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Du, Changling, David Anthony Fikhman i Mary Beth Browning Monroe. "Shape Memory Polymer Foams with Phenolic Acid-Based Antioxidant Properties". Antioxidants 11, nr 6 (1.06.2022): 1105. http://dx.doi.org/10.3390/antiox11061105.
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Phenolic acids (PAs) are natural antioxidant agents in the plant kingdom that are part of the human diet. The introduction of naturally occurring PAs into the network of synthetic shape memory polymer (SMP) polyurethane (PU) foams during foam fabrication can impart antioxidant properties to the resulting scaffolds. In previous work, PA-containing SMP foams were synthesized to provide materials that retained the desirable shape memory properties of SMP PU foams with additional antimicrobial properties that were derived from PAs. Here, we explore the impact of PA incorporation on SMP foam antioxidant properties. We investigated the antioxidant effects of PA-containing SMP foams in terms of in vitro oxidative degradation resistance and cellular antioxidant activity. The PA foams showed surprising variability; p-coumaric acid (PCA)-based SMP foams exhibited the most potent antioxidant properties in terms of slowing oxidative degradation in H2O2. However, PCA foams did not effectively reduce reactive oxygen species (ROS) in short-term cellular assays. Vanillic acid (VA)- and ferulic acid (FA)-based SMP foams slowed oxidative degradation in H2O2 to lesser extents than the PCA foams, but they demonstrated higher capabilities for scavenging ROS to alter cellular activity. All PA foams exhibited a continuous release of PAs over two weeks. Based on these results, we hypothesize that PAs must be released from SMP foams to provide adequate antioxidant properties; slower release may enable higher resistance to long-term oxidative degradation, and faster release may result in higher cellular antioxidant effects. Overall, PCA, VA, and FA foams provide a new tool for tuning oxidative degradation rates and extending potential foam lifetime in the wound. VA and FA foams induced cellular antioxidant activity that could help promote wound healing by scavenging ROS and protecting cells. This work could contribute a wound dressing material that safely releases antimicrobial and antioxidant PAs into the wound at a continuous rate to ideally improve healing outcomes. Furthermore, this methodology could be applied to other oxidatively degradable biomaterial systems to enhance control over degradation rates and to provide multifunctional scaffolds for healing.
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Woolley, W. D. "Are Foams a Fire Hazard?" Cellular Polymers 4, nr 2 (marzec 1985): 81–115. http://dx.doi.org/10.1177/026248938500400201.
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Over the last decade growing concern has been voiced about the fire hazards of cellular polymers used in building and transport applications. Some of this concern is justified as illustrated by recent fires and experimental simulations where rapid fire development has occurred with potential for death or injury from the spread of combustion products within very short periods of time. Many technical difficulties have arisen in the use of synthetic foams. Their introduction has presented problems since the test methods used traditionally to assess performance have been somewhat inadequate to cope effectively with the new properties of polymers and polymer composites. Major progress is being made in understanding the fire behaviour of cellular polymers. This involves studies of ignitability, flame spread, heat release, and the production of smoke and toxic gases. In parallel to this, important technical advances have been made by industry in the development of new formulations of cellular materials and composites with improved fire behaviour. It is now time to bring together the current knowledge of all aspects of cellular polymers in fire so that further applications of these materials can continue safely allowing full use of their potential for improving the comfort and efficiency of our lives. This paper examines the basic problems which have occurred during the use of cellular polymers with regard to fire. Recent fire scenarios which have attracted attention to cellular materials and the ways the hazard is being addressed and mitigated are discussed. To aid this the paper also examines the basic mechanisms of burning of the polymers and the associated hazard to life. Finally it should be emphasised that much of this paper is directed, intentionally, to understanding circumstances where untoward events may occur to place life in jeopardy. This approach is necessary for the elimination of potentially hazardous situations and to enable the continuing use of cellular polymers in a safe way.
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Suethao, Supitta, Darshil U. Shah i Wirasak Smitthipong. "Recent Progress in Processing Functionally Graded Polymer Foams". Materials 13, nr 18 (13.09.2020): 4060. http://dx.doi.org/10.3390/ma13184060.
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Polymer foams are an important class of engineering material that are finding diverse applications, including as structural parts in automotive industry, insulation in construction, core materials for sandwich composites, and cushioning in mattresses. The vast majority of these manufactured foams are homogeneous with respect to porosity and structural properties. In contrast, while cellular materials are also ubiquitous in nature, nature mostly fabricates heterogeneous foams, e.g., cellulosic plant stems like bamboo, or a human femur bone. Foams with such engineered porosity distribution (graded density structure) have useful property gradients and are referred to as functionally graded foams. Functionally graded polymer foams are one of the key emerging innovations in polymer foam technology. They allow enhancement in properties such as energy absorption, more efficient use of material, and better design for specific applications, such as helmets and tissue restorative scaffolds. Here, following an overview of key processing parameters for polymer foams, we explore recent developments in processing functionally graded polymer foams and their emerging structures and properties. Processes can be as simple as utilizing different surface materials from which the foam forms, to as complex as using microfluidics. We also highlight principal challenges that need addressing in future research, the key one being development of viable generic processes that allow (complete) control and tailoring of porosity distribution on an application-by-application basis.
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Hamdi, Ouassim, i Denis Rodrigue. "Auxetic Polymer Foams: Production, Modeling and Applications". Current Applied Polymer Science 4, nr 3 (grudzień 2021): 159–74. http://dx.doi.org/10.2174/2452271604666211130123921.
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: Auxetic materials have high potential due to their exceptional properties resulting from a negative Poisson’s ratio. Recently, several auxetic polymer-based materials have been developed. In fact, several applications are looking for a lightweight material (less material consumed in production and transport) while having high mechanical performances (impact absorption, rigidity, strength, resistance, etc.). So, a balance between density and toughness/strength is highly important, especially for military, sporting, and transport applications. So auxetic materials (especially foams) can provide high impact protection while limiting the material’s weight. This article presents a review of recent advances with a focus on auxetic polymers, with particular emphasis on the auxetic polymer foams in terms of their fabrication methods and processing conditions (depending on the nature of the cellular structure), the effect of the fabrication parameters on their final properties, as well as their models and potential applications.
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Kishimoto, Satoshi, Toru Shimizu, Fu Xing Yin, Kimiyoshi Naito i Yoshihisa Tanaka. "Mechanical Properties of Metallic Closed Cellular Materials Containing Polymer Fabricated by Polymer Penetration". Materials Science Forum 654-656 (czerwiec 2010): 2628–31. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.2628.
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Metallic closed cellular materials containing polymer were fabricated by the penetrating polymer into metal foam. The aluminum and stainless steel foams were selected for the metal foam and epoxy resin and polyurethane resin were selected for the penetrated polymer. The many kinds of mechanical properties of this material were measured. The results of the compressive tests show that these materials have different stress-strain curves among the specimens that containing different materials in the cells. Also, this metallic closed cellular materials containing polymer have higher compressive strength, higher Young’s modules, higher energy absorption and higher internal friction than that of metallic closed cellular material without any polymer.
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Fan, Zhi Geng, Chang Qing Chen i Wen Jun Hu. "A Numerical Study on the Large Deformations of Polymer Foams with Spherical Pores". Advanced Materials Research 295-297 (lipiec 2011): 1581–85. http://dx.doi.org/10.4028/www.scientific.net/amr.295-297.1581.
