Composite granule deriving from different organic sources and related production process

Abstract

A process for producing a composite granule obtained from a thermoplastic polymer material and a material recovered from the tanning industry, consisting of tanned leather scraps, and usable in the processes for producing objects by injection molding, compression, extrusion, comprises a plurality of steps including: a step of screening the tanned leather scraps aimed at separating any metal and plastic components from the tanned leather scraps; a step of pulverizing and drying the leather scraps output from the previous screening step aimed at both obtaining a particle size between 20 μm and 2 mm suitable for incorporating said scraps with the thermoplastic matrix and removing traces of moisture and maintaining the scraps under conditions such as not to allow a hydration thereof, and wherein said pulverization step is carried out in a mill provided with at least one multistage chamber containing a plurality of rotors / stators, up to a maximum of three in number, and provided with a closed cooling circuit which allows working with non-solid materials; a step of mixing the pulverized and dried scraps with the polyolefin matrix and suitable additives, at least one of which is a stabilizing additive which is used to promote the interfacial adhesion between said thermoplastic matrix and the scraps and at least another one is an antioxidant additive required to prevent the degradation of the basic components; and a step of extruding and granulating the mixture to obtain the final composite granule, where said extrusion is carried out by means of a co-rotating twin-screw extruder with a temperature ramp from an initial value of 150°C and culminating with a value not exceeding 200°C, to avoid possible degradation of the leather scraps, and wherein the rotation of the screws is between 40 and 600 rpm.

Description

[0001] COMPOSITE GRANULE DERIVING FROM DIFFERENT ORGANIC SOURCES AND RELATED PRODUCTION PROCESS

[0002] Field of the invention

[0003] [1] The present invention relates to a process for producing a composite granule deriving from different organic sources, and a related product, in which said granule is produced from materials recovered from various industries and / or from urban post-consumer waste .

[0004] [2] Such a granule is then usable in all those transformation processes typical of the field of plastics, for example for producing objects by injection molding, compression molding and extrusion .

[0005] [3] By way of non-limiting example, the invention can be used in the field of clothing for producing hangers, packaging and furnishing objects .

[0006] Prior art

[0007] [4] To date, plastic granules made from natural or synthetic polymers are known .

[0008] [5] Plastic granules made from recovered raw materials, such as food waste or the like, are also known, which are produced after careful selection of the input load, and following screening thereof, in order to eliminate all unwanted components and proceed with the subsequent recovery of the plastic material and the consequent transformation into granules .

[0009] [6] Therefore, the screening operation is crucial for producing the granules, as not all the elements present in the waste can be used to make granules which can be used in all those transformation processes typical of the field of plastics . [7] For example, waste from companies in the tanning industry usually requires specific treatments given the presence of dangerous substances and pollutants due to the particular processes which the leather undergoes .

[0010] [8] The presence of such dangerous substances, together with the particular nature of hide as a type of waste, usually require dedicated equipment for the recovery of usable elements .

[0011] [9] Moreover, in almost all cases, the enhancement of the products recovered from said tanning industries passes through the reuse thereof as a base material for fabrics in the automotive industry or for clothing or accessories; in fact, the very nature of hide does not allow, to date, the combined use with other raw materials for making a composite .

[0012] Task of the invention

[0013]

[0010] It is the task of the present invention to overcome the limits of the prior art by suggesting a process which allows both plastic waste and that deriving from the tanning industry to be simultaneously enhanced in a composite product usable in all those injection molding processes typical of the field of plastics .

[0014] Suggested solution

[0015]

[0011] The suggested solution is a process for making a composite granule deriving from recovered thermoplastic polymer material and from material recovered from the tanning industry, and a related product in which the leather is incorporated in a thermoplastic matrix.

[0016] List of figures

[0017]

[0012] A better understanding of the invention will be achieved by means of the following detailed description and with reference to the accompanying figures, which show a preferred embodiment thereof merely given by way of a nonlimiting example.

[0018] In the drawings :

[0019] Figure 1 shows a block diagram of the process according to the invention;

[0020] Figure 2 shows, respectively, the composite granule according to the invention in image la and an enlargement thereof in image lb;

[0021] Figure 3 shows a stereo microscopic image of the integral composite granule according to the invention;

[0022] Figure 4 shows the stereo microscopic analysis of the longitudinal section of the composite granule according to the invention;

[0023] Figure 5 shows the trend of the differential scanning calorimetric analysis (DSC) of the composite granule according to the invention;

[0024] Figure 6 shows the thermal decomposition curve obtained during the thermogravimetric analysis (TGA) of the composite granule according to the invention;

[0025] Figure 7 shows the oxidative stability curve trend of the OIT analysis (oxidation induction time) of the composite granule according to the invention;

[0026] Figure 8 shows the oxidative stability curve trend (OIT) for the composite granule according to the invention after 10 heating / cooling cycles;

[0027] Figure 9 shows the spectrum of the analysis in Fourier transform infrared spectroscopy (FT-IR) of the composite granule according to the invention;

[0028] Figure 10 shows the trend of the melt volume flow rate (MVR) of the composite granule according to the invention; Figures 11a, lib, 11c, lid, lie, Ilf show the scanning electron microscope (SEM) analysis images at different magnifications of the composite granule according to the invention, respectively;

[0029] Figures 12a, 12b, 12c show the stereo microscopic analysis at different magnifications of the composite granule according to the invention post-molding, respectively.

