Process for the recovery of polyurethane from waste soles

Abstract

The process for the recovery of polyurethane from waste soles comprises at least the following phases: - supplying at least one waste sole (2) made at least partly of polyurethane; - reducing the waste sole (2) into fragments (3) of less than 10 mm in size; - grinding the fragments (3) to obtain a polyurethane powder (1) having a predefined particle size of less than 500 μm.

Description

[0001] PROCESS FOR THE RECOVERY OF POLYURETHANE FROM

[0002] WASTE SOLES

[0003] Technical Field

[0004] The present invention relates to a process for the recovery of polyurethane from waste soles.

[0005] Background Art

[0006] With special reference to sports and / or casual shoes of the sneaker type, the use of soles is widespread mainly made of polyurethane (PU) and produced, from such material, by plastic deformation (e.g. injection) or molding processes.

[0007] Regardless of the technological process, it is well known that before each sole produced can be placed on the market, it must be inspected by means of the quality control, i.e. subjected to deep analysis aimed at tracing any defects that may jeopardize the functionality and / or appearance thereof.

[0008] In this regard, only one part of the manufactured soles, that is, those having such characteristics as to make them pass the various controls and inspections, can be introduced into the market and duly marketed, while the remaining part, as differing from the pre-set quality requirements, must necessarily be discarded.

[0009] The latter soles are, nowadays, sent as industrial waste to special disposal sites, where they undergo various treatment processes allowing the raw materials thereof to be at least partly recovered.

[0010] It is clear, however, that this fact results in wasting huge amounts of resources for companies in the sector which, having to discard the soles unsuitable for trade, find themselves forced to deprive themselves entirely of the materials that constitute them.

[0011] To understand the entity of this problem, one must consider the fact that the amount of annually discarded soles comes to exceed, in some industrial contexts, values of more than 180 tons by weight; bearing this in mind, it is not difficult to appreciate that the current management of discarded soles represents a heavy source of expense that severely penalizes the budgets of the aforementioned companies.

[0012] What is more, it is worth considering that the high production of waste material stands in stark contradiction to the increasingly stringent regulations governing the amount of waste from industrial processing and its subsequent release into the environment.

[0013] In other words, the management of soles deemed inappropriate for marketing, now produces a large number of environmental pollutants that makes it completely unsustainable not only from the economic, but also environmentfriendly point of view.

[0014] Description of the Invention

[0015] The main aim of the present invention is to devise a process for the recovery of polyurethane from waste soles which enables the recovery of polyurethane in waste soles and, therefore, to cut down material waste and the associated costs compared with the aforementioned state of the art.

[0016] Within the aforementioned main aim, one object of the present invention is to devise a process for the recovery of polyurethane from waste soles wherein such material thus recovered may be effectively used in the production of other soles, that is, without its use resulting in any alteration of the mechanical and technicalaesthetic characteristics of the latter.

[0017] It is another object of the present invention to devise a process for the recovery of polyurethane from waste soles which is environmentally sustainable and with low impact for the environment.

[0018] Another object of the present invention is to devise a process for the recovery of polyurethane from waste soles which allows the aforementioned drawbacks of the prior art to be overcome within the framework of a simple, rational, easy and effective to use as well as affordable solution.

[0019] The aforementioned objects are achieved by this process for the recovery of polyurethane from waste soles having the characteristics of claim 1.

[0020] Brief Description of the Drawings

[0021] Other characteristics and advantages of the present invention will become more apparent from the description of a preferred, but not exclusive, embodiment of a process for the recovery of polyurethane from waste soles, illustrated by way of an indicative, yet non-limiting example, in the accompanying tables of drawings in which:

[0022] Figure 1 shows the reduction and grinding phases of the process according to the invention;

[0023] Figure 2 shows a sole produced with the powder obtained from the process according to the invention.

[0024] Embodiments of the Invention

[0025] With particular reference to these figures, reference numeral 1 globally denotes a polyurethane powder obtained by means of the process according to the invention.

