Multifunctional Foams Research Articles

Sustainable foams from hemp, lignin, xylan, pectin, and glycerol: tunable via reversible citric acid crosslinking for absorption and insulation applications

This study investigates the development of sustainable multifunctional foams utilizing hemp stalk waste, lignin, xylan, pectin, glycerol, and citric acid. Using the freeze-drying method for foam formation in combination with industrial waste products and renewable resources, we emphasize a green, scalable material development approach. In total, 25 distinct formulations were prepared and methodically examined, mainly focusing on the roles of citric acid, pectin, and glycerol. Thermal crosslinking, conducted at 140°C, was analyzed using FTIR, confirming the formation of ester bonds. The microstructural characterization of the foams revealed distinct variations from nanofibrillar to microfibrillar structures based on composition. The bulk density of the foams ranged from 13 to 152 mg/cm3, and porosity values varied from 97 % to 99 % for most of the compositions. Foams showed up to 50 g/g water, 51 g/g rapeseed oil, and 46 g/g kerosine absorption. Foam absorption capacity changes were examined through 10 iterative cycles in water, demonstrating that most compositions retained near-original absorption capacities. Adding glycerol conferred exceptional hydrophobic properties to the foam surfaces, as evidenced by water contact angles ranging between 140° and 150°. The thermal conductivity of foams ranged from 0.040 to 0.046 W/mK. The mechanical properties of foams were assessed using compression testing, which showed highly tunable structures ranging from soft to rigid. This study illustrates the broad applicability of these foams, emphasizing their utility in thermal insulation, filtration systems, and environmental cleanup, among other potential uses.

Green preparation of antibacterial shape memory foam based on bamboo cellulose nanofibril and waterborne polyurethane for adaptive relief of plantar pressure

This study developed an aqueous solution blending and freeze-drying method to prepare an antibacterial shape memory foam (WPPU/CNF) based on waterborne PHMG-polyurethane and cellulose nanofibers derived from bamboo in response to the increasing demand for environmentally friendly, energy conserving, and multifunctional foams. The obtained WPPU/CNF composite foam has a highly porous network structure with well-dispersed CNFs forming hydrogen bonds with the WPPU matrix, which results in a stable and rigid cell skeleton with enhanced mechanical properties (80 KPa) and anti-abrasion ability. The presence of guanidine in the polyurethane chain endowed the WPPU/CNF composite foam with an instinctive and sustained antibacterial ability against Escherichia coli and Staphylococcus aureus. The WPPU/CNF composite foam exhibited a water-sensitive shape memory function in a cyclic shape memory program because of the chemomechanical adaptability of the hydrogen-bonded network of CNFs in the elastomer matrix. The shape-fixation ratio for local compression reached 95 %, and the shape-recovery rate reached 100 %. This allows the WPPU/CNF pad prototype to reversibly adjust the undulation height to adapt to plantar ulcers, which can reduce the local plantar pressure by 60 %. This study provides an environmentally friendly strategy for cellulose-based composite fabrication and enriches the design and application of intelligent foam devices.

Lightweight and recyclable hybrid multifunctional foam based cellulose fibers with excellent flame retardant, thermal, and acoustic insulation property

The development of eco-friendly and good-performance foam materials is essential for the environment and energy saving. Conventional inorganic and organic foams suffer from brittleness and contamination problems. Here, we report a facile and scalable hybrid strategy to prepare shape-stable cellulose-based multifunctional foam via physical cross-linking of PVA and stabilization of HGMs. The prepared foam exhibits ultra-low density (27.0 mg/cm3), enhanced flame-retardant performance (the PHRR decreased from 161.8 to 89.1 kW/m2, LOI value up to 26.2%), low thermal conductivity (48.2 mW/mK), good acoustic insulation property (NRC of 0.41), and good mechanical properties (with specific compressive modulus of 15.3 MPa cm3/g). Moreover, the foam can be recycled under simplified procedures. Our approach provides a novel alternative to the manufacture of low-cost, eco-friendly, and scalable foam materials. This multifunctional lightweight material is highly sought after for modern engineering construction applications.

