Neste trabalho foram preparados nanocompósitos de Poliestireno (PS) e argilas organofílicas. As argilas, inicialmente hidrofílicas, foram modificadas organicamente utilizando três sais quaternários de amônio diferentes: Cloreto de hexadecil trimetil amônio (CTAC), Cloreto de alquil dimetil benzil amônio (Dodigen) e Cloreto de dimetil dioctadecil amônio (Praepagen). A argila organofílica Cloisite 20A foi também utilizada neste estudo. Os nanocompósitos foram preparados por intercalação no polímero fundido por três técnicas diferentes: adição de argila em suspensão de álcool etílico por uma bomba dosadora de líquidos durante a extrusão, adição de argila em pó por um alimentador mecânico durante a extrusão e adição de suspensão de argila em álcool etílico durante obtenção por batelada. Os materiais obtidos foram caracterizados por difração de raios-X (DRX), microscopia óptica (MO) e microscopia eletrônica de transmissão (MET) e ensaios reológicos de Cisalhamento Oscilatório de Pequenas Amplitudes (COPA). As propriedades térmicas foram analisadas por análise termogravimétrica (TG) e as propriedades mecânicas foram analisadas por ensaios de tração e impacto Izod. As três técnicas se mostraram eficazes na preparação dos nanocompósitos, e seus resultados apresentaram uma similaridade muito grande. Os resultados de DRX e microscopia mostraram que a maioria dos nanocompósitos apresentou estruturas compostas de fases intercaladas e esfoliadas. As análises térmicas mostraram que a adição de argila ao PS o tornou mais estável termicamente, suportando maiores temperaturas antes de iniciar o processo de degradação. Os ensaios reológicos de COPA e ensaios mecânicos dos nanocompósitos obtidos não apresentaram grandes variações em relação ao PS puro. / In this work nanocomposites of polystyrene (PS) and organophilic clays were prepared. The clays were organically modified using three different ammonium quaternary salts: cetyltrimethyl ammonium chloride (commercial name: CTAC), alquildimethyl benzyl ammonium chloride (commercial name: Dodigen) and distearyl dimethyl ammonium chloride (commercial name: Praepagen). The organoclay Cloisite 20 A was also used in this work. The nanocomposites were prepared by melt intercalation using three different techniques: adding the organoclay as a diluted organic solvent supension to the extruder using a motor-driven metering pump, adding the organoclay as powder to the extruder using a mechanical feeder and adding the organoclay as a diluted organic solvent suspension to the mixer. The materials obtained were characterized by X-ray diffraction (XRD), optical microscopy (OM), transmission electron microscopy (TEM) and by rheological studies through small amplitude oscillatory shear tests (SAOS). The thermal properties were studied by thermogravimetrical analyses (TG) and the mechanical properties were studied by tensile and impact Izod strength tests. The three techniques were efficient to prepare nanocomposites, and their results were very similar. The DRX and microscopy results showed that the most nanocomposites presented structures composed by intercalated and exfoliated phases. The thermal analyses showed that the addition of organoclay turned PS more thermally stable, increasing their degradation temperatures. The results of rheological studies (SAOS) and the mechanical tests did not present significant variations compared to the neat PS.

