Composition comprising recycled glass powder

Abstract

The present invention relates to a composition comprising a glass powder having an X50 ranging from 20 to 80 pm, a polymeric binder preferably of natural origin and water. The invention also relates to a process for producing this composition, and the process for forming and firing a product obtained with the aforesaid composition.

Description

COMPOSITION COMPRISING RECYCLED GLASS POWDERDESCRIPTIONFieldof the invention:The present invention relates to a composition comprising glass powder capable of being worked by means of extrusion and lamination techniques, in particular glass. The invention relates to a composition comprising waste glass powder, i.e., recycled glass from industrial processes or from household uses generally not reused in production processes and hence destined for landfill.The impending need to reduce greenhouse gas emissions and consumptions of raw materials, combined with the constant growth of the global population, poses one of the most important challenges that humanity is facing. Reaching efficient circular economy and carbon neutrality requires the development of new technologies for recycling and recovering materials for their reuse.One of the materials most suitable to be recycled is glass, which is potentially endlessly recyclable without any loss of material or of quality. As it does not release energy or greenhouse gas if burnt, and as it is not biodegradable, recycling glass produces a noteworthy saving of energy and of raw materials. However, not all types of glass are recyclable. Where packaging, such as bottles and jars, can be easily recycled, other types of glass, such as glassware, mirrors or decorative glass, and in general any type of glass mixed with other materials in origin, at the state of the art is not recyclable.Glass is an amorphous and isotropic material, without an ordered crystalline structure, which is formed through rapid cooling of a molten mixture mainly composed of silicates. From a chemical viewpoint, glass mainly consists of silica sand (SiO₂), which represents the main structural component, sodium carbonate (Na₂CO₃), and calcium carbonate (CaCO₃). The composition can be further modified with the addition of metal oxides or other compounds to obtain specific properties, for example, boron oxide (B₂OR₃) or lead oxide (PbO).From the viewpoint of processing, glass can be produced in different forms, depending on application. The main categories include hollow glass, used for containers such as bottles and jars, flat glass, destined for windows and mirrors and obtained through the float process, and artistic glass, handcrafted to create decorative objects or works of art. There are also special types of glass, such as those for optical applications (lenses, objectives, eyepieces) or industrial applications for thermal or acoustic insulation (glass wools), for reinforcement inside composite materials (glass yarns), for pharmaceutical applications (glass tubes), or optical fibres, destined to satisfy specific technical requirements.The definition of non-recyclable waste glass is any vitreous material which, due to contaminations or irreversible modifications, cannot be reintroduced into standard remelt processes, and therefore is destined for landfill or for down-cycling processes. Within the characterization of glass waste, the non-recyclable waste fraction differs from cullet, i.e., recyclable glass, as the latter is suitable to be reused directly in the production of new glass.This category includes types of glass modified by surface treatments, such as screen printing, coatings or other processes that make recovery of the original properties impossible. Moreover, glass becomes non-recyclable waste when it is permanently coupled with foreign materials, such as plastics, metals, or when it has intrinsic contaminations. A typical example of intrinsic contamination is the addition of metal oxides to the formulation.Therefore, there is the need to recycle, recover and reuse those types of glass that currently cannot be recycled with conventional recycling methods. EP1441999A1 describes a method for converting waste glass into ceramic products. However, the processing method described therein does not allow the production of products that are easily workable, in particular by extrusion or 3D printing, and requires the use of components that are unsafe for humans and the environment.US 6,284,176 describes a method for processing waste glass comprising particles of glass smaller than 5mm and, preferably having an average size of 1 mm mixed with suitable binders. However, this composition has a consistency that limits its uses and workability, narrowing the fields of application and making inefficient process steps directly attributable to the characteristics of the paste necessary, as the sizes of the glass particles are too large, resulting in a hard paste that is difficult to work.Therefore, it would be desirable to have a composition based on glass, preferably waste glass, which can be easily and inexpensively produced and is capable of being easily worked. It would also be desirable to have a process for producing this composition which can be easily implemented in the