1,720,965 research outputs found
Advanced polymeric and nanostructured coatings for Cultural Heritage conservation and restoration
No full textLa ricerca e lo sviluppo di nuove tecnologie riguardanti materiali plastici e nanostrutturati hanno fornito un'ampia varietà di formulazioni a Restauratori e Conservatori, le quali possono essere utilizzate in modo versatile come leganti pittorici e da ritocco, adesivi, consolidanti, materiali di rivestimento, vernici o riempitivi per parti mancanti. Tuttavia, le prestazioni e la durata dei trattamenti a lungo termine, nonché la compatibilità tra l'opera d'arte e il prodotto applicato, vengono testate solo in casi molto limitati prima che il prodotto sia utilizzato nell’intervento conservativo. Negli ultimi anni, invece, la consapevolezza che trattamenti conservativi effettuati senza test preliminari possono causare danni o accelerare processi di degradazione, ha portato a un crescente interesse verso lo studio della stabilità e della durata dei materiali.
In questo lavoro sono stati studiati e confrontati i meccanismi di degrado di diversi prodotti commerciali polimerici e nanostrutturati, in particolare due copolimeri acrilici (Acril33 e Acril ME), due resine sintetiche (Aquazol 500 e Laropal A81), un consolidante a base di silice (Estel 1000) e due dispersioni di nanoparticelle (NanoEstel e NanoRestore), scelti per il loro diffuso utilizzo e per le loro diverse caratteristiche fisico-chimiche e applicazioni. Le potenzialità come consolidanti o materiali da ritocco sono state determinate in seguito alla caratterizzazione dei prodotti commerciali mediante Analisi Termogravimetrica (TGA), Dynamic Light Scattering (DLS), Analisi in Campo Centrifugale (CSA), Viscosimetria, Cromatografia ad Esclusione Dimensionale (SEC) e Spettroscopia Infrarossa in Trasformata di Fourier (FT-IR). Successivamente, gli invecchiamenti accelerati di tipo termo-ossidativo, effettuati alle temperature di 80, 100, 120 e 140 ° C per un massimo di 15000 ore e gli invecchiamenti di tipo foto-ossidativo UVA λ=254 nm e UVC λ=366 nm, effettuati per un massimo di 2000 ore, hanno permesso, mediante analisi SEC, FT-IR, misure colorimetriche e di gloss, di definire i comportamenti prestazionali a lungo termine, i parametri cinetici di degradazione e i meccanismi di degradazione di ciascun prodotto commerciale studiato.
Infine, sono stati sintetizzati e testati materiali luminescenti con lo scopo di ottenere una facile discriminazione tra aree originali e ritoccate o consolidate del manufatto. A tale fine, i complessi luminescenti Eu(NO3)3(phen)2 e Tb(NO3)3(phen)2 sono stati preparati e dispersi nei prodotti commerciali polimerici e nanostrutturati qui studiati. Apprezzabile fotoluminescenza è stata osservata per entrambi i complessi dispersi nelle singole matrici e in seguito a loro invecchiamento foto-ossidativo UVA (λ=254 nm) per un massimo di 2000 ore.Development of techniques and research on plastic and nanostructured materials have provided a wide variety of formulations with versatile uses, such as binding and retouching media, adhesives, consolidants, coating materials, varnishes, or fillers for missing parts. However, the compatibility between artwork and applied products and their durability are tested only in very limited cases before application. In recent years, the awareness of the fact that conservative treatments applied without preliminary tests can cause damages or promote degradations processes, had leads to a growing interest towards the stability and durability of the materials used in conservation practices.
In this work were studied and compared the degrading mechanisms occurring in different polymeric and nanostructured commercial products, in particular two acrylic co-polymers (Acril33 and Acril ME), two synthetic resins (Aquazol 500 and Laropal A81), a silicate consolidant (Estel 1000) and two nanoparticles dispersions (NanoEstel and NanoRestore), chosen for their widespread use and different physical-chemical characteristics and applications. The potentiality as consolidants or retouching materials was determined by means of Thermogravimetric Analysis (TGA), Dynamic Light Scattering (DLS), Centrifugal Separation Analysis (CSA), Viscometry, Size Exclusion Chromatography (SEC) and Fourier Transform Infrared Spectroscopy (FT-IR). Afterwards, thermal (80, 100, 120 and 140°C up to 15000 hours) and photo-oxidative (UVA λ=254 nm, UVC λ=366 nm up to 2000 hours) accelerated aging tests allowed to define behaviours, long-lasting performances, degradation kinetic parameters as well as degradation mechanisms of each commercial product by means of SEC, FT-IR, colorimetric and gloss measurements.
