Foam Density Research Articles

Influence of natural exposure on castor oil based polyurethane reinforced with waste tire rubber

Waste tire rubber (WTR) has been extensively generated worldwide due to mobility needs growth. About 1.5 billion units are generated annually, constantly discharged in the environment with a few reusability alternatives. Therefore, rubber recovery methods and these residues’ transformation into a cost-effective product have gained attention. Aiming to minimize the usage of fossil resources and contributes to a circular economy, it was analyzed the usage of WTR particles (5–20% by weight) in castor oil-based polyurethane foams under natural aging to promote a holistic view of all factors involved in the performance of the foams. Morphological, thermal, chemical, and mechanical properties were determined before and after exposure to open air to observe the impact of photo-oxidation and hydrolysis. The increase in viscosity of pre-polymer during the rubber loading produced greater density foams with smaller cell sizes than neat PU, in which the average cell size increased after the weathering. The rubber contributes to enhancing the compressive behavior in the non-exposed samples. After exposure, the results suggest that degradation may act to increase the crosslinking density even with the presented structural changes such as yellowing and voids. Regarding thermal stability, the rubber promotes a slight decay in the ability to resist a heat flow before and after weathering. Still, the char yield increased, showing a possibility of better fire retardancy for composites. FTIR and UV–vis showed chemical structure changes as Photo-Fries network rearrangement, Norrish I random chain scission, and Norrish II β-scission. Besides, UV–vis revealed the maximum absorbance in the UVB region, showing that the PU reinforced by WTR can be a promising material for civil coatings.

Modeling the x-ray enhancement in foams for laser-driven soft x-ray sources

This paper investigates the mechanism that causes x-ray enhancement in high-Z foams for laser-driven soft x-ray sources. By simulation of one-dimensional radiation-hydrodynamics, it is found that the x-ray enhancement is mainly due to the effect that, in a foam target, shock wave compression significantly reduces the energy loss of hydrodynamic motion (kinetic energy). In a solid target this effect is negligible for its low compressibility. Expressions of kinetic energy reduction (ΔE k = E k,solid − E k,foam) are given to model the improvement of the laser-to-x-ray conversion efficiency. The ΔE k given by the model agrees with the simulation result with about a 15% error for foam density 0.07 – 0.3 g/cc and for laser intensity 0.4 × 1015–2.0 × 1015 W cm−2. The model indicates that the x-ray enhancement is more efficient with a lower foam density and higher laser intensity, which is also presented by the simulation results.

Recycling rice husk ash as a filler on biodegradable cassava starch-based foams.

Starch-based foams can be used in packaging development to replace nonbiodegradable petrochemical plastics. However, starch-based materials possess poor mechanical properties and low water resistance. These properties can be improved by adding plasticizers and fillers to the bulk composition. In the present work, the effect of rice husk ash content on physical, morphological, and mechanical properties of cassava starch-based foams produced by thermal expansion was investigated. The composites were formed by mixing cassava starch, rice husk ash (content varying from 0 to 60%), water, and glycerol. The obtained dough was placed in a metallic mold and then expanded in a thermohydraulic press machine. The addition of 20-50% of ash content improved thermal stability, density, and biodegradation of starch-based foams and decreased water absorption capacity. Filled starch-based foams also exhibited smallerpores in internal structure. Compared to foams without ash filler, the addition of 20-40% ash increased the flexural tensile strength and the addition of more than 50% dropped the mechanical resistance. Hence, based on the results obtained, rice husk ash can be a great filler in biodegradable starch-based foams.

Experimental and Finite Element Simulation of Polyolefin Elastomer Foams Using Real 3D Structures: Effect of Foaming Agent Content.

