Supercritical Carbon Dioxide Treatment Research Articles

Supercritical Carbon Dioxide Treatment of Porous Silicon Increases Biocompatibility with Cardiomyocytes.

Porous silicon is of current interest for cardiac tissue engineering applications. While porous silicon is considered to be a biocompatible material, it is important to assess whether post-etching surface treatments can further improve biocompatibility and perhaps modify cellular behavior in desirable ways. In this work, porous silicon was formed by electrochemically etching with hydrofluoric acid, and was then treated with oxygen plasma or supercritical carbon dioxide (scCO2). These processes yielded porous silicon with a thickness of around 4 μm. The different post-etch treatments gave surfaces that differed greatly in hydrophilicity: oxygen plasma-treated porous silicon had a highly hydrophilic surface, while scCO2 gave a more hydrophobic surface. The viabilities of H9c2 cardiomyocytes grown on etched surfaces with and without these two post-etch treatments was examined; viability was found to be highest on porous silicon treated with scCO2. Most significantly, the expression of some key genes in the angiogenesis pathway was strongly elevated in cells grown on the scCO2-treated porous silicon, compared to cells grown on the untreated or plasma-treated porous silicon. In addition, the expression of several apoptosis genes were suppressed, relative to the untreated or plasma-treated surfaces.

Regulation of selenium composition by supercritical carbon dioxide for CZTSSe solar cells efficiency improvement

Se-rich selenization offers remarkable benefits for grain growth of Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers, which is critical for solar cells fabrication. However, low-activity selenium often forms Se-clusters and trapped in CZTSSe absorber layers. These trapped Se-clusters increase carrier recombination in CZTSSe absorber layers, thus decreasing efficiency of CZTSSe solar cells. Herein, supercritical carbon dioxide (SCCO2) treatment was demonstrated to regulate selenium composition of CZTSSe absorber layers for solar cells efficiency improvement. Compared with untreated CZTSSe absorber layers, selenium composition of CZTSSe absorber layers were significantly reduced by SCCO2 treatment. The open circuit voltage (VOC) and fill factor (FF) of CZTSSe solar cells improved pronouncedly due to carrier recombination reduction and carrier transport enhancement. As a consequence, the power conversion efficiency (PCE) was increased from 9.26 % (ref device) to 11.43 % (SCCO2 device). This unique SCCO2 treatment may offer new ideas for other selenization-based optoelectronic devices performance improvement.

Combination of supercritical CO2 and high-power ultrasound for the inactivation of fungal and bacterial spores in lipid emulsions

For the first time, this study addresses the intensification of supercritical carbon dioxide (SC-CO2) treatments using high-power ultrasound (HPU) for the inactivation of fungal (Aspergillus niger) and bacterial (Clostridium butyricum) spores in oil-in-water emulsions. The inactivation kinetics were analyzed at different pressures (100, 350 and 550 bar) and temperatures (50, 60, 70, 80, 85 °C), depending on the microorganism, and compared to the conventional thermal treatment. The inactivation kinetics were satisfactorily described using the Weibull model.Experimental results showed that SC-CO2 enhanced the inactivation level of both spores when compared to thermal treatments. Bacterial spores (C.butyricum) were found to be more resistant to SC-CO2 + HPU, than fungal (A.niger) ones, as also observed in the thermal and SC-CO2 treatments. The application of HPU intensified the SC-CO2 inactivation of C.butyricum spores, e.g. shortening the total inactivation time from 10 to 3 min at 85 °C. However, HPU did not affect the SC-CO2 inactivation of A.niger spores. The study into the effect of a combined SC-CO2 + HPU treatment has to be necessarily extended to other fungal and bacterial spores, and future studies should elucidate the impact of HPU application on the emulsion’s stability.

Isolation and Characterization of Alpha and Nanocrystalline Cellulose from Date Palm (Phoenix dactylifera L.) Trunk Mesh.

