Preparation Of Foams Research Articles

Extruded polylactide bead foams using anhydrous supercritical CO2 extrusion foaming

AbstractPolylactic acid (PLA) is a bio‐based and biodegradable polymer. It is challenging to prepare PLA bead foams at a large scale in an efficient manner. Herein, beads of modified PLA are foamed by one‐step anhydrous supercritical CO2 extrusion. This dramatically shortens the production time, prevents the PLA from pyrohydrolysis, and avoids wastewater generation. The melt strength of the PLA is increased from 0.8 to 16.7 cN using a chain extender. The morphologies and microstructures of bead foams are analyzed. In the case of the PLA bead foam obtained by extrusion foaming combined with wind‐cooling pelletizing technology, the expansion ratio is higher than 13, the pore morphology is typical cellular structures, and the surface is glossy. The advantages and shortcomings of the PLA beads are also investigated. It is beneficial to promote the continuous preparation of PLA bead foams and other polymer beads like PS, and PP, which can be used in the fields of green packing, sound absorption, cold‐chain logistics, and so forth.

Preparation and characterization of oligomeric thermal phase change polyurethane foam

The generation of a large amount of heat during the formation process of polyurethane foam (PU) hinders the large-scale applications of the materials. Phase-change materials (PCM) can be introduced into PU to reduce the amount of heat accumulation inside PU. Silica-based urea-formaldehyde heteroshell phase-change microcapsules (S-MPCM) containing polydopamine were fabricated, followed by the fabrication of a novel composite polyurethane foam (PU/S-MPCM) doped with S-MPCM. The latter was fabricated using 4,4′-diphenylmethane diisocyanate and polyether polyol as the primary raw materials. The results revealed that the modifying effect of polydopamine resulted in the SiO2 layer deposited on the surface of the microcapsules improved the densification of S-MPCM, and the encapsulation rate of S-MPCM was 76.5 %, and the enthalpy of melting was 162.4 J/g. The compatibility of S-MPCM with the foam was also further improved, increasing the toughness of the composite foam and maximizing its retention of morphology after compression testing. The maximum internal temperature of the composite foam blended with 10 % S-MPCMs was reduced to 53.7 °C, showing excellent thermal regulation performance. The oligomeric thermal phase change polyurethane foam prepared in this study can be considered for applications such as building insulation and mine grouting.

High thermal conductivity of porous graphite/paraffin composite phase change material with 3D porous graphite foam

Phase change materials (PCMs) are widely used in the field of thermal management and energy storage, but both low thermal conductivity and leakage problem limit their broad applications. In this work, a 3D porous graphite (PG) foam was prepared by a pressing and drying method with solid mixture of graphite powder and ammonium bicarbonate (NH4HCO3), and it was used as the thermal conductive skeleton and shape stabilizer of PCMs. PG/paraffin composite PCMs (CPCMs) were then prepared by the vacuum impregnation of liquid paraffin into PG foam. It showed that the skeleton of 3D PG foam greatly improves the thermal conductivity of CPCMs. The prepared PG/paraffin CPCMs exhibited an ultra-high thermal conductivity of 19.27 Wm-1K−1 at a volume fraction 35.55% of graphite, which is about 76.08 times higher than that of paraffin. The heat conduction mechanism of the PG/paraffin CPCMs are analyzed, and it is found that Maxwell-Eucken model can be used to accurately predict its thermal conductivity. Moreover, the CPCMs show good performance of thermal shape stability and exhibit superior anti-leakage characteristic. The proposed method for the preparation of 3D PG foam is robust, and the excellent performance of their based CPCMs will be promising in the field of heat dissipation and thermal storage.

Study on the preparation and properties of colloidal gas foam concrete to prevent spontaneous combustion of coal

Colloidal gas foam concrete (CFC) was successfully prepared by high water retention of colloidal gas aphrons (CGA) and cement slurry. The preparation conditions of colloidal gas foam concrete with optimal performance and the addition ratio between its components were determined based on single-factor experiments and orthogonal tests. Then, the compressive strength, water retention, water content, and ability to inhibit coal spontaneous combustion of colloidal gas foam concrete were systematically studied. CFC's performance test to prevent spontaneous combustion of coal showed that CFC could form a hard protective shell of oxygen barrier on the surface of coal, thus inhibiting spontaneous combustion of coal. In addition, compared with traditional aqueous foam concrete (AFC), the water content of CFC increased from 0.65 to 1.40, and the protective shell formed by CFC could still retain some water after seven days without cracking. The programmed temperature rise experiment showed that CFC inhibited coal spontaneous combustion better than traditional AFC, and the cross-point temperature of coal treated by CFC was higher. This paper provides a high-performance mine fireproof material, which is important for the safe and efficient production of mines.

