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In this work, highly filled composites made of a commercial polypropylene resin and low melting point Tin particles, up to 50 vol.% in loadings, have been prepared by melt blending process. The introduction of stearic acid (SA), a common dispersant, was investigated in compositions. The developed systems were characterized in terms of dynamic rheological testing. Final results confirmed a reduction of linear viscoelastic domain, by increasing filler loadings, with an effect more emphasized in the presence of SA. Contrary to literature studies, at equal filler content (50%), both moduli resulted to be superior for formulations containing the dispersing agent. A further rheological characterization continued on systems at 30 vol.% of particle loadings for highlighting differences depending on the SA addition. Specific tests were also performed at temperatures above the melting of Tin particles. Finally, optical microscopic analyses were carried out for gaining insight on sample microstructure, in controlled conditions of temperature and shear rate.

The global production of plastic is increasing, and plastic represents one of the most popular materials, widespread in countless applications in commercial and industrial fields and everyday life [...]

The purpose of this study is to limit the environmental impact of packaging applications by promoting the recycling of waste products and the use of sustainable materials in additive manufacturing technology. To this end, a commercial polylactide acid (PLA)-based filament derived from waste production of bio-bags is herein considered. For reference, a filament using virgin PLA and one using a wood-based biocomposite were characterized as well. Preliminary testing involved infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The effect of printing parameters (namely bed temperature, layer thickness, top surface layers, retraction speed, and distance) on the final aesthetics of 3D printed parts was verified. The results allow us to attest that the thermal properties of recycled polymer are comparable to those of virgin PLA and biocomposite. In the case of recycled polymer, after the extrusion temperature, bed temperature, and printing speed are estabilished the lowest allowable layer thickness and an appropriate choice of retraction movements are required in order to realize 3D-printed objects without morphological defects visible to the naked eyes. In the case of wood biocomposite, the printing process was complicated by frequent obstructions, and in none of the operating conditions was it possible to obtain an aesthetically satisfying piece of the chosen geometry (Lego-type bricks) Finally, mechanical testing on the 3D printed parts of each system showed that the recycled PLA behaves similarly to virgin and wood/PLA filaments.

This work aims to review the literature studies based on the application of stearic acid (SA) in a large range of industrial and academic formulations, given the benefits arisen from this additive on the functional and structural properties of the manufactured products. The SA is characterized by a long hydrocarbon non-polar chain endowed with a terminal polar carboxyl group. In primary usefulness consists in a lubricant effect, by positively affecting the materials workability, and in the ability to interact with various surfaces through physical or chemical mechanisms, by creating layer structures. In these conditions, a reduction of the surface energy and an increase of the hydrophobic character have been promoted in the treated surfaces. These aspects have played an interesting role in the compounding phase of a composite system, by promoting a reduction of the mixture viscosity, an increase of filler/matrix compatibility, and an improvement of filler dispersion.

In the current scientific scenario, basalt fibers (BF) have been proposed as an alternative to synthetic reinforcements of polymeric resins due to their relatively low cost, good mechanical characteristics and reduced environmental impact. In this context, the aim of this work has been to analyze the effect of basalt fibers on the processing behaviour of a commercial polypropylene resin (PP) and to compare their performances to glass fibers (GF), which are commonly used as synthetic reinforcement of polymers. GF/PP and BF/PP composites containing varying wt% of reinforcement (GF or BF) were prepared by melt blending and characterized via thermal conductivity tests, thermogravimetric analysis, differential scanning calorimetry, capillary and rotational rheology, and scanning electron microscopy (SEM) to gain information on the heat transfer ability, thermal stability, melting and crystallization parameters, flow properties and morphology. The obtained results showed similar performance of basalt and glass fibers in many aspects. More specifically, an improvement of thermal conduction was always observed when increasing the amount of the reinforcement in the composite material. A higher thermal stability was confirmed in almost all compounds. The addition of fibers did not lead to alterations in the melting point or in the degree of cristallinity of the PP. At the typical process shear rate, the real viscosity of the composites remained unchanged and similar to that of the neat matrix, even at the highest fibers loading. Both glass and basalt fibers appeared homogeneously dispersed in the matrix as supported by SEM and oscillatory dynamic tests.

