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Sodium montmorillonite was incorporated into a poly(epsilon-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. (C) 2008 Elsevier Ltd. All rights reserved.

Intercalation compounds of Layered Double Hydroxide (LDH) modified with different organic molecules were prepared via co-precipitation method obtaining very small and disordered crystallites. The obtained organic–inorganic hybrids were dispersed in Poly(ethylene terephthalate) (PET) by High Energy Ball Milling (HEBM) and a good delamination and dispersion of the organic–inorganic hybrids in the polymer phase was achieved for all PET–LDH composites. Structural, thermal and oxygen barrier properties analyses were conducted. The PET–LDH composites showed a similar thermal degradation trend of pure PET, indicating a high thermal stability. All the composites showed oxygen diffusion and permeability coefficients lower than that for pure PET, due to the presence of highly dispersed clay platelets. These composites can be considered candidates for food packaging applications.

This work describes a successful attempt toward the development of composite materials based on nanofilled epoxy resins for the realization of structural aeronautic components providing efficient lightning strike protection. The epoxy matrix is prepared by mixing a tetrafunctional epoxy precursor with a reactive diluent which allows the moisture content to be reduced and facilitates the nanofiller dispersion step. The reactive diluent also proves to be beneficial for improving the curing degree of nanofilled epoxy mixtures. It increases the mobility of reactive groups resulting in a higher cure degree than the epoxy precursor alone. This effect is particularly advantageous for nanofilled resins where higher temperature treatments are needed, compared to the unfilled resin, to reach the same cure degree. As nanofiller, different carbon nanostructured fiber-shaped fillers are embedded in the epoxy matrix with the aim of improving the electrical properties of the resin. The results highlight a strong influence of the nanofiller nature on the electrical properties especially in terms of electrical percolation threshold (EPT) and electrical conductivity beyond the EPT. Among the analyzed nanofillers, the highest electrical conductivity is obtained by using multiwalled carbon nanotubes (MWCNTs) and heat-treated carbon nanofibers (CNFs). The achieved results are analyzed by considering the nanofiller morphological parameters and characteristics with respect to the impact on their dispersion effectiveness.

In this paper, we report the study and characterization of a multifunctional autonomically healing composite containing solid particles of Grubbs’ first generation catalyst and poly(urea-formaldehyde) microcapsules filled with liquid DCPD. This system, already reported in literature, in some respects shows great potential for epoxy structural composites: however, other aspects have to be explored in order to put to use in advanced applications. Here, we have determined the curing process to obtain the best mechanical performance without deactivating the self-repair activity of the material. It has been found that, for the same curing cycle, the presence of catalyst powder causes a slight decrease in the elastic modulus value with respect to the epoxy matrix. A large recovery in this performance is gained for the self-healing specimen, proving that the microcapsules contribute to improve the mechanical characteristics of the self-healing sample.

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.

Advances in the growing use of polymer composites in aerospace applications explore the possibility in the development of smart materials capable of self-repair. In this article, we have formulated and characterized a multifunctional autonomically healing composite inspired by the design of White et al. Microcapsules containing dicyclopentadiene (DCPD) and powders of Grubbs first generation catalyst were embedded in an epoxy formulation and both the epoxy precursor and the composite were cured up to the temperature of 120 °C that preserves the activity of the catalyst. The results on the cure behavior of an epoxy matrix for self-healing material and the influence of the components related to self-healing function on the dynamic-mechanical properties are investigated. The presence of catalyst powder causes a slight decrease in the elastic modulus value with respect to the epoxy matrix. At variance, a large recovery in this parameter is gained for the self-healing specimen, proving that well-distributed microcapsules contribute to improve the mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Syndiotactic polystyrene (sPS) samples were quenched at low temperature (0 degrees C) in the presence of Multi-Walled Carbon Nanotubes (MWCNT) at different concentrations. The influence of carbon nanotubes on the structure and physical properties of sPS composites was investigated by SEM, X-ray diffractograms, DSC (Differential Scanning Calorimetry), and Dynamic Mechanical Analysis (DMA). A good dispersion of the carbon nanotubes in the sPS matrix was found, at least for the low MWCNT concentration, whereas opposite effects were noticed on T-g and elastic modulus, depending on concentration. The pristine sPS sample was almost amorphous at 0 degrees C, whereas in the filled samples the crystallinity increased on increasing the MWCNT concentration, indicating a strong nucleation effect of the nanotubes. Interestingly, in spite of the low temperature, the beta crystallinity was induced and this crystalline form increases on increasing the carbon nanotube concentration, being dominant (68% of the total crystallinity) already at 3 wt% of MWCNT concentration.