In this study, polyolefin elastomer (POE) foams were prepared without any curing agent using a single-step foaming technique. The effect of azodicarbonamide (ADC) content as a chemical foaming agent on the foams' morphology and mechanical properties was studied using scanning electron microscopy (SEM), mechanical properties (tension and compression) and hardness. The results showed that increasing the ADC content from 2 to 3, 4 and 5 phr (parts per hundred rubber) decreased the foam density from 0.75 to 0.71, 0.65 and 0.61 g/cm3, respectively. The morphological analysis revealed that increasing the ADC content from 2 to 4 phr produced smaller cell sizes from 153 to 109 µm (29% lower), but a higher cell density from 103 to 591 cells/mm3 (470% higher). However, using 5 phr of ADC led to a larger cell size (148 µm) and lower cell density (483 cells/mm3) due to cell coalescence. The tensile modulus, strength at break, elongation and hardness properties continuously decreased by 28%, 21%, 16% and 14%, respectively, with increasing ADC content (2 to 5 phr). On the other hand, the compressive properties, including elastic modulus and compressive strength, increased by 20% and 64%, respectively, with increasing ADC content (2 to 5 phr). The tensile and compression tests revealed that the former is more dependent on foam density (foaming ratio), while the latter is mainly controlled by the cellular structure (cell size, cell density and internal gas pressure). In addition, 2D SEM images were used to simulate the foams' real 3D structure, which was used in finite element methods (FEM) to simulate the stress-strain behavior of the samples at two levels: micro-scale and macro-scale. Finally, the FEM results were compared to the experimental data. Based on the information obtained, a good agreement between the macro-scale stress-strain behavior generated by the FEM simulations and experimental data was obtained. While the FEM results showed that the sample with 3 phr of ADC had the lowest micro-scale stress, the sample with 5 phr had the highest micro-scale stress due to smaller and larger cell sizes, respectively.

Flow and heat transfer irreversibility in partial filled metal foams

This paper presents the analysis of entropy generation, exergy and heat transfer through metal foams partially and completely filled in a vertical channel. The assembly of heater located in between two aluminum plates is located at the core of the channel and for the purpose of heat transfer augmentation aluminum metal foam of pore density 10 with porosity 0.95 are located on either side of the plates. Four different filling rates of 25%, 50%, 75% and 100%, and three metal foam thicknesses of 10 mm, 20 mm and 30 mm are examined in this research for a fluid velocity ranging from 0.1 to 3 m/s. Darcy Extended Forchheimer (DEF) model and local thermal non-equilibrium (LTNE) model is used for forecasting the flow features and heat transfer through the metal foam. The numerical methodology adopted in this research is confirmed by comparing the results with the literature and found fairly good agreement between them. The flow physiognomies in terms of friction factor, heat transfer performance in terms of Nusselt number and performance factor, exergy transfer in terms of mean exergy based Nusselt number, and entropy generation i.e., total irreversibility in terms of Bejan number and entropy generation number are presented and discussed. Results showed that the effect of partially filled metal foams are found to be better in terms of entropy generation, and exergy transfer, and the effect of higher metal foam thickness is found to be better in terms of exergy and heat transfer, but in terms of total entropy generation resulting in terms of both heat transfer and pressure drop smaller metal foam thickness exhibits better performance.

Evaluation of the Nature and Concentration of the Surfactant on the Properties of Red Mud/Metakaolin Porous Geopolymers Foamed with Aluminium.

The chemical foaming technique is possibly the most common method of producing porous geopolymers. Despite this, to date, the role of the content and type of surfactant on the pore size distribution of porous geopolymers is not fully perceived, as constant surfactant dosages are usually employed. In addition, the comparison of literature studies is challenging since a distinct mixture of designs is employed. This investigation intends to provide additional insights on the topic, focusing on synthesizing red mud/metakaolin geopolymer foams and envisioning their use in thermal insulating applications. Various mixtures were prepared using three commercially available surfactants, namely Hostapur OSB, sodium dodecyl sulfate (SDS), and Triton X114. The content of the surfactant (0.025, 0.05, and 0.075 wt.%) and the amount of the foaming agent (aluminum powder, Al; 0.05, 0.075, and 0.10 wt.%) was modified, keeping the binder composition constant and the physical properties of the produced geopolymers were characterized. Results show that the combination between sodium dodecyl sulfate (0.025 wt.%) and aluminum (0.10 wt.%) leads to the strongest reduction in the foam density, the lowest value here reported being -400 kg/m3. On the other hand, samples produced with Hostapur OSB have much higher open porosity (up to 47.7%) and water absorption (up to 80.4%) values, showing that this surfactant leads to a pore network with higher connectivity. In addition, the microstructure of the foams, particularly pore morphology (size and shape) and connectivity between the produced pores are highly dependent on the type of surfactant, sodium dodecyl sulfate generating coarser pore size distribution with round, but mostly closed pores, while a narrower pore size distribution coupled with smaller size pores is seen with the Hostapur. These results suggest the feasibility of tuning the foams' properties (porosity and mechanical performance) according to the application by the proper combination of the type of surfactant and their concentration, enabling their use as thermal and acoustic insulators or as filters/membranes in wastewater treatment systems.