This work aimed to review the recent scientific research, focused on the application of recycled fibers, taken from textile waste, in the field of composite materials to fulfill the eco-sustainability requirements of textile manufacturing, and promote actions for a circular economy. The yarns and fabric production represent one of the most polluting processes of the industrial world. The harmful environmental impact of the textile process has been described by reporting the different treatments involving the raw material and the filament fabrication, and concerning the uses of insecticides, fertilizers, and many other chemicals for improving the quality of the final products. In addition, solid textile waste constituted a further additional issue for the environmental sustainability of fabric production. Various strategies have been discussed and in part already adopted by many companies to recover waste fibers and prevent them from ending up in landfills. The alternatives of fiber recycling for composite realization have been presented by reporting several recent studies involving the uses of recycled fibers from the textile waste embedded in different matrices: thermoplastic polymer, thermosetting resins, natural constituents, and concrete in light of specific applications.

This study aims to provide an overview of the latest research studies on the use of biopolymers in various textile processes, from spinning processes to dyeing and finishing treatment, proposed as a possible solution to reduce the environmental impact of the textile industry. Recently, awareness of various polluting aspects of textile production, based on petroleum derivatives, has grown significantly. Environmental issues resulting from greenhouse gas emissions, and waste accumulation in nature and landfills, have pushed research activities toward more sustainable, low-impact alternatives. Polymers derived from renewable resources and/or with biodegradable characteristics were investigated as follows: (i) as constituent materials in yarn production, in view of their superior ability to be decomposed compared with common synthetic petroleum-derived plastics, positive antibacterial activities, good breathability, and mechanical properties; (ii) in textile finishing to act as biological catalysts; (iii) to impart specific functional properties to treated textiles; (iv) in 3D printing technologies on fabric surfaces to replace traditionally more pollutive dye-based and inkjet printing; and (v) in the implants for the treatment of dye-contaminated water. Finally, current projects led by well-known companies on the development of new materials for the textile market are presented.

Polyurethane is a polymer adaptable to different scientific and industrial requirements, nevertheless it is also extremely susceptible to UV radiation, which compromises the physical and mechanical functionality. In this framework, our study investigated the effect of waterborne polyurethane dispersion (WPUD) applied to a polyester (PET)-based fabric, through the impregnation method, on the puncturing and water resistance of the pristine material, before and after UV weathering. Results confirmed an increment of both features in the prepared fabrics, attributed to the PUR textile treatment, but a partially loss of the gained properties in the samples due to the UV weathering. In order to improve the efficiency of the impregnating dispersions, in protecting the durability of the treated materials, the addition of different UV light stabilizers, or/and of crosslinking agent into WPUD was also tested. From the experimental data, it can be concluded that formulations based on WPUD, containing both the crosslinker and UV organic absorber, have displayed an increment of their perforation and water resistance for the treated samples with respect to the starting textile, and contemporary have preserved the features against the UV light. Finally, microscopic and spectroscopic analyses have been performed as further characterization techniques of the samples surface.

Commercial waterborne polyurethane (PU) dispersions, different in chemistry and selected on the basis of eco-friendly components, have been applied to a common polypropylene (PP)-based woven fabric. Impregnation has been chosen as a textile treatment for improving the features of basic technical textiles in light of potential applicability in luggage and bag production. The effect of drying method, performed under conditions achieved by varying the process temperature and pressure, on the features of the treated textiles, has been verified. The prepared specimens were characterized in terms of mechanical behavior (tensile, tear and abrasion resistance) and water resistance (surface wettability and hydrostatic pressure throughout the treated textiles). The experimental results suggest an incremental improvement of the tensile features for all the investigated specimens. For tear strength, no augmentation compared to that of the neat textile, could be verified as a consequence of polyurethane treatment. Remarkable improvements of abrasion resistance were displayed for all the impregnated PP textiles. Benefits in water resistance could be attributed to the presence of hydrophobic PU in the textile weaving of the PP samples. The ultimate improvement in water resistance was dependent on drying conditions.