industrial, as well as in the home or hobby sector.Moreover, it would be desirable to have a process for forming products which allows the production of objects of various shapes and sizes that are mechanically strong and resistant to chemical agents, and which is also economically sustainable.The object of the present invention is therefore to provide a composition comprising glass powder capable of overcoming the problems described above.Yet another object of the present invention is a to provide a composition and a production process of a composition based on glass such as to allow upgrading of all those types of glass which, in the current state of the art, are considered non-recyclable and undergo down-cycling processes or end up in landfill, creating environmental and economic damage for the community.A further object of the present invention is to provide a process for working glass such as to produce an environmentally friendly final product, being mono-material and entirely composed of waste glass, without plastics, resins and which can be subsequently upgraded / recycled by means of the same process.A further object of the present invention is to provide a process for working glass such as to allow a high saving in economic and energy terms, and avoid the use of products that are flammable and / or harmful for the health of the operator.These and other objects are achieved by means of a composition as claimed in claim 1.An aspect of the invention relates to a process for preparing a composition as described above comprising:70-87.6% by weight with respect to the total weight of the composition, of a glass powder having an X50 ranging from 20 to 80 µm;0.5-2.4% by weight with respect to the total weight of the composition, of a binder selected in the group consisting of:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives;10-29.5% by weight with respect to the total weight of the composition of water.In this way, a composition is obtained that is easily workable both by extrusion and by lamination or pressing and which allows products with elaborate shapes and sizes to be obtained.Preferably, the composition further comprises 0.1-3% by weight with respect to the total weight of the composition, of a metal oxide selected in the group consisting of zirconium oxide, silicon oxide, praseodymium oxide, vanadium oxide, iron oxide, cadmium oxide, sulphur oxide, manganese oxide, cobalt oxide, chrome oxide, nickel oxide, aluminium oxide, copper oxide.In this way, it is possible to modify the chemical, physical or aesthetic properties of the final material.Preferably, the glass powder is present in an amount by weight with respect to the total weight of the composition ranging from 75 to 84.8%, the binder is present in an amount by weight with respect to the total weight of the composition ranging from 1.8 to 2.2, water is included in an amount by weight with respect to the total weight of the composition ranging from 13 to 23.2.In this way, a composition with the best mechanical, physical, chemical and workability characteristics is obtained. Preferably, the binder is selected in the group consisting of: keratin, fibroin, cellulose, carboxymethyl cellulose (CMC), chitin, corn starch, rice starch, grain starch, wheat starch, potato starch, casein, natural glues, for example deriving from bone and fish bone waste, gum arabic or mixtures thereof.In this way, substances of plant origin and from renewable sources are used, which are not in the slightest harmful for human health and which can be thermally degraded in the subsequent firing steps of the product produced with the composition.Preferably, the glass powder is recycled glass powder from industrial waste and / or from household waste.This contributes to reducing processing waste from the glass industry and at the same time reuse glass that would be destined for landfill without the possibility of being used again, with a considerable impact on the environment and human health.Preferably, the composition further comprises 5-30% by weight with respect to the total weight of the composition, of a compound selected from Na₂CO₃, K₂CO₃, Na₂B₄OR₇.In this way, the sintering temperature, i.e., the firing temperature of the products produced, can be reduced, making the process more sustainable and economically advantageous.A further aspect of the present invention relates to a process for preparing a composition as described above and defined in the claims.In particular, an aspect of the invention relates to a process for preparing a composition as defined above, comprising the following steps:i. providing a binder selected in the group consisting of:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives;in an amount ranging from 0.5-2.4% by weight with respect to the total weight of the composition;ii. adding water in an amount ranging from 10-29.5% by weight with respect to the total weight of the composition;iii. stirring the mixture obtained in step ii for a time ranging from 1-5 minutes at a temperature ranging from 5-35°C;iv. adding, to the colloidal dispersion obtained in step iii, a glass powder having an X50 ranging from 20 to 80 µm in an amount ranging from 70-87.6% by weight with respect to the total weight of the composition;v. stirring