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Mariaenrica Frigione, Associate professor - SSD ING-IND 22

Related publications

Cure kinetics of thermosetting polymers and modelling of cure kinetics

  • C. Esposito Corcione, A. Cataldi, M. Frigione: "Measurements of Size Distribution Nanoparticles in Ultraviolet-Curable Methacrylate-Based Boehmite Nanocomposites". Journal of Applied Polymer Science, Vol. 128, pp. 4102-4109 (2013). DOI: 10.1002/app.38639

    A deep study on the possibility to increase the quality of the dispersion of organically modified Boehmite nanoparticles into photo-polymerizable methacrylic-siloxane monomers, to be used as coatings, was conducted using unconventional indirect analyses. The nanocomposite were produced using two different procedures, starting from the conventional ‘‘solvent dispersion method.’’ The two procedures used differ for the technique used to obtain the dispersion of Boehmite, i.e., sonication or magnetic stirring and for the time used in each procedure. The efficiency of each method of preparation of nanostructured systems was analyzed, both in the liquid (uncured) and ultraviolet (UV) cured state. First, dynamic light scattering and rheological measurements were performed on the liquid suspensions, supplying experimental data used in proper theoretical models to estimate the dimensions and distribution of Boehmite particles. The suspensions obtained with the two different methods were, then, UV cured obtaining thin and thick films, on which scanning electron microscopy and transmittance measurements were performed.

  • M. Frigione, A. Maffezzoli: "Curing agents". In: Encyclopedia of Composites, 2nd Edition, Luigi Nicolais and Assunta Borzacchiello Eds., pp. 643-648 (2012). ISBN: 978-0-470-12828-2. Publisher: John Wiley & Sons, Hoboken, New Jersey.

    Reactive compounds in thermosetting matrices of composite materials are monomers or oligomers characterized by a functionality that ranges from a minimum of two up to six or more, in order to produce a crosslinked network. The generic term of resin is usually referred either to the monomer present in the larger amount either to the mix containing the main monomer and all other reactive components, i.e. curing agents, catalysts and initiators. The same base monomer can thus be used to produce crosslinked polymers characterized by properties strongly different depending on the curing agents. In this section, the curing agents involved in and strictly necessary to the curing reactions, are only considered. In very basic terms, curing agents are divided in two classes depending on the role they play in the curing reactions. In step reactions curing agents participate to form the crosslinked network being present in a significant amount and are often referred as hardeners. In radical chain reactions the initiator, producing the first radical promoting the initiation step, is present in a very limited amount in the reactive mixture (a few percent by weight). The discussion will be essentially limited to epoxy resin and partly to polyester and vinylester resins.

  • C. Esposito Corcione, M. Frigione: "Rheological and Kinetic Characterization of UV Photopolymerizable Formulations as a Function of the Boehmite Nanoparticle Content". The Open Materials Science Journal, Vol. 6, pp. 68-76 (2012). DOI: 10.2174/1874088X01206010068

    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.

  • C. Esposito Corcione, M. Frigione: "Characterization of Nanocomposites by Thermal Analysis". Materials, Vol. 5, pp. 2960-2980 (2012). DOI:10.3390/ma5122960, ISSN: 1996-1944

    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.

  • C. Esposito Corcione, M. Frigione: "Factors influencing photo-curing kinetics of novel UV-cured siloxane-modified acrylic coatings: oxygen inhibition and composition". Thermochimica Acta, Vol. 534, pp. 21-27 (2012). DOI:10.1016/j.tca.2012.01.023.

    An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings of stone substrates. The kinetics of the radical photopolymerization mechanism induced by UV radiations in presence of a suitable photoinitiator was studied by a calorimetric analysis by varying the atmosphere (oxygen or nitrogen) and the composition of the mixtures, in particular of the UV photoinitiator. The reactivity, expressed in terms of both heat developed and rate of reaction, was generally found to decrease when the photopolymerization was carried out in air, due the inhibiting action of the oxygen towards the free radical polymerization. The addition of a proper thiol to the acrylic modified resin was found to reduce the adverse effect of oxygen on the kinetic reaction and on the degree of conversion. This result allowed to reduce the content of the photoinitiator and to increase the content of the siloxane in the acrylic based mixtures. The effect of the change of the composition of the formulations on the kinetic behaviour of the acrylic based resins was also analysed by calorimetric analysis. Calorimetric experimental data were fitted to a simple kinetic model for radical photopolymerization reactions. Finally, a proper relationship between the glass transition temperature and the total extent of reaction was applied to the experimental data. A good agreement between the experimental data and both the theoretical models was generally found.

  • C. Esposito Corcione, A. Previderio, M. Frigione: "Kinetics characterization of a novel photopolymerizable siloxane-modified acrylic resin", Thermochimica Acta, Vol. 509, pp. 56-61 (2010).

    An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings. The kinetics of the radical photopolymerization mechanism induced by UV and visible radiations in presence of suitable photoinitiators was studied by a calorimetric analysis by varying the testing conditions (temperature, light power emission, atmosphere). The reactivity, expressed in terms of both heat developed and rate of reaction, was generally found to decrease when the photopolymerization was carried out in air, due the inhibiting action of the oxygen towards the free-radical polymerization. The addition of both a silane coupling agent or a high molecular weight polysiloxane monomer to the acrylic resin was found to reduce the heat of reaction. Experimental data were fitted to a kinetic model to quantify the effects of light intensity and temperature on reaction rates and extent of reaction. A good agreement between the experimental data and the theoretical model was generally found.

  • C. Esposito Corcione, G. Malucelli, M. Frigione, A. Maffezzoli: "UV-curable Epoxy Systems containing Hyperbranched Polymers: kinetics investigation by photo-DSC and real-time FT-IR experiments", Polymer Testing, Vol. 28, pp. 157-164 (2009).

    The effect of the presence of a hyperbranched OH-functionalized polymer (HBP) on the kinetics of cationic photopolymerization of an epoxy system was investigated employing two complementary techniques, photo-DSC and real-time FT-IR spectroscopy.
    Lower rates of cross-linking reactions and higher conversion degrees were obtained in photo-DSC experiments with respect to real-time FT-IR spectroscopy. A limited amount (10% wt) of HBP influenced to a certain extent the cure kinetics of the epoxy resin followed by RT-IR; a final conversion of epoxy groups equal to 100% was achieved by increasing the content up to 20% wt The addition of 10% wt of HBP leaves the cure kinetics of the CE resin studied by p-DSC almost unchanged. By increasing the HBP content, a slightly lower reaction rate is observed at lower reaction times. The presence of the HBP produced a continuous decrease of the Tg of the UV-cured epoxy resin but only modest reductions in its thermo-oxidative stability.

  • C. Esposito Corcione, M. Frigione, A. Maffezzoli, G. Malucelli: "Photo – DSC and Real Time FT – IR Kinetic Study of a UV Curable Epoxy Resin containing O-Boehmites". European Polymer Journal, Vol. 44, pp. 2010-2023 (2008).

    Nanocomposite coatings based on a cycloaliphatic epoxy resin (3,4-epoxycyclohexylmethyl-30,40-epoxycyclohexane carboxylate – CE) with two different o-Boehmites (content ranging from 5 to 10 wt.%) were prepared by cationic photopolymerization. Two different in situ monitoring techniques, photocalorimetry (p-DSC) and real time FT-IR spectroscopy (RT-IR) were used in order to investigate the kinetics of the photopolymerization process. A theoretical approach for establishing the equivalence of the irradiation conditions in the two experimental set-ups was developed in order to compare the obtained results. A substantial correspondence of the two techniques was found for the qualitative trend of the final conversion of the epoxy groups of the filled formulations relatively to the pure CE resin. Conversely, the final conversion of the epoxy groups and the reaction rate were found to be quite different. Higher kinetic profiles were obtained in RT-IR experiments, in which were also observed lower final conversions of the epoxy groups relatively to the p-DSC measurements. The presence of the nanofillers resulted in a decrease in the reactivity of the epoxy system, which was attributed to the light absorbance of Boehmites due to scattering from the clusters in the micron-size range. All the nanocomposites exhibited a high level of transparency and high Tg values, which were found to decrease slightly with increasing the nanofiller content.

