Low density polycarbonate foams containing different amounts of graphene nanoplatelets with variable cellular morphologies were prepared using a supercritical carbon dioxide two-step foaming process, which consisted of the dissolution of supercritical CO2 into moulded foam precursors and their later expansion by double contact restricted foaming. The effects of the processing conditions and graphene content on the cellular morphology of the obtained foams were investigated, showing that the addition of increasingly higher amounts of graphene nanoplatelets resulted in foams with increasingly smaller cell sizes and higher cell densities, due on the one hand to their effectiveness as cell nucleating agents and on the other to their platelet-like geometry, which limited CO2 loss during foaming due to a barrier effect mechanism. Especially significant was the addition of 5 wt.% graphene nanoplatelets, as the high concentration of graphene limited CO2 escape and cell coalescence during expansion, enabling to obtain highly expanded microcellular foams.
The present work considers the preparation of medium-density polyetherimide foams reinforced with variable amounts of graphene nanoplatelets (1–10 wt%) by means of water vapor-induced phase separation (WVIPS) and their characterization. A homogeneous closed-cell structure with cell sizes around 10 µm was obtained, with foams exhibiting zero crystallinity according to X-ray diffraction (XRD). Thermogravimetric analysis under nitrogen showed a two-step thermal
decomposition behaviour for both unfilled and graphene-reinforced foams, with foams containing graphene presenting thermal stability improvements, related to a physical barrier effect promoted by the nanoplatelets. Thermo-mechanical analysis indicated that the specific storage modulus of the nanocomposite foams significantly increased owing to the high stiffness of graphene and finer cellular morphology of the foams. Although foamed nanocomposites displayed no further sign of graphene nanoplatelets exfoliation, the electrical conductivity of these foams was significant even for low graphene contents, with a tunnel-like model fitting well to the evolution of the electrical conductivity with the amount of graphene.
Several commercial polyolefin-based flexible foams produced by extrusion foaming were characterized in terms of their cellular morphology and fracture behaviour using the concept of the Essential Work of Fracture (EWF), focusing on the influence of foam's chemical nature, expansion ratio and cellular structure on the values of the fracture parameters. Correction procedures were proposed in order to take into account the complexity of foams in the obtained fracture parameters, particularly a correction procedure based on their expansion ratio, and a second one based on the fraction of polymer
present in the foams determined from cellular structure characterization. Although doubts remain about the applicability of the EWF methodology to LDPE foams, the correction procedure based on the expansion ratio seemed to provide more accurate results than that
based on polymer fraction, with EWF effectively distinguishing between polyolefin foams having different chemical nature. Comparatively, foams based on a P-E copolymer presented the highest values of the essential work of fracture in the MD direction, while significant differences were only observed in the TD direction for foams having a highly oriented cellular structure. All PP-based foams showed similar non-essential work of fracture values in both MD and TD directions.
De Sousa Pais, M.; Cano, Á.; De Redondo, V.; Arencon, D.; Velasco J.I. International Journal of Composite Materials Vol. 4, num. 5A, p. 27-34 DOI: 10.5923/j.cmaterials.201401.04 Date of publication: 2014-11 Journal article
In the present work we prepared and characterized several polyurethane (PU) composite foams by combining variable concentrations of nanoclay (montmorillonite, MMT) with metal wires or low cost cellulosic-based reinforcements, with the objective of developing multi-scalar rigid foams for structural applications. The addition of MMT promoted foaming and the formation of finer and more homogeneous cellular structures, resulting in foams with compressive elastic moduli and collapse stresses lower than that of the unfilled PU foams. However, a comparative analysis versus the foams’ relative density demonstrated that both mechanical properties follow one single trend for the two materials. The combination of MMT and the macroscopic metal wires or cellulosic-based reinforcements further reduced the cell size of foams and resulted in foams with similar compressive collapse strengths as the unfilled ones for considerably lower relative densities, hence demonstrating their effectiveness as mechanical reinforcements of rigid PU foams and opening up new possibilities in terms of developing low cost lightweight materials.
