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Self-healing rubbers have steadily been growing during the last decades. Various strategies have been studied to transform the vulcanized rubber into a reversible cross-linked network with multiple repair cycles. However, a detailed description on how the chemical constituents of a rubber formulation affect the healing properties of the vulcanizate is unknown and has not been reported until now. In this research, the individual effects of both the curing agent (sulfur and peroxide) and the activating complex (zinc oxide and stearic acid) have been assessed on the healing capability of a styrene-butadiene rubber (SBR) compound. The analysis of different healing conditions revealed that pristine materials should be subjected to the same thermal treatment as the healed samples to obtain scientifically sound values of the healing efficiency. Results also showed that each component affected the healing at different time scales, with the activating complex being responsible for the initial physical healing stage. Meanwhile, sulfur would act at later stages as dynamic healing moiety, enabling disulfide exchange reactions. In conclusion, the mechanical recovery of a rubber network can be potentially tailored depending on the relation between the chemical components of the rubber formulation., he authors acknowledge the State Research Agency of Spain (AEI) for a research contract (PID2019-107501RB-I00) and M. Hernández Santana for a Ramón y Cajal contract (RYC-2017-22837)

Dielectric elastomers have been regarded as truly artificial muscles for their electro-mechanical (EM) actuation performance. However, they require large driving voltages to present adequate actuation strains. The main pursued route to solve it has been the development of elastomeric composites with high dielectric permittivity. Unfortunately, such approach reinforces the matrix and has a detrimental effect on the EM actuation and the dielectric breakdown strength. Here, we study a complementary strategy to improve the dielectric permittivity without increasing its stiffness. We analyze the effect of thermoplastic PU elastomer on the actuation response of a thermoplastic dielectric elastomer, such as poly(styrene-ethylene-butadiene-styrene). The addition of 10 wt% PU resulted in an improved EM actuation without reducing its dielectric breakdown strength. This result was ascribed to the interaction of the urethane hard segments of the PU and the styrene moieties of the SEBS. The results revealed that DEAs can be developed through a simple blending procedure, where a proper selection of the polymer systems is key for their actuation performance., This research was supported by National Commission for Scientific and Technological Research, Chile, under Postdoctoral fellowship Nº 3170104 granted to H. Aguilar-Bolados. RV acknowledges financial support from Consejo Superior de Investigaciones Cientificas, Spain through grant project number 201660I032

The management of end-of-life tires (ELTs) is one of the main environmental issues that society faces nowadays. Recycling of ELTs appears as one feasible option for tackling the problem, although their incorporation as ground tire rubber (GTR) in other rubber matrices is limited due to poor compatibility. In this research, we report a successful combination of a cryo-grinding process with a chemical treatment for modifying the surface of GTR. Various cryo-grinding protocols were studied until a particle size of 100–150 µm was achieved. Chemical treatments with different acids were also analyzed, resulting in the optimal modification with sulfuric acid (H2SO4). Modified GTR was added to a styrene-butadiene rubber (SBR) matrix. The incorporation of 10 phr of this filler resulted in a composite with improved mechanical performance, with increments of 115% and 761% in tensile strength and elongation at break, respectively. These results validate the use of a recycled material from tire waste as sustainable filler in rubber composites.

Composite coatings are used in order to reduce the friction and protect contacting surfaces against wear with good adhesive to substrate. The present study deals with two sizes of solid particles used in composite coatings. As received graphite G1, the mean size is 20µm and the crushed one, obtained by ball mill, is 10µm. The resulting tribological behavior and micromechanical properties were discussed and compared. As expected, the smaller the particle size the greater reduction in the coefficient of the friction and wear rate. The experimental findings show that adding 5 wt% of crushed graphite provide similar COF than when introducing 10 wt% of as received graphite. Coatings scratch behavior is affected by the size and percentage of fillers inside the polyester matrix. In fact, the scratch resistance is observed with polyester coatings filled at 5 wt% G2 and 10 wt% G1.

The influence of 0.5, 0.75, and 1 wt.% of graphene oxide (GrO) in nanocomposite coating on scratch behavior and tribological performance was analyzed. Graphite was oxidized using the Marcano and Tour method to obtain graphite oxide, which is thermally exfoliated at 700°C getting graphene oxide. The transformation of graphite to graphene oxide was evaluated via Raman spectroscopy and X-ray diffraction. Effects of graphene oxide content on the friction and wear behavior of polyester composite coatings were evaluated under dry sliding conditions. Experimental findings showed that the addition of 0.5 wt.% GrO was effective in reducing the friction coefficient of polyester coating. Meanwhile, under the same sliding conditions, the wear results revealed that the polyester coating filled with 1 wt.% GrO has better antiwear ability compared to those filled with 0.5 and 0.75 wt.% GrO. From the scratch analyses, we deduced that coating scratch behavior was highly affected by the amount of fillers inside the polyester matrix. In fact, the best friction characteristic and scratch resistance were observed in the case of polyester coatings filled with the lower amount of GrO, namely 0.5 wt.%.

