Javier Rodríguez Pinto

Characterization of the cellular structure based on user-interactive image analysis procedures

This work addresses the development of a novel user-interactive image analysis computed technique to determine the main characteristics of the cellular structure of cellular materials with any density, morphology, and/or cell size from micrographs obtained from any source—scanning electron microscopy, optical microscopy, etc. The specific analyzed parameters are cell size (mean cell diameter), cell anisotropy, cell size distribution, and cell density. A comparison with several conventionally used methods is also presented in this work. The development of such application offers a quick (<3 min per micrograph) and complete characterization of the cellular structure, with reproducible results and good agreement with the typical manual measurement methods.

Solid Skin Characterization of PMMA/MAM Foams Fabricated by Gas Dissolution Foaming over a Range of Pressures

A new model for solid skin formation on submicrocellular foams based on PMMA is presented. Structural foams has been produced by the solid state foaming technique using as precursor material a blend of poly (methyl methacrylate) PMMA and a triblock copolymer [poly (methyl methacrylate)-block poly (butyl acrylate)-block poly (methyl methacrylate), MA. An analysis on the skin thickness and densification has been carried based on x-ray high resolution radiography. The obtained results have been related to the fabrication parameters, i.e. MAM content of the blend and foaming pressure, and provide us a new vision about the processes that control the formation of a solid unfoamed, or partially unfoamed, skin in these materials.

Improving the extensional rheological properties and foamability of high-density polyethylene by means of chemical crosslinking

Obtaining high-density polyethylene-based microcellular foams is a topic of interest due to the synergistic properties that can be obtained by the fact of achieving a microcellular structure using a polymer with a high number of interesting properties. However, due to the high crystallinity of this polymer, the production of low-density microcellular foams, by a physical foaming process, is not a simple task. In this work, the proposed solution to produce these materials is based on using crosslinked high-density polyethylenes. By crosslinking the polymer matrix, it is possible to increase the amount of gas available for foaming and also to improve the extensional rheological properties. In addition, the foaming time and the foaming temperature have also been modified with the aim of analyzing and understanding the mechanisms taking place during the foaming process to finally obtain cellular materials with low densities and improved cellular structures. The results indicate that cellular materials with relative densities of 0.37 and with cell sizes of approximately 2 µm can be produced from crosslinked high-density polyethylene using the appropriate crosslinking degree and foaming parameters.

Latent communities of digital publications: The role of editors, followers, and advertisers

Abstract This research explores how digital publications may be turned into something more than just a meeting point for people who are seeking information and may become a latent community. The paper proposes that the network of editors, followers, and advertisers of digital publications determine the user sense of community towards the publication. While the pattern of connections among editors and followers reinforces the sense of community, advertisers act as intruders who weaken the feasibility of building a community. Data were collected from followers of digital publications. The dynamics of the sense of community is described as a process in which informational value and identification are essential to nurturing readers’ soft or hard commitment. Findings indicate that the strong ties between editors and followers as well as the diversity positively impacts on informational value and identification, whereas advertising intrusiveness diminishes the informational value.

A novel route to produce structural polymer foams with a controlled solid skin-porous core structure based on gas diffusion mechanisms

A comprehensive study about a new production route of structural polymer foams is presented. This methodology is based on the one hand on a free foaming process induced by a chemical blowing agent inside a closed mold, and on the other hand on the use of a solid polymer able to absorb gas in close contact with the molten foamed polymer, establishing a competitive absorption of the blowing gas between both materials. This competitive absorption of the gas promotes the formation of a solid skin in all the areas in contact with the solid polymer. This phenomenon has been identified in-situ and evaluated in real time using a specific X-ray radioscopy set-up, being possible to relate unequivocally the apparition and thickness of the solid skin with the presence of the solid polymer and with the pressure achieved in the closed mould during the foaming process. The presented production route shows an accurate and independent control of the final foam relative density (even below 0.5) and the thickness of the solid skin, together with an excellent surface quality and a broad applicability, which allows the design and production of structural polymer foams with exceptional features.

Enhancement of Carbon Nanofibers Dispersion on Epoxy Resin Foams Leading to Remarkable Electrical Conductivity Improvement

A simple procedure to evaluate and improve the dispersion of carbon nanofibers is presented and validated, relating the observed dispersion of the nanofibers in an intermediate stage of the production process to the final macroscopic properties of the foams. Epoxy/carbon nanofiber foams with optimal nanofiber dispersion are produced taking advantage of this procedure using inexpensive industrial vapor grown carbon nanofibers. Furthermore, the main characteristics and the electrical resistivity of the foams with improved nanofibers dispersion have been determined and related to the presence of the carbon nanofibers, greatly enhancing the electrical conductivity of the epoxy/carbon nanofiber foams.

In Situ Optical Analysis of Structural Changes in Polylactic Acid (PLA) during the Gas Dissolution Process

An own-designed pressure vessel with glass windows has been employed to perform an in-situ characterization of the temporal evolution of the crystallization process of an amorphous polylactic acid (PLA) under different controlled CO2 pressures and temperatures. It has been proven that crystallinity can be related to optical parameters such as transmissivity, obtaining information about the whole process by optical measurements. The method has the advantage of measuring in-situ over bulk samples with a non-destructive tool. The obtained results have shown some unexpected trends that have been explained taking into account the complex phenomena occurring during the crystallization process of PLA in the presence of CO2 at high pressure.

Novedad, calidad, velocidad y orden de entrada en el mercado. Sinergias y "trade-offs" en el lanzamiento de nuevos productos

RESUMEN Numerosos trabajos analizan el orden de entrada como determinante del resultado de una innovacion y, en general, destacan el efecto positivo de entrar pronto en el mercado. Sin embargo, muchos argumentos para justificar este efecto aluden a otros factores de exito como la calidad o la novedad del producto y tambien se aprecia en la literatura cierta confusion entre orden de entrada y velocidad de desarrollo que lleva a asumir que ser pionero en el lanzamiento de un nuevo producto es sinonimo de haber tenido un proceso de desarrollo rapido. La presente investigacion desgrana los efectos de estas variables y examina las interacciones entre orden de entrada, por un lado, y novedad, calidad y velocidad, por otro. Los resultados empiricos del estudio apuntan que la entrada temprana influye positivamente en el exito de un nuevo producto, pero este efecto queda condicionado por su grado de novedad y su calidad. Se aprecia asimismo que un desarrollo mas rapido que la competencia es particularmente beneficioso para las empresas que entran en posiciones intermedias en el mercado.