Gedler, G.; De Sousa Pais, M.; Rende, D.; Schadler, L.; Velasco J.I.; Ozisik, R. International Conference on Foam Materials & Technology Presentation's date: 2014-09-11 Presentation of work at congresses
The microstructural characteristics of polycarbonate-graphene nanocomposite foams prepared using supercritical CO2 foaming are investigated using small and wide angle X-ray diffraction to understand the effect of graphene, cellular microstructure and polymer morphology on electromagnetic interference shielding effectiveness. The observed microstructural changes suggest a preferential orientation of polycarbonate chains and graphene nanoplatelets induced by foaming, which could explain the enhancement observed in electromagnetic interference shielding effectiveness of up to five times when compared to the unfoamed material, therefore, opening up the possibility of using polycarbonate-graphene foams in electronic applications.
The increasingly demanding industrial requirements for polymers with enhanced specific properties and functional characteristics have aroused a great interest in the development of lightweight nanocomposites by combining foaming with the addition of functional nanosized fillers. In midst of these, graphene-based materials have recently generated a great attention as a way to extend the range of applications of polymers due to their combination of high mechanical and transport properties, enabling to overcome some of the limitations of common
conducting polymers, such as high cost, low thermal stability and poor mechanical performance.
Among currently available graphene-based materials scalable to mass production, graphene nanoplatelets have emerged as an interesting multifunctional filler for polymer foams. Nevertheless, there is still a considerable lack of information regarding the influence that these nanoparticles have on the microstructure and cellular structure and thus on the final properties of the resulting foams.
With the goal of analyzing the effects of graphene nanoplatelets (GnP) on the structure and mechanical and transport properties of polymer foams, polycarbonate (PC) nanocomposites containing graphene nanoplatelets prepared by melt compounding were foamed using a supercritical CO2 (scCO2) dissolution process. While an ordered non-crystalline PC phase was observed when dissolving scCO2 in PC (PC-CO2), it was only when combining the nanoplatelets and scCO2 (PC-GnP-CO2) that it was possible to promote PC’s crystallization. This induced crystallization led to foams with improved thermal stabilities and specific moduli when compared to the unfilled PC. Foams resulted electrically conductive, with their electrical conductivity increasing with increasing the expansion ratio, which was related to a reduction of the critical distance between the conductive nanoplatelets due to foaming. Additionally,
controlled deformation of the foams induced even higher electrical conductivities, suggesting their possible use for piezoelectric, EMI shielding and ESD applications.
Since the publication of the successful first edition of the book in 2010, the field has matured and a large number of advancements have been made to the science of polymer nanotube nanocomposites (PNT) in terms of synthesis, filler surface modification, as well as properties. Moreover, a number of commercial applications have been realized. The aim of this second volume of the book is, thus, to update the information presented in the first volume as well as to incorporate the recent research and industrial developments.
This edited volume brings together contributions from a variety of senior scientists in the field of polymer nanotube composites technology to shed light on the recent advances in these commercially important areas of polymer technology. The book provides the following features:
-Reviews the various synthesis techniques, properties and applications of the polymer nanocomposite systems
- Describes the functionalization strategies for single walled nanotubes in order to achieve their nanoscale dispersion in epoxy matrices
- Provides insights into the multiscale modeling of the properties of PNT
Provides perspectives on the electron microscopy characterization of PNT
- Presents an overview of the different methodologies to achieve micro-patterning of PNT
- Describes the recent progress on hybridization modifications of CNTs with carbon nanomaterials and their further applications in polymer nanocomposites
- Provides details on the foams generates with PNT
- Provides information on synthesis and properties of polycarbonate nanocomposite.
- Describes the advanced microscopy techniques for understanding of the polymer/nanotube composite interfaces and properties.