  • M. Frigione, E. Calò: "Influence of an hyperbranched aliphatic polyester on the cure kinetic of a trifunctional epoxy resin". Journal of Applied Polymer Science, Vol. 107, pp. 1744-1758 (2008).

    The influence of an OH-terminated hyperbranched aliphatic polyester on the reaction kinetics and rheology of a trifunctional triglycidyl-p-aminophenol (TGAP) epoxy resin cured with an aromatic amine, i.e., diamino-diethyltoluene (DETDA), was investigated. The hyperbranched polymer was expected to enhance the reactivity of the trifunctional epoxy resin; a limited modification in the rheology of the trifunctional epoxy resin with the addition of the hyperbranched polymer, however, was not excluded. The reaction mechanism between DETDA amine and TGAP resin is very complex; therefore, a phenomenological kinetic model was employed. The autocatalytic model chosen was able to fit the experimental calorimetric data for the trifunctional epoxy resin as well as for its mixtures with the hyperbranched polymer. The effect of the OH-terminated hyperbranched aliphatic polyester (H 30) on the reactivity of thetrifunctional epoxy resin was marked, with a decrease of the temperatures at which the crosslinking reactions begin, even though a reduced rate of the curing reactions was observed. However, the completion of the reactions occurred faster and at lower temperatures. The cure mechanism, moreover, remained broadly autocatalytic in nature, regardless of H 30 concentration. Finally, the addition of hyperbranched polymer H 30, even at low percentages, led to a noticeable increase in the viscosity of the resin. This last aspect is believed to restrict to some extent the range of application of such epoxy systems containing the hyperbranched polymer in the traditional processing techniques.

  • M. Frigione, J.M. Kenny: "Effects of Storage Aging on the Cure Kinetics of Bismaleimide Prepregs". Advances in Polymer Technology, Vol. 24, Issue 4, pp. 253-265 (2005).

    The effects of room temperature aging on the subsequent polymerization kinetics of a bismaleimide (BMI) matrix prepreg, for high performance composites, have been characterized by different time and storage conditions. The study has focused on the stability of BMI matrix carbon fiber prepregs, when exposed to controlled environmental conditions before being used in composite manufacturing. The effects of aging on glass transition temperature, reactivity, and processability have been investigated by calorimetry through dynamic, isothermal, and cure-simulating tests. A theoretical kinetic model for epoxy matrix prepregs, developed in previous studies, has been applied to the polymerization of both aged and unaged BMI matrix. The model is able to satisfactorily describe the effect of processing variables such as temperature and degree of reaction during the curing of the composite under different conditions (curing temperature and heating rate). The effects of diffusion-controlled phenomena on the reaction kinetics, associated with changes in glass transition temperature as a function of the degree of polymerization and cross-linking, have been taken into account in the formulation of an nth-order kinetic model.

  • G. Malucelli, A. Priola, F. Ferrero, A. Quaglia, M. Frigione, C. Carfagna: "Polyurethane resin-based adhesives: curing reaction and properties of cured systems". International Journal of Adhesion and Adhesives, Vol. 25, pp. 87-91 (2005).

    A polyether, moisture curable, polyurethane resin was used as an adhesive on plastic and aluminium substrates, in order to investigate the influence of the surface properties on adhesion. The curing kinetics of the adhesive, in controlled temperature and humidity conditions, was evaluated and an elastomeric product was obtained after curing. The surface properties of the cured resin and of the different substrates (PPO/PA6 blend, polypropylene and aluminium) were evaluated and compared by using a contact angle technique. Adhesion measurements were performed using single-lap joints; the strength values obtained were correlated to the structure of the adhesive and to the surface treatments performed on the substrates.

  • M. Lettieri, M. Frigione: "FT-IR Spectroscopy Applied to the Study of the Curing Process of Epoxy-Amine Systems: a Literature Review". In "Trends in Molecular and High Molecular Science", G.E. Zaikov Y.B. Monakov and A. Jimenez Eds., Ch. 6, pp. 87-102 (2005). ISBN: 1-59454-144-2.

    Epoxy resins find wide applications in many fields and have been extensively studied. In particular, great effort has been devoted to the study of the mechanism of crosslinking reactions analysing the factors affecting the molecular network and the physical properties of the hardened material. A detailed understanding of the "curing process" and of the structure-properties relationship, in fact, is essential to control and optimise the process parameters in order to tailor the performance of the of cured systems. Different analytical techniques have been employed to this aim. Among them, FTIR (Fourier transform infrared) spectroscopy has proved to be very helpful allowing quantitative measurements of the variations of functional groups during the crosslinking reactions. In the present work, a review of the scientific publications dealing with the application of FTIR to study the mechanism and the kinetic of the "curing process" of epoxy resins hardened with amines, is presented. This kind of formulation, in fact, is one of the most frequently used and, therefore, has been extensively studied. The main characteristic absorbance peaks of epoxy-amine systems have been listed and discussed. Finally, the kinetic equations more widely employed to determine the degree of conversion and the kinetic parameters, have been reported.

  • M. Frigione, E. Calò, A. Maffezzoli, C. Carfagna, G. Malucelli: "Kinetic Studies of Liquid Crystalline and Isotropic Vinyl Ester Resins". Macromolecular Chemistry & Physics, Vol. 205, pp. 2175-2184 (2004).

    The curing process of a commercial vinyl ester (VE) resin was characterized by calorimetric and spectroscopic techniques. A phenomenological kinetic model, experienced in previous studies, was employed to describe the proceeding of curing reactions. The model is able to describe the behavior of the processing variables, i.e. rate and degree of the reaction, during the curing of the resin under different conditions (heating rates). The effect of diffusion control phenomena on the reaction kinetics, associated with the evolution of the glass transition temperature as a function of the degree of polymerization and cross-linking, was taken into account in the formulation of the kinetic model. A simpler model was proposed and verified for a liquid crystalline vinyl ester resin, synthesized by the authors. The model, in particular, did not take into account the effects of vitrification. The kinetic parameters were again evaluated by processing the calorimetric data. The kinetic study of the liquid crystalline monomer is performed after isotropization and therefore, the acceleration effect, associated with the cure in liquid crystalline phase is not taken into account for the kinetic analysis. Also in this case, the comparison between theoretical and experimental data was very satisfying.

  • C. Esposito Corcione, M. Frigione, A. Greco, A. Maffezzoli: "Kinetics of Cationic Photopolymerization". In "Quantitative Level of Chemical Reactions", G.E. Zaikov and A. Jimenez Eds., Ch. 3, pp. 21-39, Nova Science Publishers, Inc., New York, USA (2003).

    Curing reactions of photoactivated epoxy resins are assuming an increasing relevance in many industrial processes, such as coatings, printing, adhesives. Besides these processes, stereolithography makes use of photoactiveted resins in a laser induced polymerization for 3D building. The kinetic behavior of photocuring is a key point for a full comprehension of the cure conditions occurring in the small zone irradiated by the laser beam. Furthermore, the kinetic analysis is very important in order to determine the cure time needed for part building in a stereolithographic equipment. The mechanisms involved in a cationic photopolymerization are complex when compared with radical photopolymerization. In this contribution, curing mechanisms of photoactivated cationic polymerization are presented. An original phenomenological mode, capable to predict the evolution of the rate of reaction as a function of the time at different light intensities and temperatures, is developed. The validity of the model is studied by comparing model predictions with experimental data obtained through photo-differential scanning calorimetry for a commercial available epoxy based resin for stereolithography.

  • M. Frigione, A. Maffezzoli, P. Finocchiaro, S. Failla: "Cure Kinetics and Properties of Epoxy Resins Containing a Phosphorous-Based Flame Retardant". Advances in Polymer Technology, Vol. 22, No. 4, pp. 329-342 (2003).

    A fire retardant phosphorous-containing bisphenol compound, bis(3-diethyl phosphono-4-hydroxyphenyl)-sulfide (DPHS), has been inserted in an epoxy network. In particular, a chain extension procedure has been used to incorporate DPHS into a standard bisphenol epoxy resin. Different amine catalysts have been tested to promote the reaction of DPHS with the epoxy oligomer. The cure kinetics of this chain-extended oligomer, using an aliphatic amine (triethylene-tetraamine, TETA) as hardener, has been studied with the aid of differential scanning calorimetry and compared with that of the standard stoichiometric epoxy/TETA formulation. For each formulation the activation energy of the curing reactions has been evaluated by the Kissinger method. The results of thermogravimetric and flammability tests indicate that DPHS promoted the formation of a char, leading to an improved fire resistance. Finally, a comparison of the thermal and mechanical properties of the standard stoichiometric formulation relative to those of the epoxy modified with DPHS, and cured with TETA, showed only marginal changes in the physical and mechanical properties.

