Fluid flow in a Porous Scaffold for Microtia by Lattice Boltzmann Method

The birth deformity of ear, known as microtia, varies from a minimal deformed ear to the absence of auricular tissue or anotia. This malformation has been treated by reconstructing the external ear, mainly by autogenous rib cartilage in auricular repair. The fabrication of the ear framework is a prolonged reconstructive procedure and depends of the surgeon’s skill. In order to avoid these inconveniences and reduce surgery time, it was proposed in a previous work to use implants made with biocompatible materials. One of these is a scaffold made by fused deposition modeling using PLA based in the three-dimensional geometry of the ear cartilage. The aim of this work is to evaluate the feasibility of this scaffold to perform cell culture in a perfusion biorreactor by estimating the flow transport characteristics in porous media using a scaffold with the porous geometry of the human auricular cartilage for microtia. Flow and heat transfer through the scaffold were simulated by the lattice Boltzmann method, and permeability and shear stress distribution were obtained at different Reynolds numbers. The permeability values of the scaffold achieved are in the order of magnitude of scaffolds used for cell culture. Linear dependencies between maximum shear stress and Reynolds number, and between maximum shear stress and permeability were obtained. The values of shear stress achieved correspond to high percentage of cell viability. The scaffolds for microtia treatment with the proposed filling pattern select is appropriate for cell culture in a perfusion bioreactor with characteristics similar to those described herein

Role of Plasticizers on PHB/bio-TPE Blends Compatibilized by Reactive Extrusion

Poly(hydroxybutyrate) (PHB) is a biopolymer biologically synthesized by controlled bac- terial fermentation from a wide variety of microorganisms. PHB is proposed as a potential green alternative to commonly used plastics in packaging, due to its biodegradability and biocompatibility. However, if PHB is to replace commodities, it has some limitations regarding its thermo-mechanical performance to overcome. Among them are its critically the low toughness values at room tem- perature and poor thermoforming ability. With the aim of overcoming these weaknesses, in this work, blends of PHB with the addition of a biodegradable thermoplastic elastomer (bio-TPE) were prepared and evaluated. Films of such compounds were made by cast extrusion. In order to enhance the compatibility of both polymers during the extrusion process, three different reactive agents (poly-hexametylene diisocianate, triglycidyl isocyanurate, and Joncryl® ADR-4368) were assessed. The morphology and mechanical- and thermal properties of the films obtained were analyzed. In addition, the thermoforming ability of the produced films was evaluated. The results show that the plasticizers present in the bio-TPE interacted with the reactive agents, making them chemical competitors and altering the outcome of the blends

DISEÑO DE UN MOLDE DE INYECCIÓN CON UN SISTEMA DE CAVIDADES INTERCAMBIABLES Y DESLIZANTES / Design of Injection Mould with a System of Interchangeable and Sliding Cavities

