A series of four water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of the foams and plaques was investigated using DMS, DSC, FTIR, TEM, SEM, swelling, WAXS, and SAXS. A high degree of phase separation occurs in these foams and the degree of phase separation is independent of water (hard segment) content. In the foam with the lowest water content the morphology is similar to that of typical segmented urethane elastomers. Small hard segment domains are present with a correlation distance of roughly 7.0 nanometers. When the water content is increased a binodal distribution of hard segments appears. There are the small hard segment domains typical of segmented urethane elastomers as well as large hard segment aggregates greater than 100 nanometers in diameter. The large domains are thought to be aggregates of polyurea that precipitated during the manufacture of the foam. The foam making process successfully incorporated the trifunctional polyols into a network indicating a high degree of polymerization for the hydroxyl-isocyanate reaction. Unreacted isocyanate is present in the foams a month after curing. It is believed to be trapped in the large urea aggregates. WAXS patterns of the foams suggest hard segment ordering that may be of a paracrystalline nature but certainly lacking in true crystallinity. / Master of Science

A set of flexible water-blown slab stock polyurethane foams and their respective compression molded plaques as well as a chemically similar polyurea-urethane elastomer, PUUE, were studied to better understand the relaxation behavior and the molecular orientation upon deformation in these systems. The two main experimental techniques used in this investigation were stress relaxation in tension and deformation-IR dichroism. The stress relaxation in the foams and their respective plaques increased with hard segment content. The stress relaxation in the foams also appeared to depend very little on its anisotropic cell geometry and hence, mainly on the material comprising, the cell-wall struts and windows. Segmental orientation was measured as a function of elongation and relaxation, as well as hysteresis behavior for several of the plaques and the PUUE elastomer. The orientation changes upon deformation in the soft segments of both materials were small. Small changes in orientation with time and upon cyclic straining were also observed for the soft segments. The orientation at the interface of the hard and soft segments was influenced more by the soft segments in comparison to the hard segments in the plaques and in the PUUE elastomer. Significant transverse orientation upon deformation was observed in the hard segments of the plaques and up to elongations of 100 percent for the PUUE elastomer. Based on this transverse orientation behavior, the polyurea aggregates in the plaques were thought to possess a lamellar-like structure with the long axis of the aggregates aligning in the stretch direction. Relaxation and hysteresis behavior were observed upon following the orientation of the hard segments of the PUUE elastomer, but were negligible in that of the hard segments of the plaques. / Master of Science

No description available.

Open cell metal foams are a type of engineered material can be characterized by high porosity, high strength to weight ratio, tortuous flow paths and high surface area to volume ratio. It is the structure that gives the metal foams the characteristics that make them well suited for many application including heat exchangers. In this work, the structure of open celled metal foams is quantitatively characterized using an image analysis based method in order to predict the evaporative heat transfer of the metal foam using the fluid permeability. Several image processing algorithms were developed to quantitatively characterize the porosity, surface area per unit volume and the tortousity of metal foams from digital images of the cross sections of the material, and an expression was used to calculate the fluid permeability. An algorithm was developed to partion the pore space in the digital images so that individual cells within the structure could also be quantitatively characterized. Tools were also developed to predict the structure of open celled foam processed using the sacrificial template method by digitally constructing microstructures based the particle packing of the sacrificial templating material.

No description available.

The use of cellular foam as a core material in light-weight structural applications is of considerable interest. However, advances in this technology have been limited due to the lack of information concerning the macroscopic material behavior of cellular foams. Of particular interest in the design of composite structures is the shear modulus, G, of the core material, which must be established with a high degree of accuracy. Current ASTM test methods for shear modulus determination were researched and found inadequate for testing cellular foam materials. The difficulty in testing foam and the inaccuracies associated with the standard test methods established the need for the development of a test method for these materials. The test method (test fixture and test procedure) developed for cellular foam materials is presented. The design of the test fixture and the finite element analysis performed to determine fixture accuracy are discussed in detail. Additionally, the test procedure is presented, as well as the results for the 32 tests performed.

