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Venkataramana, K., Ram Kumar Singh, Anindya Deb, Vivek Bhasin, K. K. Vaze i H. S. Kushwaha. "Blast Protection of Infrastructure with Fluid Filled Cellular Polymer Foam". Procedia Engineering 173 (2017): 547–54. http://dx.doi.org/10.1016/j.proeng.2016.12.088.
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Lagzdiņš, Aivars, Alberts Zilaucs, Ilze Beverte i Jānis Andersons. "Modeling the Nonlinear Deformation of Highly Porous Cellular Plastics Filled with Clay Nanoplatelets". Materials 15, nr 3 (28.01.2022): 1033. http://dx.doi.org/10.3390/ma15031033.
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Rigid low-density plastic foams subjected to mechanical loads typically exhibit a nonlinear deformation stage preceding failure. At moderate strains, when the geometrical nonlinearity is negligible, such foam response is predominantly caused by the nonlinearity of deformation of their principal structural elements—foam struts. Orientational averaging of stresses in foam struts enables estimation of the stresses taken up by foams at a given applied strain. Based on a structural model of highly porous anisotropic cellular plastics filled with clay nanoplatelets and the orientational averaging, a method for calculating their nonlinear deformation is derived in terms of structural parameters of the porous material, the mechanical properties of the monolithic polymer, and filler particles and their spatial orientation. The method is applied to predicting the tensile stress-strain diagrams of organoclay-filled low-density rigid polyurethane foams, and reasonable agreement with experimental data is demonstrated.
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Carneiro, Vitor Hugo, Hélder Puga i José Meireles. "Vibration Damping and Acoustic Behavior of PU-Filled Non-Stochastic Aluminum Cellular Solids". Metals 11, nr 5 (28.04.2021): 725. http://dx.doi.org/10.3390/met11050725.
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Aluminum-based cellular solids are promising lightweight structural materials considering their high specific strength and vibration damping, being potential candidates for future railway vehicles with enhanced riding comfort and low fuel consumption. The filling of these lattices with polymer-based (i.e., polyurethane) foams may further improve the overall vibration/noise-damping without significantly increasing their density. This study explores the dynamic (i.e., frequency response) and acoustic properties of unfilled and polyurethane-filled aluminum cellular solids to characterize their behavior and explore their benefits in terms of vibration and noise-damping. It is shown that polyurethane filling can increase the vibration damping and transmission loss, especially if the infiltration process uses flexible foams. Considering sound reflection, however, it is shown that polyurethane filled samples (0.27–0.30 at 300 Hz) tend to display lower values of sound absorption coefficient relatively to unfilled samples (0.75 at 600 Hz), is this attributed to a reduction in overall porosity, tortuosity and flow resistivity. Foam-filled samples (43–44 dB at 700–1200 Hz) were shown to be more suitable to reduce sound transmission rather than reflection than unfilled samples (21 dB at 700 Hz). It was shown that the morphology of these cellular solids might be optimized depending on the desired application: (i) unfilled aluminum cellular solids are appropriate to mitigate internal noises due to their high sound absorption coefficient; and (ii) PU filled cellular solids are appropriate to prevent exterior noises and vibration damping due to their high transmission loss in a wide range of frequencies and vibration damping.
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Moore, S. E. "Effect of Polymer Structure on the Long-Term Aging of Rigid Polyurethane Foam". Journal of Thermal Insulation 15, nr 4 (kwiecień 1992): 279–93. http://dx.doi.org/10.1177/174425919201500402.
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The effect of polymer structure on both initial and aged thermal conductivity ( K-factor) or thermal resistivity ( R-value) was explored by using a new procedure to estimate the long-term thermal resistance of gas-filled cellular plastics proposed by Norton [1], Edgecombe [2] and Bomberg [3]. This method uses a semi-logarithmic plot of thermal resistivity versus time that produces two distinct stages in the data, thermal drift and plateau with a break point separating the two stages. The plateau stage was fit with a straight line in order to estimate the long-term thermal resistance or K-factor of the foam. This concept was employed on the fourteen CFC-11 blown foams [4] in this study. The effect of me two major types of isocyanates, Specialty TDI (toluene diisocyanate) and PMDI (polymeric diphenylmethane diisocyanate), was isolated and compared. The significance of seven different types of polyol initiators was also evaluated with respect to K-factor and K-factor aging. In the case of the PMDI foams, the data correlated well with the model and the 20-year K-factor predictions appear to be reasonable when compared to the raw data curves. In the case of the TDI foams, however, it was more difficult to find a break point which would define the plateau region in the data. Most of these foams did contain break points, but the break point occurs at a slightly longer time. The 20-year K-factors of these foams could be predicted with reasonable confidence when there was a break point in the resistivity versus log (T) curves.
