Rozprawy doktorskie na temat „NANOFILLER MATERIAL”

Spent oil based drilling fluid and cutting wastes are global liabilities due to their hazardous hydrocarbon content which impacts negatively on flora, fauna, and global carbon footprint. The formulation of two demulsifiers to ensure chemically enhanced phase separation of this waste into oil, water and solid components was successfully carried out in addition to recycling the solid phase into PA6 nanocomposite materials. Initial characterisation of the untreated waste was carried out by Fourier Transform Infra Red (FTIR) for total petroleum hydrocarbon (TPH) analysis, Inductively coupled plasma optical emission spectrometry (ICPOES) for quantitative elemental analysis and Energy dispersive xray analysis (EDXA) for qualitative elemental composition amongst other characterisation methods. The analysis showed that the sample had a high hydrocarbon load of 662,500mg/kg and a high heavy metal load for Pb of 122mg/kg. No As, Cd, Hg were detected. The demulsifier formulations were composed of isopropanol, sodium dodecyl sulphate, poloxamer, sodium chloride, chitosan in 0.2M acetic acid and deionised water for demulsifier S4 and addition of phosphoric acid for demulsifier S3. Hydrocarbon reduction on the extracted solid phase nanofiller S3 and nanofiller S4 was 98.6% and 98.5% respectively after demulsification. The demulsified spent oil based drilling fluid solid extracts were below OSPAR regulation of < 1% oil on cutting by weight. However, recycling of the recovered solid was carried out in order to achieve environmentally sustainable management of the waste in Polyamide 6 (PA6) nanocomposite manufacture/fabrication. The formulation of different blends of PA6 nanocomposite materials from untreated, demulsifier treated and thermally treated drilling fluid and cuttings was successfully achieved. Nanocomposite leaching test showed Pb immobilisation. The flexural and compressive - modulus and strength of the PA6 were markedly improved in the presence of the nanofillers and glass fibre. This was attributed to the reinforcement, exfoliating, stiffening, rigidity effect of the nanofillers. S6 (untreated drilling fluid) nanofillers significantly improved the mechanical properties of PA6. This was attributed to the increased interfacial bonding between the fillers and the polymer matrix as a result of the petroleum hydrocarbon present in the sample. The Thermogravemetric analysis (TGA) results showed that nanocomposites PA6/S3 and PA6/S3/GF30 had improved the thermal stability of PA6 by 13.6% and 38.8% respectively compared to PA6/S2 and PA6/S2/GF30 (simulated commercial nanocomposite materials) that improved PA6 by 9.7% and 35.8% respectively.

2015 - 2016
The focus of this study is to design new nano-modified epoxy adhesives using carbon nanofillers such as carbon nanotubes, carbon nanofibers and exfoliated graphite. Kinetic analysis, transport properties, dynamic mechanical properties and electrical properties have shown to be a powerful means for understanding molecular structure and phase composition of the formulated nanocomposites. Kinetic analysis, performed by using an advanced iso-conversional method and the Kamal’s model-diffusion controlled respectively, has shown which, in epoxy resin, based on the tetrafunctional epoxy precursor N,N′-tetraglycidyl methylene dianiline-(TGMDA) hardened with 4,4-diaminodiphenyl sulfone (DDS), the introduction of the diluent decreases particularly the activation energy of secondary amine-epoxy reaction. The inclusion in the resin of one-dimensional fillers does not lead to big differences in the curing kinetics behaviour with respect to the raw epoxy. An increase in the activation energy is found in the case of highly exfoliated graphite. It is likely due to a reduction of free molecular segments of the epoxy network entrapped inside self-assembly structures. Transport properties have shown that, using a non-stoichiometric amount of hardener, the chemical structure of epoxy mixture exhibits unique properties concerning the water sorption for which the Equilibrium Concentration of Water is reduced up to a maximum of 30%. Dynamic mechanical analysis have shown that the nanoparticles are responsible of a more mobile phase, in the structure of the resin, determining an additional glass transition at lower temperature with respect to the main glass transition temperature. The fraction of the more mobile phase is strictly related to the amount and nature of the nanofiller and to the amount of the hardener, in fact, using a non-stoichiometric amount of hardener, also the electrical properties are improved further. The adhesive formulations based on epoxy/nanostructured carbon forms are used to obtain both adhesive and adherents to order to evaluate the adhesion properties with different joint configurations (tensile butt joint and single lap joint). The inclusion of carbon nanofillers inside the epoxy adhesive caused a significant improvement in the bond strength of the joints, changing the failure mode of joints in single lap joint shear tests. Finally, the conductive adhesive carbon nanotubes based, have been modified, by introduction of an elastomer, to order to obtain high performance in the configuration lap shear strength (LSS) with adherents in carbon fiber reinforced plastics (CFRP) used in aeronautic field. A correct combination of elastomer and carbon nanotubes, has allowed obtaining a conductive adhesive with high performance. [edited by author]
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The PhD project was details on the polyolefin nanocomposites compounding, processing and preparation. Two different types of polymer matrix with low melt flow rate for fiber forming polymers have been selected; high density polyethylene (HDPE) and isotactic polypropylene (PP). High density polyethylene was compounded with double layered hydrotalcite (LDH) while in case of polypropylene reinforcement by adding fumed silica and kaolinite was performed. In this way the influence of the nanofiller type on the thermo-mechanical properties of the prepared nanocomposites were studied. In recent years several research efforts have been focused on the preparation of polymer/layered inorganic nanocomposites because of the excellent properties in comparison to the neat polymer. The main reason of this interest lies certainly in the properties of the nanoclay, like high stiffness, and high aspect ratio, that induce enhancement of various polymer properties (thermal stability, mechanical properties, flame resistance and gas barrier) even with small amount of filler. Moreover, nanocomposites can be processed more easily than microcomposite. Recently literature evidences a lot of progress in the nanofilled bulk materials; on the other hand, there are relatively a few publications on fibers made of nanofilled polyolefins. For instance, PP fibers were produced with various types of nanofillers, e.g. layered silicates, carbon nanotubes and montmorillonite. In the case of HDPE, composite fibers containing calcium carbonate, carbon nanotubes, silica and layered silicates were reported. It is worth to mention that so far, no publication could be found on this work using the same nanofillers with the same matrix. This thesis is divided into six chapters; Introduction and Background, Experimental activities, after obtained Results with discussions are reported and finally Conclusions. In the Introduction and Background (Chapter I and II) general information about nanocomposites and characteristic of different nanofillers type were summarized. After that polymer processing method with particular attention on the melt extrusion and fiber spinning were described. Third Chapter is dedicated to the experimental part. Here, the used material characterization, nanocomposite preparation procedure and description of experimental techniques were reported. All nanocomposites were characterized by different experimental techniques. First nanofiller morphology by microscope (SEM and TEM) and X-ray diffraction technique was tested. Thermal stability was investigated by Thermal Gravimetric Analysis (TGA) and crystallization behavior by Differential Scanning Calorimetry (DSC). Finally mechanical properties were characterized by tensile test, Dynamical Mechanical Thermal Analysis (DMTA) and creep test. The Results and Discussion have been divided into two parts; first one was dedicated to the high density polyethylene layered double hydrotalcite nanocomposites (HDPE-LDH), while in the second polypropylene with fumed silica (PP-FS) and kaolinite (PP-K) nanocomposite were described. i. High density polyethylene hydrotalcite (HDPE-LDH) nanocomposites after different process of plates and fibers production will be compared in Chapter IV. At the beginning a polypropylene matrix, suitable for fiber production, was firstly melt compounded with organically modified hydrotalcite up to 5% by wt. Similar compositions with up to 3% wt. of LDH were performed by melt spinning. The incorporation of the clay into both bulk and fiber nanocomposite enhanced the thermal stability and induced heterogeneous nucleation of HDPE. Hydrotalcite positively affected the mechanical properties in term of higher Young’s modulus and tensile strength. After the preliminary characterization on bulk and as-spun material the fibers were hot drawn up to draw ratio (DR) 20. XRD analysis revealed intercalation with high degree of exfoliation for the composites with 1-2% wt. of LDH. For this compositions higher elastic modulus 9.0 GPa - 9.3 GPa (with respect to 8.0 GPa of the neat HDPE), and maintain tensile strength and deformation at break were observed. Moreover, the addition of low amount of LDH significantly improved the creep stability. ii. Nanocomposites of isotactic polypropylene fumed silica (PP-FS) were described in the Chapter V. Two types of hydrophobic fumed silica with different surface area (170m2•g-1 and 150m2•g-1) and surface treatment (treated respectively by dimethyldichlorosilane and octylsilane) up to 2% vol. were used. Similar as in case of HDPE-LDH nanocomposites plates production and characterization was a preliminary step to select the best compositions for the fiber preparation. After that, the work has been focused on the iPP-FS fiber production. Introduction of the nanofiller enhanced thermal stability and mechanical properties of the nanocomposite. Elastic modulus at draw ratio 10 increased from 5.3 GPa for neat iPP up to 7.5 – 8.6 GPa for compositions with 0.25 – 0.5% vol. Together with this improvement enhancement in strength at break and maintaining deformation at break were observed. Moreover, isothermal creep tests evidenced improvement in the creep stability due to the FS introduction, over the whole range of investigated draw ratios. iii. The last results of recent research dedicated to the polypropylene kaolinite (PP-K) nanocomposites are reported in Appendix 1. Nanocomposite fibers were successfully spun up to draw ratio (DR) 15 at very high nanofiller content up to 30% wt. The presence of kaolinite not only increased the thermal stability but also enhanced elastic modulus up to 5.6 GPa – 7.0 GPa for compositions with 1% up to 30% wt. of kaolinite, in comparison to 5.4 GPa for neat PP at draw ratio 10. Moreover, for the composition with 10% wt. of kaolinite better drawability with maximum modulus was obtained in comparison to neat PP. Finally the most important observation made on polyolefin nanocomposites fibers were summarized in the Chapter VI. It can be concluded that polyolefin fibers nanocomposites were successfully prepared by two different processing conditions: melt compounding and melt spinning followed by hot drawing. In case of plates the introduction of nanosilica remarkably improved the thermal stability and elastic modulus, with retention of the pristine tensile properties at break. Nanocomposites fibers showed a higher improvement of the elastic modulus with respect to the nanocomposites plates containing the same percentage of nanofiller. Moreover, the introduction of the nanofiller enhanced tensile dynamic mechanical properties especially for higher draw ratio. Similar behavior was also observed in case of creep compliance. Higher creep stability was observed for the drawn fibers with nanofiller in comparison to neat polymer. This behavior could be a consequence of the different orientation and morphology related to the crystallinity developed in the spinning. These results confirmed that polyolefin containing nanofiller could be easily spun into nanofilled fiber. TEM images revealed how the experienced improvements of the mechanical properties could be probably related to the orientation of nanofiller aggregates along the strain direction and to the consequent increase of the filler-matrix interfacial area.