The present study investigates the mechanical and tribological properties of an epoxy matrix filled with different graphitic particles deposited on an aluminum substrate by the electrostatic spray technique. Three different particles added to the epoxy matrix were the received graphite, the crushed graphite obtained by crushing the natural flake graphite particles using a ball mill, and graphite oxide obtained by oxidation treatment. Nanoindentation tests were conducted on the different coatings in order to evaluate the surface hardness and the contact elastic modulus. The effect of the oxidation treatment and the loading content on the tribological behavior of the above composites were also evaluated under dry-friction conditions. As expected, the smaller the particle size, the greater the reduction in the dynamic friction. The experimental findings showed that adding 5 wt % of crushed graphite (10 µm) provided a similar dynamic friction as the addition of 10 wt % of received graphite (20 µm). The epoxy filled with received graphite showed a lower wear rate than that filled with graphite oxide and crushed graphite. Moreover, both hardness and elastic modulus increased in the case of the epoxy filled with graphite oxide and crushed graphite.

© 2020 by the authors., Composite materials of poly(3,4-ethylenedioxythiophene) (PEDOT)/activated carbon (AC) were prepared by ‘in-situ’ polymerization and subsequently deposited by spray-coating onto a flexible electrolyte prepared in our laboratories. Two activated carbons were tested: a commercial activated carbon and a lab-made activated carbon from brewer’s spent grain (BSG). The porous and spongy structure of the composite increased the specific surface area, which helps to enhance the energy storage density. This procedure to develop conductive composite materials using AC prepared from biowaste has the potential to be implemented for the preparation of polymer-based conductive inks for further applications as electrodes in pseudocapacitors., Francisco González and Mario Hoyos are grateful to CONACYT-SENER for the scholarship granted (CVU559770/Registro 297710).

© 2020 by the authors., The need for electromagnetic interference (EMI) shields has risen over the years as the result of our digitally and highly connected lifestyle. This work reports on the development of one such shield based on vulcanized rubber foams. Nanocomposites of ethylene–propylene–diene monomer (EPDM) rubber and multiwall carbon nanotubes (MWCNTs) were prepared via hot compression molding using a chemical blowing agent as foaming agent. MWCNTs accelerated the cure and led to high shear-thinning behavior, indicative of the formation of a 3D interconnected physical network. Foamed nanocomposites exhibited lower electrical percolation threshold than their solid counterparts. Above percolation, foamed nanocomposites displayed EMI absorption values of 28–45 dB in the frequency range of the X-band. The total EMI shielding efficiency of the foams was insignificantly affected by repeated bending with high recovery behavior. Our results highlight the potential of cross-linked EPDM/MWCNT foams as a lightweight EM wave absorber with high flexibility and deformability, This research was funded by MICIU, grant number MAT2016-81138-R.

Self-healing polymers typically face an enforced trade-off between repairability and mechanical properties, with a high degree of self-healing being achieved mainly by materials having low mechanical strength and stiffness. This study focuses on the development of SBR compounds that can combine together self-healing properties with the use of ground tire rubber (GTR) as alternative sustainable filler. The self-healing efficiency of GTR filled SBR compounds is compared to conventional carbon black filled compounds. The influence of the vulcanization system and the addition of silane-based coupling agents are also assessed. Results show that SBR compounds vulcanized by means of a semi-efficient sulfur based system recover around 50% of their mechanical strength, being the self-healing response related to the presence of disulfide bonds. Contrary to carbon black compounds, GTR samples present similar healing efficiency to the unfilled SBR samples, improving mechanical properties in 50%. Moreover, the coupling agent enhances even more (up to 80%) the mechanical strength of the SBR-GTR compounds without adversely affecting the healing efficiency. These results can thus be seen as a starting model material for developing new sustainable applications economically and environmentally convenient with good mechanical properties as well as healing ability., M. Hernández acknowledges the Ministry of Economics and Competitiveness of Spain for a research contract (MAT2015-73392- JIN). The authors also acknowledge Signus for providing the ground tire rubber and C. Chirico (Carlos III University, Madrid) for the particle size distribution measurements

Graphene materials (GMs) are deeply studied as nanoreinforcements of polymer matrices, especially for epoxy matrices. Here, we analyze the effect of GMs on the transport properties of a poly(bisphenol A-co-epichlorohydrin) resin. In particular, we focus on the effect of the morphology, chemical composition and structure of different GMs obtained by varying the reduction temperature of the thermal/exfoliation treatment of graphite oxide synthesized by a modified Hummers method. The dispersion degree of the GMs was studied by microscopy techniques, showing a strong dependence on the specific surface area and chemical composition of the graphene material. The transport properties imposed different requirements on GMs. The thermal conductivity benefited from a high aromatic restoration. Meanwhile, the electrical conductivity required the right balance of filler/matrix interaction and aromatic restoration., The authors gratefully acknowledge the financial support of the MINECO, Spain, through the project MAT2013-48107-C3. R. Sánchez- Hidalgo thanks to MINECO, Spain for the Predoctoral grant BES-2014- 070802.

© 2020 by the authors., The technological demands imposed on dielectrics and electrical insulation materials are being increasing with the transition from traditional to smart grids. Epoxy resin/conductive polymer (CP) blends with high dielectric permittivity have been prepared by means of a straightforward methodology. Poly(3,4-ethylenedioxythiophene) (PEDOT) and polyaniline (PANI), doped with p-tosylate and ammonium peroxide sulfate (APS), respectively, were synthesized and blended with an epoxy matrix. The addition of 3 wt % of PEDOT and PANI results in permittivity values of 68.9 and 9.5, respectively at 0.1 Hz—1300 and 111 times higher than pure resin. Hence, PEDOT is more effective than PANI at improving the permittivity of the epoxy resin. Moreover, the material retains the electrical insulation of the resin and exhibits a slight increase in thermal conductivity., This research was funded by MINECO, grant number MAT2016-81138-R.