  • M. Frigione, J.M. Kenny: "Thermokinetic Effects of the Aging of Epoxy Matrix Prepregs for High Performance Composites". Polymer Composites, Vol. 23, No. 4, pp. 530-537 (2002).

    The reactivity and processability of prepregs for high performance composites have been investigated as a function of time and storing conditions. The study has been focused on the stability of epoxy matrix carbon fiber prepregs, affected by exposure to controlled environmental conditions before their use in composite manufacturing. Effects of the aging on glass transition temperature, reactivity and processability have been investigated by calorimetry. Dynamic, isothermal and cure simulating tests have been performed to this aim. Results on toughened TGDDM-DDS epoxy matrix prepregs are reported. A theoretical kinetic model proposed for the unaged system has been adapted for aged prepregs, by properly evaluating the variations of kinetic parameters with the aging time.

  • D. Acierno, M. Frigione, V. Fiumara, D. Napoli, I.M. Pinto, M. Ricciardi: "Thermal and Dielectric Properties of Thermal and Microwave Cured Thermoset Polymers". Materials Research Innovations, 2, pp. 28-32 (1998).

    We compare microwave and thermal curing of DGEBA thermosets hardened with BDMA catalyzed HHPA. The glass transition temperature and (complex) dielectric constant are monitored throughout the process, for variable hardener contents and curing times.

  • D. Acierno, L. Di Maio, M. Frigione, L. Cappetta, M. Feo, V. Fiumara, D. Napoli, V. Pierro, I.M. Pinto, M. Ricciardi: "Selected Issues in the Microwave Processing of Polymers". Microwaves: Theory and Applications in Materials Processing IV, Vol. 80, pp. 409-416 (1997).

    This paper addresses a possible approach to three different topics in microwave polymer processing: measurement of dielectric properties, numerical modelling of microwave induced cross-linking, and microwave heating with melting fronts. Some new results, open issues, and hints for future research are reviewed.

  • J.M. Kenny, A. Trivisano, M. Frigione, L. Nicolais: "Thermal Analysis of Standard and Toughened High-Performance Epoxy Matrices". Thermochimica Acta, 199, pp. 213-227 (1992).

    The reaction kinetics of commercial high-performance matrices has been characterized by differential scanning calorimetry (DSC). Standard and new toughened epoxy matrix prepregs based on tetraglycidyl diamino diphenyl methane-diamino diphenyl sulfone (TGDDM-DDS) formulations have been studied. The toughened epoxy matrix prepreg, modified by addition of a second thermoplastic phase, is characterized by a lower reactivity, probably affected by the presence of the second non-reactive thermoplastic phase. The effect of diffusion control phenomena on the reaction kinetics, associated with evolution of the glass transition temperature as a function of the degree of polymerization and crosslinking, has been considered in the formulation of a modified nth-order kinetic model. This describes incomplete reactions in isothermal tests and the heating rate dependence of dynamic test results, and can thus be used to describe the behaviour of the reactive matrix during processing under complex thermal conditions.

Properties, aging and weathering of thermosetting adhesives and composite matrices for restoration and rehabilitation applications.

  • M.S. Sciolti, M.A. Aiello, M. Frigione: "Influence of water on bond behavior between CFRP sheet and natural calcareous stones". Composites Part B: engineering, Vol. 43, pp. 3239-3250 (2012). DOI: 10.1016/j.compositesb.2012.03.002

    In this paper the effect of a long term immersion in water on bond durability is analyzed when FRPs (Fiber Reinforced Plastic) are externally applied to a masonry substrate. In the performed research a substrate made by natural calcareous stones, strengthened by CFRP (Carbon Fiber Reinforced Plastic) sheets has been analyzed. For a better comprehension of water effect on the adhesive bond between stone and CFRP, the same treatments were performed to the constituent materials, namely epoxy resins, CFRP sheets and stones. To this aim mechanical tests were carried out on stone, composite materials and epoxy resins before and after their immersion in water, evaluating the effects of this agent on the properties of the materials. The influence of the aging in water on the interface stone-reinforcement was analyzed in terms of bond strength, maximum bond stress, optimal bond length, slip-bond stress relationship and mode of failure. In addition the possibility of calibrating design relationships, taking into account the influence of environmental conditions is discussed. Detailed results on adhesives and composites aged in water have been reported in a previous paper while in the present work the significant decay of the mechanical properties of the stone is specifically investigated. With regard to the conditioning treatment a reduction of the bond strength has been observed (up to 26%) as well as a similar decrease of the maximum bond stress; in addition the aged specimens have shown a more fragile behavior. On the basis of the obtained results the empirical coefficient, reported in the available Italian Guidelines, to determine the FRP masonry bond strength seems still effective when the system FRP-masonry is aged in water once the properties of the aged materials are considered in the provided relationships.

  • M. Lettieri, M. Frigione: "Effects of humid environment on thermal and mechanical properties of a cold-curing epoxy resin". Construction and Building Materials, Vol. 30, pp. 753–760 (2012). DOI:10.1016/j.conbuildmat.2011.12.077.

    TThe effects of exposure to different humid environments in a commercial cold-cured epoxy adhesive were investigated. Samples were exposed up to one month to 55%, 75% and 100% relative humidity (RH) or immersed in liquid water, at a constant temperature (23°C). Weight changes, thermal and mechanical properties before and at different stages of the aging, were discussed. In the examined aging conditions, absorbed water remained below 1% and saturation level was not achieved. Plasticization, reactivation of curing reactions and erasure of physical aging were observed in the specimens subjected to the different humidity regimes, all affecting both the thermal and the mechanical properties of the aged samples: while the Tg was influenced by plasticization mainly at shorter times of exposure and by post-curing at longer treatment times, the mechanical characteristics were less affected by these phenomena. These effects were found more pronounced at humidity levels higher than 75% RH. Doubly hydrogen-bonded water molecules linked to the network also influenced the Tg of the system, while they did not affect noticeably their flexural properties. Finally, the effects of water exposure can be regarded as equivalent to those of a thermal treatment at temperature around the Tg, i.e. both leading to an erasure of the physical aging.

  • M. Lettieri, F. Lionetto, M. Frigione, L. Prezzi, L. Mascia: "Cold-cured epoxy-silica hybrids: effects of large variation in specimen thickness on the evolution of the Tg and related properties". Polymer Engineering and Science, Vol. 51, Issue 2, pp. 358-368 (2011).

    Experimental organic–inorganic hybrid systems, based on silane functionalized difunctional and trifunctional epoxy resins and an alkoxysilane precursor mixture, containing small amounts of ammonium molybdate, are evaluated for potential use as adhesives cured at ambient temperatures. The precursor resin mixtures are found to exhibit a large increase in viscosity with a pseudoplastic behavior. Scanning electron microscopy (SEM) analysis shows the existence of siloxane domains with nanometric dimensions, except for the presence of microscopic molybdate particles. By monitoring the evolution of the glass transition temperature (Tg) during curing, varying the thickness of the specimens between 0.2 and 4.5 mm, it is found that the organic–inorganic hybrids display a significant increase in the final Tg over the parent unmodified epoxy resins, particularly in thin specimens and when ammonium molybdate is added. Small-angle X-ray scattering (SAXS) spectra show that the dimensions and typographic features of thick and thin specimens are similar, both containing an agglomeration of primary particles of 5-6 nm.

  • M. Lettieri, M. Frigione: "Natural and Artificial Weathering Effects on Cold-Curing Epoxy Resins". Journal of Applied Polymer Science, Vol. 119, Issue 3, pp. 1635-1645 (2011).

    Three cold-cured epoxy resins, specifically designed as structural adhesives for rehabilitation or renewal applications of civil infrastructures and cultural heritage, were submitted to natural and artificial weathering. We evaluated the variations in the thermal and mechanical properties and color changes after an artificial treatment carried out at 70°C and 75% relative humidity and after natural weathering, performed in two areas of South Italy, both located adjacent to the Mediterranean Sea. The variations in properties due to both natural exposure and artificial weathering were qualitatively similar. However, the selected artificial weathering procedure appeared excessively severe compared to the weathering that occurred after outdoor exposure.