the mixture obtained in step iv for a time ranging from 1-5 minutes at a temperature ranging from 5-35°C;in this way, it is possible to produce a uniform and workable composition, which does not have criticalities during the product formation step or during the firing and sintering step thereof.A further aspect of the present invention relates to a second process for preparing a composition as described above and defined in the claims.In particular, a second process for preparing a composition as described above, comprising the following steps:i. providing a binder selected in the group consisting of:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives in an amount ranging from 0.5-2.4% by weight with respect to the total weight of the composition;ii. adding a glass powder having an X50 ranging from 20 to 80 µm in an amount ranging from 70-87.6% by weight with respect to the total weight of the composition;iii. mixing the mixture obtained in step ii for a time ranging from 1-5 min at a temperature ranging from 5-35°C;iv. adding, to the mixture obtained in step vi, water in an amount ranging from 10-29.5% by weight with respect to the total weight of the composition;v. stirring the mixture obtained in step iv for a time ranging from 1-5 minutes at a temperature ranging from 5-35°C;In this way, a process is available that is industrially faster but that at the same time allows a stable and workable composition to be obtained.Yet another aspect of the present invention relates to the product produced by means of the processes described above with a composition described in claim 1.Another aspect of the present invention relates to a process for producing a product as previously described.In particular, a process for producing a product according to the description above comprises the following steps:i. providing a composition according to claim 1;ii. forming the product by means of a forming method selected from extrusion, lamination, moulding, rolling, pressing;iii. heating the product obtained in step ii to 50-150°C above the degradation temperature of the type of binder present in the composition, with a thermal gradient of 120-180°C / hour;iv. maintaining the temperature reached in step iii for a time ranging from 10 to 30 minutes;v. heating the product obtained in step ii to 50-150°C above the glass transition temperature (Tg) of the type of glass in powder form present in the composition, with a thermal gradient of 160-300°C / hour;vi. maintaining the temperature reached in step v for a time ranging from 10 to 120 minutes;vii. cooling the product to room temperature at a thermal gradient of 50-180°C / hour.In this way, a process is available that is capable of forming and producing products with high mechanical and chemical characteristics, i.e., products that withstand impacts but at the same time that can still be worked with diamond cutters or blades in order to produce objects of high aesthetic or artistic taste.According to the present description, the term glass includes waste glass or soiled glass, i.e., glass collected from industrial and / or household waste that contains impurities, such as particles of plastic, paper, metals, etc. Any pure, waste or refuse material that mainly comprises glass or particles of glass falls within the definition of this term.According to the description, the term vitreous material is meant as a non-metallic material having the characteristics of hardness, fragility, amorphousness, chemical resistance and physical-chemical properties typical of glass.According to a general aspect of the present invention, the composition comprises glass powder, preferably deriving from non-recyclable waste, i.e., waste destined for landfill, a binder and water. These compounds can be combined in the following range of proportions (percentages by weight with respect to the total weight of the composition):Glass powder, (70-90%)Binder (0.5-2.4%)Water (10-28%)Metal oxides to recolour the paste (0-3%)Other substances to optimize the production process (0-30%)The composition according to the invention has a complex rheological behaviour, closely influenced by the ratio between the solid components (glass fraction) and the water content. In general terms, the paste behaves like a predominantly plastic and shapeable material, with a tendency to become fragile (formation of cracks and fissures) and lose plasticity as the solid fraction increases.To precisely characterize the plastic characteristics of the glass paste, the Atterberg limits were applied, adapting them to the specific contest. The Atterberg limits identify the critical water contents at which a material transits between states of different consistencies; the tests were conducted according to the European standard of reference EN ISO 17892-12.The composition according to the invention has a behaviour close to the plastic limit, exploiting the principle according to which the plasticity and the workability of the glass paste are directly proportional to the water content.A theoretical, as well as preferred, composition, with a fixed percentage of binder of 2%, 75% of glass powder and 23% of water has an optimal workability. In these conditions, it is possible to produce cylindrical threads