Multifunctional NiCo@RGO/SWNTs foam with oriented pore structure for excellent electromagnetic interference shielding

Constructing multifunctional material toward advanced electromagnetic interference (EMI) shielding has become a development trend. Carbon-based foams with excellent EMI shielding performance and structural stability for various environments are being widely studied. Here, an oriented pore structure was assembled with a carbon-based conductive skeleton, consisting of single-walled carbon nanotubes (SWNTs) and two-dimensional reduced graphene oxide (RGO), for facilitating the electromagnetic wave (EMW) to be multilevelly reflected in the confined space. In addition, magnetic NiCo nanoparticles were introduced to further improve the shielding performance by enhancing the magnetic loss. The as-prepared NiCo@RGO/SWNTs foam (NiCo@RSF) exhibited an exceptional EMI shielding effectiveness (SE) of 105 dB at the whole X band (8.2–12.4 GHz) with an ultralow density (0.0135 g cm−3). Moreover, the foam possessed extraordinary heat insulation and flame-retardant properties. Overall, the lightweight multifunctional foam with an oriented pore structure is thus promising for applications in advanced EMI shielding and other specific areas.

Thermal insulation and antibacterial foam templated from bagasse nanocellulose /nisin complex stabilized Pickering emulsion

Foam packaging with good thermal insulation and antibacterial properties is promising for cold chain delivery to strengthen food safety. This study reports a novel antibacterial foam with thermal insulation templated from bagasse nanocellulose complex particle-stabilised acrylate epoxy soybean oil (AESO) Pickering emulsions. Nanocellulose/nisin complex particles (N-CNFs) were prepared by loading positively charged nisin onto negatively charged cellulose nanofibrils via electrostatic interactions, that highly enhanced the stability of nanocellulose at the AESO/water interface and imparted the corresponding foam with good antibacterial properties. The results show that the porosity of the foam prepared with N-CNFs increased from 10.9% to 29.9% compared with that of the foam corresponding with bare nanocellulose; the thermal conductivity of the N-CNF foam decreased substantially from 0.431 W/m·K to 0.197 W/m·K. Moreover, the prepared foam exhibited good antibacterial activity, and its bacteriostatic rate against Listeria monocytogenes was 91.33%. The incorporation of antibacterial peptides into nanocellulose has enriched the study of the Pickering emulsion templating method for preparing multifunctional foam materials and is expected to broaden the application of nanocellulose in the field of food packaging.

Oxidation-Resistant MXene-Based Melamine Foam with Ultralow-Percolation Thresholds for Electromagnetic-Infrared Compatible Shielding.

To effectively avoid the drawbacks of conventional metal-based electromagnetic interference (EMI) shielding materials such as high density and susceptibility to corrosion, a multifunctional melamine foam (MF) consisting of MXene/polydimethylsiloxane (PDMS) layers with ultralow percolation thresholds was designed through the electrostatic self-assembly and impregnation strategies. The prepared lightweight foams simultaneously show multifunctional properties including EMI shielding, infrared (IR) stealth, oxidation-resistance, and compression stability. Typically, this multifunctional foam exhibits an excellent EMI shielding efficiency (EMI SE) of 45.2 dB at X-band (8.2-12.4 GHz) with only 1.131 vol % MXene filler. Moreover, the temperature difference between the upper and lower surfaces of the foam can be maintained at 45 °C due to its unique three-dimensional (3D) porous structure and low infrared emissivity. The MF skeleton with MXene/PDMS (MFMXP) displays high hydrophobicity, which remains stable in EMI SE after 60 days of exposure to air. Additionally, it shows outstanding mechanical stability after 100 cycles of compression experiments. The lightweight stealth nanocomposite foams can operate stably in complex environments and show high potential for applications in high-tech fields such as wearable electronics, the military, and semiconductors, etc.

