Despite remarkable progress made in the past century, which has revolutionized our understanding of the universe, there are numerous open questions left in theoretical physics. Particularly important is the fact that the theories describing the fundamental interactions of nature are incompatible. Einstein's theory of general relative describes gravity as a dynamical spacetime, which is curved by matter and whose curvature determines the motion of matter. On the other hand we have quantum field theory, in form of the standard model of particle physics, where particles interact via the remaining interactions - electromagnetic, weak and strong interaction - on a flat, static spacetime without gravity. A theory of quantum gravity is hoped to cure this incompatibility by heuristically replacing classical spacetime by quantum spacetime'. Several approaches exist attempting to define such a theory with differing underlying premises and ideas, where it is not clear which is to be preferred. Yet a minimal requirement is the compatibility with the classical theory, they attempt to generalize. Interestingly many of these models rely on discrete structures in their definition or postulate discreteness of spacetime to be fundamental. Besides the direct advantages discretisations provide, e.g. permitting numerical simulations, they come with serious caveats requiring thorough investigation: In general discretisations break fundamental diffeomorphism symmetry of gravity and are generically not unique. Both complicates establishing the connection to the classical continuum theory. The main focus of this thesis lies in the investigation of this relation for spin foam models. This is done on different levels of the discretisation / triangulation, ranging from few simplices up to the continuum limit. In the regime of very few simplices we confirm and deepen the connection of spin foam models to discrete gravity. Moreover, we discuss dynamical, e.g. diffeomorphism invariance in the discrete, to fix the ambiguities of the models. In order to satisfy these conditions, the discrete models have to be improved in a renormalisation procedure, which also allows us to study their continuum dynamics. Applied to simplified spin foam models, we uncover a rich, non--trivial fixed point structure, which we summarize in a phase diagram. Inspired by these methods, we propose a method to consistently construct the continuum theory, which comes with a unique vacuum state. / Trotz bemerkenswerter Fortschritte im vergangenen Jahrhundert, die unser Verständnis des Universums revolutioniert haben, gibt es noch zahlreiche ungeklärte Fragen in der theoretischen Physik. Besondere Bedeutung kommt der Tatsache zu, dass die Theorien, welche die fundamentalen Wechselwirkungen der Natur beschreiben, inkompatibel sind. Nach Einsteins allgemeiner Relativitätstheorie wird die Gravitation durch eine dynamische Raumzeit dargestellt, die von Materie gekrümmt wird und ihrerseits durch die Krümmung die Bewegung der Materie bestimmt. Dem gegenüber steht die Quantenfeldtheorie, die die verbliebenen Wechselwirkungen - elektromagnetische, schwache und starke Wechselwirkung - im Standardmodell der Teilchenphysik beschreibt, in dem Teilchen auf einer statischen Raumzeit -- ohne Gravitation -- miteinander interagieren. Die Hoffnung ist, dass eine Theorie der Quantengravitation diese Inkompatibilität beheben kann, indem, heuristisch, die klassische Raumzeit durch eine 'Quantenraumzeit' ersetzt wird. Es gibt zahlreiche Ansätze eine solche Theorie zu definieren, die auf unterschiedlichen Prämissen und Ideen beruhen, wobei a priori nicht klar ist, welche zu bevorzugen sind. Eine Minimalanforderung an diese Theorien ist Kompatibilität mit der klassischen Theorie, die sie verallgemeinern sollen. Interessanterweise basieren zahlreiche Modelle in ihrer Definition auf Diskretisierungen oder postulieren eine fundamentale Diskretheit der Raumzeit. Neben den unmittelbaren Vorteilen, die Diskretisierungen bieten, z.B. das Ermöglichen numerischer Simulationen, gibt es auch gravierende Nachteile, die einer ausführlichen Untersuchung bedürfen: Im Allgemeinen brechen Diskretisierungen die fundamentale Diffeomorphismensymmetrie der Gravitation und sind in der Regel nicht eindeutig definiert. Beides erschwert die Wiederherstellung der Verbindung zur klassischen, kontinuierlichen Theorie. Das Hauptaugenmerk dieser Doktorarbeit liegt darin diese Verbindung insbesondere für Spin-Schaum-Modelle (spin foam models) zu untersuchen. Dies geschieht auf sehr verschiedenen Ebenen der Diskretisierung / Triangulierung, angefangen