Effective and Economical 3D Carbon Sponge with Carbon Nanoparticles as Floating Air Cathode for Sustainable Electricity Production in Microbial Fuel Cells

The effective and economical 3D floating air cathodes were fabricated by a simple dipping-drying method with carbon black (CB), ethanol, and PTFE solution. Pristine Type I polyurethane sponge (5 pores/mm) and Pristine Type II polyurethane sponge (3 pores/mm) were used as the support. The deposition of CB on the Pristine Type I and Pristine Type II materials was detected by scanning electron microscopy and Fourier transform infrared spectroscopy. The carbon loss rate test exhibited good CB adhesive stability on both floating air cathodes. Besides, Type I/CB floating air cathode displayed 3.7 times higher tensile strength, 10.58 times higher elongation at break, and 3.3 times lower cost than carbon felt. The electricity production ability of carbon cloth (CC) anode with carbon felt, Type I/CB, and Type II/CB cathode MFCs (CC-CF-MFC, CC-I-MFC, and CC-II-MFC) was evaluated. After 130 days, the CC-I-MFC showed a maximum power density (PD) of 92.58 mW/m3, which was 4.6 times higher than the CC-CF-MFC. Compared with Type II/CB, Type I/CB cathode improved the maximum power density by 160% due to the smaller pores, rougher surface, and higher surface wettability. Further, CC-I-MFC exhibited the best overall oxidation-reduction performance and chemical oxygen demand removal efficiency. Consequently, Type I/CB floating air cathode opens a new opportunity for scaling up simple, inexpensive, and high-performance MFCs for energy production.

Fireproof Nanocomposite Polyurethane Foams: A Review

First introduced in 1954, polyurethane foams rapidly became popular because of light weight, high chemical stability, and outstanding sound and thermal insulation properties. Currently, polyurethane foam is widely applied in industrial and household products. Despite tremendous progress in the development of various formulations of versatile foams, their use is hindered due to high flammability. Fire retardant additives can be introduced into polyurethane foams to enhance their fireproof properties. Nanoscale materials employed as fire-retardant components of polyurethane foams have the potential to overcome this problem. Here, we review the recent (last 5 years) progress that has been made in polyurethane foam modification using nanomaterials to enhance its flame retardance. Different groups of nanomaterials and approaches for incorporating them into foam structures are covered. Special attention is given to the synergetic effects of nanomaterials with other flame-retardant additives.

It Takes Two to Tango: Synergistic Expandable Graphite–Phosphorus Flame Retardant Combinations in Polyurethane Foams

Due to the high flammability and smoke toxicity of polyurethane foams (PUFs) during burning, distinct efficient combinations of flame retardants are demanded to improve the fire safety of PUFs in practical applications. This feature article focuses on one of the most impressive halogen-free combinations in PUFs: expandable graphite (EG) and phosphorus-based flame retardants (P-FRs). The synergistic effect of EG and P-FRs mainly superimposes the two modes of action, charring and maintaining a thermally insulating residue morphology, to bring effective flame retardancy to PUFs. Specific interactions between EG and P-FRs, including the agglutination of the fire residue consisting of expanded-graphite worms, yields an outstanding synergistic effect, making this approach the latest champion to fulfill the demanding requirements for flame-retarded PUFs. Current and future topics such as the increasing use of renewable feedstock are also discussed in this article.

Efficient Hybrid Particle-Field Coarse-Grained Model of Polymer Filler Interactions: Multiscale Hierarchical Structure of Carbon Black Particles in Contact with Polyethylene

In the present study, we propose, validate, and give first applications for large-scale systems of coarse-grained models suitable for filler/polymer interfaces based on carbon black (CB) and polyethylene (PE). The computational efficiency of the proposed approach, based on hybrid particle-field models (hPF), allows large-scale simulations of CB primary particles of realistic size (∼20 nm) embedded in PE melts. The molecular detailed models, here introduced, allow a microscopic description of the bound layer, through the analysis of the conformational behavior of PE chains adsorbed on different surface sites of CB primary particles, where the conformational behavior of adsorbed chains is different from models based on flat infinite surfaces. On the basis of the features of the systems, an optimized version of OCCAM code for large-scale (up to more than 8 million of beads) parallel runs is proposed and benchmarked. The computational efficiency of the proposed approach opens the possibility of a computational screening of the bound layer, involving the optimal combination of surface chemistry, size, and shape of CB aggregates and the molecular weight distribution of the polymers achieving an important tool to address the polymer/fillers interface and interphase engineering in the polymer industry.