Preparation of thermoplastic polyurethane blend foams with controlled hydrophobicity via vapor induced phase separation

AbstractOil–water separation has attained great attention due to recent concern in environmental safety. Porous material from tailored engineering is the best candidate to selectively adsorb oil from water. Among the various porous materials, polymer based adsorbent has several advantages over others, in terms of controllable porosity and functionality. Here, we propose thermoplastic polyurethane (TPU) based blend foam through vapor induced phase separation method as a potential candidate for oil–water separation. In order to adjust hydrophobicity and compatibility of TPU blend, PDMS‐based TPU (Si‐TPU) is designed and synthesized to be blended with commercialized TPU. Si‐TPU with tailored weight ratio (PDMS/PTHF = 4/6) in synthetic level make it possible to achieve both of demanded hydrophobicity (the water contact angle increased from 85.19 ± 1.83° to 121.15 ± 3.79° after adding Si‐TPU) and controlling compatibility with CTPU during VIPS foaming. Thus, these well‐designed Si‐TPU can be utilized in various fields such as improving compatibility of polymer blend, adsorption efficiency of oil, and smart filtration, and so forth.

Combining hyperbranched polyol containing three flame retardant elements, P, N and Si, with expanded graphite to improve the flame retardancy of bio-based rigid polyurethane foam

The preparation of rigid polyurethane foam (RPUF) from vegetable oil and the improvement of its flame retardant properties are of great importance to broaden the application field of RPUF, which can satisfy the green environment and reduce the fire accidents caused by its flammability. In this paper, a reactive hyperbranched flame retardant polyol (DOPO-MASi) containing three flame retardant elements of P, N and Si was prepared by reacting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a phosphorus-containing compound, with maleic anhydride, diethanolamine and Triethoxy(3-glycidyloxypropyl)silane (KH-561), respectively, and mixed with expandable graphite (EG) to obtain a vegetable oil-based flame retardant RPUF with the multi-flame retardant system. This foam has excellent flame retardant properties and smoke-suppressing effect, with a limiting oxygen index (LOI) of 30% and a “V-0″ level in the UL-94 vertical burning test, as well as its pHRR, THR, and TSP were reduced by 47.5%, 57.9% and 62.8%, respectively. More importantly, 5% EG/20% FR-RPUF also has good mechanical properties. The above properties provide a reference for the practical application of RPUF in environmental protection and flame retardant.

Preparation and electrochemical performance of foam–like CeO2 nanofoam as negative electrode material for rechargeable lithium–ion batteries

Oxides of transition metal oxides have been discovered as candidate anode materials for lithium–ion batteries (LIBs) owing to their extraordinary specific capacity. Moreover, to improve the electrochemical performance of energy–storage devices, the use of porous electrode materials is considered one of the most effective strategies. Herein, we report highly porous cerium oxide (CeO2) nanofoam synthesized using a facile and simple solution combustion technique (SCT). In this technique, we use two different fuels to synthesis CeO2. The prepared S–CeO2 nanofoam delivers the highest specific surface area of 142.99 m2 g−1 with a highly enhanced contact area between the electrolyte and electrode. The prepared S–CeO2–based anode offers an initial specific capacity of 1154 mAh g−1 at 100 mA g−1, which is three times higher than that of carbon–based materials. Additionally, the mesoporous S–CeO2 nanofoam exhibits good rate capability at high current densities. These attractive results suggest that S–CeO2 has great potential for use in high–performance LIB applications.

Experimental study on improving salt resistance of dust suppressing foam with polymers

