Foam Beads Research Articles

Investigation of Recycled Expanded Polyamide Beads through Artificial Ageing and Mechanical Recycling as a Proof of Concept for Circular Economy.

Car manufacturers are currently challenged with increasing the sustainability of their products and production to comply with sustainability requirements and legislation. One way to enhance product sustainability is by reducing the carbon footprint of fossil-based plastic parts. Particle foams are a promising solution to achieve the goal of using lightweight parts with minimal material input. Ongoing developments involve the use of expanded particle foam beads made from engineering plastics such as polyamide (EPA). To achieve this, a simulated life cycle was carried out on virgin EPA, including mechanical recycling. The virgin material was processed into specimens using a steam-free method. One series was artificially aged to replicate automotive life cycle stresses, while the other series was not. The mechanical recycling and re-foaming of the minipellets were then carried out, resulting in an EPA particle foam with 100% recycled content. Finally, the thermal and chemical material properties were comparatively analysed. The study shows that the recycled EPA beads underwent polymer degradation during the simulated life cycle, as evidenced by their material properties. For instance, the recycled beads showed a more heterogeneous molecular weight distribution (an increase in PDI from two to three), contained carbonyl groups, and exhibited an increase in the degree of crystallization from approximately 24% to 36%.

Facile fabrication of lightweight and high expanded TPU/PBS bead blend foam with segregated microcellular network for reduced shrinkage and enhanced interface bonding

The emergence of expanded thermoplastic polyurethane foam beads (ETPU) has expanded the application range of polymer foam materials. However, most of the prepared bead foam products suffer from high shrinkage rate, high density, and poor interfacial bonding, severely affecting the mechanical stability and lightweighting of the products. Herein, this study constructed thermoplastic polyurethane/polybutylene succinate (TPU/PBS) bead blend foams with a segregated microcellular network structure (SMNS) for the first time, where the TPU/PBS continuous phase formed the SMNS and the bead phase was consisted of TPU foam beads. The results showed good interfacial bonding between the continuous and bead phases. By adding PBS to the continuous phase, the shrinkage percentage of TPU/PBS bead blend foam decreased from 79.19 % to 67.31 %, reduced by 15.0 %. In addition, the foam expansion ratio gradually decreased with increasing PBS content, dropping from 12.07 to 9.03. Moreover, TPU/PBS bead blend foams exhibited good energy absorption and mechanical stability without sacrificing thermal insulation performance. This work effectively reduced the shrinkage of TPU based foam materials, offering a simple and economical solution for the preparation of dimensionally stable, well-interfaced, and lightweight polymer foams.

Influence of foaming-induced crystallization behavior on the structure of poly(butylene adipate-co-terephthalate) supercritical foamed beads

The crystallization behavior during foaming directly affects the foaming properties. For crystalline polymers, there is no consensus on the influence of the crystallization behavior during foaming process on the stabilization of the cell structure. In this work, PBAT foamed bead and unfoamed pellets were prepared by controlling the saturated temperatures in supercritical CO2, soaking step (one or two) and the depressurization rate, respectively. Double melting peaks were observed in the DSC curve of supercritical CO2 foamed PBAT beads. By comparing the outgassing rates we find that the stretching-induced crystallization caused by the rapid expansion of the gas during foaming plays an important role in the stabilization of the cells. Although the crystalline perfection or crystal size at this time is much smaller than that of the crystalline grains formed during static cooling, the rapid crystallization is effective in stabilizing the cell structure of the foamed pores. Compared to normal supercritical foaming processes, the two-step foaming process of soaking CO2 at high temperatures followed by foaming at low temperatures results in an increase in cell size and expansion ratio. At high temperatures, more CO2 diffuses into the PBAT pellets, increasing the instantaneous gas concentration in the pellets for foaming, and the rapid stretching produces stretching-induced crystallization that raises the average size of the cells, further increasing the expansion multiplicity of individual cells. The average cell size of foam beads rises from 37.8 to 48.8 µm and the expansion ratio also increases to 8.6 with saturated temperature increasing form 95 to 105°C. The two-step soaking foaming method is a more efficient way of manufacturing industrial foamed beads, allowing for the preparation of better foam beads at low temperatures.