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Wilk-Zajdel, Klaudia, Piotr Kasza i Mateusz Masłowski. "Laboratory Testing of Fracture Conductivity Damage by Foam-Based Fracturing Fluids in Low Permeability Tight Gas Formations". Energies 14, nr 6 (23.03.2021): 1783. http://dx.doi.org/10.3390/en14061783.
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In the case of fracturing of the reservoirs using fracturing fluids, the size of damage to the proppant conductivity caused by treatment fluids is significant, which greatly influence the effective execution of hydraulic fracturing operations. The fracturing fluid should be characterized by the minimum damage to the conductivity of a fracture filled with proppant. A laboratory research procedure has been developed to study the damage effect caused by foamed and non-foamed fracturing fluids in the fractures filled with proppant material. The paper discusses the results for high quality foamed guar-based linear gels, which is an innovative aspect of the work compared to the non-foamed frac described in most of the studies and simulations. The tests were performed for the fracturing fluid based on a linear polymer (HPG—hydroxypropyl guar, in liquid and powder form). The rheology of nitrogen foamed-based fracturing fluids (FF) with a quality of 70% was investigated. The quartz sand and ceramic light proppant LCP proppant was placed between two Ohio sandstone rock slabs and subjected to a given compressive stress of 4000–6000 psi, at a temperature of 60 °C for 5 h. A significant reduction in damage to the quartz proppant was observed for the foamed fluid compared to that damaged by the 7.5 L/m3 natural polymer-based non-foamed linear fluid. The damage was 72.3% for the non-foamed fluid and 31.5% for the 70% foamed fluid, which are superior to the guar gum non-foamed fracturing fluid system. For tests based on a polymer concentration of 4.88 g/L, the damage to the fracture conductivity by the non-foamed fluid was 64.8%, and 26.3% for the foamed fluid. These results lead to the conclusion that foamed fluids could damage the fracture filled with proppant much less during hydraulic fracturing treatment. At the same time, when using foamed fluids, the viscosity coefficient increases a few times compared to the use of non-foamed fluids, which is necessary for proppant carrying capacities and properly conducted stimulation treatment. The research results can be beneficial for optimizing the type and performance of fracturing fluid for hydraulic fracturing in tight gas formations.
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Chen, Xiao Yuan, Royale S. Underhill i Denis Rodrigue. "A Simple Method to Convert Cellular Polymers into Auxetic Metamaterials". Applied Sciences 13, nr 2 (14.01.2023): 1148. http://dx.doi.org/10.3390/app13021148.
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The objective of this study was to present a simple and environmentally friendly process combining low pressure (vacuum) and mechanical compression to convert low-density polyethylene (LDPE) foams into low-density foams (76–125 kg/m3) with negative tensile and compressive Poisson’s ratios (NPR). As a first step, four series of recycled LDPE foams (electronics packaging) with starting densities of 16, 21, 30 and 36 kg/m3 were used to determine the effect of different processing conditions including temperature and pressure. Based on the optimized conditions, the tensile and compressive Poisson ratios of the resulting auxetic foams reached −2.89 and −0.66, while the tensile and compressive modulus of the auxetic foams reached 40 kPa and 2.55 kPa, respectively. The foam structure of the samples was characterized via morphological analysis and was related to the mechanical properties before and after the treatment (i.e., foams with positive and negative Poisson’s ratios). The tensile and compressive properties (Young’s modulus, strain energy, energy dissipation and damping capacity) for these auxetic foams were also discussed and were shown to be highly improved. These auxetic foams can be applied in sports and military protective equipment. To the best of our knowledge, there is only one report on vacuum being used for the production of auxetic foams.
