Development of microcellular conductive foams based on polyetherimide with graphene nanoplatelets

Tesi per compendi de publicacions, amb diferents seccions retallades per drets de l'editor.Premi Extraordinari de Doctorat, promoció 2018-2019. Àmbit d’Enginyeria IndustrialThe aim of this dissertation was to develop and investigate novel cellular foams based on polyetherimide (PEI) and carbonbased nanoparticles such as, graphene nanoplatelets (GnP) and carbon nanotubes (CNT), using two main foaming methods; One being water vapour induced phase separation (WVIPS) method and the other being one-step foaming through dissolution of carbon dioxide (CO2) at its supercritical state. WVIPS method consists of initial preparation of polymer-solvent solution and nucleation of cells through phase separation due to water vapour absorption. The dissolution of supercritical CO2 (scCO2) in a high-pressure vessel has been used in order to consequently force a sudden expansion of the nanocomposite precursor in a one-step pressure drop which results in formation of cells. In WVIPS method, the concentration of the polymer in solvent during mixture showed to have a great impact on the morphology of the foams. Additionally, the composition seems to have various effect on the cellular structure. When a blend of PEI with polyamide-imide (PAI) was prepared using this method, the cellular formation evolved drastically depending on the amounts of PAI added to the mixture. Moreover, the incorporation of GnP and CNT seem to have affected the cellular structure and morphology with various levels of impact depending on whether the ultrasonication of the nanoparticles was applied. Using the one-step scCO2 dissolution foaming method, foams were obtained with homogenous closed-cell structure. The incorporation of GnP did not seem to affect the cellular structure of the PEI foams. However, the application of ultrasonication, melt mixing and one-step foaming seem to have induced a proper level of particle dispersion which was confirmed by X-ray diffraction analysis. The studies of mechanical properties of foams prepared via WVIPS method suggested that the densities of the foams alter their viscoelastic behaviour in a direct manner. Additionally, the mechanical behaviour followed a similar increasing trend by incrementing the amount of graphene content. Surprisingly, this behaviour changed when using CNT as reinforcement; A clear decreasing trend was observed in specific storage modulus of the foams by increasing the amount of CNT. Moreover, considering the case of polymeric blends, the mechanical behaviour seem to have been affected vastly by the structural changes. The PEI/PAI polymer composition played a key role in determination of the cellular structure and therefore, the eventual mechanical behaviour of these foams. The foams prepared through scCO2 dissolution showed an increasing trend of normalized modulus (Enorm) with increasing the density and a rise in specific modulus (Espec) with increasing the GnP volume fraction. In an overall view, the nanoparticles provided a general delay in degradation temperatures of the nanocomposite foams which could provide the possibility of their application in high temperature environments. Significant enhancements were achieved regarding the electrical conductivity of the foams. The ultrasonication of the nanoparticles have provided the possibility to increase the value of electrical conductivity by six orders of magnitude from 1.8 × 10E-7 S/m to 1.7 × 10E-1 S/m for foams containing 10 wt% of GnP. The foams with 1/1 ratio of GnP and CNT reached an electrical conductivity value of 8.8 × 10E-3 S/m containing only a total amount of 2 wt% in nanoparticles.El objetivo de esta tesis doctoral fue desarrollar e investigar nuevas espumas celulares basadas en polieterimida (PEI) y nanopartículas basadas en carbono, como son las nanopartículas de grafeno (GnP) y los nanotubos de carbono (CNT). Para ello se utilizó dos métodos principales de formación de espumas, uno de ellos fue el método de separación de fases inducida por vapor de agua (WVIPS) y el otro consistió en la formación de espuma en un solo paso mediante la disolución de dióxido de carbono (CO2) en su estado supercrítico. El método WVIPS consiste en la preparación inicial de la solución de polímero-disolvente y la nucleación de las células a través de la separación de fases debido a la absorción del vapor de agua. La disolución de CO2 supercrítico (scCO2) se aplicó en un reactor para forzar consecuentemente una expansión repentina del precursor nanocompuesto en una caída de presión en un paso que dio como resultado la formación de células. En el método WVIPS, la concentración del polímero en el disolvente durante la mezcla mostró un gran impacto sobre la morfología de las espumas. Las espumas preparadas con una menor concentración de polímero en el disolvente dieron como resultado, espumas más ligeras con tamaños medios de células mayores. Además, la composición parece tener diversos efectos sobre la estructura celular. Cuando se preparó una mezcla de PEI con poliamida-imida (PAI) usando este método, la formación celular evolucionó drásticamente dependiendo de la fracción de PAI añadida a la mezcla. Por otra parte, la incorporación de GnP y CNT parece haber afectado la estructura celular y la morfología en diferentes niveles de impacto dependiendo de si se aplicó la ultrasonicación de las nanopartículas o no. Usando el método de espumación por disolución de scCO2 en un paso, espumas con homogeneidad estructural y con celdas cerradas fueron obtenidas. Sin embargo, la aplicación de ultrasonidos, mezcla en fusión y espumación en un solo paso parece haber inducido un nivel adecuado de dispersión de partículas que se confirmó mediante análisis de difracción de rayos X. Los estudios de las propiedades mecánicas de las espumas preparadas mediante el método WVIPS sugirieron que las densidades de las espumas alteran su comportamiento viscoelástico de manera directa. Además, el comportamiento mecánico sigue una tendencia similar al aumentar la fracción de grafeno. Sorprendentemente, este comportamiento cambia cuando se usa CNT como refuerzo; Se observó una clara tendencia decreciente en el módulo de almacenamiento específico con el aumento de la cantidad de CNT. Además, considerando el caso de las mezclas poliméricas, el comportamiento mecánico parece haber sido afectado enormemente por los cambios estructurales. La composición del polímero PEI / PAI desempeñó un parte clave en la determinación de la estructura celular y, por lo tanto, el comportamiento mecánico final de estas espumas. Las espumas preparadas a través de la disolución de scCO2 mostraron una tendencia creciente de módulo normalizado (E´norm) con el aumento de la densidad y un aumento en el módulo específico (E´spec) con el aumento de la fracción volumétrica de GnP. De forma general, las nanopartículas proporcionaron un retraso general en las temperaturas de degradación de las espumas nanocompuestas que podrían proporcionar la posibilidad de su aplicación en entornos de alta temperatura. Se lograron mejoras significativas con respecto a la conductividad eléctrica de las espumas. La ultrasonicación de las nanopartículas proporcionó la posibilidad de aumentar el valor de la conductividad eléctrica en seis órdenes de magnitud desde 1,8 × 10E-7 S/m hasta 1,7 × 10E-1 S/m en espumas que contienen 10% en peso de GnP. Las espumas con proporción 1/1 de GnP y CNT alcanzaron un valor de conductividad eléctrica de 8,8 × 10E-3 S/m que contenía solo un 2% en peso de nanopartícularAward-winningPostprint (published version