  El presente trabajo tuvo como objetivo principal diseñar un molde de inyección de probetas normalizadas, destinadas a ensayos mecánicos, utilizando un sistema novedoso de cavidades intercambiables y deslizantes. El diseño que se propone se basa en el uso de insertos o postizos, para el moldeo individualizado de diferentes probetas. Actualmente, existe la tendencia a diseñar moldes con postizos intercambiables que ofrecen facilidades para la obtención de probetas diversas, con la característica de fijarse al sistema de placas mediante tornillos. Al estar sujetos de esa forma, presentan dificultades importantes al momento de montarlos y desmontarlos, para un cambio rápido de cavidades de moldeo. Para ello se requiere de un gran esfuerzo manual e inversión de tiempo. Partiendo de esa experiencia y de las tendencias recientes en la industria a usar moldes con sistemas de cambio rápido, el presente trabajo plantea el diseño con un sistema de postizos intercambiables y deslizantes, bajo las especificaciones de las normas ASTM 6141 e ISO 294-1. Con tal fin, se han diseñado dos postizos, uno para la inyección de probetas tipo halterio y otro para barras rectangulares, las cuales pueden usarse en múltiples ensayos mecánicos (tracción, flexión e impacto). Para modelar y validar el molde diseñado y los postizos propuestos se usaron los programas Pro/ENGINEER y C-MOLD. Se formularon dos propuestas preliminares, considerando los dos movimientos posibles de los postizos en el sistema de placas de la máquina de inyección: vertical y horizontal. La evaluación comparativa de los pros y los contras de cada molde favoreció al sistema horizontal, debido a sus facilidades de manipulación y garantías para inmovilizar los postizos. Palabras clave   : Molde, Probetas, Diseño, Simulación, CAD/CAE. DESIGN OF INJECTION MOULD WITH A SYSTEM OF INTERCHANGEABLE AND SLIDING CAVITIES ABSTRACT The main aim of this work was the design of an injection mould with the purpose of preparing test specimens, using a new system of interchangeable and sliding cavities. The proposed mould is able to hold inserts able to, manufacture the individualized test specimen by injection moulding. Nowadays, the trend toward the design of moulds with interchangeable cavities intended for easing the process of obtaining diverse plastic parts in the same mould, present the characteristic of fixing the system of plates by means of several screws. This system presents important drawback, at the moment of a rapid change of them, like the trend of having to make a great manual effort and to spend considerable amount of time. The present work presents the design of a mould with sliding and interchangeable cavities, under ASTM 6141 and ISO 294-1 norms. The design of two interchangeable and sliding cavities is developed: one with the purpose of producing tensile test specimen and the other for manufacturing rectangular bars (for flexion or impact tests). In order to shape and validate the designed mold and the proposed cavities, the Pro/ENGINEER and C-MOLD software were used. Two preliminary designs were formulated considering horizontal or vertical possible movements of the interchangeable cavities in the system of plates of the injection mould. The comparative evaluation of the advantages and disadvantages of every mould favoured the horizontal system, due to its operational facility associated with the guaranty of an easy manipulation and immobili  zation of cavities. Keywords   : Mold, Test Specimen, Design, Simulations, CAD/CAE

CRITERIO DE CONVERGENCIA EN PIEZAS PLÁSTICAS INYECTADAS DE POLIESTIRENO / Convergence Criteria for Polystyrene Injection Plastic Parts

El objetivo de este trabajo consistió en la evaluación del criterio de la convergencia como herramienta para la obtenciónde resultados más precisos en la simulación del proceso de inyección de piezas plásticas. Se alcanzó un espectro mayor deresultados comparados con los presentados en trabajo previos, se obtuvo el número de nodos óptimo para cada parámetrode proceso. Se seleccionaron diferentes concentradores de esfuerzos (triangular, rectangular, semicircular y circular) y serealizaron mallados de las piezas con diferente número de nodos alrededor de las entallas, se usaron de 10 a 80 nodos. Seprocedió al estudio de los resultados disponibles en el programa simulador, con la finalidad de verificar la convergenciaentre ellos. Se concluyó que los resultados de temperatura de desmoldeo, temperatura de la masa al final del llenado,temperatura de la pared del molde, flujo de calor en la pared del molde, porcentaje en peso y desplazamiento en la dirección“Y” convergen a medida de que se aumenta número de nodos, mientras que la temperatura del refrigerante y el númerode Reynolds convergen sin necesidad de aumentar el número de nodos. Sin embargo, los resultados de diferencia detemperatura y desplazamiento en la dirección “Z” nunca presentan convergencia dentro del rango estudiado. Finalmente,existe una serie de resultados que, dependiendo del caso de estudio, convergen o no, entre los cuales se encuentran elporcentaje de rechupe, fuerza de cierre, presión al final del llenado, contracción volumétrica y desplazamiento en ladirección “X”.ABSTRACTThe main objective of this work involves the study and evaluation of the criteria of convergence as a significant andfundamental tool in simulations made in injected plastic parts. In the same way, it is intended to obtain a greater spectrumof results available at the time to carry out simulations different to present in the work previous, thus obtaining the optimalnumber of nodes for each of these can be established with greater ease. To achieve this, was selected in each form of stressconcentrator (triangular, rectangular, semicircular and circular) the smaller geometry and were made mesh of the parts withdifferent number of nodes around the notches, where the magnitudes employed were 10 to 80 nodes. Once have completedthe simulations, all the results available on the simulator program employee were studied, in order to verify the presenceof results that converge, results do not converge and what they do from the beginning. Finally, it was concluded that theresults of bulk temperature, bulk temperature at end of filling, mold wall temperature, mold wall heat flux, percentage totalweight and displacement in “Y” component present convergence when the nodes increment, while the coolant temperatureand the coolant Reynolds number always converge. Moreover, the results of temperature difference and displacement in“Z” component, never presented convergence within the range studied. Finally, there are some results that dependingon the case had or not convergence, among which are the sink index, clamp force, pressure at end of filling, volumetricshrinkage and displacement in “X” component.Key words: Criteria of convergence, Simulation, Nodes, Plastics parts, CAD/CAE Tools