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Cubic structures having spherical pores ranged as BCC and FCC lattices are constructed to simulate the microstructures of cellular polymers with various relative densities. The Mooney-Rivlin strain energy potential model is adopted to characterize the hyperelasticity of the constituent solid from which the foams are made. Finite element analysis on the influences of the polymer hyperelasticity upon the macroscopic mechanical properties of the foams is carried out. Numerical results show that there is no obvious buckling plateau segment in the uniaxial compressive stress-strain curves of the regular spherical cell models as most low density foams have. Moreover, it is found that the initial tangent modulus is a power function of the foam’s relative density, and the index is smaller than 2 for lower relative density models, bigger than 2 for moderate relative density models, and closed to 2 for higher relative density models.
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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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Román-Lorza, S., M. A. Rodriguez-Perez i J. A. De Saja Sáez. "Cellular Structure of Halogen-Free Flame Retardant Foams Based on LDPE". Cellular Polymers 28, nr 4 (lipiec 2009): 249–68. http://dx.doi.org/10.1177/026248930902800402.
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Composites of LDPE/ATH (up to 70 wt.%) were foamed to create new materials with good fire retardancy properties and low weight, proving the feasibility of developing cellular structures when high levels of inorganic fillers are included. An experimental study was carried out to explore the effects of chemical composition on cellular structure as well as the effect of structure on their thermal, mechanical and combustion properties. Samples fabrication was carried out using an improved compression moulding route consisting of polymer compounding, precursor preparation and foaming under pressure. The polymer matrix consisted of low density polyethylene as well as certain amount of LLDPE-g-MAH as compatibilizer agent. The inorganic filler used was aluminium trihydroxide (ATH) ranging from 0 wt.% to 70 wt.%. Furthermore, azodicarbonamide (ADC) was used as chemical blowing agent. Foamed samples with cell sizes below 100 microns were produced. These samples showed similar fire retardancy than their solid precursors. The compatibilization was proved indispensable to achieve a good adhesion between mineral filler and polymer and to improve the cellular structure. The increase of the amount of filler has an interesting effect on the cellular structure, going from a closed-cell (at low contents) to an open-cell (at higher contents) cellular structure. As a result of this investigation, halogen-free flame retardant cellular materials were processed, leading to a notable reduction of material compared to the solid one and to new properties which can result in new applications.
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Soriano-Corral, F., L. A. Calva-Nava, J. F. Hernández-Gámez, E. Hernández-Hernández, P. González-Morones, C. A. Ávila-Orta, G. Soria-Arguello, Heidi A. Fonseca-Florido, Carlos A. Covarrubias-Gordillo i Ramón E. Díaz de León-Gómez. "Influence of Ethylene Plasma Treatment of Agave Fiber on the Cellular Morphology and Compressive Properties of Low-Density Polyethylene/Ethylene Vinyl Acetate Copolymer/Agave Fiber Composite Foams". International Journal of Polymer Science 2021 (25.03.2021): 1–13. http://dx.doi.org/10.1155/2021/9150310.
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Agave fibers (AF) were incorporated either pristine (AFp) or surface treated by ethylene plasma (AFm) in low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) blends at a ratio of 1 : 1 and foamed by chemical means. The role of the AF content (3, 6, 9, 12, and 15 wt.%) and its surface modification on the cellular morphology and mechanical properties of LDPE/EVA/AF foams under compression is investigated herein. Fourier transform-infrared spectroscopy, contact angle, and water suspension of AF suggest that plasma treatment using ethylene successfully modifies the surface nature of AF from hydrophilic to hydrophobic. AF and the surface treatment have an important role on the morphological properties of the foams. Composite foams reinforced with 12 wt.% AFm exhibited the highest mechanical properties improvements. At this fiber content, the composite foams enhanced 30% of the compressive modulus and 23% of the energy absorption under compression with respect to the neat polymer blend foam, as a result to the formation of more uniform cells with smaller size and the enhancement of compatibility and spatial distribution of the AFm in the polymer composite foams due to thin clusters of polyethylene-like polymer deposited on the AF surface.
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Harikrishnan, S., Kamlesh Kumar, V. Venkateswara Rao i Ajay Misra. "Shock Wave Behaviour of Polymeric Materials for Detonation Waveshapers". Defence Science Journal 71, nr 6 (22.10.2021): 730–36. http://dx.doi.org/10.14429/dsj.71.16943.
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This paper discusses the experimental determination of explosive shock attenuation parameters of four different polymers viz., Teflon, Phenol formaldehyde, Polyethylene foam and Polypropylene foam. These polymers are candidate materials for waveshapers in shaped charge warheads. Cylindrical specimens of the polymer materials were subjected to explosive shock loading by the detonation of RDX:Wax (95:5). Shock arrival time was measured using piezo-wafers positioned at known spatial intervals in the specimens. Initial shock velocity, stabilised shock velocity and attenuation constant were determined. These parameters are essential for the design of waveshapers. Foams have better shock attenuating properties compared to solids due to their cellular structure. Polypropylene foam has the highest shock attenuating characteristic among the four materials studied.
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Rodríguez-Pérez, M. A. "The Effect of Chemical Composition, Density and Cellular Structure on the Dynamic Mechanical Response of Polyolefin Foams". Cellular Polymers 21, nr 2 (marzec 2002): 117–36. http://dx.doi.org/10.1177/026248930202100202.
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Dynamic mechanical analysis has been applied to a collection of polyolefin foams with different chemical compositions and densities and manufactured from different routes. The effect of different foam characteristics, such as density, polymer morphology and cellular structure on the dynamic mechanical response is analysed. The way in which this technique can be used to obtain information about the polymer morphology of the foam is presented. In addition, examples of the use of this technique in studying specific problems are illustrated.
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Aghelinejad, Mohammadmehdi, i Siu Leung. "Thermoelectric Nanocomposite Foams Using Non-Conducting Polymers with Hybrid 1D and 2D Nanofillers". Materials 11, nr 9 (18.09.2018): 1757. http://dx.doi.org/10.3390/ma11091757.
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A facile processing strategy to fabricate thermoelectric (TE) polymer nanocomposite foams with non-conducting polymers is reported in this study. Multilayered networks of graphene nanoplatelets (GnPs) and multi-walled carbon nanotubes (MWCNTs) are deposited on macroporous polyvinylidene fluoride (PVDF) foam templates using a layer-by-layer (LBL) assembly technique. The open cellular structures of foam templates provide a platform to form segregated 3D networks consisting of one-dimensional (1D) and/or two-dimensional (2D) carbon nanoparticles. Hybrid nanostructures of GnP and MWCNT networks synergistically enhance the material system’s electrical conductivity. Furthermore, the polymer foam substrates possess high porosity to provide ultra-low thermal conductivity without compromising the electrical conductivity of the TE nanocomposites. With an extremely low GnP loading (i.e., ~1.5 vol.%), the macroporous PVDF nanocomposites exhibit a thermoelectric figure-of-merit of ~10−3. To the best of our knowledge, this ZT value is the highest value reported for organic TE materials using non-conducting polymers and MWCNT/GnP nanofillers. The proposed technique represents an industrially viable approach to fabricate organic TE materials with enhanced energy conversion efficiencies. The current study demonstrates the potential to develop light-weight, low-cost, and flexible TE materials for green energy generation.
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Kishimoto, Satoshi. "Closed Cellular Materials for Smart Materials". Materials Science Forum 638-642 (styczeń 2010): 2074–79. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2074.