The electrical, mechanical and piezoresistive responses of vinyl ester nanocomposites made of two types of multilayer graphene sheets (GSs) and multiwall carbon nanotube hybrid fillers at different relative concentrations is presented. Two types of GSs are used in order to evaluate the role of their physicochemical properties. The best mechanical properties were achieved with hybrids at 75% relative concentration of GSs. Collaborative effects were also observed in the electrical conductivity of the hybrids at this relative concentration. The flexural piezoresistive response yielded low sensitivity (with both, positive and negative gage factors) at the compression side of the flexural coupon. On the contrary, the tensile side of the coupon always presented positive resistance changes and significantly higher piezoresistive sensitivity. The highest piezoresistive sensitivity was found for hybrid materials with 75% relative concentration of GSs, using the graphenic sheets with larger lateral dimensions and higher structural quality (lower Raman I/I ratio)., This work was sponsored by CONACYT project No. 2262. CS Acknowledges CONACYT scholarship 240300 for his Doctoral studies. Support of the infrastructure acquired through CONACYT project No. 268595 (CICY) as well as the LANNBIO facilities at CINVESTAV-M�erida under the supervision of Dr. Patricia Quintana are kindly acknowledged. Raquel Verdejo and Miguel Angel Lopez Manchado acknowledge the Ministry of Science, Innovation and Universities in Spain for project MAT2016-81138-R. Technical assistance of Dr. Alejandro May Pat is highly appreciated. Authors also wish to acknowledge assistance of Jorge Ocampo Bello for his dedicated contribution with the electrical instrumentation, as well as that of Santiago Duarte Aranda and Rossana Faride Vargas Coronado for SEM. Technical assistance of Jos�e M. Baas Lopez for BET measurements as well as facilities provided by Dr. Daniela Pacheco for using the adsorption isotherm equipment acquired through the SENER-CONACYT energetic sustainability project No. 254667 is also appreciated.

The development of self-healing rubbers is currently under investigation as a strategy to promote their reuse and, hence, reduce their waste. However, autonomous, multicycle self-healing rubbers with good mechanical properties have so far proven difficult to achieve. Here, mechanically robust composites based on epoxidized natural rubber (ENR) and thermally reduced graphene oxide (TRGO) were successfully designed and prepared with a high healing efficiency of up to 85% at room temperature without applying external stimuli. The incorporation of TRGO not only improves the mechanical performance in more than 100% in relation to pristine ENR but also promotes the hydrogen bonding interactions with the rubber. This leads to a homogenous dispersion of TRGO within the ENR matrix, which further increases its self-healing capability., The authors acknowledge the Ministry of Science, Innovation and Universities of Spain for a research contract (MAT2015- 73392-JIN) and M. Hernández Santana for a Ramón y Cajal contract (RYC-2017-22837).

Nowadays, the different types of nano-carbons such as carbon nanotubes, graphene and nano-diamond are considered as revolutionary materials, since they present outstanding electrical, thermal and mechanical properties. The expansion of the knowledge related to their syntheses and their unique properties has favored important advances in the development of new type of elastomer composites. Elastomer composites with enhanced electrical and thermal properties are possible to obtain by using low amounts of these nano-carbon based materials as filler in elastomer matrices. On the other hand, the wide range of commercially available rubbers and thermoplastic elastomers provides a number of possibilities in order to obtain tailor-made elastomeric materials. Herein, concise information concerning the preparation methods, properties and application of elastomer composites filled with nano-carbon based materials is presented. The role of nano-carbon based materials in the transport properties of resulting elastomer composites is emphasized, which is attributed to the formation of a percolation network of filler through the elastomeric matrix. Likewise, the influence of the viscoelastic properties and the behavior of elastomers in presence of oil and organic solvents on sensing properties of electrically conducting elastomer composites filled with nano-carbon based materials is discussed.

© The Author(s)., Owing to their high strength and stiffness, thermal and environmental stability, lower shrinkage, and water resistance, epoxy resins have been the preferred matrix for the development of syntactic foams using hollow glass microspheres. Although these foams are exploited in multiple applications, one of their issues is the possibility of breakage of the glass hollow microspheres during processing. Here, we present a straightforward and single-step foaming protocol using expandable polymeric microspheres based on the well-established compression molding process. We demonstrate the viability of the protocol producing two sets of nanocomposite foams filled with carbon-based nanoparticles with improved transport properties., The authors gratefully acknowledge the financial support of MINECO, through the project MAT2016-81138-R.