La polieterimida (PEI) es un termoplástico de altas prestaciones (Tg = 215 ºC), que presenta elevadas propiedades mecánicas y resistencia térmica debido a su estructura de imida aromática, buena procesabilidad por la flexibilidad del enlace éter presente, y elevada selectividad frente a ciertos gases. Por todo ello, en la actualidad se emplea en la fabricación de membranas asimétricas para nanofiltración de solventes orgánicos, absorción de gases y otros procesos de separación. El método más común de preparación es el proceso de inversión de fases, en el que la disolución del polímero, una vez vertida, es puesta en contacto con un no-solvente. El intercambio entre ambos solventes induce la separación de fases, dando lugar a la estructura porosa de la membrana. La estructura es responsable de las propiedades, y depende en gran medida de su composición y condiciones de preparación. En particular, una de las estrategias que se siguen para la regulación de la morfología de estas membranas y, en consecuencia de sus propiedades, es incorporar aditivos y nanocargas inorgánicas.
Con el fin de regular las características morfológicas y estructurales de membranas de PEI, y de determinar la influencia sobre sus propiedades, en el presente trabajo se prepararon membranas a base de nanocompuestos de PEI (Ultem 1000, Sabic) con diferentes porcentajes de nanopartículas de grafeno (GnP, XGSciences), y se caracterizaron a nivel morfológico y estructural, térmico y mecánico, principalmente, empleando para ello técnicas de microscopía electrónica de barrido (SEM), difracción de rayos-X (WAXS), calorimetría diferencial de barrido (DSC), análisis termogravimétrico (TGA) y análisis térmico mecánico dinámico (DMTA). Asimismo, debido a las propiedades conductoras de las nanopartículas de grafeno, las membranas presentan conductividad eléctrica, lo que permite extender su campo de aplicación.
Se caracterizan por DMTA espumas de policarbonato (PC) y de policarbonato con nanopartículas de grafeno, producidas mediante dos procesos diferentes de disolución de CO2 supercrítico con posterior expansión en una o en dos etapas. Se analizan los efectos derivados de la presencia del grafeno en el PC, así como la influencia de la densidad relativa de la espuma y de sus características morfológicas y microestructurales sobre su respuesta elástica y viscosa. De modo general, el módulo de almacenamiento específico se ve mejorado en las espumas de PC con la incorporación del
grafeno. Por lo que respecta a la componente de disipación viscosa, existen sendas relaciones entre la posición e intensidad del pico de tand, asociado a la transición vítrea del polímero, con la densidad relativa. No obstante, estas relaciones se ven modificadas al cristalizar el PC durante la espumación, ya que la presencia combinada de grafeno y CO2 induce la cristalización del polímero.
Closed-cell polycarbonate foams were prepared using a two-step foaming process, which consisted of the initial dissolution of supercritical CO2(scCO2) into PC foaming precursors and their later expansion by heating using a double contact restriction method. The effects of the parameters of both CO2 dissolution and heating stages on the cellular structure characteristics as well as on the physical aging of PC in the obtained foams were investigated. A higher amount of CO2 was dissolved in PC with increasing the dissolution temperature from 80 to 100 ºC, with similar CO2 desorption trends and diffusion coefficients being found for both conditions. PC foams displayed an isotropic-like microcellular structure at a dissolution temperature of 80 ºC. It was shown that it is possible to reduce their density while keeping their microcellular structure with increasing the heating time. On contrary, when dissolving CO2 at 100 ºC and later expanding, PC foams presented a cellular morphology with bigger cells and with an increasingly higher cell elongation in the vertical growth direction with increasing the heating time. Comparatively, PC foams obtained by dissolving CO2 at 100 ºC presented a more marked physical aging after CO2 dissolution and foaming, although this effect could be reduced and ultimately suppressed with increasing the heating time.