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New methods to fabricate a metallic closed cellular material for smart materials using an isostatic pressing and penetrating method are introduced. Powder particles of polymer or ceramics coated with a metal layer using electro-less plating were pressed into pellets and sintered at high temperature. These powder particles were sintered by spark plasma sintering (SPS) method. Closed cellular materials including polymer were fabricated by penetrating polymer into metallic foams. Many kinds of metallic closed cellular materials including different materials from that of cell walls were tried to fabricate. The physical and mechanical properties of these materials were measured. The results of the compressive tests show that this material has high-energy absorption and the result of measuring the internal friction show that the internal friction of these materials is larger than that of pure aluminum.
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Sun, Jiaotong, i Dan Zhou. "Advances in Graphene–Polymer Nanocomposite Foams for Electromagnetic Interference Shielding". Polymers 15, nr 15 (29.07.2023): 3235. http://dx.doi.org/10.3390/polym15153235.
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With the continuous advancement of wireless communication technology, the use of electromagnetic radiation has led to issues such as electromagnetic interference and pollution. To address the problem of electromagnetic radiation, there is a growing need for high-performance electromagnetic shielding materials. Graphene, a unique carbon nanomaterial with a two-dimensional structure and exceptional electrical and mechanical properties, offers advantages such as flexibility, light weight, good chemical stability, and high electromagnetic shielding efficiency. Consequently, it has emerged as an ideal filler in electromagnetic shielding composites, garnering significant attention. In order to meet the requirements of high efficiency and low weight for electromagnetic shielding materials, researchers have explored the use of graphene–polymer nanocomposite foams with a cellular structure. This mini-review provides an overview of the common methods used to prepare graphene–polymer nanocomposite foams and highlights the electromagnetic shielding effectiveness of some representative nanocomposite foams. Additionally, the future prospects for the development of graphene–polymer nanocomposite foams as electromagnetic shielding materials are discussed.
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Fei, Yanpei, Wei Fang, Mingqiang Zhong, Jiangming Jin, Ping Fan, Jintao Yang, Zhengdong Fei, Lixin Xu i Feng Chen. "Extrusion Foaming of Lightweight Polystyrene Composite Foams with Controllable Cellular Structure for Sound Absorption Application". Polymers 11, nr 1 (9.01.2019): 106. http://dx.doi.org/10.3390/polym11010106.
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Polymer foams are promising for sound absorption applications. In order to process an industrial product, a series of polystyrene (PS) composite foams were prepared by continuous extrusion foaming assisted by supercritical CO2. Because the cell size and cell density were the key to determine the sound absorption coefficient at normal incidence, the bio-resource lignin was employed for the first time to control the cellular structure on basis of hetero-nucleation effect. The sound absorption range of the PS/lignin composite foams was corresponding to the cellular structure and lignin content. As a result, the maximum sound absorption coefficient at normal incidence was higher than 0.90. For a comparison, multiwall carbon nanotube (MWCNT) and micro graphite (mGr) particles were also used as the nucleation agent during the foaming process, respectively, which were more effective on the hetero-nucleation effect. The mechanical property and thermal stability of various foams were measured as well. Lignin showed a fire retardant effect in PS composite foam.
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Kankanamalage, Pulitha G., Jake Puppo, Denver Schaffarzick i Bhisham Sharma. "Aluminum foams with complex pore topologies for acoustical applications". Journal of the Acoustical Society of America 153, nr 3_supplement (1.03.2023): A38. http://dx.doi.org/10.1121/10.0018067.
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Metal foams are used in various industries due to the great variety of properties they possess such as high strength-to-weight ratio, high energy absorption, and the ability to endure extreme conditions. However, despite their desirable properties, traditional metal foams lack acoustic absorption properties because of their stochastic open porous structure—a function of the foaming process. Additive manufacturing (AM) can allow the fabrication of more complex foams; however, current metal AM methods provide significant processing and scalability challenges, especially in printing aluminum parts. Here, we present an alternative method for fabricating open-celled aluminum sound absorbers with controlled cellular architectures. The method relies on modeling the cellular templates using an implicit, field-based modeling method. The templates are then fabricated by combining polymer-based AM techniques and converted into aluminum Duocel® foams using ERG Aerospace Corporation’s proprietary foaming technology. The acoustical properties of the fabricated foams are then measured using a normal incidence impedance tube method. Our results show that this method allows the fabrication of highly complex cellular architectures that may be optimized to obtain application-specific multifunctional performance.
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Li, Ruo Song, Lu Li i Tao Fang. "Producing Microporous PMMA with Supercritical CO2 and the Research on its Properties". Advanced Materials Research 560-561 (sierpień 2012): 873–79. http://dx.doi.org/10.4028/www.scientific.net/amr.560-561.873.
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The research on microcellular polymer foam (MPF) is significant in plastic processing industry. In this study, polymethyl methacrylate (PMMA) was considered to be the foam matrix via a preliminary experiment. It is because that compared with other polymers, it is easier to swell and plasticize with supercritical CO2 (SCCO2). Moreover, its absorbability in SCCO2 is much higher. The above research provides guidance for the preparation of microcellular polymer blend foams. In order to study the foam process and the optimum experimental conditions, the average cellular sizes were measured by controlling the saturation pressure, temperature and the soak time on the basis of the orthogonal experiment. The microporous structure was observed by scanning electron microscope (SEM). Then the optimum amount of nano-fillers was achieved by solution and melt blending. In addition, the mechanical properties of MPF were measured to explore the change in foaming. The obtained results would provide better insight to planners and operators in the field of chemical engineering to handle the uncertainties effectively.
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Borrero-López, Antonio M., Vincent Nicolas, Zelie Marie, Alain Celzard i Vanessa Fierro. "A Review of Rigid Polymeric Cellular Foams and Their Greener Tannin-Based Alternatives". Polymers 14, nr 19 (23.09.2022): 3974. http://dx.doi.org/10.3390/polym14193974.
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This review focuses on the description of the main processes and materials used for the formulation of rigid polymer foams. Polyurethanes and their derivatives, as well as phenolic systems, are described, and their main components, foaming routes, end of life, and recycling are considered. Due to environmental concerns and the need to find bio-based alternatives for these products, special attention is given to a recent class of polymeric foams: tannin-based foams. In addition to their formulation and foaming procedures, their main structural, thermal, mechanical, and fire resistance properties are described in detail, with emphasis on their advanced applications and recycling routes. These systems have been shown to possess very interesting properties that allow them to be considered as potential substitutes for non-renewable rigid polymeric cellular foams.
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Laguna-Gutierrez, Ester, Javier Pinto, Vipin Kumar, Maria L. Rodriguez-Mendez i Miguel A. Rodriguez-Perez. "Improving the extensional rheological properties and foamability of high-density polyethylene by means of chemical crosslinking". Journal of Cellular Plastics 54, nr 2 (5.12.2016): 333–57. http://dx.doi.org/10.1177/0021955x16681454.
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Obtaining high-density polyethylene-based microcellular foams is a topic of interest due to the synergistic properties that can be obtained by the fact of achieving a microcellular structure using a polymer with a high number of interesting properties. However, due to the high crystallinity of this polymer, the production of low-density microcellular foams, by a physical foaming process, is not a simple task. In this work, the proposed solution to produce these materials is based on using crosslinked high-density polyethylenes. By crosslinking the polymer matrix, it is possible to increase the amount of gas available for foaming and also to improve the extensional rheological properties. In addition, the foaming time and the foaming temperature have also been modified with the aim of analyzing and understanding the mechanisms taking place during the foaming process to finally obtain cellular materials with low densities and improved cellular structures. The results indicate that cellular materials with relative densities of 0.37 and with cell sizes of approximately 2 µm can be produced from crosslinked high-density polyethylene using the appropriate crosslinking degree and foaming parameters.