The PhD project was details on the polyolefin nanocomposites compounding, processing and preparation. Two different types of polymer matrix with low melt flow rate for fiber forming polymers have been selected; high density polyethylene (HDPE) and isotactic polypropylene (PP). High density polyethylene was compounded with double layered hydrotalcite (LDH) while in case of polypropylene reinforcement by adding fumed silica and kaolinite was performed. In this way the influence of the nanofiller type on the thermo-mechanical properties of the prepared nanocomposites were studied. In recent years several research efforts have been focused on the preparation of polymer/layered inorganic nanocomposites because of the excellent properties in comparison to the neat polymer. The main reason of this interest lies certainly in the properties of the nanoclay, like high stiffness, and high aspect ratio, that induce enhancement of various polymer properties (thermal stability, mechanical properties, flame resistance and gas barrier) even with small amount of filler. Moreover, nanocomposites can be processed more easily than microcomposite. Recently literature evidences a lot of progress in the nanofilled bulk materials; on the other hand, there are relatively a few publications on fibers made of nanofilled polyolefins. For instance, PP fibers were produced with various types of nanofillers, e.g. layered silicates, carbon nanotubes and montmorillonite. In the case of HDPE, composite fibers containing calcium carbonate, carbon nanotubes, silica and layered silicates were reported. It is worth to mention that so far, no publication could be found on this work using the same nanofillers with the same matrix. This thesis is divided into six chapters; Introduction and Background, Experimental activities, after obtained Results with discussions are reported and finally Conclusions. In the Introduction and Background (Chapter I and II) general information about nanocomposites and characteristic of different nanofillers type were summarized. After that polymer processing method with particular attention on the melt extrusion and fiber spinning were described. Third Chapter is dedicated to the experimental part. Here, the used material characterization, nanocomposite preparation procedure and description of experimental techniques were reported. All nanocomposites were characterized by different experimental techniques. First nanofiller morphology by microscope (SEM and TEM) and X-ray diffraction technique was tested. Thermal stability was investigated by Thermal Gravimetric Analysis (TGA) and crystallization behavior by Differential Scanning Calorimetry (DSC). Finally mechanical properties were characterized by tensile test, Dynamical Mechanical Thermal Analysis (DMTA) and creep test. The Results and Discussion have been divided into two parts; first one was dedicated to the high density polyethylene layered double hydrotalcite nanocomposites (HDPE-LDH), while in the second polypropylene with fumed silica (PP-FS) and kaolinite (PP-K) nanocomposite were described. i. High density polyethylene hydrotalcite (HDPE-LDH) nanocomposites after different process of plates and fibers production will be compared in Chapter IV. At the beginning a polypropylene matrix, suitable for fiber production, was firstly melt compounded with organically modified hydrotalcite up to 5% by wt. Similar compositions with up to 3% wt. of LDH were performed by melt spinning. The incorporation of the clay into both bulk and fiber nanocomposite enhanced the thermal stability and induced heterogeneous nucleation of HDPE. Hydrotalcite positively affected the mechanical properties in term of higher Young’s modulus and tensile strength. After the preliminary characterization on bulk and as-spun material the fibers were hot drawn up to draw ratio (DR) 20. XRD analysis revealed intercalation with high degree of exfoliation for the composites with 1-2% wt. of LDH. For this compositions higher elastic modulus 9.0 GPa - 9.3 GPa (with respect to 8.0 GPa of the neat HDPE), and maintain tensile strength and deformation at break were observed. Moreover, the addition of low amount of LDH significantly improved the creep stability. ii. Nanocomposites of isotactic polypropylene fumed silica (PP-FS) were described in the Chapter V. Two types of hydrophobic fumed silica with different surface area (170m2•g-1 and 150m2•g-1) and surface treatment (treated respectively by dimethyldichlorosilane and octylsilane) up to 2% vol. were used. Similar as in case of HDPE-LDH nanocomposites plates production and characterization was a preliminary step to select the best compositions for the fiber preparation. After that, the work has been focused on the iPP-FS fiber production. Introduction of the nanofiller enhanced thermal stability and mechanical properties of the nanocomposite. Elastic modulus at draw ratio 10 increased from 5.3 GPa for neat iPP up to 7.5 – 8.6 GPa for compositions with 0.25 – 0.5% vol. Together with this improvement enhancement in strength at break and maintaining deformation at break were observed. Moreover, isothermal creep tests evidenced improvement in the creep stability due to the FS introduction, over the whole range of investigated draw ratios. iii. The last results of recent research dedicated to the polypropylene kaolinite (PP-K) nanocomposites are reported in Appendix 1. Nanocomposite fibers were successfully spun up to draw ratio (DR) 15 at very high nanofiller content up to 30% wt. The presence of kaolinite not only increased the thermal stability but also enhanced elastic modulus up to 5.6 GPa – 7.0 GPa for compositions with 1% up to 30% wt. of kaolinite, in comparison to 5.4 GPa for neat PP at draw ratio 10. Moreover, for the composition with 10% wt. of kaolinite better drawability with maximum modulus was obtained in comparison to neat PP. Finally the most important observation made on polyolefin nanocomposites fibers were summarized in the Chapter VI. It can be concluded that polyolefin fibers nanocomposites were successfully prepared by two different processing conditions: melt compounding and melt spinning followed by hot drawing. In case of plates the introduction of nanosilica remarkably improved the thermal stability and elastic modulus, with retention of the pristine tensile properties at break. Nanocomposites fibers showed a higher improvement of the elastic modulus with respect to the nanocomposites plates containing the same percentage of nanofiller. Moreover, the introduction of the nanofiller enhanced tensile dynamic mechanical properties especially for higher draw ratio. Similar behavior was also observed in case of creep compliance. Higher creep stability was observed for the drawn fibers with nanofiller in comparison to neat polymer. This behavior could be a consequence of the different orientation and morphology related to the crystallinity developed in the spinning. These results confirmed that polyolefin containing nanofiller could be easily spun into nanofilled fiber. TEM images revealed how the experienced improvements of the mechanical properties could be probably related to the orientation of nanofiller aggregates along the strain direction and to the consequent increase of the filler-matrix interfacial area.