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Acosta, Andrey, Arthur B. Aramburu, Rafael Beltrame, Darci A. Gatto, Sandro Amico, Jalel Labidi i Rafael de Avila Delucis. "Wood Flour Modified by Poly (Furfuryl Alcohol) as a Filler in Rigid Polyurethane Foams: Effect on Water Uptake". Polymers 14, nr 24 (16.12.2022): 5510. http://dx.doi.org/10.3390/polym14245510.
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The use of lignocellulosic fillers in rigid polyurethane foams (RPUFs) has been receiving great attention due to their good mechanical and insulation properties and the high sustainable appeal of the obtained cellular polymers, although high water uptakes are found in most of these systems. To mitigate this detrimental effect, RPUFs filled with wood flour (2.5% wt) were fabricated with the addition of furfuryl alcohol (FA) to create a polymer grafted with the wood filler. Two concentrations of FA (10 wt% and 15 wt%) were investigated in relation to the wood flour, and the RPUFs were characterized for cell morphology, density, compressive properties, thermal stability, and water uptake. The introduction of wood flour as a filler decreased the cell size and increased the anisotropy index of the RPUFs and, in addition to that, the FA grafting increased these effects even more. In general, there were no significant changes in both mechanical and thermal properties ascribed to the incorporation of the fillers. On the other hand, a reduction of up to 200% in water uptake was ascribed to the FA-treated fillers.
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Katkeaw, Kuntida, Matthana Khangkhamano i Rungrote Kokoo. "Microbubble technology for natural rubber latex foam production: The use of various gas-filled microbubbles". Cellular Polymers 41, nr 1 (23.10.2021): 21–29. http://dx.doi.org/10.1177/02624893211053672.
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In recent years, microbubble technology has attracted great attention in many application fields including water treatment, food processing, oil recovery, surface cleaning, and therapeutic applications. In this paper, microbubbles (MBs) of air, nitrogen, and argon were applied to produce natural rubber latex foams (NRLFs). The bubbles were generated by flowing the gas through a porous diffuser and latex. The effect of gas source on cellular structure, density, elasticity, indentation hardness, and flammability of the bubbled foams was discussed. Argon MBs offered the latex foams with fine cell diameters and uniform cell size distribution resulting in enhanced elasticity and physical properties of the foams. Indentation hardness index and limiting oxygen index value depended significantly on the gas used. By using the microbubble technique, the future prospects in NRLF production can be expected due to its ability in controllable cellular structure.
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Schonberg, William P. "Extending the NNO Ballistic Limit Equation to Foam-Filled Dual-Wall Systems". Applied Sciences 13, nr 2 (6.01.2023): 800. http://dx.doi.org/10.3390/app13020800.
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A key component in the quantitative assessment of the risk posed to spacecraft by the micrometeoroid and orbital debris (MMOD) environment is frequently referred to as a ballistic limit equation (BLE). A frequently used BLE for dual-wall configurations (which are commonly used on spacecraft to protect them against the MMOD environment) is the New Non-Optimum, or “NNO”, BLE. In design applications where a BLE is needed for a new structural system that has not yet been tested, but resembles to a fair degree a dual-wall system, it is common practice to equivalence the materials, thicknesses, etc., of the new system to the materials, thicknesses, etc., of a dual-wall system. In this manner, the NNO BLE can be used to estimate the failure / non-failure response characteristics for the new system. One such structural wall system for which a BLE does not yet exist is a dual-wall system that is stuffed with a lightweight polymer-based foam material. In this paper we demonstrate that the NNO BLE, in its original form, frequently over- or under-predicts the response of such a system. However, when the NNO BLE is modified to more properly include the effects of the presence of the foam as well as the actual material properties of the walls and the impacting projectile, there is a marked improvement in its predictive abilities.
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Huh, Chun, i William R. Rossen. "Approximate Pore-Level Modeling for Apparent Viscosity of Polymer-Enhanced Foam in Porous Media". SPE Journal 13, nr 01 (1.03.2008): 17–25. http://dx.doi.org/10.2118/99653-pa.