Assessing the performance of foams stabilized by anionic/nonionic surfactant mixture under high temperature and pressure conditions

Foam flooding is an effective tertiary recovery method for oil and gas reservoirs. However, foam performance is very sensitive to the reservoir temperature and pressure. In this study, the formation and collapse of a water-based foam stabilized by a mixed ionic and nonionic surfactant system under typical reservoir conditions (up to 150 °C and 50 MPa) were investigated. A multifunctional foam analyzer, an interfacial rheometer, and a coiled tube are used to assess foam microstructure, surface tension and bulk viscosity under 25 – 80 °C and 0.1 – 10 MPa. Results show that the foam comprehensive value is highest under low temperature and high pressure. With increasing temperature, the gas bubbles become larger, fewer in number, and more irregular in shape coupled with a thinner liquid film. Increased pressure, on the other hand, decreases the bubble size, increases the number of bubbles and contributes to a more uniform and dense foam. At constant temperature, the surface tension decreases as the pressure increases, while at constant pressure, a minimum surface tension is observed with increasing temperature, which in turn increased with increasing pressure. Foam viscosity displayed an opposite trend to that of the surface tension. Understanding the variation of foam properties with temperature and pressure is key toward successful application of foam flooding.

Hydrophobic and flame-retardant multifunctional foam for enhanced thermal insulation and broadband microwave absorption via a triple-continuous network of RGO/MWCNT-melamine composite

Multifunctionalization is the future development trend for electromagnetic wave absorption (EMA) materials to satisfy practical scenarios. In this manuscript, a lightweight RGO/MWCNT modified melamine sponge (CGMFs) with a 3D porous triple-continuous network is developed, which exhibit much enhanced microwave absorption performance and multifunctional characteristics. The micro/nano-structure and EMA performance of CGMFs can be effectively controlled by adjusting the concentration and proportion of RGO and MWCNT. It is found that excellent impedance matching property from the 3D porous structure and strong electromagnetic wave (EMW) dissipation property of RGO and MWCNT network can synergistically enhanced the broadband EMA performance. The CGMFs present remarkable effective absorption bandwidth (EAB, reflection loss value ≤ −10 dB) of 10.8 GHz and extremely high reflection loss value of −50.43 dB at a thickness of 4.6 mm. Moreover, the CGMFs exhibit good mechanical stability, which can be compressed, bent, and twisted arbitrarily. Benefiting from enhanced hydrophobicity, heat insulation, and nonflammability, the CGMFs also exbibit attractive functions of self-cleaning, thermal insulation, infrared stealth, and flame retardancy. This study paves the way for scalable fabrication of next-generation multifunctional high-performance broadband EMA materials for practical application.

Foams with guest phases: multifunctional foam materials from multiphase composite materials

Foam materials have characteristics that make them especially suitable for a multitude of technological applications. Currently, one of the most widespread techniques for the manufacture of foam materials consists of manufacturing a composite material formed by a matrix and inclusions of a certain nature, which can be afterwards eliminated under controlled conditions (dissolution, chemical reaction, etc.). This method is known as replication and leads to interconnected pore foams. So far, for more than 50 years since its original patent, the replication method has allowed the generation of foams of metals, polymers and even mesophase pitch, from which it has been possible to obtain high-performance graphite foams. The functionality of the foam materials that have been manufactured so far depends on the material from which the foam is made, as well as the size, shape and size distribution of its pores. Recently the author of the present work has developed a new family of multifunctional materials, formed by interconnected pore foams obtained from composite materials by the replication method in which in the pore cavities there are host phases that give different functionalities to the material. The present work presents preliminary results obtained from aluminum foams with guest phases of silicon carbide (SiC) particles for thermal management applications.

Frequency-dependent damped vibrations of multifunctional foam plates sandwiched and integrated by composite faces

Frequency-dependent damped vibrations of multifunctional foam plates sandwiched and integrated by composite faces

Predicting thermal and mechanical performance of stochastic and architected foams

This study conducted pore-scale simulations to estimate the stagnant thermal conductivity and mechanical performance of stochastic metal foams and architected metal foams. The stagnant thermal conductivity of 5-, 10-, 20- and 40-ppi commercial aluminum foams were estimated to be 6.74, 6.49, 5.97, and 7.16 W/m/K, respectively. Thermal conductivity depended mainly on porosity and was not a strong function of pore size. The pore-scale models simulated thermal conductivities of 40-ppi Al foam along three orthogonal directions are 7.16, 7.92, and 7.56 W/m/K, respectively, indicating a strong isotropic nature. Compared with stochastic foams, the architected foam with a triply periodic minimal surface showed 103% higher thermal conductivity, 488% higher stiffness, and 265% more energy absorption capability. The findings reported here not only provide a fundamental understanding of the interplay between performance and architecture but also open a new avenue to create multifunctional foams.