[0030] Detailed description of the invention

[0031]

[0013] As already mentioned, the present invention is a process for producing composite granule deriving from different organic sources, hereinafter referred to for the sake of brevity as " ReLeather'' , obtained by combining a thermoplastic matrix consisting of polyolefins and leather scraps from tanneries .

[0032] Feedstocks

[0033]

[0014] According to the invention, said thermoplastic matrix consists of the following polymers, either pure or mixed : polyethylene (PE) , both low and high density (LDPE, HDPE) , polypropylene (PP) , ethylene vinyl acetate (EVA) , poly vinyl alcohol (PVA) , poly lactic acid (PLA) , polyamides (PA) , polyethylene terephthalate (PET) , polystyrene (PS) .

[0034]

[0015] Furthermore, according to a preferred embodiment of the invention, said polymers forming the thermoplastic matrix derive from urban post-consumer recycling; advantageously, the origin of this (post-consumer) plastic allows having a partially degraded material and, therefore, such as to have a series of functional groups which can facilitate the incorporation of polar charges, such as leather or mineral fillers .

[0035]

[0016] In the preferred non-limiting embodiment described, said thermoplastic matrix consists of polyethylene (PE) , low density polyethylene (LDPE) , linear low density polyethylene (LLDPE) , very low density polyethylene (VLDPE) and / or high density polyethylene (HDPE) , and polypropylene (PP) , said polymers being present in a range of compositions between 10-98% by weight for polyethylene and between 2-90% by weight for polypropylene, respectively.

[0036]

[0017] In this case the reference thermoplastic matrix of the ReLeather granule can be defined as a polyolefin thermoplastic matrix.

[0037]

[0018] According to the invention, the polyolefin thermoplastic matrix is present in a range between 50-90% by weight in the ReLeather granule .

[0038]

[0019] The need to manage leather scraps from tanneries without having to landfill them, and thus face the problems and burdens related to this activity, has led to the development of a process which allows said scraps to be incorporated in the polyolefin matrix described above, allowing the recovery thereof, stabilization with a thermoplastic matrix and, therefore, reuse as a composite material in injection molding, compression and extrusion processes .

[0039]

[0020] Therefore, in the process according to the invention, said tanned leather scraps must be appropriately treated in order to be incorporated in the polyolefin matrix.

[0040]

[0021] In particular, the tanning of the leather scraps is important because, if they had not undergone such a treatment upstream of the process of the present invention, they could degrade in the final composite material, not allowing the desired physicochemical properties to be obtained .

[0041]

[0022] In a preferred but non-limiting embodiment, the amount of hide waste to be added to the polyolefin is between 5-20% by weight .

[0042]

[0023] In a preferred but non-limiting embodiment, the leather scraps used in the present invention were provided by the company Pellemoda; however, results similar to that obtained are obtainable using other leather scraps from other companies .

[0043] Process

[0044]

[0024] According to the present invention, the process for incorporating the tanned hide scraps with the polyolefin matrix includes the following steps :

[0045] • Screening the leather scraps aimed at eliminating any unwanted components which would be deleterious to the final structure of the ReLeather granule;

[0046] • Pulverizing and drying the leather scraps output from the previous screening step, aimed at obtaining a particle size between 20 pm and 2 mm suitable for incorporating said scraps in the thermoplastic matrix, maintaining the chemical-physical properties of the resulting composite, removing traces of moisture and maintaining the scraps under conditions such as not to allow the "hydration" thereof, which would reduce the performance features of the composite granule deriving from different organic final ReLeather sources;

[0047] • Mixing the pulverized and dried scraps with the polyolefin matrix and adding appropriate compounds adapted to both promote stabilization and enhance the mechanical performance of the final composite granule;

[0048] • Extruding and granulating the mixture, aimed at obtaining the composite granule deriving from different organic ReLeather sources . Scrap screening

[0049]

[0025] In this first step, tanned leather scraps, coming from other industries, are separated from any metal and plastic components deriving from previous processing; such a step is fundamental since the presence of plastic or metal components not compatible with the polyolefin matrix would alter the final structure of the granule, altering the final chemical and mechanical properties of the ReLeather granule . PuLverizing and drying

[0050]

[0026] According to the invention, the first step of the process consists of pulverizing the leather scraps, said step being aimed at obtaining a particle size between 20 pm and 2 mm .

[0051]

[0027] The range indicated above is essential for incorporating the scraps in the polyolefin matrix; higher particle size values do not allow them to be incorporated in the polymer matrix, therefore not allowing a granule to be obtained .

[0052]

[0028] Advantageously, such a pulverizing operation can be carried out in two different modes, depending on the particle size to be obtained .

[0053]

[0029] In the preferred but non-limiting embodiment described, the pulverization is carried out in a mill provided with a multistage chamber containing 3 to 6 rotating blades and 2 to 5 fixed blades, carrying out several passes with gradually decreasing diameters of the sorting grid holes, respectively:

[0054] • A first pass with 8 mm grid holes;

[0055] • A second pass with 4 mm grid holes;

[0056] • A third pass with 2 mm grid holes .

