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Highlights: [•] Modified layered double hydroxide prepared via co-precipitation method. [•] Nanohydrids dispersed in Poly(ethylene terephthalate) by High Energy Ball Milling. [•] Good delamination and dispersion of the nanohydrids into the polymer matrix. [•] Composites showing a decreasing of diffusion and permeability coefficients. [•] Composites as candidates for food packaging applications. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this work was the preparation of a new fluoride-releasing dental material characterized by a release of fluoride relatively constant over time without any initial toxic burst effect. This type of delivery is obtained by a matrix controlled elution and elicits the beneficial effect of a low amount of fluoride on human dental pulp stem cells (hDPSCs) towards mature phenotype. Methods: The modified hydrotalcite intercalated with fluoride ions (LDH-F), used as filler, was prepared via ion exchange procedure and characterized by X-ray diffraction and FT-IR spectroscopy. The LDH-F inorganic particles (0.7, 5, 10, 20 wt.%) were mixed with a photoactivated Bis-GMA/TEGDMA (45/55 wt/wt) matrix and novel visible-light cured composites were prepared. The dynamic thermo-mechanical properties were determined by dynamic mechanical analyzer. The release of fluoride ions in physiological solution was determined using a ionometer. Total DNA content was measured by a PicoGreen dsDNA quantification kit to assess the proliferation rate of hDPSCs. Alkaline phosphatase activity (ALP) was measured in presence of fluoride resins. Results: Incorporation of even small mass fractions (e.g. 0.7 and 5 wt.%) of the fluoride LDH in Bis-GMA/TEGDMA dental resin significantly improved the mechanical properties of the pristine resin, in particular at 37 8C. The observed reinforcement increases on increasing the filler concentration. The release of fluoride ions resulted very slow, lasting months. ALP activity gradually increased for 28 days in hDPSCs cell grown, demonstrating that low concentrations of fluoride contributed to the cell differentiation. Conclusions: The prepared composites containing different amount of hydrotalcite filler showed improved mechanical properties, slow fluoride release and promoted hDPSCs cell proliferation and cell differentiation. [ABSTRACT FROM AUTHOR]

Abstract: Nanohybrids of layered double hydroxide (LDH) with intercalated active molecules: benzoate, 2,4-dichlorobenzoate, para-hydroxybenzoate and ortho-hydroxybenzoate, were incorporated into pectins from apples through high energy ball milling in the presence of water. Cast films were obtained and analysed. X-ray diffraction analysis showed a complete destructuration of all nanohybrids in the pectin matrix. Thermogravimetric analysis showed a better thermal resistance of pectin in the presence of fillers, especially para-hydroxybenzoate and ortho-hydroxybenzoate. Mechanical properties showed an improvement of elastic modulus in particular for LDH-para-hydroxybenzoate nanohybrid, due probably to a better interaction between pectin matrix and nanohybrid layers. Barrier properties (sorption and diffusion) to water vapour showed improvement in the dependence on the intercalated active molecule, the best improvement was achieved for composites containing para-hydroxybenzoate molecules, suggesting that the interaction between the filler phase and the polymer plays an important role in sorption and diffusion phenomena. Incorporation of these active molecules gave antimicrobial properties to the composite films giving opportunities in the field of active packaging. [Copyright &y& Elsevier]

Abstract: The origin of the unusual and puzzling elasticity of drawn sPP samples was investigated. The mechanism responsible of the elasticity was studied for drawn samples characterized by a very simple structural organization, where there are no involvements of crystallographic modifications with different chain conformation. The elastic behavior of the drawn samples, valued through the hysteresis cycles, was determined at different temperatures. At room temperature the samples show remarkable elastic properties, whereas decreasing the temperature the elastic behavior becomes worse and worse, disappearing at temperatures lower than 0°C. The elasticity also disappears in drawn samples after a long aging under tension. Thermomechanical and structural investigations, as well as shrinkage as a function of temperature and aging at room temperature of the fixed drawn samples, support the idea that the elastic behavior of sPP can be explained by the model of the plastic deformation of semicrystalline polymers. The interpretation is based on the presence of “tie” molecules axially connecting the crystals in the oriented samples, whose extension, chain conformation and/or crystallization determine the retractive stress of the oriented sample, as well as other mechanical properties. We show that many experiments on the drawn samples, either fixed or relaxed, are strictly connected to the morphology of the drawn sample, derived by the transition between the lamellar initial and the fibrillar final structure. By applying the model we can answer the questions derived from the experimental facts not yet well clarified, giving a new insight into the interesting elasticity of sPP. [Copyright &y& Elsevier]

