Nanocomposites: the contribution of multiscale modelling to improve the dispersion levels

Tese de Doutoramento em Ciência e Engenharia de Polímeros e CompósitosPolymer/layered silicate nanocomposites are a new class of materials that have raised much enthusiasm in scientiVc and technological domains due to their remarkable properties. However, tailoring their morphology and properties still remains a challenge. The present thesis combines experimental and theoretical approaches to further improve the knowledge available on the behavior of such materials. A new on-line rotational rheometer to monitor the compounding process at the lab and industrial scales was designed and assessed, with a view to practical process monitoring and control. On-line measurements were performed during nanocomposite production in order to establish relationships between material formulation and processing conditions. Namely, the aim is to determine whether changes in clay type, clay content and process parameters (e. g., feed rate and screw speed) cause detectable alterations in the rheological response and thus in the level of dispersion. The analysis of the data was supported by XRD and electron (scanning and transmission) microscopy observations. Secondly, multiscale simulations are undertaken based on coarse-graining methods, in order to capture the most relevant properties of bulk polymers and polymer nanocomposites. In the literature the amount of work dealing with coarse-graining simulations of polymers is inumerous, but little attention is given on how the magnitude of coarse-graining aUects the accuracy of the local and global behavior of polymer chains. At a mesoscopic scale, particles enclose an arbitrary number of monomers with dimensions beyond the Kuhn length. Consequently, the resolution of local subtleties (e. g., fastest mode relaxations) is deteriorated and the scaling laws predicted by theory are scarcely applicable. A comprehensive analysis about how the magnitude of coarse-graining aUects the equilibrium and non-equilibrium properties of linear polymer chains, at diUerent molecular weights, is given. The results were quantitatively compared with molecular dynamics simulations, theoretical models and available experimental data. The parameters for mesoscopic simulations were empirically obtained from all-atom molecular dynamics simulations, and a time-mapping protocol is used to accurately accommodate the systems dynamics to the correct time-scale. Additionally, non-equilibrium simulations are used with the aim of studying the adjustability of the mesoscopic friction coeXcient regarding the time-scale when steady and transient shear Wows are imposed. Finally, the procedure followed for the polymer/layered-silicate nanocomposite system allowed access to the large-scale morphology, providing a good starting point to further studies. Here, the eUective potentials governing the mesoscopic interactions are estimated invoking the Iterative Boltzmann Inversion protocol. While atomistic simulations provide a detailed understanding of the clay interlayer structure and accurate predictions of the basal distance, mesoscopic simulations provide the information necessary of the dispersion state of particles in the matrix.Nanocompósitos à base de matrizes poliméricas e nanoargilas são novos materiais que, devido às suas excelentes propriedades, têm despertado bastante interesse tanto a nível cientíVco como tecnológico. Todavia, controlar a sua morfologia de forma a obter propriedades especíVcas constitui ainda um desa Vo. Esta tese pretende analisar, propor e testar metodologias experimentais e teóricas inovadoras que forneçam uma melhor compreensão sobre o seu comportamento. Um novo reómetro rotacional em linha para monitorizar o processo de mistura numa escala laboratorial e industrial foi projetado, implementado e validado, com o intuito prático de monitorizar e controlar o processo. Durante o processamento de nanocompósitos foram efetuadas medições em linha com a Vnalidade de se estabelecerem relações entre as formulações, as condições operatórias e a morfologia dos materiais obtidos. A inWuência do tipo e quantidade de nanoargila incorporada na matriz polimérica, assim como os principais parâmetros utilizados no processamento de nanocompósitos (débito e velocidade do parafuso da extrusora) no comportamento reológico e foi avaliada o grau de dispersão. A análise foi complementada com ensaios de difração de raios-X e microscopia electrónica de varrimento e transmissão. Numa segunda vertente, simulações multi-escala com base em métodos de coarse-graining foram realizadas de forma a determinar as propriedades mais relevantes de polímeros e nanocompósitos à base de matrizes poliméricas. Embora o volume de publicações presentes na literatura abordando o tema seja vasto, a exploração do conhecimento sobre o modo de como o nível de coarse-graining afeta a precisão do comportamento local e global das cadeias do polímero é ainda limitada. Na meso-escala, cada partícula representa um número arbitrário de monómeros que se extende a comprimentos superiores ao de Kuhn. Consequentemente, a resolução das sutilezas locais (como por exemplo, as relaxações dos modos de Rouse mais rápidos) é afetada e as leis previstas pela teoria são apenas parcialmente aplicáveis. Uma análise detalhada sobre o modo como a magnitude do coarse-graining afeta as propriedades de equilíbrio e não-equilíbrio considerando diferentes pesos moleculares foi realizada. Os resultados foram comparados quantitativamente com simulações de dinâmica molecular, modelos teóricos e dados experimentais disponíveis. Os parâmetros utilizados nas simulações mesoscópicas foram obtidos empiricamente através de simulações atomísticas, e o mapeamento do tempo através de um protocolo para acomodar a dinâmica do sistema à escala de tempo correta. Adicionalmente, simulações em não-equilíbrio foram realizadas com o objetivo de estudar a ajustabilidade do coeVciente de fricção mesoscópico relativamente à escala de tempo em situações de Wuxos estacionários e transientes. Finalmente, foi desenvolvido um procedimento multi-escala que permite avaliar o estado da morfologia de sistemas contendo nanocompósitos à base de matriz polimérica e nanoargila, tornando-se um ponto de partida para estudos mais detalhados. Os potenciais efetivos de interação foram obtidos através do algoritmo iterativo de inversão de Boltzmann. Enquanto que as simulações atomísticas proporcionaram um estudo detalhado da morfologia inter-lamelar e da distância basal, as simulações mesoscópicas forneceram informações essenciais sobre o estado de dispersão das nanopartículas na matriz polimérica