bei wenigen Simplizes bis hin zum Kontinuumslimes. Im Regime weniger Simplizes wird die bekannte Verbindung von Spin--Schaum--Modellen zu diskreter Gravitation bestätigt und vertieft. Außerdem diskutieren wir dynamische Prinzipien, z.B. Diffeomorphismeninvarianz im Diskreten, um die Ambiguitäten der Modelle zu fixieren. Um diese Bedingungen zu erfüllen, müssen die diskreten Modelle durch Renormierungsverfahren verbessert werden, wodurch wir auch ihre Kontinuumsdynamik untersuchen können. Angewandt auf vereinfachte Spin-Schaum-Modelle finden wir eine reichhaltige, nicht-triviale Fixpunkt-Struktur, die wir in einem Phasendiagramm zusammenfassen. Inspiriert von diesen Methoden schlagen wir zu guter Letzt eine konsistente Konstruktionsmethode für die Kontinuumstheorie vor, die einen eindeutigen Vakuumszustand definiert.

Dielectric materials are used as spacers in antennas. The design of the dielectric determines the properties of the antenna. The insertion of high dielectric materials in a specific pattern into a low dielectric matrix material is one means to accomplish this. This thesis studies the means to insert metal cylinders (wire or nails) into polymer foams to produce such a material. Depending on the antenna properties desired, the patterns and number of nails varies tremendously. To decrease the manufacturing time and, therefore, the cost of creating these materials, an automatic machine capable of rapidly inserting wires to a predetermined pattern is developed. This thesis has two parts. In the first part, the ballistic impact of nails into foam is modeled. Experimental observations of the nails impacting the foam are used to verify the model. Penetration equations are developed to express the penetration capability of a nail into foam. All of this allows one to predict the forces required for a nail to be inserted into foam to a desired depth, thereby facilitating manufacture of these dielectric materials. In the second part, a fully automatic nail insertion device is designed, fabricated, and tested with the experimental tests used as control settings.

O uso de polietileno pós-consumo (p-PE) em espumas de polietileno de baixa densidade (LDPE) que utilizam como agente expansor azodicarbonamida (ACA) é assunto deste trabalho. Os polímeros utilizados foram caracterizados, e o p-PE é constituído por uma mistura de LDPE e polietileno de alta densidade (HDPE). Para a preparação das formulações das espumas foram avaliados o desempenho do misturador tipo Drais e do misturador de rolos. Foram testadas formulações de espumas sem agente reticulante e com agente reticulante (peróxido de dicumila). O misturador de rolos mostrou-se mais eficiente para a preparação de espumas por permitir melhor controle de temperatura e por eliminar etapas intermediárias de processo. As espumas que não utilizam agente reticulante apresentaram colapso das células e menores níveis de expansão. Foram analisados os efeitos da incorporação de diferentes teores de p-PE sobre a morfologia e propriedades mecânicas das espumas de LDPE com 0,5% (em massa) de agente reticulante. As composições de espumas de LDPE/p-PE (em massa) testadas foram: 100/0, 85/15, 70/30, 60/40, 50/50 e 30/70. As micrografias (MEV) das espumas tratadas com software de imagem permitiram verificar forma, distribuição de tamanho e área das células. O p-PE apresenta maior viscosidade em relação ao LDPE virgem, ocorrendo aumento na quantidade de células menores à medida que se incrementa o teor de p-PE na mistura. As espumas obtidas apresentaram elevado grau de heterogeneidade das células em função do baixo teor de agente reticulante utilizado (0,5% em massa), da diferença de viscosidade entre os polietilenos utilizados e pelo fato de o p-PE conter diferente tipo de polietileno em relação ao material virgem. As propriedades mecânicas das espumas com incorporação de p-PE são superiores em relação à espuma confeccionada com LDPE virgem pelo fato de o p-PE conter HDPE, que é um material mais rígido em relação ao LDPE. É possível verificar que existe uma relação entre a matriz polimérica utilizada na espuma e as propriedades do material expandido. O uso de material reciclado em espumas é uma alternativa para reciclagem de polímeros, possibilitando obter espumas com propriedades interessantes do ponto de vista tecnológico e mercadológico, considerando a aplicação em embalagens de proteção de produtos frágeis. O acréscimo de até 70% em massa de p-PE em formulações contendo 5% de agente expansor dá origem a espumas com faixas de densidade ideal para aplicação em embalagens (25 a 90 