This PhD thesis investigated the incorporation of Polyhedral Oligomeric Silsesquioxanes (POSS) in thermoplastic base materials via melt-blending procedures. Particularly, a focus is taken on the enhancement of the thermal resistance through the addition of different types of POSS on two popular engineering plastics known by their low thermal stability, one being a semi-crystalline copolymer i.e. polyoxymethylene (POM) and the other an amorphous copolymer i.e. acrylonitrile butadiene styrene grafted with maleic anhydride (ABS-g-Ma). Different nanocomposites have been produced, from which its morphology, miscibility, structure, thermal properties and appearance behaviour before and during the thermoxidative degradation is herein quantified and discussed together with the resulting benefits and drawbacks. All the nanocomposites have been produced via melt-blending, using the nanofillers Glycidyl, Glycidyl-Isobutyl, Aminopropyl-isobutyl and Poly(ethylene-glycol) for the POM matrix, and Amino-Propyl Isobutyl, Glycidyl, and Trisilanol for the ABS-g-Ma matrix. The incorporation adequacy of the nanofillers into the matrix has been pre-assessed with the Hoy¿s solubility calculation method and later on corroborated with scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The quantification of the thermal degradation behaviour of each sample at different temperatures and exposure times was carried out through Fourier transform infrared spectrography (FTIR), thermogravimetric analysis (TGA) including the degradation kinetics and, ultimately, the sample appearance progress has been assessed in terms of yellowing by means of colour spectrophotometry (Cielab). The results showed that the presence of different POSS's used with the POM matrix improves dramatically the thermal stability of the base material and that such improvement is proportionate to the solubility compatibility between matrix and the nanofiller. The best performance was found with Aminopropyl-isobutyl, whereby the temperature of maximum rate of degradation (TMAX) increased by 22ºC. Said improvement is also seen in the conditions at which the nanocomposite developed only 2% of carbonyl yield and 8% of yellowing compared to the standard POM copolymer, which is taken as the base reference with 100% deterioration suffered in the above two indicators. However, the performance of the different nanocomposites produced in this work with ABS-g-Ma has not been as encouraging as the POM-based nanocomposites described above. Although the SEM morphological analysis show adequate incorporation and miscibility of the nanofillers into the matrix, the GPOSS and the TPOSS nanocomposites provided no relevant improvements in thermal stability when compared to the base ABS-g-Ma, and the APOSS blend exhibits a very slight decay in almost all the quantitative analysis carried out in this work.
Los avances producidos en años recientes en el campo de la nanotecnología y sus aplicaciones en los materiales están aportando grandes mejoras en el rendimiento de los mismos en áreas como la resistencia mecánica, estabilidad térmica, propiedades ópticas y eléctricas, entre otras. Por otro lado, el mundo de la ingeniería y el diseño de componentes plásticos está llevando los materiales cada vez más a su límite, con el fin de poder ofrecer el máximo rendimiento al mínimo coste. Esta realidad implica la necesidad creciente de customizar estructuras poliméricas con propiedades mejoradas en áreas específicas para cada aplicación. A pesar de los desarrollos que se han estado produciendo últimamente en nanocompuestos termoplásticos, el conocimiento en este campo es aún limitado, y requiere de más iniciativas de investigación y desarrollo sobre el amplio campo de posibilidades que nos ofrecen los nanocompuestos. El objetivo de esta tesis es contribuir en el conocimiento de los nanocompuestos a través del estudio de los efectos de varias nanocargas del tipo Polyhedral Oligomeric Silsesquioxanes (POSS) en el comportamiento de la resistencia térmica del copolímero semicristalino polióxido de metileno (POM) y del terpolímero amorfo acrilonitrilo‐butadieno‐estireno (ABS), los cuales son dos plásticos técnicos susceptibles a la termoxidación. Diferentes nanocompuestos se han elaborado con el fin de estudiar su morfología, miscibilidad, estructura, propiedades térmicas y apariencia, así como los beneficios y contrapartidas que resultan de ellos. Los nano‐compuestos han sido elaborados mediante el método de mezcla en estado fundido (melt‐blending), utilizando cuatro nano‐cargas distintas para el POM, siendo Glicidil, Glicidil‐Isobutil, Aminopropil‐isobutil y Poli(etilen‐glicol), y tres nano‐cargas para el ABS, siendo Amino‐Propil Isobutil, Glicidil y Trisilanol La compatibilidad teórica de las nano‐cargas se ha calculado mediante el método de solubilidad de “Hoy”, y se ha corroborado con microscopia electrónica de barrido (SEM) y calorimetría diferencial de barrido (DSC). Posteriormente, cada material base y sus distintas variantes de nano‐compuestos se han sometido a diferentes condiciones de termo‐oxidación en términos de temperatura y tiempo de exposición. El comportamiento a la degradación de cada muestra se ha cuantificado mediante los métodos de espectroscopia de infrarrojos por transformada de Fourier (FTIR), análisis de termogravimetría (TGA) incluyendo cinética de degradación, y finalmente mediante espectrofotometría (Cielab) para definir el progreso de la apariencia de la muestra en términos de amarilleamiento. Los resultados derivados de la inclusión de los diferentes POSS utilizados en la matriz de POM han mejorado sustancialmente la estabilidad térmica del mismo, y dicha mejora es proporcional a la compatibilidad de solubilidades entre el POM y los POSS utilizados. El mejor comportamiento se produce con la incorporación de la nanocarga aminopropilisobutil, con una temperatura de máxima degradación (TMAX) incrementada en 22 ºC sobre la TMAX del POM original tomado como referencia. Esta mejora se refleja también con una reducción muy notable en la formación grupos carbonilo y en el amarilleamiento sufrido en la superficie de la muestra, siendo un 2% y 8% respectivamente comparados con los resultados obtenidos con la muestra equivalente del material POM original. En referencia a los nanocompuestos basados en ABS‐g‐Ma, a pesar de la adecuada solubilidad teórica entre la matriz y las diferentes nano‐cargas, así como la buena miscibilidad obtenida en la elaboración de las muestras y evidenciada en el análisis morfológico SEM, no se han podido obtener mejoras en términos de estabilidad térmica. Concretamente, la adición de GPOSS y TPOSS no han aportado beneficios relevantes en las propiedades del nanocompuesto final, y la nanocarga APOSS ha incluso afectado negativamente a la matriz con una ligera caída de la resistencia térmica.
Els avenços produïts en els últims anys tant en el camp de la nanotecnología com en les seves aplicacions en els materials, està contribuint en la millora del rendiment dels mateixos en àeras com la resistència mecànica, l’estabilitat tèrmica, i les propietats òptiques i elèctriques entre d’altres. Per altra banda, el món de l’enginyería i el disseny de components plàstics està portant els materials cada vegada més al seu límit amb la finalitat de poder oferir el màxim rendiment al mínim cost, i això comporta una necessitat creixent de customitzar les estructura polimèriques amb propietats especificament millorades en àreas molt concretes en funció de l’aplicació requerida. A pesar del desenvolupament que s’ha estat produint últimament en l’àrea de nanocompostos plàstics, el coneixement en aquest camp és encara limitat, i requereix de més iniciatives d’investigació per cobrir el potencial que ofereix aquesta classe de materials, així com conèixer també les seves limitacions. L’objectiu d’aquesta tesi es el de contribuïr en l’enteniment dels nanocompostos plàstics a través de l’estudi dels efectes de vàries nanocàrregues del tipus Polyhedral Oligomeric Silsesquioxanes (POSS) en el comportament de la resistència tèrmica del poli(òxid de metilè) (POM) com a material semicristalí, i l’acrilonitril‐butadiè‐estirè (ABS) com a material amorf. Val a dir que la selecció d’aquests dos polímers tècnics ha estat en part motivada per la seva susceptibilitat inherent a la termodegradació. Diferents nanocompostos basats amb aquests materials s’han elaborat amb la finalitat d’estudiar la seva morfología, miscibilitat, estructura, propietats tèrmiques i aparença, així com els beneficis i contrapartides que resulten d’ells. La preparació dels nanocompostos ha sigut mitjançant el mètode de barreja en estat fos (melt‐blending), util.litzant quatre nano‐càrregues diferentes per el POM, siguent glicidil, glicidil‐Isobutil, aminopropil‐isobutil y poli(etilenè‐glicol), i tres nano‐càrregues per el ABS, siguent amino‐propil isobutil, glicidil i trisilanol. La compatibilitat teòrica de les nano‐càrregues s’ha calculat mitjançant el mètode de solubitat de “Hoy”, i s’ha corroborat amb microscopia electrònica d’escombrat (SEM) i calorimetría diferencial d’escombrat (DSC). Posteriorment s’ha sotmès cada material base i les seves diferents variants de nanocompostos a diferents condicions de termo‐oxidació en termes de temperatura i temps d’exposició. El comportament a la degradació de cada mostra s’ha quantificat mitjançant els mètodes d’espectroscopía d’infraroigs per transformada de Fourier (FTIR), anàlisis de termogravimetría (TGA) incloent cinemàtica de degradació, i finalment mitjançant espectrofotometría (Cielab) per a definir el progrés de l’aparença de la mostra en termes d’engroguiment. Els resultats han mostrat, per una banda, que la inclusió dels diferents POSS util.litzats en la matriu de POM ha millorat substancialment l’estabilitat tèrmica del mateix, i aquesta millora és proporcional a la compatibilitat entre les solubitats del POM i del POSS. El millor comportament s’ha produït amb l’adició de la nano‐càrrega d’aminopropilisobutil, amb una temperatura de màxima degradació (TMAX) millorada en 22ºC en relació a la obtinguida amb la matriu de POM. Aquesta millora també es reflexa amb una reducció molt notable en la formació de grups carbonil i en l’engroguiment sofert en la superfície de la mostra, siguent un 2% i 8% respectivament comparats amb els resultats obtinguts amb la mostra equivalent del material POM original. En contrast, els nanocompostos basats en ABS‐g‐Ma no han ofert millores en termes d’estabilitat tèrmica, a pesar d’una adequada solubitat teòrica entre la matriu i les diferents nano‐càrregues util.litzades, així com la bona miscibilitat obtinguda en l’elaboració de les mostres i posteriorment evidenciada en l’anàlisi morfològic SEM. Concretament l’adició de GPOSS i de TPOSS no han aportat beneficis en les propietats del nanocompostos final, i la nano‐càrrega APOSS ha afectat negativament a la matriu amb una lleuguera caiguda de la resistència tèrmica

Composite resins are the most modern, widespread, aesthetic and conservative materials in the field of direct restorative dentistry. During the last years, the manufacturers of dental materials have launched onto the market composite resins with inorganic nanofillers with diameter less than 100 nm. These materials are considered nowadays the state of the art in terms of filler formulation. Nanofilled and nanohybrid composite resins have been introduced fairly recently in the clinical practice, so that there is less information about their properties and clinical effectiveness in comparison to traditional materials. The present work of thesis examined in both the laboratory and clinical setting the performance of several composite resins with nanofillers. The following items were analysed in five different phases: 1) roughness and microhardness of nanohybrid composites; 2) sealing ability of a nanohybrid flowable composite; 3) influence of finish line on the marginal seal of nanohybrid composite crowns after periodontal scaling; 4) two-year in vitro and in vivo evaluation of surface roughness of a flowable nanohybrid composite; 5) clinical effectiveness of nanofilled and nanohybrid composite resins: a systematic review.

Ultra high temperature ceramics (UHTC) are candidate materials for high temperature applications such as leading edges for hypersonic flight vehicles, thermal protection systems for spacecraft, and rocket nozzle throat inserts due to their extremely high melting points. Tantalum and Niobium Carbide (TaC and NbC), with melting points of 3950°C and 3600°C, respectively, have high resistivity to chemical attack, making them ideal candidates for the harsh environments UHTCs are to be used in. The major setbacks to the implementation of UHTC materials for these applications are the difficulty in consolidating to full density as well as their low fracture toughness. In this study, small amounts of sintering additive were used to enhance the densification and Graphene Nanoplatelets (GNP) were dispersed in the ceramic composites to enhance the fracture toughness. While the mechanisms of toughening of GNP addition to ceramics have been previously documented, this study focused on the anisotropy of the mechanisms. Spark plasma sintering was used to consolidate both bulk GNP pellets and near full relative density TaC-NbC ceramic composites with the addition of both sintering aid and GNP and resulted in an aligned GNP orientation perpendicular to the SPS pressing axis that allowed the anisotropy to be studied. In situ high load indentation was performed that allowed real time viewing of the deformation mechanisms for enhanced analysis. The total energy dissipation when indenting the bulk GNP pellet in the in-plane GNP direction was found to be 270% greater than in the out-of-plane orientation due to the resulting deformation mechanisms that occurred. In GNP reinforced TaC-NbC composites, the projected residual damaged area as a result of indentation was 89% greater when indenting on the surface of the sintered compact (out-of-plane GNP orientation) than when indenting in the orthogonal direction (in-plane GNP orientation) which is further evidence to the anisotropy of the GNP reinforcement.