Highly pure cellulosic polymers obtained from waste lignocellulose offer great potential for designing novel materials in the concept of biorefinery. In this work, alpha-cellulose and nanocrystalline cellulose were isolated from the date palm trunk mesh (DPTM) through a series of physicochemical treatments. Supercritical carbon dioxide treatment was used to remove soluble extractives, and concentrated alkali pretreatment was used to eliminate the lignin portion selectively to obtain alpha-cellulose in approximately 94% yield. Further treatments of this cellulose yielded nanocrystalline cellulose. The structure–property relationship studies were carried out by characterizing the obtained polymers by various standard methods and analytical techniques such as Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), energy dispersive X-ray diffraction (EDX-XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Almost 65% yield of pure cellulose was achieved, out of which 94% is the alpha-cellulose. This cellulose shows good thermal stability and crystallinity. The microscopic analysis of the nanocellulose showed a heterogeneous mix of irregular-shaped particles with a size range of 20–60 nm. The percentage crystallinity of alpha-cellulose and nanocellulose was found to be 68.9 and 71.8, respectively. Thus, this study shows that, this DPTM-based low-cost waste biomass can be a potential source to obtain cellulose and nano-cellulose.

An investigation of process parameters on colour during the dyeing of polyester in supercritical carbon dioxide media

AbstractInnovative supercritical carbon dioxide (scCO2) treatment conditions in fluidised media technology were examined for polyester dyeing. The different dyeing processes in scCO2 media were carried out under a constant dyeing temperature of 120°C (at pressures ranging from 9 to 29 MPa), a constant pressure of 25 MPa (at dyeing temperatures ranging from 40 to 140°C) and a constant density range of 500‐550 kg/m3 (at combinations of dyeing temperatures ranging from 80 to 130°C and dyeing pressures ranging from 18 to 28 MPa). The constant dyeing temperature, constant dyeing pressure and constant density (120°C, 25 MPa, 500‐550 kg/m3, respectively) were selected according to the best results in the literature and recommendations from industrial applications for polyester dyeing in scCO2 media. The different conditions of the studied parameters and their influence are discussed. Colour difference (ΔE) and colour strength (K/S), as well as washing fastness and bursting strength properties, were investigated and compared. Acceptable colour properties (similar to those for standard [control reference] fabric: dyed in scCO2 media at 120°C, 25 MPa pressure and 506 kg/m3 density for 90 minutes) on polyester fabric, with commercially acceptable and quite high washing fastness levels and comparable bursting strength values (similar to those for standard fabric without significant or drastic strength loss), could be achieved with the following scCO2 dyeing processes: at a lower dyeing pressure with the same dyeing temperature (in scCO2 media at 120°C, 21 MPa pressure and 423 kg/m3 density for 90 minutes), at a lower dyeing temperature with the same dyeing pressure (in scCO2 media at 100°C, 25 MPa pressure and 588 kg/m3 density for 90 minutes) and at both a lower dyeing pressure and a lower dyeing temperature with a constant density range of 500‐550 kg/m3 (in scCO2 media at 110°C, 24 MPa pressure and 526 kg/m3 density for 90 minutes). Satisfactory and successful dyeing properties and performance similar to polyester fibre dyed under standard scCO2 dyeing conditions with less energy consumption could be achieved with the correct scCO2 dyeing process parameter optimisation. For instance, the dyeing process in the scCO2 environment at the same dyeing temperature with the standard scCO2 dyeing process (at 120°C), but with a lower dyeing pressure (at 21 vs 25 MPa), resulted in a 17 kWh decrease in energy consumption. In conclusion, it is very important to choose the correct dyeing pressure to obtain level dyeing in the polyester dyeing process carried out in a scCO2 environment and to achieve a reduction in energy consumption during dyeing in a scCO2 medium.

Ultrasonic-assisted supercritical CO2 inactivation of bacterial spores and effect on the physicochemical properties of oil-in-water emulsions

A combined supercritical carbon dioxide and high power ultrasound treatment (SC-CO2 + HPU) to inactivate spores while minimizing the physicochemical changes in emulsions was investigated. The inactivation kinetics were obtained for Bacillus subtilis, Bacillus pumilus and Geobacillus stearothermophilus spores and the effect of the treatment conditions on the quality of the emulsions was explored using response surface methodology. The treatment for 20 min at 95 °C and 350 bar was effective at inactivating B. subtilis and B. pumilus. Treated emulsions showed, in general, minimal changes in density and good stability, although the pH decreased and the droplet size increased. The treatment at 600 bar, 95 °C and 12.5 min permitted satisfactory B. subtilis and B. pumilus inactivation with minimal physicochemical changes in the emulsions. Therefore, the use of SC-CO2 + HPU could be a viable alternative for the preservation of emulsions using temperatures lower than those of thermal treatments.