Effects of carbon nanotubes/graphene nanoplatelets hybrid systems on the structure and properties of polyetherimide-based foams

Foams based on polyetherimide (PEI) with carbon nanotubes (CNT) and PEI with graphene nanoplatelets (GnP) combined with CNT were prepared by water vapor induced phase separation. Prior to foaming, variable amounts of only CNT(0.1–2.0wt%) or a combination of GnP(0.0–2.0 wt %) and CNT (0.0–2.0 wt %) for a total amount of CNT-GnP of 2.0 wt %, were dispersed in a solvent using high power sonication, added to the PEI solution, and intensively mixed. While the addition of increasingly higher amounts of only CNT led to foams with more heterogeneous cellular structures, the incorporation of GnP resulted in foams with ¿ner and more homogeneous cellular structures. GnP in combination with CNT effectively enhanced the thermal stability of foams by delaying thermal decomposition and mechanically-reinforced PEI. The addition of 1.0 wt % GnP in combination with 1.0 wt % CNT resulted in foams with extremely high electrical conductivity, which was related to the formation of an optimum conductive network by physical contact between GnP layers and CNT, enabling their use in electrostatic discharge (ESD) and electromagnetic interference (EMI) shielding applications. The experimental electrical conductivity values of foams containing only CNT ¿tted well to a percolative conduction model, with a percolation threshold of 0.06 vol % (0.1 wt %) CNTPostprint (published version

Effects of graphene nanoplatelets and cellular structure on the thermal conductivity of polysulfone nanocomposite foams

Polysulfone (PSU) foams containing 0–10 wt% graphene nanoplatelets (GnP) were prepared using two foaming methods. Alongside the analysis of the cellular structure, their thermal conductivity was measured and analyzed. The results showed that the presence of GnP can a ect the cellular structure of the foams prepared by both water vapor induced phase separation (WVIPS) and supercritical CO2 (scCO2) dissolution; however, the impact is greater in the case of foams prepared by WVIPS. In terms of thermal conductivity, the analysis showed an increasing trend by incrementing the amount of GnP and increasing relative density, with the tortuosity of the cellular structure, dependent on the used foaming method, relative density, and amount of GnP, playing a key role in the final value of thermal conductivity. The combination of all these factors showed the possibility of preparing PSU-GnP foams with enhanced thermal conductivity at lower GnP amount by carefully controlling the cellular structure and relative density, opening up their use in lightweight heat dissipatorsPostprint (published version