TPV Foaming by CO2 Extrusion: Processing and Modelling.

This work focuses on the extrusion foaming under CO2 of commercial TPV and how the process influences the final morphology of the foam. Moreover, numerical modelling of the cell growth of the extrusion foaming is developed. The results show how a precise control on the saturation pressure, die geometry, temperature and nucleation can provide a homogeneous foam having a low density (<500 kg/m3). This work demonstrates that an optimum of CO2 content must be determined to control the coalescence phenomenon that appears for high levels of CO2. This is explained by longer residence times in the die (time of growth under confinement) and an early nucleation (expansion on the die destabilizes the polymer flow). Finally, this work proposes a model to predict the influence of CO2 on the flow (plasticizing effect) and a global model to simulate the extrusion process and foaming inside and outside the die. For well-chosen nucleation parameters, the model predicts the final mean radius of the cell foam as well as final foam density.

Polylactic Acid Chemical Foaming Assisted by Solid-State Processing: Solid-State Shear Pulverization and Cryogenic Milling.

A chemical foaming process of polylactic acid (PLA) was developed via the solid-state processing methods of solid-state shear pulverization (SSSP) and cryogenic milling. Based on the ability of solid-state processing to enhance the crystallization kinetics of PLA, chemical foaming agents (CFA) are first compounded before foaming via compression molding. Specifically, the effects of the pre-foaming solid-state processing method and CFA concentration were investigated. Density reduction, mechanical properties, thermal behavior, and cell density of PLA foams are characterized. Solid-state processing of PLA before foaming greatly increases the extent of PLA foaming by achieving void fractions approximately twice that of the control foams. PLA's improved ability to crystallize is displayed through both dynamic mechanical analysis and differential scanning calorimetry. The solid-state-processed foams display superior mechanical robustness and undergo low stress relaxation. The cell density of the PLA foams also increases with solid-state processing, especially through SSSP. Additionally, crosslinking of PLA during the pre-foaming processing step is found to result in the greatest enhancement of crystallization but decreased void fraction and foam effectiveness. Overall, SSSP and cryogenic milling show significant promise in improving chemical foaming in alternative biopolymers.

Design and the transient thermal control performance analysis of a novel PCM-based active-passive cooling heat sink

In this present work, a novel active–passive cooling heat sink thermal management system based on the composite of phase change materials and metal foam is designed. It is aimed to improve the thermal performance of the active antenna unit device for the fifth-generation mobile communication technology base station. The numerical investigation of the thermal performance of the novel active cooling heat sink thermal management system is conducted, while the effect of transient heat flux is taken into consideration. The influences of the phase change temperatures, the porosity of the metal foam, and the pore density of the metal foam on the heat sink’s thermal performance are studied. Results indicate that the novel active-cooling heat sink thermal management system presents better thermal performance than traditional active cooling heat sinks without phase change materials and metal foam. Compared with the traditional active cooling heat sinks, the maximum temperature of the designed heat sink could be decreased by 10 K, and its temperature control efficiency could be enhanced by up to 19 %. The optimum porosity of the metal foam is approximately 0.95, and the maximum temperature control efficiency could reach as much as 19.8 %.

Measuring and mathematical modeling of cushion curves for polymeric foams

In this paper, we created a general mathematical equation for the cushion curves of polymeric foams, using the measurement results of drop weight impact tests on commercially available, closed-cell ethylene-vinyl acetate and cross-linked polyethylene foams of different densities. We found exponential relationship between the results of the drop tests and the static load, and investigated the effect of the input parameters on the fitted constants using analysis of covariance and multiple linear regression. In the second part of the study, we used a novel approach to theoretically determine the cushion curves of different thicknesses. We predicted material behavior using the Burgess method on the fitted exponential equations and assessed the limitations and accuracy of this extrapolation approach by comparing the measured and simulated data. We validated the results by quantifying the permanently damaged volume of the foams with the use of a 3D optical measuring system.