Comparison of Mechanical Properties of Steam-Free and Steam-Based Specimens Made of Expanded Polypropylene Beads.

Reducing the CO2 emissions of plastic parts is crucial in terms of sustainable product and process designs. Approaches include the use of recycled materials and reducing the energy demands of processes through more efficient technologies. In this context, this study shows the potential of the steam-free processing of particle foam beads into thin-walled moulded parts. Expanded polypropylene (EPP) particle foam beads have been processed in both a steam-free and steam-based process. For this purpose, specimens with different part densities and thicknesses were produced, the mechanical properties were investigated, and the surface quality was discussed. Specimens made of EPP with a part thickness of 5 to 20 mm and part densities of 60 to 185 g/L were produced steam-free. Lower part thicknesses and higher densities increase the mechanical properties. As the density increased, the homogeneity of the surfaces of the steam-free specimens also increased. In comparison, specimens with a thickness of 10 mm and part densities of 35 to 90 g/L were produced on a steam-based process. The results of the mechanical test were compared with those of the steam-free specimens. The steam-based specimens showed higher mechanical properties for the same density.

Influence of dielectric properties of polybutylene terephthalate and respective foam beads on process behavior in radio‐frequency welding

AbstractRadio‐frequency welding shows great potential for a more sustainable manufacturing of lightweight bead foam products based on local dielectric heating of the part. This study provides the first insight into the material‐process interactions required to enable interdiffusion between foam particles and thus adhesion. The complex relative permittivity is analyzed by impedance spectroscopy of the bulk polymer and foam beads using specially designed measurement cells. Due to the increased flexibility of the polymer chains at elevated temperatures, the relaxation mechanisms are promoted, resulting in a shift of the curves to higher frequencies. At a fixed frequency, a peak in the imaginary part is observed above temperature, revealing the superposition of these two parameters. The foamed beads show similar trends with an attenuated signal due to the high volumetric fraction of air within the multiphase system. The linear dependence between and volumetric power as direct process feedback due to dielectric heating was observed during welding. Compared to the delayed signals from the shielded temperature sensors, the analysis of power consumption allows for higher quality real‐time monitoring throughout the process cycle. The correlation also allows prediction of power levels at defined temperatures.

Flexural fatigue behaviour and damage mechanism of polystyrene bead foams—Influence of the foam density

Polystyrene-based bead foams are used in various applications under non-steady loading conditions, ranging from sports protectors to automobiles. However, the cyclic dynamic behaviour of bead foams and the influence of density on flexural fatigue behaviour have not yet been investigated. In this context, an analysis is conducted on both the morphology of the foam beads and the resulting morphology of the moulded parts produced from these beads. Furthermore, the influence of density on the quasi-static compressive and flexural properties was investigated. These results serve as a basis for conducting load-controlled flexural fatigue tests on various dense bead foams.It was found that the density dependence of the mechanical properties in the quasi-static tests follows the power law. In the flexural tests, the predominant damage mechanism is mainly influenced by the foam density but also by the processing.Surprisingly, the specific dissipated energy and stiffness remain constant for different densities until fast progressing failure occurs. Design criteria can be derived from the fatigue results. Under fatigue load, the stress should not exceed 40% of the quasi-static flexural strength, regardless of density.