Polyetherimide foams filled with low content of graphene nanoplatelets prepared by scCO2 dissolution

Polyetherimide (PEI) foams with graphene nanoplatelets (GnP) were prepared by supercritical carbon dioxide (scCO2) dissolution. Foam precursors were prepared by melt-mixing PEI with variable amounts of ultrasonicated GnP (0.1–2.0 wt %) and foamed by one-step scCO2 foaming. While the addition of GnP did not significantly modify the cellular structure of the foams, melt-mixing and foaming induced a better dispersion of GnP throughout the foams. There were minor changes in the degradation behaviour of the foams with adding GnP. Although the residue resulting from burning increased with augmenting the amount of GnP, foams showed a slight acceleration in their primary stages of degradation with increasing GnP content. A clear increasing trend was observed for the normalized storage modulus of the foams with incrementing density. The electrical conductivity of the foams significantly improved by approximately six orders of magnitude with only adding 1.5 wt % of GnP, related to an improved dispersion of GnP through a combination of ultrasonication, melt-mixing and one-step foaming, leading to the formation of a more effective GnP conductive network. As a result of their final combined properties, PEI-GnP foams could find use in applications such as electrostatic discharge (ESD) or electromagnetic interference (EMI) shieldingPostprint (published version

Recent advances in carbon-based polymer nanocomposites for electromagnetic interference shielding

Carbon-based nanoparticles have recently generated a great attention, as they could create polymer nanocomposites with enhanced transport properties, overcoming some limitations of electrically-conductive polymers for high demanding sectors. Particular importance has been given to the protection of electronic components from electromagnetic radiation emitted by other devices. This review considers the recent advances in carbon-based polymer nanocomposites for electromagnetic interference (EMI) shielding. After a revision of the types of carbon-based nanoparticles and respective polymer nanocomposites and preparation methods, the review considers the theoretical models for predicting the EMI shielding, divided in those based on electrical conductivity, models based on the EMI shielding efficiency, on the so-called parallel resistor-capacitor model and those based on multiscale hybrids. Recent advances in the EMI shielding of carbon-based polymer nanocomposites are presented and related to structure and processing, focusing on the effects of nanoparticle’s aspect ratio and possible functionalization, dispersion and alignment during processing, as well as the use of nanohybrids and 3D reinforcements. Examples of these effects are presented for nanocomposites with carbon nanotubes/nanofibres and graphene-based materials. A final section is dedicated to cellular nanocomposites, focusing on how the resulting morphology and cellular structures may generate lightweight multifunctional nanocomposites with enhanced absorption-based EMI shielding propertiesPostprint (author's final draft

Enhancing the electrical conductivity of polyetherimide-based foams by simultaneously increasing the porosity and graphene nanoplatelets dispersion

Significant improvement in electrical conductivity of graphene nanoplatelets-filled polyetherimide (PEI) foams was achieved by simultaneously increasing the porosity and graphene nanoplatelets dispersion. Foams were prepared by means of water vapor-induced phase separation using a concentration of graphene nanoplatelets (GnP) between 1 and 10 wt%. To obtain two sets of foams having different density and porosity, PEI's concentration in N-methyl pyrrolidone (NMP) solvent prior to foaming was set at 15 and 25–30 wt%, respectively. High-power sonication was applied to GnP-NMP suspension before PEI's addition for the foam series with higher porosity (15 wt% PEI). All foams were later characterized in terms of cellular structure, thermal stability, dynamic-mechanical properties, and electrical conductivity. A notable enhancement in electrical conductivity was observed with foaming, especially when increasing the porosity and applying sonication, with foams reaching values as high as 1.7 × 10-1 S/m while maintaining the thermal stability and mechanical performancePostprint (author's final draft

Preparation of nanocomposite foams based on polysulfone and carbon-based nanoparticles using WVIPS

Postprint (published version

The acute effects of Water-pipe smoking on Ankle Brachial Index: A cross-sectional Study