The reactivity of polylactic acid (PLA) with epoxidized natural rubber (ENR50) was confirmed by monitoring the changes in melt viscosity during mixing and by TGA runs. The plasticization resulting from a partial miscibilization of ENR50 during mixing was found to have opposite effects on the crystallization of the PLA matrix, depending on the temperature scanning mode. An increase in heat of crystallization (ΔHc) with increasing temperature scanning rate was observed when heated from the glassy state, while a corresponding reduction in ΔHc was obtained in cooling scans from the melt. Studies on the kinetics of events have shown that the classical Kissinger plots for crystallization by heating from the glassy state display a variable activation energy for the case of the reactive blend. The vitrification kinetics, on the other hand, could be modelled quite accurately with the Mahadevan method for all systems, including an intrinsically amorphous PLA.

In the last few years, there has been a growing interest in laminated composites based on a thermoplastic matrix because of the environmental impact and lower cost per part. In addition, thermoplastic matrix-based materials can be more easily recycled and reused after their operating life [1], and this fulfils the requirements of an environment safeguard.

Cellulose/PLA-based blends (up to 77 vol./vol.% of the added fibers) for applications in extrusion-based technology were realized in an internal mixer by setting different operating conditions. In particular, both the mixing time and temperature were increased in order to simulate a recycling operation (10 or 25 min, 170 or 190 &deg, C) and gain information on the potential reuse of the developed systems. The torque measurements during the compound&rsquo, s preparation, and the compound&rsquo, s mechanical tensile features, both in the static and dynamic mode, were evaluated for each investigated composition. The final results confirmed a reduction of the torque trend over time for the PLA matrix, which was attributed to a possible degradation mechanism, and confirmed by infrared spectroscopy. The mechanical behaviour of the pristine polymer changed from elastoplastic to brittle, with a significant loss in ductility going from the lower mixing temperatures up to the higher ones for the longest time. Through the addition of cellulose fibers into the composite systems, a higher stabilization of the torque in the time and an improvement in the mechanical performance were always verified compared to the neat PLA, with a maximum increase in the Young modulus (+100%) and the tensile strength (+57%), and a partial recovery of the ductility.

Pregelled mixes of an epoxidized natural rubber, known as ENR50, containing dodecenyl succinic anhydride (DDSA) as cross-linking agent and dimethyl benzyl amine (DMBA) as catalyst, were cured isothermally at 160 °C, and the progress of the reactions was followed by both thermal analysis (differential scanning calorimetry and thermogravimetric analysis [TGA]) and infrared spectroscopy (Fourier transform near-infrared and attenuated total reflection). The curing reactions were found to be approximately first order for both heat of reaction associated with cross-linking and the disappearance of the epoxy groups, even though the reduction of epoxy group concentration was found to be substantially greater than the amount expected from reactions with the anhydride, because of the formation of large quantities of vicinal OH groups. The TGA data have indicated that the pregelled mixes undergo more extensive anaerobic degradation at higher temperatures than the un–cross-linked elastomer, which is accelerated by the presence of the DMBA catalyst.

This study reports the results of photodegradation experiments performed on biodegradable nanocomposite blown films based on a commercial grade of poly(3-hydroxybutyrate-co−3-hydroxyvalerate)/poly(butylene adipate-co-terephthalate) blend added with different amounts (3, 5, and 10 wt%) of tubular halloysite nanoclays, natural and organomodified. The films, subjected to photooxidative weathering in a climatic chamber under UV exposure, were systematically analyzed to check the chemical and physical changes induced by the aging protocol, taking the as-produced films as the reference materials. In particular, the samples were characterized using several techniques [colorimetry, water contact angle tests, UV–vis, attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectrophotometry, X-ray diffraction, oxygen permeability, and mechanical tests]. The experiments demonstrated that all nanocomposite films, when compared with the unfilled one, show higher changes in the total color difference ΔE* and higher reduction in the average transparency due to the changes in the molecular structure of the polymer (hydrolysis of the ester linkage, multiple chain scissions, and crosslinking), as observed from ATR-FTIR analysis. The phenomenon, which basically involves the amorphous phase, tends to increase with the nanofiller percentage in the films and is more relevant in the presence of the organomodified halloysite. As a consequence of the photodegradation of the amorphous polymer chains that increase their molecular mobility, the oxygen permeability worsens, even in the presence of nanofillers. Instead, in terms of mechanical response, the addition of pure and organomodified halloysite to polymer matrix had positive effects on tensile properties both before and after photooxidation. POLYM. COMPOS., 36:1169–1175, 2015. © 2015 Society of Plastics Engineers