Conventional carbon fiber-reinforced plastics (CFRP) have extensively been used as structural elements in a myriad of sectors due to their superior mechanical properties, low weight and ease of processing. However, the relatively weak compression and interlaminar properties of these composites limit their applications. Interest is, therefore, growing in the development of hierarchical or multiscale composites, in which, a nanoscale filler reinforcement is utilized to alleviate the existing limitations associated with the matrix-dominated properties. In this work, the fabrication and characterization of hierarchical composites are analyzed through the inclusion of graphene to conventional CFRP by vacuum-assisted resin infusion molding., This research was funded by the Spanish Ministerio de Economía y Competitividad (MINECO), grant number MAT2016-81138-R, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The design of materials with tailored properties capable of tuning their performance is a topical challenge. Here, we demonstrate that it is possible to modulate the mechanical and transport properties of silicone rubber nanocomposites by controlling the structure, chemical composition and morphology of the graphene material. Intrinsic graphene properties, such as remaining oxygen groups, specific surface area, and aspect ratio, among others, have a profound effect on the final properties of the nanocomposite. Thus, the thermal conductivity benefits from larger filler size and high aromatic restoration. Whereas mechanical properties and electrical conductivity require a proper balance between filler/polymer matrix interaction and a partial aromatic restoration., This research was funded by MINECO, grant number MAT2016-81138-R. R.S. thanks to MINECO for the Predoctoral grant BES-2014-070802, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Self-healing polymers are currently receiving widespread attention as a strategy to extend the product's lifetime. Thermosetting polymers, particularly epoxies, are the most studied materials due to their uses as coatings, adhesives, or structural elements, among others. Scarcely noticed studies have reported the inherent healing capacity in arrested cracks of unmodified epoxy resins. Here, we present that healing can also occur in non-arrested cracks and its mechanism is a combination of an already described physical phenomenon and a chemical phenomenon, due to the formation of reversible hydrogen bonds. Here, we exemplify the need for fixing a set of standard testing conditions and propose they require complete and non-arrested cracks to do so.

Carbon nanofibres (CNFs) and graphite flake microparticles were added to thermoplastic polystyrene polymer with the aim of making new conductive blends suitable for 3D-printing. Various polymer/carbon blends were evaluated for suitability as printable, electroactive material. An electrically conducting polystyrene composite was developed and used with commercially available polystyrene (HIPS) to manufacture electrodes suitable for electrochemical experiments. Electrodes were produced and evaluated for cyclic voltammetry of aqueous 1, 1’-ferrocenedimethanol and differential pulse voltammetry detection of aqueous Pb2+ via anodic stripping. A polystyrene/CNF/graphite (80/10/10 wt%) composite provides good conductivity and a stable electrochemical interface with well-defined active geometric surface area. The printed electrodes form a stable interface to the polystyrene shell, give good signal to background voltammetric responses, and are reusable after polishing.

Hybrid ethylene-propylene-diene-monomer (EPDM) nanocomposite foams were produced via compression molding with enhanced electromagnetic wave absorption efficiency. The hybrid filler, consisting of 20 phr ferroelectric barium titanate (BT) and various loading fractions of multi-wall carbon nanotubes (MWCNTs), synergistically increased the electromagnetic (EM) wave absorption characteristics of the EPDM foam. Accordingly, while the EPDM foam filled with 20 phr BT was transparent to the EM wave within the frequency range of 8.2&ndash, 12.4 GHz (X-band), the hybrid EPDM nanocomposite foam loaded with 20 phr BT and 10 phr MWCNTs presented a total shielding effectiveness (SE) of ~22.3 dB compared to ~16.0 dB of the MWCNTs (10 phr). This synergistic effect is suggested to be due to the segregation of MWCNT networks within the cellular structure of EPDM, resulting in enhanced electrical conductivity, and also high dielectric permittivity of the foam imparted by the BT particles. Moreover, the total SE of the BT/MWCNTs loaded foam samples remained almost unchanged when subjected to repeated bending due to the elastic recovery behavior of the crosslinked EPDM foamed nanocomposites.

Supplementary data related to this chapter can be found at http://dx.doi.org/10.1016/j.polymer.2017.02.046., In this work it is provided the first evidence of the polymer chains confinement within self-standing pore walls of nanoporous materials based on poly (methyl methacrylate) (PMMA). This was made possible by producing a series of porous samples with a wide range of pore sizes between 90 nm and 3 μm using processes combining CO sorption, selective block copolymer swelling or homogeneous physical foaming. Mobility restrictions of the PMMA chains in the porous samples with pore size below 200 nm was consistently demonstrated with several experimental techniques, including differential scanning calorimetry, Raman spectroscopy, and broadband dielectric spectroscopy. In addition, several scale-reduction phenomena related to the constitutive elements of the porous materials, both in the polymeric and gaseous phases, and to the porous architecture are identified. The significance of these phenomena on macroscopic electrical conductivity and permittivity of the nanoporous materials is demonstrated, and the presented observations support previous explanations of improved mechanical properties and thermal insulation of this type of nano-materials., Financial support from The Dow Chemical Company USA, FPI grant BES-2013-062852 (B. Notario) from the Spanish Ministry of Education, MINECO (MAT 2012-34901), and the Junta of Castile and Leon (VA035U13) is gratefully acknowledged. J. Pinto and B. Notario contributed equally to this work.