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.

Mg-Al Hydrotalcite-like clay (LDH) intercalated with diclofenac anions (HTlc-DIC) was introduced into poly(-caprolactone) (PCL) in different concentrations by the electrospinning technique, and mats of nonwoven fibers were obtained and compared to the pristine pure electrospun PCL. The fibers, characterized by X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry, show an exfoliated clay structure up to 3 wt%, a good thermal stability of the diclofenac molecules and a crystallinity of PCL comparable to the pure polymer. The scanning electron microscopy revealed electrospun PCL and PCL composite fibers diameters ranging between 500 nm to 3.0 m and a generally uniform thickness along the fibers. As the results suggested the in vitro drug release from the composite fibers is remarkably slower than the release from the corresponding control spun solutions of PCL and diclofenac sodium salt. Thus, HTlc-DIC/PCL fibrous membranes can be used as an antinflammatory scaffold for tissue engineering.

The effect of the electrical field on the conductivity of linear low-density polyethylene/carbon nanotubes/ (LLDPE/CNT) composites during temperature cycling has been investigated. Under applied voltage a positive resistivity temperature coefficient was observed during heating already at low (2–3 wt%) CNT content, followed by a large negative temperature coefficient during cooling whose value depends on the applied voltage. The resistivity values after thermal cycling were markedly lower, while they slightly increased in the absence of an electrical field. The effects of thermal cycling on structural and physical properties of the composites have been evaluated by X-ray diffraction and differential scanning calorimetry.

Novel composites based on poly(e-caprolactone) (PCL) and an organically modified layer double hydroxide (LDH) obtained using the melt-extrusion technique have been characterized through structural, thermal, and mechanical analyses. Although exfoliation has not been achieved and despite the very low content of filler (from 1 to 3% by weight), significant enhancements are obtained in the physical and mechanical properties of the composites with respect to neat PCL. As a consequence, LDHs can substitute other nanofillers, in particular, cationic clays for polymeric matrices. They can be modified by a large number of organic anions, generally more numerous than the cationic ones, and can be mixed in very simple ways with polymers. This makes such nanofillers suitable to obtain new hybrid materials for a series of applications, from active food packaging to intelligent materials for biomedical device, for example, controlled drug release. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 945–954, 2007

A sample of syndiotactic polypropylene (sPP) was prepared by solvent casting in orthodichlorobenzene at 70 °C. Its structure and morphology were analyzed by X-rays, Atomic force microscopy (AFM), and transport properties of vapors at low activity. The structural parameters were compared to those of samples thermally crystallized at 25 and 100 °C. The presence of the helical form I was recognized in either sample with crystal dimensions strictly dependent on the crystallization temperature. The crystallite sizes, determined by X-rays, were found to be surprisingly high, pointing to an unusual ability of lamellar crystals of sPP helical modifications to host defects without loosing coherence. Different from the thermally crystallized samples, the phase composition of the sample obtained by casting was particularly simple with a wide fraction of amorphous component and an almost complete absence of trans-planar mesophase. The oriented sample obtained by drawing the solvent cast sample up to I ) 7.0 showed the presence of the trans-planar form III, as well as of the trans-planar mesophase. On release of the tension the crystalline form III almost completely transformed into the mesophase, and only weak reflections of the helical form appeared in the diffraction spectrum of the drawn sample. The elastic behavior of the oriented sample was investigated by obtaining the hysteresis curves at increasing draw ratios. The permanent set and the energy dissipated were obtained and compared to those of thermally crystallized samples. The elasticity was analyzed with the Mooney-Rivlin equation. A truly elastic range was recognized between I ) 4.0 and I ) 5.8. In this range, the X-ray analysis did not show any change of the structure. For higher strain values, an upturn appears in the curve ascribable, by X-rays studies, to a strain-induced crystallization.

