Polymer Foams Research Articles

Structural features of biobased composite foams revealed by X-ray tomography.

Polymer foams can have heterogeneous and complex internal structures, especially when material blends or particles have been integrated to create composites. It becomes even more challenging to probe and understand foam structure/properties when using non-uniform particles, such as biobased fillers. Optical or SEM imaging can only provide limited information as these are two-dimensional (2D) surface techniques. In this study, 3D X-ray tomography was applied to comprehensively analyze the structural features of biobased polyurethane foams containing porous rice hull fillers. The in-depth characterization at a wide range of length scale enabled us to quantify and obtain statistics of the unique trends in foam pore size and pore orientation corresponding to rice hull particle fraction and particle size. Rice hull particles were found to induce smaller cell formation. In addition, these biobased particles influenced cell expansion and caused cells to have less consistent orientation. Furthermore, after foam samples were subjected to cyclic compressive loading, X-ray tomography showed fractures in large (>100 μm) particles. This helps reveal the premature failing mechanism of composite foams with highly porous and coarse particles. The study elucidates novel microstructural evolution and deformation mechanisms using 3D X-ray tomography. The results offer new insights on internal structures for biobased composites and foams that are not previously possible through the conventional characterization tools.

Current progress and frontiers in three-dimensional macroporous carbon-based aerogels for electromagnetic wave absorption: a review.

In the present era of rapid development in electronic information technology, electromagnetic (EM) pollution is increasingly receiving widespread concerns due to its potential threats to electronic devices and human health. EM wave absorbing materials (EWAMs) play an increasingly important role in preventing exposure to EM waves because they can attenuate incident EM waves through sustainable energy dissipation. Among the numerous EWAMs developed in recent years, three-dimensional (3D) macroporous carbon-based aerogels have been considered one of the most promising candidates as high-performance EWAMs not only due to their flexible component options and the beneficial synergies between their different components but also for their open skeletons, which provide a unique structural contribution to accelerating the consumption of EM waves. In this review, we focus on the current progress of 3D macroporous carbon-based aerogels toward EM absorption and highlight different strategies for their preparation, including biomass transformation, template method, hydrothermal/solvothermal self-assembly, polymer foaming, and metal-organic frameworks (MOFs) topological transformation. Moreover, we discuss and analyze the effects of composition, optimization and structural engineering on their EM absorption performances. After a comprehensive evaluation of the performance of 3D macroporous carbon-based aerogels, we further propose some challenges and perspectives for the development of 3D macroporous carbon-based aerogels, and envision their broad application prospects in the future.

Fumed nanosilica as filler for semi-rigid palm oil-based polyurethane foam: Mechanical, material, thermal, and fire response

Incorporating nano-sized fillers into bio-based polyurethane (PU) foams typically enhances their properties. In present investigation, palm oil-based PU foams are fabricated with varied loadings (0 to 5 wt%) of fumed nanosilica. The foams are then characterized for their fire-retardancy, thermal stability, foam morphology, and also mechanical properties. Marginal improvement in Limiting Oxygen Index (LOI) values, as well as failure to be rated under UL-94 Vertical Combustion Test indicate limited potential of fumed silica in improving flammability of organic polymeric foams; suggesting exorbitant amount is required for any distinguishable effect to manifest. Interestingly; results from Thermogravimetry Analysis (TGA) shows marked improvements in terms of char residue with more than seven-fold increase at 5 wt% filler loading, possibly owed to the inert filler nature of fumed nanosilica forming a char barrier and acting as fuel diluent. Filled PU foams displayed an increased open-cell content, likely because the filler functioned as a cell opener. Removing the influence of density, the normalized compressive properties showed notable improvement up until a certain loading, which could be credited to the increased stiffness imparted by the filler itself. The results portray the potential of fumed nanosilica as filler for bio-based PU foams, offering enhanced thermal stability and limited fire retardancy.