The Impact of Atmospheric Parameters on the Dielectric Permittivity Values of SikaBlock®-M150 and Other Rigid Polyurethane Foams Measured with a Capacitive One-Side Access Sensor.

A shortage of research on the impact of atmospheric parameters on the measured dielectric permittivity values of rigid polyurethane (PU) foams was identified. Therefore, the impact of temperature, pressure, and relative humidity of air in the test room on the measured values of dielectric permittivity of rigid PU foams of different densities as well as monolithic polyurethane was investigated in a year-long experimental research study with a capacitive one-side access sensor. It was shown that relative humidity has the highest correlation with the dielectric permittivity values of rigid PU materials. The detected values of parameters were linked to the water vapour mass in ambient air and its correlation with permittivity of the investigated materials was determined. The warm-up drift and warm-up time of the spectrometer were estimated experimentally. A novel methodology was demonstrated to determine the true permittivity spectrum of rigid PU foams without any involvement of the environmental chamber, desiccators, or saturated salt/water solutions. A relative increase in the measured dielectric permittivity value was estimated numerically for the entire density range of rigid PU foams, i.e., 33–1280 kg/m3 (including monolithic PU).

Fracture performance of epoxy foam: Low density to bulk polymer

Epoxy foams with densities ranging from 180 to 500 kg/m3 were prepared and mechanically tested in compression, tension, and single-edge notched bending (SENB) configurations. Fracture results revealed a marked transition in behaviour at a critical density, between 227 kg/m3 and 249 kg/m3. Lower density foams failed at low SENB displacement, producing low toughness and fracture energy results, whereas higher density foams failed at higher SENB displacements, with correspondingly higher values of toughness and fracture energy. The stress-intensity factor increased monotonically with density, from 0.1 to 0.79 MPa m1/2. The fracture energy, GIc, of the foams reached values of up to 3.5 times that of the bulk polymer, 268 J/m2. Lower density foams below the transition in fracture behaviour exhibited a small number of large cells, caused by cell coalescence, and a wider cell size distribution than the denser foams. This distribution appears linked to the transition in fracture behaviour. The behaviour revealed in this paper raises the point whether in future design criteria, where foams are now often used in composite sandwich structures, allowance should be made for denser foams to be used as appreciable increases in fracture energy of the foam core are achievable.

Superior energy dissipation mechanisms compounded within composite AA6061/H130 foam structures

Significant demand exists for sacrificial energy absorbers which can achieve ideal mechanical performance (i.e., near-constant reaction forces) utilizing lightweight, readily available materials to simultaneously improve occupant safety and minimize vehicle mass to address growing calls to further improve efficiency in the transportation sector. A novel energy dissipation system comprised of AA6061 extrusions subjected to hybrid cutting/clamping and axially compressed H130 PVC foam, which could compound the ideal mechanical performance of each lightweight constituent component, was conceptualized and experimentally tested under quasi-static loading conditions. Since the extrusions remained intact above the blades the foam cores experienced uniform compression without in-plane deformation, leading to uniquely negligible extrusion/foam interaction effects. Extrusions with a T4 temper condition further benefited from resistance to circumferential distortion attributed to internal support from the foam cores. This behavior was in stark contrast to complementary structures subjected to a conventional axial crushing mode which experienced unstable combinations of lateral kinking, brittle lobe fracture and highly fluctuating reaction forces due to inconsistent interaction effects. The average TEA and energy absorbing effectiveness factor (EAEF) improved by 13 % and 38 %, respectively, for the composite structures subjected to novel compounded cutting/clamping compared to the traditional crushing mode, quantifying the enhancements over the current state-of-the-art. An analytical modeling procedure which could accurately (> 5 % error) replicate the newly observed, compounded force/displacement responses was derived and utilized in a parametric study identifying maximizing extrusion diameter and minimizing wall thickness and/or foam density as effective approaches to balance load bearing capacity and SEA.