Nanocomposite materials were prepared by incorporating multiwall carbon nanotubes (MWNTs), obtained by acetylene catalytic chemical vapor deposition (CCVD) on Co/Fe‐modified MgO, within poly(vinyl alcohol) (PVA). Before incorporation, nanotubes were oxidized to obtain better compatibilization with the polymer. It has been found that the addition of COOH‐functionalized and purified MWNTs improves the mechanical response, increases the glass transition temperature, and delays the thermal oxidation of PVA. Furthermore, the PVA crystallinity seems to be enhanced by the presence of nanotubes.

12-Hydroxydodecanoate (HD) anions were intercalated, via an ionexchange procedure, onto a Mg/Al hydrotalcite-like compound with the formula [Mg 0.65 Al 0.35 (OH) 2 ](NO 3 ) 0.35 .0.56H 2 O. The obtained intercalate, characterized by chemical and thermal analyses, X-ray powder diffraction, and Fourier transform infrared spectroscopy, had the formula [Mg 0.65 Al 0.35 (OH) 2 ](NO 3 ) 0.08 (HD) 0.28 .0.56H 2 O and an interlayer distance of 2.27 nm. Structural considerations indicated that the charge-balancing HO-(CH 2 ) 11 -COO - anions were accommodated in the interlayer region as a monofilm of partially interdigitated alkyl chains in a trans planar conformation and bearing the alcoholic group. The organically modified hydrotalcite was used to prepare novel composites based on poly(e-caprolactone) (PCL) with different procedures: (1) solvent casting, (2) ring-opening polymerization of e-caprolactone, and (3) blending of precursors consisting of a PCL intercalated oligomer with a high-molecular-weight PCL. Microcomposites were obtained by the solvent casting of a mixture of a high-molecular-weight PCL and the modified hydrotalcite. The ring-opening polymerization of e-caprolactone initiated by the -OH groups of the alkyl chains intercalated in the hydrotalcite led to hybrid materials in which a low-molecular-weight PCL was in part intercalated into the modified hydrotalcite. Nanocomposites containing exfoliated hydrotalcite were obtained through the mixing, in different weight ratios, of hybrids consisting of PCL oligomers and modified hydrotalcite with a commercial high-molecular-weight PCL.

The influence of the initial phase composition and crystallite size on the mechanical properties and the elastic behavior of oriented syndiotactic polypropylene (sPP) was investigated. Two samples (A25 and B100) were crystallized from the melt respectively at 25 and 100 °C, obtaining the same crystalline forms but different morphologies, in terms of crystallinity, crystal dimensions, and phase composition. X-ray diffraction was used to determine the crystallinity and the crystal dimensions, whereas the vapor transport properties allowed to evidence and quantify the presence of an intermediate phase. Sample A25 shows smaller crystals, lower crystallinity, and a lower amorphous fraction but a larger mesomorphic component as compared to B100. The two samples were then stretched to a draw ratio of 7. They showed very different stress−strain curves, which appear to correlate with the initial structure. On releasing the tension both fibers undergo a large shrinkage, reaching λ = 4. The presence of the trans-pla...

The elusive helical form II of syndiotactic polypropylene (sPP), not yet fully clarified, was recognized in a fiber drawn at 90°C and its thermally induced transitions were followed by x‐ray diffraction and dynamic‐mechanical analysis as a function of temperature. It was found that this form is stable up to 100°C; afterwards a melting and recrystallization phenomenon occurs leading to the ordered form I. In correspondence to this structural change, the dynamic‐mechanical analysis shows a strong dissipation peak that can be unambiguously associated to the transition and, therefore, can be considered distinctive evidence of the presence of form II.

The thermal behavior and overall isothermal crystallization kinetics of a series of organophilic modified montmorillonite–poly(ϵ-caprolactone) nanocomposites were investigated. In general, the thermal behavior was influenced more by the type of dispersion than by the clay content. For nanocomposites in which silicate platelets were predominantly dispersed in the polymer matrix to give exfoliated structures, the thermal properties were improved with respect to those of neat poly(ϵ-caprolactone), whereas in those cases in which simply intercalated structures were attained, the thermal properties regularly decayed as the clay content increased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1321–1332, 2004

