http://hdl.handle.net/2117/3620 Fri, 24 May 2013 05:14:35 GMT 2013-05-24T05:14:35Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/19348 Title: Novel polycarbonate-graphene nanocomposite foams prepared by CO2 dissolution Authors: Gedler, Gabriel; Sousa Pais Antunes, Marcelo de; Redondo Realinho, Vera Cristina de; Velasco Perero, José Ignacio Abstract: Polycarbonate foams reinforced with 0,5 wt% of graphene were obtained by firstly melt-mixing the polycarbonate and graphene in an internal mixer, compression-moulding the melt-compounded grinded material and lastly dissolving CO2 inside a high pressure vessel. The CO2 desorption behaviour in the unfilled polycarbonate and nanocomposite was studied in terms of the CO2 saturation concentration and desorption diffusion coefficient, with the graphene-filled nanocomposite displaying a higher CO2 loss rate when compared to the neat polycarbonate. The cellular structure of the foams was found to be highly dependent on the saturation/foaming temperature, with smaller cell sizes being obtained with decreasing the temperature. Another parameter that had an important influence was the residual pressure, with higher residual pressure values resulting in foams with more uniform and regular cells. Description: Originally published as "IOP Conference Series: Materials Science and Engineering", vol. 31, no 1, 2012. DOI:10.1088/1757-899X/31/1/012008. <http://iopscience.iop.org/1757-899X/31/1/012008>. Fri, 17 May 2013 14:42:23 GMT http://hdl.handle.net/2117/19348 2013-05-17T14:42:23Z Gedler, Gabriel; Sousa Pais Antunes, Marcelo de; Redondo Realinho, Vera Cristina de; Velasco Perero, José Ignacio no Polycarbonate foams reinforced with 0,5 wt% of graphene were obtained by firstly melt-mixing the polycarbonate and graphene in an internal mixer, compression-moulding the melt-compounded grinded material and lastly dissolving CO2 inside a high pressure vessel. The CO2 desorption behaviour in the unfilled polycarbonate and nanocomposite was studied in terms of the CO2 saturation concentration and desorption diffusion coefficient, with the graphene-filled nanocomposite displaying a higher CO2 loss rate when compared to the neat polycarbonate. The cellular structure of the foams was found to be highly dependent on the saturation/foaming temperature, with smaller cell sizes being obtained with decreasing the temperature. Another parameter that had an important influence was the residual pressure, with higher residual pressure values resulting in foams with more uniform and regular cells. http://hdl.handle.net/2117/19337 Title: Influence of foaming process on the structure-properties relationship of foamed LDPE/silica nanocomposites Authors: Saiz Arroyo, Cristina; Rodríguez Pérez, Miguel Ángel; Velasco Perero, José Ignacio; Saja, José Antonio de Abstract: 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. Fri, 17 May 2013 13:27:52 GMT http://hdl.handle.net/2117/19337 2013-05-17T13:27:52Z Saiz Arroyo, Cristina; Rodríguez Pérez, Miguel Ángel; Velasco Perero, José Ignacio; Saja, José Antonio de no A. Foam, A. Particle-reinforcement, B. Microstructures, B. Mechanical properties 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. http://hdl.handle.net/2117/19151 Title: Multifunctional nanocomposite foams based on polypropylene with carbon nanofillers Authors: Sousa Pais Antunes, Marcelo de; Gedler, Gabriel; Velasco Perero, José Ignacio Abstract: 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 morphology. Thu, 09 May 2013 14:05:52 GMT http://hdl.handle.net/2117/19151 2013-05-09T14:05:52Z Sousa Pais Antunes, Marcelo de; Gedler, Gabriel; Velasco Perero, José Ignacio no Graphene nanoplatelets, carbon nanofibres, multifunctional foams, polypropylene, supercritical CO2 dissolution 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 morphology. http://hdl.handle.net/2117/19040 Title: Structure-property evaluation of trisilanolphenyl POSS®/polysulfone composites as a guide to POSS melt blending Authors: Milliman, Henry; Sánchez Soto, Miguel; Arostegui, Asier; Schiraldi, David A. Abstract: A series of polysulfone/phenyl trisilanol POSS nanocomposites were produced by melt blending by twin screw batch mixing. These materials were then injec- tion molded, and their thermal, mechanical, and morpho- logical properties were tested. The tensile properties of polysulfone were moderately compromised by the addition of phenyl TPOSS, because of the formation of large ( 1 l m) voided POSS aggregates. These domains however did cause the improvement of the impact