  • M.S. Sciolti, M. Frigione, M.A. Aiello: "Wet Lay-Up Manufactured Frp’s for Concrete and Masonry Repair. Influence of Water on the Properties of Composites and of Their Epoxy Components". ASCE Journal of Composites for Construction, Vol. 14, Issue 6, pp. 823-833 (2010).

    The assessment of durability of fiber-reinforced polymers (FRP), used to strengthen masonry or concrete structures, if subjected to weathering is a knotty problem. Environmental factors can have a significant effect on their performance in service. In order to investigate on this aspect, the mechanical behavior of two commercial composites, reinforced with unidirectional carbon and glass fibers, respectively, was analyzed after a long term immersion in distilled water. For comparison purposes, three different commercial epoxy resins, used as primer, putty or adhesive to manufacture and apply the composites through the wet lay-up technique to the surfaces to strengthen, were subjected to the same treatment. In order to take into account the peculiarities of the three cold-curing epoxy resins, a novel procedure to dry the specimens before the immersion treatment was used. The mechanical tests, performed on the composites before and after their immersion in water, evidenced that this agent has a limited effect only on the in-plane tensile strength of wet lay-up manufactured GFRP, while the mechanical properties of CFRP are substantially unaffected by water. On the other hand, the effect of water on the thermal and mechanical characteristics of the three epoxy resins is quite severe, with significant reductions in the glass transition temperature, stiffness and strength.

  • M. Lettieri, M. Frigione, L. Prezzi, L. Mascia: "Novel cold-cured epoxy-silica hybrids as potential adhesives for concrete/masonry rehabilitation: environmental aging". Restoration of Buildings and Monuments, Vol. 16, No. 4/5, pp. 353-365 (2010).

    The effects of environmental aging at various levels of humidity were studied on the experimental formulations of epoxy-silica hybrids, specifically designed for curing at ambient temperature to be employed as adhesives for concrete and/or masonry structures. The addition of small amounts of ammonium molybdate to the amine hardener was investigated using thick section specimens (4.5 mm thick) capable of retaining substantial amounts of ethanol either originally added to the resin mixture or subsequently formed by the sol-gel hydrolysis and condensation reactions. The changes taking place during aging were evaluated in terms of variations in glass transition temperature (Tg), water absorption and mechanical properties. It has been found that during environmental aging in moist atmosphere the siloxane domains of the epoxy-silica hybrids undergo additional sol-gel reactions, which bring about a further increase in Tg and substantial increases in Young’s modulus (Eflex) and flexural strength (σmax flex). The observed effects were found to be enhanced by the addition of small amounts of ammonium molybdate to the formulation. Furthermore, the moisture in the atmosphere was found to assist the extraction of the residual ethanol in the specimens.

  • M. Frigione: "Durability of Adhesives and Matrices for Polymer Composites used in Restoration and Rehabilitation of Building Structures under Natural and Accelerated Weathering Conditions". In: “Encyclopedia of Polymer Composites: Properties, Performance and Applications”, Mikhail Lechkov and Sergej Prandzheva Eds., Ch 8, pp. 319-344 (2009). ISBN: 978-1-60741-717-0. Nova Science Publishers, Inc. New York, USA, 2009.

    The success of the fiber-reinforced polymer (FRP) systems in the restoration and rehabilitation of civil and monumental structures is due to their excellent properties, generally superior than those of traditional building materials. Of great importance, however, is the behavior of the repaired structure under loading and its durability in the outside climate. The lack of specific standards for durability investigation of materials employed in such applications makes difficult the assessment of reliable theoretical models. As an example, the available standard tests for adhesives generally refer to resins cured at elevated temperatures, neglecting the peculiarities of “cold-cured” adhesives. In this chapter, the durability of the base components of FRP specifically designed for civil engineering industry, is reviewed. The most common environmental agents, mostly responsible for the deterioration of the materials performance, are examined. Finally, standardized accelerating tests are discussed as an effective method to predict the long term behavior of the weathered materials.

  • M. Frigione, M. Lettieri: "Procedures Conditioning the Absorption/Desorption Behavior of Cold-Cured Epoxy Resins". Journal of Polymer Science Part B: Polymer Physics, Vol. 46, pp. 1320-1336 (2008).

    The absorption/desorption behavior of a commercial cold-cured bisphenolic epoxy resin, subjected to different treatments prior to exposure to water, was analyzed. The epoxy system has been already used as both matrix and adhesive for the manufacture and application, respectively, of fiber reinforced polymers composites employed for rehabilitation procedures. The effects of different curing, conditioning, and storing conditions on the water absorption/desorption process taking place in the cured resin were evaluated. The different conditioning procedures used to dry the specimens before their exposure to water caused a different extent of physical aging and of curing on each system, influencing the amount and the rate of diffusion of the water molecules inside the specimens. Moreover, if the specimens are subjected to thermohygrometric cycles prior to immersion in water, the rate of diffusion and the amount of water also depends on the presence of water molecules inside the cured resins not easy to remove by any drying treatment. During all the hygrometric treatments performed, a deaging process took place. The kinetic of this deaging process for the not-fully cured systems depends on the additional crosslinking taking place in the samples. The different procedures used to condition the specimens also affect the variations in glass transition temperature (Tg) of the cured systems during and after immersion in water. Finally, the different drying procedures employed proved to be not equally appropriate for cold-cured epoxy resins.

  • M. Frigione: "Durability Aspects of Polymer Composites Used for Restoration and Rehabilitation of Structures". In: "Leading-Edge Composite Material Research", Tobias G. Wouters Ed., Ch 1, pp. 23-69, Nova Science Publishers, Inc. New York, USA (2007).

    The acceptance of the fiber-reinforced polymers (FRP) in the strengthening of civil and monumental structures is due to a combination of suitable properties and manufacture/installation capability. With respect to traditional building materials, such as steel and concrete, polymer composites offer high strength/weight ratio, good resistance to fatigue, excellent chemical and corrosion resistance. The long term behavior of FRP subjected to weathering is still not well understood. Environmental factors can have a crucial effect on their performance in service. The various environmental factors that have been identified as having a deleterious effect on the durability of FRP are: moisture, temperature changes, freeze-thaw, alkaline environment, ultraviolet radiations. The durability in severe environments, however, is one of the key factor which has contributed to the acceptance of polymer composites in demanding applications, such as the aerospace industry. In this chapter, the properties of several FRP's employed in civil engineering applications are analyzed in relation to the environmental agents to which they can be exposed. Specific interactions can be identified between the different external agents and the based materials composing the FRP. Different thermosetting matrices and fibers, employed for restoration and strengthening applications, are considered. Epoxy, vinyl ester and polyester matrices are reviewed, evidencing the susceptibility of their mechanical properties and adhesive strength to weathering. The performance of an FRP exposed to a harsh environment depends also on the vulnerability of fibers towards the external agents. The fibers most commonly used in FRP for structural reinforcements are based on three types of compounds: carbon, glass and aramidic. Laboratory simulations of environmental agents are compared to natural exposure, emphasizing advantages and limits when reproducing the weather conditions with laboratory procedures. Some remarks and considerations are, finally, drawn.

  • M. Frigione, M.A. Aiello, C. Naddeo: "Water effects on the bond strength of concrete/concrete adhesive joints". Construction and Building Materials, Vol. 20, pp. 957-970 (2006).

    The paper discusses the experimental work by the authors investigating bond strength of epoxy adhesives and their efficiency when joining to concrete elements; the epoxies studied were those currently used in the construction industry. Flexural tests were undertaken to determine the mechanical properties of the exposed and the control specimens of three different epoxy adhesives. In addition, the water resistance of concrete/concrete epoxy joints was investigated by comparing bond strength with those of control samples; the maximum period of immersion was one month. A reduction in the glass transition temperature and the stiffness at short immersion time was found for all the adhesives employed, with a subsequent slight increase for prolonged immersion, while the effects on the strengths resulted almost proportional to their initial values. The effect of water on the adhesion of the joints was found to be significant, especially at longer immersion times; the bond strength of concrete-adhesive specimens reduced by 30% after one month of immersion in water.