The wear resistance of several thermoplastic polyurethanes (TPUs) having different chemical nature and micron- scale arrangement of the hard and soft segments has been investigated by means of erosion and abrasion tests. The goal was correlating the erosion performances of the materials to their macroscopic mechanical properties. Unlike conventional tests, such as hardness and tensile measurements, viscoelastic analysis proved to be a valuable tool to study the erosion resistance of TPUs. In particular, a strict correlation was found between the erosion rate and the high-frequency (~10 7 Hz) loss mod- ulus. The latter reflects the actual ability of TPU to dissipate the impact energy of the erodent particles.

Films of semicrystalline poly(ε-caprolactone) (PCL) are fabricated by casting drops of fully biocompatible ethyl lactate (EL) and ethyl acetate (EA) solutions onto a glass substrate. The main goals of this work are: i) to assess the interplay among the physico-chemical properties of the solution and its interaction with the casting substrate; and ii) determine how the solution/substrate interactions influence the formation of the films and their final surface morphology and hydrophilicity. The competition between the rates of solution drop spreading and solvent evaporation controls the polymer crystallization process and the final film properties. Compared with EA, EL provides better wetting properties and a slower evaporation rate, eventually resulting in thinner films. The film thickness increases with polymer concentration in the solution; this parameter also affects the crystalline structure and, ultimately, the film surface roughness. As a result, the film hydrophilicity is finely tunable by changing the solution composition, so as to control the crystal nucleation density.

The low velocity impact behaviour of composites made of polypropylene (PP) as matrix and glass fibre fabric as reinforcement has been investigated. Two PP grades, differing for their melt flow index, have been used as matrix, and maleic anhydride has been used to manage the polymer/glass fibre interface strength. Impact tests at four energies (5, 20, 40 and 105 J) have been carried out to evaluate the main dissipation mechanisms occurring in each impact condition and to identify the role of the interface strength. Quasi-static flexural tests confirmed that the compatibilizer improves both flexural modulus and strength, as well as strain at yield. A different performance trend is shown by low velocity impact tests. Not compatibilized samples have exhibited, since the lowest impact energy (5 J), significant energy dissipation resulting from the interface failure occurring at very low strains, as confirmed by lock-in thermographic analysis. Conversely, compatibilized samples showed no or small damages. As the impact energy increases not compatibilized samples outperformed compatibilized samples by large margins showing better impact resistance. This result has been related to the large energy dissipation occurring at the polymer/fibre interface. Furthermore, the broad interface failure and slipping act as crack blocker, preserving the integrity of fibres and allowing for higher load bearing. Managing the interface strength can be a viable option to design thermoplastic based composites with improved impact damage tolerance and balanced quasi-static properties. © 2014 Elsevier Ltd. All rights reserved.

Composites based on a commercial grade polystyrene (PS) resin containing non commercial perovskite particles were prepared by melt mixing and analyzed in terms of mechanical properties, dynamic-mechanical behavior and morphology. In particular, with the aim to study the influence of the filler size on the ultimate properties of PS based composites micro- and nano-sized perovskite La0.5Sr0.5MnO3 crystal particles, synthesized by using an efficient and rapid microwave-assisted hydrothermal route, were considered. Measurements of flexural parameters such as modulus and strength by static tests and storage modulus and damping factor by dynamic-mechanical evaluations showed better performance for nanofilled systems with respect to the ones containing micro particles, with the same filler content. Mechanical evidences were explained also by morphological observations from which a different level of filler dispersion seems to be obtained with the organization of perovskite nanosized crystals in superstructures able to support viscoelastic results.