resistance of the composites as described by the mechanism of crack pinning and bow- ing. Flexural properties remained essentially unchanged, which is attributed to the formation of an aggregate free- skin layer, which formed in the injection molded parts. Thermal behavior of the composites also remained largely unchanged due to the lack of POSS-polymer interactions on the molecular/chain segment scale. Initially, it was hypothesized that a high degree of POSS-polymer interac- tions would be present in these composited based on exami- nation of their chemical structures. This however, was not the case as phase separation was clearly present. This work highlights the need for a better understanding of the predic- tion of POSS-polymer interaction. Mon, 29 Apr 2013 16:56:24 GMT http://hdl.handle.net/2117/19040 2013-04-29T16:56:24Z Milliman, Henry; Sánchez Soto, Miguel; Arostegui, Asier; Schiraldi, David A. no interactions, nanocomposite, polysulfone, POSS, properties, structure A series of polysulfone/phenyl trisilanol POSS nanocomposites were produced by melt blending by twin screw batch mixing. These materials were then injec- tion molded, and their thermal, mechanical, and morpho- logical properties were tested. The tensile properties of polysulfone were moderately compromised by the addition of phenyl TPOSS, because of the formation of large ( 1 l m) voided POSS aggregates. These domains however did cause the improvement of the impact resistance of the composites as described by the mechanism of crack pinning and bow- ing. Flexural properties remained essentially unchanged, which is attributed to the formation of an aggregate free- skin layer, which formed in the injection molded parts. Thermal behavior of the composites also remained largely unchanged due to the lack of POSS-polymer interactions on the molecular/chain segment scale. Initially, it was hypothesized that a high degree of POSS-polymer interac- tions would be present in these composited based on exami- nation of their chemical structures. This however, was not the case as phase separation was clearly present. This work highlights the need for a better understanding of the predic- tion of POSS-polymer interaction. http://hdl.handle.net/2117/18881 Title: Effect of humidity in charge formation and transport in LDPE Authors: Aragoneses Aguado, Andrés; Tamayo, Ildaberto; Lebrato, Alexander; Cañadas Lorenzo, Juan Carlos; Diego Vives, José Antonio; Arencón Osuna, David; Belana Punseti, Juan Thu, 18 Apr 2013 16:39:21 GMT http://hdl.handle.net/2117/18881 2013-04-18T16:39:21Z Aragoneses Aguado, Andrés; Tamayo, Ildaberto; Lebrato, Alexander; Cañadas Lorenzo, Juan Carlos; Diego Vives, José Antonio; Arencón Osuna, David; Belana Punseti, Juan no http://hdl.handle.net/2117/18730 Title: The role of notch sharpening on the J-fracture toughness of thermoplastic polymers Authors: Salazar, Alicia; Rodríguez, Jesús; Martínez Benasat, Antonio Abstract: The effect of the notch sharpening on the fracture toughness obtained under Elastic–Plastic Fracture Mechanics (EPFMs) approach has been analyzed in two different types of thermoplastic polymers, a semicrystalline multi-phase ethylene–propylene block copolymer and an amorphous polycarbonate. The samples for fracture characterization were sharpened using a steel razor blade and the femtosecond laser ablation technique. Both notching techniques gave rise to the very same size of crack tip radii, 1–2 μm. For all the materials under study, the fracture toughness values of the specimens sharpened through femtosecond laser ablation were lower than those measured on samples sharpened using a steel razor blade. The largest differences were achieved for the amorphous polycarbonate. The damage produced ahead of the crack tip through plastic deformation in the steel razor blade sharpened samples over against the lack of damage in the femtolaser sharpened specimens explains the disparity in the fracture values. Besides, the stress state ahead of the crack tip is closely related to the plastic deformation zone to specimen thickness ratio. The fracture toughness values determined from the femtolaser sharpened samples were all in plane strain conditions while the values of the fracture toughness obtained from the steel razor blade sharpened specimens were not. Tue, 09 Apr 2013 11:27:36 GMT http://hdl.handle.net/2117/18730 2013-04-09T11:27:36Z Salazar, Alicia; Rodríguez, Jesús; Martínez Benasat, Antonio no The effect of the notch sharpening on the fracture toughness obtained under Elastic–Plastic