Search

As one of the mainstream biodegradable materials, poly(butylene adipate-co-terephthalate) (PBAT) foams offer a sustainable alternative to traditional plastic foams, effectively reducing environmental pollution. However, the high cost and poor mechanical performance of PBAT foams impede their practical application. Herein, the glycidyl methacrylate-grafted biomass lignin (GML) was used to produce a PBAT/GML composite foam with good foaming performance and mechanical properties at high lignin-filling amounts by twin-screw melting free radical polymerization and supercritical CO2 foaming process. The compatibility of GML in the PBAT matrix was improved due to the formation of ester bonds in modified lignin, endowing the PBAT/GML (PGML) composite foam with exceptional foaming performance. Additionally, the mechanical properties of PGML composite foam were remarkably enhanced due to the introduction of the abundant aromatic structures of GML and the construction of a stable covalent crosslinking network. The compressive strengths and compression modulus of the PGML foam were improved by 2.53 times and 2.47 times, while its bending strength and bending modulus were improved by 1.27 times and 3.92 times compared to the neat PBAT. This research affords a new strategy for developing low-cost biodegradable biomass PBAT/lignin composite foam materials with good foaming performance and mechanical properties. [ABSTRACT FROM AUTHOR]

Plastic foams, near-ubiquitous in everyday life and industry, show properties that depend primarily on density. Density measurement, although straightforward in principle, is not always easy. As such, while several methods are available, plastic foam industry is not yet supported with a standard technique that effectively enables to control density maps. To overcome this issue, this paper proposes Terahertz (THz) time-of-flight imaging using normal reflection measurements as a fast, relatively cheap, contactless, non-destructive and non-dangerous way to map plastic foam density, based on the expected relationship between density and refractive index. The approach is demonstrated in the case of polypropylene foams. First, the relationship between the estimated effective refractive index and the polypropylene foam density is derived by characterizing a set of carefully crafted samples having uniform density in the range 70–900 kg/m3. The obtained calibration curve subtends a linear relationship between the density and the refractive index in the range of interest. This relationship is validated against a set of test samples, whose estimated average densities are consistent with the nominal ones, with an absolute error lower than 10 kg/m3 and a percentage error on the estimate of 5%. Exploiting the calibration curve, it is possible to build quantitative images depicting the spatial distribution of the sample density. THz images are able to reveal the non-uniform density distribution of some samples, which cannot be appreciated from visual inspection. Finally, the complex spatial density pattern of a graded foam sample is characterized and quantitatively compared with the density map obtained via X-ray microscopy. The comparison confirms that the proposed THz approach successfully determines the density pattern with an accuracy and a spatial scale variability compliant with those commonly required for plastic foam density estimate. [ABSTRACT FROM AUTHOR]

Poly(lactide acid) (PLA) foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams, such as polystyrene (PS) foams. Nevertheless, PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength. In this study, a high-performance PLA foam with well-defined cell morphology, exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding (MIM) process. Differential scanning calorimetry (DSC) results revealed that the added hydrazine-based nucleating agent (HNA) significantly increased the crystallization temperature and accelerated the crystallization process of PLA. Remarkably, the addition of a 1.5 wt% of HNA led to a significant reduction in PLA's cell size, from 43.5 µm to 2.87 µm, and a remarkable increase in cell density, from 1.08×107 cells/cm3 to 2.15×1010 cells/cm3. This enhancement resulted in a final crystallinity of approximately 55.7% for the PLA blend foam, a marked improvement compared to the pure PLA foam. Furthermore, at 1.5 wt% HNA concentration, the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improvements of 136% and 463%, respectively. Additionally, the Vicat softening temperature of PLA blend foam increased significantly to 134.8 °C, whereas the pure PLA foam exhibited only about 59.7 °C. These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance, which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications. [ABSTRACT FROM AUTHOR]

A metallic foam specimen was plastically joined with a resin (polymethyl methacrylate, PMMA) sheet by applying friction stir incremental forming (FSIF) process. In FSIF process, a rotating flat-ended (no probe) rod tool was pushed vertically and fed horizontally against the resin sheet which was placed on the foam. The tool operation heated frictionally the resin and deformed incrementally to the resin, while the tool operation did not deform plastically to the cellular matrix of the foam. Due to the plastic flow of the heated resin, the bottom of the resin was interlocked mechanically to the pores near the top surface of the foam. In this study, the relationship between the pore morphology (form and size) and the joining characteristics (joinability, flow thickness of the resin, and joining strength) was investigated using commercial open-cell nickel and closed-cell aluminum foams. According to the experimental investigations, the foam with small size and low depression angle of the surface pore showed better results in relation with the joining strength and the (flow thickness of the resin)/(depth of the surface pore). [ABSTRACT FROM AUTHOR]