[0030] To overcome any packing problems of the pulverized scraps, essentially due to the gradually decreasing size of the scrap and the very nature of leather, which retains moisture, during the second and third pass it is preferable to add an anti-packing additive; in the preferred but nonlimiting embodiment, 1% by weight of calcium carbonate (CaCO3) was added .

[0057]

[0031] Before being directed to the extrusion step, the pulverized leather scraps must be dried .

[0058]

[0032] This step is necessary to remove the H20 contained in the scraps which, as a hygroscopic material, tend to absorb naturally, and therefore prevent gas bubbles from forming during extrusion, which lead to the formation of a porous, non-homogeneous and unpleasant-smelling composite .

[0059]

[0033] In the preferred but non-limiting embodiment described, the drying is carried out in a forced convection oven at a temperature range between 70-80°C for a time not less than 24 hours .

[0060]

[0034] The coarse dried scraps must be kept under vacuum until mixing with the thermoplastic matrix to ensure that the hide does not reabsorb water; such a mixing step occurs immediately before extrusion .

[0061] 2^ mode - fine grinding

[0062]

[0035] Alternatively, according to the invention, it is possible to carry out a finer pulverization aimed at obtaining particle sizes less than 2 mm .

[0063]

[0036] Such an operation is generally carried out in several successive steps, respectively:

[0064] • A first coarse grinding step in which the hide waste, previously cleaned of unwanted components, is subjected to grinding by means of a mill such as that described above which is provided with a multistage chamber with at least two passages and contains 6 to 9 rotating blades and 5 to 8 fixed blades (25-40 blades) , said grinding being aimed at reducing the size of the scraps in a range between 8-12 mm; in this step an anti-packing additive can be added in a concentration range between 0-0.5% by weight; in the preferred but non-limiting embodiment, calcium carbonate (CaCO3) has been added;

[0065] • A step of heat treating the scraps from the previous coarse grinding step in which the coarsely ground product undergoes a heat treatment in an autoclave at a temperature between 110°C and 140°C for a time interval of 6-24 hr; in this step alkalis are added in a concentration of 1-8% by weight and phenolic antioxidants in a concentration of 0.05-0.2% by weight; specifically, such additives mainly have the task of promoting the denaturation of the collagen of the hide;

[0066] • A second fine pulverization step in the wet phase, in which the product output from the previous heat treatment step and having a moisture content in a range of 20-50% by weight, is reduced in size to a particle size of 20- 400 pm by means of passage in a multistage rotor / stator and in which said pulverization step is carried out in a mill provided with at least one multistage chamber containing a plurality of rotors / stators, up to a maximum of three in number, and provided with a closed cooling circuit which allows working with non-solid materials, but working with a concentrated slurry with an average particle size of 20-400p;

[0067] • A drying step in which the pulverized product output from the previous fine grinding step is dried in a disc dryer under weak vacuum at a temperature of 110-130°C;

[0068] • A final screening step adapted to make the particle size of the pulverized hide scraps homogeneous .

[0069] Mixing and Adding

[0070]

[0037] Next, the pulverized and dried scraps are intimately mixed with the thermoplastic matrix, to obtain a product which is as homogeneous as possible .

[0071]

[0038] The mixing can be carried out either cold, by mechanically mixing the granule forming the thermoplastic matrix with the pulverized hide, or by adding the hide to a flow of molten thermoplastic polymer; the choice largely depends on the shape of the twin-screw extruder supplied, in particular if it has gravimetric or volumetric dispensers placed along the extrusion screw.

[0072]

[0039] According to the invention, to increase the miscibility between said thermoplastic matrix and said pulverized scraps, and thus improve the morphology and the resulting properties of the mixture, a compatibilizing additive is added, either silane-based or maleic anhydride- based, which is used to promote the interfacial adhesion between said thermoplastic matrix and the pulverized scraps; generally such additives are compatible with one of the phases and tend to concentrate at the interfaces, thus allowing a finer dispersion of mutually incompatible pairs .

[0073]

[0040] Furthermore, in order to slow down or prevent the oxidation mechanisms within the mixture, at least one antioxidant agent, for example phosphites and phenolics, is added, mainly to prevent the degradation of the basic components .

[0074]

[0041] In particular, according to the present invention, the amount of antioxidant additive added also depends on the type of tanning carried out on hide scraps : in fact, if the tanning was carried out using chromium, the antioxidant additive also has the function of preventing the oxidation of Cr(III) to Cr(VI) ; instead, in the event of vegetable tanning processes (for example based on tannins) , the amount of antioxidant additive to be added is reduced, and limited to that necessary to safeguard the components of the composite during the extrusion step .

[0075]

[0042] In the preferred but non-limiting embodiment described, said stabilizing additive is added together with a process and post-extrusion antioxidant additive in a range of 1-5% by weight .