Construction of designable and high-temperature resistant composite foams for tunable electromagnetic shielding

Conductive polymer composite (CPC) foams have been extensively studied for electromagnetic interference (EMI) shielding due to their lower density and relatively low EM reflectivity. However, most CPC foams are difficult to structurally design to regulate performance, and also limited in high-temperature application scenarios owing to the low-temperature resistance of the matrix themselves. Herein, high-performance expanded polyetherimide (EPEI) foam beads were fabricated by subcritical foaming technology with organic solvents/CO2 as co-blowing agents, and designable EPEI/CNS (carbon nanostructures) composite foams with segregated networks and high-temperature resistance were then manufactured through CNS dip-coating and epoxy bonding. The resultant EPEI/CNS composite foams showed the shielding effectiveness (SE) of ∼11.9–39.5 dB with CNS loading of only ∼0.25–0.72 vol%, along with R coefficient of only ∼0.26–0.56. The construction of asymmetric gradient structure in the foams via orderly assembling can further reduce the EM reflection in comparison with uniform structure, thereby remitting the secondary EM pollution. Moreover, the EPEI/CNS composite foams can not only maintain the structural integrity after being treated at ∼200 °C, but also maintain relatively stable EMI SE and most of their mechanical properties, enabling their applications in high-temperature environments. This work provides a simple and effective method for constructing high-temperature resistant CPC foams for tunable EMI shielding.

Snow Particle Analyzer for Simultaneous Measurements of Snow Density and Morphology

AbstractThe detailed characterization of snow particles is critical for understanding the snow settling behavior and modeling the ground snow accumulation for various applications such as prevention of avalanches and snowmelt‐caused floods, etc. In this study, we present a snow particle analyzer for simultaneous measurements of various properties of fresh falling snow, including their size, shape, type, and density. The analyzer consists of a digital inline holography module for imaging falling snow particles in a sample volume of 88 cm3 and a high‐precision scale to measure the weight of the same particles in a synchronized fashion. The holographic images are processed in real‐time using a machine learning model and post‐processing to determine snow particle size, shape, and type. Such information is used to obtain the estimated volume, which is subsequently correlated with the weight of snow particles to estimate their density. The performance of the analyzer is assessed using monodispersed spherical glass and foam beads, irregular salt crystals, and thin disks with various shapes with known density, which shows <10% density measurement errors. In addition, the analyzer was tested in a number of field deployments under different snow and wind conditions. The system is able to achieve measurements of various snow properties at single particle resolution and statistical robustness. The analyzer was also deployed for 4 hr of operation during a snow event with changing snow and wind conditions, demonstrating its potential for long‐term and real‐time monitoring of the time‐varying snow properties in the field.

Polishing of Metal, Foam, and Si-Doped GDP Capsules for Use as ICF Targets

Spherical targets with a smooth uniform surface are required for inertial confinement fusion experiments. This paper examines polishing as a method of decreasing the surface roughness of tungsten (W) capsules, chromium (Cr) capsules, SiCH [Si-doped glow discharge polymer (GDP)] capsules, and GDP-coated General Atomics–Carbon Hydrogen (GA-CH) foam beads. As expected, increasing the time spent polishing metal (W, Cr) capsules corresponded to decreasing roughness. Despite the decrease in overall surface roughness of Cr capsules, defects present in the batch initially were amplified through polishing. For SiCH capsules, increasing polishing time decreased the surface roughness, though the yield of usable capsules was affected by cracks induced through polishing. While polishing results for GDP-coated foam beads did not show consistent decrease in roughness, the polishing process did not result in the collapse of any of the foams, demonstrating the potential for polishing as a method of decreasing roughness.

Tailoring Light-Weight Aggregates for Concrete 3D Printing Applications

Concrete 3D printing is a sustainable solution for manufacturing efficient designs and creating less waste, and selecting the optimal materials to use can amplify the advantages of this technology. In this study, we explore printing lightweight concrete by replacing normal weight aggregate with lightweight aggregates such as cenospheres, perlite, and foam beads. We adopt a systematic approach to investigate mixtures using different formulation methods such as the specific gravity and packing factor methods to improve the printing and mechanical performances of the mixtures. The rheological results showed significant improvement in the flow characteristics of the different mixtures using both the specific gravity method and the packing factor method to formulate the mixtures. Furthermore, a statistical tool was used to achieve optimal performance of the mixtures in terms of high specific compressive strength, high flow characteristics, and good shape retention capability by maximizing the specific compressive strength ratio, slump flow, and the static yield stress, while minimizing the slump, dynamic yield stress, and plastic viscosity. With the above design objectives, the optimal percentages of the aggregate replacements (cenosphere, perlite, and EPS foam beads) were 42%, 68%, and 44%, respectively. Finally, the optimized results also showed that the mixture with cenosphere aggregate replacement had the highest specific strength.

