Process for modifying rigid thermosetting polyurethane

Abstract

A method for modifying rigid thermosetting polyurethane (A), the method comprising the following steps: a) providing a solution comprising a solvent (S) and an activation molecule (B) intended to activate exchange reactions of said polyurethane (A), the at least one activation molecule (B) comprising a grafting function and an activation function, b) adding particles of said polyurethane (A) to said solution, c) applying a first heat treatment to reach a temperature higher than that of glass transition of said polyurethane (A) so as to impregnate said polyurethane (A) with the at least one activation molecule (B), d) evaporating the solvent (S) so as to obtain particles of said impregnated polyurethane (Ai) with the at least one activation molecule (B), e) applying a second heat treatment to the particles of impregnated polyurethane (Ai) so as to graft, by formation of a covalent bond,the activation function of the at least one activation molecule (B) to said impregnated polyurethane (Ai) and to obtain a modified polyurethane powder (A'). Figure 1,

Description

Title of the invention: Method for modifying rigid thermosetting polyurethane

[0001] The present invention relates to the field of post-treatment of rigid thermosetting polyurethanes. In particular, the invention relates to a method for modifying rigid thermosetting polyurethane and a method for reshaping the latter. According to another aspect, the invention relates to a modified polyurethane making it possible to facilitate the exchange reactions of dynamic covalent bonds and its post-treatment.

[0002] Rigid thermosetting polyurethanes are used in many applications requiring physical and chemical robustness, as well as heat resistance, such as building insulation, interior trim for vehicles or body parts, sporting goods, etc. In the form of foams or solid parts, this material is generally obtained from the polymerization of polyols and isocyanates. Polymerization is generally carried out by mixing the two monomers which react in a mold to give the final shape to the part.

[0003] The shaping of this material depends greatly on the final application. Since the polymerization of polyols and isocyanates naturally generates CO2 in the presence of water, this polymer is particularly suitable for the manufacture of foams. It is possible to obtain non-foamed structures with particular attention paid to the quantity of water during the process.

[0004] Due to the nature of the monomers used in their manufacture, polyurethanes are generally crosslinked, that is to say that the final thermosetting polymer material (therefore not plastic) is in the form of a network of interconnected chains. This gives polyurethanes their chemical and thermal resistance. However, this advantage becomes a disadvantage when recovering this material at its end of life. Unlike thermoplastic polymers (PE, PP, PET, etc.) which can be melted, thermosets and in particular thermosetting polyurethanes are infusible and insoluble, which prevents their reuse in other forms. The solutions existing today for managing PUs at the end of their life, or production waste, are landfill, incineration and the use of the material as a filler in new parts.The last option limits the range of reuse of the material as well as the performance of the objects thus produced.

[0005] A known reshaping method uses reaction exchange activators, taking advantage of the dynamic and covalent chemical bonds of the polyurethane as indicated below:

[0006] [Chem.l] At C $

[0007] However, this method is limited to the dissolution of activators in the polymer matrix, such as organometallic compounds or organic acids and bases, and does not offer a sustainable solution in the treatment of polyurethanes at the end of their life. Indeed, over time and depending on the intended applications, the activators migrate out of the matrix more or less quickly. Given the large number of everyday objects or industrial products that contain rigid polyurethane, it is necessary to find solutions allowing its reuse, in particular through reshaping.

[0008] Thus, one of the aims of the present invention is to overcome the aforementioned drawbacks. To this end, the invention proposes a method for modifying rigid thermosetting polyurethane so as to activate dynamic chemical exchange reactions of said polyurethane, the method comprising the following steps:

[0009] a) providing a solution comprising a solvent and at least one activation molecule intended to activate said exchange reactions of said polyurethane, the at least one activation molecule comprising a grafting function and an activation function,

[0010] b) adding particles of said polyurethane to said solution so as to obtain a suspension,

[0011] c) applying a first heat treatment to the suspension with stirring to reach a temperature higher than that of the glass transition of said polyurethane so as to impregnate said polyurethane with at least one activation molecule,

[0012] d) evaporation of the solvent so as to obtain particles of said polyurethane impregnated with at least one activation molecule,

[0013] e) applying a second heat treatment to the impregnated polyurethane particles so as to graft, by formation of a covalent bond, the activation function of the at least one activation molecule to said impregnated polyurethane and to obtain a modified polyurethane powder.