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Betke, Ulf, Katja Schelm, Andreas Rodak i Michael Scheffler. "Cellular Nickel-Yttria/Zirconia (Ni–YSZ) Cermet Foams: Manufacturing, Microstructure and Properties". Materials 13, nr 11 (26.05.2020): 2437. http://dx.doi.org/10.3390/ma13112437.
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Open-celled ceramic composite foams were prepared from NiO and yttria-stabilized zirconia (YSZ) powders by the polymer sponge replication (Schwartzwalder) technique using the respective aqueous dispersions. Mechanically stable NiO–YSZ foams with an average porosity of 93 vol.% were obtained. After chemical reduction of the NiO phase with hydrogen, cellular Ni–YSZ cermet structures were obtained. They are characterized by an electric conductivity up to 19∙103 S∙m−1 which can be adjusted by both, the Ni volume fraction, and the sintering/reduction procedure. The NiO–YSZ ceramic foams, as well as the cellular Ni–YSZ cermets prepared therefrom, were characterized with respect to their microstructure by scanning electron microscopy, confocal Raman microscopy and X-ray diffraction with Rietveld analysis. In addition, the compressive strength, the electric conductivity and the thermal conductivity were determined. The collected data were then correlated to the sample microstructure and porosity and were also applied for modelling of the mechanical and electric properties of the bulk Ni–YSZ strut material.
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Izzard, V. G., C. H. Bradsell, H. Hadavinia, V. J. Morris, P. J. S. Foot, L. M. Wilson i K. Hewson. "Performance of Nylon Based Polymer Foams at Elevated Temperature under Tensile Loading". Key Engineering Materials 488-489 (wrzesień 2011): 286–89. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.286.
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One of the primary applications of polymer based cellular solids is to act as an energy absorbing material during impact where compressive strain rates may reach 500-800/s. In reality, impacts occur over a wide range of temperatures and velocities at different angles of incidence. Understanding and modelling the behaviour of the polymer foams requires characterisation of the material response in detail. The stress-strain response that covers both compressive and tensile behaviour for a wide range of strain rates and temperatures are needed to characterize the mechanical performance of polymer foams as polymeric foams are highly nonlinear materials that undergo large deformation in crashworthiness related cases. It is reported in literature that any increase or decrease in temperature over the glass transition region can cause changes by order of magnitude in elastic modulus of polymeric foams. However, creation of cross linking at high temperature can affect the elastic modulus. In this work, the behaviour of two, polyamide-6 (PA-6) based closed cell foams at elevated temperatures were investigated covering the glass transition temperature. This work presents the variation of elastic and tangent modulus of two low densities PA-6 and PA-6/polyolefin (Nylon alloy) based foams. Empirical equations have been proposed to allow the prediction of modulus over a temperature range of 23°C to 120°C for these materials.
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Himmelsbach, Andreas, Tobias Standau, Johannes Meuchelböck, Volker Altstädt i Holger Ruckdäschel. "Approach to quantify the resistance of polymeric foams against thermal load under compression". Journal of Polymer Engineering 42, nr 4 (10.02.2022): 277–87. http://dx.doi.org/10.1515/polyeng-2021-0312.
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Abstract Nowadays, numerous techniques are used to quantify the resistance of cellular polymers against a thermal load. These techniques differ in significance and reproducibility and are all dependent on foam density, structure (i.e., cell size and -distribution) and sample geometry. Very different behaviors are expected for extrusion- and bead foams, as well as for amorphous and semi-crystalline polymers. Moreover, established tests use temperature ramps which would lead to temperature gradients within the sample and thus to faulty results. In this study, we developed a new approach from an engineering perspective to minimize these influences. In this approach, the resistance against the thermal load is derived from a steady creep test with defined temperature steps under a mechanical load, which is specifically set for each foam sample depending on its static compression behavior at room temperature. The two-stage test therefore combines (i) a standard quasi-static compression test at room temperature and (ii) a creep test with stepwise increased thermal loading. For each foam type, a rather low mechanical load (stress) is determined from the quasi-static compression test at room temperature; low enough to remain below the collapse strength and avoid irreversible deformation (i.e., buckling and/or breaking of the cell walls). This load is then applied in a creep test where the temperature is increased in defined steps from room temperature to a temperature close to T g or T m . The stepwise increase and holding of the temperature for a defined time enables a homogeneous temperature in the test specimen. The approach was applied to (i) polystyrene extrusion and bead foams (i.e., XPS and EPS), which have different foam structure, (ii) amorphous and semi-crystalline bead foams of polystyrene (EPS) and polypropylene (EPP), (iii) bead foams with different densities (30, 60, 120, and 210 kg/m3) and (iv) to a new type of bead foam made of the engineering polymer polybutylene terephthalate (E-PBT). The termination criterion for the test is defined as the temperature at which a relative compression of 10% is reached in the creep test with temperature steps. We suggest calling it the heat stability temperature T HS. For the studied foams, the procedure delivers characteristic T HS values that allow a good comparison between different polymer matrices and densities. The heat stability temperature T HS of amorphous PS foams (i.e., XPS and EPS) was determined to be 98 °C, which is close to the glass transition temperature T g . Using the same approach, values of 99–107 °C were determined for EPP and 186 °C for the semi-crystalline bead foam E-PBT.
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Zhao, Biao, Ruoming Wang, Yang Li, Yumei Ren, Xiao Li, Xiaoqin Guo, Rui Zhang i Chul B. Park. "Dependence of electromagnetic interference shielding ability of conductive polymer composite foams with hydrophobic properties on cellular structure". Journal of Materials Chemistry C 8, nr 22 (2020): 7401–10. http://dx.doi.org/10.1039/d0tc00987c.
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Wang, Long, Kiyomi Okada, Yuta Hikima, Masahiro Ohshima, Takafumi Sekiguchi i Hiroyuki Yano. "Effect of Cellulose Nanofiber (CNF) Surface Treatment on Cellular Structures and Mechanical Properties of Polypropylene/CNF Nanocomposite Foams via Core-Back Foam Injection Molding". Polymers 11, nr 2 (2.02.2019): 249. http://dx.doi.org/10.3390/polym11020249.
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Herein, lightweight nanocomposite foams with expansion ratios ranging from 2–10-fold were fabricated using an isotactic polypropylene (iPP) matrix and cellulose nanofiber (CNF) as the reinforcing agent via core-back foam injection molding (FIM). Both the native and modified CNFs, including the different degrees of substitution (DS) of 0.2 and 0.4, were melt-prepared and used for producing the polypropylene (PP)/CNF composites. Foaming results revealed that the addition of CNF greatly improved the foamability of PP, reaching 2–3 orders of magnitude increases in cell density, in comparison to those of the neat iPP foams. Moreover, tensile test results showed that the incorporation of CNF increased the tensile modulus and yield stress of both solid and 2-fold foamed PP, and a greater reinforcing effect was achieved in composites containing modified CNF. In the compression test, PP/CNF composite foams prepared with a DS of 0.4 exhibited dramatic improvements in mechanical performance for 10-fold foams, in comparison to iPP, with increases in the elastic modulus and collapse stress of PP foams of 486% and 468%, respectively. These results demonstrate that CNF is extraordinarily helpful in enhancing the foamability of PP and reinforcing PP foams, which has importance for the development of lightweight polymer composite foams containing a natural nanofiber.