Mechanical and acoustic absorption properties of lightweight fly ash/slag-based geopolymer concrete with various aggregates

Acoustic absorption and thermal insulation play a key role in modern buildings to make living comfortable and energy-saving. This paper aims to study the workability, physical and mechanical properties, thermal conductivity, and acoustic absorption of modified geopolymer concrete (GPC) with various types of lightweight aggregates (LWA) such as extruded polystyrene foam beads waste (EPS), vermiculite, or lightweight expanded clay aggregate (LECA). The mixtures of geopolymer concrete have been modified by substituting for the ordinary aggregates (dolomite) by volume with various ratios of 0, 25, 50, 75, and 100% for each type of LWA. Besides, the mechanisms of specimens were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and mapping. The results illustrated that the compressive strength values range between 8.5 and 47.50 MPa. The hardened density of concrete was between 1500 and 2450 kg/m3, and thermal conductivity was between 0.45 and 1.16 W/m.K. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. EPS, vermiculite, and LECA will be beneficial for applications in lightweight geopolymer concrete due to their capability to reduce weight and excellent thermal conductivity, and the property of improving acoustic absorption. The mechanical results indicated that 25% LECA was the best compared with the ratios of other LWA and gained 35.0, 2.7, and 4.3 MPa of compressive, splitting tensile and flexural strength, respectively. It had positive workability; the thermal conductivity was 1.1 W/m.K, and hardened density was decreased to 10% compared to the control. In addition, LECA is considered the superior and suitable material for acoustic absorption compared with other aggregates.

Autoclave foaming and steam-chest molding of polypropylene/polybutene-1 blend bead foams and their crystallization and mechanical properties

Expanded polypropylene (EPP) foams have showed wide applications in our daily life, such as automotive and packaging. Usually, autoclave foaming combined with steam-chest molding is the main artwork to prepare the high-precision EPP foam products. However, the foaming behavior of EPP and the excessive pressure required for molding still need to be further improved, which is great significance for energy saving and cost saving, etc. Herein, this study finds that adding a certain amount of polybutene-1 (PB-1) into the PP can help to reduce the temperature and pressure required for foaming/molding, and to broaden the foaming temperature. For example, in order to make the foam beads bonding well and with the expansion ratio of 20, the molding pressure should be higher than 2.7 bar for Neat PP foams, but just 1.5 bar for PP/PB-1 mixtures. Moreover, the effects of PB-1 content on the crystallization properties and foaming/molding behaviors of the PP/PB-1 bead foams are illustrated, and then the mechanical properties are also studied. Furthermore, the low-pressure foaming strategy presented here is beneficial for reducing the barriers of energy consumption and promoting the development of new bead foam materials.

Study of the internal temperature of rigid polyurethane bodies using temperature sensors

This paper investigates the effect of filling polystyrene foam beads (EPS) on the foaming temperature regulation of rigid polyurethane (RPUF) composites and describes the temperature change process of the first 400 s of the foaming reaction for two systems with high foaming temperature and low foaming RPUF. Different contents of expandable EPS were used to regulate the foaming temperature of RPUF to reduce the internal structural defects of the composite foam material caused by excessive internal foaming temperature which is effectively optimized for its use and low cost. RPUF with HCFC-141B as the physical blowing agent and expandable EPS as the filler were studied. MATLAB software was used to simulate the foaming process of pure RPUF for both systems and to predict the foaming temperature. The comparison with experimental data was made, and it was concluded that the foaming temperature of pure RPUF was too high. In addition, the temperature of the EPS-doped PUF porous composites in the core region and the temperature variation of the upper and lower surfaces during the foaming process were measured using a probe temperature sensor. The internal temperature is represented by a three-dimensional temperature trapezoid. The maximum temperature of the foaming process decreases more rapidly with increasing EPS content. In addition, the high RPUF heat loss and the smaller EPS growth energy lead to an increase in the mass fraction.