[0026] The process for the recovery of polyurethane from waste soles comprises at least the following phases: supplying at least one waste sole 2 made at least partly of polyurethane; reducing the waste sole 2 into fragments 3 of less than 10 mm in size; grinding the fragments 3 to obtain a polyurethane powder 1 having a predefined particle size of less than 500 pm.

[0027] Specifically, the phase of reducing the waste sole 2 into fragments 3 first of all comprises at least one step of first reduction, wherein the waste sole 2 is coarsely shredded into a plurality of shreds.

[0028] This step is preferably carried out by means of shredding means 4, schematically shown in Figure 1.

[0029] For example, the shredding means 4 are of the type of knife mills or similar devices.

[0030] The reduction then comprises at least one step of second reduction of the waste sole 2 which is carried out subsequently to the first reduction and adapted to obtain the fragments 3 starting from the aforementioned shreds.

[0031] The second reduction occurs, conveniently, using a fine-mesh grinder, not shown in the figures.

[0032] In particular, the meshes of the fine grinder have a size so as to reduce the size of the shreds until fragments 3 of the desired grain size are obtained.

[0033] In this regard, the fragments 3 thus obtained have a size of between 2 mm and 7 mm, better still of between 3 mm and 6 mm, preferably of between 4 mm and 5 mm.

[0034] In fact, this size allows the fragments 3 to be effectively ground into the subsequent grinding phase so as to obtain the aforementioned polyurethane powder 1.

[0035] In this regard, grinding comprises at least one step of micronization of the fragments 3, wherein the latter are pulverized to the aforementioned predefined particle size.

[0036] In this regard, the predefined particle size is, precisely, of between 160 pm and 240 pm.

[0037] More precisely, the predefined particle size is of between 160 pm and 200 pm. Conveniently, micronization is carried out at a temperature above -180 °C.

[0038] Preferably, micronization is carried out at a temperature of between -180 °C and -160 °C.

[0039] Such temperatures allow, in fact, greatly increasing the structural fragility of the fragments 3 and make, thus, the grinding of the latter very smooth and effective. Conveniently, micronization comprises at least one sub-step of injection of at least one inert working fluid F adapted to interact with the fragments 3 to reduce them into powder 1.

[0040] Preferably, the injected working fluid F comprises nitrogen.

[0041] More preferably, the working fluid F consists of nitrogen.

[0042] Being, in fact, an inert, non-toxic fluid which is lighter than air, the use of nitrogen is particularly convenient for reducing the fragments 3 into powder 1.

[0043] It cannot, however, be ruled out that the working fluid F may be different from the preferred one just outlined and may, e.g., comprise compressed air and / or another fluid still known to the expert in the field that would, in any case, allow the fragments 3 to be structurally embrittled so that they can be properly ground. Conveniently, micronization comprises at least the following sub-steps: preparing at least one micronizing device 5 provided with at least one grinding chamber 5 a; loading the fragments 3 into the grinding chamber 5 a.

[0044] In this regard, the sub-step of injection is carried out by insufflating the aforementioned working fluid F into the micronizing device 5, e.g., directly into the grinding chamber 5 a or through one or more ducts conveying it to the latter (as schematically shown in Figure 1).

[0045] Specifically, the working fluid F is stored into the micronizing device 5 in the liquid phase at -196°C (at atmospheric pressure).

[0046] In this regard, the sub-step of injection can be carried out after the preparing substep and before the loading one, or it can be carried out after the latter.

[0047] In other words, the injection of the working fluid F can occur indifferently either before or after loading the fragments 3 into the grinding chamber 5 a.

[0048] In all cases, as already anticipated, the interaction between the working fluid F and the fragments 3 allows obtaining a polyurethane powder 1 having the aforementioned predefined particle size.

[0049] In this regard and according to another aspect of the invention, the present invention also relates to a polyurethane powder 1 obtainable by the process just described.

