Efficient process for recycling thermosetting foam material.

Abstract

The present disclosure relates to an efficient process for recycling thermosetting foam material, e.g. from shoe soles, in order to provide a general circular and sustainable process concerning consumer goods comprising thermosetting foam materials.

Description

[0001] EFFICIENT PROCESS FOR RECYCLING THERMOSETTING FOAM MATERIAL.

[0002] DESCRIPTION

[0003] Technical field

[0004] The present invention falls within the field of industrial processes relating to the recycling of materials, in particular thermosetting materials, more particularly thermosetting foam materials, such as, for example, those of certain types of shoe soles.

[0005] State of the art

[0006] In today’s modern world, there is a great need for sustainable industrial processes and materials, i.e. those that result in minimal impact on the environment and the resources around us. In order to promote and steer the existing processes and technologies towards sustainability and respect for the environment and, in particular, towards eco-sustainability, according to the recent principles of ESG (Environmental, Social, Governance), nowadays there is much talk of the circular economy, i.e., configuring processes so that, with their circularity, they have no impact or a more limited impact on the environment and the resources drawn therefrom with respect to the past.

[0007] The concept of the circular economy becomes particularly important when it relates to industrial technologies concerning the production of materials that are in the first instance non-recyclable, such as those generated by three- dimensional polymerisation, i.e. the generation of three-dimensional cross-links between different linear polymer chains, or those relating to the vulcanisation of rubber. The result of these productions are thermosetting materials, i.e. materials that have hardened through heating and can no longer return to a molten or liquid state through heating, as thermoplastics do, and thus remain solids. It is therefore particularly difficult to recycle these cross-linked materials, such as car tyres, which are made of vulcanised rubber.

[0008] Equally difficult are the recycling of thermosetting foam materials such as, for example, shoe soles, which are typically disposed of only by incineration, thus not giving rise to any circular process and thus being considered no longer sustainable processes in the modern era.

[0009] In addition, there is now a desire to transform thermosetting materials such as those based on cross-linked polymers into thermoplastic materials, i.e. materials that can be liquefied by heat. Summary of the invention

[0010] The problem addressed by the present invention is therefore to make available a process for the recycling of thermosetting foam material for the preparation of a thermoplastic material.

[0011] Therefore, the present invention solves the aforementioned problem by means of a process for preparing a thermoplastic material by recycling thermoset foam material.

[0012] Further features and advantages of the present invention will result from the description of some examples of embodiments, provided as an indication of the invention itself.

[0013] Detailed description of the invention

[0014] For the purposes of the description of the present document, the term “and / or”, when used in a list of two or more items, means that any one of the listed items may be used alone, or in any combination of two or more of the listed items.

[0015] For example, if a combination is described as containing components A, B and / or C, or, A and / or B and / or C, the composition can contain only A; only B; only C; A and B in combination; A and C in combination; B and C in combination; or A, B and C in combination.

[0016] The terms “comprises”, “comprising” or any other variation thereof are intended to cover a non-exclusive inclusion such that a process, method, use, etc. which comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent in such a process, method, use, etc.

[0017] An element followed by “comprises a...” does not preclude, without further constraints, the existence of further identical elements in the process or use comprising the element.

[0018] An object of the present invention is therefore a process for preparing a thermoplastic material by recycling thermosetting foam material comprising the following steps: a) coarsely grinding and then reducing the thermosetting foam material for recycling to powder with a particle size of less than 10 mm, b) mixing the powdered material from step a) with a quantity of thermoplastic virgin resin, where said quantity of resin is such that the thermoplastic material obtained at the end of step c) comprises 1% to 90% by weight of thermosetting foam material powder from step a), c) adding wetting and / or dispersing and / or compatibilising additives to the mixture from step b), d) extruding the mixture from step c) by means of a twin-screw extruder and, while mixing in the extruder, simultaneously degassing the mixture, e) granulating said mixture using a granulator, and granulating said mixture using a granulator, and cooling.