Isotactic polypropylene nanocomposites were obtained by the melt blending of polypropylene-graft-maleic anhydride and organophilic layered silicate (OLS) consisting of synthetic fluorohectorite modified by cation exchange with protonated octadecylamine. The composition of the inorganic clay was varied between 2.5 and 10 wt %, and films of the composites were obtained via hot-press molding. X-ray analysis showed that nanocomposites in which silicate layers were either delaminated or ordered as in an intercalated structure were obtained. The elastic modulus of the samples was higher than that of the pure polymer over a wide temperature range and increased with increasing inorganic content. The transport properties, sorption and diffusion, were measured for two organic vapors, dichloromethane and n-pentane. For both vapors, the sorption was not very different from that of the pure polymer, whereas the zero-concentration diffusion parameter strongly decreased with increasing OLS content. Therefore, the permeability, that is, the product of sorption and diffusion, decreased for both vapors as a result of the decreased value of the diffusion parameter. The decrease was higher for the less interacting n-pentane. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1798–1805, 2003

Different experimental procedures were investigated for incorporating Multi walled Carbon nanotubes (MWCNT) into epoxy diglycidil-ether bisphenol-A (DGEBA), cured with 4,4' diamine-dibenzyl-sulfone (DDS): (i) mechanical mixing for either 60 or 120 minutes; (ii) high energy ball milling for 30 minutes; (iii) ultrasonication for 20 minutes. The mechanical properties of the obtained samples were monitored and used in order to guide the selection of the most promising composite system. The best results were obtained by using, as method of incorporation of carbon nanotubes in the resin, sonication for 20 minutes. Moreover it was found that the presence of an accelerating agent, BF3, commonly used for the cure reaction, is ineffective in the presence of carbon nanotubes, besides leading to composites with a lower glass transition. Afterwards resins with increasing MWCNT concentration were prepared and the thermal properties analyzed, showing a slight improvement in either the glass transition or the degradation temperature. The electrical conductivity of the selected composite system is characterised by a percolation threshold (lower than 0.1%) comparable to that found for similar systems, but beyond threshold it assumes greater values. The conductivity is characterised by only a slight increase with temperature in the range 30-90 degrees C. The positive temperature coefficient can be related to a decrease of the small gaps separating the CNTs clusters. A simple power law describes the relation between the composite conductivity and CNT concentration near the percolation threshold. A dependence of all the parameters of the power law on the temperature has also been evidenced, and it should be properly considered and indicated when using such a model in describing the behaviour of composites near the percolation threshold.

The resistive behavior of multi-walled carbon nanotube (MWCNT)/epoxy resins, tested under mechanical cycles and different levels of applied strain, was investigated for specimens loaded in axial tension. The surface normalized resistivity is linear with the strain for volume fraction of MWCNTs between 2.96 × 10−4 and 2.97 × 10−3 (0.05 and 0.5% wt/wt). For values lower than 0.05% wt/wt, close to the electrical percolation threshold (EPT) a non-linear behavior was observed. The strain sensitivity, in the range between 0.67 and 4.45, may be specifically modified by controlling the nanotube loading, in fact the sensor sensitivity decreases with increasing the carbon nanotubes amount. Microscale damages resulted directly related to the resistance changes and hence easily detectable in a non-destructive way by means of electrical measurements. In the fatigue tests, the damage is expressed through the presence of a residual resistivity, which increases with the amount of plastic strain accumulated in the matrix.

Polyethylene (PE) from postuse automotive fuel tanks is considered a valuable material for mechanical recycling, and we assessed its properties, paying particular attention to transport properties and processability. The characterization included the study of the sorption-desorption isotherms, the rheological analysis of the molten materials and their processability. In particular, we obtained, sorption-desorption isotherms using a model molecule (n-heptane) to simulate contact with the fuel. The measurements were carried out on films of PE blend for tanks and separately on the components of the blend. Rotational rheometry was carried out on scraps from used tanks and on virgin material for comparison. We performed some extrusion tests to evaluate the possibility of mechanical recycling of the postuse materials. In particular, we examined the melt-fracture incoming conditions by making use of a twinscrew extruder with a round die. Stress-strain measurements were carried out on films of virgin and used material, obtained with a press on a laboratory scale to evaluate the change of the mechanical properties of a manufacture obtained by reprocessing a polymer aged in contact with a mixture of liquids.

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 degrees 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. (C) 2009 Elsevier Ltd. All rights reserved.