Mine dust is a prevalent pollutant generated during the mining process, often leading to explosion accidents and causing pneumoconiosis. Foam dust suppression technology has emerged as a promising method for efficient dust control due to its high-efficiency dust collection and ease of use. However, the application of foam in the field has revealed higher concentrations of inorganic salts in the mine dust suppressants, resulting in suboptimal foaming performance. As a result, additional foaming agent and increased concentration are often required to achieve the desired effect, which escalates the cost of mine dust control. To address this issue, this study proposes optimizing the performance of mine dust suppression foam through the incorporation of polymers with excellent salt resistance. In this investigation, foam liquids comprising xanthan gum (XG) and sodium carboxymethyl cellulose (CMC) were tested using FoamScan to evaluate their foaming performance and foam stabilization at various concentrations of inorganic salt. Additionally, the rheological properties of the foam liquids were analyzed by measuring the viscoelastic modulus using an interfacial rheometer. Experimental results demonstrated that the addition of XG and CMC did not compromise the foaming ability of sodium fatty alcohol polyoxyethylene ether sulfate (AES). Moreover, the liquid-carrying capacity of bubbles, in terms of foam stability, was enhanced. Specifically, the foam stabilization remained relatively stable when the XG concentration exceeded 0.5‰, even under different salt concentrations. Interfacial rheological tests revealed that the addition of XG substantially increased the viscoelastic modulus of the foam liquid. Furthermore, the phase angle remained below 45°, indicating the dominant role of the elastic modulus in the foam liquid, resulting in improved bubble resistance to interference and deformation. This experimental study successfully resolved the issue of poor stability in mine dust suppression foam caused by high salt content during the foam preparation process. The findings can significantly contribute to the widespread adoption and application of dust suppression foam technology in mining operations.

Agar composites containing Zinc zeolite infused with Quillaja saponins exhibit improved structural properties and anti-Candida activity

Candida strains are opportunistic pathogens frequently responsible for severe and dangerous infections. Therefore, the need for biomaterials with antifungal properties is urgent. To obtain a safe environment, biocompatible and biodegradable polysaccharide porous materials the agar foams were prepared. To provide antifungal properties, both zinc zeolite and saponins of Quillaja saponaria were applied. Moreover, the saponins, as surfactants, were chosen as foaming agents. The study includes zinc zeolite synthesis, foams preparation and spectral analysis of the obtained product. Finally, the foams toxicity against Candida albicans PCM 2566 strain was investigated. The results presented that the zeolite was successfully introduced in the agar structure. Saponins addition significantly increases the porosity and homogeneity of the foam, which was observed using scanning electron and infrared microscopy. The microbiological tests proved that foams containing zinc zeolite or saponins caused a 25% reduction in C. albicans cells viability. However, the foams containing both zinc zeolite and Q. saponaria saponins decreased yeast activity by over 80%. That confirmed that the agar-based foams with zinc zeolite and saponins can be valuable environmental-friendly biomaterials with antifungal properties.

Novel Preparation of Graphene Foam with Adjustable Dielectric Properties for Efficient Microwave Absorption.

Graphene foams (GFs) prepared via a hydrothermal method can be vacuum-dried directly without the need for freezing by adding naphthalene to the graphene hydrogels. By optimizing the GF preparation process, it is also possible to adjust the GF's dielectric properties by varying the amount of naphthalene added. Based on the comparison results, it was observed that controlling the addition of naphthalene could also modify the internal structure of GF and effectively regulate its dielectric properties. GF-80, synthesized with 80 g of naphthalene, exhibited exceptional microwave absorption (MA) performance. At a mass content of only 2% and a matching thickness of 3.38 mm, a minimum reflection loss (RLmin) of -55.89 dB was achieved. Moreover, GF-80, with a thickness of 2.31 mm, was shown to achieve a bandwidth of RL less than -10 dB across 6.88 GHz.

Nano-composite semi-flexible polyurethane foams containing montmorillonite intercalated/exfoliated in situ during the synthesis of the intermediate polyester-polyols obtained from PET wastes

Low-cost nano-composite semi-flexible polyurethane foams with improved thermal and mechanical features were obtained using a cost-saving and environmentally friendly preparation process of an intermediate composite, obtained from polyethyleneterephthalate (PET) wastes, depolymerization/chemical modification agents from renewable resources and unmodified natural montmorillonite. The process implies tailoring the polyester-polyols chemical structure/ composition and using specific catalysts, aiming to intercalate the montmorillonite layers during the synthesis reactions, while maintaining the appropriate properties of the products required for the preparation of polyurethane semi-flexible foams, thus avoiding conventional treatments of the nanofiller, involving the use of solvents, additional energy consumption by heating and stirring, as well as longer processing time. The polyester-polyols composites and the polyurethane semi-flexible foams obtained therefrom were investigated by specific analytical methods. In this regard, the foams showed an improvement of the thermal stability, and values of Young’s moduli and compression strengths about double or higher, compared to conventional semi-flexible polyurethane foams of same density. The potential applications of such foams target shock wave damping sandwich systems for marine structures.