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Summary Foam is used in the oil industry in a variety of applications, and polymer is sometimes added to increase foam's stability and effectiveness. A variety of surfactant and polymer combinations have been employed to generate polymer-enhanced foam (PEF), typically anionic surfactants and anionic polymers, to reduce their adsorption in reservoir rock. While addition of polymer to bulk foam is known to increase its viscosity and apparent stability, polymer addition to foams for use in porous media has not been as effective. In this pore-level modeling study, we develop an apparent viscosity expression for PEF at fixed bubble size, as a preliminary step to interpret the available laboratory coreflood data. To derive the apparent viscosity, the pressure-drop calculation of Hirasaki and Lawson (1985) for gas bubbles in a circular tube is extended to include the effects of shear-thinning polymer in water, employing the Bretherton's asymptotic matching technique. For polymer rheology, the Ellis model is employed, which predicts a limiting Newtonian viscosity at the low-shear limit and the well-known power-law relation at high shear rates. While the pressure drop caused by foam can be characterized fully with only the capillary number for Newtonian liquid, the shear-thinning liquid requires one additional grouping of the Ellis-model parameters and bubble velocity. The model predicts that the apparent viscosity for PEF shows behavior more shear-thinning than that for polymer-free foam, because the polymer solution being displaced by gas bubbles in pores tends to experience a high shear rate. Foam apparent viscosity scales with gas velocity (Ug) with an exponent [-a/(a+2)], where a, the Ellis-model exponent, is greater than 1 for shear-thinning fluids. With a Newtonian fluid, for which a = 1, foam apparent viscosity is proportional to the (-1/3) power of Ug, as derived by Hirasaki and Lawson. A simplified capillary-bundle model study shows that the thin-film flow around a moving foam bubble is generally in the high-shear, power-law regime. Because the flow of polymer solution in narrower, water-filled tubes is also governed by shear-thinning rheology, it affects foam mobility as revealed by plot of pressure gradient as a function of water and gas superficial velocities. The relation between the rheology of the liquid phase and that of the foam is not simple, however. The apparent rheology of the foam depends on the rheology of the liquid, the trapping and mobilization of gas as a function of pressure gradient, and capillary pressure, which affects the apparent viscosity of the flowing gas even at fixed bubble size. Introduction When a gas such as CO2 or N2 is injected into a mature oil reservoir for improved oil recovery, its sweep efficiency is usually very poor because of gravity segregation, reservoir heterogeneity, and viscous fingering of gas, and foam is employed to improve sweep efficiency with better mobility control (Shi and Rossen 1998; Zeilinger et al. 1996). When oil is produced from a thin oil reservoir overlain with a gas zone, a rapid coning of gas can drastically reduce oil production rate, and foam is used to delay the gas coning (Aarra et al. 1997; Chukwueke et al. 1998; Dalland and Hanssen 1997; Thach et al. 1996). During a well stimulation operation with acid, a selective placement of acid into a low-permeability zone from which oil has not been swept is desired, which can be accomplished with use of foam (Cheng et al. 2002). For environmental remediation of subsurface soil using surfactant, foam is used to improve displacement of contaminant, such as DNAPL, from heterogeneous soil (Mamun et al. 2002).
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Antunes, Marcelo, Hooman Abbasi i José Ignacio Velasco. "The Effect of Microcellular Structure on the Dynamic Mechanical Thermal Properties of High-Performance Nanocomposite Foams Made of Graphene Nanoplatelets-Filled Polysulfone". Polymers 13, nr 3 (29.01.2021): 437. http://dx.doi.org/10.3390/polym13030437.
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Polysulfone nanocomposite foams containing variable amounts of graphene nanoplatelets (0–10 wt%) were prepared by water vapor-induced phase separation (WVIPS) and supercritical CO2 (scCO2) dissolution. WVIPS foams with two ranges of relative densities were considered, namely, between 0.23 and 0.41 and between 0.34 and 0.46. Foams prepared by scCO2 dissolution (0.0–2.0 wt% GnP) were obtained with a relative density range between 0.35 and 0.45. Although the addition of GnP affected the cellular structure of all foams, they had a bigger influence in WVIPS foams. The storage modulus increased for all foams with increasing relative density and GnP’s concentration, except for WVIPS PSU-GnP foams, as they developed open/interconnected cellular structures during foaming. Comparatively, foams prepared by scCO2 dissolution showed higher specific storage moduli than similar WVIPS foams (same relative density and GnP content), explained by the microcellular structure of scCO2 foams. As a result of the plasticizing effect of CO2, PSU foams prepared by scCO2 showed lower glass transition temperatures than WVIPS foams, with the two series of these foams displaying decreasing values with incrementing the amount of GnP.