Orientador: Lafayette Nogueira Júnior
Co-orientador: Marcos Massi
Banca: Renato Sussumu Nishioka
Banca: Argemiro Soares da Silva Sobrinho
Banca: Eron Toshio Colauto Yamamoto
Banca: Rubens Nisei Tango
Resumo: Esta pesquisa objetivou avaliar o efeito de diferentes nanofilmes depositados a plasma na resistência de união entre cimento resinoso e cerâmica à base de zircônia. 120 blocos/espécimes (15,2 x 12,5 x 1,7 mm) e 18 discos (11,0 x 1,4 mm) de zircônia (Y-TZP) (VITA In-Ceram Zirconia, Vita Zahnfabrik, Alemanha) receberam diferentes tratamentos de superfície (n = 20 para os blocos) (n = 3 para discos): zircônia sem tratamento (Zrpolida), jateamento de alumina revestida por sílica (30 μm) (Zrjat#), nanofilme à base de sílica (ZrSiO2), jateamento de alumina (45 μm) + nanofilme à base de sílica (Zrjat+SiO2), e nanofilme à base de fluoreto (ZrF) e jateamento de alumina (45 μm) + nanofilme à base de fluoreto (Zrjat+F). Os nanofilmes foram depositados por meio da técnica a plasma PECVD. As superfícies cerâmicas foram caracterizadas pela morfologia (MEV e MFA), química (XPS) e molhabilidade (ângulo de contacto), realizada nos discos. O agente de união silano foi aplicado em cada superfície e um cilindro de cimento resinoso foi construído sobre os espécimes tratados. Metade dos espécimes de cada grupo (n = 10) foram submetidos a 6.000 ciclos térmicos. A resistência de união foi avaliada pelo teste de cisalhamento e análise fractográfica pelo estereomicroscópico, MEV e EDS. Para análise estatística utilizou-se ANOVA 1-Fator e o teste de Tukey, para presença e ausência de envelhecimento (p = 0,05). A zircônia apresentou-se mais hidrofílica após a deposição dos nanofilmes. Ligações químicas entre Si-O foram encontradas em ZrSiO2; ZrF promove um processo de fluoração na superfície da cerâmica Y-TZP, convertendo-a em oxifluoreto de zircônio. Os valores de resistência de união iniciais obtidos pelos tratamentos de superfície a plasma não superaram os valores de união da silicatização. Após o envelhecimento, todas as amostras do grupo ZrSiO2(TC) sofreram falhas pré-teste. OS valores de resistência de....
Abstract: This study aimed to evaluated the effects of differents plasma nanofilms on the bond strength between resin cement and zirconia ceramic. 120 blocks / specimens (15.2 x 12.5 x 1.7 mm) and 18 discs (11.0 x 1.4 mm) of zirconia (Y-TZP) (VITA In-Ceram Zirconia, Vita Zahnfabrik, Germany) received differents treatments surface (n = 20 for the blocks) (n = 3 for discs): untreated zirconia (Zrpolida), silica-coated (30 μm) (Zrjat#), silica nanofilm (ZrSiO2), sandblasted by air-borne particle abrasion with aluminum oxide particles (45 μm) + silica nanofilm (Zrjat+SiO2) and fluoride nanofilm (ZrF) and sandblasted by air-borne particle abrasion with aluminum oxide particles (45 μm) + fluoride nanofilm (Zrjat+F). The nanofilms were deposited by PECVD technique of the plasma. The ceramic surfaces were characterized by morphology (SEM and AFM), chemical (XPS) and wettability (Contact angle), that was performed on discs. The silane agent was applied to each surface treatment and a cylinder of resin cement was built on the specimens. Half of the samples of each group (n = 10) were subjected to 6.000 thermalcycles. The bond strength was evaluated by shear test and fractographic analysis by stereoscopic, SEM and EDS. Statistical analysis was performed using one-way ANOVA and Tukey's test for the presence and absence non-aged (p = 0.05). Zirconia presented more hydrophilic after nanofilms deposition. Chemical bonds between Si-O were found in ZrSiO2; ZrF promotes a process of fluorination on the Y-TZP surface, promoting the conversion of zirconia in zirconium oxyfluoride. The initial values of bond strength obtained by plasma treatment did not exceed the bond values of the silica-coated. After aging, all samples of the group ZrSiO2 (TC) falied. The values of bond strength of ZrF (TC) (3.8 MPa) were lower than Zrjat# (TC) (15.4 MPa) and Zrpolida (TC) (6.3 MPa). The silica nanofilm showing detachment after shearing. Adhesive failures were predominant among the...
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Esta pesquisa objetivou avaliar o efeito de diferentes nanofilmes depositados a plasma na resistência de união entre cimento resinoso e cerâmica à base de zircônia. 120 blocos/espécimes (15,2 x 12,5 x 1,7 mm) e 18 discos (11,0 x 1,4 mm) de zircônia (Y-TZP) (VITA In-Ceram Zirconia, Vita Zahnfabrik, Alemanha) receberam diferentes tratamentos de superfície (n = 20 para os blocos) (n = 3 para discos): zircônia sem tratamento (Zrpolida), jateamento de alumina revestida por sílica (30 μm) (Zrjat#), nanofilme à base de sílica (ZrSiO2), jateamento de alumina (45 μm) + nanofilme à base de sílica (Zrjat+SiO2), e nanofilme à base de fluoreto (ZrF) e jateamento de alumina (45 μm) + nanofilme à base de fluoreto (Zrjat+F). Os nanofilmes foram depositados por meio da técnica a plasma PECVD. As superfícies cerâmicas foram caracterizadas pela morfologia (MEV e MFA), química (XPS) e molhabilidade (ângulo de contacto), realizada nos discos. O agente de união silano foi aplicado em cada superfície e um cilindro de cimento resinoso foi construído sobre os espécimes tratados. Metade dos espécimes de cada grupo (n = 10) foram submetidos a 6.000 ciclos térmicos. A resistência de união foi avaliada pelo teste de cisalhamento e análise fractográfica pelo estereomicroscópico, MEV e EDS. Para análise estatística utilizou-se ANOVA 1-Fator e o teste de Tukey, para presença e ausência de envelhecimento (p = 0,05). A zircônia apresentou-se mais hidrofílica após a deposição dos nanofilmes. Ligações químicas entre Si-O foram encontradas em ZrSiO2; ZrF promove um processo de fluoração na superfície da cerâmica Y-TZP, convertendo-a em oxifluoreto de zircônio. Os valores de resistência de união iniciais obtidos pelos tratamentos de superfície a plasma não superaram os valores de união da silicatização. Após o envelhecimento, todas as amostras do grupo ZrSiO2(TC) sofreram falhas pré-teste. OS valores de resistência de....
This study aimed to evaluated the effects of differents plasma nanofilms on the bond strength between resin cement and zirconia ceramic. 120 blocks / specimens (15.2 x 12.5 x 1.7 mm) and 18 discs (11.0 x 1.4 mm) of zirconia (Y-TZP) (VITA In-Ceram Zirconia, Vita Zahnfabrik, Germany) received differents treatments surface (n = 20 for the blocks) (n = 3 for discs): untreated zirconia (Zrpolida), silica-coated (30 μm) (Zrjat#), silica nanofilm (ZrSiO2), sandblasted by air-borne particle abrasion with aluminum oxide particles (45 μm) + silica nanofilm (Zrjat+SiO2) and fluoride nanofilm (ZrF) and sandblasted by air-borne particle abrasion with aluminum oxide particles (45 μm) + fluoride nanofilm (Zrjat+F). The nanofilms were deposited by PECVD technique of the plasma. The ceramic surfaces were characterized by morphology (SEM and AFM), chemical (XPS) and wettability (Contact angle), that was performed on discs. The silane agent was applied to each surface treatment and a cylinder of resin cement was built on the specimens. Half of the samples of each group (n = 10) were subjected to 6.000 thermalcycles. The bond strength was evaluated by shear test and fractographic analysis by stereoscopic, SEM and EDS. Statistical analysis was performed using one-way ANOVA and Tukey's test for the presence and absence non-aged (p = 0.05). Zirconia presented more hydrophilic after nanofilms deposition. Chemical bonds between Si-O were found in ZrSiO2; ZrF promotes a process of fluorination on the Y-TZP surface, promoting the conversion of zirconia in zirconium oxyfluoride. The initial values of bond strength obtained by plasma treatment did not exceed the bond values of the silica-coated. After aging, all samples of the group ZrSiO2 (TC) falied. The values of bond strength of ZrF (TC) (3.8 MPa) were lower than Zrjat# (TC) (15.4 MPa) and Zrpolida (TC) (6.3 MPa). The silica nanofilm showing detachment after shearing. Adhesive failures were predominant among the...

Polymer electrolyte films based on poly(trimethylene carbonate) (PTMC) mixed with LiTFSI salt in different compositions were synthesized and investigated as electrolytes for lithium ion batteries, where the ionic conductivity is the most interesting material property. Electrochemical impedance spectroscopy (EIS) and DSC were used to measure the ionic conductivity and thermal properties, respectively. Additionally, FTIR and Raman spectroscopy were used to examine ion coordination in the material. Additives of nanosized TiO2 and powders of superionically conducting Li1.3Al0.3Ti1.7(PO4)3 were investigated as enhancers of ionic conductivity, but no positive effect could be shown. The most conductive composition was found at a [Li+]:[carbonate] ratio of 1, corresponding to a salt concentration of 74 percent by weight, which showed an ionic conductivity of 2.0 × 10–6 S cm–1 at 25 °C and 2.2 × 10–5 S cm–1 at 60 °C, whereas for even larger salt concentrations, the mechanical durability of the polymeric material was dramatically reduced, preventing use as a solid electrolyte material. Macroscopic salt crystallization was also observed for these concentrations. Ion coordination to carbonyls on the polymer chain was examined for high salt content compositions with FTIR spectroscopy, where it was found to be relatively similar between the samples, possibly indicating saturation. Moveover, with FTIR, the ion-pairing was found to increase with salt concentration. The ionic conductivity was found to be markedly lower after 7 weeks of aging of the materials with highest salt concentrations.