Fracture Mechanics (EPFMs) approach has been analyzed in two different types of thermoplastic polymers, a semicrystalline multi-phase ethylene–propylene block copolymer and an amorphous polycarbonate. The samples for fracture characterization were sharpened using a steel razor blade and the femtosecond laser ablation technique. Both notching techniques gave rise to the very same size of crack tip radii, 1–2 μm. For all the materials under study, the fracture toughness values of the specimens sharpened through femtosecond laser ablation were lower than those measured on samples sharpened using a steel razor blade. The largest differences were achieved for the amorphous polycarbonate. The damage produced ahead of the crack tip through plastic deformation in the steel razor blade sharpened samples over against the lack of damage in the femtolaser sharpened specimens explains the disparity in the fracture values. Besides, the stress state ahead of the crack tip is closely related to the plastic deformation zone to specimen thickness ratio. The fracture toughness values determined from the femtolaser sharpened samples were all in plane strain conditions while the values of the fracture toughness obtained from the steel razor blade sharpened specimens were not. http://hdl.handle.net/2117/18709 Title: Influence of the injection-molding parameters on the cellular structure and thermo-mechanical properties of ethylene-propylene block copolymer foams Authors: Gómez Gómez, Jaime Francisco; Arencón Osuna, David; Sánchez Soto, Miguel; Martínez Benasat, Antonio Abstract: Microcellular injection-molding technology is capable of producing lightweight polymeric products. The foam morphology is determined by the injection-molding parameters, and it has been observed that depending on the parameter variations, the cell structure may exhibit substantial morphological differences through the entire section along the melt flow direction of the injected part. The effects of varying injection-molding parameters on foam morphology and thermal mechanical properties of a multiphase ethylene-propylene block copolymer (EPBC) were tested on 5-mm plaque specimens using a constant temperature profile. It has been found that injection speed does not have a significant effect on the thermal-mechanical properties of the foam, whereas shot volume and mold temperature do have a significant influence. Low shot volume produces uniform density cellular structures and larger cores, whereas lower mold temperatures help maintain small cell sizes. Furthermore, the effect of the copolymer’s crystalline phase on foam morphology has been observed. This study identifies the achievable foam morphologies and the thermal-mechanical performance of cellular molded EPBC parts. Mon, 08 Apr 2013 16:23:26 GMT http://hdl.handle.net/2117/18709 2013-04-08T16:23:26Z Gómez Gómez, Jaime Francisco; Arencón Osuna, David; Sánchez Soto, Miguel; Martínez Benasat, Antonio no Microcellular injection-molding technology is capable of producing lightweight polymeric products. The foam morphology is determined by the injection-molding parameters, and it has been observed that depending on the parameter variations, the cell structure may exhibit substantial morphological differences through the entire section along the melt flow direction of the injected part. The effects of varying injection-molding parameters on foam morphology and thermal mechanical properties of a multiphase ethylene-propylene block copolymer (EPBC) were tested on 5-mm plaque specimens using a constant temperature profile. It has been found that injection speed does not have a significant effect on the thermal-mechanical properties of the foam, whereas shot volume and mold temperature do have a significant influence. Low shot volume produces uniform density cellular structures and larger cores, whereas lower mold temperatures help maintain small cell sizes. Furthermore, the effect of the copolymer’s crystalline phase on foam morphology has been observed. This study identifies the achievable foam morphologies and the thermal-mechanical performance of cellular molded EPBC parts. http://hdl.handle.net/2117/17501 Title: Films of native and modified starch reinforced with fiber: influence of some extrusion variabels using response surface methodology Authors: Galicia Garcia, Tomás; Martínez Bustos, F; Jiménez Arévalo, Omar; Arencón Osuna, David; Gamez Pérez, José; Martínez Benasat, Antonio Abstract: Corn starch (native and phosphorylated) and potato films containing glycerol as