kg.m-3) / Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-05-05T19:46:59Z No. of bitstreams: 1 DISSERTACAO MARCELO GIUSTI DE ALMEIDA.pdf: 4151354 bytes, checksum: ef5211daac2f789f497a134bf5f6babd (MD5) / Made available in DSpace on 2014-05-05T19:46:59Z (GMT). No. of bitstreams: 1 DISSERTACAO MARCELO GIUSTI DE ALMEIDA.pdf: 4151354 bytes, checksum: ef5211daac2f789f497a134bf5f6babd (MD5) / The use of waste polyethylene (p-PE) in low-density polyethylene (LDPE) foams that have azodicarbonamide (ACA) as blowing agent is the topic of this paper. It characterizes used polymers, and p-PE is made of a mixture of LDPE and high-density polyethylene (HDPE). To prepare foams formulations, it evaluated performance of the Drais mixer and Banbury batch. It also tested foams formulations with and without cross-linking agent (dicumyl peroxide). The Banbury batch showed itself as more efficient to foam processing because it allows a better temperature control and eliminates intermediate steps in the process. Foams without cross-linking agent present cell collapse and lower foaming rates. It analyzed the effect of different amounts of p-PE over the morphology and mechanical properties of LDPE foams that contain 0.5% (weight) of cross-linking agent. Proportions of LDPE/p-PE (weight) tested in foams were: 100/0, 85/15, 70/30, 60/40, 50/50, and 30/70. Foams micrographies (SEM) were treated in image software to verify shape, size distribution, and area of cells. Because p-PE has higher viscosity related to LDPE, it is verified that as the p-PE amount increases in the formulation the number of cells with smaller size and areas increase. Foams presented high degree of cells heterogeneity because of the low amount of cross-linking agent used (0.5% weight), because of the difference in viscosity for used polyethylene, and because p-PE has a different kind of polyethylene in relation to virgin material. Mechanical properties of foams that use p-PE in their formulation are superior than foams made from LDPE, because p-PE contains HDPE, which is more rigid than LDPE. It is possible to verify that there is a relationship between polymeric matrix and expanded material properties. Using recycled material in foams is an alternative to recycle polymers. It makes possible to get foams with interesting properties from the technological and market point of view, considering the application in protection package for fragile products. Adding up to 70% of p-PE (weight) in formulations that contain 5% of blowing agent generates foams with ideal density rage to apply in packages (25 to 90 kg.m-3

Une alternative aux produits industriels de type phénol ou résorcinol peut être des tanins ou de la lignine. Les deux sont des polyphénols naturels, le tanin est extrait de différentes parties de plantes, tandis que la lignine est habituellement obtenue comme sous-produit dans les industries papetières. Ces deux produits sont la base principale sur laquelle j’ai travaillé pendant le développement de cette thèse. Dans une première partie, une étude de caractérisation et de différenciation entre différents tannins ayant la même origine mais que présentent un comportement différent lorsqu'ils sont utilisés dans la même application dans les mêmes conditions a été effectuée. Cette étude met en évidence la GPC comme technique fondamentale pour la différenciation des tanins de quebracho sulfités. D'autre part, les interactions entre différentes substances avec du tanin et de la lignine ont été étudiées. Comme l’étude de la réaction entre les diamines (telles que l'hexaméthylènediamine) avec du tanin et de la lignine pour obtenir des résines polycondensées. En outre, dans cette section ont été obtenus des polyuréthanes avec au moins 70% de substances naturelles dans leur préparation sans utiliser d'isocyanate dans le procédé. De plus, des aldéhydes dérivés de la lignine, comme la vanilline, ont été utilisés avec le tanin de pin pour la fabrication d'adhésifs dans la préparation de panneaux de particulaires, obtenant des résultats satisfaisants selon les normes européennes et des substances complètement naturelles. Enfin, dans le cadre d'un projet industriel les étapes initiales pour le développement d'une mousse de tanin rigide applicable par projection pour l'isolation thermique des bâtiments ont été réalisées. Lorsqu'un nouveau système de moussage mécanique a été développé pour des mousses de tanin basées sur des mousses de lutte contre incendie à base de tanin ou dans les mousses des opérations d’ouverture du tunnel, ce nouveau système de moussage évite les problèmes de retrait lors de la formation