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Noureddine, Boumdouha, Safidine Zitouni, Boudiaf Achraf, Chabane Houssém, Duchet-Rumeau Jannick i Gerard Jean-François. "Development and Characterization of Tailored Polyurethane Foams for Shock Absorption". Applied Sciences 12, nr 4 (20.02.2022): 2206. http://dx.doi.org/10.3390/app12042206.
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In this paper, different types of polyurethane foams (PUR) having various chemical compositions have been produced with a specific density to monitor the microstructure as much as possible. The foam may have a preferential orientation in the cell structure. The cellular polyurethane tends to have stubborn, typical cellular systems with strong overlap reversibility. Free expansion under atmospheric pressure enables formulas to grow until they are refined. Moreover, the physicochemical characterization of the developed foams was carried out. They later are described by apparent density, Shore hardness, Raman spectroscopy analysis, X-ray diffraction analysis, FTIR, TGA, DSC, and compression tests. The detailed structural characterization was used by scanning electron microscope (SEM) and an optical microscope (MO) to visualize the alveolar polymer’s semi-opened cells, highlighting the opened-cell morphology and chemical irregularities. Polyurethane foams with different structural variables have a spectrum characterization that influences the phase separation and topography of polyurethane foam areas because their bonding capability with hydrogen depends on chain extender nature. These studies may aid in shock absorption production; a methodology of elaboration and characterization of filled polyurethane foams is proposed.
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Anbuchezhiyan, G., B. Mohan i R. V. Karthikeyan. "Development of Magnesium Matrix Syntactic Foams Processed through Powder Metallurgy Techniques". Applied Mechanics and Materials 766-767 (czerwiec 2015): 281–86. http://dx.doi.org/10.4028/www.scientific.net/amm.766-767.281.
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The presence of Hollow particles instead of gas porosity provides a closed cell structure called Syntactic foams. Syntactic foams have gained significant attention in recent years due to their low density, moisture absorption and thermal expansion coefficient compared to other cellular materials, such as open and closed cell structured foams. In terms of mechanical behavior, it is generally more insightful to compare metal matrix syntactic foams with metal foams and metal matrix composites. In comparison with metal foams, they have high compressive yield strength and more homogenous mechanical properties but usually higher densities and lower plasticity. In comparison with metal matrix composites, they have lower strength but offer compressibility, which is not existence in metal matrix composites. Syntactic foams have been extensively studied for aluminum based metal matricesand polymer matrices. Importance in magnesium foams is increasing in recent periods due to their very low density. Only a few studies are available on magnesium matrix syntactic foams processed through powder metallurgy techniques. This review presents an overview of hollow particle filled magnesium matrix (AZ91D/microballons) syntactic foams using powder metallurgy methods.
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Hilyard, N. C., i P. Collier. "A Structural Model for Air Flow in Flexible PUR Foams". Cellular Polymers 6, nr 6 (listopad 1987): 9–26. http://dx.doi.org/10.1177/026248938700600602.
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A new structural model based on the two term fluid flow equation of Gent and Rusch is described. The classical theory of flow through porous packed beds is used to relate the permeability and flow inertia coefficients to the average cell diameter, the tortuosity of the flow path and a skin friction coefficient. The model is used to predict how air flow is influenced by compression of the cellular matrix. Results of laboratory investigations are presented and compared with the model. For the most part good agreement is obtained for compressions up to about 60%. It is shown that the permeability is governed by cell size and the flow inertia parameter is governed by cell size, tortuosity and a roughness parameter. It is concluded from data obtained from crushed and uncrushed foams that the roughness parameter is strongly associated with cell membrane density. It is proposed that the experimental procedure can be used to quantify separately the effects of cell size and cell membranes.
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Olszewski, Adam, Paulina Kosmela, Adam Piasecki, Mateusz Barczewski i Aleksander Hejna. "The Impact of Isocyanate Index and Filler Functionalities on the Performance of Flexible Foamed Polyurethane/Ground Tire Rubber Composites". Polymers 14, nr 24 (19.12.2022): 5558. http://dx.doi.org/10.3390/polym14245558.