plasticizer, and bagasse sugar cane as fiber, were produced by extrusion-calendering process, and characterized for the mechanical properties (tensile stress at rupture rr, elongation at break eb, and Young’s modulus E), water disintegration index (WDI), water absorption capacity (WAC), and luminosity. The evaluated processing variables were: feed moisture, fiber content, and type of starch. The response surface methodology was applied to analyze, and the model of significance was justified by a variance analysis (F-test). The inclusion of fiber provides a mechanical reinforcement to the starch matrix favoring the elongation at break (eb) in thickness films (280–350 lm). Samples formulated with potato starch within the values of feed moisture 18.25, 20.5, and 5 wt % of fiber content, showed an increment in values of tensile stress at rupture (3.80–4.4 MPa) and Young’s modulus (78.47–68.04 MPa). Corn starch films with high fiber content (10%) and low feed moisture (18.25%) values showed a decrement in elongation at break (12.93%). WAC and WDI were low with minimum and intermediate levels of feed moisture and fiber content (0–5%). Luminosity values were an indicative that do not exist degradation in film materials due to condition extrusion process used. Wed, 23 Jan 2013 14:37:09 GMT http://hdl.handle.net/2117/17501 2013-01-23T14:37:09Z Galicia Garcia, Tomás; Martínez Bustos, F; Jiménez Arévalo, Omar; Arencón Osuna, David; Gamez Pérez, José; Martínez Benasat, Antonio no Corn starch (native and phosphorylated) and potato films containing glycerol as plasticizer, and bagasse sugar cane as fiber, were produced by extrusion-calendering process, and characterized for the mechanical properties (tensile stress at rupture rr, elongation at break eb, and Young’s modulus E), water disintegration index (WDI), water absorption capacity (WAC), and luminosity. The evaluated processing variables were: feed moisture, fiber content, and type of starch. The response surface methodology was applied to analyze, and the model of significance was justified by a variance analysis (F-test). The inclusion of fiber provides a mechanical reinforcement to the starch matrix favoring the elongation at break (eb) in thickness films (280–350 lm). Samples formulated with potato starch within the values of feed moisture 18.25, 20.5, and 5 wt % of fiber content, showed an increment in values of tensile stress at rupture (3.80–4.4 MPa) and Young’s modulus (78.47–68.04 MPa). Corn starch films with high fiber content (10%) and low feed moisture (18.25%) values showed a decrement in elongation at break (12.93%). WAC and WDI were low with minimum and intermediate levels of feed moisture and fiber content (0–5%). Luminosity values were an indicative that do not exist degradation in film materials due to condition extrusion process used. http://hdl.handle.net/2117/17247 Title: Influence of the injection moulding parameters on the microstructure and thermal properties of microcellular polyethylene terephthalate glycol foams Authors: Gómez Gómez, Jaime Francisco; Arencón Osuna, David; Sánchez Soto, Miguel; Martínez Benasat, Antonio Abstract: Microcellular injection moulding is capable of producing lightweight polymeric products. The present study analyses the influence of several representative injection moulding parameters on the foam’s morphology, apparent density and thermo-mechanical properties of PETG, poly(ethylene terephthalate-co-1,4-cyclohexylene-dimethylene terephthalate) specimens. A strong variation of the cell morphology along the melt flow direction has been found, as well as a dependence on the shot volume. The most homogeneous microcellular structure is achieved when low shot volume, intermediate injection speed and low mould temperature are employed. The skin–core structure of the injected parts, determined the thermo-mechanical features of the specimen, which are ruled by the skin layer. Wed, 09 Jan 2013 18:45:19 GMT http://hdl.handle.net/2117/17247 2013-01-09T18:45:19Z Gómez Gómez, Jaime Francisco; Arencón Osuna, David; Sánchez Soto, Miguel; Martínez Benasat, Antonio no Microcellular injection moulding is capable of producing lightweight polymeric products. The present study analyses the influence of several representative injection moulding parameters on the foam’s morphology, apparent density and thermo-mechanical properties of PETG, poly(ethylene terephthalate-co-1,4-cyclohexylene-dimethylene terephthalate) specimens. A strong variation of the cell morphology along the melt flow direction has been