Polyolefinic nanocomposite foams: Review of microstructure-property relationships, applications, and processing considerations

In this review, we survey the state of the art on polymeric foams incorporating nano-scale fillers. Particular focus of the review is on foams from polyolefinic nanocomposite formulations incorporating a wide variety of fillers. The nano-scale additives can influence the foam structure and properties in two ways: Firstly, they can act as composite reinforcement to enhance the mechanical properties and functionality of the matrix polymer; and secondly, they can act as foaming-processing aids through modification of the rheological, thermal and crystallization properties of the matrix as well as serving as heterogeneous nucleation sites. Through a combination of these influences, and using advanced processing techniques it is possible to achieve nanocomposite foams that have higher cell density, and more uniform cell size or controlled cell-size distribution. Such controlled foam morphologies, in turn, can yield better specific mechanical properties resulting in more effective light-weighting solutions. Further, the nano-scale additives can impart additional desired functionality resulting in multi-functional foams. In this article, we provide an overview of the mechanical, thermal and a few other relevant functional properties – such as piezoelectric sensitivity, acoustics, and filtration efficiency – of foams prepared using nanocomposite formulations, along with the processing considerations for achieving high quality foams using such materials.

Hierarchical Cellular Poly(m‐phenylene isophthalamide) with High Flame Retardancy, Mechanical Robustness, and Heat Resistance at Extreme Situation

AbstractHigh‐performance cellular foams with superior mechanical properties and heat resistance are urgently needed to fulfill the applications in extreme environments. However, they are difficult to be prepared because of low gas diffusion rate in high‐performance polymers. In this work, a facile solution‐foaming strategy to prepare multifunctional foams based on poly(m‐phenylene isophthalamide) (PMIA) is reported. The achieved PMIA foams show a hierarchically cellular structure containing macropores and mesopores. Due to their high porosity, the PMIA foams exhibit low thermal conductivity (0.0447–0.0498 W m−1 K−1) and high sound absorption coefficient at different frequency. A bimodal distribution on acoustic absorption is observed. With a bulk density range of 0.089–0.122 g cm−3, PMIA foams possess compressive moduli of 3.2–14.2 MPa and bending strength of 1.1–2.1 MPa, respectively. Moreover, they exhibit a recoverable deformation of 55.4% after 10 cycling 10% strain compressions and maintain a dimensional stability under harsh environment (–196 to 250 °C). Despite generated byproducts like polyurea, they still show a limiting oxygen index (25.2–26.3%) and relatively low heat release rate (178.3 kW m−2). This work provides a facile strategy to efficiently prepare high‐performance PMIA foams for broad application prospects.

Multifunctional polyurethane foams with thermal energy storage/release capability

In this work, polyurethane (PU) insulating panels containing different amounts of a microencapsulated paraffin with a nominal melting temperature of 24 °C, used as phase change material (PCM), were produced. The resulting panels behaved as multifunctional materials able to thermally insulate and simultaneously storing/releasing thermal energy near room temperature. The panels were characterized from a microstructural, thermal and mechanical point of view. Viscosity measurements highlighted an increase in the viscosity values of the PU liquid precursors due to the addition of the capsules, and this could lead to some difficulties during the production stages, especially in the mixing and foaming phases. From optical microscopy micrographs and density measurements, it was observed that the introduction of paraffin tended to destroy the cellular structure of PU foams, and for PCM contents above 30 mass/% the foams were characterized by an open-cell morphology. SEM observations showed that PCM was preferentially distributed in the cell walls intersection, and a rather limited interfacial adhesion between capsules and PU could be detected. Thermogravimetric analysis evidenced that the introduction of the PCM tended to increase the degradation resistance of the foams, while from differential scanning calorimetry tests it was possible to conclude that PCM addition was able to impart good thermal energy storage properties to the foams, with specific melting enthalpy values of 70 J g−1 for a microcapsules concentration of 50 mass/%. As expected, thermal conductivity (λ) of the foams increased with PCM amount, but this enhancement was not directly related to the higher λ of the PCM itself, but rather than to the cell opening effect promoted by the PCM introduction. The microcapsules addition progressively increased the stiffness of the foams, reducing the failure properties both under quasi-static and impact conditions. Moreover, the mechanical properties were strongly affected by the testing temperature (i.e. the physical state of the wax contained in the microcapsules).