Influencia de las condiciones de procesamiento sobre el comportamiento a fractura de un homopolímero de polipropileno y un copolímero etileno-polipropileno moldeados por inyección

El estudio se basa en la influencia de los parámetros de procesamiento (inyección) en el comportamiento a fractura de dos tipos de polipropileno (PP). Se aplicó el método integral J para determinar la resistencia a la fractura de los polímeros; se determinó, además, la micro-estructura ya que es un factor influyente en el comportamiento a fractura. Para ello se calcularon índices termo-mecánicos a partir de simulaciones de flujo para establecer una relación directa entre propiedades termo-mecánicas variables de la fractura. Referente al diseño se usó la metodología de Taguchi, para así minimizar el número de experimentos. Finalmente, se obtuvo que la resistencia a la fractura era, principalmente, influenciada por la temperatura de fundido (Tf). A bajo valor de Tf, la morfología se caracteriza por tener mayor espesor de piel y por ende, el núcleo es más pequeño, lo que implica una menor cristalinidad y mayores valores de Jc.The influence of injection process conditions over the fracture behavior of two types of polypropylene (PP) was studied. The J integral to determine the fracture toughness of polymers was applied; also the micro-structure as an influential factor over the fracture behavior was determined. For this, the hermo-mechanical indexes were calculated using flow simulations, to establish a relationship between thermo-mechanical properties. The Taguchi methodology design was used to reduce the number of experiments applied. The injection temperature (Tf) is a process conditions that affects the tensile strength of the polymers. At low Tf , the morphology is characterized by increased skin thickness and thus, the core is smaller, implying a lower crystalinity and higher values of Jc.Fil: Santaella, Daniela C.. Universidad Simón Bolívar; Venezuela. Universidad Nacional de Mar del Plata; ArgentinaFil: Frontini, Patricia Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Pettarin, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Fasce, Laura Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Candal, María V.. Universidad Simón Bolívar; Venezuel

Valorization of Agricultural Waste Lignocellulosic Fibers for Poly(3-Hydroxybutyrate-Co-Valerate)-Based Composites in Short Shelf-Life Applications

Biocircularity could play a key role in the circular economy, particularly in applications where organic recycling (composting) has the potential to become a preferred waste management option, such as food packaging. The development of fully biobased and biodegradable composites could help reduce plastic waste and valorize agro-based residues. In this study, extruded films made of composites of polyhydroxybutyrate-co-valerate (PHBV) and lignocellulosic fibers, namely almond shell (AS) and Oryzite® (OR), a polymer hybrid composite precursor, have been investigated. Scanning electron microscopy (SEM) analysis revealed a weak fiber–matrix interfacial interaction, although OR composites present a better distribution of the fiber and a virtually lower presence of “pull-out”. Thermogravimetric analysis showed that the presence of fibers reduced the onset and maximum degradation temperatures of PHBV, with a greater reduction observed with higher fiber content. The addition of fibers also affected the melting behavior and crystallinity of PHBV, particularly with OR addition, showing a decrease in crystallinity, melting, and crystallization temperatures as fiber content increased. The mechanical behavior of composites varied with fiber type and concentration. While the incorporation of AS results in a reduction in all mechanical parameters, the addition of OR leads to a slight improvement in elongation at break. The addition of fibers improved the thermoformability of PHBV. In the case of AS, the improvement in the processing window was achieved at lower fiber contents, while in the case of OR, the improvement was observed at a fiber content of 20%. Biodisintegration tests showed that the presence of fibers promoted the degradation of the composites, with higher fiber concentrations leading to faster degradation. Indeed, the time of complete biodisintegration was reduced by approximately 30% in the composites with 20% and 30% AS