with a diameter of less than 2 mm and a length greater than 1000 mm, without cracks or fragmentation occurring. These threads also have a plasticity such as to be able to be reworked manually to create even complex objects (e.g., knots). At the same time, this formulation allows manufacture through additive extrusion methods (for example 3D printing with 3 mm nozzle), allowing the production of a cylinder with a diameter of 50 mm and a height of 200 mm, with print layers variable from 1 to 2.5 mm.The workability limit, corresponding to the plastic limit which, according to Atterberg’s definition, is reached with a water content of 10%. Below this threshold, the paste loses its shapeability, compromising the possibility of advanced processes such as extrusion or fine shaping.According to the present invention, the glass powder present in the composition has a very fine particle size. In particular, the preferred particle size for this powder provides that at least 50% of the size distribution (X50) is between 20-80 μm. Alternatively, a particle size of the powder in which at least 10% of the size distribution (X10) is between 5-15 μm can be considered. In yet a different embodiment, a particle size of the powder in which at least 90% of the size distribution (X90) is between 100-250 μm can be considered.The particle sizes can be calculated using a laser diffraction instrument (for example Mastersizer 3000 manufactured by Malvern Panalytical) in conformity with the standard EN ISO 13320:2009 (Particle size analysis - Laser diffraction methods).The glass powder can advantageously be produced by crushing. This crushing can be carried out using electromechanical or electrohydraulic machinery, such as jaw crushers, hammer mills, disk mills, bead mills, cone crushers or impact crushers, or any crushing technique known to those skilled in the art.Advantageously, crushed glass having a particle size ranging from 25 mm to 250 μm can be added to the composition. These particles can have various shapes and compositions and allow a final product in which a “Venetian terrazzo” type effect is reproduced to be obtained. Moreover, due to the addition of these particles, it is possible to increase the translucence of the end product.According to the present invention, the binder can be selected from different chemical types of compounds, in particular can be selected from:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives.Advantageously, the amount of binder ranges from 0.5-2.4% by weight with respect to the total weight of the composition.In an ideal system, the binder would not be required and the water content could be minimum; however, the particle size of the powder would have to be so small that it would create problems for the operators (particles that are too fine can be inhaled and deposited in depth causing health problems) as well as production difficulties.The use of small amounts of binder and of water limits phenomena of shrinkage and cracking of the object during firing or sintering of the product, making the process more efficient and the products stronger and without possible defects.According to a preferred embodiment, the binder is water-based.According to an embodiment, the binder comprises a polymer, preferably a natural polymer, dispersed in water.According to an embodiment, the binder is formed by one or more of the following components, dispersed or dissolved in water:– keratin– fibroin– cellulose– carboxymethyl cellulose (CMC)– chitin– starch, for example corn, rice, grain, wheat, potato starch– casein– natural glues, for example deriving from bone and fish bone waste– gum arabic– silica based compounds.Advantageously, the aforesaid components are of natural origin and are soluble in water.Many of the aforesaid components are also edible and used in foods, and therefore absolutely safe for humans.With further advantage, the aforesaid binders are removed completely during the subsequent firing step, described below. This allows a finished product made entirely of glass to be obtained.The composition according to the present invention can be produced following two main methods, which, while having the same basic principle, differ in the order of the steps.In the first method, a colloidal solution is first prepared by dissolving the binder in water. This is mixed thoroughly until complete hydration and dissolution of the binder. Subsequently, the glass powder is added to the colloidal solution and the two components are amalgamated, manually or mechanically, using suitable and known mixing means, for a few minutes to obtain a uniform paste.Instead, in the second method the glass powder and the binder are initially mixed dry for a few minutes, manually or with a mechanical mixer, in order to obtain a homogeneous compound, i.e., the two elements are evenly distributed.Water is added gradually to the aforesaid mixture, in controlled amounts (generally between 150 and 500 ml per minute), until the desired composition is obtained. This approach eliminates the need to prepare the colloidal solution in advance, but consumes more water with respect to the previous method.Optionally, substances suitable to modify the chemical, physical or aesthetic properties of the final material can