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No presente trabalho, foi desenvolvido e caracterizado um sistema híbrido formado pela evaporação térmica de um nanofilme molecular de complexo de terra rara sobre um filme fino metálico, obtido por um processo bottom-up. Para a produção do novo híbrido, o complexo fotônico Eu(btfa)3bipy foi depositado sobre um substrato recoberto por um filme de prata nanoestruturado formado pela redução térmica de íons de prata seguido do crescimento e migração de nanopartículas de prata para a superfície do material vítreo. A luminescência do complexo de terra rara sobre o substrato vítreo foi monitorada em função do tempo de tratamento na temperatura de transição vítrea (Tg), e do crescimento do nanofilme autoformado, este, por sua vez, monitorado por microscopia de força atômica (AFM). Amostras de dois sistemas GAPAgF e GAPAgO foram obtidas pela fusão dos materiais de partida em um forno resistivo, seguido por um tratamento térmico próximo da Tg para produzir um filme de prata nanoestruturado na superfície das amostras, apresentando uma aparência metálica. O novo substrato vítreo ativo GAPAgO possui uma enorme velocidade de crescimento do nanofilme se comparada com a cinética de crescimento do vidro ativo GAPAgF, previamente estudado. O crescimento das nanopartículas foi monitorado por AFM em ambos os sistemas, em função do tempo de tratamento térmico, apresentando o crescimento de nanoestruturas de prata com 100 nm somente em dois minutos de tratamento térmico. A energia de ativação E relacionada com cristalização, e o fator de freqüência υ foi calculado para êtsr composições do sistema GAPAgO. O resultado indica uma instabilidade deste vidro se relacionado com o sistema GAPAgF previamente estudado. A morfologia da superfície foi avaliada em função da atmosfera durante o tratamento térmico. O sistema GAPAgO apresentou uma geometria preferencial de crescimento do nanofilme na superfície do vidro. Medidas de fluorescência do íon Eu3+ no complexo Eu(btfa)3 Palavras chave: Nanopartículas de prata, Plásmons, processo bottom up. bipy foram analisadas como uma função do tempo de tratamento, mostrando um melhor aumento da luminescência em amostras com superfícies mais rugosas. As propriedades fotônicas das amostras foram analisadas, e os sistemas foram caracterizados por DRX, AFM e XPS. O objetivo final deste trabalho é de usar esses novos materiais, como substratos ativos para nanodispositivos

In this study, polypropylene (PP) based nanocomposites were prepared by incorporating different kinds and amounts of silica nanoparticles and graphite nanoplatelets (GNP). The role of various percentages of compatibilizer polypropylene grafted with maleic anhydride (PPgMA) into PP nanocomposites was also investigated. In order to analyze the effect of the manufacturing process on the material’s properties, the samples were produced by (i) melt compounding and compression molding and (ii) extrusion and injection molding. It was found that injection molding provides significantly greater stiffness and strength compared to compression molding for all types of PP nanocomposites. Several characterization techniques were used in order to correlate the microstructure to the physical and mechanical properties of the materials. Both silica and GNP were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization and favoring the nucleation of the the β- phase, which manifests superior impact strength and toughness compared to the most common α-form crystals. Graphite nanoplatelets were found more efficient in inducing polymorphism and favoring the formation of a transcrystalline phase on the filler surface. A significant correlation between the tensile modulus, glass transition temperature and the amount of constrained phase, as assessed through tensile and DMA analyses, revealed the presence of a secondary reinforcing mechanisms, which, concurrently to the primary stiffening effect of the high modulus filler, contributes to the enhancement of the bulk properties. A complex constrained phase, responsible for providing a secondary reinforcing mechanism, was modeled as immobilized amorphous and transcrystalline regions located at the filler surface. The non-linear viscoelastic creep of the composites, successfully studied by the application of the time strain superposition principle (TSSP), showed a considerable enhancement of the creep stability in nanocomposites with respect to unfilled PP, especially for higher creep stresses. The study of creep dependance on the temperature showed that the stabilizing effect provided by the nanoparticles was more effective at high temperatures and, considering the time temperature superposition principle (TTSP), at long loading times. The equivalence between the time strain- and time temperature- superposition principle was substantiated by comparing the correspondent superimposed master curves. The nanofilled PP matrices have also been used for the preparation of microcomposites reinforced with short glass fibers (GF). Interfacial shear strength (ISS) was measured by means of the single fiber fragmentation test on various PP/GF microcomposites. Results show that the strength at the fiber/matrix interface can be remarkably increased when using nanocomposite systems, especially in the case of dimethyldichlorosilane-functionalized silica nanoparticles and GNP platelets, and that the improvement is further increased when the nanoparticles are used in combination with PPgMA. The thermodynamic fiber/matrix work of adhesion, estimated by contact angle measurements, showed a good correlation with the ISS values. Hybrid composites reinforced with short glass fibers and nanofillers were produced and characterized in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e. micro- and nano- scale). The stronger fiber/matrix adhesion combined with the enhancement of the matrix properties resulted in superior tensile properties and impact resistance and improved viscoelastic behavior. As means of comparison, thermosetting hybrid composites based on epoxy resin were also produced by incorporation of GNP and short GF.

In this study, polypropylene (PP) based nanocomposites were prepared by incorporating different kinds and amounts of silica nanoparticles and graphite nanoplatelets (GNP). The role of various percentages of compatibilizer polypropylene grafted with maleic anhydride (PPgMA) into PP nanocomposites was also investigated. In order to analyze the effect of the manufacturing process on the material’s properties, the samples were produced by (i) melt compounding and compression molding and (ii) extrusion and injection molding. It was found that injection molding provides significantly greater stiffness and strength compared to compression molding for all types of PP nanocomposites. Several characterization techniques were used in order to correlate the microstructure to the physical and mechanical properties of the materials. Both silica and GNP were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization and favoring the nucleation of the the β- phase, which manifests superior impact strength and toughness compared to the most common α-form crystals. Graphite nanoplatelets were found more efficient in inducing polymorphism and favoring the formation of a transcrystalline phase on the filler surface. A significant correlation between the tensile modulus, glass transition temperature and the amount of constrained phase, as assessed through tensile and DMA analyses, revealed the presence of a secondary reinforcing mechanisms, which, concurrently to the primary stiffening effect of the high modulus filler, contributes to the enhancement of the bulk properties. A complex constrained phase, responsible for providing a secondary reinforcing mechanism, was modeled as immobilized amorphous and transcrystalline regions located at the filler surface. The non-linear viscoelastic creep of the composites, successfully studied by the application of the time strain superposition principle (TSSP), showed a considerable enhancement of the creep stability in nanocomposites with respect to unfilled PP, especially for higher creep stresses. The study of creep dependance on the temperature showed that the stabilizing effect provided by the nanoparticles was more effective at high temperatures and, considering the time temperature superposition principle (TTSP), at long loading times. The equivalence between the time strain- and time temperature- superposition principle was substantiated by comparing the correspondent superimposed master curves. The nanofilled PP matrices have also been used for the preparation of microcomposites reinforced with short glass fibers (GF). Interfacial shear strength (ISS) was measured by means of the single fiber fragmentation test on various PP/GF microcomposites. Results show that the strength at the fiber/matrix interface can be remarkably increased when using nanocomposite systems, especially in the case of dimethyldichlorosilane-functionalized silica nanoparticles and GNP platelets, and that the improvement is further increased when the nanoparticles are used in combination with PPgMA. The thermodynamic fiber/matrix work of adhesion, estimated by contact angle measurements, showed a good correlation with the ISS values. Hybrid composites reinforced with short glass fibers and nanofillers were produced and characterized in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e. micro- and nano- scale). The stronger fiber/matrix adhesion combined with the enhancement of the matrix properties resulted in superior tensile properties and impact resistance and improved viscoelastic behavior. As means of comparison, thermosetting hybrid composites based on epoxy resin were also produced by incorporation of GNP and short GF.

Le nanotecnologie rappresentano un nuovo approccio tecnologico basato sulla conoscenza e sulla manipolazione della materia su scala nanometrica. Numerosi sono i settori industriali interessati a queste nuove tecnologie. L’elaborato di tesi rientra nell’ambito dell’ingegneria elettrica e riguarda, in particolare, materiali isolanti additivati con particelle nanometriche conduttive. Le principali applicazioni sono rappresentate dagli accessori per cavi elettrici, quali ad esempio giunti e terminali, dove è necessario gradare il campo elettrico e la corrente, evitando che stress eccessivi danneggino il materiale. L'obiettivo del seguente lavoro è quello di sviluppare un modello computazionale che permetta di determinare la concentrazione di nanofiller che sarà necessario additivare al materiale di base per ottenere un determinato incremento di conducibilità, richiesto per limitare gli sforzi elettrici a cui sono sottoposti i dielettrici. Il lavoro è stato organizzato in più fasi: 1. Analisi di un modello computazionale 2D realizzato in precedenza e sviluppo di un nuovo modello 3D mediante il software Comsol with Matlab; 2. Sintesi dei materiali nanocompositi; 3. Caratterizzazione dielettrica dei campioni realizzati; 4. Confronto con i risultati ottenuti da elaborazioni precedenti, durante le quali sono stati utilizzati tre diversi filler lamellari (GO, G2 e G3); 5. Confronto tra gli incrementi di conducibilità previsti dai modelli computazionali e i risultati ottenuti sperimentalmente. Essendo questo ambito ancora in via di sviluppo, le conoscenze stanno progredendo gradualmente, eseguendo prove e test sui materiali. Le tematiche e le sperimentazioni riguardanti questo tema saranno oggetto di elaborazioni successive e continueranno ad essere studiate e approfondite, in modo da portare la ricerca in direzione di una maggiore precisione e certezza.