Graphene oxide (GO) can be produced through diverse synthetic routes in large quantities that lead to clear differences in the resulting graphene morphology and properties. Here, we analysed the effect of several thermally reduced graphene oxides (TRGOs), at two different concentrations, on the electrical and mechanical properties of epoxy resin nanocomposites. Natural graphite was oxidised using two methods, Brodie (GO-B) and Hummers (GO-H), and, then, thermally reduced at different temperatures, 700, 1000, and 2000 °C. Intrinsic graphene properties, such as remaining oxygen groups, specific surface area, and aspect ratio, among others, have a profound effect on the final properties of the nanocomposite. The dispersion state was heavily influenced by the specific surface area and the remaining oxygen groups on the graphene. Meanwhile, the electrical and mechanical properties showed a strong and opposite dependency with the reduction temperature, with low temperatures resulting in flakes with high reinforcing characteristics and high temperatures in flakes with high electrical conductivity performance. Finally, TRGOs synthesised via Hummers and reduced at low temperatures appeared to be more suited as reinforcing particles, while TRGOs synthesised via Brodie were more effective as electrically conductive nanofillers., The authors gratefully acknowledge the financial support of the State Secretariat for Research, Development and Innovation of the Spanish Ministry of Economía y Competitividad, through the project MAT2013-48107-C3.

Reactive flexible polyurethane (PU) foams were synthesized with two contents of hard segments (HS) and filled with multi-walled carbon nanotubes (MWCNTs), functionalized MWCNTs (f-MWCNTs) and functionalized graphene sheets (FGS). The effect of the HS content and the carbon nanofillers on the kinetics of polymerization and the kinetics of phase-separation have been studied by Fourier transform infrared spectroscopy (FT-IR) and synchrotron small-angle X-ray scattering (SAXS). A slow down on the rate of polymerization and on the development of the polymer structure due to the increase of the HS content and the inclusion of the nanoparticles was observed. Therefore, this work demonstrates that there is a relationship between the kinetics of polymerization and the kinetics of phase separation in flexible PU nanocomposite foams. SAXS data was used to generate 3D microstructures of PU nanocomposite foams and the phase-separated morphology was observed by atomic force microscopy (AFM)., The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA (NMP3-LA-2008-213277). MMB and MMG also acknowledge the FPI and JAE-Pre programs from MICINN and CSIC, respectively. The authors thank Dr. Angel Marcos-Fernández for helpful discussions and Dr. Gema Rodriguez for AFM images.

Flexible polyurethane (PU) foams filled with a fixed amount of carbon-based nanofillers, in particular multiwall nanotubes and graphenes, have been studied to clarify the influence of the morphology and functional groups on the physical properties of these polymeric foams. The effect of the carbon nanoparticles on the microphase separation has been analyzed by FT-IR spectroscopy revealing a decrease in the degree of phase separation of the segments. Variations of the glass transition temperature and an improved thermal stability were observed due to the presence of the nanoparticles. The EMI shielding effectiveness of flexible PU foams has also been enhanced, in particular for FGS 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.

Flexible polyurethane (PU) foams, with loading fractions of up to 0.2 wt% carbon nanotubes (CNTs), were made by free-rising foaming using water as blowing agent. Electron microscopy revealed an open cellular structure and a homogeneous dispersion of CNTs, although the incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. The compressive response of the foams did not show an unambiguous improvement with CNT content due to the variable foam structure. However, dense films generated by hot pressing the foams indicated a significant intrinsic reinforcement of the polymer, even at low loadings of CNTs. Most significantly, CNTs were found to increase the acoustic activity monotonically at concentrations up to 0.1 wt%.

Free-rising silicone foams were made with loading fractions of up to 0.25 wt.-% functionalized graphene sheets (FGS) and up to 1.0 wt.-% carbon nanotubes (CNTs) using hydrogen as blowing agent. Scanning electron microscopy of the samples revealed an open cellular structure and a homogeneous dispersion of both types of nanofillers. The incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. Transmission electron microscopy revealed the formation of a CNT network throughout the sample, while FGS presented an exfoliated and intercalated dispersion. The thermal stability of the samples was drastically affected by the presence of both nanofillers. Both nanofillers showed a positive effect on the compressive response of the foams. However, the nanocomposite foams were found to decrease the acoustic absorption with nanofiller content probably due to the variable foam structure and improved stiffness.

An experimental evidence of a remarkable enhancement of strain-induced crystallization in natural rubber nanocomposite under uniaxial stretching, due to the presence of nanoclay particles, is described. Synchroton wide-angle X-ray diffraction (WAXD) have been used to monitor structure changes and crystallinity development during deformation. The results showed a dual crystallization mechanism in nanocomposites, which consists of spatial reorganization of organoclay at low strains, followed by rapid strain-induced crystallization of natural rubber. The presence of nanoparticles introduces new energy-dissipating mechanisms, and the mechanical property enhancement refers to the nanoparticle mobility and orientation during deformation. In-situ experiments were also carried out to relate the stress-strain behavior with structure determination using WAXD., The authors gratefully acknowledge the financial support of the Spanish Ministry of Education (MEC) through its project MAT 2004-00825. J. Carretero-González wishes to thank the Spanish Ministry of Education (MEC) for the concession of a FPI grant and R. Verdejo also acknowledges a Juan de la Cierva contract from the MEC. BH also acknowledges the support by the NSF (DMR-0405432).

In recent years, there has been a significant interest of the scientific community on nanocellular polymeric foams as a possible next generation of materials with a low dielectric constant for microelectronics applications In this work, the dielectric behavior of microcellular and nanocellular poly (methyl methacrylate) (PMMA) based foams has been characterized, both as a function of frequency and temperature, in order to analyze the effect of reducing the cell size to the nanoscale on the dielectric properties. Experimental results have shown clear differences in the dielectric behavior of the samples with cell sizes in the nanoscale as well as a sharp reduction of the dielectric constant when the porosity increases., Financial support from FPI grant BES-2013-062852 (B. Notario) from MINECO and FEDER program (MAT 2012 – 34901) MINECO, FEDER, UE (MAT2015-69234-R) and the Junta de Castile and Leon (VA035U13) are gratefully acknowledged

A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foam reduces heelstrike cushioning, and is a possible cause of running injuries.