be added to the mixture; these substances are added in place of the glass powder. In particular, it is possible to integrate variable percentages (0.1-3%) of metal oxides such as (non-exhaustive list) Zr, Si, Pr, V, Fe, Cd, S, Mm, Co, Cr, Ni, Al, Cu, in order to modify the final colour.To optimize the production process, chemical compounds (5%-30%) such as Na₂CO₃, K₂CO₃, Na₂B₄OR₇ can also be added, in order to reduce the sintering temperature and make the process more sustainable and economically advantageous.Optionally, in order to make the mixture more aesthetically distinctive, fragments of glass having particles sizes in a range from 25 mm to 250 μm can be added. This addition makes it possible to obtain surfaces with “Venetian terrazzo” effect. Subsequently, the composition obtained, which is in the form of a shapeable paste, can be worked / shaped using many processes, each suitable for different applications and product types in order to obtain a product with the desired shapes and sizes.The possible methods include extrusion, which represents one of the most versatile. Extrusion can be conducted in direct or indirect mode, making it possible to create continuous shapes such as tubes, profiles or sheets, by applying a constant force through a nozzle. A particular case of extrusion is represented by the use of 3D printers, which use an extrusion system to construct objects through the superimposition of layers.Another forming method of the products is moulding, which makes it possible to form three-dimensional objects by using moulds.Further methods are lamination and rolling, similar methods that use rollers to compress and shape the paste in specific thicknesses, guaranteeing dimensional homogeneity and uniform density. While lamination is ideal for producing sheets and panels, rolling is particularly suitable for creating surface details or specific textures on the final product.Finally, pressing makes it possible to shape the paste by applying a uniform pressure in rigid moulds. This process is particularly efficient to produce dense and compact objects, with high dimensional precision and mechanical strength. Once the desired product has been formed, it is subjected to a sintering, or firing, cycle. Sintering is a process by means of which powders (in this case glass) are transformed into a solid and compact body by heating them to a temperature above their glass transition temperature (Tg) but below the melting point. During heating, the particles become soft and bind due to viscous flow and to phenomena of surface diffusion, reducing the porosity and increasing the density of the material. The process takes account of the chemical characteristics of the binder and of the glass waste used. Indicatively, the sintering curve is the following:heating with thermal gradient ranging from 120-180°C / h and reaching the temperature of 50-150°C above the thermal degradation temperature of the binder;holding for 10-30 min at the temperature reached;heating with thermal gradient ranging from 160-300°C / h and reaching the temperature of 50-150°C above Tg (glass transition temperature);holding for 10-30 min at the temperature reached;switching off the furnace and gradual descent to room temperature at a gradient ranging from 50-180°C / h.The sintering curve, thus defined and developed, not only allows perfect and gradual discharge / elimination of the binder, guaranteeing an essentially mono-material, but also prevents undesirable phenomena of crystallization or devitrification of the glass. These phenomena, if not prevented, would compromise both the mechanical and the aesthetic characteristics of the finished object, reducing the overall quality of the product.A further significant advantage is given by the fact that the process operates within a range of peak temperatures from 570°C to 710°C for most types of glass. This range not only allows considerable energy saving, but also reduces the complexity of the instruments required for working, making the process more sustainable and economically advantageous.The degradation temperature of the binder varies based on nature and on amounts used; mainly the degradation temperature ranges from 380-500°C. From thermogravimetric analysis (TGA) conducted it was noted that already at 300°C the majority of binders lose more than 50% of mass and then undergo further decreases at 400-500°C. In particular conditions, some binders can degrade at around 700°C.With regard to the glass transition temperatures, also in this case they can vary based on the nature and on the additives used in production. By way of example, some glass transition temperatures of some types of glass are provided. Murano glass, depending on the furnace, has a Tg of 520-560°C;industrial glass (such as flat glass produced with the float method) has values similar to the previous example even if peaks of 580°C are reached;borosilicate glass is instead around 560-660°CThe products obtained from the process described above are compact and have a shiny appearance. They can be further worked by cutting, milling or etching using diamond grinders or cutters. Moreover, the surface can be etched or sanded. The products have a good level of translucency (intended as the optical property of a material that allows the passage of light through it, but with a diffusion such as to prevent a clear view of objects located on the other side) when the thicknesses are below 8 mm; nonetheless, this characteristic depends not only on the type of glass used, but also on the type of contamination to which the glass has been subjected. In some cases, translucency may not occur.The examples provided below illustrate some embodiments of the invention and are provided by way of non-limiting example. EXAMPLE1: (3d printing with plastic mixture) binder 15g 1.5%water 225g 22.5% glass powder 760g 76.0% A colloidal solution composed of 15g of carboxymethyl cellulose (CMC) was dissolved in 225g of water by means of mechanical stirring. 