РОЛЬ ТЕХНОЛОГИЧЕСКИХ ФАКТОРОВ В ФОРМИРОВАНИИ СТРУКТУРЫ ОТКРЫТОПОРИСТЫХ ВСПЕНЕННЫХ МАТЕРИАЛОВ НА ОСНОВЕ ЭТИЛЕН-ПРОПИЛЕН-ДИЕНОВЫХ СОПОЛИМЕРОВ ПУТЕМ КОМПРЕССИОННОГО ФОРМОВАНИЯ

Ethylene-propylene copolymers (EPDM) are known for a wide range of useful properties. EPDM-based rubbers have weather resistance, resistance to aggressive environments and wide operating temperatures. EPDM-based blends allow to create composite materials such as open-cell polymer foam. Due to their unique composition, open-cell elastomeric foam based on EPDM can have different structures, densities and properties. This paper presents a study of the possibilities of technologies of first-stage and second-stage foaming in vulcanization presses in order to regulate the pore structure of open-cell material based on ethylene-propylene-diene copolymer.

Preparation and characterization of potato crust-based polyurethane Foam-II

In this research study, environmentally friendly and biodegradable PU polymer foam was synthesized from starch-containing potato crust to be used as a thermal insulation material by reducing reliance on fossil resources and utilizing biomass resources. Biopolyols were obtained by reacting with active solvents at different reaction times, in the presence of different catalysts and at different catalyst concentrations. The most suitable polyol in terms of biomass content, density, viscosity and acid-hydroxyl number was selected for PU foam synthesis. Reactions for PU synthesis were tried and PU foam was synthesized. The synthesized PU foam was examined by Scanning Electron Microscope (SEM) and Thermo Gravimetric Analysis (TGA). Its morphological structure, thermal degradation properties, sound transmission coefficient and water absorption properties were determined by comparing it with a commercial PU foam. SEM images showed a heterogeneous pore distribution with closed and open cells, the majority of which were closed. From the TGA results, it was determined that a two-step degradation occurred and incorporating biomass into its structure improved the total thermal degradation properties. The sound transmission rate of starch-containing PU foam, when used as a thermal insulation material, was measured to be lower than the concrete structure, but partially close to and higher than that of commercial PU foam. The water absorption properties of the synthesized PU foam were found to be significantly higher compared to commercial PU foam and and contributed to its usability as a thermal insulation material. Thermal insulation material PU foam is synthesized in terms of its properties.

Improved electromagnetic interference shielding performance of silicone rubber/CNTs composites by porous structure design via green supercritical CO2 foaming

In this study, the relationship between porous structure and electromagnetic interference (EMI) shielding performance of polymer foams is established. A green supercritical CO2 foaming technology is utilized to construct silicone rubber (PMVS)/carbon nanotubes (CNTs) foams with tunable porous structures (porosity, cell size, cell density and cell gradient structure). Notably, the introduction of moderate porosity (within 40 %) simultaneously enhanced the total EMI shielding effectiveness (SET) and absorption coefficient (A). PMVS/CNTs foam reached a maximum SET of 62.3 dB, a 35.4 % increase over solid PMVS/CNTs composite. Additionally, small-cell PMVS/CNTs foam shows a higher A under the same porosity, while large-cell foam exhibits higher SET. Moreover, gradient porous PMVS/CNTs, combining advantages of large and small cells, maintains a high A (78 %) and exhibits superior SET (52.7 dB), along with exceptional EMI shielding stability (with SET and A retaining 97.7 % and 99 %, respectively, after 1000 cycles of compression). This work provides a theoretical foundation for optimizing EMI shielding performance by regulating porous structures.

Rapeseed Oil as Feedstock for Bio-Based Thermoset Foams Obtained via Michael Addition Reaction.

