Fundamentals of cell opening in polymer foaming

Polymeric foams are ubiquitous in foods and industrial manufacturing. Since, they are used in a number of applications as thermal and acoustic insulators, in some cases it is desirable to create foams with cells not interconnected (i.e. closed cells), while in others cases an efficient interconnections between cells (i.e. opened cells) is required, as instance for culture substrates for living cells. In both cases, a fundamental understanding of the physics governing the cell opening process is needed to improve the final product and reduce the polymeric manufacturing cost. In this dissertation, the physical mechanisms leading to cell opening in foams is investigated from a fundamental point of view. As such, the complex foaming process (i.e. involving different physical mechanisms) was studied with a bottom-up process, dividing it in four elementary steps namely: 1) cells growth, 2) cells interaction, 3) rupture and 4) retraction of the cells walls. Different experimental techniques are employed in this thesis; most of them were designed during the Ph.D. to reproduce particular experimental conditions, which are difficult to be obtained with typical foaming equipment. In fact, different new experimental apparatus were developed (i.e. Mini-batch, Interfacial bubble, Breaking bubble) and specifically designed to make unique measurements. The new apparata are particularly useful for testing theoretical predictions on some types of simplified systems useful for the study of the foaming process. The main and novel result of this thesis is the fundamentals understanding of the entire foaming process that leads to a fundamental comprehension of how to produce a particular foam morphology, called fully opened cell. In the literature, there was not fundamentals understanding of the mechanisms behind the cell opening in thermoplastic foaming, since the reported foaming models stop the modeling at the rupture event in the cell walls, without considering the retraction event of the produced hole. The introduction of the retraction as the fundamental step to produce a fully open cell morphology is the novelty of this thesis. Moreover, the comprehension of the retraction step, leads to us to identify the importance of the role of the viscoelasticity for making a fully opened cell foam, that is a new concept that is unique and it was not covered earlier in the previous literature. Moreover, a model of the entire foaming process was developed and it was identified a criterion that employs the computed stresses, the elongational rate and the film thickness among the bubbles to predict the rupture of the polymeric layer between the bubbles and its retraction. As a result, the foaming process model is able to make predictions on the final foam morphology, starting from any polymer/gas solution. Independent experiments to assess the validity of each step of the proposed approach were performed. In conclusion, the developed methodology allows to design the materials and processing conditions to control foam morphology. In the first part of this thesis, a general overview of the foaming process is supplied, focusing the attention on the crucial points of each foaming steps pointed out by the existent literature. The main part will be occupied by the contributions published during the years of this Ph.D. because they represent the steps ahead achieved with respect to the literature

Microfoamed Strands by 3D Foam Printing

We report the design, production, and characterization of microfoamed strands by means of a green and sustainable technology that makes use of CO2 to create ad-hoc innovative bubble morphologies. 3D foam-printing technology has been recently developed; thus, the foaming mechanism in the printer nozzle is not yet fully understood and controlled. We study the effects of the operating parameters of the 3D foam-printing process to control and optimize CO2 utilization through a maximization of the foaming efficiency. The strands' mechanical properties were measured as a function of the foam density and explained by means of an innovative model that takes into consideration the polymer's crystallinity content. The innovative microfoamed morphologies were produced using a bio-based and compostable polymer as well as polylactic acid and were then blown with CO2. The results of the extensive experimental campaigns show insightful maps of the bubble size, density, and crystallinity as a function of the process parameters, i.e., the CO2 concentration and temperature. A CO2 content of 15 wt% enables the acquirement of an incredibly low foam density of 40 kg/m3 and porosities from the macro-scale (100-900 μm) to the micro-scale (1-10 μm), depending on the temperature. The foam crystallinity content varied from 5% (using a low concentration of CO2) to 45% (using a high concentration of CO2). Indeed, we determined that the crystallinity content changes linearly with the CO2 concentration. In turn, the foamed strand's elastic modulus is strongly affected by the crystallinity content. Hence, a corrected Egli's equation was proposed to fit the strand mechanical properties as a function of foam density

Retraction of thin films coated by insoluble surfactants

We investigate the retraction of a circular thin film coated with insoluble surfactants, which is punctured at its centre. We assume that the surface pressure of the liquid-gas interface is related to the number density of surfactants through a linear equation of state, which is characterized by a single parameter: the Gibbs dilation modulus. To solve the governing equations and track the deformation of the domain, we use the finite element method with an arbitrary Lagrangian-Eulerian approach where the film surface is sharp. Our simulations show that the surface elasticity introduced by the surfactants slows down the retraction and introduces oscillations at early times. In agreement with previous experiments and theoretical analysis, we find that the presence of surfactants introduces perturbations of the film thickness over progressively larger distances as the surface elasticity increases. The surface perturbations travel faster than the retracting edge of the film at a speed proportional to the Gibbs modulus. For large values of the Gibbs modulus, the interface behaviour approaches that of an incompressible two-dimensional solid. Our analysis sheds light on the effect of insoluble surfactants on the opening of a circular hole in a thin film and can be extended to investigate the onset of surface cracks and fractures. © 2022 Author

A microcapillary rheometer for microliter sized polymer characterization

Abstract We report the design of a microcapillary rheometer (μCR) that allows to perform experiments rapidly and in a broad range of shear rates (i.e., from 0.1 to 1000 s−1), using small amounts of material (i.e., just few milligrams). Additionally, multiple measurement parallelization makes it suitable for High-Throughput Rheological Experimentation of polymer melts (HT-Rheo-E). The novel rheometer consists of a set of three cylindrical microcapillaries in which the fluid flows driven by a controlled pressure. A camera, placed at the capillary exit, records the fluid motion to measure its flow rate, from which the fluid viscosity can be determined. The optimization of the setup allowed for reliable and fast viscosity measurements using ca. 10 mg of material. The current work reports the design of the rheometer and validation measurements on several model fluids. The microfabricated μCR is of potential interest for applications in quality control and research where rapid and repeated measurements using limited milligrams of polymer are required, as well as for High-Throughput-Experimentation of complex fluids (e.g., biological systems)

Temperature profile of ex-vivo organs during radio frequency thermal ablation by fiber Bragg gratings.