Recent developments on on-line rheometry to monitor the extrusion process

On-line rheometers are generally inserted between extruder and die and generate data that is typically utilized for quality control purposes. However, on-line rheometers have also the potential to detect changes in structure, morphology, or composition of a given material system, thus assisting materials research and processing optimization, if they can be used along the axis of the extruder or compounder. The authors have previously developed on-line capillary and rotational/oscillatory rheometers that can be inserted and used at specific locations along the extruder. Since these devices are operated manually, their manipulation may be cumbersome and data may lack reliability. This work presents new versions of these rheometers, with improved functionalities and motorized operation. Details on the validation of one of them is also given.This study was carried out within the frame of the MULTIHYBRIDS IP 026685-2IP project, 6th Framework EC Program. The authors also gratefully acknowledge funding by FEDER via FCT, Fundação para a Ciência e Tecnologia, under the POCI 2010 and Plurianual programs

Experimental assessment of a numerical modelling code developed for the profile extrusion cooling stage

One of the critical stages in the extrusion of thermoplastic profiles is the cooling of the profile, which is usually undertaken in a metallic calibrator. In order to assure the highest possible productivity, the profile thermal energy must be removed as fast as possible. However, due to the typical low diffusivity of thermoplastic materials, the cooling stage is relatively long and the temperature gradients along the profile thickness are high, promoting the development of thermal residual stresses, which should be minimized. Consequently, designing an optimum calibration system that ensures fast and low level of thermal residual stresses is always a difficult task, especially when dealing with complex geometry profiles. In this work, we firstly report the experimental assessment of a previously developed numerical modelling code [1], which is able to model the thermal interchanges that take place at the profile extrusion calibration stage, and was developed in the framework of the OpenFOAM® [2] computational library. This task is undertaken with an industrial case study: a cooling system, composed by three calibrators in series, used in the production of a swimming pool cover profile. The experimental data of the temperature evolution along the calibration length was found to be similar to the numerical predictions, with a maximum relative error of circa 8.6% near the inlet of the second calibrator unit, which allowed the numerical code validation. Upon the experimental assessment the numerical code was used to support the redesign of the calibration system. This study led to an alternative calibration system design, which has a simpler constructive solution and a better performance than the original one, considered in the validation of the numerical code. As main conclusions, the results reported in this work prove the accuracy of the numerical code developed to compute the temperature distribution in the cooling/calibration extrusion stage, and its suitability to support the design of these systems.This work is funded by UID/CTM/50025/2013 - LA0025, with the financial support of FCT/MEC through national funds and when applicable by FEDER co-funded, within the partnership agreement PT2020