Introduction: Numerous studies have shown that waterpipe smokers as well as cigarette smokers are at increased risk of cardiovascular diseases. In this study we sought to evaluate the acute effects of waterpipe smoking (WPS) on ankle brachial index (ABI), an indicator of atherosclerosis and an independent predictor of mortality.Methods: This prospective cross-sectional study was conducted in October 2017. Twenty nine healthy male volunteers who had a history of WPS were enrolled. Demographic data and cigarette and WPS status were recorded via self-reporting questionnaire. Resting heart rate and brachial systolic and diastolic blood pressures of participants were recorded first and ABI measurements were done. Then subjects smoked waterpipe for about 20 minutes and ABI was measured immediately after WPS.Results: A total of 29 male adults with a mean age of 32 ± 9 years were included. The right-sided ABI was 1.05 ± 0.11 before WPS and significantly decreased to 0.98 ± 0.13 after WPS (P value = 0.006). The left-sided ABI before and after WPS were 1.09 ± 0.20 and 0.95 ± 0.18 respectively and the decrease was statistically significant (P value = 0.037). Vital signs before and after one session of WPS showed significant changes in heart rate (P < 0.001) and no significant changes in systolic and diastolic blood pressures (P = 0.09, and P = 0.14, respectively).Conclusion: WPS has an acute effect on ABI as well as heart rate so it should be considered as a potential risk factor for cardiovascular diseases

The global burden of adolescent and young adult cancer in 2019 : a systematic analysis for the Global Burden of Disease Study 2019

Background In estimating the global burden of cancer, adolescents and young adults with cancer are often overlooked, despite being a distinct subgroup with unique epidemiology, clinical care needs, and societal impact. Comprehensive estimates of the global cancer burden in adolescents and young adults (aged 15-39 years) are lacking. To address this gap, we analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019, with a focus on the outcome of disability-adjusted life-years (DALYs), to inform global cancer control measures in adolescents and young adults. Methods Using the GBD 2019 methodology, international mortality data were collected from vital registration systems, verbal autopsies, and population-based cancer registry inputs modelled with mortality-to-incidence ratios (MIRs). Incidence was computed with mortality estimates and corresponding MIRs. Prevalence estimates were calculated using modelled survival and multiplied by disability weights to obtain years lived with disability (YLDs). Years of life lost (YLLs) were calculated as age-specific cancer deaths multiplied by the standard life expectancy at the age of death. The main outcome was DALYs (the sum of YLLs and YLDs). Estimates were presented globally and by Socio-demographic Index (SDI) quintiles (countries ranked and divided into five equal SDI groups), and all estimates were presented with corresponding 95% uncertainty intervals (UIs). For this analysis, we used the age range of 15-39 years to define adolescents and young adults. Findings There were 1.19 million (95% UI 1.11-1.28) incident cancer cases and 396 000 (370 000-425 000) deaths due to cancer among people aged 15-39 years worldwide in 2019. The highest age-standardised incidence rates occurred in high SDI (59.6 [54.5-65.7] per 100 000 person-years) and high-middle SDI countries (53.2 [48.8-57.9] per 100 000 person-years), while the highest age-standardised mortality rates were in low-middle SDI (14.2 [12.9-15.6] per 100 000 person-years) and middle SDI (13.6 [12.6-14.8] per 100 000 person-years) countries. In 2019, adolescent and young adult cancers contributed 23.5 million (21.9-25.2) DALYs to the global burden of disease, of which 2.7% (1.9-3.6) came from YLDs and 97.3% (96.4-98.1) from YLLs. Cancer was the fourth leading cause of death and tenth leading cause of DALYs in adolescents and young adults globally. Interpretation Adolescent and young adult cancers contributed substantially to the overall adolescent and young adult disease burden globally in 2019. These results provide new insights into the distribution and magnitude of the adolescent and young adult cancer burden around the world. With notable differences observed across SDI settings, these estimates can inform global and country-level cancer control efforts. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd.Peer reviewe

The global burden of cancer attributable to risk factors, 2010-19 : a systematic analysis for the Global Burden of Disease Study 2019

Background Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. Methods The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk-outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. Findings Globally, in 2019, the risk factors included in this analysis accounted for 4.45 million (95% uncertainty interval 4.01-4.94) deaths and 105 million (95.0-116) DALYs for both sexes combined, representing 44.4% (41.3-48.4) of all cancer deaths and 42.0% (39.1-45.6) of all DALYs. There were 2.88 million (2.60-3.18) risk-attributable cancer deaths in males (50.6% [47.8-54.1] of all male cancer deaths) and 1.58 million (1.36-1.84) risk-attributable cancer deaths in females (36.3% [32.5-41.3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20.4% (12.6-28.4) and DALYs by 16.8% (8.8-25.0), with the greatest percentage increase in metabolic risks (34.7% [27.9-42.8] and 33.3% [25.8-42.0]). Interpretation The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.Peer reviewe