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The structure and performance of polyurethane (PU) foams are strongly driven by the stoichiometry of the polyaddition reaction, quantitatively described by the isocyanate index. It determines the balance between isocyanate and hydroxyl groups in the reacting system and is affected by the introduction of additional functionalities originated, e.g., from applied fillers. Nevertheless, this issue is hardly taken into account in research works. Herein, the structure and performance of PU/ground tire rubber (GTR) composites differing in their isocyanate index (from 0.8 to 1.2) and prepared with and without considering the GTR functionalities in formulation development were investigated. Incorporating GTR into the PU matrix led to a reduction in average cell diameter (from 2 to 30% depending on the isocyanate index) compared to unfilled foams. However, formulation adjustments did not show a significant impact on cellular structure. The only decrease in open cell content was noted, from 10% for the 0.9 index to 40% for 1.2. Such changes were related to the increasing strength of the PU cellular structure able to maintain inside the increasing amount of carbon dioxide. On the other hand, considering hydroxyl values of GTR noticeably affected the thermomechanical performance of composites. The shift of glass transition temperature (Tg), even by 10 °C for 1.2 isocyanate index, enhanced the performance of materials, which was expressed in an 8–62% drop in the composite performance factor, pointing to the enhanced reinforcing effect resulting from filler incorporation. The stiffening of foams, related to the variations in PU segmental structure, also caused minor changes in the course of thermal degradation of PU/GTR composites due to the inferior thermal stability of hard segments. The obtained results provide important insights into the development of formulations of PU composites filled with materials containing reactive functional groups able to disrupt the stoichiometric balance of the polyaddition reaction.
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Greene, W. B., D. S. Raso, M. C. Willingham, R. M. Silver, A. S. Greene i J. A. Makeeff. "Silicon in rat knee joints after subcutaneous injection of dimethylpolysiloxane gel breast implant material". Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994): 182–83. http://dx.doi.org/10.1017/s0424820100168645.
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Clinically, Electron Probe X-ray Microanalysis (EPMA) studies have detected elemental silicon (Si) in remote sites of chronic inflammation (skin, finger, knee and elbow) in patients who were previously implanted with a silicone polymer-filled breast augmentation prostheses. Subsequent biopsy material obtained from the fibrous tissue capsule surrounding the implant was found to contain abundant silicon in foamy macrophages. In the remote biopsies, the elemental silicon is believed to be derived from macrophages that originated in the connective tissue capsule.In order to study the possible cellular distribution of silicone in an animal model, 120gm female SD rats were injected subcutaneously at the nape of the neck with 2ml of breast prothesis silicone gel (1.7% of total body weight). The injection correlates to a 0.9kg silicone prostheses implanted in a 55kg human recipient. Adjuvant arthritis was produced after 8 weeks in Si injected and control animals by the subdermal injection of 0.75 mg of heat killed Mycobacterium butyrium (MB) over the left rear knee. Si injected only, Si plus MB, MB only and untreated control animals were sacrificed by Metofane inhalation at 16, 24 and 32 week intervals and tissues were processed for routine light microscopy and TEM. Decalcified knee joints were sectioned longitudinally and sent to JEOL USA, Inc. for blind, collaborative SEM x-ray microanalysis studies.
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Yetgin, Salih Hakan, i Hüseyin Unal. "A study of the cell morphology and mechanical properties of bumper material PP-T-EPDM composite foam". Cellular Polymers, 23.01.2023, 026248932311513. http://dx.doi.org/10.1177/02624893231151363.
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In this study, cellular polypropylene based composite foams were prepared using an universal injection moulding machine. The chemical foaming agent was added to neat polypropylene (PP) polymer, talc filled polypropylene (PP-T) composite and talc filled polypropylene/ethylene-propylene-diene blend (PP-T-EPDM) composite materials at the ratio of 1% and 2% by weight. The influence of foaming agent content on the mechanical and cellular properties of both neat PP polymer and PP composites was investigated. The results showed that the tensile strength, tensile modulus, impact strength, hardness, cell diameter, foam density and viscosity values and skin layer thickness decreased while volume expansion ratio increased with the increment in chemical blowing agent content.