In this study, the double-layered thermo-expandable microcapsules with n-hexane as the core and styrene maleic anhydride copolymer (SMA) / polyurea (PUA) as the shell materials are prepared by combination of interfacial polymerization and co-precipitation method. The successful encapsulation of n-hexane in the PUA microcapsules is confirmed by simultaneous thermal analyzer (TG-IR). The properties of the thermo-expandable microcapsules (TEMs) are investigated by thermo-gravimetric analyzer (TGA), laser particle size analyzer, optical microscope and thermo-mechanical analyzer (TMA), respectively. The results show that polyurea shows a good encapsulation effect on n-hexane. When the dosage of n-hexane is 60 wt%, the microcapsules with polyurea as the shell have the encapsulation efficiency as high as 96.7%. However, the thermo-expandable performance of PUA-TEMs is poor. Double-layered thermo-expandable microcapsules with SMA/PUA as the shell (SMA/PUA-TEMs) are then obtained by introducing SMA copolymer as a second layer to enhance the thermo-expandable performance of the microcapsules. The introduction of styrene-maleic anhydride copolymer onto the PUA-TEMs reduces the encapsulation amount of n-hexane in the microcapsules, but the thermo-expandable performance is significantly improved. When the mass ratio of SMA to PUA-TEMs is 2:1, the SMA/PUA-TEMs with the encapsulation efficiency of n-hexane of 41.1% and the particle size of about 2.5 μm are obtained. SMA/PUA-TEMs show onset and peak expansion temperatures of 195 and 216 °C, respectively, and the expansion ratio of 2.4 time. The tentative investigation of the foaming performance of the SMA/PUA thermo-expandable microcapsules in polyvinyl butyral matrix shows that the thermo-expandable microcapsules can be well dispersed in the polymer matrix and have good expandable performance. This study provides a novel kind of thermo-expandable microcapsules with high onset and peak expansion temperatures which are beneficial to produce plastic foam with high Tg or Tm. [ABSTRACT FROM AUTHOR]

A more sustainable future calls for bio-based alternatives to replace plastic foams for various applications, such as packaging, insulation and cushioning. Some bio-based foams emerging in scientific publications are fabricated using liquid foam templating and methyl cellulose as well as fibers as main constituents. Scaling up of the production, however, requires a comprehensive understanding of the rheology of the foam during the shaping and drying processes. In this article, we report rheological studies of cellulose based systems in the context of thermal gelation. In more precise terms, we study how the presence of cellulose fibers and other additive materials influences the thermal gelation properties of methyl cellulose. We observe that the rheological properties, while heavily dependent on the material composition, are reasonably adjustable by appropriate material choices. The fibers are seen to decrease the temperature required for methyl cellulose to undergo a viscoelastic transition which is useful in the solid foam fabrication process. We anticipate that in the present application, the fibers increase the stability of the desired structure during the drying stage of the foam. [ABSTRACT FROM AUTHOR]

To investigate the plastic sources and aging, the number and weight ratios of 4 main plastic categories, namely hard plastics, membranous plastics, fibrous plastics, and foam plastics in the Shanghai coast were determined. Aging of polyvinyl chloride, polyethylene, and polystyrene includes the appearance of scratches and damage and even the forming of cracks and micropores. Composite packaging plastics were cracked from the external surface. Aging plastics showed new bands at around 1700 cm−1 for carbonyl functional groups, and 1000 cm−1 for C–O bonds, indicating the surface oxidation and adsorption of organic matter. The number of foam plastics was the highest among the different types of plastics, probably due to their lowest density. The sources of foam plastics varied because they are used in both the daily life of the city resident and ocean fishing and farming. This study provides scientific data for the management of Shanghai marine plastics. [ABSTRACT FROM AUTHOR]

In the present investigation, AA 5083 foam structures were fabricated, and the quasi-static uniaxial loading behavior of AA 5083 foam with varying concentration of blowing agent (CaCO3) was studied. Also, the effect of the CaCO3 blowing agent on the foam features such as pore size, pore circularity, pore distribution, and cell wall thickness was also carried out. It was observed that with the increase in CaCO3 (wt%), the relative density of the foam and the plateau stress, and the energy absorption of the foam get reduced. The influence of blowing agent on the pore features such as pore size and distribution seemed to be minimal; therefore, no significant improvement in the pore circularity was found. The quasi-static compression test results have got affected due to the varying plastic strength of the foam that resulted due to changes in the pore size and circularity. However, a detailed analysis of the dependence of these AA 5083 foam features (porosity, pore size distribution, and circularity) on CaCO3 blowing agent is discussed in this article. [ABSTRACT FROM AUTHOR]

Foams are commonly used as sound absorbers and thermal insulators for many industrial and construction applications. The insulating materials market is currently dominated by inorganic fibres like glass and mineral wool, as well as plastic foams. However, worldwide plastics consumption produces huge amounts of waste, generating concerns about soil, air and especially seawater pollution. Hence, new methods for recycling marine microplastic litter according to cleaner production criteria are being sought. This paper presents a novel, sustainable and eco-friendly foamy material made of microplastic waste, namely polyethylene terephthalate (PET) and polystyrene (PS), incorporated into a bio-based matrix. Samples with different compositions were prepared and then characterized for sound absorption properties. Evidence is presented of very good acoustic performances and of how the acoustic characteristics of the end product can be customized using different microplastic content and type. This allows envisioning many industrial and civil applications for this novel open-cell material. [ABSTRACT FROM AUTHOR]

Melamine-formaldehyde resins are widely used in the production of various technical and household products. By foaming a special resin, it is possible to obtain various foam plastics, including melamine sponges (MS), which, due to their unusual mesh structure and properties, absorb and wash away contamination quite well and have well-pronounced abrasive characteristics. The area of application of melamine sponges can be significantly expanded by their modification. Radiation-synthesized telomeres of tetrafluoroethylene (TFE) are of considerable interest for MS modification, as they make it possible to create protective hydrophobic coatings on various materials and products. This work presents the results of studies of the MS hydrophobization process, using TFE telomeres, synthesized in acetone and the binary solvent of freon 113 + ammonia. The composition and structure of hydrophobized melamine sponges have been studied by the methods of X-ray photoelectron and Raman spectroscopy, optical and scanning electron microscopy. It is shown that the treatment with tetrafluoroethylene telomere solutions makes it possible to give the initial hydrophilic material a highly hydrophobic state, characterized by a contact angle of wetting of the order of 135°–140°. This treatment significantly improves the performance characteristics and expands the practical application possibilities of melamine sponges. The morphology and composition of the modified samples have been studied. It is shown that the telomere can exist in two different states in the MS spatial network: closely bound and loosely bound fractions. The loosely bound fraction can be removed mechanically, the closely bound fraction remains on the MS surface even after several treatments with solvents, ensuring the stability of the hydrophobic properties of the sponge. [ABSTRACT FROM AUTHOR]