I nanocompositi sono una nuova classe di materiali che mostrano proprietà uniche tipicamente non condivise dai materiali convenzionali. La dispersione di particelle nanometriche, organiche o inorganiche, all’interno di una matrice polimerica può determinare l’incremento delle proprietà del composito e nel contempo può donare nuove proprietà funzionali. Il grosso interesse rivolto verso i nanocompositi dipende dalle potenzialità che tali materiali mostrano e dalle possibili applicazioni che essi possono trovare. Film rigidi o flessibili in nanocomposito, troverebbero applicazione nel packaging, vista la tendenza a conservare la trasparenza della matrice e le proprietà di impermeabilità all’ossigeno che l’utilizzo di nanocariche può determinare. Nel presente lavoro è stata messa a punto una rapida procedura di fabbricazione di film spessi in nanocomposito poliestere-montmorillonite per consentirne un’applicazione industriale. Le proprietà dinamo-meccaniche dei film sono state valutate tramite test al DMA, svolti nella particolare configurazione di trazione. I risultati ottenuti da tale prova hanno consentito di studiare la complessità dell’interazione tra nanocariche e matrice. I coatings sono spesso utili per diverse applicazioni ingegneristiche, da coating resistenti al graffio a coating che fungono da barriera termica. Poiché danni superficiali o all’interfaccia con il subtrato, possono influenzare le prestazioni finali, è importante adottare una buona tecnica di caratterizzazione per i coating. Le più recenti pubblicazioni scientifiche, a tal proposito, parlano di nanoindentazione di coating o bulk in nanocomposito. In questo lavoro viene utilizzata la tecnica di macro-indentazione strumentata per la caratterizzazione meccanica di coating, in nanocomposito poliestere-montmorillonite, depositati per spin coating su substrati in alluminio e polietilene ad alta densità. La macro-indentazione è meno sensibile alle intrinseche inomogeneità dei nanocompositi è da utili informazioni circa la resistenza dei coating. In più, in questo caso, la preparazione del campione può essere meno accurata rispetto al caso della nanoindentazione. Nell’appendice, è riportato un esempio di applicazione di macroindentazione per la caratterizzazione meccanica di materiale polimerico. In particolare il test consentiva di valutare l’effetto del contenuto locale di rinforzo in materiali polimerici caricati a gradiente. Dopo lo studio di film e coating in nanocomposito, è stato studiato il comportamento di nanocompositi nella forma di bulk. Provini bulk possono mostrare diverse proprietà rispetto ad i coating, in più, lo studio del comportamento del materiale di campioni bulk risulta più semplice e consente di approfondire alcuni aspetti. La combinazione di nanoparticelle e di una nuova tecnologia di schiumatura ha generato una nuova classe di materiali leggeri, ad alta resistenza e multifunzionali: le schiume in nanocomposito. Attualmente, risulta di grossa utilità trovare nuove, veloci ed economiche tecnologie che consentano di realizzare nanocompositi su larga scala. E’ stata sviluppata una nuova tecnologia di schiumatura per materiali termoindurenti che non richiede l’utilizzo di agenti esterni e che è stata chiamata di schiumatura allo stato solido. L’utilizzo di questa nuova tecnologia è stata utilizzata per la realizzazione di schiume nanocaricate. Lo sviluppo di materiali polimerici per applicazioni strutturali o tribolgiche, sta divenendo una domanda sempre più pressante. I compositi a matrice polimerica hanno le potenzialità per essere utilizzati per questo tipo di applicazioni; componenti in polimero, come camme, alberi e ruote dentate, sono tipicamente realizzati mediante la tecnologia dello stampaggio ad iniezione. Ciò è dovuto alla semplicità ed al basso costo di tale tecnologia che consente la realizzazione di componenti anche a geometria complessa. Tuttavia l’effetto del processo di stampaggio ad iniezione sulle proprietà di bulk di nanocompositi polimerici è ancora oggetto di studio. Nel presente lavoro, sono state studiate le proprietà tribologiche e meccaniche di di nanocompositi a matrice polimerica (PA6, PA66 and POM) , prodotti per stampaggio ad iniezione.
Nanocomposites are a relatively new class of materials with unique properties typically not shared by conventional microcomposites. The dispersion of nanometric organic or ingorganic particles in polymer matrix, may cause an increase in performances of composite materials and give new functional properties. The interest in polymer nanocomposites depends on the potential applications of these materials. Dealing with flexible or rigid films, packaging is a potential application because of the material transparency and the oxygen-barrier properties. In the present work, dynamic mechanical properties of polyester–montmorillonite nanocomposite thick films, prepared by the in situ intercalative polymerization method, were evaluated in a tensile mode. A fast fabrication procedure was chosen according to industrial applications and tensile DMA results permitted to study the interaction between nanofiller and matrix. Surface coatings are used in different engineering applications, from scratch-resisting coatings to thermal barriers. Nanocomposites have the potential for being high-performance coatings. As surface damage and interfacial failure may affect the final coating performances, the reliable characterisation of the coated film strength is critical. Recent scientific contributions mainly deal with the nanoindentation of nanocomposite coatings or bulk materials. In this work the use of instrumented macro-indentation is suggested for mechanical characterization of polyester–montmorillonite nanocomposite coatings deposited on aluminium and high-density polyethylene substrates by the spin coating method. Macro-indentation is less sensitive to material non-homogeneities and provides reliable information about the coating strength. Moreover, the sample preparation is less critical than for nanoindentation. In the appendix a particular instance of the use of macroindentation test is reported, instrumented macroindentation test was used to measure the effect of the local filler content in polymer functional graded materials . After the study of nanocomposite coatings and films, the study of bulk nunocomposites was performed to investigate the material beahviour. In fact, bulk samples exhibit different properties than coatings, moreover the study of bulk materials is easier and allow to deepen several scientific aspects. The combination of functional nanoparticles and foaming technology has generated a new class of lightweight, high strength, and multifunctional materials: the nanocomposite foams. Nowadays, the challenge is to find new fast and cheap production processes that are able to provide complex nanocomposite structures on a large scale. A new foaming technology called ‘solid-state foaming’ has recently been developed to foam thermosetting materials without using any external agent. This new technology is very easy and special equipments are not necessary. In the present work, this method was used for fabricating nanocomposite foams. Nowadays, the development of advanced materials for tribological purposes is becoming a pressing demand of manufacturing industries. Polymer-based composites have the capability of operating for a long time without lubrication in conditions of cryogenic and elevated temperatures. Components, such as gears and cams are typically produced by injection molding of thermoplastic matrix composites. In fact, the ease and economics of manufacturing complex parts by injection molding are well recognized, but the effect of the injection molding process on the bulk properties of nanocomposites is still under investigation. In this study, the author evaluated the tribological and mechanical behavior of neat and nanofilled functional polymers (PA6, PA66 and POM) produced by injectiono moulding.

Com o aumento da expectativa de vida da população mundial há uma tendência crescente de incorporar dispositivos artificiais no corpo humano. Portanto, a necessidade de buscar o melhor desempenho de biomateriais tem focado fortemente a atenção para projetar e fabricar dispositivos médicos com diversos tipos de materiais. Nesse contexto, a utilização de telas de polipropileno (PP) para o tratamento de hérnias e de grandes defeitos abdominais tem aumentado de forma significativa, e apesar da disseminação contínua do seu uso, as telas disponíveis não podem ser consideradas ideais, em face às possíveis reações orgânicas do hospedeiro ao material, provocando complicações infecciosas que ocorrem em até 8% dos casos, trazendo graves consequências físicas e psicológicas nestes pacientes. A técnica de deposição a plasma frio é uma ferramenta que permite alterar a característica superficial da tela sem comprometer suas propriedades físicas e mecânicas. Utilizando a técnica de magnetron sputtering foi possível modificar a superfície das telas de PP através do revestimento com filmes finos de DLC dopados com nanopartículas de prata. O recobrimento com filmes finos nanoestruturados ou nanopartículas, acrescenta novas características ao material, tais como: modificação da topografia, morfologia, estrutura e físico-química da superfície do material, bem como a inserção da ação antimicrobiana para diferentes tipos de bactérias e fungos devido a presença da prata. A inclusão da ação antimicrobiana às telas cirúrgicas pode diminuir a incidência de complicações infecciosas, e a presença do DLC possivelmente facilite o processo de reparação tecidual e cicatrização, minimizando efeitos adversos e sendo portanto fortemente indicado para aplicação industrial.

In this work, SnS2 is used as a nanofiller material to improve the response of the polymer-based piezoelectric nanogenerator because of its better inherent piezoelectric properties in comparison to other 2D materials. For this, first, nanoflakes of tin sulfide (SnS2) were synthesized via the hydrothermal method, where the high purity of SnS2 powder is confirmed by Raman spectroscopy and X-ray diffraction studies. The obtained powder of SnS2 was then mixed with PVDF-TrFE in different weight percentages (0%, 1%, 3%, 5%, and 7%) of SnS2 to synthesize polymer composite film via the drop-casting method. These films are then characterized with XRD and FTIR spectrometers, which show enhancement in the electroactive beta phase of the nanocomposite films after doping with SnS2 powder, from 58.30% to 93.07%, which is in agreement with the polarization versus electric field (P-E) measurements that show increased remnant polarization after doping. These films are then used to fabricate a piezoelectric nanogenerator by adhering aluminum tape to both sides of the films. The piezoelectric nanogenerator's (PENG) output performance is analyzed by measuring the open-circuit voltage (Voc) and short-circuits (Isc) by tapping the nanogenerator with the help of a dynamic shaker, which shows that the output performance of Trifluoroethylene (PVDF-TrFE) based PENGs gets enhanced after the introduction of SnS2 powder. The maximum piezoelectric voltage corresponding to the PENG made with 5% SnS2 was 14.4 V, which was almost 1.5 times that of the PENG made with bare PVDF-TrFE. The output piezoelectric current followed a similar trend, with the 5% SnS2 PENG producing 3.9�A of current, which was roughly 1.62 times more than the output of the bare PVDF TrFE thin film. As a result, the present study demonstrates that adding SnS2 to the PVDF matrix can significantly improve energy harvesting technologies based on PVDF's piezoelectric properties.