The present work deals with the development of new rigid polypropylene composite foams filled with high amounts of flame-retardant systems based on synthetic hydromagnesite, a basic magnesium carbonate obtained from an industrial by-product. A partially-interconnected cellular structure with a cell size around 100 micrometers was obtained for the hydromagnesite-filled PP foams. A 40% reduction of this cell size was observed when a small amount of a combination of montmorillonite and graphene layered nanoparticles was added to the hydromagnesite. The combination of hydromagnesite with an intumescent additive (ammonium polyphosphate) and layered nanoparticles led to improved thermal stability. In particular, the intumescent additive delayed the beginning of the thermal decomposition temperature and the layered nanoparticles split the second step of thermal decomposition in a third peak observed
at higher temperatures. Improved flame retardancy, measured by means of cone calorimetry, was observed in the samples containing the intumescent additive. A novel normalized parameter, called foam efficiency ratio (FER), which takes into account the expansion ratio of the foam and the relation of its fire properties with that of the base solid, was also analyzed.
Increasingly demanding industry requirements in terms of developing polymer-based components with higher specific properties have recently aroused a great interest around the possibility of combining density reduction through foaming with the addition of small amounts of functional nanosized particles. Particular interest has been given to the creation of lightweight conductive polymers by incorporating conductive carbon-based nanoparticles, related to processing improvements in attaining homogeneous nanoparticle dispersion and distribution throughout the polymer as well as new processes that enable a higher control and throughput of highly pure carbon nanoparticles, which could overcome some of the common problems of conductive polymers, such as high cost and poor mechanical properties. This review article considers the use of carbon nanoparticles in polymer foams, initially focusing on the important aspects of foam preparation, the main results found in the literature about conductive polymer composites containing carbon nanoparticles, as well as the main polymer foaming processes and types of foams. The main section is dedicated to the properties of multifunctional polymer foams with carbon nanoparticles, with special focus being given to the electrical and transport properties of these materials.
De Sousa Pais, M.; De Redondo, V.; Gedler, G.; Arencon, D.; Velasco J.I. Journal of nano research Vol. 26, p. 63-74 DOI: 10.4028/www.scientific.net/JNanoR.26.63 Date of publication: 2014-01 Journal article
This work considers the study of the diffusion of carbon dioxide in polypropylene and amorphous polymers containing carbon nanoparticles, particularly carbon nanofibres and graphene, as well as nanoclays, to be used in microcellular foaming. The diffusion of CO2 out and into the nanocomposites was studied during high pressure CO2 dissolution, as the amount of CO2 dissolved into the nanocomposite and CO2 desorption rate are crucial in order to have a proper control of foaming. Comparatively, platelet-like nanoparticles slowed down the desorption of CO2 out of the nanocomposites by means of a physical barrier effect, enabling a higher concentration of CO2 to remain in the polymer and be used in foaming. As a consequence of the higher amount of CO2 retained in the polymer and the cell nucleation effect promoted by the nanoparticles, polymer nanocomposite foams presented finer microcellular structures, in the case of PMMA even submicrocellular, and higher specific moduli and electrical conductivities when compared to their pure counterparts.
Changes in the crystallinity of polycarbonate (PC) induced by the simultaneous presence of 0.5 wt% graphene nanoplatelets (GnP) and supercritical carbon dioxide (sc-CO2) were examined by means of Raman spectroscopy, WAXS, SAXS and DSC. Composites were prepared by melt-mixing, compression-molding and dissolving sc-CO2 at high pressure and temperature. It was found that dissolved CO2 induced the formation of an ordered non-crystalline phase in PC during slow cooling under pressure. A fast depressurization and cooling did not cause such an effect in the resultant foams. GnP induced a higher crystallinity in PC, especially when combined with sc-CO2, even during fast depressurization and cooling. Raman spectroscopy enabled to correlate changes in the PC vibration modes with the presence of ordered phases, as well as to detect interactions between GnP and PC. Additionally, evidence of GnP exfoliation in the composites could be explained by the intensity reduction of the (002) graphite diffraction peak.
A highly topical subject in Materials Science considers the development of multifunctional materials with improved specific properties by combining the low density of polymers with the incorporation of functional nanofillers. This is the case of graphene, a two-dimensional nanosized material that has recently attracted a great interest due to its unique combination of properties and that has been shown to result in significant property enhancements when added into polymers even at extremely low concentrations.
This presentation covers the most recent applications of graphene in polymer-based materials with the goal of developing multifunctional lightweight materials with a vast range of applications.