A repeat impact machine was developed to analyse changes in the mechanical response of ethylene vinyl acetate copolymer foams used in running shoes. Impacts of energy 0.6 J were repeated at 1.7 Hz frequency, with daily recovery periods, to simulate the typical shoe use of long distance runners. Piezoelectric force measurement and non-contact extensometry was used to generate the compressive stress strain curve of the foam. The peak stresses were approximately 500 kPa, comparable with stresses measured at the foot-shoe interface. Foam material parameters, such as cell gas pressure and polymer yield stress, were generated.

Three areas, where polymer foam products are used in personal protection, are reviewed to contrast the foam micromechanisms and the use of Finite Element Analysis (FEA) for engineering design. For flexible open-cell foams used for seating cushions, the main deformation mechanism is cell edge bending; regular cell models can predict much of the compressive response. Hyperelastic FEA models can then predict the forces for foam indentation. For flexible closed-cell foams used in shoe midsoles, cell air compression dominates the response; diffusive air loss leads to foam deterioration with use. Hyperelastic FEA models can predict the interaction between the foam and the heelpad. Finally, for rigid closed-cell foams used in helmets, the permanent stretching and wrinkling of cell faces dominates the response. Crushable foam FEA models, which consider the yield surface and hardening, predict different responses for impacts on the road and on a kerbstone.

Here we report the effect of multi-walled carbon nanotubes (MWCNTs) and thermally reduced graphene (TRG) on the miscibility, morphology and final properties of nanostructured epoxy resin with an amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The addition of nanoparticles did not have any influence on the miscibility of PEO-PPO-PEO copolymer in the resin. However, MWCNTs and TRG reduced the degree of crystallinity of the PEO-rich microphases in the blends above 10 wt.% of copolymer while they did not change the phase morphology at the nanoscale, where PPO spherical domains of 20-30 nm were found in all the samples studied. A synergic effect between the self-assembled nanostructure and the nanoparticles on the toughness of the cured resin was observed. In addition, the nanoparticles minimized the negative effect of the copolymer on the elastic modulus and glass transition temperature in the resin.

Mechanical tests were performed on foamed blends of Ethylene – Styrene Interpolymer (ESI) with low density polyethylene (LDPE). In compressive impact tests the foams, of density around 50 kg m-3, have higher initial yield stresses than Ethylene Vinyl Acetate (EVA) foam of the same density. Impact, Instron and creep tests were analysed to estimate the effective air pressure in the undeformed foam cells, and the initial yield stress. The rate dependence of the latter increases slightly with increasing ESI content. The ESI/LDPE foams have improved impact properties, compared with EVA foams of similar density, for leg protection applications. Analysis of creep tests shows that air diffuses from the cells at a similar rate to EVA foams of a greater density. The ESI/LDPE foams have potential to replace higher density EVA foams in running shoes.

Bionanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HHx) (13 % by mol of HHx) with multiwalled carbon nanotubes (MWCNTs) were prepared to obtain semiconductive nanocomposites for potential applications as scaffolds for nerve repair. The effect of the polymer/nanotube interface on the composite properties was studied using oxidized (oxi-MWCNTs) and surface modified MWCNTs with low-molecular weight P3HB3HHx (pol-MWCNTs), in a ratio from 0.3 to 1.2 wt % for each type of MWCNTs employed. Morphology and conductive properties of the composites indicated a good interaction between pol-MWCNTs and the polymer matrix. Composites with improved conductivity were obtained with only 0.3 wt % of pol-MWCNTs added. However, agglomeration and lower conductivity was observed for samples with oxi-MWCNTs. Cell viability studies carried out with neurospheres showed that samples with 1.2 wt % of pol-MWCNTs are not cytotoxic and, in addition favors the neurospheres growth on the composite surface. Considering the electrical properties and biological behavior, nanocomposites of P3HB3HHx and pol-MWCNTs are promising substrates for the regeneration of nerve tissue. © 2013 Wiley Periodicals, Inc.

In this work we investigate the effect of the dispersion degree of as-received multiwall carbon nanotubes (MWNTs) in the liquid-solid transitions (LST) of polydimethylsiloxane (PDMS). The physical LST of the suspensions showed a strong dependence on the nanotubes dispersion degree due to the formation of an interconnected network as the dispersion time increased. These MWNTs acting as >effective physical cross-links> also influenced the dynamic viscoelastic properties, accelerating the chemical LST (or chemical cross-linking) and giving rise to an increase in the cross-linking density of the composite samples., The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA (NMP3-LA- 2008-213277). The authors would like to thank Dr. José Luis García Fierro for XPS measurements.

This paper compares the filler percolation network of multi-walled carbon nanotubes (MWCNTs) grown by chemical vapor deposition and thermally reduced functionalized graphene sheets (FGSs) in an epoxy resin. The filler network was evaluated by the plate-plate rheological response of un-cured dispersions and the electrical properties of cured materials. We found that FGS did not raise the viscosity of the system as much as MWCNT, maintaining the Newtonian behavior even at 1.5 wt.% FGS. MWCNT readily formed a filler network compared to FGS, evidenced by lower electrical and rheological percolation thresholds, presence of yield stress and higher storage modulus of the dispersions. On the other hand, the mechanical performance of the cured FGS nanocomposites outperformed the MWCNT, with enhancements of 50% and 15% of Young's modulus and strength, respectively. This combination of good processing properties with low viscosity and enhanced mechanical properties makes FGS great candidates to develop multifunctional polymer materials.