[0076]

[0043] Advantageously, other additives can be added, for examples;

[0077] • Mineral fillers comprising for example calcium carbonate (CaCO3) , phyllosilicates such as talc and mica, kaolin, dolomite, wollastonite, fiberglass, added as a powder or carried within polymers compatible with the starting thermoplastic matrix, said fillers being effective to modulate the final mechanical properties of the granule, in particular those of the bending modulus (E) to make the final product in line with the values of the bending modulus of polystyrene (PS) and acrylonitrile-butadiene- styrene (ABS) and of other virgin thermoplastic polymers;

[0078] • Drying additives based on calcium oxide (CaO) , carried within polymers compatible with the starting thermoplastic matrix, suitable to absorb any traces of residual moisture (H20) present in the thermoplastic / scrap mixture;

[0079] • Anti-odor additives, such as zinc oxide (ZnO) , zinc salts (Zn) , activated carbon, zeolites, added in powder or carried within polymers compatible with the starting thermoplastic matrix, suitable for neutralizing traces of unpleasant odors .

[0080]

[0044] According to the invention, said mineral fillers can be added in a range of 0-50% by weight .

[0081]

[0045] Furthermore, said drying additives can be added in a range of 0-6% by weight .

[0082]

[0046] Finally, said anti-odor additives can be added in a range of 0-5% by weight .

[0083]

[0047] In the preferred but non-limiting embodiment described, the additives indicated above were mixed cold with the pulverized and dried polyolefin / scrap mixture.

[0084]

[0048] However, such additives can also be added to the flow of molten plastic polymer, depending on the shape of the extruder supplied, if it has gravimetric or volumetric dispensers placed along the extrusion screw.

[0085]

[0049] Advantageously, such additives are commercially available; according to the preferred embodiment described, the following products were used :

[0086] • A mineral filler consisting of talc, carried in polypropylene (PP) at 65% by weight, and added to the mixture at 30% by weight;

[0087] • Caloxol MB70 containing calcium oxide (CaO) as a drying additive, carried in polyethylene and added at 4% by weight;

[0088] • Silmastab AE3061 containing a stabilizing additive, process and post-extrusion antioxidants, and also a lubricant and pH corrector, said additive being carried in polyethylene and added at 2% by weight;

[0089] • Tenray Z2E Evercare as an anti-odor additive, added as a nanometric powder at 1% by weight .

[0050] In particular, talc was used to increase the flexural modulus of the composite granule deriving from different final ReLeather sources, given that the starting polyolefin thermoplastic matrix has a flexural modulus value of 763 MPa, too far from the flexural modulus values of polystyrene (PS, 1200 MPa) and acrylonitrile-butadiene-styrene (ABS, 1900 MPa) and other virgin polymers (2000-2500 MPa) with which this type of items are generally made .

[0090]

[0051] According to the invention, the choice fell on talc as it provides better results with respect to calcium carbonate (CaCO3) , by virtue of the greater shape ratio thereof .

[0091]

[0052] According to the invention, the added talc is carried in polypropylene (PP) at 65% from industrial recycling and allows obtaining high flexural modulus values .

[0092]

[0053] Advantageously, the other additives serve to perform multiple functions, for example Caloxol MB70 is a drying agent (CaO in polyethylene PE as a carrier) useful for sequestering the H20 which is possibly present in both the leather and in the polyolefin matrix, in addition to capturing the gases (C02) which are formed by the degradation processes during extrusion .

[0093]

[0054] Silmastab, also carried in polyethylene, is instead useful as a compatibilizer between chromium-tanned leather scraps and the polyolefin matrix, as an antioxidant and acidifier to prevent the oxidation of Cr (III) to Cr (VI) given the toxicity problems thereof and as a lubricant to promote the melt extrusion process .

[0094]

[0055] Finally, Tenray Z2E Evercare was also used, a nanometric powder of zinc oxide (ZnO) useful for reducing the unpleasant smell of the composite; furthermore, the use in combination with talc allows amplifying the anti-odor effect thereof .

[0095] Extrusion

[0096]

[0056] The mixture output from the mixing and adding step is sent to the next extrusion step .

[0097]

[0057] Such a step is decisive for producing constant-section granules which have suitable chemical-physical features for the subsequent uses of the material (absence of porosity, sufficiently homogeneous density, etc . ) .

[0098]

[0058] To this end, it was necessary to optimize the characteristic extrusion parameters such as temperature, screw revolutions and type of screw profile .

[0099]

[0059] In particular, the temperatures have been specified so as not to degrade the leather; furthermore, the additives mentioned were chosen in that they resist during the process .

[0100]

[0060] In essence, the extruder, in addition to fulfilling the role for which it is intended, acts as a sort of reactor for obtaining the final ReLeather granule .

[0101]

[0061] According to the invention, and following various tests carried out, it was possible to verify that the best operating condition consists in working with a co- rotating twin-screw extruder, with a temperature ramp starting from an initial value of 150°C and culminating with a value equal to and not exceeding 200°C to avoid possible degradation of the leather scraps and within a rotation range of 40-600 rpm, depending on the extruder model used .

[0102]

[0062] In the preferred but non-limiting embodiment, the ideal rotation of the screws is 60 rpm .

[0103] Product

[0104]

[0063] The ReLeather composite granule obtained with the process described above has been subjected to numerous tests aimed at determining the chemical-physical properties while allowing the process itself to be fine-tuned by identifying the best operating conditions (dosages, temperatures, sequence of operations, residence times) .