Gedler, G.; De Sousa Pais, M.; Sanchez, M.; Maspoch, M.; Velasco J.I. International Conference on Diffusion in Solids and Liquids p. 222- Presentation's date: 2013-06-25 Presentation of work at congresses
De Sousa Pais, M.; De Redondo, V.; Gedler, G.; Arencon, D.; Velasco J.I. International Conference on Diffusion in Solids and Liquids p. 189- Presentation's date: 2013-06-25 Presentation of work at congresses
Gedler, G.; De Sousa Pais, M.; De Redondo, V.; Martinez, A.; Velasco J.I. International Symposium Frontiers in Polymer Science p. P3.103 Presentation's date: 2013-05-23 Presentation of work at congresses
There is still lack of information regarding changes in the microstructure of polycarbonate (PC) due to the addition of secondary phases and processing.
In this work, PC composites with graphene were expanded using supercritical CO2 (sc-CO2). Raman spectroscopy, XRD and DSC demonstrated that the presence of graphene and CO2 induced PC’s crystallization during saturation. Double melting behavior indicated the presence of crystals with different thermal stabilities. Saturation temperature, time and CO2 pressure had a direct effect on PC's melting temperature, indicating that processing parameters may be regulated to achieve different crystalline microstructures. Raman spectroscopy enabled to correlate changes in PC’s crystallinity with processing conditions, showing that graphene and sc-CO2 favored the formation of an ordered non-crystalline phase. This induced crystallization, combined with graphene, led to composites with specific moduli that were up to 15% higher than that of unfilled PC.
This work considers the preparation and characterization of polypropylene foams with
variable concentrations of graphene and carbon nanofibres, focussing on the influence
of the foaming process and the nanofillers on the microstructural and dynamic-mechanical-
thermal properties of the foams. Great differences were found in terms of foam
morphology depending on the type of foaming process, with foams prepared by physical
foaming showing a vertically deformed cell structure, while chemical foams presented
an isotropic-like cellular structure. The addition of graphene resulted in foams with
higher cell densities and more uniform cellular structures when compared to the ones
with nanofibres. All these considerations are of extreme importance, as some of
the most promising applications of these polymer foams require a good electromagnetic
interference shielding efficiency, which greatly depends on the developed foam
Maspoch, M.; Loaeza, D.; Martinez, A.; Arencon, D.; De Sousa Pais, M.; Velasco J.I. Encuentro del Grupo Español de Fractura p. 495-500 Presentation's date: 2013-03-14 Presentation of work at congresses
One of the key objectives of nanotechnology is to develop our knowledge to manipulate matters at nanoscale level to create novel, smart, cost effective and eco-friendly macrostructures to improve quality of human life. Recent advancement in development of nano-materials and structures motivate engineers to design nano-modified smart, effective, high performance and sustainable macro-units. This volume contains recent research progresses on development and application on construction based nanomaterials, market potential, problems regarding conventional building system and nanostructures characterized by higher potency, greater robustness and resilience, increased speed of construction, and lessened environmental impact. It contains vivid discussion on methods, mechanical properties, electrical and resistive properties, thermal conductive and damping properties of nanomaterials like titanium dioxide and carbon nanotubes, ultra high pressure –sensitive cement based composites and their potential applications. Authors lucidly and ornately discussed about self cleaning rods, fabrics, electricity generating coatings, heating/ cooling installation systems, micro-electromechanical systems (MEMS) in automobiles, development of nano based structures for disaster protection, waste and pollutant treatment, aviation and land transportation systems, and their applications. Nanotechnology not only finds its use in building highways, dams, bridges and flyovers, but also in making eco-friendly and smart nano-surfaces in ceramics and glasses which currently holds a very potential market globally. This volume will not only expand the knowledge and enhance the analytical ability of the students and researchers, but also help the industrial scientists, engineers, constructors and developers, to address many unsolved problems regarding production and characterisation of construction materials and their prospective applications.