Formation of micro-cracks is a critical problem in polymers and polymer composites during their service in structural applications. In this context, materials endowed with self-healing features would lead to the next polymers generation. In the present paper, an epoxy system integrating Diels-Alder epoxy adducts is investigated by thermal and spectroscopic analysis. The direct and retro D-A reaction have been studied by FTIR and specific absorption bands have been identified. Finally, mechanical tests have been performed on the system. The polymer is able to heal fracture and micro-cracks recovering its stiffness after a thermal treatment.

Composite laminates based on polyolefin wastes coming from two different sources are compared with similar systems involving a virgin polypropylene in terms of damage behavior. In particular, this paper reports the response of film-stacked composite laminate plates subjected to falling weight impact tests. As expected, samples based on recycled polyolefins show lower impact parameters with respect to the latter ones even if a partial improvement of the performances can be obtained by modification of the matrix by an adequate coupling agent. Despite the inferior impact behavior, potential uses of new systems provide an opportunity to develop valuable products by reducing the environmental impact of plastic wastes.

The influence of the main film production technologies, i.e. chill-roll extrusion and film blowing on the structural characteristics and mechanical performances of films based on a commercial thermoplastic polyurethane resin reinforced with carbon nanotubes has been studied. Structural investigations by means of X-ray diffraction and FTIR spectroscopic analysis have shown how the different processing conditions determine the mutual arrangement of soft and hard domains characteristic of the polyurethane matrix as well as the orientation and the final distribution of the included nanotubes as confirmed by electron microscopy observations. The higher the carbon nanotubes content, the higher the content and the size of segregated hard domains. Furthermore the film blowing process, characterized by relatively longer cooling times with respect to the extrusion process, allows a better self-assembly of hard domains maximizing the interdomain distance and, apparently, ensuring a worse distribution of the filler. By focusing on samples with 0.5 wt.% of carbon nanotubes, an increase of the tensile modulus with respect to neat TPU ones, approximately equal to 90% and 30% has been shown for flat and blown films, respectively. Morphological and structural considerations have provided a reasonable explanation of the mechanical behavior exhibited by the investigated films.

The introduction of thermo-reversible covalent bonds in the molecular network is a recent approach to prepare self-healing polymers upon a suitable thermal trigger. Among reversible reactions, Diels–Alder (D-A) cycloaddition is an ideal candidate for the synthesis of mendable polymers, such as epoxy resins, with improved operative life. The D-A adduct, referred to as 2Ph2Epo, was synthetized and crosslinked with a mixture of aliphatic and aromatic amines. The resin formulation aimed at reaching a compromise between the mending capability of cured material and its dimensional stability at high temperatures, required during healing cycles. The latter result was achieved by mixing the adduct with commercial DGEBA monomer. The ability of the adduct to give direct D-A and reverse D-A (r D-A) has been verified by FT-IR and rheological analysis on 2Ph2Epo. Mechanical tests were performed for assessing the self-healing efficiency of the crosslinked 2Ph2Epo/DGEBA system. The multiple healing feature of the system was proved. The hybrid epoxy resin is able to recover damages, still exhibiting the pristine stiffness, while the strength of the system decreases after progressing healing cycles. POLYM. ENG. SCI., 57:674–679, 2017. © 2017 Society of Plastics Engineers

Polyamide 6 (PA6) based sheets are produced by a typical hot compaction procedure and characterized in terms of thermal properties, mechanical behavior and morphological features. Starting from two commercial clothes mainly constituted by woven PA6 fibers, single polymer composites (SPCs) involving 24, 30 and 36 layers of each fabric were prepared and investigated taking compression molded plates based on a commercial neat PA6 grade as the reference material. All materials were prepared under similar processing conditions in terms of pressure profile and duration of the various stages of compaction but using a higher consolidation temperature for the neat PA6 with respect to composite laminated systems. The improvement of both static and dynamic flexural moduli and the simultaneous reduction of the Charpy impact parameters, by increasing of the reinforcement effect, confirmed the typical need to balance stiffness and toughness performances, well established for conventional composite systems, unless optimized production process and/or hybridization approaches are considered. In fact, a good compromise of mechanical performances was detected for the thickest SPC laminates based on a hybrid PA6/polyurethane fabric and ascribed to the occurrence of more efficient failure mechanisms rather than the simple fiber breakage as witnessed by morphological analyses.