760g of glass powder (X50 45 μm) was then added to the compound in order to obtain a paste.The mixture, thus obtained, was inserted into a cylinder with a diameter of 85mm, at the top of which a piston that applies a pressure of 4Mpa was positioned. The paste was sufficiently plastic to be extruded continuously through a nozzle with a diameter of 1.5 mm (or larger); a cylinder with a diameter of 50mm and height of 50mm was produced using additive technology.The object thus formed was then subjected to a sintering cycle in the furnace; the glass used was of sodium-calcium type and had a Tg 520-550°C; accordingly, the sintering curve had the following ramp:­ 160°C / h to 450°C = holding for 10 min­ 200°C / h to 600°C = holding for 10 minSwitching off the furnace and gradual descent to room temperature (50-180°C / h)The result was a compact object, with a moderately shiny and translucent surface. EXAMPLE2: (3Dprinting withmixture at the limit) binder 20g 2.0%water 130g 13.0% glass powder 850g 85.0% A colloidal solution composed of 20g of carboxymethyl cellulose (CMC) was dissolved in 130g of water by means of mechanical stirring. 850g of glass powder (X50 22 μm) was then added to the compound in order to obtain a paste.The mixture, thus obtained, was inserted into a cylinder with a diameter of 85mm, at the top of which a piston was positioned. The paste was close to its plastic limit (according to Atterberg parameters) and was extruded continuously using only nozzles with an upper diameter of 3 mm at a pressure of 8Mpa. A cylinder with a diameter of 50 mm and height of 50 mm was produced using additive technology (3 mm nozzle).The object thus formed was then subjected to a sintering cycle in the furnace; the glass used was of sodium-calcium type and had a Tg 520-550°C; accordingly, the sintering curve had the following ramp:­ 160°C / h to 450°C = holding for 10 min­ 200°C / h to 600°C = holding for 15 minSwitching off the furnace and gradual descent to room temperature (50-180°C / h)The result was a compact object, with a moderately shiny and translucent surface. EXAMPLE3: (3D printing with plastic re-coloured mixture) binder 15g 1.5%water 215g 21.5% glass powder 760g 75.0%TiO2 20g 2.0%  A colloidal solution composed of 15g of Gum arabic in powder was dissolved in 215g of water by means of mechanical stirring. 760g of glass powder (X50 38 μm) and 20g of TiO2 were then added to the compound in order to obtain a white paste.The mixture, thus obtained, was inserted into a cylinder with a diameter of 85mm, at the top of which a piston that applies a pressure of 5Mpa was positioned. The paste was sufficiently plastic to be extruded continuously through a nozzle with a diameter of 3 mm; a cylinder with a diameter of 50mm and height of 50mm was produced using additive technology.The object thus formed was then subjected to a sintering cycle in the furnace; the glass used was of sodium-calcium type and had a Tg 580°C; accordingly, the sintering curve had the following ramp:­ 160°C / h to 450°C = holding for 10 min­ 200°C / h to 680°C = holding for 15 minSwitching off the furnace and gradual descent to room temperature (50-180°C / h)The result was a compact object, with a moderately shiny and white surface. The addition of an oxide used to re-colour the paste causes the product to lose any type of transparency. EXAMPLE4: (3D printing with re-coloured paste at the limit) binder 20g 2.0%water 110g 11.0% glass powder 850g 85.0%TiO2 20g 2.0%  A colloidal solution composed of 20g of Gum arabic in powder was dissolved in 110g of water by means of mechanical stirring. 850g of glass powder (X50 20 μm) and 20g of TiO2 were then added to the compound in order to obtain a white paste.The mixture, thus obtained, was inserted into a cylinder with a diameter of 85mm, at the top of which a piston was positioned. The paste was at its plastic limit (according to Atterberg parameters) and was extruded continuously using only nozzles with a diameter of 3 mm at a pressure of 8Mpa. A cylinder with a diameter of 50 mm and height of 50 mm was produced using additive technology (3 mm nozzle).The object thus formed was then subjected to a sintering cycle in the furnace; the glass used was of sodium-calcium type and had a Tg 580°C; accordingly, the sintering curve had the following ramp:­ 160°C / h to 450°C = holding for 10 min­ 200°C / h to 680°C = holding for 15 minSwitching off the furnace and gradual descent to room temperature (50-180°C / h)The result was a compact object, with a moderately shiny and white surface.The addition of an oxide used to re-colour the paste causes the product to lose any type of transparency. EXAMPLE 5: (terrazzo lamination) binder 20g 2%water 150g 15% glass powder 700g 70%glass fragments 130g 13% A colloidal solution composed of 20 g of hydroxypropyl cellulose was dissolved in 150 g of water by means of mechanical stirring. 