de la mousse / An alternative to industrial phenol or resorcinol industrial products may be tannins or lignin. Both are natural polyphenols, the tannin is extracted from different parts of plants, while lignin is usually obtained as a secondary product in the pulp and paper mill. These two products are the main basis on which I have worked during the development of this thesis. In a first part, a study of characterization and differentiation between different tannins with the same origin and that present a different behavior when used in the same application under the same conditions has been done. Highlighting the GPC as a fundamental technique for the differentiation between sulphited quebracho tannins. On the other hand, the interactions between different substances with tannin and with lignin have been studied. As the study of the reaction between diamines (such as hexamethylenediamine) with tannin and lignin to obtain a polycondensed resins. Also, in this section have been obtained polyurethanes with at least 70% of natural substances in their preparation without using any isocyanate in the process. In addition, aldehydes derived from lignin, such as vanillin, have been used next to pine tannin for the manufacture of adhesives in the preparation of particleboards, obtaining satisfactory results according to European standards and from completely natural substances. Finally, within an industrial project the initial steps have been carried out for the development of a rigid tannin foam applicable by projection for the thermal insulation of buildings. Where a new mechanical foaming system has been developed for tannin foams based in fire-fighting foams or in the foams of the tunneling operations, this new system of foaming avoids the problems of shrinkage during the formation of the foam

Made available in DSpace on 2014-06-11T19:31:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-08-14Bitstream added on 2014-06-13T18:42:35Z : No. of bitstreams: 1 simoes_rd_dr_bauru.pdf: 3657789 bytes, checksum: 0f75cbf5a9ed07aa12a486e70e6189f6 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Filmes auto-sustentáveis de polifluoreto de vinilideno (PVDF) e de polifluoreto de vinilideno com trifluoretileno (P(VDF-TrFE)) contendo amido de milho e/ou látex da borracha natural foram produzidos visando à obtenção de blendas biocompátiveis. Estas blendas foram produzidas pela técnica de prensagem a quente a qual não necessita fazer uso de solventes orgânicos para dissolver os polímeros sintéticos (PVDF e P(TrFE)). Tal processamento, além de não utilizar solventes tóxicos, possibilita a fabricação de filmes auto-sustentáveis com propriedades físicas e químicas apropriadas para aplicações como um material biocompatível. Os filmes de PVDF ou P(VDF-TrFE) com os polímeros naturais (amido e/ou látex de borracha natural) foram caracterizados através das técnicas de espectroscopia vibracional (absorção no infravermelho com transformada de Fourier (FTIR) e espalhamento Raman), análise termogravimétrico (TG), calorimetria exploratória diferencial (DSC), análise dinâmico-mecânica (DMA), microscopia ótica (MO), microscopia ótica (MO), microscopia eletrônica de varredura (MEV), difração de raios-X, densidade, índice de fluidez (MFI), dureza e condutividade térmica. Os resultados que os polímeros naturais estão bem dispersos na matriz de PVDF ou P(VDF-TrFE) em nível micrométrico e não interagem quimicamente com os polímeros sintéticos. As blendas apresentaram elevada estabilidade térmica, cujo módulo de elasticidade está na mesma ordem de grandeza do osso humano. Entretanto, observou-se que a adesão dos polímeros naturais é melhor para as blendas com P(VDF-TrFe). Adicionalmente, as estruturas cristalinas do PVDF-α e do P(VDF-TrFE) ferroelétrico são mantidos em todas as blendas. A densidade, a dureza, o índice de fluidez e os valores de condutividade térmica das blendas seguiram o que deve se esperar de misturas físicas... / Films of poly(vinylidene fluoride), PVDF, and poly(vinylidene fluoride - trifluoroethylene), P(VDF-TrFE), containing corn starch and latex of natural rubber were produced visioning to obtain biocompatible blends. These blends were produced by compressing/annealing, which discards the necessity of using organic solvents to dissolve the synthetic polymers (PVDF and P(VDF-TrFE)). This process, besides discarding the use of toxic solvents, allows obtaining self-standing films with suitable physical and chemical properties considering their application as biocompatible materials. The PVDF or P(VDF-TrFe) films with different percentage of the natural