Preparation and characterization of whey protein isolate nanoparticles in supercritical CO2

Protein nanoparticles represent a promising system for the encapsulation and delivery of bioactive compounds or highly sensitive ingredients. In this study, whey protein isolate nanoparticles (WPINs) were prepared by using supercritical carbon dioxide (scCO2) treatment. The effects of scCO2 on the size and stability of the WPINs were investigated. The average particle diameter ranged from 100 to 300 nm when the WPIN solution was treated with scCO2 at 8–24 MPa and 45 °C for 30 min. ScCO2-treated WPINs had more uniform size distribution and smaller particles than WPINs prepared without scCO2. However, particle aggregation was observed during heating to 55–75 °C. Fluorescence and differential thermogravimetric analysis showed that CO2 pressure did not cause secondary and tertiary structure changes or denaturation of WPINs. The change in WPINs size was likely caused by the high diffusibility of scCO2, which could slightly modify WPINs local structure, affecting hydrophobic interactions and hydrogen bonding within the molecule. These results indicate that the size of nano-particles can be modulated by adjusting CO2 pressure, which may facilitate WPINs use in food and biomedical products.

Evolution Characteristics of Mechanical Properties under Supercritical Carbon Dioxide Treatment in Shale Reservoirs.

Supercritical carbon dioxide (SC-CO2) has been progressively used in the development of shale oil and gas. However, the interaction between CO2 and shale can change the mineral composition and the pore structure, thus affecting the mechanical properties of shale. To study the influence of SC-CO2 on shale, shale samples collected from the Songliao Basin in China are treated with SC-CO2 at various time intervals. Then, a series of tests are performed, such as the mineral composition analysis test, the pore structure analysis test, and the macro mechanics test. The results show that the mechanical properties of shale gradually decrease exponentially with the increase of SC-CO2 treatment time. The loss of elastic modulus reaches about 47% after the treatment of 14 d. X-ray diffraction analysis shows that the mineral (except quartz) content decreases after SC-CO2 treatment, and in particular, the proportions of carbonate minerals significantly decrease by about 12%. The primary pores and fractures are eroded through dissolution, and new pores and fracture structures are developed on the surface microstructure. In addition, the proportion of micropores and mesopores decreases, while the proportion of macropores increases after SC-CO2 treatment. The specific surface area and average pore size present upward trends during SC-CO2 treatment. The changes of mineral assemblage and pore structure lead to the obvious decline of mechanical properties in shale reservoirs. This study contributes to understanding the evolution characteristics of mechanical properties under SC-CO2 treatment, which is of great significance for the efficient exploitation in shale reservoirs.

Non-thermal pasteurization of lipid emulsions by combined supercritical carbon dioxide and high-power ultrasound treatment.

Supercritical carbon dioxide (SC-CO2) is a novel method for food pasteurization, but there is still room for improvement in terms of the process shortening and its use in products with high oil content. This study addressed the effect of high power ultrasound (HPU) on the intensification of the SC-CO2 inactivation of E. coli and B. diminuta in soybean oil-in-water emulsions. Inactivation kinetics were obtained at different pressures (100 and 350bar), temperatures (35 and 50°C) and oil contents (0, 10, 20 and 30%) and were satisfactorily described using the Weibull model. The experimental results showed that for SC-CO2 treatments, the higher the pressure or the temperature, the higher the level of inactivation. Ultrasound greatly intensified the inactivation capacity of SC-CO2, shortening the process time by approximately 1 order of magnitude (from 50 to 90min to 5-10min depending on the microorganism and process conditions). Pressure and temperature also had a significant (p<0.05) effect on SC-CO2+HPU inactivation for both bacteria, although the effect was less intense than in the SC-CO2 treatments. E. coli was found to be more resistant than B. diminuta in SC-CO2 treatments, while no differences were found when HPU was applied. HPU decreased the protective effect of oil in the inactivation and similar microbial reductions were obtained regardless of the oil content in the emulsion. Therefore, HPU intensification of SC-CO2 treatments is a promising alternative to the thermal pasteurization of lipid emulsions with heat sensitive compounds.