[0105]

[0064] In general, the analyses carried out show that the scraps are well incorporated within the polyolefin matrix; that is, it implies that the granule has substantially homogeneous chemical-physical features .

[0106]

[0065] Furthermore, the analyses confirm that larger particle sizes of the scrap, in any case not exceeding 2 mm, entail a lower dispersion and the average properties are substantially homogeneous, but locally variable given the size of the scrap; conversely, smaller particle sizes of the scrap, less than 2 mm and up to 20 pm, allow having a greater dispersion within the matrix and substantially homogeneous section properties both on average and locally.

[0107]

[0066] Such a ReLeather granule, obtained according to the present invention, is shown in Figures 2a and 2b.

[0108]

[0067] All the analyses carried out on the ReLeather composite obtained from a polyolefin thermoplastic matrix consisting of low density (LDPE) , linear (LLDPE) , very low density (VLDPE) and high density (HDPE) polyethylene (PE) , and polypropylene (PP) , present in a range of compositions, related to the polyolefin matrix, between 10-98% by weight for polyethylene and between 2-90% by weight for polypropylene, respectively, are reported below.

[0109]

[0068] Such a polyolefin matrix is processed to incorporate the tanned leather scraps .

[0110]

[0069] By way of non-limiting example, a typical composition of the ReLeather granule mixture output from the mixing process and destined for extrusion is presented in Table 1. Stereomicroscopic anaLysis

[0111]

[0070] This type of analysis was carried out with a Nikon SMZ 800 stereomicroscope.

[0112]

[0071] The ReLeather granule has a substantially pseudo- cylindrical pellet shape, with dimensions of about 4x5 mm .

[0113]

[0072] By way of non-limiting example, Figure 3 shows the result of stereomicroscopic analysis of a ReLeather granule used as a sample.

[0114]

[0073] From the analysis of Figure 3, it can be seen that the exterior is slightly corrugated anthracite black, while the cutting surface has some empty spaces and some clearly visible inclusions .

[0115]

[0074] Figure 4 instead shows the result of the stereomicroscopic analysis of the ReLeather granule used as a longitudinally cut sample .

[0116]

[0075] Analyzing the longitudinal cutting section of the granule, it is possible to observe some cavities deriving from the extrusion process carried out and also some colored inclusions deriving from the addition of chrome-tanned leather .

[0117]

[0076] The margins around the leather are not empty or inhomogeneous, which suggests a good compatibility of the organic charge formed by the scrap within the polyolefin matrix.

[0118] DifferentiaL scanning caLorimetry (DSC) anaLysis

[0119]

[0077] Some granules of the Releather composite were shredded and subjected to DSC analysis with the following thermal program :

[0120] • First heating from -10°C to 280°C, with heating ramp of 20°C / min in inert atmosphere (N2) ;

[0121] • Cooling from 280°C to -10°C, with cooling ramp of - 20°C / min in inert atmosphere (N2) ;

[0122] • Second heating from -10°C to 280°C, with heating ramp of 20°C / min in inert atmosphere (N2) .

[0123]

[0078] Figure 5 shows the DSC thermogram related to the ReLeather granule obtained according to the present invention .

[0124]

[0079] As can be seen from the different melting points of the thermogram shown in Figure 5, the DSC analysis shows that the granule mainly consists of three components such as low density polyethylene (LDPE, LLDPE) , high density polyethylene (HDPE) and polypropylene (PP) .

[0125]

[0080] The relative percentages are shown in Table 2.

[0126]

[0081] The analysis does not detect the presence of PET and PVC, determined by the presence / absence of the glass transition in the 1st and 2nd heating DSC curve .

[0127]

[0082] The percentage estimate (%) in the mixture of LLDPE / LDPE, HDPE, PP is calculated as the percentage ratio between the AHf (3 / g) of the compound and the sum of the AHf (3 / g) of all the compounds present in the mixture .

[0128]

[0083] In more detail, all the AHf (3 / g) are calculated using the 2nd heating DSC curve .

[0129] Thermogravimetric anaLysis (TGA)

[0130]

[0084] The Releather granule obtained according to the present invention was subjected to a thermogravimetric analysis (TGA) with the following thermal program :

[0131] • from 30°C to 800°C in an inert atmosphere (N2) with heating ramp of 20°C / min;

[0132] • continuous measurement over time (isotherm) of the change in mass as a function of time of the granule at 800°C in an oxidizing atmosphere (02) for 5 min .

[0133]

[0085] The thermal decomposition curve obtained during the thermogravimetric analysis (TGA) is shown in Figure 6.

[0134]

[0086] As can be seen from the analysis of such a curve, there is a weight loss of 4.4% at about 350°C associated with the degradation of additives and / or oils .

[0135]

[0087] This is followed by a weight loss of 67.9% at about 520°C and associated with the degradation of the polymer component .

[0136]

[0088] Finally, there is a weight loss of 3.1% due to the degradation of inorganic compounds with temperature .

[0137]

[0089] The analysis of the curve also show a final residue equal to 24.6% associated with the mineral fillers present in the composite .

[0138] PIT anaLysis

[0139] Oxidative stability is determined by evaluating the temperature or oxidation induction time (OIT) .