Os polímeros espumados são materiais do futuro, com um leque abrangente de aplicações. Podem ser usados em estruturas de isolamento, por exemplo, ou para reduzir custos com materiais. Este trabalho remete para a extrusão de misturas de Polipropileno isotático (iPP) / Polipropileno com Alta Resistência do Fundido (HMSPP), para a obtenção de espumas. O comportamento reológico do polímero fundido, principalmente a viscosidade na temperatura de processamento, tem um papel decisivo nas aplicações nas quais prevalece o fluxo extensional, como no caso da espumagem. Se a viscosidade for muito baixa, correspondente a uma baixa resistência do fundido, como no caso do homopolímero linear (PP isotático), a espumagem ficará prejudicada, face à impossibilidade de expansão acentuada. Entretanto, se a viscosidade for muito alta (HMSPP), com uma alta resistência do fundido, a espuma colapsará imediatamente após sua formação. A fim de obter espumas com uma estrutura celular homogênea e definida, foram efetuadas misturas 50% em peso entre o homopolímero linear (PP isotático) e o polipropileno ramificado (HMSPP), modificado por radiação gama, em ambiente contendo acetileno e na dose de 12,5 kGy. O processo de extrusão empregou a metodologia de espumagem solúvel, segundo o princípio de processamento/dissolução, que envolve a dissolução de um agente físico de sopro (PBA = Physical Blowing Agent), na pressão em torno de 30 bar, homogeneamente misturado com o fundido polimérico. As condições de extrusão, que, geralmente, compreendem o controle de temperatura, pressão e fluxo do material viscoelástico, foram investigadas experimentalmente para definir as características dominantes em prol da obtenção de espumas. O agente físico de sopro usado foi o nitrogênio. As principais características do PP e HMSPP foram obtidas via medidas reológicas (Índice de Fluidez e Resistência do Fundido) e análises térmicas (DSC/TGA), a fim de viabilizar e reproduzir a posteriori as espumagens pelo processo de extrusão. A morfologia celular das espumas foi investigada minuciosamente, com e sem a adição de talco, como agente nucleante, usando o Microscópio Eletrônico de Varredura. As propriedades mecânicas foram investigadas, via DMA, com base no Módulo de Young e tangente delta. A Rigidez Específica contribuiu com algumas considerações sobre a cristalinidade. As micrografias obtidas apontaram para espumas de células fechadas, nas quais a pressão é mantida durante o estágio de formação da célula. As espumas podem ser usadas em: mobílias; transporte; aterro sanitário; isolamentos; eletrodomésticos; como absorvedora de choque e de som; construção civil, incluindo chapas isolantes, proteção para pisos, perfis para acabamento, acabamentos de interiores; indústria automobilística, em painéis espumados; mercado de embalagem, em geral, incluindo embalagens para freezer e micro-ondas; acondicionamento de artigos médicos como seringas, catéteres intravenosos, frascos, materiais de sutura. fios e cabos e para finalidades estruturais (espumas estruturais), substituindo madeira, metais ou plásticos sólidos. As análises de densidade efetuadas nas espumas do presente trabalho apresentaram resultados típicos de espumas de alta densidade (faixa de 320 a 800 kg/m3), em torno de 500 kg/m3, usadas para fios e cabos e para finalidades estruturais (espumas estruturais), substituindo madeira, metais ou plásticos sólidos. As espumas estruturais têm densidades relativamente altas (acima de 320 kg/m3) e as estruturas celulares são compostas principalmente de vazios. / Foamed polymers are future materials, with a comprehensive application field. They can be used in order to improve appearance of insulation structures, for example, or to reduce costs involving materials. This work address to Isotactic Polypropylene / High Melt Strength Polypropylene blends, for foams production. Rheological behavior of polymer melt, especially referring to viscosity in processing temperature, plays a decisive role in applications where dominates extensional flow, as in case of foaming. If the viscosity is very low, it will correspond to a low melt strength, as in case of linear homopolymer (Isotact PP), and the foam will be prejudiced, due to the impossibility of expansion. Otherwise, if the viscosity is very high, with a high melt strength, the foam will collapse immediately after its formation. In order to get foams with an homogeneous and defined cellular structure, there were accomplished blends, 50% in weight, between linear homopolymer (isotactic PP) and HMSPP, from PP modified as per gamma radiation, in acetylene environment and at a 12.5 kGy dosis. Extrusion process used a soluble foaming methodology, according to a processing/dissolution principle, which involves the dissolution of a Physical Blowing Agent (PBA), under 30 bar pressure, homogeneously mixed with polymeric melt. Extrusion conditions, that generally involve temperature, pressure and viscoelastic material flow control were experimentally investigated to define prevalent characteristics for producing foams. Nitrogen was the used PBA and process extrusion parameters were adapted to PP, HMSPP and their 50% in weight mixtures thereof. Major PP and HMSPP characteristics were obtained via melt Index and melt strength and thermal analyses (DSC/TGA), in order to make viable and to reproduce foaming as per extrusion process. Foams cellular morphology of PP, HMSPP and their 50% in weight mixtures thereof was investigated, with and without talc addition, as nucleating agent, by using Scanning Electron Microscope (SEM). Micrographs obtained pointed to closed cells foams, in which the pressure is kept during all cell formation stage, informing that closed cells foams are used in thermal insulation in Civil Construction and in thermal vials. Density analyses accomplished in foams produced in our work showed typical results for high density foams (320 to 800 kg/m3 range), around 500 kg/m3, used for wire and cables and for structural purposes (structural foams), by replacing wood, metals or solid plastics. Structural foams have high density (above 320 kg/m3) and cellular structures are specially composed by holes.