[0019] It was, in fact, surprisingly found that the aforementioned process allows thermosetting foam material to be efficiently recycled by converting it into a recycled material that preserves the characteristics of a thermoplastic material, such as a compound, which can then be used for the production of new items.

[0020] In particular, it should be noted that the fact of pulverising, not a simple thermosetting material, but a thermosetting foam material, implies that the particles of thermosetting material are unevenly shaped and have cavities, which greatly increases the contact surface between thermosetting solid and thermoplastic resin. The use of a thermosetting foam material in the above- mentioned process thus allows for intimate mixing between the thermosetting material and the thermoplastic virgin resin. This implies the creation of intimate contact between the two phases and this contact takes place over a much larger surface area, as the surface area of the thermosetting foam material is much larger than that of a non-expanded thermosetting material. Thus, the improved contact between the two phases and the increased extension of said contact are responsible for the improved mechanical properties of the thermoplastic material produced by this process, which are significantly higher than those of processes using non-expanded thermoset materials.

[0021] In fact, the product obtainable from the process described above, when used together with a first-rate product (and sometimes even used as such), after re-curing generates items very similar to those made using only a first-rate product.

[0022] As the powder particles of thermosetting foam material originate from a foam material, they are very unevenly shaped and therefore when well dispersed by the twin-screw extruder have very good adhesion to the polymer matrix, thus generating mechanical properties of the finished thermoplastic material that are very similar to the first-rate product.

[0023] Furthermore, in addition to using a foam material, this process includes a degassing phase during processing in the extruder. In fact, together with the use of foam material, this phase is also responsible for the increased adhesion or more intimate contact between the thermosetting material phase and the thermoplastic resin. In fact, degassing removes air bubbles present on the thermosetting material by increasing the contact surface with the thermoplastic material.

[0024] Therefore, to produce products of improved quality, it is essential that there is intimate contact between thermosetting material and the thermoplastic material. For this to happen, it is essential to use a thermosetting foam material and that degassing of the mixture takes place during the extrusion phase.

[0025] It must also be emphasised that thermosetting foam material can be based on Ethylene Vinyl Acetate (EVA), Polyethylene (PE) and TPU polyurethane, which cannot be recycled as such as it has a tyre-like consistency and would therefore be destined for landfill or combustion.

[0026] The problem with recycling these materials is that, when used as such, they tend to result in agglomerates, so further mixtures produced from these materials are non-homogeneous. This additional problem is effectively solved by the process of the present invention.

[0027] The term thermoplastic material means a material of a polymeric nature that, at a certain temperature, passes from the solid phase to the liquid phase or fluid phase (before undergoing degradation). In its fluid state, thermoplastic material can be processed by normal transformation processes such as extrusion, injection moulding, compression moulding, blow moulding, etc.

[0028] The term thermosetting material means that the plastic material has undergone a cross-linking and / or curing process during the final processing, which makes it impossible to melt. In fact, in the chemical state, the cross-linking process generates three-dimensional bonds between the polymer molecules, locking them in a state that no longer allows the molecules to slide relative to each other. Even when the temperature is raised, this polymer will not become more fluid but will simply degrade.

[0029] The term foam means that, during the last transformation process, gas was introduced to the polymer material (typically nitrogen, carbon dioxide, etc.) that has generated more or less dense air bubbles in the polymer which create a lightening of the molten material, first, and of the solid material, after, subsequent to cooling.

[0030] The solid foam material obtained will therefore be of a more or less spongy consistency and of a lower density than the non-expanded, hence compact, material.

[0031] The introduction of gas can take place by chemical methods (by adding additives that degrade at a certain temperature) or by physical methods (e.g. by injecting gas during the mixing phase of the polymer melt in an extruder).

[0032] Therefore, a thermosetting foam material is a thermosetting material containing gas, such as carbon dioxide and / or nitrogen, within it.

[0033] In addition, a thermosetting foam material is a thermosetting material comprising bubbles within it to contain gas, such as carbon dioxide and / or nitrogen.