  • M. Frigione, M. Lettieri, A.M. Mecchi: "Environmental effects on epoxy adhesives employed for restoration of historical buildings". Journal of Materials in Civil Engineering, Vol. 18, Issue 5, pp. 715-722 (2006).

    Fiber-reinforced composites based on epoxy resins are used in the restoration of historical buildings, for example, in the restoration of the Basilica di S. Francesco (Assisi, Italy). In this study, the epoxy resin that served as a matrix in the composite was analyzed, focusing attention on the factors that could affect its durability in service. The curing process of the epoxy resin was monitored. Thermal, chemical, and mechanical properties were measured on samples exposed, after curing, to levels of humidity, temperature, and water above the ordinary values. The properties of the cured resin were calculated before and after the treatments. The thermal treatments led to an increase in glass-transition (Tg) temperature and a strengthening of the system; the exposition to moisture or water yields a reduction in Tg, while it does not affect considerably the mechanical properties of the resin; the effects of thermohygrometric treatments are more complex.

  • M. Frigione: "The Transport of Water and its Effects on Properties of Cold-Curing Epoxy Adhesives". In "Homolytic and Heterolytic Reactions. Problems and Solutions", G.E. Zaikov, Y.B. Monakov and A. Jimenez Eds., Ch. 13, pp. 283-305, Nova Science Publishers, Inc. New York, USA (2004).

    This review assesses the hygrothermal effects in epoxy adhesives, illustrates the different types of interactions between molecules of water and the polymer network and evidences what are the parameters that influence the absorption process. Although the study would be addressed to cold-curing epoxy adhesive, most of the available literature refers to heat-curing epoxies. Great attention is also devoted to the test procedures used to measure the diffusion parameters of water absorption, evidenced how these procedures can affect the properties of the samples before the immersion. Finally, a brief outlook is given to the accelerated tests regarding the effects of water on properties of epoxy resins, underlining the effectiveness and limits of the mentioned tests.

  • M.A. Aiello, M. Frigione, D. Acierno: "Effects of Environmental Conditions on Performance of Polymeric Adhesives for Restoration of Concrete Structures". Journal of Materials in Civil Engineering, Vol. 14, No. 2, pp. 185-189 (2002).

    The effects of exposure to different environmental conditions on the bond strength between a thermosetting adhesive and concrete were investigated. In particular, the influence of temperatures higher than room temperature and the presence of water on adhesion properties were studied. The results were compared with those relative to specimens tested in ordinary conditions. The increase of test temperature caused a reduction of the bond strength irrespective of the concrete used. The effect of temperature was almost completely reversible because the bond properties were recovered when the temperature was lowered. The presence of water also caused a decrease in adhesion properties, at least to a minor extent. These conditions also affected the mechanism of failure occurring in the samples. On the basis of the obtained results, it is suggested that the environmental conditions in which the adhesive is employed be carefully examined to avoid the occurrence of unexpected failure of the bond and compromising the effectiveness of the repairing technique.

  • M. Frigione, M.A. Aiello, D. Acierno: "Effects of Environmental Agents on Properties of Adhesives - Concrete Joints". Materials Engineering, Vol. 12, No. 3, pp. 443-454 (2001).

    The adhesion properties of different adhesives, based on epoxy resins and suitable for different application in repairing concrete structures, have been analyzed in relation to the service environmental conditions most frequently encountered. In previous studies, it has been found that laboratory exposure referring to high temperatures and water absorption (i.e. environmental agents typically encountered during the service life of structures) causes a noticeable reduction of both the mechanical properties of the adhesives and of the adhesive-concrete joint strength. In the present paper an experimental investigation has been carried out in order to analyze the performance of adhesive-concrete joints naturally exposed for different periods of time, up to one year. The bond strength of exposed specimens has been evaluated and compared with that obtained from tests performed on unexposed samples.

  • M. Frigione, A. Maffezzoli, V.A.M. Luprano: "Correlation between Ultrasonic and Static Mechanical Properties during Curing of Cold-Curing Epoxy Adhesives". Journal of Polymer Engineering, Vol. 21, No. 5, pp. 445-468 (2001).

    Ultrasonic wave propagation has been used to monitor the progress of the curing reactions of an epoxy adhesive employed in civil engineering applications. Ultrasonic velocity and attenuation have been measured in isothermal conditions on the neat resin, as well as in a coupled concrete-resin-concrete system. The evolution of ultrasonic properties has been correlated with the dramatic increase of mechanical properties changing from those of viscous liquid to a glassy polymer. The change of velocity during cure has been used as a measure of the progress of the reaction in order to have a precise indication of the hardening of the adhesive. Correlation charts between static and dynamic properties have been produced both for the neat resin and for the multi-layer system. Such correlation charts, developed for a given epoxy system, can be considered as a powerful tool to measure the progress of curing reactions and, in turn, the development of mechanical and adhesive strength of the bonded structure.

  • M. Frigione, C. Naddeo, D. Acierno: "Cold-Curing Epoxy Resins: Aging and Environmental Effects. II - Mechanical Properties". Journal of Polymer Engineering, Vol. 21, No. 4, pp. 349-367 (2001).

    Thermosetting adhesives, suitable to join different materials in structural applications, are influenced during their service life by various effects which might cause them damage and that are not deeply experienced. They can be, in fact, exposed to atmospheric influences as well as subjected to physical aging as a consequence of their glassy non-equilibrium nature. In the first part of this study, the influences of natural exposure and physical aging, occurring separately or concurrently, on thermal properties of cold-curing epoxy adhesives have been examined. This second part analyzes weathering influences on the mechanical properties of the same adhesives. For this purpose, the different aging processes have been first separated, in order to investigate any single effect, and then their simultaneous influences have been evaluated. The specimens only physically aged exhibit the highest values of static modulus and yield strength, in accordance with current literature. The exposure to natural weathering (i.e. to chemical and physical agings) determines a fluctuation of mechanical properties, whose average values, however, remain close to the initial ones. The effects of chemical aging have been found particularly severe on the filled adhesive. A de-aging treatment, able to erase only physical aging and to remove a limited amount of sorbed water, results in an incomplete recovery in modulus and strength. This effect is partially due to the crosslinking reactions taking place in the cold-cured adhesives. It is thought that the results of this qualitative study can be extended to longer periods of natural exposure, even in the absence of any critical external agent, and that the behavior observed for the selected adhesives can be considered comparable to that of other cold-curing epoxy adhesives

  • M. Frigione, C. Naddeo, D. Acierno: "Cold-Curing Epoxy Resins: Aging and Environmental Effects. I - Thermal Properties". Journal of Polymer Engineering, Vol. 21, No. 1, pp. 23-51 (2001).

    The effects of physical and chemical aging have been investigated on two cold-curing epoxy adhesives. One of the two has been physically aged at different temperatures below its glass transition (i.e. 10, 23, 30 and 40°C) and then subjected to enthalpy relaxation measurements in a differential scanning calorimeter (DSC). According to recent literature, DSC studies have suggested that enthalpy relaxation gradually increases with aging time to a limiting value, depending on the temperature, until structural equilibrium is reached. Specimens of both adhesives, previously cured at room temperature for 10 days, have been aged in a dry-dark atmosphere or in a freezer (-20°C) for a prolonged time, measuring Tg and enthalpy relaxation at different time spans. When the structural equilibrium is reached, the samples aged in the dark-dry atmosphere exhibit Tg and relaxation peak values similar to those found in the earlier analysis for samples isothermally cured at 23°C. Samples aged at -20°C, the curing time suggested by suppliers, which was not sufficient to cure the adhesives completely, have glass transition temperatures that are always lower. The cured adhesives have also been exposed to natural weather for up to 36 months. Some samples, taken at different periods of time, have been analyzed in DSC. Other samples have been subjected to a de-aging procedure (24 hours at 50°C) before the thermal analysis. The natural exposition, regarded as chemical aging, determines a cycling change of Tg of both adhesives around average values slightly lower than the initial ones. This behavior cannot be erased by the de-aging procedure, which is able to delete only the effects due to physical aging. Enthalpy relaxation peaks, characteristics of physical aging, are observed only for exposed samples not subjected to de-aging procedure. These samples, finally, are subjected during the natural exposition to aging and de-aging processes taking place in non-isothermal conditions and, therefore, not predictable. The presented study must be regarded as a qualitative analysis of the aging phenomena taking place in cold curing epoxy resins.