[0140]

[0090] The Releather granule was subjected to a first differential scanning calorimetry (DSC) analysis with the following thermal program repeated 10 times :

[0141] • Heating from 40°C to 220°C, with heating ramp of 20°C / min in inert atmosphere (N2) ;

[0142] • Isotherm at 220°C, for 3 min in an oxidizing environment (02) .

[0143]

[0091] The DSC analysis shows no signs of oxidation after 10 cycles of the set thermal program .

[0144]

[0092] The calorimetric curve related to these 10 tests is shown in Figure 7.

[0145]

[0093] After this series of heating / cooling cycles, the Releather composite was subjected to OIT analysis with the following thermal program :

[0146] • Heating from 25°C to 200°C, with heating ramp of 20°C / min in inert atmosphere (N2) ; • Isotherm at 200°C, for a total time of 35 min, of which 5 min in an inert atmosphere (N2) and subsequent switching to an oxidizing environment (02) .

[0147]

[0094] The resulting thermogram after 10 heating / cooling cycles of the Releather pellet is shown in Figure 8.

[0148]

[0095] The temperature value or oxidation induction time (OIT) is determined, according to ASTM D3895-14, by measuring the time in minutes from the moment in which the switching from inert environment (N2) to oxidizing environment (02) occurs during the isothermal stabilization .

[0149]

[0096] The sample of the Releather composite showed no signs of oxidation and therefore it is deduced that it has an OIT greater than 30 minutes .

[0150]

[0097] This excellent oxidation resistance could depend on the antioxidants added during the additive step .

[0151] Fourier Transform Infrared Spectroscopy (FT-IR) ana Lysis

[0152]

[0098] The ReLeather granule was then subjected to a nondestructive analysis which allows the composition of the material to be determined and the presence of contamination agents to be verified by Fourier transform infrared spectroscopy (FT-IR) , the spectrum of which is shown in Figure 9.

[0153]

[0099] The following bands are noted :

[0154] • Stretching of the OH- ion associated with the presence of calcium oxide (CaO) at 3645 cm- 1;

[0155] • Asymmetrical stretching of CH3at 2951 cm- 1;

[0156] • Asymmetric stretching of CH2at 2917 cm- 1;

[0157] • Symmetrical stretching of CH2at 2850 cm- 1;

[0158] • Symmetrical stretching of C=0 of amide I at 1642 cm1

[0159] • Symmetrical bending of CH3of polypropylene (PP) at 1461 cm- 1; • Symmetrical bending of CH3of polypropylene (PP) and of polyethylene (PE) at 1376 cm- 1;

[0160] • Wagging C-H at 1156 cm- 1;

[0161] • Rocking of the CH2of low-density polyethylene ( LDPE) and high-density polyethylene (HDPE) at 719 cm- 1.

[0162]

[0100] Furthermore, other characteristic bands are noted between 1750 and 1700 cm- 1which are attributable to the carbonyls formed due to the oxidation or degradation of the material .

[0163]

[0101] The bands at 1014 and 670 cm- 1are associated with the presence of talc, based on the comparisons made with the FT- IR spectrum thereof .

[0164] Me Lt FLow Rate (MFR)

[0165]

[0102] The ReLeather composite was subjected to MFR analysis according to ASTM D1238A with a weight of 2.16 kg, setting a temperature of 230°C, preheating the sample for 180 seconds and recovering the material for 60 seconds .

[0166]

[0103] The instrument also measures the Melt Volume Rate (MVR) over the course of the test .

[0167]

[0104] The results of MFR and average MVR are shown in Table 3, while the trend of the melt volume rate (MVR) is shown in Figure 10.

[0168] FLexuraL moduLus ana Lysis

[0169]

[0105] The bending test was carried out on the specimens printed from the ReLeather granule according to the ISO 178 standard .

[0170]

[0106] The results of some tests are shown in Table 4; the analysis shows that the average flexural modulus (E) value of the ReLeather granule is equal to 1576 MPa, that is, it is perfectly intermediate between the flexural modulus values of polystyrene (PS, 1200 MPa) and acrylonitrile- butadiene-styrene (ABS, 1900 MPa) .

[0171] Determination of Cr(VI) content of ReLeather composite sampLe

[0172]

[0107] The ReLeather granule was subjected to an analysis according to the UNI EN 71-3 2021 standard aimed at determining the migration (or passage) of some elements, in particular the hexavalent Cr(VI) originally present in leather scraps and deriving from the processing of hide in tanneries .

[0173]

[0108] In fact, as is known, hexavalent chromium compounds are very toxic if ingested or if the fumes are inhaled .

[0174]

[0109] From what can be seen from Table 5, which shows the result of the examination, the Cr(VI) level is below the quantification limit .

[0175] Scanning ELectron Microscope (SEM) ana Lysis

[0176]

[0110] The images in Figure 11a, lib, 11c, lid, lie, Ilf obtained with a scanning microscope (SEM) show how the filler consisting of talc, the polyolefin thermoplastic matrix and hide are well compressed together without leaving empty spaces .

[0177]

[0111] The filler has a light-colored plaque appearance while the hide has a fibrous appearance .

[0178]

[0112] Overall, the ground leather scraps and mineral fillers seem to be homogeneously incorporated into the plastic matrix.