The current thrust towards the compaction of electrical power equipment, resulting in increased insulation electrical stress levels, necessitates new electrical insulating materials. In the last few decades, polymeric materials that exhibit light weight, excellent mechanical properties, low cost, and some with unique non-wetting surface characteristics, have surpassed the use of the conventional porcelain and glass insulating materials. Despite these advantages, polymeric materials are incapable of withstanding the high heat from surface arcing that is instigated by the synergism of pollution, moisture, and voltage. Surface arcing results in material loss due to heat ablation and/or the electrical tracking of polymeric materials. To overcome such issues, inorganic fillers are added to the base polymers to enhance their resistance to surface discharge activities and other performances. Since their addition can significantly reduce material costs, their use is compelling. Micron-sized fillers, here after defined as microfillers, have been used to acquire these desirable properties, but due to limitations in material processability, the further application of such fillers is limited. Consequently, nano-sized fillers, here after defined as nanofillers, have been viewed as replacements or assistant combinations to microfillers. Nanofillers are characterized by large surface areas, resulting in increased bond strengths that yield significant improvements in the various properties at fill levels well below that of microfillers. However, the primary problem of using nanofillers is their characteristic property of agglomeration due to their physical size and the forces between the fillers. Conventional mechanical mixing of nanofillers does not adequately separate the nanofillers, leading to behaviour similarly to that of microfillers. Therefore, the implementation of nanofillers is not completely effective. In chemical dispersion techniques, for example, the use of surfactants, are normally very elaborate and complicated. Due to the negative impact of agglomeration, the successful dispersion of nanofillers is pivotal in the further development of nanodielectrics for various insulation applications. In this thesis, electrospinning is proposed and realized as a new dispersal method for nanofillers in polymeric materials. This novel technique facilitates polymeric nanocomposites with improved properties due to the uniform distribution of fillers. Scanning electron microscopy (SEM) images and energy dispersive X-ray analysis (EDX) clearly indicate that electrospun nanocomposites demonstrate a better filler distribution than nanocomposites, produced by conventional mechanical mixing. Also electrospinning introduces the possibility of separating different nanofillers in different base polymers. The mechanical properties: tensile strength and hardness; the electrical properties: permittivity, tracking, and erosion resistance; and the thermal properties: thermal conductivity, thermal degradation, and heat erosion resistance of electrospun nanocomposites are compared to those of conventional nanocomposites for silicone rubber and cycloaliphatic epoxy-based polymers. All the experimental studies in this thesis confirm that electrospun nanocomposites exhibit better thermal performances than the conventional composites which are attributed to the improved distribution of the nanofillers by the newly developed electrospinning process. Also in this investigation, a two-dimensional thermal model is developed in COMSOL MultiphysicsTM by using the finite element method (FEM) to theoretically address the benefits of using nanofillers and the effects of filler dispersion. The model confirms that electrospun nanocomposites have much more uniform temperature distribution than conventional nanocomposites. This thesis presents the possible mechanisms by which nanofillers improve the heat and erosion resistance of silicone rubber nanocomposites, and also addresses the possible mechanism by which electrospinning improves nanofiller dispersion.

Thermal Energy Storage systems (TES), using phase change materials (PCM) in building sector, are widely investigated technologies and a fast developing research area. The use of PCM in building solutions and components appear as a potential solution to increase the thermal efficiency in buildings, either new or refurbished, since they can storage more energy, in latent form, than the typical sensible energy stored by common construction materials. However, the low thermal conductivity of PCM limits their full potential use because it slows down the heat transfer response associated to the charging and discharging processes. The present work approaches this frailty exploring the development of building solutions which incorporate synthetized PCM based on nanofillers and other additives to enhance the thermal conductivity. The evaluation in terms of thermal performance of different polyurethane foams (PUFs) formulations incorporating first, commercial microencapsulated PCM and a second, synthetized PCM based on paraffin and calcium carbonate. For comparison comparative analysis of three thermal conductivity testing procedures to characterize and determine the thermal conductivity. Next, a numerical model was developed to be calibrated resourcing to experimental data to then carry out a parametric study to assess the thermal performance of rigid PUFs panels incorporating PCM. Finally, the thermal performance of an alternative to rigid PUFs, specifically that of a poly(vinyl chloride) (PVC) structural layer incorporating commercial microencapsulated PCM and the two synthetized PCM was evaluated. This work presents promising results of the synthesized PCM in comparison to the commercial PCM and their incorporation into the different polymeric matrices (PUFs and PVC) revealing potential in LHTES applications. In addition, according the used acceptance criteria, the results of the numerical model presented a good agreement and reliability and were considered calibrated with well prediction data. The results reveal the PCM potential for the thermal regulation of indoor spaces as well as improving the energy efficiency of the indoor spaces.
Os sistemas de armazenamento de energia térmica (TES), usando materiais de mudança de fase (PCM) no setor da construção, são tecnologias amplamente investigadas e uma área de estudo em rápido desenvolvimento. O uso de PCM em soluções e componentes construtivas aparece como uma potencial solução para aumentar a eficiência energética de edifícios novos e reabilitados, uma vez que eles podem armazenar mais energia, de forma latente, do que a típica energia sensível armazenada por materiais comuns utlizados na construção. No entanto, a baixa condutividade térmica dos PCM limita o seu potencial uso, pois diminui a resposta da transferência de calor associada aos processos de carga e descarga. O presente trabalho aborda essa fragilidade, explorando o desenvolvimento de soluções construtivas que incorporam PCM sintetizados com base em nanofillers e outros aditivos para aumentar a sua condutividade térmica. Foi estudada a avaliação em termos de desempenho térmico de diferentes formulações de espumas de poliuretano (PUFs) incorporando, primeiro PCM microencapsulado de origem comercial, e um segundo PCM sintetizado à base de parafina e carbonato de cálcio para comparação. Foi realizada uma análise comparativa de três abordagens de ensaio para a caracterização e determinação da condutividade térmica em função da temperatura. Em seguida, foi construído um modelo numérico, com o objetivo de validar o mesmo, com recurso aos dados experimentais, para posteriormente realizar um estudo paramétrico para avaliar o desempenho térmico de painéis de PUFs rígidos incorporando PCM comercial e PCM sintetizado com carbonato de cálcio. Finalmente, foi avaliado o desempenho térmico de uma alternativa aos painéis de PUFs rígida, especificamente o de uma “layer” estrutural de poli (cloreto de vinila) (PVC) incorporando PCM microencapsulado comercial e os dois PCM sintetizados. Este trabalho apresenta resultados promissores para o PCM sintetizado em comparação com o PCM comercial e a sua incorporação nas diferentes matrizes poliméricas (PUFs e PVC) mostrando possíveis aplicações de LHTES. Além disso, de acordo com os critérios de validação analisados, os resultados do modelo numérico foram considerados calibrados e validados. Os resultados obtidos provam o potencial dos materiais de mudança de fase na regulação térmica e na otimização da eficiência energética de espaços interiores.
Programa Doutoral em Nanociências e Nanotecnologia