Introdução ao Python para alunos de Engenharia de Polímeros

UCI-3 (2016/2017)O objectivo deste texto não é apenas o de iniciar os seus utilizadores à programação. Nos dias de hoje, uma mais valia importante para qualquer Engenheiro ou Investigador é a capacidade de correlacioanar resultados e optimizar processos. O Python é uma ferramenta ideal para estes fins. Neste texto não se ensina só a escrever programas ou scripts. Fornecem-se aos alunos um conjunto de rotinas que podem por eles serem utilizadas na análise dos mais variados resultados experimentais, obtidos pelos instrumentos existentes no Departamento de Engenharia de Polímeros como o DSC, DMA, reómetros, resultados de microscopia óptica, …. Espera-se que outros colegas possam ganhar também com este esforço. Aproveita-se para se ensinar e relembrar outros conceitos como o cálculo vectorial e matricial, a resolução de integrais e equações diferenciais, a aplicação de métodos de diferenças finitas e volumes finitos, entre outros.info:eu-repo/semantics/draf

A multiscale modelling approach to simulate complex fluids flows : from atomistic towards continuum scales

Fundação para a Ciência e a Tecnologia (FCT) - POCI 2010 e programas plurianuai

The flow complex fluids: a multiscale modeling approach

Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/48512/200

Measuring the rheological properties of polymer melts with on-line rotational rheometry

Since the rheological response of a polymer system to an imposed stress is sensitive to composition, morphology, degree of mixing or temperature, on-line rheometry carried out along the length of the processing or compounding equipment - and able to follow the evolution of physical–chemical processes - is of great technical and scientific significance. This work presents and validates a computer controlled on-line rotational rheometer capable of quickly collecting material samples from within an extruder at different axial locations and performing the usual measurements of typical bench top commercial instruments. Validation of the prototype is made by direct comparison of its measurements with those carried out conventionally, including off-line measurements at room and high temperatures and on-line measurements. In order to illustrate its usefulness, the instrument is then used to monitor the evolution of the rheological behavior of three different materials along the axis of a twin screw extruder.Projecto MultiHybrids IP 026685-2IP Fundação para a Ciência e Tecnologia (FCT

On-line rheometry: a tool to monitor polymer nanocomposites production

The high potential of polymer nanocomposites has attracted the interest of both industrial and scientific communities. The final properties of these materials depend not only on the characteristics of the matrix and nanofillers, but also on the degree of dispersion of the nanofiller in the polymeric matrix. There are different methods to promote the dispersion of nanofillers in polymeric matrices, but the most promising is based on melt mixing, where the dispersion is achieved through the application shear and elongational stresses on a mixture of the polymer melt and nanofiller, usually performed on complex mixing devices. In order to improve the knowledge of the phenomena involved in the melt mixing process, several research groups are developing on/in-line adequate monitoring techniques, among these the online rheometry has shown to be a suitable choice. This work presents a new accessory conceived for a previously developed automated on-line rheometry system, which allows to couple easily the rheometer to any extruder. The developed system was subsequently used to study the effect of some process parameters related to the melt mixing process, which evidences the adequacy of these tools for monitoring purposes.Fundação para a Ciência e a Tecnologia (FCT) - Projecto MultiHybrids IP 026685-2IP 2010, Bolsa de doutoramento SFRH/BD/48512/2008, POCI 201