[0014] Thus, thanks to the invention, the rigid thermosetting polyurethane is modified by formation of at least one new covalent bond with an activation function capable of lowering the activation energy of the exchange reactions. These allow the rearrangement of the network topology of the modified polyurethane allowing for new shaping. Modification by formation of a covalent bond prevents the activation function from migrating outside the material. This ensures that the modified polyurethane acquires a sustainable reshaping capacity over time while limiting the risk of migration and contact between the activation molecule and users.

[0015] The term 'impregnate' is understood in this document to mean bringing into intimate contact. In other words, the activation molecule penetrates the polyurethane network to be as close as possible to the urethane function so as to facilitate the grafting reaction.

[0016] It can be defined in this document that a polyurethane is rigid when its elongation at break does not exceed 10% and with a breaking stress of at least 100Pa. The application of the tensile test and the values ​​of elongation and breaking stress makes it possible to distinguish a rigid polyurethane from a flexible polyurethane.

[0017] In the case of PU foams, rigid PU foams often have a closed cell structure while flexible foams generally have open cells.

[0018] According to one arrangement, the solution provided in step a) comprises a solvent capable of dissolving the activation molecule and which has a boiling point higher than the glass transition temperature of the polyurethane. Preferably, it has sufficient affinities with the polyurethane to penetrate into the polymer network, and to transport the at least one activation molecule as close as possible to the methane functions. The solvent is chosen from nucleophilic aromatic ethers, such as anisole, 3-methylanisole, ethoxybenzene, dimethoxybiphenyl, 2-methoxynaphthalene, 1.4-dimethoxybenzene or 1.2-dimethoxy benzene.

[0019] According to one possibility, the particles of said polyurethane provided in step b) comprise a micrometric average dimension, for example an average dimension of between 50 and 100 micrometers.

[0020] According to one arrangement, the application of the first heat treatment according to step c) is carried out until a temperature of between 110 and 130°C is reached, for example a temperature of approximately 130°C. These temperatures are in fact above the glass transition temperature of the polyurethane.

[0021] According to one possibility, step d) consists of drying the particles, for example in a rotary evaporator or in a vacuum oven. Drying ensures intimate contact between the activation molecules and the polyurethane. According to one possibility, the solvent evaporation conditions are chosen to ensure that the activation molecule is not evaporated with the solvent. A simple weighing after step d) confirms that the mass of the polyurethane combined with that of the activation molecule is indeed found at the end of step d).

[0022] According to one possibility, the application of the second heat treatment according to step e) further comprises the application of pressure so as to carry out thermocompression e') on the modified polyurethane powder. The application of pressure is intended to reduce the duration of step e) and / or to reduce the temperature of the second heat treatment. This embodiment requires the use of a pressure application device but it makes it possible to limit the risks of loss of the properties of the polyurethane which could occur after a stronger and / or longer heat treatment than that required for thermocompression.

[0023] According to one arrangement, prior to the thermocompression step e'), the method comprises carrying out a step i) of arranging the impregnated polyurethane particles in a mold delimiting a cavity of a determined shape, so as to obtain a solid part made of modified polyurethane of the determined shape at the end of the method. Indeed, thermocompression carried out on the modified polyurethane powder, placed in a mold, makes it possible to obtain the coalescence of the grains of the powder and its conformation according to the shape of the mold. Once returned to room temperature, the new part obtained has the mechanical properties of the original thermosetting polyurethane.

[0024] According to one characteristic, the solid part made of modified polyurethane obtained according to the process is a massive part. The viscosity of the polyurethane is not low enough to allow foaming to be carried out by reaction of water on the isocyanate groups. Thus, the reshaping of the modified polyurethane makes it possible to form massive, non-foamed parts.

[0025] According to one possibility, the grafting function of the at least one activation molecule, intended for the formation of a covalent bond with the polyurethane, is a nucleophilic function, in particular an alcohol function or a primary or secondary amine function.

[0026] According to one arrangement, the activating function is a sulfonic acid or a tertiary amine. The sulfonic acid may comprise an aromatic chain or an aliphatic chain. In both cases, the acidic or basic nature of the activating function destabilizes the urethane, which causes it to open, and the formation of an alcohol and an isocyanate.

