Mariaenrica Frigione

Recycling of PET bottles as fine aggregate in concrete

An attempt to substitute in concrete the 5% by weight of fine aggregate (natural sand) with an equal weight of PET aggregates manufactured from the waste un-washed PET bottles (WPET), is presented. The WPET particles possessed a granulometry similar to that of the substituted sand. Specimens with different cement content and water/cement ratio were manufactured. Rheological characterization on fresh concrete and mechanical tests at the ages of 28 and 365days were performed on the WPET/concretes as well as on reference concretes containing only natural fine aggregate in order to investigate the influence of the substitution of WPET to the fine aggregate in concrete. It was found that the WPET concretes display similar workability characteristics, compressive strength and splitting tensile strength slightly lower that the reference concrete and a moderately higher ductility.

Characterization of Nanocomposites by Thermal Analysis

In materials research, the development of polymer nanocomposites (PN) is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. PN are polymer matrices (thermoplastics, thermosets or elastomers) that have been reinforced with small quantities of nano-sized particles, preferably characterized by high aspect ratios, such as layered silicates and carbon nanotubes. Thermal analysis (TA) is a useful tool to investigate a wide variety of properties of polymers and it can be also applied to PN in order to gain further insight into their structure. This review illustrates the versatile applications of TA methods in the emerging field of polymer nanomaterial research, presenting some examples of applications of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and thermal mechanical analysis (TMA) for the characterization of nanocomposite materials.

Assessment of collagen crosslinking and denaturation for the design of regenerative scaffolds

Crosslinking and denaturation were two variables that deeply affected the performance of collagen-based scaffolds designed for tissue regeneration. If crosslinking enhances the mechanical properties and the enzymatic resistance of collagen, while masking or reducing the available cell binding sites, denaturation has very opposite effects, as it impairs the mechanical and the enzymatic stability of collagen, but increases the number of exposed cell adhesive domains. The quantification of both crosslinking and denaturation was thus fundamental to the design of collagen-based scaffolds for selected applications. The aim of this work was to investigate the extents of crosslinking and denaturation of collagen-based films upon dehydrothermal (DHT) treatment, that is, one of the most commonly employed methods for zero-length crosslinking that shows the unique ability to induce partial denaturation. Swelling measurements, differential scanning calorimetry, Fourier transform infrared spectroscopy, colorimetric assays for the quantification of primary amines, and mechanical tests were performed to analyze the effect of the DHT temperature on crosslinking and denaturation. In particular, chemically effective and elastically effective crosslink densities were evaluated. Both crosslinking and denaturation were found to increase with the DHT temperature, although according to different trends. The results also showed that DHT treatments performed at temperatures up to 120°C maintained the extent of denaturation under 25%. Coupling a mild DHT treatment with further crosslinking may thus be very useful not only to modulate the crosslink density, but also to induce a limited amount of denaturation, which shows potential to partially compensate the loss of cell binding sites caused by crosslinking.

Microgel Modified UV-Cured Methacrylic-Silica Hybrid: Synthesis and Characterization

An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was firstly carried out. The O-I hybrid first proposed in this study was obtained from organic precursors with a high siloxane content, which are mixed with tetraethoxysilane (TEOS) in such a way to produce co-continuous silica nanodomains dispersed within the crosslinked organic phase, as a result of the sol-gel process. The first part of the research deals with the selection and optimization of suitable systems through appropriate chemical modifications, in order to ensure that curing reactions can be carried out at room temperature and in the presence of UV radiation. Firstly, the silica domains are formed, followed by crosslinking reactions of the acrylic groups in the oligomer via a free radical polymerization. The crosslinking reaction was controlled with the use of a suitable photoinitiator. Most of the experimental work was devoted to understanding the morphology of the hybrid system, both in uncured and cured states, and to assess its final thermal and optical properties, using different experiential techniques.

Cold-Curing Structural Epoxy Resins: Analysis of the Curing Reaction as a Function of Curing Time and Thickness

The curing reaction of a commercial cold-curing structural epoxy resin, specifically formulated for civil engineering applications, was analyzed by thermal analysis as a function of the curing time and the sample thickness. Original and remarkable results regarding the effects of curing time on the glass transition temperature and on the residual heat of reaction of the cold-cured epoxy were obtained. The influence of the sample thickness on the curing reaction of the cold-cured resin was also deeply investigated. A highly exothermal reaction, based on a self-activated frontal polymerization reaction, was supposed and verified trough a suitable temperature signal acquisition system, specifically realized for this measurement. This is one of the first studies carried out on the curing behavior of these peculiar cold-cured epoxy resins as a function of curing time and thickness.

Novel Epoxy-Silica Hybrid Adhesives for Concrete and Structural Materials: Properties and Durability Issues

Novel epoxy-silica hybrid systems based on silane-functionalized epoxy resins containing interpenetrating silica domains were investigated as structural adhesives with the aim to achieve a good retention of properties when the adhesives are exposed to severe environmental conditions or weathered. Durability experiments have been conducted on the experimental hybrid adhesives by monitoring their mechanical properties, on both cast specimens and on adhesive joints composed of cylindrical concrete or masonry blocks, in ordinary conditions or after exposure to different environmental agents (moderate temperature, immersion in water, outdoor exposure).