A syndiotactic poly(propylene) film (sPP), quenched from the melt at 0°C, was drawn at room temperature up to a draw ratio of λ = 6. The fibre was analysed under tension by X-ray analysis and FTIR spectroscopy, showing the presence of the oriented crystalline form III described by Chatani, with the chains in transplanar conformation. Then it was unhooked, undergoing a large shrinkage, and reaching a length corresponding to a draw ratio of λ = 3.8. X-ray and FTIR analysis showed that in the relaxed fibre, a conformational transition from the trans-planar to the helical form occurred. The relaxed fibre was again submitted to increasing extensions up to λ=6, step by step, and the elastic behaviour was analysed through the Mullins' curve and hysteresis cycles. It showed good elastic properties, which appear to be closely correlated to the conformational transition between helical and trans-planar forms.

A study concerning the temperature dependence of some electrical properties of multiphase nanocomposite systems based on epoxy matrix, loaded with a 1% of multi-walled carbon nanotube (MWCNT) and different amounts of Hydrotalcite clay (HT), is presented. An extensive electrical characterization in DC was carried out highlighting that, consistently with the fluctuation-induced tunneling model, the electrical resistivity of the composites are characterized by a negative temperature coefficient (NTC) since it decreases monotonically with increasing temperature in the range 30-110°C. Furthermore, current-voltage (I-V) and temperature-voltage (T-V) characteristics with a perfect linear behavior are detected. The influence of different clay content on the electrical performance of the composites is also investigated. The interesting results open a new routes for such composites due their possible applications in the field of temperature sensor.

The drawing behaviour of amorphous and solvated structure of syndiotactic polystyrene has been analysed. By means of X-ray analysis and infra-red spectrometry we have studied the conformational transitions induced by the drawing processing.

Three different organo-modified clays have been incorporated by sonication into a high performance epoxy resin before the cross-linking reaction. The X-ray analysis indicated that, depending on the organoclay type, partially exfoliated and partially intercalated composites have been obtained. As shown by the DSC analysis, the clay addition seems to interact with the cross-linking reaction. The incorporation of organoclay into epoxy increased free volume and micro-voids in the samples. Sorption of water in the composite samples resulted higher than that of the pristine resin, whereas the diffusion coefficient is significantly lower. The lower value of diffusion makes the permeability at ambient conditions lower than the pristine resin. The elastic modulus of the composite sample results higher than that of the pristine resin, especially in the temperature region around the glass transition. The presence of organoclay in epoxy matrix decreased the glass transition temperature, whether the nanocomposites were in a dry or wet condition.

Purpose The purpose of this work was to achieve detailed biomaterials characterization of a drug delivery system for local cancer treatment based on electrospun titanocene trichloride-loaded resorbable polycaprolactone (PCL) fibers. Methods The PCL fibers were characterized for their structural, morphologic and physical properties. The drug release kinetics of the titanocene complex was investigated at different concentrations, to obtain a set of correlations between structure and tuneable release. After exposing cancer cells directly onto the surface of PCL fibers, the anti-proliferative effects of titanocene-loaded PCL were assessed by: (i) counting viable cells via live/dead staining methods, and (ii) analyzing cell apoptosis. Results and Conclusions Titanocene concentration influenced fiber diameters reduced for PCL filled with titanocene. X-ray analysis suggested that the titanocene, encapsulated into the PCL fibers, is not allowed to crystallize and exists as amorphous aggregates into the fibers. The titanocene release curves presented two stages unrelated to PCL degradation: an initial burst release followed by a release linear with time, extending for a very long time. All of the titanocene-loaded fibers revealed sustained drug release properties suggesting their potential clinical applicability for the treatment of local cancer diseases.

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 1 wt% 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 0.6 wt% of HT with 1 wt% 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.

The structural organization and the physical properties of a new copolymer styrene–ethylene have been analyzed. The composition was 80% of ethylene units, corresponding to 52% in weight, with a distribution of styrene units in the chain implying the absence of styrene–styrene sequences. The length of the polyethylene chains, limited by the insertion of the phenyl group, is not sufficient to allow good crystallization, and in fact the copolymer shows a very low crystailinity, of the order of 5–10%, and a broad melting range, with a peak centered at 120°C. The small crystalline domains are segregated into an amorphous matrix, producing a thermoplastic elastomer. The mechanical properties at large deformation were analyzed at different temperatures. The copolymer shows good elastic properties, in terms of deformation reversibility as well as of energy dissipation in the hysteresis cycles. Also the stress level and the elastic recovery are very good, if compared with others thermoplastic elastomers. © 1995 John Wiley & Sons, Inc.