Rapeseed oil was used to develop thermoset foams via Michael addition reaction by mixing two liquid components, Michael donor and Michael acceptor. The foaming of the curing thermoset was achieved by the physical blowing agent which expanded from the reacting foam mass due to an exothermic curing reaction. The influence of the rapeseed oil-based Michael donor functionality on the foaming process and the characteristics of the obtained thermoset foams was studied. The 1,1,3,3-tetramethylguanidine catalyst's influence on the foaming process kinetics was studied using FOAMAT equipment. The curing of the bio-based thermoset was analysed using a dielectric polarisation sensor. The morphology of the developed thermoset foam was analysed using a scanning electron microscope and the obtained foams were characterized using TGA, DSC, DMA and mechanical analysis tests. A direct correlation between the thermoset foam polymer crosslinking density and foaming reactivity, mechanical properties and glass transition temperature were determined. Obtained rapeseed oil based thermoset foams had a relatively low thermal conductivity of 33.9-35.4 mW/(m·K) which allows their use as thermal insulation material in civil engineering applications.

Vertical compression performance of fiber-reinforced polymer (FRP) foam sandwich composites in hygrothermal environment

The safety of utilizing composites has garnered significant attention due to their widespread application in civil engineering, aerospace, and other fields. In the present investigation, fiber-reinforced foam sandwich composites were fabricated using the vacuum-assisted resin injection (VARI) process. The constant temperature and humidity test chamber is used to carry out damp-heat aging experiments on the specimen, and the mechanical properties after damp-heat aging are studied. The present study aims to examine the vertical compression characteristics of fiber-reinforced foam sandwich composites under the influence of hygrothermal aging. This paper also elucidates the mechanism by which the hygrothermal environment affects these composites. The results indicate that the mechanical properties of the specimens decrease after damp-heat aging. The unidirectional stacked fibers exhibit better resistance to the damp-heat environment compared to the orthogonal stacked fibers. Additionally, the inclusion of drainage holes in the setup can enhance the resistance of the specimens to the damp-heat environment.

On the determination of viscoelastic properties of EPP foam in dependence on pre-strain and loading direction

Understanding the viscoelastic properties of EPP foams is of crucial importance for their use in industrial applications. However, mechanical testing of polymeric foams is challenging due to the difficulties that arise from their morphology. For this reason, here currently available DMA methods using a single drive and a multi-drive rheometer as well as multiple loading directions are investigated in detail. Experimental challenges are highlighted and discussed with regard to foam-specific properties. Special focus is laid on the influence of compressive pre-strain. Based on the results, guidelines to perform reproducible DMA tests on the investigated type of material are derived. In addition, the results give deeper insight into the deformation behavior of bead foams at small strain levels and reveal an early onset of the transition from linear to plateau regime.

Investigation of both thermal parameters and applications of closed-cell plastic thermal insulation foams with building energetic aspects

Nowadays, if one wants to renovate or build a building, the question of thermal insulation is an essential construction process. Polyurethane is a key thermal insulation material that belongs to plastic foams. It can be applied as a spread or board heat-insulating material. Its thermal insulation properties are superior compared to polystyrene, but still a bit neglected. In this article, we would like to perform thermal investigations executed on a new type of polymeric foam such as polyisocyanurate. We will present acceptably low thermal conductivity (~ 0.022 W m-1 k-1), raised specific heat capacity (~ 1400 J kg-1 K-1) and calorimetric (bomb and differential) measurement results completed with optical microscopic images. Moreover, scanning electron microscopic analysis and X-ray diffractometry will be also presented. The results will be used for cost calculations applied by buildings and will show justified reasons for its application based on structural measurements too. The results are extremely encouraging.

Constitutive modeling and simulation of polyethylene foam under quasi-static and impact loading

In this paper, quasi-static and dynamic compression experiments were carried out on polyethylene foam by a universal material testing machine and a drop tower impact device. The mechanical response characteristics and energy absorption capacity of polyethylene foam under quasi-static and moderate strain rate (4 × 10−3–102s−1) loading conditions were obtained. An improved constitutive model of strain-rate term coupling strain and strain rate was established based on the Sherwood–Frost phenomenological constitutive model and Johnson–Cook constitutive model. Low Density Foam model combined in the finite element software ABAQUS with the improved constitutive model was used as the parameter definition of polyethylene foam material in the simulation. The drop-tower impact tests at different heights were simulated, and the simulation results were compared with the actual drop tower impact test results. The results showed that the peak acceleration errors between simulation and experiment were less than 7.1%, verifying the accuracy of the constitutive model. This study provides a method of constitutive models and finite element simulation to the performance of polymer foams.