Multifunctional PDMS polyHIPE filters for oil-water separation and antibacterial activity

Herein, we present the fabrication of multifunctional polydimethylsiloxane (PDMS) foams with antibacterial, hydrophilic, and underwater superoleophobic properties for the separation of oil-water mixtures and simultaneous water disinfection. The PDMS foams, prepared following the high internal phase emulsion templating method, exhibit a porous interconnected structure and were further functionalized with a polydopamine (PDA) layer and in-situ grown silver nanoparticles (Ag NPs) upon successive dipping processes in dopamine and silver nitrate solutions. We demonstrate the successful use of the developed foams as 3D filters for the gravity-driven separation of oil-water mixtures and the subsequent disinfection of the filtered water. The flow rate of oil-water mixtures is strongly correlated to the in-situ grown Ag NPs density present on the foams, in contrary to the oil rejection efficiency, which is above 99.99% in all the studied cases. In fact, the flow rate values increase with the increasing density of the in-situ formed Ag NPs starting from 1937.7 ± 580.4 L m−2 h−1 for the foam without Ag NPs and reaching 4043.0 ± 710.7 L m−2 h−1 for the foam with the highest amount of NPs. Taking the latter as an example, we prove that the foams can be used for several filtration cycles without any modification of their oil rejection efficiency. In addition to efficient oil-water separation, the foams have antibacterial properties and are able to disinfect the permeate. The simple preparation method, effective gravity-driven filtration, robust nature, and antibacterial capability make the herein engineered multifunctional foams promising for highly efficient filtration processes.

Manuka honey and bioactive glass impart methylcellulose foams with antibacterial effects for wound-healing applications

Wound dressings able to deliver topically bioactive molecules represent a new generation of wound-regeneration therapies. In this article, foams based on methylcellulose cross-linked with Manuka honey were used as a platform to deliver borate bioactive glass particles doped additionally with copper. Borate bioactive glasses are of great interest in wound-healing applications due to a combination of favorable features, such as angiogenic and antibacterial properties. The multifunctional composite providing the dual effect of the bioactive glass and Manuka honey was produced by freeze-drying, and the resulting foams exhibit suitable morphology characterized by high porosity. Moreover, the performed tests showed improved wettability and mechanical performance with the addition of bioactive glass particles. Dissolution studies using simulated body fluid and cell biology tests using relevant skin cells further proved the excellent bioactivity and positive effects of the foams on cell proliferation and migration. Most interestingly, by the dual release of Manuka honey and ions from the copper-doped bioactive glass, an antibacterial effect against E. coli and S. aureus was achieved. Therefore, the multifunctional foams showed promising outcomes as potential wound dressings for the treatment of infected wounds.

Thermoplastic polyurethane–graphene nanoplatelets microcellular foams for electromagnetic interference shielding

The incorporation of graphene-related materials as nanofiller can produce multifunctional foams with enhanced specific properties and density reduction. Herein we report on the preparation of microcellular thermoplastic polyurethane/graphene foams by batch foaming. Solution blending was first adopted to disperse graphene nanoplatelets (GNP) in the elastomeric matrix. Then, a foaming process based on the use of supercritical CO2 was adopted to produce the microcellular TPU/GNP composite foams with graphene content up to 1 wt%. The EMI shielding behaviour of the TPU/GNP foams has been assessed in the THz range, and has revealed their potential in comparison with other graphene-filled foams presented in the literature, that exhibit similar specific shielding effectiveness but at much higher content of graphene-related materials (10-30 wt%).