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Agrawal, A. K., B. Singh, Y. S. Kashyap, M. Shukla, B. S. Manjunath i S. C. Gadkari. "Gamma-irradiation-induced micro-structural variations in flame-retardant polyurethane foam using synchrotron X-ray micro-tomography". Journal of Synchrotron Radiation 26, nr 5 (16.08.2019): 1797–807. http://dx.doi.org/10.1107/s1600577519009792.
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Flame-retardant polyurethane foams are potential packing materials for the transport casks of highly active nuclear materials for shock absorption and insulation purposes. Exposure of high doses of gamma radiation causes cross-linking and chain sectioning of macromolecules in this polymer foam, which leads to reorganization of their cellular microstructure and thereby variations in physico-mechanical properties. In this study, in-house-developed flame-retardant rigid polyurethane foam samples were exposed to gamma irradiation doses in the 0–20 kGy range and synchrotron radiation X-ray micro-computed tomography (SR-µCT) imaging was employed for the analysis of radiation-induced morphological variations in their cellular microstructure. Qualitative and quantitative analysis of SR-µCT images has revealed significant variations in the average cell size, shape, wall thickness, orientations and spatial anisotropy of the cellular microstructure in polyurethane foam.
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Maier, Johanna, Thomas Behnisch, Vinzenz Geske, Matthias Ahlhelm, David Werner, Tassilo Moritz, Alexander Michaelis i Maik Gude. "Investigation of the Foam Development Stages by Non-Destructive Testing Technology Using the Freeze Foaming Process". Materials 11, nr 12 (6.12.2018): 2478. http://dx.doi.org/10.3390/ma11122478.
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With a novel Freeze Foaming method, it is possible to manufacture porous cellular components whose structure and composition also enables them for application as artificial bones, among others. To tune the foam properties to our needs, we have to understand the principles of the foaming process and how the relevant process parameters and the foam’s structure are linked. Using in situ analysis methods, like X-ray microcomputed tomography (µCT), the foam structure and its development can be observed and correlated to its properties. For this purpose, a device was designed at the Institute of Lightweight Engineering and Polymer Technology (ILK). Due to varying suspension temperature and the rate of pressure decrease it was possible to analyze the foam’s developmental stages for the first time. After successfully identifying the mechanism of foam creation and cell structure formation, process routes for tailored foams can be developed in future.
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Llovera-Segovia, Pedro, Gustavo Ortega-Braña, Vicente Fuster-Roig i Alfredo Quijano-López. "Charging of Piezoelectric Cellular Polypropylene Film by Means of a Series Dielectric Layer". Polymers 13, nr 3 (21.01.2021): 333. http://dx.doi.org/10.3390/polym13030333.
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Piezoelectric polymer cellular films have been developed and improved in the past decades. These piezoelectric materials are based on the polarization of the internal cells by means of induced discharges in the gas inside the cells. Internal discharges are driven by an external applied electric field. With this polarization method, cellular polypropylene (PP) polymers exhibit a high piezoelectric coefficient d33 and have been investigated because of their low dielectric polarization, high resistivity, and flexibility. Charging polymers foams is normally obtained by applying a corona discharge to the surface with a single tip electrode-plane arrangement or a triode electrode, which consists of a tip electrode-plane structure with a controlled potential intermediate mesh. Corona charging allows the surface potential of the sample to rise without breakdown or surface flashover. A charging method has been developed without corona discharge, and this has provided good results. In our work, a method has been developed to polarize polypropylene foams by applying an insulated high-voltage electrode on the surface of the sample. The dielectric layer in series with the sample allows for a high internal electric field to be reached in the sample but avoids dielectric breakdown of the sample. The distribution of the electric field between the sample and the dielectric barrier has been calculated. Experimental results with three different electrodes present good outcome in agreement with the calculations. High d33 constants of about 880 pC/N have been obtained. Mapping of the d33 constant on the surface has also been carried out showing good homogeneity on the area under the electrode.
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Román-Lorza, Silvia, J. Sabadell, J. J. García-Ruiz, Miguel A. Rodríguez-Pérez i J. A. S. Sáez. "Fabrication and Characterization of Halogen-Free Flame Retardant Polyolefin Foams". Materials Science Forum 636-637 (styczeń 2010): 198–205. http://dx.doi.org/10.4028/www.scientific.net/msf.636-637.198.
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Mayor advances have been made in the field of halogen-free flame retardant composites in the last years, mainly due to increasing regulatory pressures. This paper focuses in aluminium trihydroxide (ATH) as the halogen-free flame retardant and low density polyethylene (LDPE) as the polymer matrix of the fire retardancy foam. The attempt of this article is to achieve a cellular structure by foaming these materials, when high loading levels (up to 60wt %) of ATH are introduced. This is a difficult task due to the high amount of filler in the formulation. The aim is to reduce density without losing thermal and mechanical properties. In order to characterize the cellular structure as well as the thermal, mechanical and combustion properties, a complete study of the foamed samples was made by means of scanning electronic microscopy (SEM), thermogravimetric analysis (TGA), melt flow index (MFI), air pycnometry, mechanical testing at low strain rates, limiting oxygen index (LOI) and calorimeter bomb tests.
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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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Hamdi, Ouassim, Frej Mighri i Denis Rodrigue. "Optimization of the cellular morphology of biaxially stretched thin polyethylene foams produced by extrusion film blowing". Cellular Polymers 37, nr 4-6 (lipiec 2018): 153–68. http://dx.doi.org/10.1177/0262489318797517.
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This work presents the production of cellular polymer films using extrusion blowing to impose biaxial stretching on the cellular structure while processing. The materials selected are linear low-density polyethylene (LLDPE) and low density polyethylene (LDPE) as the matrix, azodicarbonamide as the chemical blowing agent, and talc as the nucleating agent. The processing parameters, namely, the temperature profile, screw speed, feed rate, take-up ratio, blow-up ratio, and the matrix composition were all optimized to produce a homogeneous cellular structure with defined morphologies. The optimized films had a thickness below 300 µm, a relative density around 0.6, a cell density above 2 × 106 cells/cm3, and biaxially stretched cells with aspect ratios above 4 longitudinally and 3.8 transversally.
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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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Marter, Alex D., Alexander S. Dickinson, Fabrice Pierron, Yin Ki (Kiki) Fong i Martin Browne. "Characterising the compressive anisotropic properties of analogue bone using optical strain measurement". Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 233, nr 9 (18.06.2019): 954–60. http://dx.doi.org/10.1177/0954411919855150.
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The validity of conclusions drawn from pre-clinical tests on orthopaedic devices depends upon accurate characterisation of the support materials: frequently, polymer foam analogues. These materials often display anisotropic mechanical behaviour, which may considerably influence computational modelling predictions and interpretation of experiments. Therefore, this study sought to characterise the anisotropic mechanical properties of a range of commonly used analogue bone materials, using non-contact multi-point optical extensometry method to account for the effects of machine compliance and uneven loading. Testing was conducted on commercially available ‘cellular’, ‘solid’ and ‘open-cell’ Sawbone blocks with a range of densities. Solid foams behaved largely isotropically. However, across the available density range of cellular foams, the average Young’s modulus was 23%–31% lower (p < 0.005) perpendicular to the foaming direction than parallel to it, indicating elongation of cells with foaming. The average Young’s modulus of open-celled foams was 25%–59% higher (p < 0.05) perpendicular to the foaming direction than parallel to it. This is thought to result from solid planes of material that were observed perpendicular to the foaming direction, stiffening the bulk material. The presented data represent a reference to help researchers design, model and interpret tests using these materials.