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Walong, Alif, Bencha Thongnuanchan, Nattapon Uthaipan, Tadamoto Sakai i Natinee Lopattananon. "Enhancing cellular structure, mechanical properties, thermal stability and flame retardation of EVA/NR blend nanocomposite foams by silicon dioxide-based flame retardant". Progress in Rubber, Plastics and Recycling Technology, 31.08.2021, 147776062110420. http://dx.doi.org/10.1177/14777606211042028.
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Flame retardant rubber foams of ethylene vinyl acetate (EVA)/natural rubber (NR)/layered silicate blends filled with silicon dioxide (SiO2) were prepared by using azodicarbonamide (ADC) as a blowing agent. Specifically, SiO2 was added in EVA/NR blend nanocomposites to produce good flame retardant foams. The properties of EVA/NR blend nanocomposite foams with different SiO2 loading (0, 20, 30, 40 parts per hundred rubber, phr) were investigated through transmission electron microscopy (TEM), scanning electron microscopy (SEM), rheological property test, mechanical property measurement, flammability tests, thermogravimetry analysis (TGA) and pyrolysis-gas chromatography-mass spectrometry (Pyrolysis-GC-MS). Compared with the simple EVA/NR blend nanocomposite, the added SiO2 increased the blend compatibility between EVA and NR phases and melt strength/viscosity of the EVA/NR blend nanocomposites, thus promoting cellular structure of the EVA/NR nanocomposite foams. Increasing SiO2 loading resulted in higher cell density, smaller cell size, and lower volume of void. These improvements caused higher strength and elastomeric recovery. The LOI test results showed that flame retardancy of the EVA/NR blend nanocomposite foams increased at higher SiO2 loading as a result of formation of insulation silicon dioxide-based char. TGA and pyrolysis-GC-MS analyses also validated the finding that the silicon dioxide-based char in the foamed samples containing higher SiO2 loading was more effective on improving thermal stability, which was responsible for lower material combustibility and better flame retardancy. Based on our finding, it was concluded that a good flame retardant EVA/NR blend nanocomposite foam with the best improvement in strength and elastomeric recovery was achieved when combined with 40 phr SiO2.
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Du, Ngoc Uy Lan, Christian Bethke, Shuaiping Gong, Volker Altstaedt i Holger Ruckdaeschel. "Foaming epoxy-amine-carbamate: The effect of different neat amines on rheological and cellular morphology". Journal of Cellular Plastics, 23.03.2023, 0021955X2311660. http://dx.doi.org/10.1177/0021955x231166007.
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The use of carbamate to foam epoxy depends significantly on the precured modulus to stabilize the cellular structure. The optimum precured modulus is developed from the reaction of epoxy resin and the neat amine. The selection of the neat amine relies on its reaction temperature with epoxy, which is required to be below the decomposition temperature of carbamate. This study investigates the effect of three different neat amines on the rheological behavior of foaming epoxy-carbamate-amine. They are bisphenol-A diglycidyl ether epoxy (DGEBA), isophorone diamine carbamate (IDPA.CO2), N-aminoethylpiperazine (AEP), 2,4-Diamino-1-methyl-cyclohexan (DMC) and isophorone diamine (IDPA). The mixtures of DGEBA-amine-carbamate are filled in 25% and 75% of the volume of a closed mold. Precuring is carried out at 60°C for 2 h. The foaming and complete curing are conducted at 180°C for 1 h. Having H-active at piperazine, AEP reacts with DGEBA faster and develops a higher precured modulus compared to DMC and IDPA. It is important to note that DGEBA-AEP-IDPA.CO2 exhibits viscoelastic behavior beyond 138°C, seen by its rheological storage modulus lower than loss modulus and its tan delta larger than 1. The reaction between DGEBA and the H-active piperazine of AEP leads only to linear linkage and is unable to further crosslink compared to the primary amine (-NH2). This results in a lower glass transition temperature Tg of DGEBA-AEP-IPDA.CO2. The effect of amine on foaming is more obviously at 25% filling level. DGEBA-AEP-IPDA.CO2 has more spherical and homogeneous cellular structure and the density of 285 kg/m3. Having quite similar chemical structure, both DGEBA-DMC-IPDA.CO2 and DGEBA-IPDA-IPDA.CO2 produce the epoxy foams having cell-interconnection and coalescence; their densities are also similar 301 kg/m3 and 305 kg/m3, respectively. All the foams are closed-cell at 75% of filling level. The cell morphologies are well reflecting the foaming modulus and tan delta behavior.