The effect of dielectric and thermal properties of plastic mold materials on the high frequency welding of three‐dimensional foam components

AbstractHigh‐frequency heating processes are widely used in industry, for example, for food processing, wood drying, or plastic welding. A recent development in this field uses radio‐frequency heating to fuse particle foam beads to complex components. The aim of using the modified process is to reduce the energy consumption of particle foam fusion. Within this process, the molds used must be electrically insulating to ensure the building of an electrical field. For this purpose, mold made of two different plastics were analyzed. Additional to the dielectric, mechanical, and thermal expansion, the thermal conductivity of the mold materials are of great interest. Although welding is finished quickly, cooling to the demolding temperature is comparably long. To achieve shorter cooling and therefore shorter process times, the mold materials were modified by two different thermal conductive but electrically insulating fillers. By the use of the thermally optimized mold materials, a reduction in cooling time of up to 40% was possible. At the same time, the heating step was hardly affected. Mechanical properties were enhanced while thermal expansion was reduced.

EVALUACIÓN DE LA ILUMINACIÓN HÍBRIDA DE CONCRETO LIVIANO CON CANTIDADES DIFERENTES DE FIBRA ÓPTICA PLÁSTICA A4b

The objective of this research is to quantify the contribution of light produced by hybrid lighting through translucent concrete panels, as well as to specify the mechanical properties of lightweight translucent concrete. To obtain data, it was proceeded to design common concrete, to which polystyrene foam beads were added, in different dosages, until the designation of light concrete was achieved. Later, plastic optical fibers were added in its structure forming specimens which were tested by translucency and mechanical tests. The results obtained were lightweight concrete panels made at 3%, by volume, fiber optic with translucency of 0.165% and 6.89 lux on average. It was concluded that lightweight concrete offers good support for the installed optical fibers, offering acceptable mechanical characteristics up to a maximum of 4% added fiber.

Vitrimer bead foams: Cell density control by cell splitting in weld-compression molding

The fabrication of weldable and recyclable polyolefin bead foams remains a great challenge. Here, we report a convenient pathway to transform polyolefin elastomer (POE) into vitrimers based on classical ester-hydroxyl transesterification through reactive extrusion. The dynamic behaviors and mechanical properties of POE vitrimers could be readily regulated by varying the dosage of the cross-linker. POE vitrimer bead foams are prepared by a simple and feasible free foaming technology. We suggest two approaches to reprocess and recycle POE vitrimer bead foams by weld-compression molding and re-foaming. POE vitrimer bead foams could be well bonded with adjustable cell density and performance through weld-compression molding strategy. The dynamic transesterification can not only promote the fusion of foam beads, but also induce the fusion of contact buckling cell walls under compression. This investigation would motivate further sustainable development in the designing and recycling of polymer bead foams.

Behaviour of a Foam Mixture as a Lightweight Construction Material

Building on weak soils is very challenging in engineering projects, especially highway and railway projects. To overcome these problems, especially in the construction of embankments and abutments, it is necessary to reduce the settlement of soil and increase the bearing capacity. This paper investigates the characteristics of expanded polystyrene (EPS) foam beads mixture as a lightweight construction material. EPS foam is characterized as a lightweight, economic and environmentally friendly material. Samples of different mixtures were prepared using EPS foam beads with sand, cement and water at different ratios. A series of rigorous tests were carried out to evaluate density, shear strength parameter, compressibility, and crushing strength of the prepared mixtures. The mixture of foam beads and sand was mixed in ratios 1:1, 1.5:1 and 1:2 by volume and mixed with cement content of 7%, 8%, 9% and 10% of sand weight using the optimum water content. From the results it was found that the best ratio between sand and foam beads by volume was 1:1, and high cement ratio of 10% formed lightweight mass with acceptable crushing strength, CBR and compressibility characteristics. The results proved that, the characteristics of the mixture are linearly proportional with cement content and curing time. Practically, the mixture can be used as a subgrade material to overcome the problems of weak soils especially in highway construction.

