Instituto de Ciencia y Tecnología de Polímeros

Graphene has attracted the attention of a growing number of scientists from several disciplines due to its remarkable physical properties and chemical functionalisation capabilities. This review presents an overview of graphene/polymer nanocomposites discussing preparation, properties and potential applications. The challenges and outlook of these emerging polymer nanocomposites are also discussed.

Nanocomposite films were prepared by the addition of cellulose nanocrystals (CNCs) eventually surfactant modified (s-CNC) and silver (Ag) nanoparticles in the polylactic acid (PLA) matrix using melt extrusion followed by a film formation process. Multifunctional composite materials were investigated in terms of morphological, mechanical, thermal and antibacterial response. The nanocomposite films maintained the transparency properties of the PLA matrix. Thermal analysis showed increased values of crystallinity in the nanocomposites, more evident in the s-CNC based formulations that had the highest tensile Young modulus. The presence of surfactant favoured the dispersion of cellulose nanocrystals in the polymer matrix and the nucleation effect was remarkably enhanced. Moreover, an antibacterial activity against Staphylococcus aureus and Escherichia coli cells was detected for ternary systems, suggesting that these novel nanocomposites may offer good perspectives for food packaging applications which require an antibacterial effect constant over time.

ADVERTISEMENT RETURN TO ISSUECommunication to the...Communication to the EditorNEXTPolymeric Modification of Graphene through Esterification of Graphite Oxide and Poly(vinyl alcohol)Horacio J. Salavagione*, Marián A. Gómez, and Gerardo MartínezView Author Information Instituto de Ciencia y Tecnología de Polímeros, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain*Corresponding author: Fax +34 915 644 853; Tel +34 915 622 900; e-mail [email protected]Cite this: Macromolecules 2009, 42, 17, 6331–6334Publication Date (Web):August 13, 2009Publication History Received17 April 2009Revised24 July 2009Published online13 August 2009Published inissue 8 September 2009https://doi.org/10.1021/ma900845wCopyright © 2009 American Chemical SocietyRequest reuse permissionsArticle Views10009Altmetric-Citations482LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (775 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Hydroxyls,Organic reactions,Polymers,Redox reactions,Two dimensional materials Get e-Alerts

We propose a timeline classifying self-healing polymers in generations based on the healing mechanism, and correlated with historical development.

Poly(lactic acid) (PLA) is the most used biopolymer for food packaging applications. Several strategies have been made to improve PLA properties for extending its applications in the packaging field. Melt blending approaches are gaining considerable interest since they are easy, cost-effective and readily available processing technologies at the industrial level. With a similar melting temperature and high crystallinity, poly(hydroxybutyrate) (PHB) represents a good candidate to blend with PLA. The ability of PHB to act as a nucleating agent for PLA improves its mechanical resistance and barrier performance. With the dual objective to improve PLAPHB processing performance and to obtain stretchable materials, plasticizers are frequently added. Current trends to enhance PLA-PHB miscibility are focused on the development of composite and nanocomposites. PLA-PHB blends are also interesting for the controlled release of active compounds in the development of active packaging systems. This review explains the most relevant processing aspects of PLA-PHB based blends such as the influence of polymers molecular weight, the PLA-PHB composition as well as the thermal stability. It also summarizes the recent developments in PLA-PHB formulations with an emphasis on their performance with interest in the sustainable food packaging field. PLA-PHB blends shows highly promising perspectives for the replacement of traditional petrochemical based polymers currently used for food packaging.

In this study, different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (selected as phase change material) with nanoparticles using the direct-synthesis method. The thermal properties of the nanofluids obtained were investigated. These nanofluids can be used in concentrating solar plants with a reduction of storage material if an improvement in the specific heat is achieved. The base salt mixture was a NaNO3-KNO3 (60:40 ratio) binary salt. The nanoparticles used were silica (SiO2), alumina (Al2O3), titania (TiO2), and a mix of silica-alumina (SiO2-Al2O3). Three weight fractions were evaluated: 0.5, 1.0, and 1.5 wt.%. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements on thermophysical properties were performed by differential scanning calorimetry analysis and the dispersion of the nanoparticles was analyzed by scanning electron microscopy (SEM). The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of 15% to 57% in the solid phase and of 1% to 22% in the liquid phase. In particular, this research shows that the addition of silica-alumina nanoparticles has a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. These results deviated from the predictions of the theoretical model used. SEM suggests a greater interaction between these nanoparticles and the salt.