Carbon composite foams from the wasted banana leaf for EMI shielding and thermal insulation

Low-density fire-resistant materials with high EMI shielding effectiveness and low thermal conductivity are extremely important in aerospace and defence applications. Utilization of agricultural residues for achieving this reduces CO2 emission as well as produces wealth for the farmers. Herein, a fibre extracted from the wasted matured banana leaf by a simple chopping and grinding using a mixture-grinder is used for the preparation of carbon composite foams. The banana leaf fibres dispersed in sucrose solution are consolidated by filter-pressing followed by freeze drying to produce banana leaf fibre-sucrose composites. The carbon produced from sucrose during carbonization binds the carbonized banana leaf fibre to produce the carbon composite foams. The XRD pattern and Raman analysis indicated the turbostratic nature of the carbon, and XPS analysis shows the presence of oxygen-containing functional groups. The textural property measurement and TEM analysis indicated the presence of micro and meso pores in the carbon composite foams. The foam density (0.14–0.28 g cm−3), compressive strength (0.14–0.88 MPa), electrical conductivity (3.7–8.7 S m−1), and thermal conductivity (0.095–0.144 W m-1 K−1) of the carbon composite foams increases with an increase in sucrose solution concentration (300–700 g L−1). The carbon composite foams exhibit a reflection-dominated EMI shielding with high total shielding effectiveness in the range of 48.3–77.5 dB. The multiple internal reflections within a range of macropores available in the carbon composite foams, leading to enhanced absorption, are responsible for the excellent EMI shielding characteristics.

Study on the foaming behavior of density‐controllable epoxy resin composite foam under negative pressure environment

AbstractThe incomplete decomposition of foaming agent and tedious process during the preparation of epoxy resin composite foam (ERCF) will reduce the mechanical properties and lead to more complex production. Therefore, in this study, a new and simple negative pressure foaming method was designed innovatively to prepare ERCF under negative pressure using strong gas adsorption capacity of inorganically modified calcium silicate (MCS) particles as air carriers instead of foaming agent, and the density and expansion ratio of ERCF could be precisely controlled by adjusting the negative pressure value in a vacuum oven. The results showed that the density of ERCF could reach a very low value of 0.056 g/cm3 at 15 wt% MCS content with decreased negative pressure, but the negative pressure decreases would damage the quality of cells. At the same time, it was found that a rapid rise in the viscosity of the epoxy composite material system under negative pressure of −0.080 MPa owing to the increase in MCS content, when the MCS content was higher than 15 wt%, the MCS dispersion was reduced, leading to a decrease in the quality of the cells. In addition, the ERCF products prepared by the negative pressure foaming method in this study could be easily molded and possessed a better compressive strength among epoxy foams of similar density.

Analysis of pore morphology evolution of all-wastes ceramic foams based on the variation of composition and sintering process

Utilization of wastes for the preparation of ceramic foams has gradually become a major direction in the development of new building materials. In this paper, all wastes-based ceramic foams based on electrical insulators waste (EIW) and red mud (RM) were prepared through the high-temperature foaming method. The factors affecting the increase in pore size under different preparation conditions (RM content, temperature and time) were investigated separately by studying the changes in pore size. With the increase of RM content, sintering temperature and sintering time, the pore morphology gradually evolved from a regular spherical shape to a polygonal or irregular shape with a corresponding increase in pore size, albeit at different rates. The pore size enhancement ascribed to changes in RM content was primarily attributed to the synergistic influences of a plurality of factors including glass phase content, viscosity, and gas phase content. Sintering temperature mainly affected the balance between the forces acting inside and outside the pores and the gas phase solubility in the liquid phase to adjust the size of pores. The influence of sintering time on pore size and morphology emanated from the glass phase viscosity and the resulting changes in the release rate of gas phase. In summary, the study will help to investigate the actual controlling factors of composition and process on the pore structure, and provides significant insights into the optimization and adjustment of pore structure for samples obtained by high-temperature sintering.

Supported Catalyst Enables Synthesis of Colorless CO2-Polyols with Ultra-Low Molecular Weight.

Ultra-low molecular weight (ULMW) CO2-polyols with well-defined hydroxyl end groups represent useful soft segments for the preparation of high-performance polyurethane foams. However, owing to the poor proton tolerance of catalysts towards CO2/epoxide telomerization, it remains challenging to synthesize ULMW yet colorless CO2-polyols. Herein, we propose an immobilization strategy of constructing supported catalysts by chemical anchoring of aluminum porphyrin on Merrifield resin. The resulting supported catalyst displays both extremely high proton tolerance (~8000 times than equivalent of metal center) and independence of cocatalyst, affording CO2-polyols with ULMW (580 g mol-1) and high polymer selectivity (> 99%). Moreover, the ULMW CO2-polyols with various architectures (tri-, quadra-, and hexa-arm) can be obtained, suggesting the wide proton universality of supported catalysts. Notably, benefiting from the heterogeneous nature of the supported catalyst, colorless products can be facilely achieved by simple filtration. The present strategy provides a platform for the synthesis of colorless ULMW polyols derived from not only CO2/epoxides, but also lactone, anhydrides et al. or their combinations.