Research and development of bio-nanocomposite materials for food applications such as packaging and other food contact surfaces is expected to grow in the next decade with the advent of new polymeric materials and composites with inorganic nano-particles. This article reviews different types of new bio-based materials, such as edible and biodegradable nanocomposite films, their commercial applications as packaging materials, regulations and future trends. Special emphasis is given to the advantages of nanotechnology application in order to improve the mechanical and oxidation stability, the barrier properties, and eventually the biodegradability of conventional polymeric matrices. [Copyright &y& Elsevier]

Films of a new linear low-density polyethylene (LLDPE) were exposed to natural weathering in southern Italy, for increasing times. Infrared analysis was used to detect the degradation products and the carbonyl index was related to the photooxidation products. The changes in mechanical properties due to the chemical degradation were followed by determining the drawing curve and the elastic modulus. All the mechanical parameters were correlated to the exposure time and to the carbonyl index, determined on the same samples. The change in the carbonyl index and the mechanical parameters with the exposure time allowed the determination of the point beyond which the material becomes useless. Furthermore, it was possible to calculate the ratio between natural and artificial time of degradation, which was found to be about 30. [Copyright &y& Elsevier]

Syndiotactic polypropylene (sPP) nanocomposites were obtained by melt blending synthetic fluorohectorite modified octadecyl ammmonium ions (OLS), and maleic-anhydride-grafted isotactic polypropylene (iPP-g-MA) as compatibilizer. The composition of the inorganic material was varied between 5 and 20 w/w%. Films of the composites were obtained by hot press molding the pellets. Melt-direct polymer intercalation of sPP into the OLS gave rise to nanocomposites in which the silicate layers were delaminated at low clay contents, and ordered to intercalated structures at the highest clay content. The elastic modulus was higher than for the pure polymer in a wide temperature range and increased with the inorganic content. The transport properties were measured for dichloromethane and n-pentane. The sorption was reduced compared to pure sPP. There were not significative differences between the samples having different inorganic contents. The diffusion coefficient decreased with increasing clay content. Permeability (P) showed a strong decreasing dependence on the clay content. The improvement of the barrier properties was largely caused by the reduced diffusion. [Copyright &y& Elsevier]

Different compositions of poly(ϵ-caprolactone) (PCL) and (organo-modified) montmorillonite were prepared by melt blending or catalyzed ring opening polymerization of ϵ-caprolactone. Microphase composites were obtained by direct melt blending of PCL and sodium montmorillonite (MMT-Na+). Exfoliated nanocomposites were obtained by in situ ring opening polymerization of ϵ-caprolactone with an organo-modified montmorillonite (MMT-(OH)2) by using dibutyltin dimethoxide as an initiator/catalyst. Intercalated nanocomposites were formed either by melt blending with organo-modified montmorillonite or in situ polymerization within sodium montmorillonite. The barrier properties were studied for water vapor and dichloromethane as an organic solvent. The sorption (S) and the zero concentration diffusion coefficient (D0) were evaluated for both vapors. The water sorption increases with increasing the MMT content, particularly for the microcomposites containing the unmodified MMT-Na+. The thermodynamic diffusion parameters, D0, were compared to the value of the parent PCL: both microcomposites and intercalated nanocomposites show diffusion parameters very near to PCL. At variance exfoliated nanocomposites show much lower values, even for small montmorillonite content. In the case of the organic vapor, the value of sorption at low relative pressure is mainly dominated by the amorphous fraction present in the samples, not showing any preferential adsorption on the inorganic component. At high relative pressure the isotherms showed an exponential increase of sorption, due to plasticization of the polyester matrix. The D0 parameters were also compared to those of the unfilled PCL; in this case, both the exfoliated and the intercalated samples showed lower values, due to a more tortuous path for the penetrant molecules. [Copyright &y& Elsevier]