In a recently published paper (doi.org/10.3390/molecules26113116) on self-propelled motion of objects on the water surface, we described a novel surface-active plastic material obtained by dissolution of camphor and polypropylene in camphene at 250 ∘ C. The material has wax-like mechanical properties, can be easily formed to any moldable shape, and allows for longer and more stable self-propelled motion if compared with pure camphor or pure camphene or of a camphene-camphor wax. Here we use scanning electron microscopy to visualize and characterize the microporous structure of the solid polypropylene foam formed in the plastic for different polypropylene contents. The topology of foams remaining in the material after camphor and camphene molecules have been removed through evaporation or dissolution is similar to polypropylene foams obtained using thermally-induced phase separation. We show that the foams have a superhydrophobic surface but strongly absorb non-polar liquids, and suggest an array of potential scientific and industrial applications. [ABSTRACT FROM AUTHOR]

To investigate the effect of invasive Alternanthera philoxeroides mats on native leaf litter decomposition, we allocated two native leaf species of contrasting recalcitrance (Neosinocalamus affinis and Ficus virens) in litterbags with four different mesh sizes (0.025, 0.042, 0.5, and 5 mm) and the bags were either incubated under floating A. philoxeroides mats (Vegetated site) or under floating plastic foam boards without A. philoxeroides mats (Unvegetated site) for 65 days in Jianhu Lake, China, in July 2020. The average decomposition rates increased with pore size of litterbags. The interaction intensity of the site effect in leaf mass loss was negative in 0.025 mesh and positive in other meshes, while no significance existed between two native species in the same mesh sizes and sites. The contribution of microbes to decomposition was more than 50% in both sites. The contribution in the vegetation site was as follows: microbes > microinvertebrates > meioinvertebrates > macroinvertebrates, compared with microbes > macroinvertebrates > meioinvertebrates > microinvertebrates in the unvegetated site. The results suggest that A. philoxeroides mats can promote the decomposition of native leaf litter, and that the roles of micro-, meio-, and macroinvertebrates in decomposition are important but underestimated. [ABSTRACT FROM AUTHOR]

Vertebrate cellular immunity displays substantial variation among taxa and environments. Hematological parameters such as white blood-cell counts have emerged as a valuable tool to understand this variation by assessing the immunological status of individuals. These tools have long revealed that vertebrate cellular immune systems are highly plastic and respond to injury and infection. However, cellular immune systems may also be able to anticipate a high risk of injury from environmental cues (e.g., predation-related cues) and respond plastically ahead of time. We studied white blood-cell (leukocyte) profiles in African cichlids Pelvicachromis taeniatus that were raised for 4 years under different levels of perceived predation risk. In a split-clutch design, we raised fish from hatching onwards under chronic exposure to either conspecific alarm cues (communicating high predation risk) or a distilled water control treatment. Differential blood analysis revealed that alarm cue-exposed fish had twice as many lymphocytes in peripheral blood as did controls, a condition called lymphocytosis. The presence of a higher number of lymphocytes makes the cellular immune response more potent, which accelerates the removal of invading foreign antigens from the bloodstream, and, therefore, may be putatively beneficial in the face of injury. This observed lymphocytosis after long-term exposure to conspecific alarm cues constitutes first evidence for an anticipatory and adaptive plastic response of the cellular immune system to future immunological challenges. [ABSTRACT FROM AUTHOR]

Porous plastics are used in various fields of industry, including radio- and electrotechnical fields. They are characterized by good heat- and sound proofing, dielectric and mechanical properties, and resistance to various external factors during operation. The problem of predicting the effective permittivity of foam-polymer materials with a large volume fraction of pores, in particular, polyepoxide foam materials, are considered. Two methods for solving it, both based on the matrix composite model are proposed. In the first method, the matrix is considered as a polyepoxide binder, and cavities filled with gas are taken as inclusions. In the second method, polyepoxide walls separating cavities are taken as inclusions, and gas filling cavities are considered as a matrix. To obtain the calculation formulas, the generalized singular approximation of the random field theory is used in both cases. Based on the derived expressions, model calculations of the effective permittivity are performed for macroscopically isotropic foam plastic with polymer binder based on ED-20 and cavities filled with freon, depending on the apparent material density. The calculations in the generalized singular approximations are performed for the case where the matrix is considered as the reference medium and using the self-consistent method. In the calculations using the second approach, two shapes of material cells are considered, i.e., weakly leaked and heavily leaked polyhedron. The dependences calculated by all methods show qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Epithelial to mesenchymal transition (EMT) is a complex plastic and reversible cellular process that has critical roles in diverse physiological and pathological phenomena. EMT is involved in embryonic development, organogenesis and tissue repair, as well as in fibrosis, cancer metastasis and drug resistance. In recent years, the ability to edit the genome using the clustered regularly interspaced palindromic repeats (CRISPR) and associated protein (Cas) system has greatly contributed to identify or validate critical genes in pathway signaling. This review delineates the complex EMT networks and discusses recent studies that have used CRISPR/Cas technology to further advance our understanding of the EMT process. [ABSTRACT FROM AUTHOR]