polymers (starch and/or latex of natural rubber) were characterized using thermogravimetry (TG), differential scanning calorimetry (DSC), and dynamicalmechanical analysis (DMA). Fourier transform infrared spectroscopy (FTIR) and Raman scattering, optic microscopy, scanning electric microscopy, scanning electric microscopy (SEM), X-ray diffraction, density, melt flow index, hardness, and thermal conductivity. The results showed that the natural polymers are well dispersed within the matrix of PVDF or P(VDF-TrFE) at micrometer level and do not interact chemically with the synthetic polymers. The blends present high thermal stability with elasticity modulus at the same order of magnitude of the bone. However, it was observed that the adhesion of the natural polymers is better for the blends of P(VDF-TrFE). Besides, the crystalline structures of the α-PVDF and ferroelectric P(VDF-TrFE) are kept in the blends. The density, hardness, melt flow index and thermal conductivity values of the blends followed what shoud be expected from physical mixtures. The tests of biocompatibility for these materials were carried out implanting the films at the subcutaneous region of rats the results showed histological characteristics favorable to the compatibility in vivo...(Complete abstract click electronic access below)

Cette thèse vise à faire progresser notre connaissance du comportement rhéologique des mousses dans les milieux poreux. Pour cela, nous avons réalisé une étude pétrophysique systématique complète de l'écoulement de mousse dans des milieux poreux pour déterminer l'impact de la qualité de la mousse, du débit, de la perméabilité, de la pression et de la composition du gaz. Nos résultats montrent que les données obtenues sur une gamme de qualités de mousse, de vitesses interstitielles et de perméabilités, convergent vers une courbe maîtresse de loi de puissance, indépendamment du régime d'écoulement, une fois le comportement rhéologique de la mousse forte est exprimé comme la viscosité apparente en fonction du taux de cisaillement. La courbe maîtresse obéit à une loi de puissance avec un exposant universel de -2/3. Nous avons trouvé des preuves expérimentales et théoriques dans la littérature pour la valeur de l'exposant. Nos résultats ont montré aussi que la mousse était moins efficace pour réduire la mobilité des gaz lorsque la pression augmentait, et qu'à des pressions suffisamment basses, la composition du gaz n'avait aucun effet sur la performance de la mousse. Cependant, à haute pression, la composition du gaz devient un paramètre déterminant, et tous les composants doivent être pris en compte. Nous avons trouvé une courbe maîtresse pour la performance de la mousse que nous permet d'extrapoler l'efficacité de la mousse pour différentes compositions à différentes pressions. Donc, les deux approches et les corrélations ci-dessus peuvent être utilisées pour affiner la modélisation d'injection des mousses, améliorant ainsi la simulation du procédé Foam-EOR et sa fiabilité. / This thesis aimed at advancing our knowledge of the rheological behavior of foams in porous media. For that, we performed a comprehensive systematic petrophysical study of foam flow in porous media to determine the impact of foam quality, flow rate (interstitial velocity), permeability, pressure and gas composition on foam performance. Our findings show that the data obtained over a range of foam qualities, interstitial velocities and permeabilities converged to a power law master curve, independently of the flow regime, once the rheological behavior of strong foam was expressed in terms of apparent viscosity as a function of shear rate. The master curve obeys a power law with a universal exponent of -2/3. We found experimental and theoretical evidence in the literature for the value of the exponent. Our results also showed that foam was less effective in reducing gas mobility as pressure increased and that at sufficiently low pressures, the gas composition has no effect on foam performance. However, at high pressures, the gas composition becomes a determinant parameter, and all components must be considered. We found a master curve for foam performance which allows us to extrapolate foam efficiency for different compositions at different pressures. The experimental correlations obtained by these original approaches hold immense potential to advance the physical modeling of foam flow in porous media. Therefore, both approaches and correlations above can be used to refine foam flooding modeling, thus improving the simulation of Foam-EOR process and its reliability.

