Edible films have been studied as potential substitutes for conventional plastics in food packaging. Their development provides a new alternative for the application of hydrocolloids, following global trends of environmental preservation. Taking this into account, the aim of this study was to develop and evaluate physicochemical properties (thickness, solubility in water and acid, water vapor permeability, opacity, tensile strength and elongation at break) of composite films based on corn starch (native, modified waxy or waxy) and gelatin, plasticized with glycerol or sorbitol. After this initial screening, the formulation presenting the physicochemical properties more appropriate was applied as an edible composite coating onto Red Crimson grapes to extend the shelf-life. The addition of gelatin significantly increased mechanical strength, solubility in water, permeability to water vapor, and thickness of the biofilms, while also decreasing the opacity. Composite films prepared with sorbitol had significantly lower permeability to water vapor and higher tensile strength than the films plasticized with glycerol. Improved appearance was observed in coated grapes after 21 days storage under refrigerated conditions, which had lower weight loss than the control group. Sensory evaluation showed that all the coatings did not affect acceptability scores. (C) 2015 Elsevier B.V. All rights reserved.
The present work considers the preparation of medium-density polyetherimide (PEI)/polyamide-imide (PAI) blend foams by means of water vapor-induced phase separation (WVIPS) and their characterization. While pure polymer foams showed homogeneous cellular structures with average cell sizes of 10-12 µm, PEI/PAI blend foams presented two distinctive closed-cell structures depending on the composition of the blend. At the lowest concentration of PAI (25 wt%) foams showed a very fine homogeneous microcellular structure with an average cell size of 1.4 µm, consequence of good miscibility between both polymers, while at the highest studied concentration of PAI (50 wt%) foams presented a dual cellular structure formed by small cells (around 1 µm in size) within the walls of considerably bigger ones (22 µm in size) due to polymer phase separation. The blend foams presented a thermal decomposition behavior similar to that of pure unfoamed polymers, with the foam with 25 wt% PAI showing a slightly higher thermal stability. Furthermore, this particular foam presented an improved specific storage modulus compared to pure PEI foam and to the one with 50 wt% PAI. X-ray diffraction (XRD) analysis indicated that no polymer crystallization was induced by foaming.
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.
Toughened carbon fibre fabric-reinforced composites were obtained by compression moulding of powder prepregs, using a modified cyclic butylene terephthalate (pCBT) matrix and a bi-directional [0°/90°] carbon fibre fabric. Modification of the pCBT matrix was done by adding small amounts of epoxy resin or isocyanates, acting as toughening agents. Homogeneous CBT/epoxy and CBT/isocyanate blends were obtained by melt blending in a lab-scale batch mixer by applying low temperatures and short processing times. Melt blending was stopped before the ring-opening polymerization of CBT could start. This was assured by monitoring the torque of the batch mixer. Modified CBT was then used as matrix for carbon fibre reinforced pCBT composites prepared by a simple powder prepreg method with subsequent in situ polymerization during compression moulding. Physical properties such as composite density, fibre- and void content were not significantly altered by the presence of the toughening agents. Mechanical properties were assessed by short beam interlaminar shear strength and flexural tests. ILSS, flexural strength and failure strain of the chemically modified composites increased up to 50-60% with respect to unmodified pCBT composites. Nevertheless, the flexural moduli slightly decreased due to the toughening effect of the chain extender on the pCBT matrix. Moreover, it was found that thermal properties and stability were not affected by the presence of modifiers.
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.
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.
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.
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 μm 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.
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.
Los aerogeles son una clase de materiales que se caracteriza por su extrema ligereza y alto contenido de aire. En este trabajo se han preparado diferentes aerogeles polímero/arcilla (PVOH/Na+-MMT) mediante un proceso simple de congelación y liofilización. Mediante esta técnica se han preparado aerogeles modificados conteniendo diferentes agentes ignifugantes en forma de partículas. La adición de dichos agentes causó un ligero incremento de la densidad aparente. Las propiedades mecánicas en compresión tanto a baja como a alta velocidad en general se vieron ligeramente reducidas debido a una menor unión entre el polímero y la arcilla. La excepción fue la muestra modificada con Al(OH)3 que incrementó la rigidez de los compuestos y la tensión a máxima deformación. En cuanto a las propiedades térmicas, la presencia de polifosfato de amonio (APP) o de silica gel (SG) redujo notablemente la velocidad de descomposición de los aerogeles en el rango de temperaturas entre 250ºC y 650ºC, sin embargo, la temperatura de inicio de descomposición no se vio sensiblemente alterada. El comportamiento a fuego se analizó mediante calorimetría de cono y los resultados han indicado que tanto la presencia de Al(OH)3 como de APP retardan la combustión del sistema y reducen la tasa de liberación de calor.