This thesis focuses on designing thermoplastic nanocomposites with good mechanical, thermal and electrical properties. Thermoplastic nanocomposites, which are used in this work, are composed of thermoplastic polyurethane (TPU) matrices and graphene nanofillers (GNFs). TPUs were synthesised with large ratios of hard segments (HS), including 60, 70 and 80 Wt. % HS. The influences of HS content and annealing treatment at 80oC on the thermal, electrical and mechanical properties of TPUs and TPUs/GNFs samples have been investigated. The crystallinity, Tg, tensile strength, yield strength, and tensile modulus of all pure TPU samples are seen to increase after annealing treatment due to microphase separation. This also depends on the HS content in order to achieve better properties with various annealing times. The nanofillers include graphene nanoplatelets (GNP), graphene oxide (GO), and reduced graphene oxide (rGO). Various dispersion routes have been utilised to achieve better dispersion and distribution of the nanofillers. In-situ polymerisation, melt-compounding and solution-mixing techniques have been used to study dispersion effects and further moulding by injection moulding to prepare new TPU nanocomposites. Filler-matrix and filler-filler interfaces significantly influence the final performance of TPU nanocomposites. There is therefore a balance to be struck in the design of graphene-based TPU nanocomposites between the ability to achieve higher loadings of reinforcement and the reduction in effective Young’s modulus of the reinforcement as the number of layers in the nanofillers is increased. Effective stress transfer is achieved as a result of both dispersion and interfacial interaction. It has been demonstrated that graphene plays a reinforcing role in nanocomposites through its effective modulus as well as bonding with TPU phases. The first nanofiller studied is GNP, which shows good mechanical, thermal and electrical properties. The in-situ polymerisation approach was found to be the best dispersion method compared to melt compounding and solution mixing, as the optimum properties of GNP nanofillers can be achieved in the TPU/70 HS matrix. The TPU/70 HS had higher values compared to both TPU/60 HS and TPU/80 HS. However, the preparation of GO and rGO incorporating TPU/70 HS was not successfully synthesised due to the suppression of chain growth during polymerisation. Thus, the melt-compounding process was used instead for both GO- and rGO-based TPU matrices. TPU/70/GO nanocomposites displayed better mechanical performance compared to TPU/70/rGO nanocomposites, as a result of greater interaction between TPUs chains and fillers surfaces. It was found that the percolation thresholds for GO- and rGO-filled nanocomposites were significantly lower than that of GNP-filled nanocomposites due to their higher aspect ratio. Annealing treatment showed lower mechanical properties of TPU nanocomposite samples compared to non-annealed TPU nanocomposite samples, resulting from disruption of phase separation and restacking of nanofillers. The tensile moduli of nanocomposites were predicted using modified Halpin-Tsai models. Results showed good agreement at low loadings of GNP (≤1, 3 and 5 Wt. %), which depend on the effect of TPU phase interaction. However, poor agreement was observed at higher loadings of nanofillers, where the TPU nanocomposites displayed reduced reinforcement efficiency. This is due to the fact that the model assumes perfect adhesion between the nanofillers and the matrix, uniform particle dispersion and distribution, and complete exfoliation and total orientation in the direction of applied stress. This also correlates with results from SEM, TEM, POM and diffusivity mapping images, which showed aggregation, agglomeration and poorer distribution of nanofillers in the TPU matrix at higher loadings.

As a part of a larger effort towards the fundamental understanding of structureproperty relationship in nanoplatelet-reinforced polymer nanocomposites, a set of model epoxy systems containing α-Zirconium Phosphate (α-ZrP) have been prepared and studied in this dissertation. A new surface modification approach, i.e., the porous pathway approach, for improving intercalation efficiency and exfoliation of layered nanoplatelets has been proposed and the effectiveness has been demonstrated. In order to clearly understand the roles of nanofillers and the effects of their geometric factors on the physical and mechanical properties of nanocomposites, variables such as nanoplatelet loading level, degree of exfoliation, and aspect ratio have been carefully controlled in the epoxy matrices. Morphological information of the prepared nanocomposites was unambiguously confirmed by carrying out X-ray diffraction and transmission electron microscopy (TEM). Tensile and thermo-mechanical properties of the model epoxy/α-ZrP nanocomposites have been investigated. Furthermore, fracture behavior of the model nanocomposites is examined in this study. This work has enhanced the understanding of the effects of nanoplatelet, i.e., loading level, degree of exfoliation, aspect ratio, and the type of surface modifiers, on the mechanical properties and fracture behavior of polymer nanocomposites.