Nacre-Mimetic Green Flame Retardant: Ultra-High Nanofiller Content, Thin Nanocomposite as an Effective Flame Retardant

A nacre-mimetic brick-and-mortar structure was used to develop a new flame-retardant technology. A second biomimetic approach was utilized to develop a non-flammable elastomeric benzoxazine for use as a polymer matrix that effectively adheres to the hydrophilic laponite nanofiller. A combination of laponite and benzoxazine is used to apply an ultra-high nanofiller content, thin nanocomposite coating on a polyurethane foam. The technology used is made environmentally friendly by eliminating the need to add any undesirable flame retardants, such as phosphorus additives or halogenated compounds. The very-thin coating on the polyurethane foam (PUF) is obtained through a single dip-coating. The structure of the polymer has been confirmed by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The flammability of the polymer and nanocomposite was evaluated by heat release capacity using microscale combustion calorimetry (MCC). A material with heat release capacity (HRC) lower than 100 J/Kg is considered non-ignitable. The nanocomposite developed exhibits HRC of 22 J/Kg, which is well within the classification of a non-ignitable material. The cone calorimeter test was also used to investigate the flame retardancy of the nanocomposite's thin film on polyurethane foam. This test confirms that the second peak of the heat release rate (HRR) decreased 62% or completely disappeared for the coated PUF with different loadings. Compression tests show an increase in the modulus of the PUF by 88% for the 4 wt% coating concentration. Upon repeated modulus tests, the rigidity decreases, approaching the modulus of the uncoated PUF. However, the effect of this repeated mechanical loading does not significantly affect the flame retarding performance.

Combustion behaviour and dominant shrinkage mechanism of flexible polyurethane foam in the cone calorimeter test

The shrinkage is an important thermal response of flexible polyurethane foam (FPUF) in fire, which couples its first combustion stage and influences the initial fire spread. In this paper the combustion and shrinkage behaviours are quantitatively investigated and the shrinkage mechanisms are discussed. The critical heat flux for the shrinkage is about 13 kW/m², between the critical heat flux for piloted ignition and that for non-piloted ignition. Above the critical value the shrinkage rate increases linearly with increasing the heat flux. As the foam density decreases both the shrinkage rate and the first peak of Figra curve which reflects the initial fire spread rate increase. The perceptible shrinkage originates from the decomposition via which the struts convert to the melts. Both the shrinking of struts and the gasification play a minor role. The collapse of porous structure, namely the melts filling into the pores to form the tar layer, dominates the shrinkage. The tar is composed of polyols produced after the first decomposition stage. Beneath the tar layer the porous structure is unchanged. To reduce the fire hazards of FPUF by its heat insulation merit it needs to maintain the porous structure at the first decomposition stage.

Fire Phenomena of Rigid Polyurethane Foams

Rigid polyurethane foams (RPUFs) typically exhibit low thermal inertia, resulting in short ignition times and rapid flame spread. In this study, the fire phenomena of RPUFs were investigated using a multi-methodological approach to gain detailed insight into the fire behaviour of pentane- and water-blown polyurethane (PUR) as well as pentane-blown polyisocyanurate polyurethane (PIR) foams with densities ranging from 30 to 100 kg/m³. Thermophysical properties were studied using thermogravimetry (TG); flammability and fire behaviour were investigated by means of the limiting oxygen index (LOI) and a cone calorimeter. Temperature development in burning cone calorimeter specimens was monitored with thermocouples inside the foam samples and visual investigation of quenched specimens’ cross sections gave insight into the morphological changes during burning. A comprehensive investigation is presented, illuminating the processes taking place during foam combustion. Cone calorimeter tests revealed that in-depth absorption of radiation is a significant factor in estimating the time to ignition. Cross sections examined with an electron scanning microscope (SEM) revealed a pyrolysis front with an intact foam structure underneath, and temperature measurement inside burning specimens indicated that, as foam density increased, their burning behaviour shifted towards that of solid materials. The superior fire performance of PIR foams was found to be based on the cellular structure, which is retained in the residue to some extent.