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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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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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Magiera, Anna, Monika Kuźnia, Wojciech Jerzak, Magdalena Ziąbka, Radosław Lach i Bartosz Handke. "Microspheres as potential fillers in composite polymeric materials". E3S Web of Conferences 108 (2019): 02009. http://dx.doi.org/10.1051/e3sconf/201910802009.
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Microspheres used in our work were acquired from one of Kazakhstan coal-fueled power plant. The size of the microspheres varied between 45 and 400 μm, the median particle size (D50) was 158 μm. Microscopic analysis revealed that the material consisted mainly of cenospheres. The results of elemental and oxide analysis showed that microspheres were composed of aluminosilicates. Identified crystalline phases were mullite (approx. 12 %) and trace amount of quartz (silica). Microscopic observations of the cross-sectional surface of both unmodified PUR foam and foams modified with microspheres showed a well formed, cellular structure of all materials. The observed cells are polyhedron in shape, most of them are closed, microspheres were uniformly distributed within polymer matrix and placed between cells. The apparent densities calculations of the samples showed that when microspheres were added to the polymer matrix, apparent density of the resulting composite materials increased. The results of elemental analysis pointed out the highest content of all three elements in unmodified PUR foam sample. The addition of the microspheres to the system resulted in decrease of the concentration of all three elements.
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Manninen, Allan R., Hani E. Naguib, A. Victoria Nawaby, Xia Liao i Michael Day. "The Effect of Clay Content on PMMA-Clay Nanocomposite Foams". Cellular Polymers 24, nr 2 (marzec 2005): 49–70. http://dx.doi.org/10.1177/026248930502400201.
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In this study the CO2 sorption at 45 °C in PMMA nanocomposite films containing 2 wt.% of nanoclay has been measured using an in-situ gravimetric technique. The films examined were prepared by compression moulding material obtained by dry-blend and solvent co-precipitation techniques. The CO2 diffusion coefficients were found to be higher for the dry-blended nanocomposite due to the larger agglomerations of the organoclay agglomerations, which prevented the polymer chains from fully wetting and intercalating the clay particles. The Tg-p profile for PMMA nanocomposite containing 2 wt.% nanoclay in the presence of CO2 was also measured using high-pressure DSC. The glass transition phase envelope was shifted vertically by approximately 10 °C when compared to the value reported in the literature for neat PMMA. This result suggests that the nanoclay affects the plasticization behaviour of PMMA under high-pressure CO2 conditions. The cellular morphologies obtained for these PMMA nanocomposite foams produced by batch processing with subcritical CO2 are strongly dependent upon the clay content and the dispersion of the nanoclay in the material. In the case of intercalated nanocomposites, most clay particles exist as agglomerated stacks of silicate sheets. On foaming the cells tend to form around the clay particles causing either irregular-shaped cells or layers to be produced. As a result, the cell density increases and the mean cell size decreases in the foamed nanocomposite on increasing the nanoclay content. Accordingly, the resulting cell structures are highly non-uniform and show large variations in cellular morphologies throughout the foam.
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Hrimchum, Kittipong, Darunee Aussawasathien i Todsapol Kajornprai. "Injection Moldable Poly(Lactic Acid)-Poly(Butylene Succinate)-Activated Carbon Composite Foams: Effects of PLA/PBS Ratios". Key Engineering Materials 798 (kwiecień 2019): 322–30. http://dx.doi.org/10.4028/www.scientific.net/kem.798.322.
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Poly (lactic acid) (PLA)-poly (butylene succinate) (PBS)-activated carbon (AC) composites were foamed via an injection molding process. Azodicarbonamide (ADC) was used as a chemical blowing agent. The effect of PLA/PBS ratios (0/100, 10/90, 20/80, 30/70, 40/60, 50/50 wt% and vice versa) on the cell formation and properties of composite foams such as cellular structure, foam density (ρf), void fraction (Vf), cell density, melt flow index (MFI), thermal and mechanical properties and crystallinity were investigated. At same ADC and AC loadings (5 phr), PBS acted as nucleating sites for cell generation and expansion at low contents ( 40 wt%). However, the cell size had a tendency to decrease at high PBS concentrations (> 40 wt%). The cell density of composite foams was somewhat constant at PLA/PBS ratios up to 60/40 wt% and then continuously increased as the PBS dosage was higher than 40 wt%. The maximum reduction of foam density with the void fraction of 20% was obtained at the PLA/PBS ratio of 60/40. The melt viscosity of composite foams increased with the increase of PBS loadings. The tensile strength and Young’s modulus of composite foams decreased while the elongation at break and impact strength increased as the proportion of PBS increased. The cold crystallization temperature (Tcc) of PLA in the composite foam tended to decrease with the reduction of PLA contents while the melting temperatures (Tm) of PLA in composite foams fluctuated without any trend compared with those of the unfoamed PLA. The Tcc of PLA in composite foams could not be detected when the content of PBS was higher than 40 wt%. The crystallization temperature (Tc) and Tm of PBS in composite foams was almost unchanged for each PLA/PBS proportion compared with those of the unfoamed PBS. The crystallinity (Xc) of PLA in composite foams increased compared with the unfoamed PLA at PBS contents of 0-20 wt% due to the nucleating effect of PBS and AC. The Xc of PLA (at PBS > 20 wt%) and PBS in composite foams decreased with the reduction of each polymer.
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Weingart, Nick, Daniel Raps, Mingfu Lu, Lukas Endner i Volker Altstädt. "Comparison of the Foamability of Linear and Long-Chain Branched Polypropylene—The Legend of Strain-Hardening as a Requirement for Good Foamability". Polymers 12, nr 3 (24.03.2020): 725. http://dx.doi.org/10.3390/polym12030725.
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Polypropylene (PP) is an outstanding material for polymeric foams due to its favorable mechanical and chemical properties. However, its low melt strength and fast crystallization result in unfavorable foaming properties. Long-chain branching of PP is regarded as a game changer in foaming due to the introduction of strain hardening, which stabilizes the foam morphology. In this work, a thorough characterization with respect to rheology and crystallization characteristics of a linear PP, a PP/PE-block co-polymer, and a long-chain branched PP are conducted. Using these results, the processing window in foam-extrusion trials with CO2 and finally the foam properties are explained. Although only LCB-PP exhibits strain hardening, it neither provide the broadest foaming window nor the best foam quality. Therefore, multiwave experiments were conducted to study the gelation due to crystallization and its influence on foaming. Here, linear PP exhibited a gel-like behavior over a broad time frame, whereas the other two froze quickly. Thus, apart from strain hardening, the crystallization behavior/crystallization kinetics is of utmost importance for foaming in terms of a broad processing window, low-density, and good morphology. Therefore, the question arises, whether strain hardening is really essential for low density foams with a good cellular morphology.
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Güzel, Kübra, Jan-Christoph Zarges i Hans-Peter Heim. "Effect of Cell Morphology on Flexural Behavior of Injection-Molded Microcellular Polycarbonate". Materials 15, nr 10 (19.05.2022): 3634. http://dx.doi.org/10.3390/ma15103634.