Expanded polystyrene foams are lightweight and cheap, but they have excellent strength and insulation properties. However, their inability to biodegrade in traditional landfill situations makes their disposal problematic. Starch, a polysaccharide, has the potential to replace synthetic thermoplastics for some applications but starch-based foams are hydrophilic, which limits their applications. In this work, polylactide (PLA), a sustainably derived and industrially compostable polymer, was added to starch/cellulose composite foams to enhance their water barrier properties. PLA powder at various weight % was mixed with moistened starch and cellulose mixture, and composite foams were prepared by compression moulding at 220 °C. The thermomechanical and viscoelastic properties of the produced foam materials were analysed by thermogravimetric analysis, dynamic mechanical thermal analysis, mechanical testing, and also by the 3-point compressive mechanical quasi-static testing. It was found that the tensile strength of the composite foams increased with an increase in the PLA loading, which increased from 2.50 MPa for 0% PLA to 3.27 MPa for 9.72% PLA loading. The flexural strength also increased from 345.91 kPa for the 0% PLA to 378.53 kPa for the composite foam containing 4.86% PLA; beyond which the flexural strength started decreasing with an increase in PLA loading. Similarly, the stiffness of the starch/cellulose composite also increased with an increase in PLA loading up to 4.86%, and further increase in PLA loading decreased the stiffness. The flexural modulus of the composite foams increased from 522 MPa for 0% PLA loading to 542.85 MPa for the 4.86% PLA loading. The thermal stability of the starch/cellulose composite foams also increased and the water absorbency decreased with the increased PLA loading. [ABSTRACT FROM AUTHOR]

Novatein® is a patented thermoplastic biopolymer produced from denatured haemoglobin and serum albumin proteins, in blood meal. This material is biodegradable after processing, and when foamed could provide an alternative to expanded polystyrene and polyurethane for short-term applications such as packaging. This study aims to investigate the effect of processing temperature on foam density and morphology and how these properties effect compression behaviour. Unconstrained rapid expansion produced a range of foam densities, 0.28-0.45 g/cm3, which were strongly dependant on temperature. The foams had compressive strengths between 200 and 600 kPa and an elastic moduli between 2.2 and 8 MPa. Under compression, high-density foams behaved like traditional plastic foams, while at low density they behaved more elastomeric. Models for open and closed cells successfully predicted the compression modulus and strength in the linear elastic region. The foams demonstrated a mixed mode morphology (open and closed cells) and an irregular distribution of cells, which explained the deviation from the models. [ABSTRACT FROM AUTHOR]

Hard wood-polymer composite (HWC) was prepared, based on hot press technique, by mixing air-dried rice straw waste as a filler into a molten of chemically recycled extended polystyrene foam waste (PS) and its maleated form (PS-g-MA) as a matrix. Two fire retardants (FRs), namely zinc borate (ZB) and/or anhydrous magnesium hydroxide (MH), were dispersed into the composite to compensate for the poor thermal stability and flammability of the composite. Thermal properties of the reached HWC were evaluated by different techniques including thermogravimetric analysis, differential scanning calorimetric, in addition to, flammability analyses. Mechanical characterization was, also, rated based on tensile strength and elongation at break measurements. It was found that incorporation of the nominated fire retardants improved the thermal stability of the final products. Besides, flammability resistance was enhanced as ZB and/or MH was added to the hard wood-polymer composite formulation. The onset temperature of degradation and mass loss rates were significantly reduced in the presence of the FRs. The tensile strength of HWC was reinforced by marked additions of the FRs. The obtained data can fulfill the required optimal performance of the HWC to fire and mechanical characterizations which are necessary for many applications in the residential construction, transportation and furniture industries. [ABSTRACT FROM AUTHOR]

Flammability of two kinds of two extruded polystyrene foam was tested by micro-scale combustion calorimeter and cone calorimeter. Maximum specific heat release rate, specific heat release, heat release temperature, combustion time and fire growth rates from micro-scale combustion calorimeter tests, and time to ignition, effective net heat of combustion, heat release rate from cone calorimeter tests, were used to compare the flammability of two foams. These two methods would draw different results in evaluating flammability of the foams. This confliction is due to the test scale and combustion condition. The relationship between these two methods can be established with ignition temperature; thus, micro-scale combustion calorimeter can be used to predict time to ignition in cone calorimeter tests. Joint using of micro-scale combustion calorimeter and cone calorimeter leads to a comprehensive evaluation of flammability of polymers. [ABSTRACT FROM AUTHOR]

Terminally differentiated cells can be reprogrammed to pluripotency or directly to another differentiated cell type in vitro, a capacity termed cellular plasticity. Plasticity is not limited to in vitro manipulations but rather represents an important aspect of the regenerative response to injury in organs. Differentiated adult cells retain the capacity to dedifferentiate, adopting a progenitor-like phenotype after injury or, alternatively, to transdifferentiate, directly converting to a different mature cell type. Emerging concepts on cellular plasticity have relevance to our understanding of repair after kidney injury, including epithelial regeneration. Here we discuss work published in the past 5 years on the cellular hierarchies and mechanisms underlying kidney injury and repair, with a particular focus on potential roles for cellular plasticity in this response. [ABSTRACT FROM AUTHOR]

This study is dedicated to the development of a numerical finite-element solution to determine the effective thermal conductivity of extruded polymeric foam with different levels of open and closed porosity. The implemented numerical method is derived from periodic homogenization techniques used for the simulation of laser welding of composite materials. For a validation purpose, it was applied to the calculation of the effective thermal conductivity of polyethylene extruded foam for which the input data (density, cell size and distribution, porosity ratio, and extinction coefficient) were characterized experimentally. The computed results were compared with experimental data obtained by the transient plane source technique and analytical results derived from the literature. The deviation from the experimental data is five times lower than that of analytical methods. Moreover, the proposed numerical solution allows reaching higher porosity ratio and makes it possible to reduce the computation time while ensuring the same compactness ratio regardless of the calculation. [ABSTRACT FROM AUTHOR]