found, as well as a dependence on the shot volume. The most homogeneous microcellular structure is achieved when low shot volume, intermediate injection speed and low mould temperature are employed. The skin–core structure of the injected parts, determined the thermo-mechanical features of the specimen, which are ruled by the skin layer. http://hdl.handle.net/2117/17211 Title: Low flammability, foam-like materials based on ammonium alginate and sodium montmorillonite clay Authors: Chen, Hong-Bing; Wang, Yu-Zhong; Sánchez Soto, Miguel; Schiraldi, David A. Abstract: Low flammability, foam-like materials based on bio-based, renewable ammonium alginate and sodium montmorillonite clay were fabricated through a simple, environmentally-friendly freeze-drying process in which water is used as solvent. These materials exhibit mechanical properties similar to those of rigid PU foams or balsa; the compressive modulus (1–97 MPa) and density (0.047–0.174 g/cm3) increase with increasing solids content, with an associated change from a layered to network microstructure structure. Calcium ions, either added directly or indirectly via CaCO3/gluconolactone (GDL) are an effective crosslinking agent for alginate, with the GDL route providing the greatest enhancement of mechanical properties. The thermal stability of the aerogels is also enhanced by the presence of crosslinking. The alginate/clay aerogels possess inherently low flammability, as measured by cone calorimetry, with heat release values decreasing as the proportion of clay in the composites is increased. Tue, 08 Jan 2013 12:25:20 GMT http://hdl.handle.net/2117/17211 2013-01-08T12:25:20Z Chen, Hong-Bing; Wang, Yu-Zhong; Sánchez Soto, Miguel; Schiraldi, David A. no Low flammability, foam-like materials based on bio-based, renewable ammonium alginate and sodium montmorillonite clay were fabricated through a simple, environmentally-friendly freeze-drying process in which water is used as solvent. These materials exhibit mechanical properties similar to those of rigid PU foams or balsa; the compressive modulus (1–97 MPa) and density (0.047–0.174 g/cm3) increase with increasing solids content, with an associated change from a layered to network microstructure structure. Calcium ions, either added directly or indirectly via CaCO3/gluconolactone (GDL) are an effective crosslinking agent for alginate, with the GDL route providing the greatest enhancement of mechanical properties. The thermal stability of the aerogels is also enhanced by the presence of crosslinking. The alginate/clay aerogels possess inherently low flammability, as measured by cone calorimetry, with heat release values decreasing as the proportion of clay in the composites is increased. http://hdl.handle.net/2117/17208 Title: Thermal stabilization ability of polyhedral oligomeric silsesquioxane nanofillers Authors: Vilà Ramirez, N.; Sánchez Soto, Miguel Abstract: The polyhedral oligomeric silsesquioxane nanofillers examined in this study provided little or no improvement to the thermal properties of melt-blended acrylonitrile butadiene styrene polymer composites. Description: Electronic version of an article published as "Plastics research online", 17 December 2012 <http://www.4spepro.org/pdf/004523/004523.pdf> Tue, 08 Jan 2013 11:51:37 GMT http://hdl.handle.net/2117/17208 2013-01-08T11:51:37Z Vilà Ramirez, N.; Sánchez Soto, Miguel no The polyhedral oligomeric silsesquioxane nanofillers examined in this study provided little or no improvement to the thermal properties of melt-blended acrylonitrile butadiene styrene polymer composites. http://hdl.handle.net/2117/17192 Title: Teaching engineering with autonomous learning tools: good practices in GRAPAU-RIMA Authors: Marcé Nogué, Jordi; Salán Ballesteros, Maria Núria; Aragoneses Aguado, Andrés; Bernat Masó, Ernest; Escrig Pérez, Christian; Otero Calviño, Beatriz; Rupérez de Gracia, Elisa; Illescas Fernandez, Silvia Fri, 04 Jan 2013 11:39:40 GMT http://hdl.handle.net/2117/17192 2013-01-04T11:39:40Z Marcé Nogué, Jordi; Salán Ballesteros, Maria Núria; Aragoneses Aguado, Andrés; Bernat Masó, Ernest; Escrig Pérez, Christian; Otero Calviño, Beatriz; Rupérez de Gracia, Elisa; Illescas Fernandez, Silvia no http://hdl.handle.net/2117/17131 Title: Moulded polypropylene foams produced using chemical or physical blowing agents: structure–properties relationship Authors: Saiz-Arroyo, Cristina; Saja, José Antonio de; Velasco Perero, José Ignacio; Rodríguez-Pérez, Miguel Ángel Abstract: 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 