocomposite real permittivity and Tg with respect to filler loading, a dual nanolayer interface model is utilized to explain the interaction dynamics and according to the model, interactions between epoxy chains and nanoparticles lead to the formation of two epoxy nanolayers around the nanoparticle. Analysis shows that the characteristics of the interface region have a strong influence on the dielectric behaviors of the nanocomposites and the suggested interface model seems to fit the characteristics obtained for the different dielectric/electrical insulation properties rather well. Further investigations are performed to understand the nature of interaction between nanoparticles and epoxy chains through FTIR studies and results show that there is probably an occurrence of hydrogen bonding between the epoxide groups of the epoxy resin and the free hydroxyl (OH) groups present on the nanoparticle surfaces. The results obtained for the dielectric properties of epoxy nanocomposites in this study have widened the scope of applications of these functional materials in the electrical sector. The occurrence of lower values of real permittivity for nanocomposites is definitely unique and unexpected and this result has huge potential in electronic component packaging applications. Further, the advantages related to tan delta and electrical discharge resistance for these materials carry lot of significance since, electrical insulating materials with enhanced electrical aging properties can be designed using nanocomposite technology. Although the characteristics of AC dielectric strengths and DC volume resistivities are not found to be strictly advantageous for epoxy nanocomposites at the investigated filler loadings, these properties can be optimized when designing insulation systems for practical applications. In spite of all these advantages, serious and systematic research efforts are still desired before these materials can be successfully utilized in electrical equipment.

The developments in mobile/portable electronics and alternative energy vehicles prompted engineers and researchers to develop electrochemical energy storage devices called supercapacitors, as the third generation type capacitors. Most of the research and development on supercapacitors focus on electrode materials, electrolytes and hybridization. Some attempts have been directed towards increasing the energy density by employing electroactive materials, such as metal oxides and conducting polymers (CPs). However, the high cost and toxicity of applicable metal oxides and poor long term stability of CPs paved the way to alternative electrode materials. The electroactive materials with carbon particles in composites have been used substantially to improve the stability of supercapacitors. Furthermore, the use of carbon particles and CPs could significantly reduce the cost of supercapacitor electrodes compared to metal oxides. Recent developments in carbon allotropes, such as carbon nanotubes (CNTs) and especially graphene (G), have found applications in supercapacitors because of their enhanced double layer capacitance due to the large surface area, electrochemical stability, and excellent mechanical and thermal properties. The main objective of the research presented in this dissertation is to increase the energy density of supercapacitors by the development of nanocomposite materials composed of graphene and different CPs, such as: (a) polyaniline derivatives (polyaniline (PANI), methoxy (-OCH3) aniline (POA) and methyl (-CH3) aniline (POT), (b) poly(3-4 ethylenedioxythiophene) (PEDOT) and (c) polypyrrole (PPy). The research was carried out in two phases, namely, (i) the development and performance evaluation of G-CP (graphene in conducting polymers) electrodes for supercapacitors, and (ii) the fabrication and testing of the coin cell supercapacitors with G-CP electrodes. In the first phase, the synthesis of different morphological structures of CPs as well as their composites with graphene was carried out, and the synthesized nanostructures were characterized by different physical, chemical and thermal characterization techniques, such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), UV-visible spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, BET surface area pore size distribution analysis and Thermogravimetric Analysis (TGA). The electrochemical properties of G-CP nanocomposite-based supercapacitors were investigated using Cyclic Voltammetry (CV), galvanostatic charge-discharge and Electrochemical Impedance Spectroscopy (EIS) techniques in different electrolytes, such as acidic (2M H2SO4 and HCl), organic ( 0.2 M LiClO4) and ionic liquid (1M BMIM-PF6) electrolytes. A comparative study was carried out to investigate the capacitive properties of G-PANI derivatives for supercapacitor applications. The methyl substituted polyaniline with graphene as a nanocomposite (G-POT) exhibited a better capacitance (425 F/g) than the G-PANI or the G-POA nanocomposite due to the electron donating group of G-POT. The relaxation time constants of 0.6, 2.5, and 5s for the G-POT, G-PANI and G-POA nanocomposite-based supercapacitors were calculated from the complex model by using the experimental EIS data. The specific capacitances of two-electrode system supercapacitor cells were estimated as 425, 400, 380, 305 and 267 F/g for G-POT, G-PANI, G-POA, G-PEDOT and G-PPy, respectively. The improvements in specific capacitance were observed due to the increased surface area with mesoporous nanocomposite structures (5~10 nm pore size distribution) and the pseudocapacitance effect due to the redox properties of the CPs. Further, the operating voltage of G-CP supercapacitors was increased to 3.5 V by employing an ionic liquid electrolyte, compared to 1.5 V operating voltage when aqueous electrolytes were used. On top of the gain in the operating voltage, the graphene nano-filler of the nanocomposite prevented the degradation of the CPs in the long term charging and discharging processes. In the second phase, after studying the material's chemistry and capacitive properties in three-electrode and two-electrode configuration-based basic electrochemical test cells, coin cell type supercapacitors were fabricated using G-CP nanocomposite electrodes to validate the tested G-CPs as devices. The fabrication process was optimized for the applied force and the number of spacers in crimping the two electrodes together. The pseudocapacitance and double layer capacitance values were extracted by fitting experimental EIS data to a proposed equivalent circuit, and the pseudocapacitive effect was found to be higher with G-PANI derivative nanocomposites than with the other studied G-CP nanocomposites due to the multiple redox states of G-PANI derivatives. The increased specific capacitance, voltage and small relaxation time constants of the G-CPs paved the way for the fabrication of safe, stable and high energy density supercapacitors.