[0027] According to one possibility, the at least one activation molecule is chosen from: - a sulfonic acid carrying alcohol or amine functions, of general formula R-(SO3H)x-(OH)y(NH2)z where R is a carbon radical which can be aromatic or aliphatic, x is the number of sulfonic acids (x>=1), y the number of hydroxyl groups (y>=1) and z the number of amine groups primary or secondary (z>=l) and in particular 4-hydroxy-3-amino-benzenesulfonic acid, and / or - a tertiary amine carrying one or more alcohols, of general formula Nm-(R'OHn)o with R' a carbon radical (m>=l) (o>=l) carrying one or more hydroxyl functions (n>=l) and in particular tetrahydroxyethylethylenediamine.

[0028] According to one arrangement, the mass percentage of activation molecules in the suspension is in a range from 0.05% to 10% by mass, and in particular in a range between approximately 0.1 and 5% by mass.

[0029] According to one possibility, the thermocompression step e') is carried out in a temperature range from 120°C to 250°C and a pressure of between 30 and 70 bars for a duration of from 1 min to 40 min, in particular at 200°C under a pressure of approximately 40 bars applied for 20 min.

[0030] According to other characteristics, the method according to the invention comprises one or more of the following optional characteristics considered alone or in combination:

[0031] - The modification method comprises, before step b), a step k) of putting into powder of at least one piece of thermosetting and rigid polyurethane, in particular by grinding or by micronization.

[0032] - The rigid thermosetting polyurethane part used in step k) is present in the form of foam.

[0033] - The first heat treatment is carried out for one hour.

[0034] - Step d) of evaporation of the solvent can be completed by arranging the particles impregnated with heat treatment under reduced pressure, under pressure and temperature conditions that do not allow the activator to evaporate. In particular, heat treatment at a maximum temperature of 140°C and a pressure of 10 mbar.

[0035] According to another aspect, the invention provides a method for reshaping modified polyurethane parts comprising the steps of:

[0036] g) providing at least one part made of modified polyurethane obtained as previously described,

[0037] h) powdering of Water less a piece of modified polyurethane,

[0038] i) arrangement of the powder in at least one mold delimiting at least one cavity of a second determined conformation,

[0039] j) application of thermocompression e') so as to obtain at least a second piece of modified polyurethane shaped according to the second determined conformation.

[0040] According to another aspect, the invention provides a modified polyurethane comprising at at least one activation function grafted by covalent bond to said polyurethane, the at least one activation function making it possible to activate exchange reactions in the dynamic covalent chemical bonds of the polyurethane, so as to facilitate the rearrangement of the network topology of the modified polyurethane. A shaping by a thermocompressive treatment of the modified polyurethane can be carried out and repeated several times because the activation function is linked by a covalent bond which is therefore stable, to the polyurethane.

[0041] The properties of modified polyurethane also make it possible to carry out repair operations by a thermocompression treatment step e').

[0042] According to a particular embodiment, the modified polyurethane comprises at least one activation function derived from sulfonic acid and / or a ternary amine group.

[0043] Other characteristics and advantages will appear on reading the detailed description below, of a non-limiting example of implementation, made with reference to the appended figures in which:

[0044] [Fig-1] schematically illustrates the dynamic chemical exchange reactions involved in polyurethane and used in the method according to one embodiment of the invention.

[0045] [Fig.2] illustrates two types of activation molecules used in the process of the invention.

[0046] [Fig.3] illustrates two examples of activation molecules of the method of the invention.

[0047] [Fig.4] illustrates steps a) to d) of the method according to the invention.

[0048] [Fig.5] illustrates step e) of the method according to the invention.

[0049] [Fig.6] illustrates the thermocompression step e)' of the method according to the invention.

[0050] As illustrated in [Fig.l], the principle used in the modification method of the invention takes advantage of the dynamic and covalent chemical bonds existing in the methane functions of polyurethane (PU - [Fig.l]). Thanks to this, exchange reactions can occur between chains and rearrange the topology of the polymer network. As a result, the crosslinked polymer network of PU has the ability to change from characteristics of thermosetting materials at low temperature to characteristics of thermoplastic materials at high temperature. The methane functions A are subject to associative type reactions ([Fig.l]- a), during which the crosslinking rate remains constant, as well as to dissociative reactions (figure 1- d), during which the methane bond A decomposes into an isocyanate C and an alcohol D.