Study on the coupling effect of silica‐reinforced silicone foam material in irradiation and corrosive solution environment

AbstractTo evaluate the suitability of silica‐reinforced silicone foam materials under extreme conditions, we studied the coupling effect of silica‐reinforced silicone foam material in irradiation and corrosive solution environment. The results showed that irradiation at 5 wt% KMnO4 attenuated the increase in crosslink density of silicone foams, while a different observation was found when the samples were treated with a 5 wt% HNO3 solution. The HNO3‐treated samples showed a significant decrease in elongation at break compared to the untreated samples. Mechanical properties, swelling, TGA, SEM, and XPS showed that HNO3 had a severe effect on the structure of the silicone foam. This may be due to the fact that the highly corrosive HNO3 disrupts the connecting structure between the silicone foam matrix and the filler. Based on this analysis, the damage mechanism of silicon foam material under the coupling conditions of corrosive solution and irradiation was proposed.

Tuning the Mechanical Behavior of Density-Graded Elastomeric Foam Structures via Interlayer Properties.

The concept of density-graded foams has been proposed to simultaneously enhance strain energy dissipation and the load-bearing capacities at a reduced structural weight. From a practical perspective, the fabrication of density-graded foams is often achieved by stacking different foam densities. Under such conditions, the adhesive interlayer significantly affects the mechanical performance and failure modes of the structure. This work investigates the role of different adhesive layers on the mechanical and energy absorption behaviors of graded flexible foams with distinct density layers. Three adhesive candidates with different chemical, physical, and mechanical characteristics are used to assemble density-graded polyurea foam structures. The mechanical load-bearing and energy absorption performances of the structures are evaluated under quasi-static and dynamic loading conditions. Mechanical tests are accompanied by digital image correlation (DIC) analyses to study the local strain fields developed in the vicinity of the interface. Experimental measurements are also supplemented by model predictions that reveal the interplay between the mechanical properties of an adhesive interlayer and the macroscale mechanical performance of the graded foam structures. The results obtained herein demonstrate that the deformation patterns and macroscale properties of graded foam composites can be tuned by selecting different bonding agents. It is also shown that the proper selection of an adhesive can be a practical way to address the strength–energy dissipation dichotomy in graded structures.

Mikrodalga Destekli Köpük Kurutma Yöntemi ile Kurutulan Ejder Meyvesi Tozlarının Kuruma Kinetiği ve Toz Ürün Özelliklerinin İncelenmesi

In this study, dragon fruit was dried by a microwave-assisted foam drying method and the effect of different microwave powers (350, 460 and 700W) on the drying kinetics and powder product properties were investigated. The properties (foam stability, expansion and density) of the foams obtained by adding egg white to dragon fruit puree were examined. The highest R2 and lowest RMSE and χ2 values of foam dried samples obtained from the Silva models. The effective moisture diffusion coefficient values of the samples (5.93×10-8-1.16×10-7 m2/s) increased due to the increase of microwave power. Activation energy values were calculated as 74.77 W/g. The effects of different microwave powers on moisture, water activity, color and powder product properties of dragon fruit powders dried by foam drying method were determined. In addition, in all conditions where microwave foam drying is performed, dragon fruit powders showed very good flowability and low stickiness.

Development of soy protein concentrate/hemp fiber-based biocomposite foams: Effects of alkaline treatment and poly(lactic acid) coating

Petroleum-based foams are used in packaging applications where thermal insulation and shock absorption are needed. However, their associated environmental problems motivate the development of bio-based alternatives. Here, biocomposite foams were prepared using soy protein concentrate (SPC) and alkali-treated hemp fibers. The hemp fibers were treated with 6% NaOH to remove non-cellulose components. The foams were coated by dipping in a poly(lactic acid) (PLA) solution. A concentration of 4% PLA was determined to be optimal for the coating. The mechanical and water barrier properties of the PLA-coated foams were evaluated. The compression modulus, compression strength, and bulk density of the PLA-coated foams were 1045.7 kPa, 2022.5 kPa, and 118.6 mg/mL, respectively, being significantly higher than those of the uncoated foams (404.0 kPa, 590.7 kPa, and 69.4 mg/mL). The moisture uptake and water uptake of the PLA-coated foams were significantly decreased by the coating procedure, indicating 16.2% and 138.3%, respectively. By contrast, the uncoated foams had a moisture uptake and water uptake of 31.8% and 1399.3%, respectively. The observed improvement in mechanical and water barrier properties is likely due to the hydrophobic nature of PLA. • Biobased foams were made using soy protein concentrate and hemp fibers. • The hemp fibers were treated with 6% NaOH to remove non-cellulose components. • The foams were coated with 4% polylactic acid (PLA). • The PLA-coated foams showed enhanced mechanical properties and water resistance.