Polyimide/clay nanocomposites were synthesized via two processes. The one-step process is a polymer-diffusion process, and the two-step process is a monomer-diffusion/in-situ polymerization process. Effect of clay loading, surfactant, solvent-release, and clays on the structural formation and properties of the hybrids were studied. XRD (X-ray-diffractometer), TEM (transmission electron microscopy), FTIR (Fourier-transform infrared spectroscopy), DLS (dynamic light scattering), TGA (thermo-gravimetric analyzer), TMA (thermo-mechanical analyzer), DMA (dynamic mechanical analyzer), and GPA (gas permeability analyzer) were used for the characterization of the clays and composites. For the effect of clay-loading, it is found that the threshold of clay loading capable of efficiently improving the properties of polyimide (PI) matrix, should be larger than 0.08 ~ 0.31 wt% for the clay with aspect ratio of 200 ~ 50, as judged by the calculation of classical excluded volume argument. For the effect of surfactant, a thermally stable organoclay of 1-methyl-3-octyl-imidazolium chloride modified montmorillonite (8M) displayed the degradation temperature at maximum rate (Td.max) 91 0C higher than that of dodecyl-amine hydrochloride modified montmorillonite (12M). For PI8M hybrid with 5 wt% clay loading, the T10% Loss and Td.max increased 4 0C and 15 0C respectively as compared to that of the neat PI. Besides, two organoclays with improved affinity to solvent NMP (N-methyl-2-pyrrolidone) 18M {octadecylmethyl-bispolyoxylene [15] ammonium chloride modified montmorillonite} and 30B (Methyltallow-bis-2-hydroxyethyl ammonium ion modified montmorillonite) were used to prepare PI/clay nanocomposites. The relative oxygen permeation rate decreased to 0.5 upon the incorporation of these organoclays of 1 wt%, displaying superior improvement on the gas barrier property of polyimide. For the solvent-release effect, the intercalation behavior of the structural formation of PI/clay nanocomposites was studied. The reduction of d-spacing (~1.30 nm) of clay exists in PI/clay nanocomposites even with the case of 1 wt% clay-loading as characterized by XRD and TEM observation. An opposite argument was presented about the explanation to the contraction in galleries of clay with d001~1.30 nm for PI/clay nanocomposites, after the examination of PAA/clay, organoclay/NMP, organoclay, and pristine clay subjected to a specific heating process. We suggest this phenomenon cannot be ascribed to a poly(amic acid) monolayer adopts a flattened conformation is intercalated in the gallery upon thermal elimination of the solvent. And found it is irrelevant to the intercalation of PAA or PI molecules, but is primarily in consequence of the out-flow NMP together with the out-bound surfactants molecules, partial degradation of surfactants, and the re-aggregation of clays induced by the increasing concentration (volume fraction) of clays upon evaporation of NMP. For the effect of different methods of preparation, PI/clay nanocomposites prepared by monomer-diffusion into non-reactive clay (M) process show the higher relative oxygen permeation rate of 0.1, and Td.max of 11 0C as compared to that of hybrids synthesized by polymer-diffusion process. For the effect of different clays, properties of PI/clay nanocomposites prepared by a reactive layered silicic acid of hydrogen-magadiite (H) and nonreactive clay of montmorillonite were studied. The latter displayed a higher Td.max of 7 0C, and the lower relative oxygen permeation rate of 0.07 as compared to the former, demonstrating the better improvement on thermal, and gas barrier properties.

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Abstract Physical chemistry and microstructure of polyimide / clay nanocomposites were investigated in this study. Diffusion of diamine monomers into the clay gallery prior to polymerization was carefully controlled in order to demonstrate the physical constraint during the formation of the nanocomposites. In addition, diamines with different chemical reactivity were employed to show the effect of chemical reaction on the resultant composites. The microstructure and morphology were identified with X-ray diffraction (XRD) and transmission electron microscopy (TEM), while thermal gravimetric analysis (TGA) was performed to demonstrate the thermal stability of the composites. XRD and TEM results indicate that the final properties and microstructure of the PI / clay nanocomposites were profoundly affected by both the diffusion and chemical reactivity of the monomers prior to the formation of polyamic acid and the subsequent thermal imidization had almost no effect. It should be emphasized that diffusion and chemical reactivity of the monomers are highly competitive. An exfoliated or intercalated nanocomposites can be formed only with a low-reactivity diamine and long enough diffusion time; this ensures polymerization was taken place within the clay gallery. On the other hand, a PI / clay blend is formed with insufficient diffusion time and high diamine reactivity. Under this circumstance, nearly all monomers were captured outside the clay gallery and a homo-polyimide was formed independent of clay. These results were consistent with observations from TGA. The maximum degradation temperature (Td) of the nanocomposite increased with increasing diffusion time; Td of the nanocomposites with low-reactivity 1,3-phenylenediamine was 30oC greater than the nanocomposites with high-reactivity 4,4¡¦-oxydianiline.

Traitedness has been described as the “the degree to which a particular trait structure is approximated in a given person” (Tellegen, p. 28, 1991) and has been hypothesized as one explanation for findings of weak trait-behavior relationships. That is, if traits are differentially applicable to different individuals, then trait-behavior relationships may be moderated based on the strength with which an individual fits with a given trait model. This study used moderated multiple regression to test the moderating effects of four different traitedness indicators to increase the prediction of diagnostic consistency in four personality disorders, and also tested the main effects of traitedness estimates to predict cross-situational consistency of functional impairment. Traitedness estimates performed better in the prediction of increased diagnostic consistency, though there were some isolated findings of traitedness increasing crosssituational consistency of functional impairment. orientation of the clay in the nanocomposite and the simple shear process. It is found that the modulus, strength, and heat distortion temperature of the nanocomposites decrease as the clay aspect ratio and degree of orientation are reduced. The micromechanics-based models accurately describe the relationship between clay structural parameters and the corresponding moduli for exfoliated nanocomposites. The impact fracture mechanisms of polypropylene (PP)-calcium carbonate (CaCO3) nanoparticles have been investigated. A detailed investigation reveals that the CaCO3 nanoparticles act as stress concentrators to initiate massive crazes, followed by shear banding in the PP matrix.