blowing agent. Thu, 13 Dec 2012 19:15:19 GMT http://hdl.handle.net/2117/17131 2012-12-13T19:15:19Z Saiz-Arroyo, Cristina; Saja, José Antonio de; Velasco Perero, José Ignacio; Rodríguez-Pérez, Miguel Ángel no 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 blowing agent. http://hdl.handle.net/2117/17102 Title: Isocyanate toughened pCBT: reactive blending and tensile properties Authors: Abt, Tobias Martin; Martínez de Ilarduya Sáez de Asteasu, Domingo Antxon; Bou Serra, Jordi; Sánchez Soto, Miguel Abstract: Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate. All reactions took place in a batch mixer. The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymerized cyclic butylene terephthalate (pCBT), from 8 to above 100%. The stiffness and strength of the modified pCBT, however, were found to slightly decrease. Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism. Gel content measurements suggest a linear structure for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content. Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content. No phase separation was detected by scanning electron microscopy (SEM) analysis. Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals. Description: Electronic version of an article published as "Express polymer letters" vol. 7, nº. 2, February 2013, p. 172-185. <http://www.expresspolymlett.com/> Tue, 11 Dec 2012 15:45:30 GMT http://hdl.handle.net/2117/17102 2012-12-11T15:45:30Z Abt, Tobias Martin; Martínez de Ilarduya Sáez de Asteasu, Domingo Antxon; Bou Serra, Jordi; Sánchez Soto, Miguel no Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate. All reactions took place in a batch mixer. The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymerized cyclic butylene terephthalate (pCBT), from 8 to above 100%. The stiffness and strength of the modified pCBT, however, were found to slightly decrease. Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism. Gel content measurements suggest a linear structure for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content. Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content. No phase separation was detected by scanning electron microscopy (SEM) analysis. Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals. http://hdl.handle.net/2117/17081 Title: Effect of the strain rate and drawing temperature on the mechanical behavior of EVOH and EVOH composites Authors: Franco Urquiza, Edgar Adrian; Gamez Pérez, José; Velázquez Infante, Julio César; Santana Pérez, Orlando Onofre; Martínez Benasat, Antonio; Maspoch Rulduà, Mª Lluïsa Abstract: The effect of the strain rate and draw temperature on the mechanical behavior of ethylene vinyl alcohol (EVOH) and EVOH composites was analyzed. When EVOH is stretched at moderate strain rates, evidence of strain-induced crystallization and recrystallization was observed. Higher strain rates produced less structural variation because the homogeneous flow of the chains and the crystalline perfection are restricted due to the rapid drawing. In reference to the drawing temperature, EVOH showed a diffusive yielding, and the mechanical parameters were reduced due to the softening of the crystalline region. For EVOH composites, the filler hinders the molecular mobility, causing an increase in the strength and restricting the plastic flow. However, the higher temperature, higher molecular mobility, and ductility are not so affected by the filler content. Wed, 05 Dec 2012 12:08:27 GMT http://hdl.handle.net/2117/17081 2012-12-05T12:08:27Z Franco Urquiza, Edgar Adrian; Gamez Pérez, José; Velázquez Infante, Julio César; Santana Pérez, Orlando Onofre; Martínez Benasat, Antonio; Maspoch Rulduà, Mª Lluïsa no The effect of the strain rate and draw temperature on the mechanical behavior of ethylene vinyl alcohol (EVOH) and EVOH composites was analyzed. When EVOH is stretched at moderate strain rates, evidence of strain-induced crystallization and recrystallization was observed. Higher strain rates produced less structural variation because the homogeneous flow of the chains and the crystalline perfection are restricted due to the rapid drawing. In reference to the drawing temperature, EVOH showed a diffusive yielding, and the mechanical parameters were reduced due to the softening of the crystalline region. For EVOH composites, the filler hinders the molecular mobility, causing an increase in the strength and restricting the plastic flow. However, the higher temperature, higher molecular mobility, and ductility are not so affected by the filler content.