Rheological and Kinetic Characterization of UV Photopolymerizable Formulations as a Function of the Boehmite Nanoparticle Content

Several innovative photopolymerizable siloxane-modified acrylic formulations were characterized, both in presence or absence of organically Boehmite (OMB) nanoparticles, in order to assess their rheological and kinetic behavior. The experimental formulations were mainly intended for the surface protection of porous stones or wood elements. The importance of the experimental investigation lies in the specific requirements necessary for the proposed applications, i.e. the innovative UV coatings developed should possess adequate viscosity, photopolymerization reaction rate and time. The kinetics of the radical photopolymerization mechanism, induced by UV radiations, was studied by calorimetric analysis and FTIR spectroscopy as function of the mixtures composition and test conditions (air or nitrogen atmosphere). The addition of a silane coupling agent or a high molecular weight polysiloxane monomer to the acrylic resin was found to reduce the heat of reaction. On the other hand, the presence of Boehmite nanoparticles in the UV photopolymerizable formulations does not seem to modify the reactivity of the siloxane-modified acrylic formulations. The effect of the presence of oxygen on the kinetic reaction was also investigated and correlated to the composition of the systems. Finally, the viscosity of the formulations was studied at ambient temperature with a parallel plates rheomether as a function of composition and shear rate. The viscosity curves were also fitted according to theoretical models as function of shear rate and composition, obtaining a good agreement between experimental data and model predictions.

Miscibilization of low molecular weight functionalized polyethylenes in epoxy resins. I. Effects of composition and modifications chemistry

Toughening of epoxy resins is traditionally carried out by adding small proportions of a low T g oligomer containing reactive end groups. These induce the precipitation of crosslinked rubbery particles during curing. In this study, an investigation was carried out to examine the possibility of using randomly functionalized low molecular weight polyethylene for the same purpose. In the first part of the work we examined the miscibility of binary and ternary blends of several low molecular weight polyethylenes, containing either hydroxyl or acid functional groups, with two types of epoxy resins and two anhydrides, respectively. Various chemical reactions were performed on some of the polyethylenes, as well as on a bisphenol epoxy resin, with the view to increase the miscibility between the components prior to the curing. From these experiments it was established that by modifying the polyethylene component with a monofunctional epoxy resin it is possible to substantially improve their miscibility with both types of difunctional epoxy resins, but to a lesser extent in the presence of anhydride hardeners.

Cure kinetics and physical characterization of epoxy/modified boehmite nanocomposites

Abstract Nanocomposites based on a cross-linked epoxy matrix with the addition of a reinforcing organically modified boehmite nano-phase were realized and characterized with the aim to produce systems possessing enhanced properties over commercial epoxy systems. Different amounts of a commercially available organically modified boehmite were added to a diglycidyl ether of bisphenol A (DGEBA) epoxy matrix. The rheological characteristic and kinetic behavior of the liquid nano-filled mixtures were analyzed and compared to those displayed by the un-filled resin. A mathematical model was applied to the experimental rheological data in order to assess the aspect ratio of the nano-filler. A proper equation was employed to model the cure kinetics of the nano-filled epoxy systems. The nanocomposites were heat-cured in the presence of an aromatic amine hardener. They were, then, characterized by scanning electron microscopy with EDS analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, and Flexural and Hardness tests. Significant increase in the glass transition temperature, Shore D hardness and maximum flexural strength was found. The experimental results demonstrated the effectiveness of the o-boehmite nano-filler to improve the physical and mechanical properties of the epoxy resin. Further studies are in progress to verify the protective efficiency of the epoxy-boehmite nanocomposite when applied on different substrates as adhesive or coating for construction materials, such as porous stones, concrete, wood, and metal.

Solubility and Durability of Cardanol Derived Plasticizers for Soft PVC

Abstract The aim of this work is the analysis of the suitability of cardanol derivatives as primary plasticizer for polyvinyl chloride (PVC). Cardanol derived plasticizers (CDP) were obtained by acetylation of cardanol, followed by epoxidation of the side chain double bonds. The developed procedures allowed to achieve high yields of acetylated cardanol, whereas plasticizers characterized by different yields of epoxidation were obtained, according to the used synthesis procedure. Rheological analysis was used in order to study the gelation process of PVC plastisols with CDP. A comparison of commercial phthalate and natural derived plasticizers showed that the CDP are characterized by adequate gelation properties, involving a complete absorption of the plasticizers at relatively low temperatures. The gelation properties showed a strong dependence on the yield of the epoxidation. In particular, lower gelation temperatures, higher plasticizer absorption and faster gelation were observed for higher epoxy content in the plasticizer. Finally, ageing tests were performed on soft PVC produced by the CDP. The weight loss of soft PVC with CDP is comparable to that of commercial plasticizers, particularly at high yields of epoxidation.