In this article we report the successful manufacture of a novel functionalized graphene sheet (FGS)/silicone porous nanocomposite. Both the cellular microstructure and the properties of the porous nanocomposite were investigated in detail. The thermal properties show great stability and heat dissipation efficiency, highlighting their potential in applications with intense thermal requirements. Additionally, compression measurements indicate that there was a favourable interaction between the graphene nanosheets and the polymer.

Titanium (Ti) is broadly used for clinical purposes in various medical fields related to bone repair because of its favorable mechanical properties and its ability to osseointegrate in host bone tissue. Nowadays, Ti surfaces can be functionalized in order to provide potentially beneficial additional properties. In this review, we summarize different surface modifications of Ti implants, focusing on biological relevance and the biological issues targeted by each specific approach. We first define the historical relevance of Ti as an implantable material, the osseointegration process, and the main complications related to it before describing the biological rationale which motivates Ti surface modification in implantable devices. Then, we explore a variety of physical and chemical modifications feasible on Ti surfaces. Thereafter, we focus on inorganic and organic coatings being developed for implantable Ti devices that are currently under investigation. Finally, we summarize the surface-modification approaches clinically available or undergoing clinical trials.

Poly(vinylalcohol)/reduced graphite oxide nanocomposites have been synthesised by reducing graphite oxide in the presence of the polymer matrix and coagulating the system with 2-propanol. It has been observed that some interactions occur between the polymer and the reduced graphite oxide layers, mainly by hydrogen bonding. These interactions are responsible for a remarkable change in the thermal behaviour of the nanocomposites. In addition, high electrical conductivity has been achieved at concentrations beyond 7.5 wt% of reduced graphite oxide (∼0.1 S cm−1), with a percolation threshold between 0.5 and 1 wt%.

Abstract 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 significant improvements in mechanical properties, heat distortion temperatures, thermal stability, flame 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 justifies the growing interest of both academia and industry in the development of these hybrid materials. In this paper we describe the most significant findings in the clay/polymer nanocomposites field considering three polymer families: elastomers, thermosets and polymers from natural resources or biopolymers.

Biodegradable nanocomposites were prepared by adding ZnO nanoparticles to bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) via solution casting technique. The morphology, thermal, mechanical, antibacterial, barrier, and migration properties of the nanocomposites were analyzed. The nanoparticles were uniformly dispersed within PHBV without the aid of coupling agents, and acted effectively as nucleating agents, raising the crystallization temperature and the level of crystallinity of the matrix while decreasing its crystallite size. A gradual rise in thermal stability was found with increasing ZnO loading, since the nanofillers hinder the diffusion of volatiles generated during the decomposition process. The nanocomposites displayed superior stiffness, strength, toughness, and glass transition temperature, whereas they displayed reduced water uptake and oxygen and water vapor permeability compared to the neat biopolymer, related to the strong matrix-nanofiller interfacial adhesion attained via hydrogen bonding interactions. At an optimal concentration of 4.0 wt % ZnO, the tensile strength and Young's and storage moduli showed a maximum that coincided with the highest crystallinity and the best barrier properties. PHBV/ZnO films showed antibacterial activity against human pathogen bacteria, and the effect on Escherichia coli was stronger than on Staphylococcus aureus. The overall migration levels of the nanocomposites in both nonpolar and polar simulants dropped upon increasing nanoparticle content, and were well below the limits required by the current normative for food packaging materials. These sustainable nanomaterials with antimicrobial function are very promising to be used as containers for beverage and food products as well as for disposable applications like cutlery or overwrap films.