The experimental results concerning the correlation between morphological and electrical characteristics of a MWCNT/epoxy based composites are presented. The impact of a nanoclay filler is investigated on the DC conductivity of a matrix loaded with different concentrations of MWCNT in order to evaluate the improvements on the dispersion of CNT inside the epoxy matrix. The dispersion is deemed to be very influencing on the electrical conductivity of the nanocomposite. A detailed morphological and structural characterization allows to interpret the electrical behaviour of the nanocomposites. © 2012 IEEE.

A study concerning the characterization of a multiphase nanocomposite systems based on epoxy matrix, loaded with a 1% of hydrotalcite clay and a range of MWCNT is presented. The electromagnetic properties are measured over a very ample range of frequency (from dc to 12GHz). The use of the clay may determine a low aggregation of the MWCNT in the resin thus improving the EM performances of the nanocomposites.

Different amounts of multi-walled carbon nanotubes (MWCNT) were incorporated into an epoxy mixture composed of TetraGlycidyl-MethyleneDiAnilina (TGMDA) and 1-4 Butandioldiglycidylether (BDE). The epoxy mixture was cured with 4,4'-diamino diphenil sulfone. Scanning electron microscopy (SEM) shows a good level of the nanofiller dispersion in the polymeric matrix. Electrical conductivity DC data furnishes a predicted percolation threshold of 0.22% of MWCNT inclusion. The acceptability of the predicted value is confirmed by the AC behaviour of the electrical property. The obtained exponent of the percolation law suggests a 3D organization of the percolating structure.

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.

The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, the mechanical and electrical properties of composites was investigated. Samples based on epoxy resin with different weight percentage of MWCNTs or COOH-functionalized carbon nanotubes (MWCNT–COOH) were prepared and characterized. Dynamic-mechanical thermal analysis shows that the storage modulus increases with the addition of MWCNTs, whereas a constant value or even a weak reduction was observed for functionalized nanotubes. Two phases were suggested in the composites with MWCNT–COOH, both by dynamic-mechanical properties and by water transport. Chemical functionalization of MWCNTs increases the compatibility with the epoxy matrix due to the formation of an interface with stronger interconnections. This, in turn, causes a significant decrease in the electrical conductivity of this type of composite with respect to the untreated MWCNTs which can be explained in terms of tunnelling resistance between interacting nanotubes.

Polymeric nanocomposites are increasingly adopted for replacing conventional insulation to provide enhanced performances such us reliability, environmental compatibility and power rating in new generation inverter-fed Adjustable Speed Drives electrical motors. This paper describes an experimental study aimed at evaluating the performances of several candidate nanocomposites obtained by adding different clays to an epoxy matrix already used for manufacturing motor insulation system. The electrical, thermal and mechanical properties of the nanocomposites are investigated in order to evaluate their performances as new impregnation materials in multilayered insulation systems. The effect of the different clays on the dc conductivity and permittivity is investigated as a function of the electric field and temperature applied to the nanocomposites.

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.

Since syndiotactic polystyrene (SPS) was fi rst synthesized in the 1980s, it has stimulated interest from both technological and theoretical points of view. From the technological point of view, SPS presents various desirable properties such as high melting temperature, low dielectric constant, low permeability to gas, and good mechanical properties. At the same time, the very complex polymorphic behavior and the extreme sensitivity to the processing conditions spurred many investigations on this polymer. The great number of papers and patents that appeared on this polymer in the last years are the main results of these studies. The principal objective of these studies was the crystallization behavior of SPS, the structure of the ordered forms, and the properties of SPS with the respect to the processing conditions. The possibility of controlling the conditions for obtaining controlled structures indeed is particularly interesting in view of the different physical properties that the various polymorphic structures show. In this chapter, an attempt is made to synthesize the principal founding on this polymer and analyze it in terms of structural organization and crystal morphology .