[0179]

[0113] Moreover, the silane compatibilizer, by virtue of the action mechanism thereof, manages to bind the hydroxyl groups exposed on the surface of the leather and those of the talc very well, stabilizing them in the plastic polymer, which is also partially degraded and therefore receptive to the compatibilizer and to other organic charges .

[0114] Obviously the size of the leather, and in particular the particle size, affects the homogeneity of the final granule : a high particle size does not help to obtain a homogeneous composite, as in the case shown in the stereomicroscopic analysis of Figures 11a, lib, 11c, lid, lie, Ilf , where large leather inclusions are apparent inside the granule .

[0180] Stereomicroscopic ana Lysis of the printed Re Leather composite

[0181]

[0115] Finally, the ReLeather granule, immediately after compounding, was printed in order to obtain demonstration plates .

[0182]

[0116] These were broken and the breaking surface was analyzed under the stereomicroscope, the images of which are shown in Figures 12a, 12b, 12c .

[0183]

[0117] As can be seen from Figures 12a, 12b, 12c, the printed piece does not have empty spaces therein despite the large inclusions deriving from the presence of leather with a very high size .

[0184]

[0118] The polymer matrix seems to incorporate the different organic charge without problems .

[0185]

[0119] This derives, as already mentioned above, from the fact that a post-consumer plastic is partially degraded and therefore exposes a series of functional groups which can facilitate the compatibilization of polar charges, such as skin or talc itself .

[0186]

[0120] Furthermore, the addition of the compatibilizer Silmastab, with the silane compatibilizer thereof, further helps this process by covalently bonding the plastic matrix to the leather component and to the mineral filler.

[0187] Advantages

[0121] Advantageously, the process according to the invention, and the related composite granule deriving from different organic sources, allow the effective recovery of the products deriving from the tanning industry in a product usable in all those injection molding, compression and extrusion processes, thus opening up various fields of possible reuse of leather scraps which do not only contemplate recycling as a material for fabrics or interiors in the automotive field .

[0188] Examples , experimental tests , tables

[0189] TabLe 1 - Mixture composition

[0190] TabLe 2 - Re Leather granuLe composition

[0191] TabLe 3 - MFR test resuLts TabLe 4 - FLexuraL mo du Lus (E) vaLues

[0192] TabLe 5 - Chromium VI content determination

Claims

Claims1. A process for producing a composite granule obtained from a thermoplastic polymer material and a material recovered from the tanning industry, consisting of tanned leather scraps, and usable in the processes for producing objects by injection molding, compression, extrusion, characterized in that said process comprises the following steps :• A step of screening the tanned leather scraps aimed at separating any metal and plastic components from the tanned leather scraps;• A step of pulverizing and drying the leather scraps output from the previous screening step aimed at both obtaining a particle size between 20 pm and 2 mm suitable for incorporating said scraps with the thermoplastic matrix and removing traces of moisture and maintaining the scraps under conditions such as not to allow a hydration thereof, and wherein said pulverization step is carried out in a mill provided with at least one multistage chamber containing a plurality of rotors / stators, up to a maximum of three in number, and provided with a closed cooling circuit which allows working with non-solid materials;• A step of mixing the pulverized and dried scraps with a polyolefin matrix and suitable additives, at least one of which is a stabilizing additive which is used to promote the interfacial adhesion between said thermoplastic matrix and the scraps and at least another one is an antioxidant additive required to prevent the degradation of the basic components;• A step of extruding and granulating the mixture to obtainthe final composite granule, where said extrusion is carried out by means of a co-rotating twin-screw extruder with a temperature ramp from an initial value of 150°C and culminating with a value not exceeding 200°C, to avoid possible degradation of the leather scraps, and wherein the rotation of the screws is between 40 and 600 rpm wherein said polymer matrix consists of polymers from urban postconsumer recycling; and wherein the composite granule obtained has a Cr(VI) level not detectable or in any case lower than 0.025mg / kg .

2. A process according to the preceding claim, characterized in that the thermoplastic polymer material, or the thermoplastic matrix, consists of the following polymers, either pure or mixed : polyethylene (PE) , low density polyethylene (LDPE) , linear low density polyethylene (LLDPE) , very low density polyethylene (VLDPE) , high density polyethylene (HDPE) , polypropylene (PP) , ethylene vinyl acetate (EVA) , poly vinyl alcohol (PVA) , poly lactic acid (PLA) , polyamides (PA) , polyethylene terephthalate (PET) , polystyrene (PS) .

3. A process according to claim 2, characterized in that said thermoplastic matrix consists of polyethylene (PE) , low density polyethylene ( LDPE) , linear low density polyethylene ( LLDPE) , high density polyethylene (HDPE) , and polypropylene (PP) , present in a range of compositions, related to the polyolefin matrix, of 10-98% by weight for polyethylene and of 2-90% by weight for polypropylene, respectively.