Carbon nanotubes effectiveness, as thermally conductor, in polymer/CNTs nanocomposites, is mainly related to various key aspects as dispersion, matrix/CNT interfacial resistance and inter-CNT contact resistance. Features of raw materials and processing parameters for the realization of nanotube/polymer composites, can simultaneously affect these critical issues, also in adverse way. In this contribution, polypropylene based-composites, containing multi walled carbon nanotubes (MWNTs), are prepared by melt-blending and then characterized prevalently in term of thermal transport behavior, choosing different matrix grades, filler functionalization and process conditions. In more details, two commercial polypropylene (PP) grades with different melt flow rates are considered as matrices and three kind of MWNTs with the same aspect ratio, one neat and two chemically modified with carboxyl –COOH and amino –NH2 groups, respectively, are used as fillers. The presence of a compatibilizer, as maleic anhydride grafted polypropylene (Ma-g-PP), and the use of various processing conditions as temperature, time, screw speed, pressure, filler drying and so on, are taken into account in order to optimize the thermal conductivity enhancement of PP/MWNTs compounds.

Fully biodegradable composites based on a commercial PHBV/PBAT blend with varying concentrations of neat or silanized clay nanotubes were prepared by twin-screw extrusion and filmed by melt blowing process. Thermal analysis suggested the simultaneous occurrence for the PHBV phase of both homogeneous crystallization and heterogeneous nucleation promoted by the included fillers. These phenomena show effects of mutual entities depending on the quality of the filler‐ matrix interface and the applied cooling rate. On the contrary, for the PBAT phase, although the filler may alter kinetics and mechanisms of crystallizations, no effect is reported in terms of its degree of crystallinity. All these evidences have been supported by structural investigations. Moreover, X-ray diffraction analysis indicated that the process of film blowing enables the formation of more perfect crystals and, as expected, favors the orientation of the included nanotubes of clay. POLYM. COMPOS., 00:000‐000, a Society of Plastics Engineers

The potential of a multi-component laminate composite material in terms of improved flame retardancy and adequate mechanical performance is discussed. A double-layer system based on a biodegradable polyhydroxyalkanoates blend was obtained by compression molding. A thin halogen-free flame-retarded layer was located at the top of a kenaf-fiber-reinforced core. Kenaf fibers acted as a carbonization compound promoting charring and building up a superficial insulating layer that protected the material throughout combustion. The impact of different skin/core thickness on the thermal and fire properties was investigated. Synergistic flame retardancy occurs in the cone calorimeter. Chemical and fire investigations confirmed a changed pyrolysis behavior in multicomponent materials. Promising results are obtained in terms of mechanical performance: higher flexural and impact properties were observed in the single fiber-reinforced layer.

Three grades of polypropylene were tested in compression at room temperature, across an unusually wide range of strain rate: 10-4 to 104s-1. The quasi-static testing was done in a Hounsfield machine fitted with a digital image acquisition kit, while tests at the highest strain rates were carried out using a compression split Hopkinson pressure bar. The strain rate dependence of compressive yield stress was compared with the Eyring prediction, and found to be a nonlinear function of logio(strain-rate). The nonlinearity Is attributed to the presence of two relaxation processes in polypropylene, with differing activation volumes: the α- and β-processes. According to the Bauwens two-process model this would lead naturally to curved Eyring plots, where the apparent activation volume decreases with increasing strain-rate. Another prominent feature in the experimental results was the increase in magnitude of post-yield strain-softening with increase in strain-rate. This indicates that the dominant structural relaxation time exceeds the experimental time-scale at the highest strain-rates, but lies below It for the quasi-static tests. © 2008 American Institute of Physics.

The elasticity and structure of graphite nanoplatelets networks in polymer matrices are studied through linear viscoelastic analyses. GNPs-filled polystyrene nanocomposites at different filler content are prepared through a combination of solution and melt mixing techniques. Electrical volume conductivity experiments prove that a continuous path of conductive nanoplatelets builds up across the matrix above a critical filler content. GNP networks, however, are too tenuous to be detected through conventional dynamic-mechanical spectroscopy in the melt state. Nevertheless, we are able to estimate their elasticity by exploiting the predictive feature of a simple two-phase rheological model. Our approach, validated through the building of a master curve of the elastic modulus of samples at different composition, allows to isolate the elastic contribution of the bare GNP network, whose dynamics reveal that its elasticity follows critical behaviour as predicted by percolation theory.