Thermal conductivity and flammability of multiwall carbon nanotube/polyurethane foam composites

The thermal conductivity and fire response of multiwall carbon nanotube/polyurethane foam composites are investigated for ∼45 kg/m3 foams with multiwall carbon nanotube concentrations of 0.1, 1, and 2 wt.%. The thermal conductivity of such nanocomposites shows a modest increase with increased multiwall carbon nanotube content, which is explained by a high value of interfacial thermal resistance, as predicted by existent thermal models. A strong correlation between multiwall carbon nanotube content, foam’s cellular morphology, and fire behavior was observed. The flame propagation speed increases with the addition of 0.1 wt.% multiwall carbon nanotubes and then reduces as the multiwall carbon nanotube content increases. The mass lost after flame extinction reduces with the addition of multiwall carbon nanotubes, suggesting an increased resistance to flame attack due the multiwall carbon nanotube presence.

Human exposure to carbon-based fibrous nanomaterials: A review

In an emerging field of nanotechnologies, assessment of exposure to carbon nanotubes (CNT) and carbon nanofibers (CNF) is an integral component of occupational and environmental epidemiology, risk assessment and management, as well as regulatory actions. The current state of knowledge on exposure to carbon-based fibrous nanomaterials among workers, consumers and general population was studied in frame of the International Agency for Research on Cancer (IARC) Monographs-Volume 111 "Some Nanomaterials and Some Fibres". Completeness and reliability of available exposure data for use in epidemiology and risk assessment were assessed. Occupational exposure to CNT/CNF may be of concern at all stages of the material life-cycle from research through manufacture to use and disposal. Consumer and environmental exposures are only estimated by modeled data. The available information of the final steps of the life-cycle of these materials remains incomplete so far regarding amounts of handled materials and levels of exposure. The quality and amount of information available on the uses and applications of CNT/CNF should be improved to enable quantitative assessment of human exposure to these materials. For that, coordinated effort in producing surveys and exposure inventories based on harmonized strategy of material test, exposure measurement and reporting results is strongly encouraged.

Ultra-Fast Layer-by-Layer Approach for Depositing Flame Retardant Coatings on Flexible PU Foams within Seconds

In this letter, we are presenting a novel approach for the deposition of layer-by-layer (LbL) coatings capable of conferring flame retardant properties to flexible polyurethane foams exploiting subsecond deposition times. The process yields nanoscale coatings able to reduce by 33% one of the main fire safety parameters, namely the heat release rate peak, with a total treatment time of only 2.5 s. This new approach turned out to be three to 4 orders of magnitude faster than conventional LbL treatments. Such results make it possible for the exploit of LbL as a competitive, efficient and ecofriendly technology at industrial scale.

Comparative study of layer by layer assembled multilayer films based on graphene oxide and reduced graphene oxide on flexible polyurethane foam: flame retardant and smoke suppression properties

Flame retardant multilayer films based on graphene materials were deposited on the surface of flexible polyurethane (FPU) foam by an advanced layer by layer assembly method (hybrid bilayer approach) in an effort to reduce its flammability.

Quantification of nanoparticle release from polymer nanocomposite coatings due to environmental stressing

Certain engineered nanoparticles (ENP) reduce the flammability of components used in soft furnishings (mattresses and upholstered furniture). However, because of the ENP's small size and ability to interact with biological molecules, these fire retardant ENPs may pose a health and environmental risks, if they are released sometime during the life cycle of the soft furnishing. Quantifying the released amount of these ENPs under normal end-use circumstances provides a basis for assessing their potential health and environmental impact. In this article, we report on efforts to identify suitable methodologies for quantifying the release of carbon nanofibers, carbon nanotubes, and sodium montmorillonites from coatings applied to the surfaces of barrier fabric and polyurethane foam. The ENPs released in simulated chewing and mechanical stressing experiments were collected in aqueous solution and quantified using Ultraviolet-Visible and inductively coupled plasma-optical emission spectroscopy. The microstructures of the released ENPs were characterized using scanning electron microscopy. The reported methodology and results provide important milestones to estimate the impact and toxicity of the ENP release during the life cycle of the nanocomposites. To our knowledge, this is the first study of ENP release from the soft furnishing coating, something that can be important application area for fire safety.