[0051] These exchanges are kinetically controlled and can only take place once the glass transition temperature of the PU polymer has been exceeded (conditions the mobility necessary for the reactions) and once the minimum temperature for the reaction to take place has been reached. is reached, linked to the activation energy of the exchange reactions. The invention then provides for covalently grafting at least one activation molecule B to the PU, making it possible to lower the activation energy of the exchange reactions and to promote the reorganization of the network topology, leading to giving the PU thermoplastic properties and the possibility of modifying the shape of the PU on a macroscopic scale.

[0052] The activation molecule B comprises on the one hand an activation function, for example a sulfonic acid group (present on the molecules B, B' and B” - figures 1, 2 and 3) or a ternary amine group (present on the molecules E and E' - figures 2 and 3) and on the other hand a grafting function, intended to form a covalent bond with an isocyanate C of the PU and leads to the production of a modified polyurethane A'. The grafting function can be chosen from nucleophilic functions such as a hydroxyl group (present on the molecules E, E' or B” - figures 1, 2 and 3) or a primary amine group (present on the molecules B' or B” - figures 2, 3). The activation molecule used in the example detailed below is tetrahydroxyethylethylenediamine E' (or THEED supplied by Sigma Aldrich®). It could be replaced in another embodiment by 4-hydroxy-3-amino-benzenesulfonic acid B” (or 4H,3A-BSA supplied by Sigma Aldrich®).

[0053] Figures 4 to 6 illustrate a detailed example of the method according to the invention. It comprises on the one hand the provision of a solution of 5 g of THEED as activation molecule E' in a solvent S capable of dissolving it, and having a boiling point higher than the glass transition temperature of the PU. This is anisole used in an amount of 500 ml (step a). On the other hand, the method provides for the provision of a 100 g part made of rigid thermosetting PU which is micronized (step k) so as to obtain PU particles with an average size located in the scale of a few tens of micrometers. These particles are added to the solution so as to obtain a suspension of 5% by mass of activation molecule E' relative to the weight of the added PU (step b).The suspension is brought to a temperature of 130°C for 1 h with stirring so as to be above the glass transition temperature of the PU and to ensure a certain mobility of the network (step c). These temperature and stirring conditions allow the swelling of the polyurethane A and the loading of the activation molecule E' into the polymer network. In other words, this step allows the impregnation of the THEED into the PU. The anisole is then evaporated in a rotary evaporator under vacuum so that the THEED remains in intimate contact with the PU network recovered in the form of solid particles of impregnated polyurethane Ai (step d). According to an alternative embodiment, an additional drying phase in a vacuum oven and at tem- . higher temperature is used to completely dry the impregnated particles.

[0054] According to step e) of the method illustrated in [Fig. 5], the impregnated particles Ai are then subjected to a second heat treatment at a temperature of approximately 200°C so as to obtain grafting by formation of a covalent bond between the grafting function and the isocyanate C. Once cooled, a polyurethane modified A' by an activation function is obtained in the form of a powder. When hot, it is possible to easily activate the exchange reactions in the dynamic covalent chemical bonds of this modified polyurethane A' allowing a rearrangement of the network topology.

[0055] According to an alternative embodiment, step e) is a thermocompression step e') because it further comprises the application of a pressure making it possible to shape the impregnated polyurethane particles Ai as illustrated in [Fig.6]. To do this, the impregnated polyurethane particles Ai obtained in step d) are arranged in a mold of a predetermined shape, namely here a mold of a cylindrical shape with a radius of 3 cm in diameter preheated beforehand (step i). A thermocompression treatment e' is applied with a temperature of 200°C for 20 min and a pressure of between 30 and 70 bars. The particles coalesce thanks to the exchange of urethane activated by the activator molecule grafted during the process described above, which allows reshaping.Once cooled, the reshaping led to the formation of a first solid and homogeneous part 100 in modified PU A', rigid and crosslinked as originally, presenting thermosetting properties.

[0056] The thickness of the part 100 can be varied by changing the quantity of particles Ai added to the mold initially. The temperature as well as the compression time can be adjusted according to the thickness of the desired part. One or more of the polyurethane parts obtained by this method can be ground again (step h) and used in a thermocompression shaping process (step i, j) to reform a new part, of a different shape if necessary, for example using a mold of a second rectangular conformation of 7 cm x 7 cm.