4. A process according to claim 1, characterized in that said step of pulverizing the scraps is carried out in a mill provided with a multistage chamber containing 3 to 6 rotating blades and 2 to 5 fixed blades, carrying out several passes with gradually decreasing diameters of the sorting grid holes, respectively:• A first pass with 8 mm grid holes;• A second pass with 4 mm grid holes;• A third pass with 2 mm grid holes, such passes allowing a particle size equal to, and in any case not exceeding 2 mm to be obtained, wherein said pulverized scraps are dried in a forced convection oven at a temperature range of 70-80°C for a time not less than 24 hours so as to avoid the formation of gas bubbles during the extrusion, which lead to the formation of a porous, non- homogeneous and unpleasant-smelling composite, and wherein the dried scraps are kept under vacuum until mixing with the thermoplastic matrix to ensure that the hide does not reabsorb water .

5. A process according to claim 4, characterized in that during the second and third step, an anti-packing additive is added in order to prevent the scraps from compacting .

6. A process according to claim 5, characterized in that said anti-packing additive is l%wt calcium carbonate (CaCO3) .

7. A process according to claim 1, characterized in that said step of pulverizing the scraps is carried out in a mill provided with a multistage chamber with at least two passages and containing from 6 to 9 rotating blades and from 5 to 8 fixed blades, corresponding to 25-40 blades, saidgrinding occurring in several successive steps to obtain particle sizes less than 2 mm, respectively :• A first coarse grinding step in which the hide waste, previously cleaned of unwanted components, is subjected to grinding by means of appropriate mills aimed at reducing the size of the scraps in a range of 8-12 mm;• A step of heat treating the scraps from the previous coarse grinding step, in which the coarsely ground product undergoes a heat treatment in an autoclave at a temperature between 110° and 140°C for a time interval of 6-24 hr;• A second fine wet grinding step, in which the product output from the previous heat treatment step and having a moisture content in a range of 20-50% by weight is reduced in size by passing in a multistage rotor / stator;• A drying step in which the pulverized product output from the previous fine grinding step is dried in a disc dryer under weak vacuum at a temperature of 110-130°C;• A final screening step adapted to make the particle size of the pulverized hide scraps homogeneous .

8. A process according to claim 7, characterized in that in said first coarse grinding step, anti-packing agents are added in a concentration range of 0-0.5% by weight .

9. A process according to claim 7, characterized in that in said heat treatment step, alkalis are added in a concentration of 1-8% by weight .

10. A process according to claim 7, characterized in that in said heat treatment step, antioxidants are added in a concentration of 0.05-0.2% by weight .

11. A process according to claim 1, characterized in that said mixing step is carried out cold by mechanicallymixing the granule forming the thermoplastic matrix with the pulverized hide .

12. A process according to claim 1, characterized in that said mixing step is carried out by adding the hide to a flow of molten thermoplastic polymer .

13. A process according to one or more of the preceding claims, characterized in that in said step of mixing said dried scraps with the polyolefin matrix, in a weight percentage range of 50-90% for the polyolefin matrix and of 5-20% for the scraps, respectively, at least one stabilizing additive, which is used to promote the interfacial adhesion between said thermoplastic matrix and the hide scraps, and at least one antioxidant additive, required to prevent the degradation of the basic components, are added .

14. A process according to claim 13, characterized in that said stabilizing additive is added in an amount range of 1-5% by weight, preferably of 2%.

15. A process according to claim 14, characterized in that said stabilizing additive is silane-based .

16. A process according to claim 14, characterized in that said stabilizing additive is maleic anhydride-based .

17. A process according to claim 13, characterized in that said antioxidant additive is added in an amount range of 1-5% by weight, preferably of 2%.

18. A process according to claim 17, characterized in that said antioxidant additive is phosphite-based .

19. A process according to claim 17, characterized in that said antioxidant additive is phenol-based .

20. A process according to one or more of the preceding claims, characterized in that during the step ofmixing the dried scraps with the polyolefin matrix, the stabilizing additive, and the antioxidant additive, a mineral filler is added in the range of 0-50%, preferably of 30%, said mineral filler being such as to modulate the final mechanical properties of the granule .

21. A process according to claim 20, characterized in that said mineral fillers are selectable from calcium carbonate (CaCO3) , phyllosilicates such as talc and mica, kaolin, dolomite, wollastonite, fiberglass, added as a powder or carried within polymers compatible with the starting thermoplastic matrix .

22. A process according to one or more of the preceding claims, characterized in that during the step of mixing the dried scraps with the thermoplastic matrix, the stabilizing additive, and the antioxidant additive, a drying additive is added, carried within polymers compatible with the starting thermoplastic matrix, based on calcium oxide (CaO) in a range of 0-6% by weight, preferably of 4%.

23. A process according to one or more of the preceding claims, characterized in that during the step of mixing the dried scraps with the polyolefin matrix, the stabilizing additive, and the antioxidant additive, an antiodor additive is added, as a powder or carried within polymers compatible with the starting thermoplastic matrix, based on zinc salts, zinc oxide (ZnO) , activated carbon in a range of 0-5% by weight, preferably of 1%.

24. A composite granule usable for producing objects by injection molding, compression and extrusion, characterized in that it is produced with the process according to claims 1 to 23, said granule consisting of both polyolefin polymer material and material recovered from thetanning industry, consisting of tanned leather scraps, and wherein said leather scraps are incorporated in the polyolefin structure allowing substantially homogeneous chemical-physical features to be achieved .

25. A granule according to claim 24, characterized in that it has an average value of the flexural modulus (E) of the Releather granule equal to 1576 MPa .

Images