[0050] The powder 1 in question is thus obtainable starting from a sole made at least partly of polyurethane, e.g., from a waste sole, by reduction of the same into fragments 3 and by subsequent micronization of the same.

[0051] The powder 1 thus obtained can, therefore, be used in a multitude of different technical purposes and uses among which making additional shoe soles.

[0052] In this regard, and according to a further aspect of the invention, the present invention also relates to the use of polyurethane powder 1 obtained from the previously disclosed process for the production of soles 6 of shoes.

[0053] In this regard, the powder 1 obtained from waste soles 2 can be profitably used as a constituent element in the production of new soles 6 of shoes, thus leading to significant economic savings about the purchase of new material.

[0054] By doing so, i.e., by reusing waste material otherwise intended for landfill, it is clearly possible to drastically reduce the production of industrial waste and, at the same time, align more closely with today’s environmental sustainability goals than the aforementioned state of the art.

[0055] In this regard, it is important to explain the fact that the aesthetic-mechanical properties of the soles 6 obtained by using the powder 1 as a constituent material (and specifically providing for it in percentages ranging from 15% to 40% of the total polyurethane) are substantially the same as those obtained by using only virgin polyurethane.

[0056] Specifically, it was observed that the color change undergone as a result of accelerated aging was substantially similar between the two types of soles and, more specifically of minimal entity in the case of a 48 ± 2-hour exposure period of the soles.

[0057] Similarly, the flexural strength of the sole 6 obtained by means of the powder 1 shows no change as a result of accelerated aging for that exposure period.

[0058] Specifically, following this treatment, the flexural strength of the sole 6 obtained by means of the powder 1 has a value which is comparable to that of a sole made entirely from virgin polyurethane.

[0059] Abrasion resistance is also found to be substantially similar between the two types of soles.

[0060] Specifically, in the case of a sole produced by means of the powder 1, the length of the abraded sole, calculated in accordance with the dictates of the GB / T 3903.2 standard, is of between 9 mm and 12 mm.

[0061] As far as Shore hardness is concerned, the values of the soles 6 are quite comparable to those of the soles obtained by means of only virgin polyurethane; therefore, this parameter is also substantially invariable to the use of the powder 1 as a basic component in the production of the soles themselves.

[0062] It has in practice been ascertained that the described invention achieves the intended objects.

[0063] In particular, the fact is emphasized that the special expedient of providing for a phase of reducing a sole into fragments followed by a phase of grinding them by micronization makes it possible to obtain polyurethane powder having particle size and chemical-physical properties such that it is reusable for the production of additional shoe soles, thus lowering the waste of material and the amount of generated industrial waste compared to the aforementioned prior art.

Claims

CLAIMS1) Process for the recovery of polyurethane from waste soles, characterized by the fact that it comprises at least the following phases: supplying at least one waste sole (2) made at least partly of polyurethane; reducing said waste sole (2) into fragments (3) of less than 10 mm in size; grinding said fragments (3) to obtain a polyurethane powder (1) having a predefined particle size of less than 500 pm.2) Process according to claim 1, characterized by the fact that said grinding comprises at least one step of micronization of said fragments (3) at a temperature above -180 °C.3) Process according to claim 2, characterized by the fact that said micronization comprises at least one sub-step of injection of at least one inert working fluid (F).4) Process according to claim 3, characterized by the fact that said working fluid (F) comprises nitrogen.5) Process according to one or more of the preceding claims, characterized by the fact that said predefined particle size is between 160 pm and 240 pm.6) Process according to one or more of claims 2 to 5, characterized by the fact that said micronization comprises at least the following sub-steps: preparing at least one micronizing device (5) provided with at least one grinding chamber (5 a); loading said fragments (3) into said grinding chamber (5 a).7) Process according to one or more of the preceding claims, characterized by the fact that said fragments (3) have a size of between 2 mm and 7 mm.8) Polyurethane powder (1) obtainable from the process according to one or more of the preceding claims.9) Use of the powder (1) according to claim 8 for the production of soles (6) for shoes.

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