  • M. Frigione, D. Acierno: "Adesivi per l'Edilizia: Durabilità". L'Edilizia, No. 7-8, pp. 36-43 (2000).

  • M. Frigione, A. Maffezzoli, D. Acierno, V.A.M. Luprano, G. Montagna: "Nondestructive and In-Situ Monitoring of Mechanical Property Buildup in Epoxy Adhesives for Civil Applications by Propagation of Ultrasonic Waves". Polymer Engineering and Science, Vol. 40, No. 3, pp. 656-664 (2000).

    Ultrasonic inspection for nondestructive analysis is already widely applied to the control of structural integrity of concrete, presenting among other advantages the reliability, the simplicity and low costs. Although ultrasonic testing are mainly used for nondestructive evaluation of defects, it may be also applied to follow the changes of mechanical properties occurring in a material which evolves in time, such as during the crosslinking of thermosetting resins. These time dependent properties may be measured by longitudinal and shear ultrasonic velocity operating by pulse-echo and/or through-transmission methods. In this work, ultrasonic wave propagation has been applied to the monitoring of the progress of the curing reaction of an epoxy adhesive for civil applications. The data have been collected in isothermal conditions on the neat resin, as well as in a coupled system concrete-resin-concrete. The measurements of longitudinal and shear velocity have been used for the calculation of Young and shear moduli. The change of velocity during cure must be considered a powerful tool for the measurement of the progress of ambient temperature cure reactions like in the case of adhesives for civil applications.

  • M. Frigione, C. Naddeo, D. Acierno: "Epoxy Resins Employed in Civil Engineering Applications: Effects of Exposure to Mild Temperatures". Materials Engineering, Vol. 11, No. 1, pp. 59-80 (2000).

    Two different bisphenolic epoxy resins, employed as structural adhesives in civil engineering restorations, have been analysed in relation to their mechanical behaviour when exposed to mild temperatures, higher than the usual room temperature. It has been found that similar temperatures can be reached inside adhesives used to bond concrete structures in hot days (air temperature = 38 - 40°C). A dramatic decrease in mechanical performances has been observed when the resins work at temperatures higher than 40-50°C, due to the pass over the glass transition temperature (Tg) of the resins, even if they are heavily filled (40% in weight) with an inorganic filler. It has been found that such limitations on service temperatures is common to most of epoxy adhesives employed in civil engineering applications and it is due to intrinsic characteristic of epoxy resins when cured (i.e. hardened) at room temperatures. It has also been demonstrated, moreover, that the adhesives recover almost completely their properties when the service temperature is lowered below the glass transition temperature. The use of a curing temperature higher than the ambient temperature does not lead to higher Tg values, i.e. it is ineffective in enhancing the properties if the working temperature is increased. In conclusion, it is strongly suggested the improvement of specific resins and/or curing agents able to develop a higher Tg even when cured at room temperature, especially when superior performances are required to a structural adhesive.

  • M. Frigione, D. Acierno: "Resine Epossidiche nel Ripristino del Calcestruzzo". Recupero & Conservazione, Anno IV, No. 23, pp. 64-72 (1998).

  • M. Frigione, M.A. Aiello, D. Acierno: "Adhesives Based on Epoxy Resins Used to Repair Concrete Structures: Analysis of the Bond between Resin and Concrete". Materials Engineering, Vol. 9, No. 3-4, pp. 225-235 (1998).

    The bond strength of a polymeric adhesive, based on epoxy resin, with concrete has been analyzed and put in relation to the kind of concrete used and the thickness of the adhesive layer. To this aim, experimental tests of compression type have been performed on cylindrical samples of hardened concrete, saw-cut at an angle of 30° and bonded together with the adhesive resin. Differences in the failure mechanism have been found, which are related mainly to the thickness of the adhesive layer and to the strength of the concrete. The thickness of the adhesive, on the other hand, do not affect appreciably the bond strength.

Other materials and technologies for conservation and restoration of cultural heritage.

  • F. Lionetto, M. Frigione: "Effect of novel consolidants on mechanical and absorption properties of deteriorated wood by insect attack". Journal of Cultural Heritage, Vol. 13, pp. 195-203 (2012) DOI:10.1016/j.culher.2011.09.007.

    The influence of chemical treatments based on novel organic products on the consolidation of deteriorated wood by insect attack was evaluated on two hardwoods and one softwood: fir (Abies alba), beech (Fagus sylvatica) and deciduous oak (Quercus sp.). Degraded and intact specimens of the three wood species were impregnated with two different chemical treatments aimed to verify the potential synergic action of the novel products on wood. Then, the specimens were subjected to bending, compression parallel to the grain, impact, hardness and water absorption tests. Untreated specimens of the same botanical species, both degraded and non-degraded, were examined for comparison purposes. The experimental results showed a different effectiveness of the proposed chemical treatments to improve the mechanical and absorption properties of degraded wood. The most effective treatment was the one assuming the concurrent use of the studied novel consolidants. The species more susceptible of the enhancement in mechanical properties were fir and beech. The observed differentiations were most likely caused by the different structure of the botanical species considered, leading to a consequent different product penetration in the wood structure. The dimensional stability in terms of water repellent and antiswelling efficiency, after a three-month immersion in deionized water, was found to improve in all the treated wood specimens. Overall, experimental results showed that the impact of the chemical treatments was higher on degraded samples than on intact ones.

  • C. Esposito Corcione, M. Frigione: "UV- cured polymer- boehmite nanocomposite as protective coating for wood elements". Progress in Organic Coatings, Vol. 74, pp. 195-203 (2012). DOI:10.1016/j.porgcoat.2011.06.024.

    An organo-modified Boehmite (OMB) was used to prepare nanocomposite UV-cured coatings, based on an innovative photopolymerizable siloxane-modified acrylic formulation, for possible use as protective coatings. 3 wt.% of the nanofiller was dispersed into the mixture in the presence of a proper photoinitiator for UV curing. Different amounts of a silane coupling agent were added to the mixture in order to enhance the compatibility between the nanofiller and the siloxane-modified acrylic formulation. The kinetics of the radical photopolymerization reaction, induced by UV radiations, was studied by photo-calorimetric analysis. The rheological behaviour of the formulations produced was studied as function of the shear rate using a plate and plate rheometer. The formulations, coated on a glass substrate, were photo-cured by using a medium pressure Hg UV lamp. On the coatings photo-polymerized in air were measured: gel content, transparency, scratch and surface hardness. The water absorption effect of the coating based on the novel organic photo-curable nanocomposite on walnut wood elements was evaluated.

  • C. Esposito Corcione, M. Frigione: "Influence of stone particles on the rheological behavior of a novel photopolymerizable siloxane-modified acrylic resin", Journal of Applied Polymer Science, Vol. 122, Issue 2, pp. 942-947 (2011). DOI: 10.1002/app.34201.

    A study was made of the effects of calcarenitic stone particles, known as pietra gentile, inclusions on the rheological behavior of photopolymerizable siloxanemodified acrylic formulations, intended as protective for the calcarenitic stone structures. Different amounts of stone particles (ranging from 15% wt to 35% wt) were added to the modified acrylic mixture to achieve a natural color matching for calcarenitic stone substrates. The presence of stone particles was expected to modify the rheological behavior of the protective formulation. Therefore, the viscosity of the mixtures was studied at ambient temperature as function of the shear rate and the solid volume fraction. A relationship was obtained to predict the modification of viscosity of each formulation as a consequence of inclusions of different amounts of stone.

  • Esposito Corcione, M. Frigione: "UV-cured siloxane-modified acrylic coatings containing birifrangent calcarenitic stone particles: photo-calorimetric analysis and surface properties". Progress in Organic Coatings, Vol. 72, pp. 522-527 (2011). DOI:10.1016/j.porgcoat.2011.06.012.

    An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings for stone substrates. Two amounts of calcarenitic stone particles (25 wt.% and 35 wt.%) were added to a siloxane-modified acrylic mixture. The effect of stone particles inclusion on the reactivity and surface properties of the photopolymerizable systems was investigated. To this aim, the kinetics of the radical photo-polymerization reaction, induced by UV radiations in the presence of a suitable photoinitiator, was studied by calorimetric analysis, both in air and nitrogen atmosphere. The formulations, coated on a glass substrate, were photo-cured by using a medium pressure Hg UV lamp in air. On the coatings photo-polymerized in air were measured: gel content, transparency, scratch and surface hardness.