Changes in protein structure and physicochemical properties of egg white by super critical carbon dioxide treatment

Supercritical carbon dioxide (SCCD) is a green, novel and practical technology in food processing. In this paper, SCCD treatment was used for enhancing the foaming properties of egg white. The possible mechanism of SCCD pressures increasing the foam ability of egg white protein (EWP) was discussed. The results showed that the maximal foaming capacity (107.7%) was obtained at 9 MPa, which was 3.6 times that of original egg white. Electrostatic force of protein molecules was reduced due to the change of pH value. Meanwhile, the particle size of EWP increased and the absolute zeta potential decreased with SCCD pressure increasing. These changes resulted in an increase of hydrophobicity and viscosity of EWP accordingly. This study found that SCCD treatment caused the exposure of EWP hydrophobic groups through the synergy of high pressure and CO2 solvent. It provided a novel path to improve the foam ability of EWP by physical technology.

Scalable preparation of water-soluble ink of few-layered WSe2 nanosheets for large-area electronics**Project supported by the National Natural Science Foundation of China (Grant Nos. 51771224, 51772087, and 51471185), the National Key R&D Program of China (Grant Nos. 2016YFJC020013 and 2018FYA0305800), and Fujian Institute of Innovation, Chinese Academy of Sciences.

Few-layer two-dimensional (2D) semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics. A general approach is developed to fast prepare uniform and phase-pure 2H-WSe2 semiconducting nanosheets at a large scale, which involves the supercritical carbon dioxide (SC-CO2) treatment and a mild sonication-assisted exfoliation process in aqueous solution. The as-prepared 2H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures, as confirmed by Raman, x-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscope (STEM). The uniform 2H-WSe2 nanosheets can disperse well in water for over six months. Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics. The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2H-WSe2 thin film have also been explored.

Mechanism of enhancing foaming properties of egg white by super critical carbon dioxide treatment

The effect of supercritical carbon dioxide (SCCD) treatment at varying processing time (30–90 min) on foaming and structure properties of egg white protein (EWP) were studied in this paper. The highest foaming ability (107.7%) was obtained after 60 min SCCD treatment, which was 3.6-fold to the control group. Foaming stability kept stable under the processing time of 75 min. Results of surface tension, surface hydrophobicity, rheological properties and particle size indicated that protein was easier to spread to the gas-liquid interface and generate molecular rearrangement. Circular dichroism (CD) and Endogenous fluorescence spectrum showed that there were slight changes on the secondary structure of EWP. The α-helical structure of the protein was destroyed and the particle size became uneven, which indicated that the protein structure became more flexible and loose. The results of this study indicate that SCCD treatment had a potential to be implemented to enhance foaming properties of EWP.

Boosting the efficiency of solution-based CZTSSe solar cells by supercritical carbon dioxide treatment

Supercritical carbon dioxide treatment proved to be efficient approach that can extract parts of organic chemicals in CZTSSe precursor films, thus reducing carbonaceous residues in CZTSSe films and boosting efficiency of CZTSSe-based solar cells.

Research Note: Microbial inactivation of raw chicken meat by supercritical carbon dioxide treatment alone and in combination with fresh culinary herbs

The objective of the present study was to assess the potential synergistic effect between supercritical carbon dioxide (SC-CO2) and fresh culinary herbs (Coriandrum sativum and Rosmarinus officinalis) on the microbial inactivation of raw chicken meat. The microbiological inactivation was performed on Escherichia coli and natural flora (total mesophilic bacteria, yeasts, and molds). High pressure treatments were carried out at 40°C, 80 or 140 bar from 15 to 45 min. Microbial inactivation had a strong dependence on treatment time, achieving 1.4 log CFU/g reduction of E. coli after 15 min, and up to 5 log after 45 min, while a pressure increase from 80 up to 140 bar was not significant on the microbial inactivation. Mesophilic microorganisms were strongly reduced (>2.6 log CFU/g) after 45 min, and yeasts and molds were below the detection limits of the technique (<100 CFU/g) in most cases. The combination of fresh herbs together with SC-CO2 treatment did not significantly increase the inactivation of either E. coli or natural flora, which was similar to the SC-CO2 alone. The synergistic effect was obtained on the inactivation of E. coli using a proper concentration of coriander essential oil (EO) (0.5% v/w), while rosemary EO did not show a significant effect. Color analysis after the treatment showed an increment of lightness (L*), and a decrease of redness (a*) on the surface of the sample, making the product visually similar to cooked meat. Texture analysis demonstrated the modification of the texture parameters as a function of the process pressure making the meat more similar to the cooked one.