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The quantitative study of the structure and properties relationship in cellular materials is mostly limited to cell diameter, cell density, skin layer thickness, and cell size distribution. In addition, the investigation of the morphology is generally carried out in two dimensions. Therefore, the interrelation between morphological properties and mechanical characteristics of the foam structure has remained in an uncertain state. In this study, during the physical foaming process, a foam morphology is locally created by using a mold equipped with a core-back insert. The variation in morphology is obtained by modifying the mold temperature, injection flow rate, and blowing agent content in the polymer melt. X-ray microtomography (μCT) is used to acquire the 3D visualization of the cells structure. The Cell Distribution Index (CDI) is calculated to represent the polydispersity in cell size distribution. The relationship between the wide range of morphological qualities and relevant flexural properties is made explicit via a statistical model. According to the results, the morphology, particularly cell shape, characterizes the mechanism of the linear elastic deformation of the closed-cell foams. IR-thermography reveals the bending failure of cellular structures in the tensile region despite the differences in cell diameter.
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Gorejová, Radka, Renáta Oriňaková, Zuzana Orságová Králová, Matej Baláž, Miriam Kupková, Monika Hrubovčáková, Lucia Haverová i in. "In Vitro Corrosion Behavior of Biodegradable Iron Foams with Polymeric Coating". Materials 13, nr 1 (2.01.2020): 184. http://dx.doi.org/10.3390/ma13010184.
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Research in the field of biodegradable metallic scaffolds has advanced during the last decades. Resorbable implants based on iron have become an attractive alternative to the temporary devices made of inert metals. Overcoming an insufficient corrosion rate of pure iron, though, still remains a problem. In our work, we have prepared iron foams and coated them with three different concentrations of polyethyleneimine (PEI) to increase their corrosion rates. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used for characterization of the polymer coating. The corrosion behavior of the powder-metallurgically prepared samples was evaluated electrochemically using an anodic polarization method. A 12 weeks long in vitro degradation study in Hanks’ solution at 37 °C was also performed. Surface morphology, corrosion behavior, and degradation rates of the open-cell foams were studied and discussed. The use of PEI coating led to an increase in the corrosion rates of the cellular material. The sample with the highest concentration of PEI film showed the most rapid corrosion in the environment of simulated body fluids.
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Yang, Yang, Shuiping Zeng, Xiping Li, Zhonglue Hu i Jiajia Zheng. "Ultrahigh and Tunable Electromagnetic Interference Shielding Performance of PVDF Composite Induced by Nano-Micro Cellular Structure". Polymers 14, nr 2 (7.01.2022): 234. http://dx.doi.org/10.3390/polym14020234.
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Lightweight and efficient electromagnetic interference (EMI) shielding materials play a vital role in protecting high-precision electronic devices and human health. Porous PVDF/CNTs/urchin-like Ni composites with different cell sizes from nanoscale to microscale were fabricated through one-step supercritical carbon dioxide (CO2) foaming. The electrical conductivity and electromagnetic interference (EMI) shielding performance of the composites with different cell sizes were examined in detail. The results indicated that the nanoscale cell structure diminishes the EMI shielding performance of the composite, whereas the microscale cell structure with an appropriate size is beneficial for improving the EMI shielding performance. A maximum EMI shielding effectiveness (SE) of 43.4 dB was achieved by the composite foams which is about twice that of the solid composite. Furthermore, as the supercritical CO2 foaming process reduces the density of the composite by 25–50%, the EMI SSE (specific shielding effectiveness)/t(thickness) of the composite reaches 402 dB/(g/cm2), which is the highest value of polymer foam obtained to the best of the authors’ knowledge. Finally, compression tests were performed to show that the composites still maintained excellent mechanical properties after the supercritical CO2 foaming process.
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Pop-Iliev, Remon. "Foaming Ability of Rotomolding Polyolefin Resins". Advanced Materials Research 875-877 (luty 2014): 1560–64. http://dx.doi.org/10.4028/www.scientific.net/amr.875-877.1560.
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The main focus of the research presented in this paper is the investigation of the ability of various polyolefin resins to be converted into integral-skin cellular composites by using the rotational foam molding process. Integral-skin foamed rotational moldings are formally denoted as cellular composites ideally having a clearly distinct surface layer of solid skin of uniform thickness that is encapsulating a seamlessly coupled fine-celled foamed core or layer of uniform cell density and distribution. A systematic comparative material characterization study that attempts to derive practical guidelines about determining the roto-foamability of polyolefins that would be useful for rotomolding processors is presented. The study included two experimental methods of characterization, a melt rheology-based and a rotational foam molding processing-based. The experimental results from both implemented characterization methods revealed good agreement. A comprehensive insight into the key polyolefin material characteristics that would ensure satisfactory results if processed using the rotational foam molding technology have been provided. The experimental results revealed that high quality polyethylene (PE) based cellular morphologies can be obtained from both dry blended and melt compounded foamable compositions for both 6-fold and 3-fold expanded foams. Unlike PE resins, it was observed that successful foaming of polypropylene (PP) resins in rotational foam molding can only be successfully accomplished over a very narrow range of melt temperatures that are close to the melting point of the polymer and by using PP grades with a quite limited range of Melt Flow Rates (MFR).
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Lian, Xinghan, Wenjie Mou, Tairong Kuang, Xianhu Liu, Shuidong Zhang, Fangfang Li, Tong Liu i Xiangfang Peng. "Synergetic effect of nanoclay and nano-CaCO3 hybrid filler systems on the foaming properties and cellular structure of polystyrene nanocomposite foams using supercritical CO2". Cellular Polymers 39, nr 5 (22.01.2020): 185–202. http://dx.doi.org/10.1177/0262489319900948.
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Supercritical fluids have been widely used to prepare various polymer nanocomposite foams due to their high-efficiency, rich-resource, and environment-friendly characteristics. In this work, we prepared polystyrene (PS) nanocomposites with different contents of hybrid fillers of nanoclay and nano-calcium carbonate (nano-CaCO3) and then were foamed by batch foaming method using supercritical carbon dioxide as a physical blowing agent. The effect of hybrid nanofillers components and foaming temperature and pressure on the foaming properties and cellular structure of PS nanocomposite foams was systematically investigated. Dynamic rheology results indicated that the complex viscosity and storage modulus were enhanced with the addition of hybrid fillers. Scanning electron microscopic images show that all samples foamed uniformly macrocells under the given conditions. More importantly, the hybrid fillers of nano-CaCO3 and nanoclay exhibit a significant synergistic effect in improving PS foaming properties, which can be ascribed to the different roles of the two fillers during cell nucleation and cell growth. For instance, the PS/0.22/0.88 nanocomposite foamed under the conditions of 20 MPa and 130°C has shown the finest cell structure (higher cell density of 1.91 × 1010 and smaller cell diameter of 2.28 µm) due to the coeffect of the hybrid nanofillers. Finally, the synergistic mechanism of these two nanofillers on PS foaming behavior was discussed.
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Santiago-Calvo, Mercedes, Haneen Naji, Victoria Bernardo, Judith Martín-de León, Alberto Saiani, Fernando Villafañe i Miguel Ángel Rodríguez-Pérez. "Analysis of the Foaming Window for Thermoplastic Polyurethane with Different Hard Segment Contents". Polymers 13, nr 18 (17.09.2021): 3143. http://dx.doi.org/10.3390/polym13183143.