The origins of the commercial exploitation of synthetic polymers and the subsequent industrial developments are reviewed, and the main landmarks are highlighted, starting from the pioneering work on the nitration of cellulose in the 19th century and progressing through various advancements to the latest innovations. This includes the contribution made by many authorities, starting from Staudinger, as the founder of polymer science, to the most recent Nobel laureates in the field. The increased awareness for the need to capture CO2 from combustion gases has stimulated interests in the possibility of using polymerization methods as a route to produce useful solid products. The available theoretical arguments and experimental evidence are presented in relation to the feasibility of producing linear polymers, both as homopolymer and copolymers, placing emphasis on stability aspects and possible uses of the products. The various claims on the possibility of opening both double bonds of molecular CO2 to produce stable networks are also analyzed. Arguments in support of the possibilities of producing mixed CO2–SiO2 glasses are provided, and the expected properties of the resulting solids are discussed. Suggestions are made for the possible utilization of such products. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 31: 179–192, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21275

We study the structure and linear viscoelasticity of interacting polymer nanocomposites based on mixtures of poly(ethylene oxide) and fumed silica particles. The filler is dispersed within the polymer using two different techniques which lead to different dispersion states. The analysis of the dynamic response of our systems highlights the formation of a stress-bearing network above a critical volume fraction, Φ(c). Extending a two-phase model used to describe weakly interacting systems, we show that above Φ(c) the melt-state elasticity of the composites arises from the independent contributions of a polymer-particle network and a viscous matrix. We also find that, although Φ(c) depends on the initial state of dispersion, the network elasticity scales with volume fraction following a universal power-law, with an exponent ν ≈ 1.8. Such a scaling law has been recently predicted for the stress-bearing mechanism governed by polymer-mediated interactions.

Magnetite (Fe3O4) nanoparticles prepared by microwave-assisted hydrothermal synthesis have been characterized in terms of morphological and structural features. Electron micrographs collected in both scanning (SEM) and transmission (TEM) modes and evaluations of X-ray powder diffraction (XRD) patterns have indicated the achievement of a monodispersed crystallite structure with particles having an average size around 15–20 nm. Structural investigations by Micro-Raman spectroscopy highlighted the obtainment of magnetite nanocrystals with a partial surface oxidation to maghemite (γ-Fe3O4). Preliminary attention has been also paid to the use of these magnetite nanoparticles as filler for a commercial polymethylmethacrylate resin. Hybrid formulations containing up to 3 wt% of nanoparticles were prepared by melt blending and characterized by calorimetric and thermogravimetric tests. For sake of comparison, same formulations containing commercial Fe3O4nanoparticles are also reported. Calorimetric characterization indicates an increase of both glass transition temperature and thermal stability of the nanocomposite systems when loaded with the synthesized magnetite nanoparticles rather then loaded with the same amount of commercial Fe3O4. This first observation represents just one aspect of the promising potentiality offered by the novel magnetic nanoparticles when mixed with PMMA.

The addition of nanoparticles to polymer systems with an existing phase-separated morphology, such as polymer blends, represents an innovative approach to controlling the microstructure and, hence, the macroscopic properties of the material. During the melt mixing of the constituents, the particles migrate toward specific regions of the material and are driven by more favorable thermodynamic interactions. Kinetic effects related to the high viscosity of the polymer melts, however, may lead to nonequilibrium morphologies. This makes the mixing procedure crucial for controlling the space distribution of the filler and, hence, the microstructure of the blend and its final properties. We focused on this topic by investigating the effect of the sequence of addition of the constituents in blends of polystyrene and polyamide 6 filled with an organoclay prepared by melt compounding. We show that the mixing procedure could bring about alterations in the onset of cocontinuity, which could be exploited to enhance the high-temperature mechanical strength of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011