International audience; A novel toughened polylactic acid (PLA) bionanocomposite with tuneable properties was successfully prepared by melt mixing PEA with natural rubber and several montmorillonites (MMTs). The organoclays were preferentially located at the interface acting as compatibilisers between both polymer phases. This location resulted in a marked improvement of the physical and mechanical properties of the system. Moreover, these properties can be controlled as a function of the nanofiller nature and the mixing procedure used.

The work was supported by the Spanish Ministry of Science and Innovation (MICINN) under project MAT 2010-18749. MMG thanks the CSIC for a JAE-Pre grant

Natural rubber (NR) and functionalized graphene sheets (FGSs) nanocomposites were prepared by conventional two-roll mill mixing. The morphology and structure of the FGS was characterized confirming the successful exfoliation of the FGS. The strong rubber-to-filler interactions accelerate the cross-linking reaction, increase the electrical conductivity and cause an important enhancement on the mechanical behavior of the NR nanocomposites. The nanofiller does not affect the molecular dynamics of NR, while the presence of vulcanizing additives slowdowns the segmental motions and decreases slightly the time scale of the global chain dynamics in NR/FGS nanocomposites. These functional properties make NR/FGS nanocomposites a promising new class of advanced materials. © 2012 Elsevier Ltd., Finnancial support of the MCINN (Grants MAT2009-07789 and MAT2010-18749). M. Hernández thanks the Venezuelan Ministry of Science and Technology for the concession of a ‘‘Misión Ciencia’’ grant.

We describe a straightforward production pathway of polymer matrix composites with increased dielectric constant for dielectric elastomer actuators (DEAs). Up to date, the approach of using composites made of high dielectric constant ceramics and insulating polymers has not evidenced any improvement in the performance of DEA devices, mainly as a consequence of the ferroelectric nature of the employed ceramics. We propose here an unexplored alternative to these traditional fillers, introducing Calcium Copper Titanate (CCTO) CaCu3Ti4O12, which has a giant dielectric constant making it very suitable for capacitive applications. All CCTO/Polydimethylsiloxane (PDMS) composites developed display an improved electro-mechanical performance. The largest actuation improvement was achieved for the composite with 5.1 vol.% of CCTO, having an increment in the actuation strain of about 100% together with a reduction of 25% in the electric field compared to the raw PDMS matrix., LJR, MH, MALM and RV gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA 55 (NMP3-LA-2008-213277). RV acknowledges the mobility grant PA1003132 from CSIC. PL, MAR and JFF kindly acknowledge financial support from the MICINN project MAT 2010-21088-C03-01.The authors are in debt to Manuel Rus, from ICTP-CSIC, for the technical support in the electro-mechanical experimental set-up.

A new functionalised graphene sheet (FGS) filled poly(dimethyl)siloxane insulator nanocomposite has been developed with high dielectric constant, making it well suited for applications in flexible electronics. The dielectric permittivity increased tenfold at 10 Hz and 2 wt.% FGS, while preserving low dielectric losses and good mechanical properties. The presence of functional groups on the graphene sheet surface improved the compatibility nanofiller/polymer at the interface, reducing the polarisation process. This study demonstrates that functionalised graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values. PACS: 78.20.Ci, 72.80.Tm, 62.23.Kn, The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA (NMP3-LA-2008- 213277). M. Hernández acknowledges the Venezuelan Science and Technology Ministry for a Mision Ciencia fellowship.

Smectite clays (e.g. montmorillonite), belonging to the structural family called 2:1 phyllosilicates, are the main choice for designing polymer nanocomposites due to their low cost and rich intercalation chemistry allowing them to be chemically modified (organoclays) and to improve the compatibility with the polymer matrix. These hybrid materials, normally called polymeric nanocomposites (PNC), represent a radical alternative to conventional polymer composites and have focused the attention of both academia and industry because of their unexpected properties, and their straightforward synthesis and processing. Such materials on the nanoscale level show signifi cant improvements in mechanical properties, heat distortion temperatures, thermal stability, fl ame retardancy and enhanced barrier properties. The combination of enhanced properties, weight reduction, and low cost has led to interesting commercial applications such as automotive and packaging, among others. All this justifi es the growing interest of both academia and industry in the development of these hybrid materials. In this paper we describe the most signifi cant fi ndings in the clay/polymer nanocomposites fi eld considering three polymer families: elastomers, thermosets and polymers from natural resources or biopolymers., Financial support provided by the Ministerio de Ciencia e Innovación (MCINN) through the Project MAT 2010-18749. N.B. thanks the CSIC for a JAE-pre contract.

This work presents the preparation of functionalized graphene sheets (FGS)/epoxy coatings cured by cationic photopolymerization with enhanced mechanical properties. The kinetics of the photopolymerization process for formulations up to 1.5 wt% of graphene were evaluated by means of Real-Time FTIR spectroscopy. The reinforcement of the cured coatings by the graphene was studied by measuring the dynamic-mechanical properties and the surface hardness. An increase of almost 40 °C in the Tg was obtained by adding 1.5 wt% of graphene to the epoxy matrix. A good dispersion state and interaction of the graphene with the matrix were observed by TEM and FESEM analyses.