The results of experiments that were performed to test the feasibility of creating sandwich structures (consisting of thin-layer sheaths of polymer composites and a cellular polymer core) with the shapememory effect as models of the transformable components of space structures have been given. The data obtained indicate that samples of sandwich structures under microgravity conditions on board the International Space Station have recovered their shape to almost the same degree as under terrestrial conditions, which makes it possible to recommend them for creating components of transformable space structures on their basis. [ABSTRACT FROM AUTHOR]

We present information on the development and operating properties of NTZP-U syntactic foam plastics based on polyurethane aqueous dispersions, glass, and polymeric microspheres and the data on the thermal properties and durability of the developed heat-shielding materials under the conditions modeling the in-flight temperature conditions formed on the surface of the coating of the nose cone of a 'DNEPR' launch vehicle. [ABSTRACT FROM AUTHOR]

Foamed materials are gaining an increased interest due to their good mechanical properties in relation to their low densities and an increased industrial demand can be expected. A few less attractive issues can however be associated with commodity foamed products. For instance the raw-material often originates from non-renewable, fossil-based, sources. Furthermore, degradation in nature is slow, therefor the disposed product is burned or end up in landfills. One possibility to reduce the impact on nature could be to produce foams from natural polymers such as starch or cellulose. In this study the possibility to produce foams from hydroxypropyl methylcellulose (HPMC) with water as blowing agent, by continuous extrusion, was investigated. A pre-study using a capillary viscometer, batch-extruder, was conducted to evaluate the foamability of HPMC. Due to promising results further experiments were conducted with a single-screw extruder. The goal was to find an adequate processing window for foaming. It was concluded that HPMC could successfully be foamed by continuous extrusion, although a careful tailoring of the processing parameters was required. Crucial parameters were here the temperature, pressure and residence time distribution in the extruder. Regions of the extruded foams were examined using optical and scanning electron microscopy and HPMC foams with a density in the range of that of fossil-based polymeric foams could be produced. [ABSTRACT FROM AUTHOR]

To solve the complicated manufacturing operation and the usage of toxic solvent problems, a simple and novel method to fabricate superhydrophobic film by surface foaming method was introduced in this paper. The superhydrophobic property of the foamed material was obtained at a contact angle >150° and a rolling angle about 8°. The foamed material can instantly generate its superhydrophobicity via peeling process. The effects of blowing agent content, foaming time and peeling rate on the foam structure and superhydrophobicity were studied. [ABSTRACT FROM AUTHOR]

In the learning of locomotion behavior of a stinkbug Erthesina fullo, the seeked principle of its locomotion can be an important inspiration on the design of six-legged robot. To achieve this goal, in this paper, locomotion behavior of stinkbugs on glass and plastic foam are recorded. Hereby, variation in spatial and temporal kinematics of level, vertical and inverted locomotion is analyzed. Differential leg function and adhesive mechanism as well as the advantage of non-isometric legs of insects are presented. With increasing stride frequency, the speed of level, vertical and inverted locomotion can be higher without adjusting stride length. Variation in gait characteristics between level and vertical locomotion is very little, but lower speed and larger duty factor of inverted locomotion can be occurred while climbing on glass. On the surface of vertical and inverted plastic foam, stinkbugs cannot walk steady and agilely due to its adhesive mechanism. [ABSTRACT FROM AUTHOR]

This paper examines the effect of biobased chitin nanowhisker fillers on the thermal, rheological, physical, mechanical and morphological properties of biobased polylactic acid (PLA) and PLA/polyhydroxybutyrate-co-valerate (PHBV) blended nanocomposites as well as the physical, mechanical and morphological properties of porous PLA and PLA/PHBV nanocomposite foams. Solid nanocomposites of PLA, PLA/PHBV and chitin nanowhiskers were manufactured through melt blending while porous nanocomposites foams were fabricated through a batch foaming process with the aid of CO as blowing agent. It was found that by incorporating small quantities of chitin nanowhiskers (<2 wt%) the mechanical properties of solid specimens are improved while strength and expandability of the foam can be significantly improved, yielding a homogenously distributed cell morphology with average cell size of 1.5 μm. [ABSTRACT FROM AUTHOR]

The production of many items, in particular for food packaging applications, is based on foam extrusion and thermoforming. These operations require the use of polymers which can grant some specific rheological properties, both under shear and elongational flow. In this work, the behavior of some biodegradable polymers [Mater-Bi and poly(lactic acid)] under shear and non-isothermal elongational flow was investigated and compared with a traditional, non-biodegradable polymer, in order to assess their suitability for industrial-scale foam extrusion and thermoforming. The rheological characterization evidenced the differences between the different biodegradable polymers and the reference polystyrene (PS), as well as the effect of humidity on their main rheological properties. This can be of great interest in helping to find an optimum solution in replacing PS for the production of food packaging items. [ABSTRACT FROM AUTHOR]

Polymer foam cored sandwich beams are widely used in load-bearing components due to their high strength to weight ratio. To improve the reliability in using sandwich beams, it is essential to understand their long-term creep response in terms of variation of stresses and deformations with time under external mechanical and environmental stimuli. This paper presents an analytical model for investigating the creep response of sandwich beams made with a viscoelastic soft core, including the effect of the variable ambient humidity under the sustained load and its influence on the creep behavior. The model is based on a high-order viscoelastic structural modeling. The soft core is modeled as a viscoelastic material using differential-type constitutive relations that are based on the linear Boltzman's principle of superposition and accounting for the deformability of the core in shear and through its thickness. Several numerical examples are presented in order to show the capability of the model and to investigate the effect of moisture on the creep behavior of sandwich beams. Finite element simulations of the creep response of sandwich beams are also performed using ABAQUS software to validate the proposed theoretical model. The results show the concentrations of shear and transverse normal stresses near the edges and their variation in time and with the change of humidity. [ABSTRACT FROM AUTHOR]