700g of glass powder (X50 25 μm), and subsequently 130 g of glass fragments with particle size ranging from 8 to 0.25 mm, were added to the compound. The mixture thus obtained was laminated in order to obtain a surface with a thickness of 10mm.The object thus formed was then subjected to a sintering cycle in the furnace; the glass used was of borosilicate type and had a Tg of 600°C; accordingly, the sintering curve had a ramp:­ 160°C / h to 450°C = holding for 10 min­ 180°C / h to 750°C = holding for 1 minSwitching off the furnace and gradual descent to room temperature (50-180°C / h)The result was a compact object, with a moderately shiny surface and with “Venetian terrazzo” effect. Subsequent sanding, using diamond grinders, allowed the surface to be perfectly flattened and the glass fragments to resurface, giving the object a particular aesthetic quality. EXAMPLE6: (re-coloured lamination) binder 20g 2%water 150g 15% glass powder 700g 70%glass fragments 100g 10%TiO2 30g 3%  A colloidal solution composed of 20 g of hydroxypropyl cellulose was dissolved in 150 g of water by means of mechanical stirring. 700g of glass powder (X50 25 μm), and 30 g of TiO2 were then added to the compound in order to obtain a white paste.Subsequently, 100 g of glass fragments with particle size ranging from 8 to 0.25 mm were added.The mixture thus obtained was laminated in order to obtain a surface with a thickness of 5mm.The object thus formed was then subjected to a sintering cycle in the furnace; the glass used was of borosilicate type and had a Tg of 600°C; accordingly, the sintering curve had a ramp:­ 160°C / h to 450°C = holding for 10 min­ 180°C / h to 750°C = holding for 1 minSwitching off the furnace and gradual descent to room temperature (50-180°C / h)The result was a compact object, with a moderately shiny surface and with “Venetian terrazzo” effect. Subsequent sanding, using diamond grinders, allowed the surface to be perfectly flattened and the glass fragments to resurface, giving the object a particular aesthetic quality. EXAMPLE7: (comparison) binder 20g 2%water 230g 23% glass powder 750g 75% A colloidal solution composed of 20g of guar gum was dissolved in 230g of water by means of mechanical stirring. 750g of glass powder (X50 110 μm, i.e., out of the range claimed in the present invention) was then added to the compound in order to obtain a paste.The mixture did not amalgamate sufficiently, making it unusable and unsuitable for any type of working.  EXAMPLE8: (comparison) binder 20g 2%water 80g 8% (out of the range claimed)glass powder 870g 87%TiO2 30g 3%  A colloidal solution composed of 20g of guar gum was dissolved in 80g of water by means of mechanical stirring. 870g of glass powder (X50 32 μm), and 30g of TiO2 were then added to the compound.The mixture did not amalgamate sufficiently, making it unusable and unsuitable for any type of working.  EXAMPLE9: (mechanical properties of theproducts)The mechanical properties of the material were determined through standardized tests, on samples prepared with different compositions and glass particles sizes. 9 specimens were produced for each test, divided into 3 groups characterized by three proportions of powder and different glass fragments and produced according to the methods described above. See Table 1  SPECIMENS.ASPECIMENS.BSPECIMENS.CBinder2%1.5%1%Water18%15%11%Glass powder: X50 ranging from 20-80 μm)80%75.5%70%Glass fragments: X50 ranging from 0.5 to 1 mm0%8%8%Glass fragments: X50 ranging from 1 to 8 mm0%0%10%Table 1The compression tests were conducted in conformity with the standard UNI EN 1926:2007 (Natural stone test methods– Determination of uniaxial compressive strength); specimens measuring 50x50x50mm were used for this test. Flexural tests were conducted according to the standard UNI EN 12372:2022 (Natural stone test methods – Determination of the flexural strength under concentrated load); specimens measuring 30x30x150mm were used for this test.Finally, the material was tested for water absorption according to the standard UNI EN 13755:2008 (Natural stone test methods – Determination of water absorption at atmospheric pressure). Specimens measuring 10x80x80mm were used for this test. The test results gave the following average values. See Table 2. SPECIMENS.ASPECIMENS.BSPECIMENS.CCompression Test (UNI EN 1926:2007)25.8 MPa29.5 MPa48.4 MPaFlexural Test (UNI EN 12372:2022)23.5 MPa21.8 MPa20.6 MPaWater absorption (UNI EN 13755:2008)<1%<1%<1%Table 2    

Claims

1. A composition comprising: 70-87.6% by weight with respect to the total weight of the composition, of a glass powder having an X50 from 20 to 80 µm;0.5-2.4% by weight with respect to the total weight of the composition, of a binder selected in the group consisting of:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives;10-29.5% by weight with respect to the total weight of the composition of water.