Resveratrol (RSV) has been shown to exhibit many biological properties that can influence bone osteogenesis. However, RSV oral clinical treatment is limited due to its poor pharmacokinetics, low water solubility, and rapid metabolism. Therefore, it is necessary to develop a valid delivery system to release RSV directly into the target site. Electrospun drug-eluting fibers have gained great attention in the regenerative dentistry due to the ease of fabrication, the high surface to volume ratio and the drug-loading efficiency. The post-extraction preservation of the alveolar socket requires to operate on the bone remodeling processes both by stimulation of bone formation by osteoblasts and inhibition of osteoclast-mediated bone resorption. In this work, uniform defect-free fibers of poly(ε-caprolactone) PCL and poly(lactic) acid (PLA) loading resveratrol were synthetized and characterized. In vitro assay demonstrated that the two membranes were able to release RSV in a tunable and sustained manner with different kinetic: PCL-RSV membrane showed an initial burst followed by a slow release, while PLA-RSV presented a much slower and continuous release over the time. Although both RSV-loaded materials showed similar in vitro osteoinductive capacity on human dental pulp stem cells, the differences on RSV release kinetic affected RANKL-induced osteoclastogenesis. Indeed, only the lower resveratrol-releasing membrane (PLA-RSV) was able both to induce osteoblast and to inhibit osteoclast differentiation, suggesting that this bioactive membrane could be used to preserve post-extraction alveolar ridge volume acting simultaneously on two fronts: first counteract bone resorption, second allows new bone formation. [ABSTRACT FROM AUTHOR]

A novel antimicrobial packaging system, as active coating on a commercial Poly(ethylene terephthalate) (PET) film, was formulated and tested in vitro against the spoilage bacteria of Mozzarella cheese. It is based on layered double hydroxide (LDHs) intercalated with salicylate and carbonate anions dispersed in a solvent-based heat seal. The population of spoilage microorganisms (total coliforms, Pseudomonas , fungi), along with the functional microbiota of Mozzarella cheese (lactic acid bacteria) was characterized. Microbial shelf life was evaluated at 18 °C, to simulate thermal abuse. Experimental results show an increase in the microbial shelf life of the packaged Mozzarella cheese of about 20 days, confirming that the investigated active coating may exert an inhibitory effect on the microorganisms responsible for spoilage phenomena, without affecting the functional microbiota of the product. [ABSTRACT FROM AUTHOR]

Poly( ϵ -caprolactone) (PCL) membranes loaded with Linezolid, chemically N -[[(5S)-3-[3-fluoro-4-(4-morpholinyl)phenyl]-2- oxo -5-oxazolidinyl]methyl]acetamide (empirical formula C 16 H 20 FN 3 O 4 ) have been prepared by electrospinning technique, at different Linezolid concentrations (0.5, 1, 2.5 and 5%, w/w). Structural characterization, morphological analysis and the study of the mechanical properties have been performed on loaded membranes and compared with neat PCL membranes. Linezolid embedded in the membranes is prevalently amorphous, with a low crystallinity showing a different polymorphic form respect to the usual Form I and Form II. The release kinetics of the drug were studied by spectrophotometric analysis (UV–vis). It allowed to discriminate between Linezolid molecules on the surface and encapsulated into the fibers. The antibacterial activity of the electrospun membranes was effective to inhibit Staphylococcus aureus. The properties of the loaded membranes and their capability for local delivery of the antibiotic make them good candidates as drug release devices for topical use. [ABSTRACT FROM AUTHOR]