  • F. Lionetto, M. Frigione: "Mechanical and Natural Durability Properties of Wood Treated with a Novel Organic Preservative/Consolidant Product", Materials and Design, Vol. 30, pp. 3303-3307 (2009).

    An organic preservative/consolidant of new formulation was selected in order to evaluate its effect on the mechanical properties of worm-eaten walnut wood. Walnut wood is widely used for the realization of artistic handworks (e.g. statues, altars, etc.) furniture and flooring. The flexural strength and modulus of elasticity, the toughness and the hardness were determined on both treated and untreated samples.
    The experimental results showed that the product increased significantly the flexural strength while the other mechanical properties were not appreciably affected by the chemical treatment. The microstructure of the samples tested was observed using scanning electron microscopy.
    The preserving character against insects of the investigated product was assessed by both visual inspection and measurements of weight loss on the treated specimens after their exposure to living insects. The samples on which the product was applied, exposed to Oligomerus ptilinoides for one year, were more resistant to decay than the corresponding untreated samples.

  • M. Fersini, M. Frigione, S. Matteo: "Dall’High-Tech alla Ceramica Tradizionale – Un esempio tutto Salentino di ricostruzione di lacune ceramiche con l’ausilio della tecnica stereolitografica laser". Quaderno 12, Museo della Ceramica di Cutrofiano, Congedo Editore, Galatina (LE), pp. 31-46 (2009).

    L’esperienza ventennale del gruppo di Scienza e Tecnologia dei Materiali dell’Università del Salento ( nel settore dei nuovi materiali e processi combinata con la professionalità e la passione del Museo delle Ceramiche di Cutrofiano per il recupero e la conservazione dei Beni Culturali ha dato luogo ad un’interessante proposta per la ricostruzione dei reperti ceramici. Viene qui descritta in modo articolato l’applicazione pratica della tecnica per la ricostruzione della parte superiore di un’anfora ottocentesca, messa a disposizione dal Museo.

Physical, mechanical and transport properties of polymeric materials, toughened resins and blends.

  • P. Russo, D. Acierno, L. Marinucci, A. Greco, M. Frigione: "Influence of Natural and Accelerated Weathering on Performances of Photoselective Greenhouse Films". Journal of Applied Polymer Science, Vol. 127, pp. 2213-2219 (2013). DOI: 10.1002/app.37914

    The research aims to investigate the effects of natural and accelerated weathering on polyethylene-based films. At this regard, monolayer films of low density/linear low density polyethylene blends, containing commercially available organic pigments and an UV absorber of the benzophenone type, have been considered. The samples were weathered on field (natural weathering) or using two different artificial procedures: UV lamp and QUV chamber. Conditioned film samples were, then, analyzed by performing several physical tests taking as-received films as a reference. Rheological measurements showed an increase in viscosity of weathered sample melts as a consequence of photodegradation phenomena, inducing the formation of double bonds and crosslinks. This latter result was also confirmed by gel content measurements. UV–visible spectroscopic tests indicated that in both cases of natural and artificial weathering an increase of the transmittance of films occurred. Tensile tests indicated the increase of films stiffness, especially in case of samples conditioned using the UV lamp, and a large decrease of the strain at break, both in machine and in transverse directions, especially for film weathered using the QUV chamber

  • L. Incarnato, M.R. Nobile, M. Frigione, O. Motta, D. Acierno: "Processing-Structure-Properties Relationships in Blends with Thermotropic Liquid Crystalline Polymers". International Polymer Processing, VIII, 3, pp. 191-199 (1993).

    In this paper the effect of the inclusion of thermotropic liquid crystalline polymers (TLCP) in the thermoplastic polymers is analyzed, with the attention to similar studies reported in the literature. Numerous results relative to TLCP containing blends are considered in terms of structure development in typical processing operations like extrusion and fiber spinning. Several system have been studied in order to emphasize that different effects can be obtained as regards processing and mechanical properties of the host matrices. As for rheological aspects, it has been verified that TLCP can be considered as effective flow aids, even at low concentrations. The addition of a low percentage (5 to 10%) of a TLCP with a viscosity lower than that of the matrix produces a significant reduction (25 to 40%) in the blend viscosity. Moreover, mechanical results have shown that an improvement of the matrix rigidity can be obtained, especially at high percentages of TLCP (30%), under processing conditions where a highly extensional flow prevails. However, a decrease in the ultimate elongation of the matrices has been found in all systems where a poor adhesion between the two phases exists.

  • M. Frigione, L. Mascia, D. Acierno: "Oligomeric and Polymeric Modifiers for Toughening of Epoxy Resins". European Polymer Journal, Vol. 31, No. 11, pp. 1021-1029 (1995).

    The enhancement of properties of cured epoxy resins by the incorporation of modifiers into standard formulations is a subject that has received a great deal of attention over the last two decades. This paper presents an overview of the principles that have been explored to overcome the main deficiencies of epoxy resins, especially their brittleness, and reviews the scientific advances that have been made in this field. Particular attention is given to improvements in properties achieved by the addition of reactive oligomeric compounds, such as: (a) carboxyl and amino terminated butadiene-acrylonitrile, low molecular weight, statistical copolymers; (b) telechelic acrylate copolymers and terpolymers; (c) amine terminated polysiloxanes; and (d) chain extended carboxyl terminated perfluoro polyethers. The use of functionalised thermally stable high molecular weight polymers, both rubbery and glassy, is also examined and their efficiency in enhancing the toughness of difunctional and multifunctional epoxy resins is considered. The polymers considered in greater detail are based on aromatic polyethers and polysiloxane elastomers, respectively.

  • M. Frigione, C. Naddeo, D. Acierno: "Crystallization Behavior and Mechanical Properties of Poly(Aryl Ether Ether Ketone)/Poly(Ether Imide) Blends". Polymer Engineering and Science, Vol. 36, No. 16, pp. 2119-2128 (1996).

    Crystallinity and mechanical properties of blends with different amounts of semicrystalline poly(aryl/ ether ether ketone) (PEEK) and amorphous poly(ether imide) (PEI) polymers have been studied. The blends, prepared by melt mixing, have been investigated by differential scanning calorimeter (DSC) to analyze the miscibility between the components and the final crystalline content. Moreover, for the 20/80 PEEK/PEI blend, crystallization in dynamic and isothermal conditions has been carefully investigated in order to find proper conditions for maximum development of crystallinity. Mechanical tests (static and dynamic) have been performed to evaluate the properties of the as-molded and crystallized blends and to compare them with those of crystalline PEEK and amorphous PEI neat resins. Finally, a few SEM observations have been performed to compare the fractured surface of the blend with those of the pure constituents.

  • M. Frigione, C. Naddeo, D. Acierno: "The Rheological Behaviour of Polyetheretherketone (PEEK) / Polyetherimide (PEI) Blends". Journal of Polymer Engineering, Vol. 16, No. 3, pp. 217-229 (1996/97).

    A study on the rheological behavior at high shear rates of PEEK/PEI blends has been performed by means of a capillary viscometer at two temperatures (350 and 370°C). PEEK (polyetheretherketone) is a tough semicrystalline polymer with properties that make it very attractive for use as a high-quality engineering thermoplastic. It has been melt-blended with amorphous PEI (polyetherimide), another high-performance polymer. From previous studies it was known that PEEK/PEI blends are miscible over the whole composition range. A hoped-for enhancement in processability has been achieved only with a medium content of PEI and at a higher temperature. Finally, a phenomenological equation (Cross equation) has been used to correlate the experimental viscosity values and to predict the rheological behavior of the PEEK/PEI blends even at very low shear rates. The model has been found to fit all the experimental data well at both 350 and 370°C.

  • M.L. Di Lorenzo, M. Frigione: "Compatibilization Criteria and Procedures for Binary Blends: A Review". Journal of Polymer Engineering, Vol. 17, No. 6, pp. 429-459 (1997).