Epithelial-mesenchymal transition is a change of cellular plasticity critical for embryonic development and tumor metastasis. CDK5 is a proline-directed serine/threonine kinase playing important roles in cancer progression. Here we show that CDK5 is commonly overexpressed and significantly correlated with several poor prognostic parameters of breast cancer.Wefound that CDK5 participated in TGF-β1-induced EMT. In MCF10A, TGF-β1 upregulated the CDK5 and p35 expression, and CDK5 knockdown inhibited TGF-β1-induced EMT. CDK5 overexpression also exhibited a potential synergy in promoting TGF-β1-induced EMT. In mesenchymal breast cancer cells MDA-MB-231 and BT549, CDK5 knockdown suppressed cell motility and tumorigenesis. We further demonstrated that CDK5 modulated cancer cell migration and tumor formation by regulating the phosphorylation of FAK at Ser-732. Therefore, CDK5-FAK pathway, as a downstream step of TGF-β1 signaling, is essential for EMT and motility in breast cancer cells. This study implicates the potential value of CDK5 as a molecular marker for breast cancer. [ABSTRACT FROM AUTHOR]

PolyHIPEs are highly porous, crosslinked polymer foams typically synthesized within high internal-phase emulsions (HIPEs). Two kinds of polyHIPEs including poly(styrene-divinylbenzene) [P(St-DVB)] and poly(methyl methacrylate-divinylbenzene) [P(MMA-DVB)] foams are synthesized in this work, which are fabricated from HIPEs template via radiation-induced polymerization at room temperature. Traditional free radical polymerization initiated by potassium peroxydisulfate (KPS) at 60 °C for producing polyHIPE P(St-DVB) foams is also conducted for comparison. It is found that the amount of emulsifier can be reduced greatly in the radiation-induced polymerization of HIPEs at room temperature, compared with the traditional polymerization approach. Besides, P(MMA-DVB) PolyHIPE foams with a fine microstructure of highly interconnected pores have been successfully fabricated via radiation-induced polymerization in this work, which is usually difficult to be prepared by thermal-initiation method because of the intermediate hydrophobicity of methyl methacrylate monomer. The influences of the fraction of internal aqueous phase and the concentration of emulsifier on the structure and performance of foams are carefully explored. The structure and compression strength of the foams are characterized by scanning electron microscopy and a mechanical testing machine, respectively. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A method for calculating the elastic constants of high-porosity cellular materials is proposed on the assumption that their oriented structure can be considered as a linear transform of some random structure. A simplified procedure to take into account the effect of gas pressure in closed-cell anisotropic solids on their elastic constants is also suggested. Calculations performed on the basis of a strut model elaborated earlier for highly porous materials are compared with experimental results for light cellular polyurethane plastics. [ABSTRACT FROM AUTHOR]

The application of rigid polymeric foam for large invest-ment casting patterns with complex geometries can im-prove the dimensional tolerances and the surface quality of the casting. However, these pattern materials have a tendency to promote crack formation in investment casting shells during pattern removal by firing. Experimental meth-ods were combined with finite element modeling to predict stress in the shell. The model takes into consideration the thermal and mechanical properties of the pattern and the shell materials to determine the heat transfer and thermal expansion stresses developed in the shell during firing. The thermal and mechanical properties of the pattern and shell were obtained from experimental tests. A 3D nonlinear fi-nite element model was developed to predict possible crack formation in the shells during pattern removal. The effects of the thermo-mechanical properties of the foam and the shell, as well as the firing process parameters were mod-eled, and extreme cases were experimentally validated. Recommendations for firing process parameters and pat-tern design to decrease stress and eliminate crack forma-tion in the shell were formulated. [ABSTRACT FROM AUTHOR]

Cellulose nanofibrils (CNFs) were blended with poly( l-lactic acid) (PLLA) to produce CNFs/PLLA composite solid foams. The dispersed CNFs' phase was partially embedded in the PLLA matrix. The CNFs not only reduced the water contact angle of the composite, but also induced the formation of hydroxyapatite (HA) on the walls of its inner pores. After incubation for 7 days in 3× simulated body fluid, a large number of HA particles were formed throughout the CNFs/PLLA composite foams. HA particles have diameters ranging from 200 nm to 2 μm and a Ca/P ratio of 1.42. The spatial distribution of calcium and phosphorus elements was uniform. A porosity of approximately 92 % was achieved after mineralization of the CNFs/PLLA composite foams. The mass of HA grown over CNFs/PLLA foams increased faster than in the case of PLLA foams. The ternary polymeric foams have potential applications in tissue engineering. [ABSTRACT FROM AUTHOR]

A model is presented for calculating the linear elastic constants of high-porosity cellular plastics by orientationally averaging the rigidity tensor of a structural element consisting of an air sheath and a loadcarrying element in the form of a straight strut with a piecewise constant cross section. The load-carrying element can resist the axial and shear loads and bending moments applied to its ends. The nonuniform orientational distribution of the elements is also taken into account. The calculation results obtained are compared with some literature data. [ABSTRACT FROM AUTHOR]

A new methodology to characterise the elastic properties of polymeric foam core materials at elevated temperatures is proposed. The focus is to determine reliable values of the tensile and compressive moduli and Poisson's ratio based on strain data obtained using digital image correlation (DIC). In the paper a detailed coverage of the source of uncertainties in the experimental procedure is provided. The uncertainties include those associated with the load introduction, the measurement and the data processing. The design of the specimens and loading jigs are developed and assessed in terms of the introduction of uniform strain. It is shown that due to the mismatch in stiffness between the jig material and the foam the introduction of a uniform strain through the cross section of the specimens is difficult to obtain. A means for correcting for the non-uniform strain across the specimen cross section is developed. To validate the methodology, tests are firstly conducted at room temperature on Divinycell PVC H100 foam. It is shown that the material is highly anisotropic with a stiffness of 50% less in the plane of the foam sheet compared to the through-thickness direction. It is also shown that because of the compliance of the foam, jig misalignment causes large errors in the measurement, and a means for correcting for this is defined. Tests are then conducted in a temperature controlled chamber at elevated temperatures ranging from 20°C to 90°C. A nonlinear reduction in Young's modulus is obtained with significant degradation occurring after 70°C. The Poisson's ratio remains fairly stable at different temperatures. A strong theme in the paper is the accuracy and precision of the DIC data and the factors which introduce scatter in the data, along with the uncertainties that this introduces. Particular attention is paid to the affect of the correlation parameters on the derived strain data. [ABSTRACT FROM AUTHOR]

