Ricerca e innovazione finalizzata all'utilizzo di "marmi" nel sistema legno per arredamenti di interni

During the 3-year PhD program, the research dealt with the characterization and use of ornamental stones such as commercial “marbles” and relative development of innovative processes in the industry of interior design. This doctorate, started in the framework of the EUREKA Project, partially supported by the Marche Region and carried out through a collaboration between S2 S.p.a. enterprise (Fermignano, PU) and the Dipartimento di Scienze Pure e Applicate (DISPEA) of the University of Urbino. S2 S.p.a. has been involving in the wood sector since 1973, producing a series of manufacts for the most prestigious Italian brands, in which various types of “marbles” often represent an essential material in the final product to be commercialized. At the first stage of the project, technical sheets of the single stone material processed by the enterprise were drawn reporting (i) petrographic classification, (ii) commercial name, (iii) main physical-mechanical features, (iv) photographic documentation showing the aesthetic aspect, (v) availability and size of blocks and slabs and (vi) appropriate finishing process and precautions for each surface treatment. In addition, the principal geological areas of exploitation and the presence of similar lithotypes that could be used as alternative stone materials, were also included. These sheets represent a fundamental background for a digital archive (database) of the overall stones processed by S2 S.p.a. During the three-years program all the steps of the productive industrial cycle were checked, from the purchase of the stone material (testing) up to the delivery of the finished product. As required by the enterprise, a “Guidelines for the selection and buying of blocks and slabs” were also performed on the basis of the experience acquired by myself during testing sessions at the quarrying sites of the different suppliers. These “Guidelines”, together with detailed reports compiled after each testing session, summarize the different purchase methods applied for each stone material. Before each testing, the technical specifications required by the different customers, such as the aesthetic features of the stone materials (i.e. background color, thickness and color of the veins), the sizes of tops (tables) achievable from the slabs and, finally, the number of slabs available in the warehouse for an efficient production planning have to be considered. All the identification data of the purchased slabs and blocks were stored into a specific database. In this way, each slab is associated with (i) a progressive identification number (ID), (ii) type of material, (iii) processing and type of finishing, (iv) length, width and thickness, (v) date of purchase and cost. This database is a useful tool both for quantifying the products obtained (and therefore their traceability) and for calculating the waste. The percentage of waste depends to some aspects including the different modes of purchases (e.g. by measure or by weigth), the type of table (dimensions) and the appropriate choice of the slabs. In the framework of a circular economy, for each block and/or slab we are able to know the number of obtained tops (tables) and the average waste, in order to reduce disposal costs and to encourage the reuse of the waste in the field of furniture and design. The slabs, having a thickness between 2 and 4 cm, produce waste which is not suitable (too thick) for floors and coverings and, for this reason, it has been hypothesized to be reused for other purposes. The enterprise production cycle consists of numerous phases: sectioning slabs, pantographing tops, drying tops in a climatic chamber setted at a temperature between 28-32°C, polish table, packaging and final delivery. A monitoring activity in the phases of drying tops was carried out, concerning temperature, relative humidity and dew point, also focussing the check on the ventilation with warm air circulation. The collection of such data allowed to estimate the temperature below which the humidity of the air condenses, creating problems during the subsequent polyester painting phases. Mostly in the winter season, the climatic chamber does not respect the established temperature and humidity values (even below 25°C). In order to avoid these inconveniences, the S2 S.p.a. enterprise, is going to set a much more innovative drying system for the tops. It is worth to note that the “marbles” slabs are involved in various industrial processing such as the adding of “marble powder” or polymers (e.g. polyester resin), whose interaction with the stone material should be monitored over time to detect the presence of possible undesirable imperfections. Investigations were therefore carried out following the national (UNI) and international (ISO) reference standards for both natural stones and the technology processing (mandatory standards for the European market, CE marking). Moreover, factors such as increase of brittleness and color variations linked to the processing techniques and to the assemblage of the manufact are often responsible for critical issues of some “marbles”. Physical-mechanical tests such as the Point Load Test and the flexural strength test, as well as the study of thin sections under the polarized light microscope were carried out. Where necessary and especially for seldom-used or newly produced materials, additional compositional analyses such as ESEM-BSE analysis and X-ray diffractometry (XRD) were performed, aimed to a more in-depth knowledge and characterization of some stone materials. Laboratory tests and compositional analyses were performed on the following lithotypes (sorted by color as commercially requested): - white “marbles”: “Arabescato Vagli”, “Calacatta Vagli”, “Calacatta Venato”, “Bianco Carrara”, “Statuarietto”, “Panda White”, “Invisible Grey”; - grey “marbles”: “Grigio Imperiale”, “Grigio Roma”, “Grigio Carnico”, “Calacatta Cielo”; - black “marbles”: “Nero Marquina”, “Portoro Silver”, “Portoro”, “Sahara Noir”; - brown “marbles”: “Dark Emperador”, “Mystic Brown”, “Valentine Grey”, “Light Emperador”; - beige “marbles”: “Castagna Limestone”, “Botticino”, “Crema Marfil”, “Travertino Romano”; - red and pink “marbles”: “Rosso Rubino Venato”, “Fior di Pesco Carnico”; - green “marbles”: “Verde Alpi”, “Verde Alpi Scuro”. The thin sections study allowed to classify the stone materials according to UNI 8458/1983. The group of commercial “marbles” includes: metamorphic marbles stricto sensu (“Arabescato Vagli”, “Calacatta Vagli”, “Calacatta Venato”, “Bianco Carrara”, “Statuarietto”, “Panda White”, “Grigio Roma”, “Calacatta Cielo”, “Fior di Pesco Carnico”), organogenic limestones (“Mystic Brown”, “Crema Marfil”, “Nero Marquina”), micritic limestone (“Sahara Noir”), brecciated limestones (“Valentine Grey”, ”Grigio Imperiale”, “Grigio Carnico”), brecciated dolomitic limestones (“Dark Emperador”, “Light Emperador”, “Invisible Grey”), slightly metamorphosed limestones (“Portoro”, “Portoro Silver”, “Botticino”), ophicalcites (“Verde Alpi Chiaro”, “Verde Alpi Scuro”, “Rosso Rubino Venato” or “Rosso Levanto”), travertines (“Travertino Romano”, “Castagna Limestone”). The Cararra marbles have a typical saccharoid texture mainly composed of calcite (<90%) and minor accessory minerals (dolomite, sulphides, oxides). The limestones include brecciated texture and microcrystalline texture with veins consisting of secondary and/or accessory minerals (clay minerals, oxides, dolomite, calcite, quartz). In the ophicalcites veins are mainly present calcite and talc. The physical-mechanical analyses showed that the “green marbles” have the highest values of Point Load Test (3525-4288 kg/cm2) and flexural strength (217-292 kg/cm2) than all the other investigated stone materials. The lowest values of Point Load Test were found in the “Rosso Rubino Venato” or “Rosso Levanto” (1168 kg/cm2) and “Travertino Romano” (1137 kg/cm2), characterized, respectively, by brecciated/fragmented texture and vacuolar structure. For the flexural strength tests, the lowest values were found in some limestones (e.g. “Sahara Noir”, 92 kg/cm2 and “Mystic Brown”, 99 kg/cm2) and travertines (“Travertino Romano”, 107 kg/cm2). In some lithotypes such as “Sahara Noir”, “Valentine Grey”, “Grigio Carnico”, “Invisible Grey”, the weak zone frequently corresponds to the presence of veins. Concerning the white Carrara marbles (“Arabescato Vagli”, “Calacatta Venato”, “Calacatta Vagli”, “Bianco Carrara”, “Statuarietto”) they show homogeneous values for the Point Load Test (between 1070-1350 kg/cm2) and the flexural strength test (between 106-137 kg/cm2). Finally, during the third year, an internship period (stage) was also carried out (from 28 May to 26 June 2019) at the University of Évora, Portugal. During this experience, some varieties of commercial Portuguese “marbles” were taken into account for comparison with those generally processed by S2 S.p.a., through visiting the exploitation areas of Vila Viçosa (part of the Estremoz Anticline) the most important marble district of Portugal, exporting stones all over the world.