The overall objective of this work was to develop processing, structure, and property relationships in graphene/polymer nanocomposites. To this end, different types of graphene platelets were produced from graphite oxide, dispersed into various thermoplastics and elastomers, and the morphology and properties of the resulting nanocomposites were evaluated. A range of tests were carried out on the nanocomposites to assess property improvements, including stress-strain testing, dynamic mechanical analysis, and thermal and electrical conductivity testing. Extensive morphological characterization, primarily through transmission electron microscopy (TEM) analysis, was performed to gain insight into the mechanisms behind the observed property improvements. The processing method used to disperse graphene platelets into a given polymer was found to exert significant influence over the nanocomposite morphology and properties. In both thermoplastics and elastomers, liquid-based dispersion methods were typically found to yield a better dispersion of graphene platelets compared with melt processing; the effectiveness of melt processing appeared to depend in part upon the method used to produce the graphene platelets. Latex compounding of graphene platelets and natural rubber generated nanocomposites with a network morphology with properties that were sensitive to further processing. The effect of graphene platelet intrinsic structure on nanocomposite properties was studied and property improvements with other nanofillers were compared to graphene platelets. The impact of platelet oxidation on nanocomposite properties was explored in two different systems and produced varying results depending on the polarity of the polymer matrix. An increased average aspect ratio of graphene platelets was not found to improve mechanical properties or a lower percolation threshold when dispersed in natural rubber. Graphene platelets produced superior reinforcement to multi-walled carbon nanotubes and exfoliated montmorillonite when dispersed in natural rubber; however, the carbon nanotubes produced the largest thermal and electrical conductivity enhancements. Qualitative observation of platelet dispersion by TEM was found to provide excellent correlation with nanocomposite properties when comparing different processing methods or filler materials. The average platelet aspect ratio of three different nanocomposite systems was determined by quantitative TEM analysis and used as a parameter in composite models to generate modulus predictions. Good agreement was found between model predictions and the experimental data. / text

Polymer nanocomposites with organoclay fillers offer improved performance and opportunities for commercial applications. The key to significant property enhancement is to exfoliate the individual organoclay platelets into the polymer matrix to utilize their high aspect ratio and modulus. The affinity between the polymer matrix and the organoclay is one of the most important factors for determining the exfoliation level. To a certain extent, the affinity can be enhanced by optimizing the organoclay structure for a given polymer matrix. Numerous studies have demonstrated that nanocomposites provide significant enhancements in stiffness and strength, flame retardancy, gas barrier properties, thermal stability and ionic conductivity. However, most polymer nanocomposites have decreased toughness relative to that of the matrix polymer. One exception to this general rule was found for nanocomposites based on poly(ethylene-co-methacrylic acid) ionomer prepared by melt compounding. My initial work investigated this system using an instrumented impact test. The data were analyzed using the essential work of fracture (EWF) methodology. Transmission electron microscopy (TEM) revealed that the clay platelets were well exfoliated in this matrix. It has also been observed that addition of organoclays to polymer blends can greatly reduce the size of the dispersed phase in some cases. It was thought that this feature might be useful for controlling rubber particle size, and, therefore, the toughness of polyamide/elastomer blends. Initially, I investigated the effect of the organoclay structure on the extent of exfoliation and properties of the nanocomposites. Nanocomposites based on the organoclays with one alkyl tail and hydroxyl ethyl groups gave well-exfoliated structures and high matrix reinforcement while nanocomposites from two-tailed organoclay contain a considerable concentration of intercalated stacks. Nanocomposites from the organoclays with one alkyl tail showed slightly better exfoliation and matrix reinforcement than those from the organoclays with hydroxyl ethyl groups. Based on this research result, the toughening response of amorphous polyamide nanocomposites using two types of elastomers, EOR and EOR-g-MA, four types of organoclays, M3(HT)1, M2(HT)2, M1H1(HT)2 and (HE)2M1T1, and two mixing protocols, has been investigated. Glass fibers (diameter ~ 12 m) are frequently used to reinforce polyamides. However, there is a practical limit to the amount of fiber that can be added while maintaining processability. Another possible use of organoclays is as an additional filler that acts on the nanoscale to complement the micro-scale reinforcement of the glass fibers. The possible synergies of simultaneous reinforcement at these very different length scales were explored and the composite moduli were compared to theoretical predictions using aspect ratios determined from TEM images. / text

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