Preparation of carbon foam from depolymerization-reforming lignin for capacitive deionization

The functionalized utilization of lignin is attracting more and more attention. In this paper, we report a 3D interconnected foamy carbon material with highly open pore structure. The carbon foam is synthesized by depolymerization reforming strategy. The foamy carbon has a deep internal pore channels and exhibits an enhanced electrosorption capacity. The highest desalination of the foamy carbon reaches 30.2 mg·g−1 in 500 mg·L−1 NaCl at 1.2 V with adsorption rate of 3.75 mg/g/min. Meanwhile, the optimal electrode PDLC-1 shows good regeneration capacity. Our work provides a usable way for the preparation of lignin-derived carbon foam with high-performance of capacitive deionization.

Introduction of the Polymer Compatibility Factor for Preparation of Pitch-Based Carbon Foams by Polymer-Assisted Template Foaming

Introduction of the Polymer Compatibility Factor for Preparation of Pitch-Based Carbon Foams by Polymer-Assisted Template Foaming

Preparation and Characterization of Natural Rubber Foam Filled with Bagasse Fiber

The properties of natural rubber foam filled with bagasse fiber of varying content (0-50 phr) and different blowing agent content (5 and 8 phr) were investigated, with rubber compounds and vulcanized rubber also examined. Rubber compound properties included measurements of scorch time, cure time, minimum torque, maximum torque, density, and percentage of expansion in the mold. When bagasse fiber and blowing agent content increased, the maximum torque value of the compounded rubber increased. For rubber compound with blowing agent loading at 5 phr, cure time increased with an increasing bagasse fiber content of 40-50 phr, while scorch time and density of the rubber compound remained unchanged. The percentage of rubber compound expansion in the mold decreased with increasing bagasse fiber content. The cell size of natural rubber foams was inspected using an optical microscope. Small and homogeneous cell size was found in natural rubber foam with blowing agent content of 8 phr and higher bagasse fiber content. The incorporation of bagasse fiber enhanced the compressive strength of the natural rubber foam. Vulcanized rubber properties such as the modulus at 100% strain, tensile strength, and strain at break were also studied. The modulus increased, whereas stress at break and strain at break decreased with increasing bagasse fiber content. On the other hand, tensile strength and strain at break increased with increasing blowing agent loading.

Feasibility Study of Bio-Composite Foam Preparation from Poly(Butylene Succinate) with Spent Coffee Grounds Using Compression Molding

Plastic foam is widely used in varying industries due to its light weight, high strength, and good heat insulation. However, most plastic foams are produced from petroleum-based polymers which cannot be naturally degraded and can release aromatic pollution to the environment when they are molten or burned. Therefore, poly(butylene succinate) (PBS) and KMnO4-treated spent coffee grounds (SCG), which are biopolymer and bio-filler, are used to prepare the bio-composite foam in this research by using azodicarbonamide (ACDA) as a chemical blowing agent. The 10, 20, and 30 phr of the treated SCG and the 6 and 10 wt% of blowing agent are compounded with PBS resin using a two-roll mill and foamed by compression molding machine to investigate the possibility of the batch foam production. All bio-composite foams are investigated for both physical and mechanical properties including morphology, compressive strength, abrasion resistance, bulk density, and water absorption. All foams were successfully prepared by a two-step technique in compression molding to melt the compounded PBS pellets first at 160°C, 90 bar and then decompose the ADCA blowing agent to generate foam cells at 200°C, 120 bar. The appearance and morphology of the obtained foams showed that the cells were smaller and more even distribution with the treated SCG addition. The compressive and abrasion resistant properties decreased as the treated SCG increasing, excepted the bio-composite foam with 30 phr of the treated SCG. whereas the addition of ADCA showed an ambiguous trend. Both filler and blowing agent contents caused a somewhat decrease bulk density and increase water absorption.

Preparation and modification of antibacterial polyurethane foam for oil–water separation

Preparation and modification of antibacterial polyurethane foam for oil–water separation