[0057] Thus, the present invention provides a method for the recovery and reuse of rigid thermosetting polyurethane materials at the end of their life or from production scraps with less material devaluation. The activation function promotes the exchange and dissociation reactions of the modified polyurethane, which allows the material to be reshaped when hot. In addition to the possibility of reshaping, the material can also be repaired by simply applying heat and pressure to the location of a possible crack, leading to a rearrangement of the localized chains, making it possible to covalently reform a partially destroyed network.

Claims

Claims

1. A method for modifying rigid thermosetting polyurethane (A) so as to activate dynamic chemical exchange reactions of said polyurethane (A), the method comprising the following steps: a) providing a solution comprising a solvent (S) and at least one activation molecule (B) intended to activate said exchange reactions of said polyurethane (A), the at least one activation molecule (B) comprising a grafting function and an activation function, b) adding particles of said polyurethane (A) to said solution so as to obtain a suspension, c) applying a first heat treatment to the suspension with stirring to reach a temperature higher than that of the glass transition of said polyurethane (A) so as to impregnate said polyurethane (A) with the at least one activation molecule (B), d) evaporating the solvent (S) so as to obtain particles of said polyurethane impregnated (Ai) with the at least one activation molecule (B),e) applying a second heat treatment to the impregnated polyurethane particles (Ai) so as to graft, by formation of a covalent bond, the activation function of the at least one activation molecule (B) to said impregnated polyurethane (Ai) and to obtain a modified polyurethane powder (A').,

2. A modification method according to claim 1, wherein applying the second heat treatment according to step e) further comprises applying pressure so as to effect thermocompression e') on the modified polyurethane powder (A').

3. Modification method according to claim 2, which comprises, prior to the thermocompression step e'), carrying out a step i) of arranging the impregnated polyurethane particles (Ai) in a mold delimiting a cavity of a determined shape, so as to obtain a solid part (100) of modified polyurethane (A') of the determined shape.

4. Modification method according to one of claims 1 to 3, in which the grafting function of the at least one activation molecule (B), intended for the formation of a covalent bond with the polyurethane (A) is a nucleophilic function.

5. A modification method according to one of claims 1 to 4, wherein the activating function is a sulfonic acid or an amine tertiary.

6. Modification method according to one of claims 1 to 5, in which the at least one activation molecule is chosen from: - a sulfonic acid carrying alcohol or amine functions, of general formula R-(SO3H)x-(OH)y(NH2)z where R is a carbon radical which may be aromatic or aliphatic, x is the number of sulfonic acids (x>=1), y the number of hydroxyl groups (y>=1) and z the number of primary or secondary amine groups (z>=1) and in particular 4-hydroxy-3-amino-benzenesulfonic acid (B”), and / or - a tertiary amine carrying one or more alcohols, of general formula Nm-(R'OHn)o with R' a carbon radical (m>=1) (o>=1) carrying one or more hydroxyl functions (n>=1) and in particular tetrahydroxyethylethylenediamine (E).

7. Modification method according to one of claims 1 to 6, in which the mass percentage of activation molecules (B) in the suspension is in a range from 0.05% to 10% by mass, and in particular in a range between approximately 0.1 and 5% by mass.

8. Modification method according to one of claims 3 to 7, in which the thermocompression step e') is carried out in a temperature range from 120°C to 250°C, and a pressure of between 30 and 70 bars for a duration ranging from 1 min to 40 min, in particular at 200°C under a pressure of approximately 40 bars applied for 20 min.

9. Method for reshaping modified polyurethane parts (A') comprising the steps of: g) providing at least one part (100) of modified polyurethane (A') obtained according to one of claims 3 to 8, h) powdering at least one part (100) of modified polyurethane (A'), i) placing the powder in at least one mold delimiting at least one cavity of a second determined conformation, j) applying thermocompression e') so as to obtain at least one second part of modified polyurethane (A') shaped according to the second determined conformation.

10. Modified polyurethane (A') comprising at least one activation function grafted by covalent bonding to said polyurethane, the at least an activation function to activate exchange reactions in the dynamic covalent chemical bonds of polyurethane, so as to facilitate the rearrangement of the network topology of the modified polyurethane (A').

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