Tese de doutoramento em Biologia Experimental e Biomidicina, no ramo de Biotecnologia e Saúde, apresentada ao Instituto de Investigação Interdisciplinar da Universidade de Coimbra
Few examples have reported the successful use of engineered cardiac tissue for drug screening/toxicology assessment. This issue is of paramount importance since cardiac toxicity has been implicated in 28% of drug withdrawals over the last 30 years (Gwathmey et al., 2009). The development of tissue engineered cardiac tissue for drug screening requires the development of scaffolds that can be easily produced, flexible, small, and preserve the long-term contractility of cardiomyocytes, ideally in the absence of complex external electrical stimulation apparatus. Here we developed a flexible scaffold relatively easy to prepare that reproduces aspects of cardiac ECM, and can preserve the contractility of fetal rat cardiomyocytes for high-throughput drug screening applications. The scaffold is formed by a nanofilm of poly(caprolactone) (NF) coated by piezoelectric microfibers (PIEZO) composed of poly(vinylidene fluoride–trifluoroethylene) (PVDF-TrFE). When a mechanical force is applied to a piezoelectric material a shift or rotation of the constitutive dipole crystals occurs resulting in the generation of an electric charge. Therefore, PIEZO fibres may act as Purkinje cells, which in the native heart tissue are responsible for initiating and synchronizing cardiac beatings. To evaluate whether NF+PIEZO scaffolds preserve CM contractility, the number of spontaneous synchronous beatings per minute was monitored at day 1 and 12 after seeding the cells. While the average rate of beats in cells cultured in poly(styrene) and NF scaffolds maintained constant from day 1 to day 12, a significant increase in beats/minute of the cells cultured on NF+PIEZO scaffolds was observed (from 18 to 106 beats/min). This indicates that, for at least 12 days, NF+PIEZO scaffold provided a better environment to preserve the spontaneous contractility of CMs. Alongside, cells cultured in NF+PIEZO scaffold displayed higher levels of functional connexin 43 and waveform-like electrochemical signalling. These observations denote the stimulation of proper cell-cell communication and action potential conduction. When compared to tissue culture poly(styrene), the piezoelectric scaffold promoted transmembrane transients of Ca2+. This was confirmed by a high concentration of intracellular Ca2+ and a higher expression of important ion channels, namely sub-units of L-type Ca2+ channels and human Ether-à-go-go-Related ion channels. These observations were accompanied by clear morphological changes when compared to poly(styrene), including a 3-fold increase in CM alignment, more organized sarcomeric structures and a higher CM surface area. In addition, a main component of the contractile machinery (α-cardiac actin) was up-regulated, while its fetal counterpart (α-skeletal actin) dropped significantly in the piezo scaffold. To evaluate the usefulness of the engineered cardiac construct for drug screening, the cell construct was tested with norepinephrine. The results showed an adequate chronotropic response denoted by the rise of intracellular Ca2+ concentration which was accompanied by an increase in beating rates. Finally, metabolic studies based on glucose consumption and lactate production demonstrated that CMs cultured in NF+PIEZO had more efficient aerobic metabolism. This profile is inverted in the presence of doxorubicin, a cardiotoxic drug, which forces CMs to a glycolytic (anaerobic) metabolism and induces cell death. Overall, the results present in this thesis highlight the advantages of a piezoelectric-based scaffold to develop cardiac constructs for cardiotoxicity assessment.
Poucos estudos reportam a utilização bem-sucedida de tecido cardíaco criado in vitro na análise de efeitos farmacológicos e toxicológicos de medicamentos. Esta falha é de extrema importância, visto que toxicidade cardíaca tem sido implicada em cerca de 28% das remoções de medicamentos do mercado nos últimos 30 anos (Gwathmey et al., 2009). O desenvolvimento de tecido cardíaco in vitro para screening de medicamentos requer o desenvolvimento de matrizes que sejam facilmente produzidas, flexíveis, de pequena dimensão e preservem a contractilidade a longo termo de cardiomiócitos, idealmente na ausência de sistemas complexos de estimulação eléctrica. Aqui é descrito o desenvolvimento de uma matriz flexível para screening de medicamentos que é de fácil produção, reproduz aspectos da matriz extracelular cardíaca e permite a preservação da contractilidade de cardiomiócitos fetais de rato. A matriz é constituída por um nanofilme de poli(caprolactona) (NF) revestido por microfibras piezoeléctricas (PIEZO) de poli(vinilideno-trifluoroetileno) (P(VDF-TrFE)). Quando uma força mecânica é aplicada sobre o material piezoeléctrico ocorre uma alteração ou rotação nos dipolos cristalinos constitutivos, resultando na geração de uma carga eléctrica. Assim, fibras piezoeléctricas podem actuar como células de Purkinje, que no tecido cardíaco nativo são responsáveis por iniciarem e sincronizarem os batimentos cardíacos. Para avaliar se a matriz de NF+PIEZO preservaria a contractilidade de cardiomiócitos, o número de batimentos sincronizados por minutos foi monitorizado ao 1º e 12º dia após semear as células. Enquanto que a média de batimentos nas células cultivadas em poli(estireno) e em NFs foi semelhante no 1º e 12º dia, um aumento significativo foi observado (de 18 para 106 batimentos/min) nas células cultivadas nas matrizes de NF+PIEZO. Isto indica que, pelo menos até 12 dias, a matriz de NF+PIEZO oferece um microambiente melhor para a preservação da contracção espontânea de cardiomiócitos. Paralelamente, as células cultivadas nas matrizes de NF+PIEZO apresentaram níveis superiores de conexina 43 funcional e uma sinalização electroquímica em forma de onda. Estas observações denotam o desenvolvimento adequado da comunicação intercelular e do potencial de acção. Quando comparado com tecido cultivado em poli(estireno), a matriz piezoeléctrica promoveu o desenvolvimento de transientes de Ca2+, como foi confirmado pelos níveis elevados de Ca2+intracelular e pela elevada expressão de canais iónicos relevantes, nomeadamente sub-unidades de canais de Ca2+ tipo-L e canais Ether-à-go-go-Related. Estes resultados foram acompanhados por claras alterações morfológicas que incluíram um aumento de 3 vezes no alinhamento de cardiomiócitos, a presença de estruturas sarcoméricas alinhadas, e uma área de superfície de cardiomiócitos superior do que na condição controlo. Adicionalmente, a expressão de um dos componentes da maquinaria contráctil (α-actinina cardíaca) foi aumentada, enquanto que o respectivo homologo fetal (α-actinina esquelética) diminuiu significativamente na matriz piezoeléctrica. De forma a avaliar a utilidade do tecido cardíaco criado in vitro no screening medicamentos, o tecido celular construído foi testado com noradrenalina. Os resultados demonstram uma resposta cronotrópica adequada, evidenciada pelo aumento da concentração intracelular de Ca2+ acompanhado por um incremento no ritmo de batimento. Para finalizar, estudos metabólicos baseados no consumo de glucose e na produção de lactato demonstraram que os cardiomiócitos cultivados nas matrizes de NF+PIEZO apresentam um metabolismo aeróbico mais eficiente. Este perfil é invertido na presença de doxorubicina, um agente farmacológico cardiotóxico que força cardiomiócitos a adquirirem um metabolismo glicolítico (anaeróbico) e induz morte celular. Em suma, o conjunto de resultados apresentados nesta tese evidenciam as vantagens que uma matriz baseada num material piezoeléctrico apresenta no desenvolvimento de tecidos in vitro para a análise de efeitos cardiotóxicos.
Fundação para a Ciência e Tecnologia

With the recent surge in the usage of electronic devices, electromagnetic interference (EMI) poses a serious threat. Unwanted electromagnetic (EM) waves not only interfere with the normal functioning of electronic components, but certain studies suggest that it is a serious threat to human health. Polymer nanocomposites serve as a promising solution for EMI shielding as they can be tuned to meet the commercial shielding requirements by incorporating suitable fillers. Moreover, polymers are lightweight, corrosion resistive, easy to process, and can be molded into complex geometries. In this dissertation, multi-layered composite structures have been fabricated and studied for EMI shielding applications. Multi-walled carbon nanotubes (CNTs) were chosen as one of the fillers owing to their electrically conducting nature. To improve the thermal conductivity and/or EM wave absorption properties, a hybrid functional filler composed of Fe3O4 decorated reduced graphene oxide (rGO) was chemically synthesized and incorporated into selected composites. Alternatively, polyurethane (PU) foam-based multi-layered structures were also fabricated to enhance the absorption-based shielding performance. As a background study, we started with polycarbonate (PC)-based composites fabricated using the conventional melt mixing approach. PC was chosen as it has a low electrical percolation threshold for CNTs (<0.5 wt%). Total shielding effectiveness (SET) of -23 dB (1 mm thick) was obtained for PC composites with 3 wt% CNT and 10 wt% rGO-Fe3O4. A high filler loading in PC may result in either processing difficulties or poor structural properties. Therefore, PC was blended with polyvinylidene difluoride (PVDF) to improve the structural stability and also to take advantage of the double percolation effect. The selective localization of CNTs in the PC component of the PC/PVDF blend resulted in double percolation, i.e., improved bulk electrical conductivity in blend-based composites compared to single polymer composites. Despite the double percolation, the maximum SET value of -24 dB (1 mm thick) was observed with 3 wt% loading of CNTs. We further added a mutually soluble homopolymer, polymethylmethacrylate (PMMA), as a compatibilizer for the PC/PVDF immiscible blend to reduce the interfacial tension and refine the blend morphology. Despite the morphology refinement, the shielding performance declined due to the diffusion of PMMA in the individual components (PC or PVDF) and the redistribution of fillers. In the subsequent chapters, multi-layered composite structures were opted over the conventional melt mixed composites to improve upon the shielding performance. Thin films of PVDF and PC nanocomposites were interfacially locked using a mutually miscible polymer (PMMA) to obtain a shield with enhanced structural properties and EMI shielding performance. By stacking multi-layered films one above the other, reaching an assembly thickness of ca. 0.5 mm, the maximum SET was found to be -26 dB, which is a significant improvement compared to melt mixed composites. In the next chapter, porous structures (synthesized foams and 3D printed mesh structure) were sandwiched between composite sheets of PC and PVDF with an aim to dissipate the EM signals through multiple internal reflections. PU neat and composite foams were synthesized through a polymerization reaction between 4,4’-Methylenebis(phenyl isocyanate) and polyethylene glycol. Using PU-CNT foam as an inner layer between composite sheets of PC and PVDF, a maximum SET of -39 dB (approx. 5.3 mm thick) with absorption-dominated shielding. In order to further enhance the shielding effectiveness, Ag was sputtered on the PU-foam, which resulted in the highest SET value of -50 dB in the X-band but with a significant reflection component. The results presented here begin to suggest that in-situ synthesized foam with non-uniform and dead pores enhances the shielding performance compared to non-porous structures. Towards the end of the dissertation, PU foam was fabricated using a simpler technique of salt-leaching. By stacking freestanding CNT papers (approx. 200 µm in thickness) on both sides of lightweight PU foam, we could limit the filler content yet maximizing the absorption-based EMI shielding performance. The multi-layered structure exhibited a high SET value of -49 dB (92% absorption @ 26.5 GHz; approx. 4.6 mm thick), whereas CNT paper by itself showed a maximum SET value of -35 dB (73% absorption @ 26.5 GHz). The porous uniform PU structure enhances the absorption component of shielding due to the trapped air, adequate impedance match, and multiple internal reflections. Further, we arrived at a remarkably interesting conclusion, i.e., if the incoming wave encounters PU foam before the CNT paper (in multi-layered structure with foam and CNT paper on one side), the absorption percentage of shielding can be further enhanced (98% absorption @both 8.2 and 26.5 GHz, SET ~ -37 dB, approx. 4.4 mm thick). In such asymmetric structures, reversing the direction of the incoming EM wave can change the absorption percentage. The results presented in this dissertation suggest the various methodology for composite fabrication and the approaches to maximize the absorption-based EMI shielding performance.