Experimental and phenomenological investigations on the strain rate sensitivity of rigid PVC foams at strain rates of 0.005 s−1 to 600 s−1

Polymeric foams are often subjected to high strain rates in various industrial applications, especially the transportation sector, and experience significant deformations. An in-depth comprehension of the dynamic mechanical characteristics of polymeric foam is essential for devising effective engineering design approaches. Previous studies have extensively utilized Split Hopkinson Pressure Bar (SHPB) apparatuses to test polymeric foams dynamically; however, these studies faced technical limitations in specimen size, preventing compliance with the ASTM D1621 standard test method for rigid cellular plastics. A customized pneumatic apparatus equipped with a massive impacting bullet and sacrificial excess energy absorbing system was employed to complete the mechanical material characterization of Polyvinyl Chloride (PVC) foams, following the ASTM D1621 standard, to address previous technical limitations. PVC foams with six different nominal densities were subjected to strain rates ranging from 0.005 s−1 to 600 s−1. Loading was conducted parallel and perpendicular to the foam rise direction to investigate dynamic anisotropic material characteristics. A comparison of tests conducted at strain rates of 0.005 s−1 and 400 s−1 revealed an average increase of 35.1 % in the plateau stress. The phenomenological Nagy model was combined with a nonlinear Avalle relationship and revised with a new term, supported by findings from the present study, to characterize the complete stress/strain response, for the range of strain rates considered in this research. The calibrated model exhibited an average error of 1.7 % in the predicted plateau stress. The results indicated that testing under a single dynamic strain rate was sufficient to characterize the rate sensitivity of the PVC foam in the dynamic regime. Furthermore, the influence of relative density on the foam rate sensitivity was quantified, revealing a plateau in the strength enhancing effect of density at a nominal relative density of 0.125.

Mechanical, Crystallization, Rheological, and Supercritical CO2 Foaming Properties of Polybutylene Succinate Nanocomposites: Impact of Carbon Nanofiber Content.

As a substitute for conventional polymers for the preparation of biodegradable microcellular polymeric foams, polybutylene succinate (PBS) presents one of the most promising alternatives. However, the low melt strength of PBS makes it difficult to produce high-performance microcellular foams. This study aimed to improve the melt strength of PBS and explore the mechanical, thermal, crystalline, rheological, and supercritical CO2 foaming properties of PBS nanocomposites by using carbon nanofibers (CNFs). This study found that nanocomposites containing 7 wt% CNF exhibited the highest tensile strength, Young's modulus, and bending strength. Moreover, the CNF nanofillers were well dispersed in the PBS matrix without significant agglomeration, even at high filler concentrations. Furthermore, the nanocomposites demonstrated improved melting temperature and crystallinity compared with pure PBS. The rheological analysis showed that the addition of CNFs significantly increased PBS viscosity at low frequencies due to the interaction between the PBS molecular chains and CNFs and the entanglement of CNFs, resulting in a more complete physical network formation when the CNF content reached above 3 wt%. During the supercritical CO2 foaming process, the addition of CNFs resulted in increased cell density, smaller cells, and thicker cell walls, with good laps formed between the fibers on the cell walls of nanocomposite foams. Moreover, the electrical conductivity and electromagnetic interference (EMI) shielding properties of the foamed material were studied, and a nanocomposite foam containing 7 wt% CNF showed good electrical conductivity (4.5 × 10-3 S/m) and specific EMI shielding effectiveness (EMI SE) (34.7 dB/g·cm-1). Additionally, the nanocomposite foam with 7 wt% CNF also exhibited good compression properties (21.7 MPa). Overall, this work has successfully developed a high-performance, multifunctional PBS-based nanocomposite foam, making it suitable for applications in various fields.

On Lightweight Shape Memory Vitrimer Composites.