Starting from calcium sulfate (gypsum) as fermentation byproduct of lactic acid production process, high-performance composites have been produced by melt-blending polylactide (PLA) and beta-anhydrite II (AII) filler, i.e., calcium sulfate hemihydrate previously dried at 500 degrees C. Characterized by attractive properties due to good filler dispersion throughout the polyester matrix and favorable interactions between components, these composites are interesting for potential use as biodegradable rigid packaging. The effect of filler content and mean particle diameter on the barrier properties such as sorption and diffusion to water vapor has been examined and compared to unfilled PLA. Even without additional treatments, the presence of the filler introduced constraints on molecular mobility in the permeable phase of amorphous PLA and the amount of solvent absorbed appears lower in the highly filled composites. Surprisingly, for PLA-30% AII compositions, by addition of filler characterized by high mean particle diameter (e.g., 43 microm) the thermodynamic diffusion parameter, D(0), decreased up to 2 orders of magnitude. The dimension of filler particles and their percentage in the continuous polymeric phase seem to be the most important parameters that determine the barrier properties of the PLA-AII composites to water vapor.

Syndiotactic polypropylene (sPP), obtained at 0 °C in the trans-planar mesophase, was drawn at room temperature up to λ = 6, and left at room temperature for 1 year with fixed or relaxed ends. Data analysis allowed the clarification of the structure of the crystalline phases and their transformations during the aging. In both oriented samples similar structural changes were observed, although they were due to different aging mechanisms. The physical aging led to the crystallization in both samples of an oriented helical form, due to a partial transformation of the mesophase and of the amorphous phase. In the oriented sample aged with fixed ends, a small fraction of the crystalline trans-planar form III became stable even by releasing the tension after 1 year. This last sample did not undergo the large shrinkage, always observed by unloaded sPP after drawing, and therefore was no more elastic. Also, the sample aged with free ends for 1 year showed a reduced elasticity in terms of both dissipated energy and permanent set. However, after a new deformation up to λ = 6, the fiber recovered its previous elasticity. Indeed a mechano-reversibility was apparent for the oriented elastic sample of sPP aged at room temperature with free ends, leading to a renewed elasticity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 599–606, 2008

High energy ball milling (HEBM) was utilized, as an innovative process, to incorporate carbon nanotubes (CNTs) into a polyethylene (PE) matrix avoiding: high temperatures, solvents, ultrasonication, chemical modification of carbon nanotubes. Composites with 1, 2, 3, 5, and 10 wt % of carbon nanotubes were prepared. Films were obtained melting the powders in a hot press. Morphology and physical properties (thermal, mechanical, electrical properties) were evaluated. The used processing conditions allowed to obtain a satisfactory level of dispersion of CNTs into the PE matrix with a consequent improvement of the physical properties of the samples. The thermal degradation was significantly delayed already with 1–2% wt of CNTs. The mechanical properties resulted greatly improved for low filler content (up to 3% wt). The electrical measurements showed a percolation threshold in the range 1–3 wt % of CNTs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 597–606, 2007

In this paper we have studied the effect of increasing carbon multi-walled nanotube (CNT) concentration in composites of syndiotactic polypropylene (sPP) having the same crystalline form but different morphologies. The attention was focused on the form I of sPP with different degrees of perfection (in terms of percentages of chains in helical conformation, crystal dimensions and crystallinity) obtained using two different quenching temperatures from the melt, i.e. 25 and 100 °C. We observed a decreasing effect of the crystallization temperature on increasing the nanotube content up to the samples with 10% of CNT, that show a very similar structural organization independent of the undercooling. Only the amorphous phase turns out more relaxed in the samples crystallized at the highest temperature. Either the thermal or the mechanical properties are improved on increasing the CNT content in both series of samples. The electrical conductivity increases in a similar manner in both series of samples and between 1 and 3 wt% it shows a sizable step of about eight orders of magnitude, a phenomenon that can be regarded as the onset of a percolating structure for which charge transport may take place.

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.