[0034] The thermosetting foam material comprises a multitude or plurality of bubbles within it.

[0035] The thermosetting foam material has a density comprised between 30 and 800 kg per cubic metre.

[0036] Preferably, the thermosetting foam material has a density comprised between 35 and 400 kg per cubic metre, more preferably between 100 and 400 kg per cubic metre.

[0037] The above density values express the degrees of expansion of the thermosetting foam material.

[0038] If the thermoset foam material is a sole for a shoe, the lower its density, the higher the performance of the product obtainable from the process of the invention.

[0039] The particle size of the thermosetting foam material in step a) is less than 10 mm, which means that, if one of the largest particles is taken from one end to the other, the length is 10 mm.

[0040] Preferably, the particle size of the thermosetting foam material from step a) is less than 5 mm, more preferably the size is less than 2 mm or between 0.1 mm and 2 mm.

[0041] Preferably, the average particle size of the thermosetting foam material from step a) is less than 2 mm or between 0.1 mm and 2 mm. Average size means the size calculated as the average of the particle sizes.

[0042] Steps b) and c) are carried out at a temperature comprised between 20°C and 60°C, preferably between 20°C and 30°C.

[0043] Steps b) and c) are preferably carried out at room temperature.

[0044] Steps b) and c) are carried out “dry”. The extrusion step d) is carried out at temperatures comprised between 130°C and 260°C, preferably between 130° and 240°C.

[0045] During the extrusion step d), the degassing / stripping of the mixture is carried out to remove gas bubbles.

[0046] The degassing in step d) is typically carried out operating at residual pressures in the range of 0.1 to 0.4 bar, although different processes of degrees of vacuum only affect the timing of the degassing, which is considered to be completed when no more bubble evolution is observed from the molten mixture.

[0047] Recycled thermosetting foam material could be polyethylene vinyl acetate (EVA) based, polyethylene (PE) based and thermosetting polyurethane (TPU) based and mixtures thereof.

[0048] It is preferable to use only one type of thermoset foam material rather than using mixtures of different materials.

[0049] Preferably, thermoplastic virgin resin has the same polymeric nature as the recycled thermosetting foam material, so an EVA-based thermosetting foam material will preferably be mixed with EVA thermoplastic virgin resin, a recycled PE-based thermosetting foam material will preferably be mixed on PE thermoplastic material, and a recycled TPU material will preferably be mixed on TPU thermoplastic material, but all combinations will be possible.

[0050] The composition of the mix will be made with a weight % of thermosetting foam material comprised between 1 % and 90%.

[0051] The mixture from step b) comprises 1 % to 90% by weight of thermosetting foam material powder from step a).

[0052] In step b) the powdered material from step a) is mixed with a quantity of thermoplastic virgin resin, where said quantity of resin is such that the thermoplastic material obtained at the end of step c) comprises 1 % to 90% by weight of thermosetting foam material powder from step a).

[0053] Preferably, the amount of thermoplastic virgin resin is such that thermoplastic material is obtained that comprises 30% to 75% by weight of thermosetting foam material powder from step a), more preferably 40% to 60% by weight.

[0054] The term virgin means that it is a resin produced by the manufacturer and not already used and therefore recycled, but any resin that is thermoplastic (even if not first-rate) can be used to be mixed with the thermosetting recycled material. The thermoplastic virgin resin may be polyethylene vinyl acetate, polyethylene, or polyethylene or thermoplastic TPU.

[0055] In step c), wetting and / or dispersing and / or compatibilising additives are added to the mixture from step b).

[0056] The dispersing additives from step c) may be polyethylene or natural waxes, gms and stearic acid derivatives, more generally triglycerides, etc.

[0057] Maleised polymers such as polypropylene (pp), polyethylene (pe), polyethylene vinyl acetate (eva) or polymers containing acrylic acid or acrylates such as EMA, EBA, MBS, etc. can be used as compatibilising additives.

[0058] The aforesaid additives help and improve the firmness and processability of the thermoplastic material obtained from this process.