Polymer Nanocomposites (PNC) are a new class of materials characterized by their large interfacial areas between the host polymer and nanofiller. This unique feature, due to the size of the nanofiller, is understood to be the cause of enhanced mechanical, electrical, optical, and barrier properties observed of PNCs, relative to the properties of the unfilled polymer. This interface can determine the miscibility of the nanofiller in the polymer, which, in turn, influences the PNC's properties. In addition, this interface alters the polymer's structure near the surface of the nanofiller resulting in heterogeneity of local properties that can be expressed at the macroscopic level. Considering the polymer-nanoparticle interface significantly influences PNC properties, it is apparent that some atomistic level of detail is required to accurately predict the behavior of PNCs. Though an all-atom simulation of a PNC would be able to accomplish the latter, it is an impractical approach to pursue even with the most advanced computational resources currently available. In this contribution, we develop (1) an equilibrium coarse-graining method to predict nanoparticle dispersion in a polymer melt, (2) a dynamic coarse-graining method to predict rheological properties of polymer-nanoparticle melt mixtures, and (3) a numerical approach that includes interfacial layer effects and polymer rigidity when predicting barrier properties of PNCs. In addition to the above, we study how particle and polymer characteristics affect the interfacial layer thickness as well as how the polymer-nanoparticle interface may influence the entanglement network in a polymer melt. More specifically, we use a mean-field theory approach to discern how the concentration of a semiflexible polymer, its rigidity and the particle's size determine the interfacial layer thickness, and the scaling laws to describe this dependency. We also utilize molecular dynamics and simulation techniques on a model PNC to determine if the polymer-nanoparticle interaction can influence the entanglement network of a polymer melt. / text

Polypropylene (PP) and ethylene-co-octene copolymer (EOC) blends were prepared at various component ratios and reinforced with silica nanoparticles (SiO2). Strategies to improve filler dispersion involved the grafting of a silane coupling agent on the PP matrix, the addition of a maleated PP (PP-g-MA) as a compatibilizer and the use of hydrophobic silica nanoparticles. These approaches resulted in a fine dispersion of the nanoparticles within the PP phase and induced a reduction of the size of the EOC domains, due to a barrier effect. Tensile and flexural properties were significantly increased, whereas ductility and impact properties were not affected. These enhancements are attributed to the favourable microstructure of the blends, featuring a segregated microstructure, and to the improved interfacial adhesion between the functionalized polymer matrix and the surface of the nanoparticles. The microstructure and rheology of model melt compounded EOC-based nanocomposites were investigated. Functionalization of the polyolefin matrix was accomplished through silane grafting, or addition of a maleated EOC (EOC-g-MA) compatibilizer. Various grades of unmodified SiO2 having different specific surface areas (SSA), as well as a surface-modified grade were added to the EOC matrix at various loadings. The formation of covalent and hydrogen bonds between the silanol groups and the functionalized polymer generated strong polymer/filler (P/F) interactions, resulting in improved filler dispersion. Bound polymer characterization revealed that in the compatibilized materials, the amount of polymer physically attached to the nanoparticles was higher than in the non-compatibilized samples. In the absence of a compatibilizer, larger SiO2 aggregates formed upon increasing SSA because of increased probability of hydrogen bonding between the particles. The increased propensity for aggregation was revealed by time sweeps as well as by the increased strain sensitivity in stress sweeps. On the contrary, the compatibilized composites exhibited a stable response and a higher critical strain for the onset of non-linearity, indicative of stronger adhesion between the fillers and the matrix. Superposition of oscillatory and creep/recovery experiments revealed that the viscoelastic properties in the terminal region were influenced substantially by the state of dispersion of the nanoparticles. In the absence of a compatibilizer, substantial enhancements in the linear viscoelastic (LVE) functions were noted and an increasing SSA resulted in more significant deviations from terminal flow. On the contrary, the SSA of the particles had no effect on the viscoelastic and mechanical properties of the compatibilized composites. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2011-04-18 15:17:52.471