Soy-polyol has been synthesized via a low energy two-step continuous route thus avoiding intermediate steps and chemicals. The functional groups of soy-polyol thus produced were identified by Fourier transform infrared (FTIR) spectroscopy which confirmed the cleavage of the double bonds, the formation of new epoxy linkages and the presence of hydroxyl groups. The change in chemical structure and physical properties of the soy polyol was further characterized and the results indicated a successful conversion with reduced unsaturation, increased hydroxyl number and increased viscosity. Polyurethane foam was prepared from soy-polyol using isocyanate and thermogravimetric analysis was used to study its thermal decomposition behaviour. Multiple transitions were identified in relation to depolymerization and bond dissociation. Density and compressive strength of the soy-foam were found to be satisfactory. An investigation of microstructure of soy foam by scanning electron microscope and X-ray computed tomography revealed the internal cell morphology and cell structure. [ABSTRACT FROM AUTHOR]

Studies on living rat hippocampal slices using point recording in the whole cell configuration addressed the efficiency of the synaptic responses of pyramidal neurons in field CA3 in conditions of minimal stimulation of mossy fibers. Paired-pulse responses were recorded before and after intracellular tetanizing hyperpolarization of pyramidal neurons. In these conditions, potentiation of excitatory synaptic transmission lasting at least 20 min was seen. This phenomenon, termed hyperpolarizing tetanization-induced long-term potentiation, could arise without simultaneous mossy fiber stimulation and showed signs of having a presynaptic origin. Administration of a Ca2+ chelator into pyramidal neurons completely suppressed this potentiation. The results obtained from these experiments suggest that induction of long-term potentiation evoked by hyperpolarizing tetanization was postsynaptic, while its expression appeared to be presynaptic. These results provide evidence of the importance of gamma-rhythm hyperpolarizing oscillations in altering the efficiency of synaptic inputs and the role of its network organization in the mechanisms of cellular plasticity. [ABSTRACT FROM AUTHOR]

One key strategy for increasing the application potential for biodegradable plastics lies in improving the physical and mechanical characteristics, which can be attained by inducing a cellular morphology in the pure polymer with the aid of a blowing agent, as well as by blending two or more polymers with the desirable properties. This paper examines the effect that blending two biodegradable polymers has on the thermal properties and morphology of the resultant foams blown with carbon dioxide (CO2). Polylactic acid (PLA), polyhydroxybutyrate-co-valerate (PHBV) and blends of both were foamed and characterized in terms of thermal characteristics, relative density, cell size, and foam morphology. The results indicate that although PLA and PHBV are immiscible, the presence of small quantities of PHBV (25 wt%) could lead to low density foams with finer, more uniform cells. Furthermore, the crystallinity of PHBV was found to be unaffected by the presence of PLA in the composite, which supports the immiscibility of PLA and PHBV. [ABSTRACT FROM AUTHOR]

The neural stem cell niche defines a zone in which stem cells are retained after embryonic development for the production of new cells of the nervous system. This continual supply of new neurons and glia then provides the postnatal and adult brain with an added capacity for cellular plasticity, albeit one that is restricted to a few specific zones within the brain. Critical to the maintenance of the stem cell niche are microenvironmental cues and cell-cell interactions that act to balance stem cell quiescence with proliferation and to direct neurogenesis versus gliogenesis lineage decisions. Ultimately, based on the location of the niche, stem cells of the adult brain support regeneration in the dentate gyrus of the hippocampus and the olfactory bulb through neuron replacement. Here, we provide a summary of the current understanding of the organization and control mechanisms of the neural stem cell niche. [ABSTRACT FROM AUTHOR]

Syntactic foams are attractive for applications that require materials with high impact strength and low thermal conductivities. Because syntactic foams are manufactured by dispersing hollow microspheres in a resinous matrix, their characteristics are functions of the type and relative amounts of these materials. In this work, a discussion of an experimental approach to measure the thermal conductivity of three-phase syntactic foams (hollow carbon microspheres in a porous APO-BMI binder, analysis of the data and the comparison to predictive models are presented. The thermal conductivity of three-phase syntactic foams is measured using a Holometrix© steady-state heat flow meter. The experimental data are found to be accurate to within a reasonable range of experimental error and are compared to three of the more reliable predictive models that have been used successfully to estimate the thermal conductivity of similar foams. It is observed that the model predictions at lower temperatures are more accurate as compared to those at higher temperatures. Also, that a model based on the concept of self-consistent field theory better predicts the thermal conductivity of syntactic foams than one based on resistance-in-series. Sensitivity studies indicate a strong dependency of the thermal conductivity of the three-phase foams on the thermal conductivity of the carbon used in the microspheres. [ABSTRACT FROM AUTHOR]