Made available in DSpace on 2014-10-09T12:52:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:36Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Dans un contexte de développement durable, de nouvelles architectures macromoléculaires biosourcées et aromatiques ont été synthétisées à partir de deux types de ressources renouvelables : des tanins, issus du bois, et des glycérides, issus de végétaux ou de microalgues, afin de développer des matériaux pour des applications dans le bâtiment. Dans un premier temps, la réaction d’alkoxylation a été étudiée sur les tanins. Des chaînes de polyéther glycol (propylène et butylène) ont été greffées sur des tanins issus de différentes espèces botaniques aboutissant à l’obtention de divers macropolyols. A partir de ces macropolyols, des polyuréthanes (PUs) ont été synthétisés en modulant les paramètres réactionnels dans le but de contrôler les propriétés finales des matériaux pour répondre à des cahiers des charges. Des membranes d’étanchéité en PUs et des mousses rigides uréthane-isocyanurates d’isolation ont été élaborées. Enfin de l’huile algale ainsi que de l’huile de colza (comme référence) ont été modifiées en époxydes et polyols. Ces nouveaux synthons ont ensuite été incorporés dans la formulation de mousses uréthane-isocyanurates en vue d’étudier l’impact du type et du nombre de fonctions réactives sur les propriétés finales de mousses rigides à cellules fermées. Ces études ont permis d’analyser l’effet de l’addition de nouveaux synthons biosourcés et renouvelables dans des architectures et matériaux polymères. Le grand potentiel des tanins et des glycérides algosourcés pour l’élaboration de nouveaux matériaux performants pour des applications en particulier dans le domaine du bâtiment, a pu être largement démontré. / In a context of sustainable development, new biobased and aromatic macromolecular architectures were synthesized from two types of renewable resources: tannins, extracted from wood, and glycerides derived from plant or from microalgae to develop innovative materials for building applications. Firstly, the alkoxylation reaction was performed on tannins. Polyether glycol (propylene or butylene) chains were grafted on tannins extracted from different botanical sources species, resulting in various macropolyols with various controlled macromolecular architectures. Based on these macropolyols, polyurethanes were synthesized by varying the reaction parameters to control the final properties of materials to fit specific requirements. PU proofing membranes and rigid urethane-isocyanurate foams for insulation were elaborated. Finally, algal oil and rapeseed oil (as reference) were modified in epoxides and polyols. These new building blocks were incorporated in the structure of urethane-isocyanurates foams to study the impact of the type and the number of reactive functions on the final properties of rigid foams.New renewable bio-based building blocks were developed and integrated in the final macromolecular architectures and materials. The great potential of tannins and glycerides from microalgae for developing high-performance materials, for building applications, especially waterproofing membranes and insulation foams has been clearly established.