Covalent binding of polymers to graphene represents an interesting alternative for the development of novel composite materials with a compendium of interfacial interactions. Through covalent linking, the concept of interface changes from a traditional view of interactions between components, such as van der Waals, hydrogen bonding, and so on, that is to say, at a polymer-filler interface, to a single compound concept where graphene forms an integral part of the polymeric chains. This feature article provides an overview of the strategies currently employed to functionalize graphene with polymers. We focus on the grafting-from and grafting-to methods used to bind polymers to graphene. The advantages and drawbacks, as well as the influence of each method on the final properties, are highlighted.

Cellulose nanocrystals (CNCs) synthesized from microcrystalline cellulose by acid hydrolysis were added into poly(lactic acid)-poly(hydroxybutyrate) (PLA-PHB) blends to improve the final properties of the multifunctional systems. CNC were also modified with a surfactant (CNCs) to increase the interfacial adhesion in the systems maintaining the thermal stability. Firstly, masterbatch pellets were obtained for each formulation to improve the dispersion of the cellulose structures in the PLA-PHB and then nanocomposite films were processed. The thermal stability as well as the morphological and structural properties of nanocomposites was investigated. While PHB increased the PLA crystallinity due to its nucleation effect, well dispersed CNC and CNCs not only increased the crystallinity but also improved the processability, the thermal stability and the interaction between both polymers especially in the case of the modified CNCs based PLA-PHB formulation. Likewise, CNCs were better dispersed in PLA-CNCs and PLA-PHB-CNCs, than CNC.

Poly(3-hydroxybutyrate) (PHB)-based bionanocomposites incorporating different contents of ZnO nanoparticles were prepared via solution casting technique. The nanoparticles were dispersed within the biopolymer without the need for surfactants or coupling agents. The morphology, thermal, mechanical, barrier, migration and antibacterial properties of the nanocomposites were investigated. The nanoparticles acted as nucleating agents, increasing the crystallization temperature and the degree of crystallinity of the matrix, and as mass transport barriers, hindering the diffusion of volatiles generated during the decomposition process, leading to higher thermal stability. The Young's modulus, tensile and impact strength of the biopolymer were enhanced by up to 43%, 32% and 26%, respectively, due to the strong matrix-nanofiller interfacial adhesion attained via hydrogen bonding interactions, as revealed by the FT-IR spectra. Moreover, the nanocomposites exhibited reduced water uptake and superior gas and vapour barrier properties compared to neat PHB. They also showed antibacterial activity against both Gram-positive and Gram-negative bacteria, which was progressively improved upon increasing ZnO concentration. The migration levels of PHB/ZnO composites in both non-polar and polar simulants decreased with increasing nanoparticle content, and were well below the current legislative limits for food packaging materials. These biodegradable nanocomposites show great potential as an alternative to synthetic plastic packaging materials especially for use in food and beverage containers and disposable applications.

Two different silver colloids were prepared by chemical reduction of silver nitrate with trisodium citrate and hydroxylamine hydrochloride to compare their characteristics in relation to their possible use in surface-enhanced Raman scattering (SERS) spectroscopy. The morphology and plasmon resonance of the single nanoparticles and aggregates integrating these colloids were characterized by means of UV-vis absortion spectroscopy and scanning electron microscopy, revealing important differences between each type of nanoparticle as concerns their physical properties. These metallic systems also manifested differences in the aggregation and the adherence to glass surfaces, revealing significant differences in the chemical surface properties of these nanoparticles. SERS and surface-enhanced IR also indicated the presence of interference bands which can overlap the spectra of the analyte, mainly in the case of the citrate colloid. All these differences have an important influence on the applicability of these nanostructured systems in SERS. In fact, the enhancement factor and spectral pattern of the SERS obtained by using alizarin as a molecule probe are different.

Equilibrium swelling is a feasible and simple experiment to determine the cross-link density of networks. It is the most popular and useful approach; however, in most of the cases, the given values are highly uncertain if not erroneous. The description of the complex thermodynamics of swollen polymer networks is usually based on the Flory−Rehner model. However, experimental evidence has shown that both the mixing term described by the Flory−Huggins expression and the elastic component derived from the affine model are only approximations that fail in the description and prediction of the rubber network behavior. This means that the Flory−Rehner treatment can only give a qualitative evaluation of cross-link density because of its strong dependence on the thermodynamic model. In this work, the uncertainties in the determination of the cross-link density in rubber materials by swelling experiments based on this model are reviewed. The implications and the validity of some of the used approximations as well as their influence in the relationship of the cross-link densities derived from swelling experiments are discussed. Importantly, swelling results are compared with results of a completely independent determination of the cross-link density by proton multiple-quantum NMR, and the correlation observed between the two methods can help to validate the thermodynamic model.