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Walong, Alif, Bencha Thongnuanchan, Tadamoto Sakai i Natinee Lopattananon. "Influence of silicon dioxide addition and processing methods on structure, thermal stability and flame retardancy of EVA/NR blend nanocomposite foams". Progress in Rubber, Plastics and Recycling Technology, 2.09.2020, 147776062095343. http://dx.doi.org/10.1177/1477760620953437.
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Rubber nanocomposite foams based on 60/40 ethylene vinyl acetate (EVA)/natural rubber (NR) were melt-mixed with flame retardant silicon dioxide (SiO2) (20 parts per hundred rubber, phr), and foamed by compression molding process. In this study, the effect of mixing phenomena of SiO2 through two different compounding techniques such as direct mixing (DM) and phase selective mixing (PSM) methods on structure, thermal stability, combustility and flame retardancy of EVA/NR blend nanocomposite foams were investigated. DM method is a melt mixing of EVA, NR, layered silicate and SiO2, followed by foaming. PSM is a new method based on pre-mixing EVA with SiO2, then melt mixing of EVA/SiO2 masterbatch with NR and layered silicate, and finally foaming. Based on TEM technique, it was found that the SiO2 was exclusively located in dispersed NR phase for the sample prepared by DM method, and the SiO2 was preferably dispersed in continuous EVA matrix when PSM method was employed. However, the different mixing methods did not significantly alter their cellular structures. The thermal stability and char residue content of foamed samples with SiO2 increased obviously when compared with those of corresponding foams without SiO2. The results based on limiting oxygen index (LOI) test and oxygen bomb calorimetry indicated that the foams combined with SiO2 had better combustion resistance and flame retardancy due to barrier effect of thermally stable silicon-based char layer. Further, the SiO2 filled foamed system obtained from the PSM method showed a higher degree of improvement in thermal stability, combustion resistance and flame retardancy than that of DM method because the homogeneous dispersion of SiO2 in EVA matrix rather than the selective dispersion in NR phase. This resulted in the continuity of flame retardant EVA/SiO2 phase in the 60/40 EVA/NR nanocomposite foams, which exerted more efficient fire barrier of the silicon-based char layer.
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Wang, Jiankang, Houjian Fa i Hongwei Lu. "Investigation into the effects of foaming variables on the cellular structure and expansion ratio of foamed TPU using response surface methodology". Journal of Cellular Plastics, 16.03.2023, 0021955X2311653. http://dx.doi.org/10.1177/0021955x231165344.
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Thermoplastic polyurethane elastomer (TPU) foams were prepared using the high-pressure autoclave with supercritical fluid carbon dioxide (SC-CO2). The effects of foaming variables (i.e. saturation temperature, saturation pressure, and depressurization rate) on cellular structure and expansion ratio were investigated. The model between expansion ratio and foaming variables was constructed using the Box-Behnken design (BBD) of response surface methodology (RSM), and analysis of variance (ANOVA) was conducted to evaluate the validity and significance of the model. Finally, the interactive effects of foaming variables on the expansion ratio were investigated, and the expansion ratios of maximum and center point from numerical model were verified by experiment. The result showed higher saturation pressure and depressurization rate resulted in the more uniform cellular structure and higher cell density, however the higher saturation temperature resulted in the bigger cell and nonuniform structure. The ranges of average cell diameter and cell density were 15.26–45.4 μm and 0.32 × 108 to 6.24 × 108 cells/cm3, respectively. The model obtained using BBD of RSM was valid to predict the expansion ratio in the design window. The saturation temperature was the most important factor influencing the expansion ratio. With the increase of saturation temperature, the expansion ratio always increases in the design window. The maximum expansion ratio from numerical optimization was 4.91, which was located at saturation temperature 190°C, saturation pressure 12.51 MPa, and depressurization rate 5 MPa/s, and the corresponding experiment value was 4.56. The error between them was 7.13%.