This paper reviews our previous studies on the diffusion behavior in polymers clay nanocomposites. A geometric model for predicting the effective diffusivity through this type of systems as a function of clay sheets orientation, volume fraction, polymer clay interaction, and aspect ratio is proposed. Model predictions are compared to the effective diffusivity generated using random walk simulations as well as with predictions obtained from already existing theoretical models. Fair agreement is found between the model prediction and the results of numerical simulations. With respect to the already existing theoretical models, the present mathematical derivation seems more adequate to describe diffusion behavior in conventional nanocomposites systems (i.e. when fillers present very low values of volume to surface ratio). Experimental diffusion tests are discussed and interpreted with the aid of the proposed model. In addition to the aspect ratio and clay concentration, the polymer clay interactions as well as the sheets orientation are the factors controlling the barrier properties of polymer-layered silicate nanocomposites. Good agreement was found in the case of samples containing exfoliated clay, whereas the model fails in the case of micro-composites, in which the inorganic lamellae are agglomerated in clusters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 265–274, 2006

The effect of the electrical field on the conductivity of linear low-density polyethylene/carbon nanotubes/ (LLDPE/CNT) composites during temperature cycling has been investigated. Under applied voltage a positive resistivity temperature coefficient was observed during heating already at low (2–3 wt%) CNT content, followed by a large negative temperature coefficient during cooling whose value depends on the applied voltage. The resistivity values after thermal cycling were markedly lower, while they slightly increased in the absence of an electrical field. The effects of thermal cycling on structural and physical properties of the composites have been evaluated by X-ray diffraction and differential scanning calorimetry.

In this chapter we review the current literature associated with the barrier properties of polymer/layer silicate nanocomposites, with a special focus on the use of clay nanoparticles to affect permeability to gases and vapours. The majority of papers on nanocomposites have been focused on the use of smectite type clays as nanoparticles. They are a group of swelling clay minerals including montmorillonite, nontronite, saponite, sauconite, and hectorite. Mostly smectite clays have been studied because they are naturally occurring minerals that are commercially available and exhibit platy morphology with high aspect ratio and substantial cation exchange capacities. The platelet structure of these aluminosilicate materials has proven its ability to improve the barrier properties of polymeric materials, according to a tortuous path model in which a small amount of platelet particles significantly reduces the diffusivity of gases through the nanocomposite. The key for nanocomposite technology is exfoliation of the clay into its individual platelets, thereby achieving the greatest barrier improvement as well as the lowest haze. The advantage of this approach is based on the use of conventional cheap polymers with barrier improvement arising from dispersion of low levels of inexpensive clay minerals. Several models for barrier properties have been proposed for predicting the behaviour of polymer nanocomposites. This chapter examines in some detail the existing literature on barrier properties of polymer nanocomposites, comparing the results and trying to correlate the different experimental results, where possible.

The technique of high energy ball milling (HEBM) was used to prepare nanocomposites of poly(e-caprolactone) (PCL) and an organically modified Mg–Al layered double hydroxide. The amount of inorganic material was varied from 0 to 6 wt%, 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 2.8 wt% 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.

We prepared several well-characterized syndiotactic polypropylene (sPP) polymorphs so as to correlate their thermal and dynamic-mechanical behaviors. A sample was crystallized in pure form I at 100°C; a second sample containing only the trans-planar mesophase was prepared by directly drawing a quenched sample at 0°C; a third sample, drawn at room temperature, contained both the trans-planar mesophase and a fraction of the helical form II. By annealing this sample at increasing temperatures, we obtained a series of samples containing either trans-planar mesophase, or form II and form I crystallinities. In the dynamic-mechanical analysis, the sample containing form I crystallinity showed only the amorphous glass transition, at 19°C, before melting at a high temperature. The trans-planar mesophase transformed, at temperatures higher than 50°C, into the helical forms, and this transition was completed at 80°C. The dynamic mechanical curve of the sample containing only the mesophase showed a peak, centered at 50°C, which could be clearly associated to this transition. The sample containing the trans-planar mesophase and the helical form II, showed in the dynamic-mechanical curve a third peak that can be associated with the melting recrystallization of form II into the most stable form I. These results are important, because it was possible to directly correlate the structural transitions of the sPP polymorphs to the dynamic-mechanical behavior. Moreover, a dynamic-mechanical analysis could help recognize the presence of the trans-planar mesophase or of the helical form II in more complex structural organizations.

Nanocomposite materials were obtained by blending multi-wall carbon nanotubes (CN), obtained by acetylene catalytic chemical vapour deposition (CVD) on Co/Fe-modified NaY zeolite, with syndiotactic poly(propylene) (sPP). The nanotubes, well dispersed in the polymer matrix, favour the crystalilization of the sPP helical chins and significantly improve the sPP thermal stability either in nitrogen or in air. The morphology of the sPP affects the behaviour of the sPP degradation in air.

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.