There is a great deal of industrial interest in the development of increasingly lighter materials based on polymer foams with improved specific properties for the most varied purposes, from flexible foams for packaging to rigid ones for structural applications. Due to its good combination of properties and reduced cost, foamed polypropylene (PP) could come as a good option. Depending on the base material, foam density and developed cellular structure and microstructure, PP foams may cover a wide range of characteristics and properties which, combined with the incorporation of functional fillers, could ultimately result in the development of multifunctional lightweight materials. This chapter presents a review of the most recent developments in polypropylene foams, starting out by the commercially available PP grades thought out for foaming applications, the different types of PP-based foams depending on their characteristics and final uses, from low-density flexible foams for cushioning and packaging to medium-high density foams for structural purposes, and the main industrial foaming processes, going from melt-like foaming to solid-state chemical and physical foaming. Recent developments in the field of PP foams are also considered, focusing on the combination of cellular structure control via foaming and the incorporation of micro and nanosized functional fillers, with the ultimate objective of developing PP-based foams with a wide range of properties and unique characteristics, from electrically conductive foams through the incorporation of conductive carbon-based nanofillers to foams with direction-dependent transport properties.
Meli, G.; Abler, C.; Jouffret, F.; De Sousa Pais, M.; Gedler, G.; Arencon, D.; Velasco J.I. International Conference on Foam Materials & Technology Presentation's date: 2012-09-12 Presentation of work at congresses
Gedler, G.; De Sousa Pais, M.; De Redondo, V.; Velasco J.I. International Conference on Modification, Degradation and Stabilization of Polymers p. 397-398 Presentation's date: 2012-09-05 Presentation of work at congresses
De Sousa Pais, M.; De Redondo, V.; Velasco J.I.; Solórzano, E.; Rodríguez-Pérez , M.A.; de Saja, J. A. Materials chemistry and physics Vol. 136, num. 1, p. 268-276 DOI: 10.1016/j.matchemphys.2012.07.001 Date of publication: 2012-09 Journal article
Solórzano, E.; De Sousa Pais, M.; Saiz-Arroyo, C.; Velasco J.I.; Rodríguez-Pérez , M.A.; de Saja, J. A. Journal of applied polymer science Vol. 125, num. 2, p. 1059-1067 DOI: 10.1002/app.34306 Date of publication: 2012-07 Journal article
Dos tipos de espumas flexibles de baja densidad . basadas en polipropileno y producidas por dos métodos diferentes de espumación (espumación física y espumación química) .se han caracterizado utilizando el concepto del trabajo esencial de fractura (EWF), con particular atención a la influencia de la densidad relativa de la espuma y a su estructura celular en los valores de los parámetros característicos. Se ha propuesto un procedimiento de corrección basado en la relación de expansión de la espuma y en la estructura celular, con el objetivo de tener en cuenta su complejidad estructural en los parámetros de fractura . Se encontraron diferencias significativas en los parámetros del EWF entre los dos tipos de espumas producidas por métodos diferentes, derivados de las diferencias en su estructura celular (tamaño, número y orientación de las celdas). En general. el término esencial específico de fractura se vio incrementado con la densidad celular de las espumas, principalmente en las espumas con una orientación celular predominante en la dirección del flujo de extrusión. En ambos tipos de espuma, los valores de los parámetros de fractura resultaron considerablemente inferiores en dirección perpendicular al flujo de extrusión. mostrándose así que el comportamiento de fractura de estos materiales resulta considerablemente anisotrópico, como consecuenci a de su estructura celular.
Gedler, G.; De Sousa Pais, M.; De Redondo, V.; Velasco J.I. IOP Conference Series: Materials Science and Engineering Vol. 31, num. 1 DOI: 10.1088/1757-899X/31/1/012008 Date of publication: 2012 Journal article
Gedler, G.; De Sousa Pais, M.; De Redondo, V.; Velasco J.I. Polymer degradation and stability Vol. 97, num. 8, p. 1297-1304 DOI: 10.1016/j.polymdegradstab.2012.05.027 Date of publication: 2012 Journal article