Finally, luminescent materials were synthesized and tested with the aim to discriminate between original and retouched or consolidated areas. The visible emitting lanthanide complexes Eu(NO3)3(phen)2 and Tb(NO3)3(phen)2 were prepared and embedded in the commercial polymeric and nanostructured products herein tested. Appreciable photoluminescence was observed for the complexes once dispersed in the different matrices and after photo-oxidative aging (UVA λ=254 nm up to 2000 hours) tests
Accelerated weathering degradation behaviour of polyester thermosetting powder coatings
No full textThe development of new products and their introduction in the market need rapid and reliable accelerated durability tests have the capacity to predict the service lifetimes of the materials. In this paper we report time-consuming standardised procedures in order to study the durability and the stability of typical polyester powder coatings, used as surface and structure white decorative finish in external architecture. SUNTEST, UVA and UVB accelerated aging tests were done in order to compare the resistance to weathering degradation of different kinds of coatings, four of standard durable and seven of superdurable type. The stability of the single formulation was determined through the evaluation of some chemicals and physical changes on aged samples respect the unaffected one. ATR measurements showed as the degradation differ mainly on the specific type of reactive binder system meanwhile the DSC measurements showed if the accelerate aging processes involved hydrolysis or an increase of the degree of polymerization. A good resistance, in term of gloss and colour retention, were also determine
Determination of degradation kinetics of two polyester thermosetting powder coatings using TGA and colorimetric analysis
No full textThermal stability and thermal degradation kinetics of two different polyester thermosetting powder coatings used as decorative finish in outdoor architectural applications, one standard durable and one superdurable, were investigated. The activation energies of the main stages of the degradation processes were determined by applying Kissinger's and Ozawa's equations on TGA data, which were obtained by using a thermobalance at different rates of heating in a mixed atmosphere of oxygen and nitrogen. The superdurable sample has an activation energy higher than that of the standard durable coating. Both the samples showed greater stability with respect to carboxylated polyesters with TGIC as cross-link agent and epoxy resins with dicyandiamide as reticulating agent. The results were compared to those obtained from aging experiment carried out in a oven at three different isothermal temperatures. The activation energy values were obtained from colorimetric measurements of the aged samples. Data from different approaches resulted closely comparable and it was possible to estimate the activation energies of the degradation processes from total chromatic changes with an error lower than 5% with respect to TGA. This last result highlights the possibility of obtaining kinetic data on these coatings also by using the colorimetric technique
SINTESI E PROPRIETÀ LUMINESCENTI DI SCORPIONATO-COMPLESSI IMPIEGATI COME MARCATORI IN INTERVENTI DI RESTAURO
No full textConsolidation of Vicenza, Arenaria and Istria stones: A comparison between nano-based products and acrylate derivatives
Full text linkNano-based formulations are emerging as successful materials besides the use of conventional products for the consolidation of carbonate works of art e.g. stone, mortars or mural paintings. In this work, the physico-chemical characteristics, performances and consolidation efficacy in terms of external appearance of commercial NanoRestore Ca(OH)2and NanoEstel SiO2dispersions were investigated and compared with two commercial acrylates derivatives, Acril 33 and Acril ME. The colloidal stability of the different consolidants was investigated by dynamic light scattering (DLS) and centrifugal separation analysis (CSA) techniques. As expected, acrylate emulsions showed a higher colloidal stability than the inorganic nanoparticle dispersions, with sedimentation velocity from 10−4to 10−2μm/s. The examined consolidants were applied on three different stones, widely used in historical buildings in Venice: Vicenza, Arenaria and Istria stones, representing macro-, meso- and microporous materials, respectively. The absorption capacity, color and gloss variation of the different stone materials were comparatively evaluated after the consolidants application. An accordance among porous structure of the substrates, hydrodynamic particle size and amount of consolidants absorbed was observed for nano-based formulations. The weathering resistance under natural and UVB aging conditions were also investigated for the consolidated stone samples, and recorded as changes of color, gloss and surface morphology. NanoRestore and NanoEstel showed the best performances under the natural aging while the UVB irradiation seemed to not induce significant modification in the surface morphology of the treated stone samples
Inorganic pigments doped with tris(pyrazol-1-yl)borate lanthanide complexes: A photoluminescence study
No full textThe inorganic pigments malachite, Egyptian blue, Ercolano blue and chrome yellow have been doped with the neutral homoleptic Ln(III) complex Ln(Tp)3 (Ln¼Eu, Tb; Tp¼hydrotris(pyrazol-1-yl)borate) in the presence of arabic gum or acrylic emulsion as binders, in order to obtain photoluminescent materials of interest for cultural heritage restoration. The doped pigments have shown emissions associated to f–f transitions in the visible range upon excitation with UV light. Thermal and UV-light ageings have been carried out. In all the cases the photoluminescent behaviour is maintained, but in the cases of acrylicbased paints emission spectra and lifetimes are strongly influenced by thermal treatments. The choice of binder and pigments influences the photoluminescent behaviour of the corresponding film paints
LE CERAMICHE DI IZNIK (XVI-XVII SEC.): CARATTERIZZAZIONE STORICO-STILISTICA E INDAGINI CHIMICO-FISICHE DI CAMPIONI RAPPRESENTATIVI
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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