The segmental chain dynamics in nonvulcanized and vulcanized natural rubber/layered silicate nanocomposites has been studied by dielectric relaxation spectroscopy. Special consideration has been devoted to the effect of clay type and loading on the time scale of the relaxation processes. Results reveal that the type and concentration of clay do not have an effect on the segmental mode of the NR matrix, while the vulcanization reaction slows down the segmental dynamics. A new mode, slower than the segmental dynamics but faster than the normal mode associated with the chain dynamics, has been observed for both vulcanized and nonvulcanized nanocomposites with fillers having high levels of intercalation. We attribute the new mode to a restricted segmental dynamics of natural rubber chains located at the clay/rubber interfacial regions. © 2009 American Chemical Society.

The remarkable intrinsic properties of carbon nanotubes, including their high mechanical strength, electrical conductivity, and nanoscale 3D architecture, create promising opportunities for the use of nanotube composites in a number of fields, particularly for composites in which conventional fillers cannot be accommodated. In the current study, 3D polyurethane (PU) nanocomposite foams were developed, and their potential biomedical applications were investigated. Multiwalled carbon nanotubes (CNTs) were synthesized by chemical vapor deposition and, following suitable chemical modification, uniformly distributed within the walls of PU foams produced by direct reaction. Although the loading fraction was too low to observe significant mechanical effects, CNT incorporation improved the wettability of the nanocomposite surfaces in a concentration-dependent manner, supporting the claim that the nanotubes are active at the pore surface. Studies of bone cell interactions with the nanocomposite foams revealed that increasing CNT loading fraction did not cause osteoblast cytotoxicity nor have any detrimental effects on osteoblast differentiation or mineralization. The application of "fixed" or embedded CNTs in nondegradable scaffolds is likely advantageous over "loose" or unattached CNTs from a toxicological point of view.

The inclusion of highly anisotropic clay nanoparticles (nanoclays) in cross-linked natural rubber (NR) provides a more homogeneous distributed network structure and induces an early onset as well as enhancement of crystallization under uniaxial deformation. The molecular structure of the polymer network and its morphological changes during deformation were characterized by using broadband dielectric spectroscopy and in situ synchrotron wide-angle X-ray diffraction, respectively. It was found that the presence of nanoclay introduces a dual crystallization mechanism due to the alignment of nanoparticles during stretching. The improved properties in NR-nanoclay nanocomposites can be attributed to both microstructural and morphological changes induced by nanoclay as well as to the nanoclay mobility in the NR matrix during crystallization. The interplay of these factors during deformation contributes to the formation of a supernetwork structure containing cross-linked chemical chains, nanofiller, and crystallizable networks with similar length scales. © 2008 American Chemical Society., The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2004-00825. This work made use of the Cornell Center for Materials Research Experimental Facilities. Additionally, J. Carretero-Gonza´lez acknowledges support from MICINN in the form of a FPI grant, R. Verdejo a Juan de la Cierva contract from MICINN, and B. S. Hsiao is supported by the National Science Foundation (DMR-0405432

Rigid polyurethane (PU) nanocomposite foams filled with multi-walled carbon nanotubes (MWCNTs), functionalized MWCNTs (f-MWCNTs) and functionalized graphene sheets (FGS) were synthesized by reactive foaming to obtain electromagnetic interference (EMI) shielding materials. Our study indicates that the electrical properties of rigid PU nanocomposite foams are strongly dependent on the foaming evolution, cellular structure and density of these materials, which are themself influenced by the morphology, aspect ratio and surface functionalization of the carbon-based nanofillers. The largest EMI shielding effectiveness was obtained for 0.35 wt% MWCNTs with an electrical conductivity increased of two orders of magnitude ascribed to the formation of a better interconnected network within the systems. © 2014 The Royal Society of Chemistry.

Nanocomposite foams are an attractive prospect in a number of fields including biomedical science, catalysis and filtration. In biomedical engineering, porous nanocomposite scaffolds can potentially mimic aspects of the nanoscale architecture of the extra-cellular matrix, as well as enhance the mechanical properties required for successful weight-bearing implants. Thermoplastic polyurethane–multi-walled carbon nanotubes (CNTs) foams were manufactured by thermally induced phase separation (TIPS). TIPS proved to be a successful manufacturing route to three-dimensional, highly porous polymers containing well-dispersed CNTs. Some CNTs are trapped perpendicular to the pore surface creating a rough, nanotextured surface. The surface character of the nanocomposites became more acidic with increasing loading fraction of oxidised CNTs. However, due to the heterogeneity of the nanocomposite surface, its wetting behaviour was not affected. CNT incorporation significantly improved the compression strength and stiffness of the nanocomposite scaffold. The biological properties of these scaffolds were studied in vitro and revealed that increasing MWNT loading fraction did not cause osteoblast cytotoxicity or detrimental effects on osteoblast differentiation or mineralisation. However, osteoblast production of the potent angiogenic factor VEGF (vascular endothelial growth factor) increased in proportion to CNT loading (after 3 days in culture), revealing the potential of the nanocomposite scaffolds to influence cellular behaviour.