Lightweight materials are highly desired in many engineering applications. A popular approach to obtain lightweight polymers is to prepare polymeric syntactic foams by dispersing hollow particles, such as hollow glass microbubbles (HGMs), in a polymer matrix. Integrating shape memory vitrimers (SMVs) in fabricating these syntactic foams enhances their appeal due to the multifunctionality of SMVs. The SMV-based syntactic foams have many potential applications, including actuators, insulators, and sandwich cores. However, there is a knowledge gap in understanding the effect of the HGM volume fraction on different material properties and behaviors. In this study, we prepared an SMV-based syntactic foam to investigate the influence of the HGM volume fractions on a broad set of properties. Four sample groups, containing 40, 50, 60, and 70% HGMs by volume, were tested and compared to a control pure SMV group. A series of analyses and various chemical, physical, mechanical, thermal, rheological, and functional experiments were conducted to explore the feasibility of ultralight foams. Notably, the effect of HGM volume fractions on the rheological properties was methodically evaluated. The self-healing capability of the syntactic foam was also assessed for healing at low and high temperatures. This study proves the viability of manufacturing multifunctional ultralightweight SMV-based syntactic foams, which are instrumental for designing ultralightweight engineering structures and devices.

Fabrication of bio-based biodegradable poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composite foams for highly efficient oil-water separation

The open-cell bio-based biodegradable polymer foams show good application prospect in dealing with the serious environmental issue caused by oil spill and organic solvents spills, while the cell structures and hydrophobic properties of the foams limit their performance. In this work, the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was selected to help prepare bio-based biodegradable poly(lactic acid) (PLA) foams. Based on a two-step foaming method, the crystallization ability of different samples was regulated by the “original crystals” together with PHBV in the foaming process, where skeleton structures were provided to facilitate the open-cell structures and promote their mechanical property. As illustrated, PHBV facilitated the formation of open-cell PLA foams, where the foams displayed superior oil-water separation capacity. The maximum volume expansion ratio of the foams was 80.08, the contact angle of deionized water reached to 134.5°, the adsorption capacity for oil or organic solvents was 10.8 g/g-51.8 g/g, and the adsorption capacity for CCl4 can still maintained 83.5 % of the initial value after 10 adsorption-desorption cycles. This work not only clarified the foaming mechanism of open-cell foams, but also provided a green and simple method for preparing bio-based biodegradable foams possessing excellent oil-water separation performance.

Comparison between antimicrobial assays of catechol-based polyurethane foam polymer and catechol-modified polyurethane foam polymer with zinc oxide nanoparticles

Comparison between antimicrobial assays of catechol-based polyurethane foam polymer and catechol-modified polyurethane foam polymer with zinc oxide nanoparticles

A comprehensive investigation on the temperature and strain rate dependent mechanical response of three polymeric syntactic foams for thermoforming and energy absorption applications

Polymeric syntactic foams (PSF) are a kind of composite material, which consists of a polymer matrix reinforced by hollow thin wall glass micro-spheres. Because of their low density, low moisture absorption, relatively high specific strength and stiffness, PSF are often employed in aerospace and submarine applications in which they are subjected to a wide range of temperature conditions. Due to the temperature sensitivity of the polymer matrix, the physical and mechanical behaviour of PSFs is highly sensitive to temperature variations. Besides, their dynamic response is significantly affected by the strain rate. This research investigates the temperature and strain rate dependence of the mechanical behaviour of polyurethane, epoxy and nylon syntactic foams under compressive and tensile loads. The selected materials have in common that their mechanical characteristics, thermal properties, and dimensional stability make them suitable for both impact engineering and thermoforming applications. The experimental results, acquired over a temperature range from −25 °C to 100 °C at low and high strain rates, reveal a clear interplay between temperature and strain rate effects on the mechanical behaviour of the materials under investigation. This synergy is observed to vary based on both the matrix material and the loading mode. Notably, the rate dependency of polyurethane and nylon syntactic foams is significantly influenced by the testing temperature during compression, while in tension the influence of the temperature on the rate dependency is moderate or negligible. In contrast, the rate dependency of the epoxy syntactic foam remains largely unaffected by the testing temperature. Deformation and failure mechanisms were analysed by examining the failure surface of the tested samples using SEM micrographs.