Ultra-lightweight, super thermal-insulation and strong PP/CNT microcellular foams

The global energy crisis has been widely concerned by the public due to the massive energy requirement caused by rapid-developing economy and society. Ultra-lightweight, super-insulating, and strong polymer foams exhibit a promising prospect, in terms of saving materials and resources, and reducing energy consumption. However, there exists a great challenge to achieve highly expanded microcellular polymer with satisfactory thermal insulation performance. Herein, polypropylene (PP) with carbon nanotubes (CNTs) was used to prepare multifunctional foams by using batch foaming process with carbon dioxide. This cost-efficient and facile process endowed PP/CNT composite a variety of unprecedented advantages, including over 50-fold expansion ratio, a rather low thermal conductivity of 28.69 mW/m·K, and remarkably improved compressive strength. Acting as both crystal and cell nucleating agents, CNTs contributed to the fabrication of such ultralight foams with refined cell structure, which led to significantly reduced solid thermal conduction and enhanced mechanical properties. Moreover, thanks to CNTs’ outstanding infrared radiation shielding capacity, the thermal radiation through the ultra-lightweight PP/CNT foam was significantly suppressed. Thus, ultra-lightweight, super thermal-insulation, and strong PP/CNT composite foams were achieved by using microcellular foaming technology, paving a way for designing and synthesizing multifunctional polymer-based composite foams for high-performance thermally insulating applications.

Three-dimensional macroassembly of hybrid C@CoFe nanoparticles/reduced graphene oxide nanosheets towards multifunctional foam

Many efforts have been focused on developing the three-dimensional (3D) foams with enhanced absorption performance, improved mechanical behavior and excellent environmental stability. 3D graphene (or reduced graphene oxide) architecture with interconnected conductive network and ultralow density make it the most promising candidate for high-performance microwave absorption application. Unfortunately, they are extremely delicate to handle for the weak van der Waals interactions between neighboring nanosheets. Here, we show a simple approach via three-dimensional macroassembly of hybrid C@CoFe nanoparticles (NPs)/reduced graphene oxide (rGO) nanosheets to fabricate multifunctional foam. Firstly, hybrid hydrogels by in situ sol-gel polymerization form directly in the framework of GO aerogel. And decomposition of metal-citric acid complexes occurs during the heat treatment and formation of metal oxides is followed. RF-derived (RF- resorcinol-formaldehyde) rich carbon source can reduce CoFe 2 O 4 to CoFe alloy via thermal treatment. Such hybrid magnetic carbon spheres not only can absorb electromagnetic (EM) wave, but also act as fillers to support stresses transferred from the reduced graphene oxide nanosheets. The compression modulus of C@CoFe/rGO (CCR) foam can reach 26 MPa. Three-Dimensional macroassembly of C@CoFe NPs/rGO nanosheets generates efficient channels for multiple reflections and scatterings in the framework, which is advantageous for electromagnetic attenuation.

Self-Assembly of Porous Boron Nitride Microfibers into Ultralight Multifunctional Foams of Large Sizes.

As a kind of macroscopic boron nitride (BN) architectures, ultralight BN cellular materials with high porosity and great resilience would have a broad range of applications in energy and environment areas. However, creating such BN cellular materials in large sizes has still been proven challenging. Here, we report on the unique self-assembly of one-dimensional porous BN microfibers into an integral three-dimensional BN foam with open-cell cellular architectures. An ultrasonic-assisted self-assembly, freeze-drying, and high-temperature pyrolysis process has been developed for the preparation of cellular BN foam with a large size and desired shape. The developed BN foam has low density, high porosity (∼99.3%), great resilience, and excellent hydrophobic-lipophilic nature. The foam also exhibits excellent absorption capacities for a wide range of organic solvents and oils (wt % of ∼5130-7820%), as well as a high recovery efficiency (∼94%). Moreover, the unique hierarchical porous structure enables the foam to demonstrate a very low thermal conductivity (∼0.035 W/K/m). The excellent thermal insulation performance, superior mechanical property, and superb chemical and thermal stability enable the developed BN foam as an integrating multifunctional material in a broad range of high-end applications.