We report on the integration of fiber optic sensors with commercial medical instrumentation for temperature monitoring during radio frequency ablation for tumor treatment. A suitable configuration with five fiber Bragg grating sensors bonded to a bipolar radio frequency (RF) probe has been developed to monitor the area under treatment. A series of experiments were conducted on ex-vivo animal kidney and liver and the results confirm that we were able to make a multipoint measurement and to develop a real-time temperature profile of the area, with a temperature resolution of 0.1°C and a spatial resolution of 5 mm during a series of different and consecutive RF discharges

Investigar en Trabajo Social: diferentes experiencias como pasantes de investigación

El presente trabajo se propone compartir tres experiencias de investigación llevadas a cabo por estudiantes (ahora licenciadas) en la Facultad de Trabajo Social de la Universidad Nacional de La Plata, en diferentes proyectos de investigación. Dos de las experiencias de pasantías se enmarcaron en el proyecto de investigación “Seguridad, Violencia y Derechos Humanos. Un estudio de las representaciones sociales en jóvenes y policías”1. La otra pasantía se inserta en el proyecto “Disputas en el espacio público: cultura, política y desigualdades socio-urbanas”2. A su vez, dos de nosotras continuamos nuestro proceso de aprendizaje del oficio de investigar a través de dos becas CIN en el marco de los proyectos de investigación acreditados, mencionados anteriormente. Haremos una breve mención respecto a esto. Por último, analizaremos las experiencias como pasantes de investigación a la luz de los aportes de distintos autores/as, haciendo hincapié principalmente en la comprensión de las competencias, habilidades y destrezas necesarias para desarrollar la práctica investigativa.Eje Teórico-metodológico en Trabajo Social-GT 27: Metodología y Trabajo Social.Facultad de Trabajo Socia

Competence Centre ICDI per Open Science, FAIR, ed EOSC - Mission, Strategia e piano d'azione

This document presents the mission and strategy of the Italian Competence Centre on Open Science, FAIR, and EOSC. The Competence Centre is an initiative born within the Italian Computing and Data Infrastructure (ICDI), a forum created by representatives of major Italian Research Infrastructures and e-Infrastructures, with the aim of promoting sinergies at the national level, and optimising the Italian participation to European and global challenges in this field, including the European Open Science Cloud (EOSC), the European Data Infrastructure (EDI) and HPC. This working paper depicts the mission and objectives of the ICDI Competence Centre, a network of experts with various skills and competences that are supporting the national stakeholders on topics related to Open Science, FAIR principles application and participation to the EOSC. The different actors and roles are described in the document as well as the activities and services offered, and the added value each stakeholder can find the in Competence Centre. The tools and services provided, in particular the concept for the portal, though which the Centre will connect to the national landscape and users, are also presented

Rheological characterization of complex fluids through a table-top 3D printer

3D printing is changing the way we conceive, design, and build 3D objects in mechanical, biomedical, aerospace, construction, automotive and maritime industries. In the current work, the nonlinear rheological behaviour of polymer melts is measured through a table-top 3D printer (3D RheoPrinter) that, smartly modified, allows inline investigation of viscosity, extrudate swell and melt fracture. By using a piezoresistive mini-transducer, the innovative system is designed to be applicable to all Fused Deposition Modelling (FDM) 3D printers by a simple and cost-effective modification of a state-of-art nozzle. The measurements of the nonlinear rheological behaviour are compared with traditional, rotational rheology. Two biodegradable polymers, i.e. polylactic acid and polycaprolactone, are investigated as model systems to test the 3D RheoPrinter. The results of the shear viscosity and the first normal stress difference coefficient, as function of shear rate, show a good agreement between the 3D RheoPrinter and rotational rheometer with an error of about 6% for a confidence interval of 96%. Moreover, the 3D RheoPrinter can still be used as 3D printer. In the last part of this work, it is presented a printing test for building 3D structures in which the results show controllable resolution by means of the measured rheological information such as the extrudate swell. The vision of this work is that an inline rheological characterization, possible with the developed 3D RheoPrinter, can enable automatic process optimization and quality assurance to the 3D printing community. The social and scientific impacts of this work are maximized by the cost-efficiency and simplicity of the design that makes it within reach of the general public. The 3D RheoPrinter opens for a rheological experimentation to a broad audience and it offers important insights to bring FDM to the next level of resolution

L'organizzazione degli eventi sportivi: fattori critici ed aspetti manageriali. Alcune rilevanti esperienze in ambito toscano

L'elaborato è incentrato nella ricerca di uno schema di operazioni legate all'organizzazione degli eventi sportivi dalla loro ideazione, passando per lo sviluppo fino alle valutazioni post-evento. A supporto dello schema teorico si propone il confronto tra le esperienze di alcuni degli organizzatori dei più importanti eventi sportivi nell'ambito toscano, in particolare sono state raccolte le testimonianze degli organizzatori del Palio di Fucecchio, della Toscana Endurance Lifestyle, della Maratona di Pisa e della Viareggio Cup. The essay is focused on the creation of a model which could be helpfull for the organization of a sport event. The teoric template, splitted in four different phases (Concept, Planning, Development,Final Evaluation), offers some tools that comes from the literature and the evidence of some of the most important tuscan events managers