Abstract: The improvement of the DC conductivity of nanocomposite based on an epoxy matrix filled with multi wall carbon nanotubes (MWs) by using an optimized Hydrotalcite clay (HT) content is discussed. Multiphase nanocomposites with fillers content less than 1wt% are considered in order to exploit the dispersion mechanism introduced by the clay. A Design of Experiment (DoE) procedure with a coarse parameter space sampling is adopted in order to explore and optimize the electrical properties of the nanocomposite without altering sensibly the mechanical ones. The implemented technique puts in evidence a non-linear dependence of the composite electrical conductivity from the clay content. Furthermore an optimized 0.6wt% of HT with 1wt% MW multiphase composite is found leading to the higher electrical conductivity in the considered parameters space. The optimized design and the non-linear effect are experimentally validated. Some possible mechanisms responsible for the obtained results are discussed. [Copyright &y& Elsevier]

Abstract: The development of smart composites capable of self-repair on aeronautical structures is still at the planning stage owing to complex issues to overcome. A very important issue to solve concerns the components’ stability of the proposed composites which are compromised at the cure temperatures necessary for good performance of the composite. In this work we analyzed the possibility to apply Hoveyda–Grubbs’ second generation catalyst (HG2) to develop self-healing systems. Our experimental results have shown critical issues in the use of epoxy precursors in conjunction with Hoveyda–Grubbs’ II metathesis catalyst. However, an appropriate curing cycle of the self-healing mixture permits to overcome the critical issues making possible high temperatures for the curing process without deactivating self-repair activity. [ABSTRACT FROM AUTHOR]

Abstract: Polymer nanocomposites with carbon nanotubes as fillers have attracted more attention than any other nanomaterials. A full development of these materials requires a deep understanding of the way they behave in the use conditions. In this work, the resistance to accelerated photooxidation of syndiotactic polypropylene/multi-walled carbon nanotube (sPP/MWCNTs) films was compared to the photooxidation behaviour of unfilled polypropylene films with the same structural organization. The chemical and structural modifications resulting from photooxidation have been followed using infrared spectroscopy and diffractometric analysis. It was found that a good dispersion degree of the nanofiller, evaluated by atomic force microscopy, contributes to reduction in the rate of photooxidation and an increase in the oxidative thermal stability of the polymeric matrix. Different concomitant effects are considered to explain these results, among which morphology and structure of the nanocomposites together with the MWCNT capacity to interact with oxygen molecules making them unavailable in the first stages of photooxidation. [ABSTRACT FROM AUTHOR]

Abstract: Intercalation compounds of ZnAl-Layered Double Hydroxide (LDH) with Benzoate (Bz), 2,4-dichlorobenzoate (BzDC), para-hydroxybenzoate (p-BzOH) and ortho-hydroxybenzoate (o-BzOH) anions, have been prepared via anion exchange procedure. The obtained inorganic–organic nano-hybrids were incorporated by High Energy Ball Milling (HEBM) into polycaprolactone (PCL), processed on laboratory scale and thin films were obtained. X-ray diffraction analyses of the samples indicated that both the nature and the position of the aromatic ring substituents affect the value of the interlayer distance and the hydrogen bonds of the nano-hybrids. Physical and barrier properties of water vapor were conducted on all the nanocomposite films, showing the influence of the exfoliation on the mechanical and barrier properties. A preliminary study on the release kinetic of the Bz anions bound to LDH was also performed, enlightening very good perspectives in the field of controlled release of active species. [Copyright &y& Elsevier]

Abstract: Different multi-walled carbon nanotube (MWCNT) concentrations were incorporated in an epoxy resin and both the epoxy precursor and the composite were cured at 110°C with a tertiary amine. Infrared spectroscopy was used to follow the curing progress by determining the decrease of the band due to the epoxy group. It was shown that the presence of MWCNTs accelerates the process, halving the time for the disappearance of the epoxy band. Atomic force microscopy demonstrated that the carbon nanotubes are well embedded in the epoxy matrix and singularly dispersed or in bundles, depending on their concentration. As a consequence of the good dispersion and interpenetration of the carbon nanotubes in the epoxy matrix, the glass transition temperature increased with increasing MWCNT concentration. Dynamic-mechanical analysis indicated a higher elastic modulus, particularly at high temperatures. The study of the transport properties, sorption and diffusion of water vapour at different activities, showed improved barrier properties on increasing the CNT concentration. [Copyright &y& Elsevier]