Investigation of the influence of supercritical carbon dioxide treatment on meta-aramid fiber: Thermal decomposition behavior and kinetics

Influence of supercritical carbon dioxide (SCF-CO2) on the thermal decomposition behavior and kinetics of meta-aramid fiber was investigated at the first time, in order to develop some fundamental bases for sustainably and cleanly manufacturing some relative products from this fiber with the supercritical green medium. Particularly, the thermal decomposition behavior of treated samples was explored and characterized by thermogravimetric and differential thermogravimetric analysis (TGA-DTGA). The kinetics of the main steps of thermal decomposition was also investigated via different kinetics models. The results show that an influence of SCF-CO2 treatment on the thermal decomposition behavior of the fiber was observed by TGA-DTGA, accompanied with successive and partially overlapped predominant two-step degradation as sample temperature from 380.0 °C to 700.0 °C, as well as a small pyrolysis Step three at 650.0 °C to 800.0 °C. Decreases in thermal property and behavior were detected by TGA-DTGA for the samples as treatment temperature from 80.0 °C to 120.0 °C. The fitted results reveal that good linear regressions of the TGA-DTGA data were achieved from the kinetics models accompanied with high values of adjusted R-Square. The kinetics parameter of the apparent activation energy (E) decreased with the treatment temperature from 80.0 °C to 120.0 °C, as well as with the conversion degree (α) of the samples. Moreover, a second-order chemical reaction mechanism for the predominant thermal decomposition steps was successfully supposed by Coats-Redfern and Achar-Brindley-Sharp-Wendworth models combined with a solid mechanism function of C2.

Extraction of Cellulose Nanofibers via Eco-friendly Supercritical Carbon Dioxide Treatment Followed by Mild Acid Hydrolysis and the Fabrication of Cellulose Nanopapers.

The conventional isolation of cellulose nanofibers (CNFs) process involves high energy input which leads to compromising the pulp fiber’s physical and chemical properties, in addition to the issue of elemental chlorine-based bleaching, which is associated with serious environmental issues. This study investigates the characteristic functional properties of CNFs extracted via total chlorine-free (TCF) bleached kenaf fiber followed by an eco-friendly supercritical carbon dioxide (SC-CO2) treatment process. The Fourier transmission infra-red FTIR spectra result gave remarkable effective delignification of the kenaf fiber as the treatment progressed. TEM images showed that the extracted CNFs have a diameter in the range of 10–15 nm and length of up to several micrometers, and thereby proved that the supercritical carbon dioxide pretreatment followed by mild acid hydrolysis is an efficient technique to extract CNFs from the plant biomass. XRD analysis revealed that crystallinity of the fiber was enhanced after each treatment and the obtained crystallinity index of the raw fiber, alkali treated fiber, bleached fiber, and cellulose nanofiber were 33.2%, 54.6%, 88.4%, and 92.8% respectively. SEM images showed that amorphous portions like hemicellulose and lignin were removed completely after the alkali and bleaching treatment, respectively. Moreover, we fabricated a series of cellulose nanopapers using the extracted CNFs suspension via a simple vacuum filtration technique. The fabricated cellulose nanopaper exhibited a good tensile strength of 75.7 MPa at 2.45% strain.

Influence of supercritical carbon dioxide treatment on the physicochemical properties of cellulose extracted from cassava pulp waste

This study aims at investigating the influence of supercritical carbon dioxide (ScCO2) treatment on the physicochemical properties of cassava–based cellulose. The ScCO2 treatment was performed in a high-pressure vessel by exposing the cellulose to ScCO2 without a co-solvent at variable pressure (P) ranging from 8 MPa to 20 MPa for 60 min. The system temperature (T) was set to 40 °C, 60 °C and 80 °C. Subsequently, a field emission scanning electron microscopy analysis showed that the average fibril diameter of the cellulose was approximately two times less than that of the untreated cellulose. Differential scanning calorimetry and thermogravimetric analyses showed higher temperature shifting of the decomposition peak, which indicated improved thermal stability of the ScCO2-treated celluloses. Additionally, a correlation test revealed that thermal stability of cellulose increased with the pressure of ScCO2.