2. The composition according to claim 1, further comprising 0.1-3% by weight with respect to the total weight of the composition, of a metal oxide selected in the group consisting of zirconium oxide, silicon oxide, praseodymium oxide, vanadium oxide, iron oxide, cadmium oxide, sulphur oxide, manganese oxide, cobalt oxide, chrome oxide, nickel oxide, aluminium oxide, copper oxide.

3. The composition according to one or more of the preceding claims, wherein said glass powder is present in an amount by weight with respect to the total weight of the composition from 75 to 84.8%, said binder is present in an amount by weight with respect to the total weight of the composition from 1.8 to 2.2%, water is comprised in an amount by weight with respect to the total weight of the composition from 13 to 23.2.

4. The composition according to one or more of the preceding claims, wherein said binder is selected in the group consisting of: keratin, fibroin, cellulose, carboxymethyl cellulose (CMC), chitin, corn starch, rice starch, grain starch, wheat starch, potato starch, casein, natural glues, for example deriving from bone and fish bone waste, gum arabic.

5. The composition according to one or more of the preceding claims, characterized in that said glass powder is recycled glass powder from industrial waste and / or from household waste.

6. The composition according to claim 1, further comprising 5-30% by weight with respect to the total weight of the composition, of a compound selected from Na₂CO₃, K₂CO₃, Na₂B₄OR₇7. A process for preparing a composition according to claim 1, characterized by the following steps:i. providing a binder selected in the group consisting of:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives;in an amount ranging from 0.5-2.4% by weight with respect to the total weight of the composition;ii. adding water in an amount ranging from 10-29.5% by weight with respect to the total weight of the composition;iii. stirring the mixture obtained in step ii for a time ranging from 1-5 minutes at a temperature ranging from 5-35°C;iv. adding, to the colloidal dispersion obtained in step iii, a glass powder having an X50 ranging from 20 to 80 µm in an amount ranging from 70-87.6% by weight with respect to the total weight of the composition;v. stirring the mixture obtained in step iv for a time ranging from 1-5 minutes at a temperature ranging from 5-35°C;8. The process for preparing a composition according to claim 1, characterized by the following steps:i. providing a binder selected from selected in the group consisting of:protein based compounds selected from: collagen and its derivatives, casein and its derivatives, fibroin and its derivatives, keratin and its derivatives;polysaccharide based compounds selected from: chitin and its derivatives, starch and its derivatives, cellulose and its derivatives in an amount ranging from 0.5-2.4% by weight with respect to the total weight of the composition;ii. adding a glass powder having an X50 ranging from 20 to 80 µm in an amount ranging from 70-87.6% by weight with respect to the total weight of the composition;iii. mixing the mixture obtained in step ii for a time ranging from 1-5 min at a temperature ranging from 5-35°C;iv. adding, to the mixture obtained in step vi, water in an amount ranging from 10-29.5% by weight with respect to the total weight of the composition;v. stirring the mixture obtained in step iv for a time ranging from 1-5 minutes at a temperature ranging from 5-35°C;9. A product produced by means of a composition according to claim 1.

10. A process for producing a product according to the preceding claim, characterized by the following steps:i. providing a composition according to claim 1ii. forming the product by means of a forming method selected from extrusion, lamination, moulding, rolling, pressing;iii. heating the product obtained in step ii to 50-150°C above the degradation temperature of the type of binder present in the composition, with a thermal gradient of 120-180°C / hour;iv. maintaining the temperature reached in step iii for a time ranging from 10 to 30 minutes;v. heating the product obtained in step ii to 50-150°C above the glass transition temperature (Tg) of the type of glass in powder form present in the composition, with a thermal gradient of 160-300°C / hour;vi. maintaining the temperature reached in step v for a time ranging from 10 to 120 minutes;vii. cooling the product to room temperature at a thermal gradient of 50-180°C / hour