Abstract: Sodium montmorillonite was incorporated into a poly(ε-caprolactone)–starch blend by means of a ball mill. The structural organization and physical (mechanical, thermal and barrier) properties were analyzed and correlated with the milling conditions. Scanning electron microscopy and X-ray characterization show that the milling process can improve the compatibilization between the PCL and the starch phases, while promotes the dispersion of clay minerals at nanometric level. The milling time strongly influences the mechanical and barrier properties. In particular, the best results in terms of elastic modulus and permeability coefficient were achieved with a complete delamination of the pristine clay structure. In summary, the milling process not only has demonstrated to be a promising compatibilization method for immiscible PCL–starch blends, but it can be also used to improve the dispersion of nanoparticles into the polymer blends. [Copyright &y& Elsevier]

Abstract: Syndiotactic polypropylene films, obtained in the trans-planar mesophase, were exposed to accelerated weathering in a UV device at 45°C for increasing times. A different series of films, characterized by the same structural organization, was annealed at 45°C for the same times, to discern the thermal effects from those due to UV irradiation. The influence of UV irradiation and thermal treatments on the structural changes in terms of phase composition, crystallite sizes, and chain conformations was studied. Diffractometric and thermal analyses show that UV radiation causes a strong increase of helical crystallinity (189% with respect to the initial value), leaving the trans-planar mesophase unchanged. The mesophase domains have a higher rigidity and hinder the oxygen diffusion slowing down the photooxidative degradation. The chain scission in the amorphous phase produces a higher mobility, allowing crystallization. The crystallinity also increases in the thermally treated samples, but the increase is limited to the first 48h and reaches about 89% of the initial value. Both in the thermally treated and UV irradiated samples the crystallite coherence length perpendicular to the 200 planes increases with time. The amorphous chains do crystallize at the beginning near the already formed crystals, thus increasing their dimensions. The carbonyl index shows an induction period of 48h, before a rapid increase which apparently is inversely proportional to the percentage of mesomorphic and crystalline phases of the irradiated samples, indicating that the photooxidative reactions took place mainly in the amorphous region. A comparison with data already published on the photooxidative behavior of samples crystallized in form I shows that the presence of compact domains in trans-planar mesophase led to an increase in the induction period and to a greater stability of the material in the first 150h of UV treatment. [Copyright &y& Elsevier]

Abstract: Two composites of apple peel pectin with 3% of either a natural or an organically modified montmorillonite clay, were prepared using a new alternative method, that relies on solid-state mixing at room temperature high energy ball milling(HEBM). This technique involves an efficient mixing of the organic and inorganic components by mechanical grinding. The milled powders were cast by water as films and characterized. The absence of the peak, corresponding to the basal spacing of the clay, in the X-ray diffractograms of the composite samples allowed us to suggest that the dispersion of the clay inside the pectin matrix takes place with the exfoliation of the clay sheets. The physical properties such as thermal degradation, elastic modulus, sorption and diffusion of water vapour and oxygen were analysed. It was found that they all were improved in the nanocomposites, in particular in the sample containing the natural sodium montmorillonite. [Copyright &y& Elsevier]

Abstract: The technique of high energy ball milling (HEBM) was used to prepare nanocomposites of poly(ε-caprolactone) (PCL) and an organically modified Mg–Al layered double hydroxide. The amount of inorganic material was varied from 0 to 6wt%, and the samples were melted and quenched in ice–water after milling. The molecular weight of PCL decreased and its distribution increased as a consequence of milling. The structural analysis of the milled samples, conducted by X-ray diffraction and infrared absorption techniques, showed that the 12 hydroxydodecanoates organic modifier was still attached to the inorganic lamellae even if a partial delamination of the layered compounds occurred. The mechanical parameters (modulus, stress at yield point, strain at break point and stress at break values) derived from the stress–strain curves, improved in the composite samples containing up to 2.8wt% of inorganic filler, with respect to the pure polymer, in spite of the molecular weight decrease. The thermodynamic diffusion coefficient of water vapor in composite samples was lower than in pure PCL, indicating an improvement of the barrier effect. [Copyright &y& Elsevier]