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A series of thermoplastic polyurethanes (TPUs) with different amounts of hard segments (HS) (40, 50 and 60 wt.%) are synthesized by a pre-polymer method. These synthesized TPUs are characterized by Shore hardness, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and rheology. Then, these materials are foamed by a one-step gas dissolution foaming process and the processing window that allows producing homogeneous foams is analyzed. The effect of foaming temperature from 140 to 180 °C on the cellular structure and on density is evaluated, fixing a saturation pressure of 20 MPa and a saturation time of 1 h. Among the TPUs studied, only that with 50 wt.% HS allows obtaining a stable foam, whose better features are reached after foaming at 170 °C. Finally, the foaming of TPU with 50 wt.% HS is optimized by varying the saturation pressure from 10 to 25 MPa at 170 °C. The optimum saturation and foaming conditions are 25 MPa and 170 °C for 1 h, which gives foams with the lowest relative density of 0.74, the smallest average cell size of 4 μm, and the higher cell nucleation density of 8.0 × 109 nuclei/cm3. As a final conclusion of this investigation, the TPU with 50 wt.% HS is the only one that can be foamed under the saturation and foaming conditions used in this study. TPU foams containing 50 wt.% HS with a cell size below 15 microns and porosity of 1.4–18.6% can be obtained using foaming temperatures from 140 to 180 °C, saturation pressure of 20 MPa, and saturation time of 1 h. Varying the saturation pressure from 10 to 25 MPa and fixing the foaming temperature of 170 °C and saturation pressure of 1 h results in TPU foams with a cell size of below 37 microns and porosity of 1.7–21.2%.
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Berek, Harry, Christos G. Aneziris, Manuel Hasterok, Horst Biermann, Steffen Wolf i Lutz Krüger. "Stress Induced Phase Transformations in TRIP-Steel / Mg-PSZ Composites". Solid State Phenomena 172-174 (czerwiec 2011): 709–14. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.709.
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Composite materials and micro- and macrostructure designs have been the focus of numerous scientific studies over the past few years according to their crashworthiness [1-3]. Crashworthiness is concerned with the absorption of energy through controlled failure mechanisms and modes that enable a defined load profile during energy absorption [4]. Cellular materials, such as metal foams, are materials which display a unique combination of physical and mechanical properties, e.g. for crash box applications. The defining characteristic of metal foams is a very high porosity, typically in the range of 70 to 90 vol. %. In principle, cellular metals can be manufactured from gas, liquid or solid phases and currently the most advanced methods involve melt-metallurgical processes [5]. Several groups have produced foam structures by using hollow spheres to form the cells of the material [5, 6]. These materials exhibited plateau stresses of 5 MPa and 23 MPa respectively, with volume specific energy absorptions SEA of 2 MJ/m3and 10 MJ/m3respectively, up to 50 % strain [6, 7]. By combining ceramics with ductile metals, failure-tolerant metal matrix composites (MMCs) can be created. With regard to application of the MMCs as wear resistant materials in metal forming tools a prolongation of the life time and the resultant reduced equipment downtimes have been achieved by active steel infiltrating of porous zirconia structures with the aid of Ti as activator [8]. A very promising approach concerning zirconia/steel - composite materials with superior mechanical properties has been demonstrated by Guo et al. using a low-alloyed TRIP steel in combination with an Y-PSZ – ceramic [9, 10]. In a previous study honeycomb structures were formed from composites of high-alloyed austenitic stainless TRIP-steel AISI 304 with Mg-PSZ with different mixing proportions due to ceramic extrusion at room temperature and sintering at 1350 °C for 2 h in an 99.9 % Argon atmosphere [11]. One of the most promising manufacturing route to produce open cell composite foams is based on the patent of Schwartzwalder [12] by the replication method using polyurethane sponge as a template. The polymer foam is impregnated in a powder slurry (this first coating contributes as an adhesive porous layer for further coating processes), the ceramic slurry is squeezed out of the functional pores and cold spray coatings are applied in order to eliminate defects out of the squeezing process and reach the critical wall thickness for acceptable mechanical properties. In [13] the authors reported about foams with 90 Vol% high alloyed TRIP-steel and 10 Vol% Mg-PSZ. Up to 50 % compressive strain a remarkable enhancement of the SEA was observed in comparison to comparable structures with TRIP-steel only.
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Soriano-Corral, Florentino, José F. Hernández-Gámez, Lyndon H. I. Durón-Sánchez, Luis Francisco Ramos de Valle, Myriam Lozano-Estrada i Yair A. Soto-Lara. "Polymer Foams Based on Low Density Polyethylene/Ethylene Vinyl Acetate/Ground Tire Rubber (LDPE/EVA/GTR): Influence of the GTR Particle Size and Content on the Cellular Morphology and Density of the Final Foamed Compounds". Key Engineering Materials 779 (wrzesień 2018): 64–70. http://dx.doi.org/10.4028/www.scientific.net/kem.779.64.
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Addition of different contents of ground tire rubber (GTR) of different particles size in crosslinked-foamed compounds based on low density polyethylene (LDPE)/ethylene vinyl acetate (EVA) was studied. Compounds were made by melt mixing in an internal mixer at 100°C and 60 rpm. Trigonox 145-45B as crosslinking agent, azodicarbonamide (ADC) as chemical blowing agent (CBA) and ZnO/SiO2as foaming co-agents, were used. GTR of 149, 74, and 44 μm particle size was incorporated as “cell nucleating agent”, each particle size at 5, 10, and 20 phr. Morphological parameters such as average cell size (d), cell size distribution and cellular density (NC) were evaluated from images acquired by scanning electron microscopy (SEM). The results obtained from the SEM characterization show a significant reduction ofd, a significance increment onNC, up to 5.81*105to 3.62*107cells/cm3and a better homogenization of the cell size distribution in the foamed compounds with high GTR contents of the smaller particle size.
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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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González-Henríquez, Carmen, Mauricio Sarabia-Vallejos i Juan Rodríguez Hernandez. "Antimicrobial Polymers for Additive Manufacturing". International Journal of Molecular Sciences 20, nr 5 (10.03.2019): 1210. http://dx.doi.org/10.3390/ijms20051210.
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Three-dimensional (3D) printing technologies can be widely used for producing detailed geometries based on individual and particular demands. Some applications are related to the production of personalized devices, implants (orthopedic and dental), drug dosage forms (antibacterial, immunosuppressive, anti-inflammatory, etc.), or 3D implants that contain active pharmaceutical treatments, which favor cellular proliferation and tissue regeneration. This review is focused on the generation of 3D printed polymer-based objects that present antibacterial properties. Two main different alternatives of obtaining these 3D printed objects are fully described, which employ different polymer sources. The first one uses natural polymers that, in some cases, already exhibit intrinsic antibacterial capacities. The second alternative involves the use of synthetic polymers, and thus takes advantage of polymers with antimicrobial functional groups, as well as alternative strategies based on the modification of the surface of polymers or the elaboration of composite materials through adding certain antibacterial agents or incorporating different drugs into the polymeric matrix.
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Cuadra-Rodriguez, Daniel, Suset Barroso-Solares i Javier Pinto. "Advanced Nanocellular Foams: Perspectives on the Current Knowledge and Challenges". Nanomaterials 11, nr 3 (2.03.2021): 621. http://dx.doi.org/10.3390/nano11030621.
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Gibson, L. J. "Cellular Solids". MRS Bulletin 28, nr 4 (kwiecień 2003): 270–74. http://dx.doi.org/10.1557/mrs2003.79.
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AbstractThis brief article describes the content of this issue of MRS Bulletin on Cellular Solids. Cork, wood, sponge, and bone are all examples of cellular solids in nature. Engineered honeycombs and foams are now made from polymers, metals, ceramics, and glasses, and their structure gives them unique properties that can be exploited in a variety of applications. The articles in this issue provide an overview of the fabrication, structure, properties, and applications of such porous solids as cellular ceramics, aluminum and other metallic foams, and scaffolds for tissue engineering, as well as discussions of techniques for understanding, modeling, and measuring their behavior and properties.