Effects of supercritical carbon dioxide and thermal treatment on the inulin chemical stability and functional properties of prebiotic-enriched apple juice.

Inulin-enriched apple juice was subjected to supercritical CO2 processing under different pressure levels (10, 15, and 20 MPa at 35 °C, 10 min and a 67% CO2 volume ratio) and to conventional thermal treatment (95 °C/1 min). Physicochemical properties (pH, soluble solid content, ζ-potential, particle size distribution and rheological behavior), organic acid (citric and malic) content, and phenolic compounds (UHPLC-ESI-MS/MS) were evaluated; moreover, antioxidant activity assays (DPPH and TEAC) as well as sugar content and fructo-oligosaccharide analyses (HPAEC-PAD) were performed. The increase in pressure levels reduced the particle size suspended in the functional juice. Supercritical processing was able to preserve all compounds responsible for the functional properties of the beverage as well as the natural nutritional components such as sorbitol, glucose, fructose and sucrose. The emerging technology did not reduce the antioxidant activity of the juice samples, thus maintaining their functionality. The inulin chemical profile was not altered by the supercritical CO2 processing, while in the thermally treated sample, there was a breakdown of the inulin chain into units of short-chain fructo-oligosaccharides. Overall, supercritical technology may be an interesting option for inulin-enriched apple juice processing.

Study of High Performance Sulfonated Polyether Ether Ketone Composite Electrolyte Membranes.

In this study, high performance composite electrolyte membranes were prepared from polyether ether ketone polymeric material. An initial sulfonation reaction improved the membrane hydrophilicity and its water absorbability and thus enhanced the ionic conductivity in electrochemical cells. Protonic conductivity was improved from 10−4 to 10−2 S cm−1 with an increasing sulfonation time from 72 to 175 h. The effects of blending nano SiO2 into the composite membranes were devoted to improve thermal and mechanical properties, as well as methanol permeability. Methanol permeability was reduced to 3.1 × 10−7 cm2 s−1. Finally, a further improvement in ionic conductivity was carried out by a supercritical carbon dioxide treatment under 20 MPa at 40°C for 30 min with an optimum SiO2 blend ratio of 10 wt-%. The plasticizing effect by the Lewis acid-base interaction between CO2 and electron donor species on polymer chains decreased the glass transition and melting temperatures. The results show that sulfonated composite membranes blended with SiO2 and using a supercritical carbon dioxide treatment exhibit a lower glass transition temperature, higher ionic conductivity, lower methanol permeability, good thermal stability, and strong mechanical properties. Ionic conductivity was improved to 1.55 × 10−2 S cm−1. The ion exchange capacity and the degree of sulfonation were also investigated.

Thermo-electrical behaviour of cyclic olefin copolymer/exfoliated graphite nanoplatelets nanocomposites foamed through supercritical carbon dioxide

In this work, novel electrically conductive cyclic olefin copolymer/exfoliated graphite nanoplatelets foams were prepared through a supercritical carbon dioxide treatment starting from the corresponding unfoamed materials prepared by melt compounding, in order to investigate their thermo-electrical properties. For both unfoamed and foamed samples, the exfoliated graphite nanoplatelets introduction led to a systematic enhancement of the thermal degradation temperature. Dynamic-mechanical thermal analysis revealed that the nanofiller addition promoted an enhancement of the storage modulus and of the glass transition temperature over the whole range of the applied foaming pressures. While for unfoamed materials exfoliated graphite nanoplatelets introduction determined an important decrease of the electrical resistivity, the foaming process induced the breakage of the conductive path, with a consequent increase of electrical resistivity. Evaluation of the surface heating upon voltage application showed that the surface temperature of unfoamed materials could be noticeably increased at relatively low voltage levels, while a less pronounced surface heating could be obtained with the corresponding nanocomposite foams.