[0059] According to a preferred embodiment, the recycled thermosetting foam material is part of shoe soles or defective shoe soles.

[0060] In particular, soles with defects are typically discarded and taken to landfill for disposal, whereas the present recovery process proposes to recover the material from such defective soles.

[0061] Preferably, the amount of thermoplastic virgin resin from step b) is such that the thermoplastic material obtained at the end of step c) comprises 40% to 60% by weight of thermosetting foam material powder from step a).

[0062] In step d) the screws of the twin-screw extruder rotate at a speed comprised between 50 and 900 rpm. Preferably, said twin-screws rotate at a speed comprised between 300 and 500 rpm.

[0063] In fact, it has been found that operating in this speed range ensures optimal dispersion of the powder and optimal degassing or stripping of the material obtained, therefore without the presence of residual air bubbles inside, which would compromise the mechanical characteristics of the material.

[0064] It is in fact important that the irregular particles resulting from the pulverisation of the thermosetting material from step a) are, in step d), in intimate contact with the thermoplastic resin and therefore all the gas bubbles still present must be stripped from the mixture.

[0065] At the end of step d) the product is extruded.

[0066] In step e), the mixture from step d) is granulated using a granulator. The granulator can be an integral part of the extruder. Once the product is granulated, it is then cooled. This results in a product in granule form, ready to be reused in new processes.

[0067] In this case, the resulting granule is ready for use in a mix or on its own as a virgin product for reuse in the same initial production process.

Claims

CLAIMS1 ) Process for the preparation of a thermoplastic material by recycling thermosetting foam material comprising the following steps: a) coarsely grinding and then reducing the thermosetting foam material for recycling to powder with a particle size of less than 10 mm, b) mixing the powdered material from step a) with a quantity of thermoplastic virgin resin, where said quantity of resin is such that the thermoplastic material obtained at the end of step c) comprises 1 % to 90% by weight of thermosetting foam material powder from step a), c) adding wetting and / or dispersing and / or compatibilising additives to the mixture from step b), d) extruding the mixture from step c) by means of a twin-screw extruder and, while mixing in the extruder, simultaneously degassing the mixture, e) granulating said mixture using a granulator and cooling.2) Process according to claim 1 , wherein the thermosetting foam material from step a) has a density comprised between 30 and 800 kg per cubic metre, or between 35 and 400 kg per cubic metre, or between 100 and 400 kg per cubic metre.3) Process according to any one of claims 1 to 2, wherein step d) is carried out under vacuum at a residual pressure of 0.1 to 0.4 bar.4) Process according to any one of claims 1 to 3, wherein the recycled thermosetting foam material is polyethylene vinyl acetate-based or polyethylene-based, and comprises further components to impart thermosetting to said foam material.5) Process according to any one of claims 1 to 4, wherein in step a) the thermosetting foam material powder has a particle size of less than 2 mm or comprised between 0.1 mm and 2 mm.6) Process according to any one of claims 1 to 4, wherein the average particle size of the thermosetting foam material of step a) is less than 2 mm or is comprised between 0.1 mm and 2 mm.7) Process according to any one of claims 1 to 6, wherein the dispersing and compatibilising additives from step c) are selected from polyethylene or natural waxes, gms and stearic acid derivatives, more generally triglycerides, malicised polymers such as polypropylene, polyethylene, polyethylene vinyl acetate, or polymers containing acrylic acid or acrylates such as EMA, EBA,MBS.8) Process according to any one of claims 1 to 7, wherein the recycled thermosetting foam material is part of the shoe soles or defective shoe soles.9) Process according to any one of claims 1 to 8, wherein the amount of thermoplastic virgin resin from step b) is such that the thermoplastic material obtained at the end of step c) comprises 40% to 60% by weight of thermosetting foam material powder from step a).10) Process according to any one of claims 1 to 9, wherein in step b) the twin-screws of the extruder rotate at a speed comprised between 50 and 900 rpm or between 300 and 500 rpm.11 ) Thermoplastic material obtainable by the process of any one of claims 1 to 10.