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.; 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
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.
In this paper LDPE/silica nanocomposites are foamed by two different processes. First one is the pressure quench method which is based on the use of a physical blowing agent and second one is the improved compression moulding technique. As the latter process uses a chemical blowing agent, both types of foamed nanocomposites will provide very useful information about the relationship between foaming process-microstructure and macroscopic properties. Results have revealed how silica nanoparticles are able to act as nucleating sites during foaming step in both processes; however, the optimum amount of particles strongly depends on the foaming route. Thermal and mechanical properties of solid and foamed nanocomposites have been analyzed by means of thermogravimetric analysis and compression tests. Results have revealed that nanosilica particles act as effective nucleating agents, not only reducing cell size and increasing cell density but also achieving more homogeneous cellular structures. Thermal and mechanical properties are improved due to the presence of silica nanoparticles. It has been found that the improvement degree reached for samples produced using chemical blowing agents is greater than that achieved for samples produced using physical blowing agents.
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
Haurie, L.; Lacasta, A.M; Ciudad, A.; De Redondo, V.; Velasco J.I. Construction & building materials Vol. 42, num. May 2013, p. 266-270 DOI: 10.1016/j.conbuildmat.2012.12.012 Date of publication: 2013-05 Journal article
In this work we have studied the effect of different flame retardants on the fire behavior and mechanical properties of epoxy mortars. Flame retardants acting under different mechanisms of action have been compared: phosphate flame retardants as well as magnesium hydroxides and carbonates. Besides the commercial flame retardants we have also used a magnesium basic carbonate obtained from an industrial by-product. The use of an alternative based on an industrial by-product combines an economic and sustainable solution. Different formulations of flame retarded epoxy mortars have been prepared and characterized. The obtained results prove the effectiveness of the tested flame retardants on the improvement of the fire properties of the epoxy mortars without a significant decrease on their mechanical properties.
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
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.
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 wich, 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.
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.
A great deal of attention has been given in the last years to the study of the
influence of incorporating nanosized particles and particularly nanoparticles
with a flat-like morphology such as nanoclays or layered double hydroxides,
in the properties of polymer nanocomposites. The high aspect ratio of these
nanofillers could result in improved interactions with polymer molecules at
low filler concentrations, maintaining some of the main advantages of
polymer composites such as reduced density. These improved interactions
could lead to mechanical improvements or enable to regulate polymer
nanocomposites' properties such as transport properties or even improve
their intrinsically low flame retardancy. Recently, polymer foam preparation
and characterization has gained a lot of attention, as foams have been shown
to extend the range of properties and thus possible applications of polymers.
The combination of foaming with the incorporation of nanosized particles
(polymer nanocomposite foams) could further extend the material's
properties, as nanoparticles could have a direct effect in the cellular structure
of the foamed material and thus in its final properties. This chapter pretends
to give a review of the most recent studies carried out on the influence of
layered nanoparticles, focusing on silicate nanoclays and layered double
hydroxides, on the mechanical and flame retardancy properties of polymer
foams, with the final goal of developing multifunctional lightweight
materials with improved properties for applications in sectors such as
construction or automotive.
In the present work polyurethane foams containing different low cost cellulosic-based reinforcements and variable concentra tions of a silicate-Jayered nanoclay were prepared and characterized. with the objective of developing multi-scalar rigid foams for strucn1ral application s.
The incorporation of an organically-modified nanoclay. though promoted the formation of foams with finer and more homog.eneou s cellular strucrures. also contributed to importan! density reductions. globally resulting in foams with lower compressiYe elastic moduli and collapse stresses when compared to the nnfilled ones. On the other hand. the addition of the macroscopic cellulosic-based materials led to foams with similar collapse strengths as the unfilled PUR foams even at lower relative densities. demonstrating their effectiveness as mechanica l reinforcements of rigid PUR foams and opening up new possibilities in tenns of developing low cost lightweight materials.
Electronic version of an article published as "FOAMS 2012: 10th International Conference on Foam Materials & Technology : Barcelona, Spain, September 12 - September 13, 2012". Society of Plastics Engineers.