This thesis deals with metal foam, a relatively new material whose tremendous potential has been identified early on. The material is an excellent shock absorber and also has a very high strength-to-weight ratio, properties that are highly desirable particularly within the aerospace and automotive industries. Despite the material’s immense potential, hardly any metal foam products have made it past the prototype stage. The reason is that the material is difficult to manufacture in the shapes required in industrial applications. Oftentimes, applications require sheets to be bent into specific shapes, yet bending is not possible with conventional methods. Laser forming is currently the only method that shows promise to bend metal foam panels to a range of shapes. In this thesis, the analysis of laser forming of metal foam was taken far beyond the experimental work that has been delivered thus far. A thorough analysis was performed of the thermo-mechanical bending mechanism that governs the deformation of metal foam during laser forming. This knowledge was then used to explain the effect of the process condition on the bending efficiency and the bending limit. Additionally, the impact of laser forming on the metal foam properties was explored. Experimental results were complemented by numerical results that were validated both thermally (using infrared imaging) as well as mechanically (using digital image correlation). Numerical models with different levels of geometrical complexities were used, and the effect of the model geometry on the predictive accuracy was explored. In the second half of the thesis, the aforementioned effort was extended to metal foam sandwich panels, in which metal foam is sandwiched between two sheets of solid metal. The material again has a high strength-to-weight ratio and excellent shock absorption capacity, while also being stiff and core-protective. Just like metal foam alone, metal foam sandwich panels are typically manufactured in flat sheets, and failure-free bending can only be achieved using lasers. The analysis was again initiated with the bending mechanism. It was revisited whether the foam core still follows the same bending mechanism, and how its deformation is affected by the interaction with the solid facesheets. This insight was then used to elucidate the bending efficiency and limit at different process conditions, as well as the impact of the process on the material performance. Additionally, the effect of the sandwich panel manufacturing method on the process outcome was investigated. This was achieved by contrasting two sandwich panel types with a different foam core structure, foam core composition, facesheet composition and facesheet attachment method. Lastly, three-dimensional deformation of metal foam sandwich panels into typical non-Euclidean shapes such as bowl and saddle shapes was explored. It was shown that a significant amount of 3D deformation can be induced. At the same time, it was discussed that the achievable deformation is limited to moderate curvatures, since only a limited amount of in-plane strains may be induced using laser forming. The aforementioned experimental efforts were again accompanied by numerical efforts. Sandwich panel models with different levels of geometrical complexity were used to study all aspects pertaining to the process, and the properties to the facesheet/foam core interface were discussed. Overall, the work in this thesis demonstrated that laser forming is capable of bending metal foam panels and metal foam sandwich panels up to large bending angles without causing failures, while maintaining the favorable properties of the material. Conceptual, experimental and numerical groundwork was laid towards a successful implementation of the material in industrial applications.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Francis Abbott Waldman. / M.S.

Au cours de ce travail de thèse, la Cellulose Nanofibrillée (CNF) a été isolée à partir de fibres de paille d’avoine puis modifiée chimiquement par des alcoxysilanes en milieu aqueux. La CNF silylée a ensuite été utilisée pour élaborer de nouveaux matériaux composites et mousses biosourcés.Le chapitre I présente quelques aspects généraux concernant les nanocelluloses, en particulier la NFC et ses applications dans le domaine des matériaux composites et des mousses.Le chapitre II est consacré à la fonctionnalisation de la CNF par le méthyltriméthoxysilane - choisi comme alcoxysilane modèle - ainsi qu’à la caractérisation du matériau silylé. Plusieurs paramètres réactionnels (pH, temps de réaction, concentration initiale en silane) ont été étudiés et optimisés, à partir de deux protocoles expérimentaux distincts. Les modifications ont été caractérisées à l’échelle moléculaire par différentes techniques physico-chimiques. Les propriétés des nanofibrilles silylées, comme la morphologie, cristallinité, mouillabilité, hygro-copicité et stabilité thermique, ont ensuite été évaluées.Dans le chapitre III, l’impact de la silylation sur les propriétés mécaniques et hygroscopiques de composites à matrice acide poly(lactique) ou matrice polydiméthylsiloxane chargés en NFC a été évalué.Pour finir, l’impact de la silylation sur les propriétés de mousses élaborées à partir de NFC lyophilisées a été étudié dans le chapitre IV (porosité, propriétés en compression, conductivité thermique, mouillabilité, hygroscopicité et oléophilicité). / In this thesis, nanofibrillated cellulse (NFC) has been isolated from oat straw and chemically modified by alkoxysilanes in water medium. Silylated NFC has been subsequently used to elaborate novel biobased composite materials and foamsChapter I presents some general aspects about nanocelluloses – in particular Nanofibrillated Cellulose (NFC) - and their use in composite materials and foams.Chapter II is dedicated to the functionalization of NFC by methyltrimethoxysilane - chosen as a model silane - and to the comprehensive examination of the silylated material. Reaction conditions such as pH, reaction time and initial silane concentration have been particularly in-vestigated and optimized using two distinct experimental protocols. The modifications have been characterized at the molecular level by various physicochemical techniques. The proper-ties of the silylated nanofibrils i.e. the morphology, crystallinity, wettability, hygroscopicity and thermal stability, have been subsequently examined. Chapter III investigates the impact of silylation on the mechanical and hygroscopic properties of NFC-reinforced composites prepared with two distinct polymeric matrices: poly(lactic acid) (PLA) and polydimethylsiloxane (PDMS).Chapter IV examines the impact of silylation on the properties of NFC-foams prepared by freeze drying, in particular on the porosity, compressive properties, thermal conductivity, wet-tability, hygroscopicity and oleophilicity.