We report tensile failure experiments on polyurethane (PU) foams. Experiments have been performed by imposing a constant strain rate. We work on heterogeneous materials for whom the failure does not occur suddenly and can develop as a multistep process through a succession of microcracks that end at pores. The acoustic energy and the waiting times between acoustic events follow power-law distributions. This remains true while the foam density is varied. However, experiments at low temperatures (PU foams more brittle) have not yielded power-laws for the waiting times. The cumulative acoustic energy has no power-law divergence at the proximity of the failure point which is qualitatively in agreement with other experiments done at imposed strain. We notice a plateau in cumulative acoustic energy that seems to occur when a single crack starts to propagate. [ABSTRACT FROM AUTHOR]

The Laguerre tessellation procedure is used for simulation of microstructures of open-cell foams. In contrast with the conventional Voronoii tessellation, the Laguerre one permits to simulate the foam microstructures with a given law of distribution of cell diameters. An original finite element method is developed for calculating the elastic properties: the ligaments are modelled as Timoshenko beams and each ligament is treated as one finite element. The size of the representative volume element for reliable calculations of the effective elastic properties is evaluated by computational experiments. Dependence of the properties on the cell size distributions and ligament shapes are analyzed. [ABSTRACT FROM AUTHOR]

The performance of a wetland system in treating lead (Pb)/zinc (Zn) mine drainage was evaluated by using the polyurethane foam unit (PFU) microbial community (method), which has been adopted by China as a standardized procedure for monitoring water quality. The wetland system consisted of four cells with three dominant plants: Typha latifolia, Phragmites australis and Paspalum distichum. Physicochemical characteristics [pH, EC, content of total suspended solid (TSS) and metals (Pb, Zn, Cd, and Cu)] and PFU microbial community in water samples had been investigated from seven sampling sites. The results indicated that the concentrations of Pb, Zn, Cd, Cu, and TSS in the mine drainage were gradually reduced from the inlet to the outlet of the wetland system and 99%, 98%, 75%, 83%, and 68% of these metals and TSS respectively, had been reduced in concentration after the drainage passed through the wetland system. A total of 105 protozoan species were identified, the number of protozoa species and the diversity index (DI) gradually increased, while the heterotrophic index (HI) gradually decreased from the inlet to the outlet of the wetland system. The results indicated that DI, HI, and total number species of protozoa could be used as biological indicators indicating the improvement of water quality. [ABSTRACT FROM AUTHOR]

The elastic deformation of plastic foams with a low (< 6%) volume fraction of solid phase is described based on a 4-rod equivalent element. A criterion is proposed which allows one to determine the parameter of structure of this element. Based on an analysis of the equivalent element, a procedure is developed for constructing the compression diagram of plastic foams in the region of large (> 70%) strains. The calculation results are compared with data found in the literature and experimental results for polyurethane foams obtained by the present authors. [ABSTRACT FROM AUTHOR]

The use of the conventional Taguchi method for determining the optimum setting of controllable factors through off-line experiments focuses on products with a single quality characteristic or response. However, most products have several qualitative characteristics or responses of interest. The Taguchi method in itself optimises a single response or performance characteristic, yielding a set of process parameters. This particular setting, however, may not give the desired results for other characteristics of the product. There is a need to obtain a single optimum setting of process parameters that can be used to produce products with optimum or near optimum quality characteristics as a whole. Multi-characteristic response optimisation may be the solution to the above problem. In this report, a case study on thermoforming polypropylene foams, utilising a simplified multi-criterion methodology based on Taguchi’s approach and utility concept, is discussed. Key processing factors affecting product quality are identified. It has been shown that the proposed Taguchi approach with the utility concept can provide an appropriate solution to yield a satisfactory product quality for a multi-response process optimisation problem. [ABSTRACT FROM AUTHOR]

Polyisocyanurate foams were prepared from polymeric 4,4′-diphenylmethane diisocyanate (MDI), soy polyol and polypropylene oxide polyol by varying isocyanate index from 110 to 350. The higher isocyanate index produced polyisocyanurate foams with higher thermal stability, improved flame resistance, tensile strength, higher modulus, and higher glass transition. Soy-based foams displayed better thermal stability, lower flammability, higher rigidity (modulus) and higher compression strength than those based on the propylene oxide polyols of the same molecular weight and functionality. [ABSTRACT FROM AUTHOR]

Seven dependent elastic constants of monotropic plastic foams with an expressed strut-like structure are calculated. For this purpose, the basic results of the previously elaborated mathematical model for light-weight plastic foams is used. The model includes a model cell of local structure for monotropic/isotropic plastic foams and an ensemble of structural elements, which allows one to calculate the seven dependent elastic constants, taking into account the pronounced polydispersity of the structure of plastic foams. The numerical values of the constants are compared with the available experimental data, and a satisfactory agreement is found to exist. As a final result, a full set of general expressions and numerical values are obtained for all 12 elastic constants of monotropic plastic foams. [ABSTRACT FROM AUTHOR]

Based on an ellipsoidal model for the cellular structure of monotropic plastic foams, their deformational properties in shear perpendicularly to the isotropy plane are predicted. The theoretical results are obtained for the case of pure shear. The deformation energy is calculated by the method of coordinates assuming that the polymer struts of the structure can change both their length and orientation. Numerical values of shear moduli are found for monotropic and isotropic plastic foams, which agree satisfactorily with the experimental data for polyurethane and polyvinylchloride foams available in the literature. [ABSTRACT FROM AUTHOR]

A new method for analyzing the deformation behavior of rigid and elastic foams with a small volume content of solid phase (ϕ < 0.2) is developed. Various structural models for describing the elastic behavior of rigid and elastic plastic foams are used and compared. The results of structural simulation of anisotropic auxetic (i.e., having a negative Poisson ratio) foams with concave cells are presented. For cyclic uniaxial compression of rigid foams and volumetric deformation of elastic foams, the stress-strain curves are obtained. The general shape of the curves agrees well with the nonlinearly elastic behavior of plastic foams observed in experiments. [ABSTRACT FROM AUTHOR]