O uso de polietileno pós-consumo (p-PE) em espumas de polietileno de baixa densidade (LDPE) que utilizam como agente expansor azodicarbonamida (ACA) é assunto deste trabalho. Os polímeros utilizados foram caracterizados, e o p-PE é constituído por uma mistura de LDPE e polietileno de alta densidade (HDPE). Para a preparação das formulações das espumas foram avaliados o desempenho do misturador tipo Drais e do misturador de rolos. Foram testadas formulações de espumas sem agente reticulante e com agente reticulante (peróxido de dicumila). O misturador de rolos mostrou-se mais eficiente para a preparação de espumas por permitir melhor controle de temperatura e por eliminar etapas intermediárias de processo. As espumas que não utilizam agente reticulante apresentaram colapso das células e menores níveis de expansão. Foram analisados os efeitos da incorporação de diferentes teores de p-PE sobre a morfologia e propriedades mecânicas das espumas de LDPE com 0,5% (em massa) de agente reticulante. As composições de espumas de LDPE/p-PE (em massa) testadas foram: 100/0, 85/15, 70/30, 60/40, 50/50 e 30/70. As micrografias (MEV) das espumas tratadas com software de imagem permitiram verificar forma, distribuição de tamanho e área das células. O p-PE apresenta maior viscosidade em relação ao LDPE virgem, ocorrendo aumento na quantidade de células menores à medida que se incrementa o teor de p-PE na mistura. As espumas obtidas apresentaram elevado grau de heterogeneidade das células em função do baixo teor de agente reticulante utilizado (0,5% em massa), da diferença de viscosidade entre os polietilenos utilizados e pelo fato de o p-PE conter diferente tipo de polietileno em relação ao material virgem. As propriedades mecânicas das espumas com incorporação de p-PE são superiores em relação à espuma confeccionada com LDPE virgem pelo fato de o p-PE conter HDPE, que é um material mais rígido em relação ao LDPE. É possível verificar que existe uma relação entre a matriz polimérica utilizada na espuma e as propriedades do material expandido. O uso de material reciclado em espumas é uma alternativa para reciclagem de polímeros, possibilitando obter espumas com propriedades interessantes do ponto de vista tecnológico e mercadológico, considerando a aplicação em embalagens de proteção de produtos frágeis. O acréscimo de até 70% em massa de p-PE em formulações contendo 5% de agente expansor dá origem a espumas com faixas de densidade ideal para aplicação em embalagens (25 a 90 kg.m-3) / The use of waste polyethylene (p-PE) in low-density polyethylene (LDPE) foams that have azodicarbonamide (ACA) as blowing agent is the topic of this paper. It characterizes used polymers, and p-PE is made of a mixture of LDPE and high-density polyethylene (HDPE). To prepare foams formulations, it evaluated performance of the Drais mixer and Banbury batch. It also tested foams formulations with and without cross-linking agent (dicumyl peroxide). The Banbury batch showed itself as more efficient to foam processing because it allows a better temperature control and eliminates intermediate steps in the process. Foams without cross-linking agent present cell collapse and lower foaming rates. It analyzed the effect of different amounts of p-PE over the morphology and mechanical properties of LDPE foams that contain 0.5% (weight) of cross-linking agent. Proportions of LDPE/p-PE (weight) tested in foams were: 100/0, 85/15, 70/30, 60/40, 50/50, and 30/70. Foams micrographies (SEM) were treated in image software to verify shape, size distribution, and area of cells. Because p-PE has higher viscosity related to LDPE, it is verified that as the p-PE amount increases in the formulation the number of cells with smaller size and areas increase. Foams presented high degree of cells heterogeneity because of the low amount of cross-linking agent used (0.5% weight), because of the difference in viscosity for used polyethylene, and because p-PE has a different kind of polyethylene in relation to virgin material. Mechanical properties of foams that use p-PE in their formulation are superior than foams made from LDPE, because p-PE contains HDPE, which is more rigid than LDPE. It is possible to verify that there is a relationship between polymeric matrix and expanded material properties. Using recycled material in foams is an alternative to recycle polymers. It makes possible to get foams with interesting properties from the technological and market point of view, considering the application in protection package for fragile products. Adding up to 70% of p-PE (weight) in formulations that contain 5% of blowing agent generates foams with ideal density rage to apply in packages (25 to 90 kg.m-3