In this communication polycarbonate foams were prepared by a supercritical CO2 dissolution one-step batch foaming process. Firstly, CO2 diffusion behavior in polycarbonate was studied by means of desorption experiments. The cellular structure of foams prepared under different foaming conditions was characterized through scanning electron microscopy. Different foaming temperatures as well as CO2 saturation pressures and times were applied. The foams displayed typical closed-cell structures with cell densities ranging from 3x10⁵ to 3x10⁶ cells/m³ and cell average sizes from around 70 to 150μm. Analysis by X-ray diffraction and differential scanning calorimetry seemed to suggest that slight crystallization took place because of the plasticizing effect of CO2 during saturation and foaming. Thermogravimetric analysis showed a higher thermal stability of the foams when compared to the compact polymer. The preliminary results shown in this work suggest the possibility of developing lightweight polycarbonate components with improved specific thermal properties through carefully controlling the foaming parameters.
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
The research consisted in evaluating the nucleation efficiency of different types of talc (with different particle size distributions, morphologies and even surface modifications) in the foaming behaviour and cellular structure os polypropylene-based materials, with the objective of developing lightweight materials with improved stiffness and lower densities. Nucleation efficiency was first evaluated in talc filled PP foamed with a physical blowing agent inside a high pressure vessel. Depending on different talc characteristics, such a particle size distribution, surface area and morphology, cell density as much as doubled. Optimized foamed PP-talc composites prepared by injection-moulding using the MuCell process displayed further weight reductions for similar stiffness values.
The present work deals with the preparation and characterizacion of an improved fire-resistant ethylene-acrylate foamed material containing calcium carbonate and a silicon elastomer. This grade, usually employed on the cable industry sector, was modified two differents synergistic FR systems : silica/zinc borate (S/ZB) and montmorillonite/graphite nanoplatelets(N). The different formulations were prepared by melt-blending and the foams by a compression-molding foaming process using Azodicarbonamide as chemical blowing agent. Thermal stability and fire behaviour, of both solid and foamed materials were characterized by means of thermogravimetric and cone calorimetric techniques, respectively.
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
Different relative density polypropylene foams were prepared by means of two foaming processes: chemical foaming by compression moulding and physical foaming by high pressure CO2 dissolution. By controlling the foaming parameters, such as blowing agent concentration, foaming temperature, pressure drop and pressure drop rate, it was possible to regulate the cellular structure, foams showing from markedly isotropic-like cellular structures to ones with highly-elongated cells in the vertical foam growth direction (honeycomb-like cell orientation). The thermal conductivity was measured using the transient plane source method. Using this technique, it was possible to measure the global conductivity and the thermal conductivity in both the axial and radial directions of a given sample. Results show that the global thermal conductivity of foams was mainly regulated by their relative density. In addition, the honeycomb-like cell orientation of the CO2 dissolution foams resulted in considerably higher values in axial direction when compared to radial, demonstrating that there was a direct influence of cellular structure on the thermal conduction behaviour of these foams, enabling the development of new polypropylene foams with direction-dependent thermal properties.
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
A novel technique to determine in situ the
free expansion kinetics of chemically foamed thermoplastic
foams, so-called optical expandometry, is presented
in this work. This technique is based on the
camera monitoring of a free-foaming material placed
inside a furnace. Images are acquired under special illumination
conditions to facilitate the later image processing.
The present article explains the experimental set-up
and the image processing methods used to determine
the free volumetric expansion of different polyolefinbased foams. The results are compared with those
obtained using thermo-mechanical analysis. In addition,
several possible applications of this method are detailed,
such as studying the effect of polymer rheology, foaming
temperature, blowing agent content and the anisotropy
of the expansion.
En el presente trabajo se han preparado y caracterizado espumas ignífugas de poliolefinas libres de halógenos. Se ha utilizado para ello una formulación comercial, empleada típicamente en la industria de cables, y se le ha añadido pequeños porcentajes másicos (entre 2 y 4%) de dos sistemas retardantes de llama: "sílice-borato de zinc" y manolaminillas de "montmorillonita y grafeno expandible". Durante la caracterización celular de las espumas, preparadas por espumación química utilizando como agente espumante azodicarbonamida, se ha constatado que la presencia de las nanopartículas promovía una estructura celular con tamaño de celda más pequeño. Mediante un análisis termogravimétrico, se ha observado un aumento del residuo inorgánico de la formulación base a temperaturas superiores a 500ºC. Esta observación puede ser debida, en cierta medida, a un efecto sinérgico entre ambos sistemas retardantes de llama, el cual promueve una mayor estabilidad térmica de la formulación base. Durante la caracterización del comportamiento frente al fuego mediante ensayos de cono calorimétrico, se ha constatado que el sistema "síliceborato de zinc" retarda en tiempo hasta ignición de la llama (mayores valores de TTI) y que la presencia de las nanopartículas disminuye el valor del PHRR (máxima tasa de liberación de calor).