Pore size and thickness of pore walls in macroporous polyacrylamide gels, so-called cryogels (pAAm-cryogels), were controlled by varying the content of monomers in the initial reaction mixture and the cross-linker used. The thickness of pore walls in pAAm-cryogels increased with increasing concentration of monomers in the initial reaction mixture. Pore volume in the supermacroporous pAAm-cryogels was in the range of 70-93% and decreased with increasing concentration of monomers in the reaction feed. The porous structure of the pAAm-cryogels was visualized using environmental scanning electron microscopy (ESEM) that allowed monitoring of the dehydration process in pAAm-cryogels. The accessibility of ligands covalently coupled to the polymer backbone for low molecular weight target, Cu() ions, and high molecular weight target, the protein lysozyme, was assessed for pAAm-cryogels produced from feeds with different monomer concentration. The amount of bound Cu() ions increased linearly with increasing monomer concentration in the reaction feed, suggesting that all ligands are equally accessible for small targets. On the contrary, lysozyme binding demonstrated a clear maximum at monomer concentration about 18% suggesting that only ligands present at the surface of pore walls are accessible for high molecular weight targets.

Electrical Properties of Polymers describes the electric phenomena responsible for determining the chemical and supramolecular structure of polymers and polymeric materials. The authors explore the properties of quasi-static dipoles, reviewing Brownian motion, Debye theory, Langevin and Smoluchowski equations, and the Onsager model. This reference displays Maxwell and entropy equations, along with several others, that depict the thermodynamics of dielectric relaxation. Featuring end-of-chapter problems and useful appendices, the book reviews molecular dynamics simulations of dynamic dielectric properties and inspects mean-square dipole moments of gases, liquids, polymers, and fixed conformations.

Abstract The effect of the incorporation of a bentonite on the vulcanization kinetics of natural rubber was investigated by means of both cure‐meter testing and differential scanning calorimetry (DSC) under dynamic and isothermal conditions. The vulcanization curves showed that the modified clay behaved as an effective vulcanizing agent, accelerating the vulcanization reaction of the elastomer. A marked decrease in the induction time and optimum cure time of the elastomer were observed in the presence of the organoclay. Although the octadecylamine itself accelerated the vulcanization process, the octadecylamine‐modified clay gave rise to a further noticeable increase in the vulcanization rate, which could be attributed to a synergetic effect between the filler and the amine. Moreover, in the presence of the organoclay, a dramatic increase in the torque value was obtained because of the formation of a higher number of crosslinks, which could be attributed to the confinement of the elastomer chains within the silicate galleries and, consequently, to better interactions between the filler and the rubber. However, no significant changes were observed in the unmodified clay composite. These results were in concordance with those obtained by DSC. In addition, the activation energy of the vulcanization process was also calculated by means of both techniques. A clear decrease in the activation energy was observed when the organoclay was added to the nanocomposite, which indicated that the layered silicate favored the processing of the elastomer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1–15, 2003

A systematic investigation of the interaction of microwave irradiation with microcrystalline cellulose has been carried out, covering a broad temperature range (150 → 270 °C). A variety of analytical techniques (e.g., HPLC, (13)C NMR, FTIR, CHN analysis, hydrogen-deuterium exchange) allowed for the analysis of the obtained liquid and solid products. Based on these results a mechanism of cellulose interaction with microwaves is proposed. Thereby the degree of freedom of the cellulose enclosed CH2OH groups was found to be crucial. This mechanism allows for the explanation of the different experimental observations such as high efficiency of microwave treatment; the dependence of the selectivity/yield of glucose on the applied microwave density; the observed high glucose to HMF ratio; and the influence of the degree of cellulose crystallinity on the results of the hydrolysis process. The highest selectivity toward glucose was found to be ~75% while the highest glucose yield obtained was 21%.