RETRACTED: Mechanical Properties Study on Sandwich Composites of Glass Fiber Reinforced Plastics (GFRP) Using Liquid Thermoplastic Resin, Elium®: Preliminary Experiments

Composite sandwich structures have been used in high performance applications such as wind turbine blades, due to their unique lightweight structure and superior mechanical properties. In the current study, a new liquid thermoplastic and thermoset resin were used to fabricate four different composite sandwich panels with two various foam types and densities. Composites made with epoxy resin are presented to comprehensively compare the mechanical properties of sandwich structures to elium resin. In the case of the mechanical properties and due to a new liquid thermoplastic resin, extensive comparisons of three-point bending, climbing drum peel, and flatwise tensile strength were investigated and compared with each other. The flexural and flatwise strength of sandwich composite increased by 53% and 75%, respectively, when using Elium resin. Then, the highest value was shown in the GF/PVC/ELIUM structure. The results revealed that Elium resin could be excellent in the case of mechanical properties to replace traditional resins to fabricate various composite structures and manage the challenge of recyclable composites. Elium resin can replace thermoset-based resins for the manufacturing of laminates and composites that are fully recyclable at room temperature with comparable mechanical properties.

Development and Evaluation of a Topical Foam Formulation for Decontamination of Warfare Agents.

Lewisite is a highly toxic and potent chemical warfare vesicating agent capable of causing pain, inflammation, and blistering. Therapeutic strategies that safely and effectively attenuate this damage are important. Early and thorough decontamination of these agents from skin is required to prevent their percutaneous absorption. In our studies, we used phenylarsine oxide (PAO), a surrogate for arsenicals, to simulate lewisite exposure. Various parameters such as determination of extraction solvents, skin extraction efficiency, donor volume, and donor concentration were optimized for decontamination of PAO. We aimed to develop a novel, easy to apply foam formulation that can decontaminate arsenicals. We screened various foaming agents, vehicles, and chemical enhancers for the development of foam. Lead formulation foam F30 was further characterized for foam density, foam expansion, foam liquid stability, foam volume stability, and foam gas fraction. The amount of PAO delivered into human skin in 30 min of exposure was 228.57 ± 28.44 μg/sq·cm. The amount of PAO remaining in human skin after decontamination with blank foam F30 was 50.09 ± 9.71, demonstrating an overall percentage decontamination efficiency of over 75%. Furthermore, the decontamination efficacy of F30 was also tested in the porcine skin model and results indicated an even higher decontamination efficacy. These studies demonstrated that the developed foam formulation can be used for effective decontamination of chemical warfare agents.

The role of hyaluronic acid in polidocanol foam: An in vitro study.

To study the role of hyaluronic acid (HA) in polidocanol (POL) foam. The dose-dependent effect of HA-POL on cultured human umbilical vein endothelial cells (HUVECs) as well as foam stability was evaluated by measuring optical density (OD) values and foam half-life time (FHT), respectively. An in vitro model was utilized for estimating the foam blood-displacement capacity by adopting maximum displacement distance (MDD) and displacement time. A comparison of foam viscosity was also carried out. The OD values of HUVECs treated with HA first increased and then decreased with the growing dosage of HA while cells treated with HA-POL died. Both FHT and displacement time were prolonged statistically with a gradually enhanced foam viscosity. As to MDD, there were no significant differences. HA was found to promote HUVECs proliferation slightly, but this was almost negligible when compared to the cell-killing capacity of 1% POL. The viscosity of POL foam was enhanced by HA indicating its positive correlation with both stability and displacement capacity of POL foam.