A review on manufacture of polymeric foam cores for sandwich structures of complex shape in automotive applications

In this work, polymeric foam thermoforming, foam injection moulding, bead foaming and film foaming were reviewed in an effort to explore feasible processes to manufacture sandwich structures of complex geometry for automotive applications. Injection moulded foams generally suffer from high density, poor cell morphologies and unnecessary skin layers. Foamable films currently available are pressure-induced. In order for foamable films to produce foam, high uniformly-distributed pressure needs to be applied, which makes it difficult to manufacture foam parts of three-dimensional complex geometry with foamable films. The majority of commercial high-performance foam cores can be thermoformed. Ideally, thermoformed foam cores would have good mechanical properties if high-performance foam sheets are used. However, the mechanical properties of foams might be reduced during the process of thermoforming, especially around corners. Bead foaming offers a high level of freedom in foam geometry to be moulded, and inserts can be integrated into foam cores during the process of moulding. Moreover, foam cores with high density in high stressed areas and low density in low stressed areas can be manufactured with foam beads of different densities. However, due to nonhomogeneous degree of fusion and weak bonds and voids between beads, bead foams generally show mechanical properties lower than their block counterpart. Relatively speaking, thermoforming with high-performance foam sheets and moulding with high-performance foam beads hold great potentials for mass production of sandwich cores of complex geometry for automotive applications. However, further investigation on the mechanical properties of thermoformed foams and high-performance bead foams is still in need to confirm their suitability.

Active Bending Mechanism Employing Granular Jamming and Vacuum-Controlled Adaptable Gripper

We propose a bending mechanism in this study capable of wrapping around objects of various shapes and increasing its stiffness simply via the evacuation of internal air. Unlike vacuum splints requiring manual wrapping and pneumatic bending devices based on granular jamming requiring a complicated combination of two separate air control systems, our proposed mechanism can wrap itself around objects using a single air evacuation system. An elastic container enveloping polystyrene foam beads and urethane sponges is employed in this mechanism. The compression of the sponges, caused by the evacuation of internal air, results in bending, while the stiffness of the mechanism increases simultaneously due to granular jamming. On embedding sponges having different stiffnesses, the resulting differences in the onset of sponge shrinkage cause sequential bending, which reduces the gaps between the mechanism and the target object. First, we developed a mattress-shaped bending mechanism that can be used as a vacuum splint and does not need to be manually wrapped around an object. Thereafter, an adaptable gripper was developed using the same bending mechanism. The gripper can wrap around objects having various shapes and increase its stiffness simply by evacuating internal air; it can even lift heavy objects.

Study on flow field in Falcon separator by high-speed dynamic photography and CFD simulation

ABSTRACT This research builds an experimental test platform to verify practicability of theoretical calculation formula and CFD simulation (Fluent software) by comparison of measured value and calculated value, including flow film thickness, recoil water velocity, fluid velocity, and particle velocity. For liquid velocity test, 1 mm polystyrene foam beads are used as tracer particles, while solid velocity test uses fine coal with a density of 1800 kg/m3 and a particle size of 0.5 mm as observation object. Measurement results show that flow film thickness measured value is consisted of that of calculated value, all relative error is less than 5%. But increase of rotational frequency can make relative error increase slightly, this may be caused by instability of flow film due to increasing rotational frequency. In terms of recoil water velocity, its measured value is almost same as calculated value and its relative error is lower. Measurement results of fluid velocity and particle velocity indicate that variation trend of tangential and axial velocity simulation value is basically same as experimental value. However, relative error of axial tangential is greater than that of tangential by 10% for fluid velocity and relative error of axial tangential is greater than that of tangential by 20% for particle motion velocity. The large deviation of axial velocity is that direction of the axial acceleration changes easily relative to the stable tangential velocity, the “relaxation phenomenon” of tracer particles in the experiment and interference from other aspects of flow field make deviation increase slightly.