Formation of layer-by-layer assembled titanate nanotubes filled coating on flexible polyurethane foam with improved flame retardant and smoke suppression properties

A fire blocking coating made from chitosan, titanate nanotubes and alginate was deposited on a flexible polyurethane (FPU) foam surface by a layer-by-layer assembly technique in an effort to reduce its flammability. First, titanate nanotubes were prepared by a hydrothermal method. And then the coating growth was carried out by alternately submerging FPU foams into chitosan solution, titanate nanotubes suspension and alginate solution. The mass gain of coating on the surface of FPU foams showed dependency on the concentration of titanate nanotubes suspension and the trilayers's number. Scanning electron microscopy indicated that titanate nanotubes were distributed well on the entire surface of FPU foam and showed a randomly oriented and entangled network structure. The cone calorimeter result indicated that the coated FPU foams showed reduction in the peak heat release rate (peak HRR), peak smoke production rate (peak SPR), total smoke release (TSR) and peak carbon monoxide (CO) production compared with those of the control FPU foam. Especially for the FPU foam with only 5.65 wt % mass gain, great reduction in peak HRR (70.2%), peak SPR (62.8%), TSR (40.9%) and peak CO production (63.5%) could be observed. Such a significant improvement in flame retardancy and the smoke suppression property for FPU foam could be attributed to the protective effect of titanate nanotubes network structure formed, including insulating barrier effect and adsorption effect.

Fabrication of carbon black coated flexible polyurethane foam for significantly improved fire safety

Fire resistant coatings, composed of nanosized carbon black (CB) and polyurethane acrylate (PUA), were synthesized through a facile and low-cost method to improve the fire safety and thermal stability of flexible polyurethane foam (FPU).

Nanocarbon composites and hybrids in sustainability: a review

There is an ever-growing need to protect our environment by increasing energy efficiency and developing "clean" energy sources. These are global challenges, and their resolution is vital to our energy security. Although many conventional materials, such as metals, ceramics, and plastics, cannot fulfil all requirements for these new technologies, many material combinations can offer synergistic effects that create improved and even new properties. The implementation of nanocarbons, such as graphene and carbon nanotubes, into nanocomposites and, more recently, into the new class of hybrids, are very promising examples. In contrast to classical nanocomposites, where a low volume fraction of the carbon component is mixed into a polymer or ceramic matrix, hybrids are materials in which nanocarbon is coated with a thin layer of the functional compound, which introduces the interface as a powerful new parameter. Based on interfacial charge and energy transfer processes, nanocarbon hybrids have shown increased sensitivities in gas sensors, improved efficiencies in photovoltaics, superior activities in photocatalysts, and enhanced capacities in supercapacitors. This review compares the characteristics and potentials of both nanocarbon composites and hybrids, highlights recent developments in their synthesis and discusses key challenges for their use in various energy applications.

Revealing the interface in polymer nanocomposites

The morphological characterization of polymer nanocomposites over multiple length scales is a fundamental challenge. Here, we report a technique for high-throughput monitoring of interface and dispersion in polymer nanocomposites based on Förster resonance energy transfer (FRET). Nanofibrillated cellulose (NFC), fluorescently labeled with 5-(4,6-dichlorotriazinyl)-aminofluorescein (FL) and dispersed into polyethylene (PE) doped with Coumarin 30 (C30), is used as a model system to assess the ability of FRET to evaluate the effect of processing on NFC dispersion in PE. The level of energy transfer and its standard deviation, measured by fluorescence spectroscopy and laser scanning confocal microscopy (LSCM), are exploited to monitor the extent of interface formation and composite homogeneity, respectively. FRET algorithms are used to generate color-coded images for a real-space observation of energy transfer efficiency. These images reveal interface formation at a nanoscale while probing a macroscale area that is large enough to be representative of the entire sample. The unique ability of this technique to simultaneously provide orientation/spatial information at a macroscale and nanoscale features, encoded in the FRET signal, provides a new powerful tool for structure-property-processing investigation in polymer nanocomposites.

Reactive Nanocomposite Foams

One of the most interesting and most accessible opportunities of nanofillers is the reinforcement of fine structures in which conventional fillers cannot be readily accommodated, such as polymer foams. This paper reviews the progress to date towards the development of reactive foam nanocomposites, in particular polyurethane and silicone foams. The discussed systems are summarized based on the types of nanofillers used, i.e. nanoparticles, rod-like, and plate-like systems. The effect of nanofillers on the foaming process, cellular structure and properties is critically reported along with a summary of the measured improvements in the mechanical, electrical and thermal properties of the resulting nanocomposites.