Influence of Relative Humidity on Electrical Properties of Textile Laminates

The aim of this paper is to determine the influence of relative humidity on the comfort and electrical resistance properties of textile laminates in order to predict possible changes in footwear protection levels. Four textile laminates of different structure and fibre nature were selected for the study. It was determined that water vapour absorption of textile laminates strongly depends on the humidity of the storage environment. The absorption ability of laminates increases about 1.8 – 3 times as relative humidity increases from 65 % up to 95 %. The degree of increase depends on the textile laminate structure and the nature of the materials layers. The electrical properties of protective footwear can be influenced by the structure, thickness, relative humidity, and voltage of textile laminates. For textile laminates composed of natural and synthetic fibres and polymer foam as insulators, the resistivity increases with the thickness of the synthetic fibre and polymer layer. At low voltage (U = 100 V), the textile laminates tested became insulating materials, as the electrical resistivity exceeded the threshold values for antistatic materials in all relative humidity ranges. At high voltage (U = 500 V) the electrical resistivity of textile the laminates drops dramatically when the relative air humidity increases and the level of protection of the laminates depend on the amount of moisture absorbed and the nature of the layer materials. The laminates possessed insulating properties in environments of up to 65 % relative humidity. In a high humidity of the environment, the insulating properties of textile laminates turned to antistatic, except for laminate without a polymeric membrane, which became conductive.

Characterisation of Gaina cocoon foam: A promising and eco-friendly alternative to synthetic materials

Increasing demand for polymeric foams, usually made of petroleum-based polymers, has raised concern about solid waste and its environmental impact, forcing scientists and researchers to find some biodegradable alternatives. However, these alternatives have limitations such as high density, more handling and processing costs, water and humidity-based degradation in cell structure, and inability to perform at elevated temperatures. This study discovers and examines a naturally occurring cellular material, the ‘Gaina’ cocoon, which is readily accessible in Uttarakhand hills and is inexpensive and biodegradable. Giana cocoon was found to have a density of 0.064 g/cc, which is lower than other natural biodegradable materials and very close to that of manufactured PLA foam. The morphological analysis revealed that the material has a cellular structure with irregularly shaped and sized cells. It has a semi-crystalline structure and is composed chiefly of carbon. Energy dispersive X-ray (EDX) spectroscopy showed that the Gaina cocoon foam has carbon and hydrogen as prime and major contributors. Fourier-transform infrared (FTIR) spectroscopy revealed various functional groups inside the cocoon, which will help understand its bonding with various matrices or materials. The differential scanning calorimeter (DSC) peak at 145°C was the largest (from 100°C to 181°C), showing a maximum heat transfer of about 278.325 J/g. The material is also thermally stable up to 260°C and has a lower density than other biodegradable foams on the market. Overall, these discoveries provide light on the features of this natural cellular material, which has potential uses in various industries, like packaging, insulation, and building.

Multiscale modeling of shape memory polymers foams nanocomposites

Shape memory polymer foams (SMPFs) are defined as lightweight cellular materials with the ability to recover their undeformed shape by applying an external stimulus like light, temperature, magnetic field, etc. Reinforcement of the material with nano-clay filler leads to a significant improvement in its physical properties. As a result, a wide range of applications is occupied by SMPFs, especially in industry and biomedical applications. Because of the heterogeneous nature of the SMPFs at different scale levels, modeling the material with one scale numerical model which able to capture all the effects of the lower scale material structure is really a complex task. Within this work, a full multiscale modeling approach is employed to investigate the thermomechanical response of the SMPFs. Furthermore, a combination of the 3D Representative Volume Element (RVE) and finite element method is used to explore the effects of the nano-filler weight fractions and the material's cellular structure at different length scales on the material dynamics. The multiscale modeling process gives great and promising results with good agreement with the experimental results. Moreover, the model shows relatively high sensitivity parameters that are initiated from the lower scale level.