In this paper, polymer foams based on a benzoxazine resin have been successfully prepared using azodicarbonamide (ADC) as a chemical blowing agent and have been characterized regarding their foaming behavior, cellular structure, and physical properties. The effect of the ADC on the curing process of the resin was analyzed using differential scanning calorimetry and blowing agent decomposition was followed by thermogravitmetric analysis (TGA). The characterization of the cellular structure of the foamed samples was done using scanning electron microscopy. The mechanical properties of the foams were determined using compression tests and the thermal conductivity was assessed using the transient plane source method. The results indicated that the curing process and gas release took place in a similar time interval. The foams showed an isotropic cellular structure with relative densities in the range 0.35–0.60, and showed compressive strengths and compressive moduli in the range of 10–70 MPa and 400–1100 MPa, respectively. Thermal conductivities were in the range of 0.06–0.12 W m−1K−1. The findings in this paper demonstrate the possibility of producing polybenzoxazine foams using a simple process in which curing and foaming take place simultaneously. In addition, the mechanical characterization of these materials indicates that they are suitable for structural applications.
Se presenta la influencia de nanopartículas y nanofibras sobre las propiedades termomecánicas de espumas poliméricas. A una formulación base polipropileno especial para espumación se le incorporaron nanocargas (silicatos laminares) y nanofibras de carbono al objeto de aportar a los materiales celulares resultantes características de multifuncionalidad (rigidezm retardancia a la llama y conductividad). En el presente trabajo se analizan los efectos que introducen las partículas incorporadas sobre las características termodinámicas de las espumas, a través de análisis térmico mecánico dinámico (DMTA), en relación con la composición de las espumas, con su densidad relativa y con su estructura celular. Los resultados han demostrado que la influencia de las nanopartículas y nanofibras añadidas al polímero base de la espuma alcanza, no sólo a su cristalidad, temperaturas de transición características o propiedades mecánicas, sino también a la generación de estructuras celulares más finas y homogéneas que las de sus homónimos de referencia sin partículas.
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.
Saiz-Arroyo, C.; de Saja, J. A.; Rodríguez-Pérez , M.A.; Velasco J.I. Journal of materials science Vol. 47, num. 15, p. 5680-5692 DOI: 10.1007/s10853-012-6357-7 Date of publication: 2012 Journal article
Polypropylene (PP) foams have become
essential items due to their excellent properties. Nevertheless,
obtaining net-shaped PP foams with medium relative
densities is a complicated issue. In this article, two
processes able to produce moulded PP foams in this density
range are presented. One of them is based on a modification
of the pressure quench foaming method and therefore
uses a physical blowing agent (CO2). The second one is the
improved compression moulding technique which uses a
chemical blowing agent (azodicarbonamide). PP foams
with relative densities in the range between 0.25 and 0.6
and cylindrical shape were prepared using these foaming
techniques. A common PP grade (instead a highly branched
one) was used to obtain the samples, showing, that by
combining the appropriate foaming technique, the adequate
moulds, suitable blowing agent and proper foaming
parameters, net-shaped PP foams with excellent properties
can be produced starting from a conventional PP grade.
Samples were characterized by analyzing their cellular
structure and their mechanical properties. Results have
showed that depending on the chosen foaming route isotropic
or anisotropic structures with cell sizes ranging from 40 to 350 lm and open cell content in the range between 0
and 65% can be obtained. Moreover, mechanical properties
are highly influenced by the production route and chemical
composition of the foams. For instance, the stiffer materials
at relative densities higher than 0.4 are the ones produced
using the chemical blowing agent while at relative densities
lower than 0.4 are the ones produced using the physical
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
A thermogravimetric study in both nitrogen and air atmospheres has been carried out on unfilled and
graphene-reinforced solid and foamed polycarbonate. Polycarbonate foams were prepared using
a supercritical CO2 dissolution one-step batch foaming process. Results showed that polycarbonate
displayed a characteristic one-step decomposition under nitrogen, while three-step degradation was
observed in air. In addition, as-received pristine graphene nanoplatelets displayed a three-step degradation
in air, compared to a mild degradation under nitrogen. It was found that the thermal stability
remarkably improved for the foamed composites, related to a combination of a heat transfer reduction
promoted by the insulating cellular structure and the presence of the platelet-like graphene, which
helped create a physical barrier effect, delaying the escape of volatile products generated during