    Polymer blends have been widely studied for the property improvement of commercial polymers. Most polymer blends, however, present coarse and unstable morphologies and poor adhesion at the interface, which is due to their immiscibility. Such problems have often been overcome with the addition of a proper compatibilizer that is able to modify the interfacial condition. In this way, it is possible to control the morphology of the material and the interphase adhesion in an appropriate manner to achieve an effective stress transfer within the blend. Compatibilization criteria and procedures, either by adding a third component ("compatibilizer") or by inducing in situ chemical reactions between blends components, are reviewed. Some theoretical aspects of compatibilization processes have also been considered, giving examples of experimental consistency. The authors also report on the different compatibilizers used for several pairs of immiscible polymers with indications of their action to promote homogenization between phases.

  • M. Frigione, D. Acierno, L. Mascia: "Miscibilization of Low Molecular Weight Functionalized Polyethylenes in Epoxy Resins. I. Effects of Composition and Modifications Chemistry". Journal of Applied Polymer Science, Vol. 73, Issue 8, pp. 1457-1470 (1999).

    Toughening of epoxy resins is traditionally carried out by adding small proportions of a low Tg 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 functionalised 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.

  • M. Frigione, D. Acierno, L. Mascia: "Miscibilization of Low Molecular Weight Functionalized Polyethylenes in Epoxy Resins: Part 2. Effects of Curing on Morphological Features and Mechanical Properties". Advances in Polymer Technology, Vol. 18, No. 3, pp. 237-253 (1999).

    An investigation was carried out to study the toughening of diglycidyl ether of bisphenol A epoxy resins (DGEBA) with several chemically modified low molecular weight polyethylenes, possessing hydroxyl functionality. The miscibility of the functionalised polyethylenes in a DGEBA resin was found to be strictly dependent on the number of functional groups contained in the chains. Solubilisation in the epoxy resin was achieved by reacting the functionalised polyethylenes with a monofunctional epoxy resin homologue, in order to produce telechelic branches attached to the chains. The addition of such chemically modified polyethylenes to an anhydride hardener/epoxy resin mixture has given rise to the formation of a two-phase microstructure in the cured systems, consisting of small spherical aggregated particles strongly bonded to the surrounding matrix, thereby providing the required mechanism for toughness enhancement. The morphology and mechanical properties of such systems are compared to those obtained with a traditional toughening agent for DGEBA epoxy resins.

  • A. Greco, M. Frigione, A. Maffezzoli, D. Acierno: "Rotational Molding of Recycled HDPE". Polymer Recycling, Vol. 6, No. 1, pp. 23-33 (2001).

    A significant fraction of the polymeric wastes consists of high density polyethylene for blow molding typically recycled in injection molding and extrusion processes but very often wasted. On the other hand, the polyethylene grades used in Rotational Molding technique are much less available as recycled polymers. In this work the rotational molding of blends of virgin LLDPE (rotational molding grade) and recycled High Density PE (r-HDPE), coming from urban wastes, has been studied. As a first approach r-HDPE and virgin LLDPE have been extrusion blended. Rheological and mechanical properties of different mixtures have been evaluated and compared with those of the virgin LLDPE. The very high viscosity of LDPE/r-HDPE, not suitable for rotational molding, suggested a direct mixing of powders of r-HDPE and LLDPE at the loading stage of the rotational molding process. The morphology and mechanical properties of a rotational molded part, obtained in this way, have been compared with those the extrusion blended samples. In particular, a composite like morphology led to improved strength and stiffness.

  • M. Frigione, E. Calò, A. Maffezzoli, D. Acierno, C. Carfagna, V. Ambrogi: "Preformed Microspherical Inclusions for Rheological Control and Physical Property Modification of Epoxy Resins". Journal of Applied Polymer Science, Vol. 100, pp. 748-757 (2006).

    Epoxy microspheres, with average diameters in the order of 4-5 µm, were first produced as insoluble gel resulting from the reactions of a bisphenolic epoxy resin with an aromatic hardener in solution. They were then used as reactive flow modifiers and toughening agents for bisphenolic epoxy resins with same chemical composition. Thermal analysis, rheological measurements, and impact tests were performed to assess their ability to modify the viscosity of the uncured resin and to determine the effects on the cured resins with respect to the glass transition temperature and impact strength. Two similar epoxy systems modified with the addition of different amounts of microspheres preserve the glass transition temperature of the cured unmodified epoxy. The addition of microspheres is responsible for secondary transition. The addition of a small fraction of microspheres does not affect the reactivity of the epoxy resin, while the inclusion of a higher content leads to a noticeable reduction in the gel time of the epoxy systems, indicating that microspheres are not inert fillers. Finally, a limited enhancement of the toughness of the epoxy resin was observed, as a consequence of strong interactions between the matrix and the microspheres.

  • C. Esposito Corcione, M. Frigione, D. Acierno: "Rheological characterization of UV - curable epoxy systems: effects of o-Boehmite nanofillers and a Hyperbranched polymeric modifier". Journal of Applied Polymer Science, Vol. 112, pp. 1302-1310 (2009).

    An organo-modified Boehmite (o-Boehmite) was used to prepare nanocomposite UV-curing coatings, based on a cycloaliphatic epoxy resin (3,4-epoxycyclohexylmethyl- 3’,4’-epoxycyclohexane carboxylate). A hyperbranched polymer (HBP) based on highly branched polyester, was also added to the resin, with the aim to modify its reactivity, such as a possible route to increase the toughness of the resin. Different amounts of the nano- filler and the HBP, ranging from 5 up to 20 wt % of resin, were dispersed into the resin in the presence of triarylsulfonium hexafluoroantimonate, as a photoinitiator for the UV curing of the resin. The rheological behavior of the formulations produced was studied as function of the shear rate and of the content of each filler using a cone and plate rheometer. A general increase in viscosity was observed with increasing the volume fraction of each filler and a moderate pseudoplastic behavior was observed when o- Boehmite filler was added. A non-Newtonian behaviour was observed with the incorporation of the HBP. The viscosity of the epoxy/boehmite resin mixtures was analyzed as function of the nanofiller volume fraction. In the case of epoxy/hyperbranched resin mixtures, the Cross equation was used to predict the viscosity of each formulation as a function of the shear rate and an appropriate relationship to predict the viscosity of each formulation as a function of the filler volume fraction, was determined.

  • C. Esposito Corcione, M. Frigione: "A Novel Procedure Able to Predict the Rheological Behavior of Trifunctional Epoxy Resin/Hyperbranched Aliphatic Polyester Mixtures". Polymer Testing, Vol. 28, pp. 830-835 (2009).

    A hyperbranched polymer (HBP), based on a highly branched polyester, was added to a trifunctional triglycidyl-p-aminophenol (TGAP) epoxy resin as a possible route to increase the toughness of the resin. Different amounts of the HBP, up to 26.5% wt. of resin, were dispersed in the TGAP resin. The rheological behavior of the formulations produced was studied as function of the shear rate and the filler content using a cone and plate rheometer. The rheological behavior of the TGAP resin, initially Newtonian, was modified displaying a pseudo-plastic trend when the hyperbranched polymer was added. An increase in the viscosity of the resin was observed with increasing volume fraction of the filler. The Cross equation was used to predict the viscosity of each formulation as a function of the shear rate. A novel procedure was developed to predict the viscosity of each mixture as a function of the filler volume fraction. This could be employed to provide quantitative information on the filler volume fraction in epoxy/HBP systems, necessary to achieve the characteristic viscosity values corresponding to the typical shear rates for a specific processing technology.

Other materials and technologies for construction

  • M. Frigione: "Concrete with polymers".In: “Eco-Efficient Concrete”, F. Pacheco Torgal and Said Jalali Eds., Ch 16, pp. 386-436 (2013). ISBN: 0 85709 424 6. ISBN-13: 978 0 85709 424 7 Woodhead Publishing Limited, Sawston, Cambridge, UK (2013).

    This chapter describes the use of different polymers that can be added to fresh or hardened hydraulic cement, or used to replace the cement. The introduction of polymers can modify the characteristics and properties of concrete, and protect or repair concrete elements. Key words: polymer admixtures, superplasticizers, polymer-modified concrete (PMC) polymer-impregnated concrete (PIC), polymer concrete, (PC), coatings, adhesives.

  • M. Frigione: "Recycling of PET Bottles as Fine Aggregate in Concrete". Waste Management, Vol. 30, pp. 1101-1106 (2010). DOI:10.1016/j.wasman.2010.01.030

    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 365 days 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.


University of Salento   Facoltà di Ingengeria    Department of Engineering for Innovation