FR3112781A1 - HEAT REPAIRING AND THERMOFORMABLE POLYURETHANE POLYMER - Google Patents

Abstract

HEAT REPAIRING AND THERMOFORMABLE POLYURETHANE POLYMER Process for preparing a hybrid polyurethane polymer, comprising a step of reacting inorganic precursors and/or inorganic/organic hybrids comprising a metal, with a polyurethane pre-polymer comprising complexing functional groups said metal, for obtaining the hybrid polyurethane polymer in which a hybridization rate, defined by the number of complexing functions on the number of metal atoms, is greater than 1. (Figure to be published with the abstract: Figure 1)

Description

HEAT REPAIRING AND THERMOFORMABLE POLYURETHANE POLYMER

The invention relates to the field of polyurethane materials, and more particularly to the recycling, thermoforming and repair of such materials.

Polyurethane polymers result from a reaction between isocyanate molecules and alcohol molecules. Polyurethanes are widely used in industry, particularly in the automotive industry, where they contribute to the manufacture of certain vehicle parts. Polyurethanes are also used to improve thermal and acoustic insulation, while ensuring protection of metal parts against rust.

Polyurethane polymers are most often in thermosetting form, which means that once cross-linked, they cannot be re-melted and reused. It is known to reinject recycled polyurethane in powder form into the virgin product at the time of injection, as filler material. This type of recycling is only partial and fails to be satisfactory.

Patent document US 2019/0359823 A1 discloses a thermoplastic polyurethane made from a composition of polyisocyanates, at least one functional chain extender and a composition of polyols. The polyols can comprise a polyester with an aromatic carboxylic acid or an alcohol function, the preferred poly-isocyanate for this polyurethane being a di-isocyanate. This polyurethane is not adapted to be self-healing, but can however be used to form the bodies of objects.

Published patent document EP 3 235 843 A1 discloses a self-healing polyurethane resin. This resin is manufactured using a mixture comprising a polyisocyanate and a polyol, the polyol comprising a carbonate group and/or an ester group. The poly-isocyanate is itself composed of a mixture between an aliphatic poly-isocyanate and/or an araliphatic poly-isocyanate. This polyurethane resin has a high hardness due to a high crosslinking rate and is intended to form coatings with a certain resistance to abrasion, light and weathering. This resin also allows self-repair of any cracks or damage that may appear on the surface. This resin is not really suitable for the production of object bodies.

The object of the invention is to overcome at least one of the drawbacks of the aforementioned state of the art. More particularly, the invention aims to manufacture an injectable, thermoformable and heat-repairing polyurethane polymer, with a view to being reused or recycled.

By heat-repairing, it is meant that the polyurethane polymer can be repaired after heating said polymer. By thermoformable is meant a material, in particular in the form of a plate, which is heated to be shaped with or without a mould.

The subject of the invention is a method for preparing a hybrid polyurethane polymer, comprising a step of reacting inorganic and/or inorganic/organic hybrid precursors, comprising a metal, with a polyurethane prepolymer comprising groups functions complexing said metal, for obtaining the hybrid polyurethane polymer in which a degree of hybridization, defined by the number of complexing functions over the number of metal atoms, is greater than 1.

By number of complexing functions is meant the number of functional groups complexing the metal.

Thus, the invention allows the manufacture of a hybrid polymer based on polyurethane with functional (or complexing) groups. This polymer has the particularity of being heat-repairing with a repair temperature preferably between 60°C and 120°C, and self-assembling. In addition, this polymer is easier to manufacture than known polymers. The polymers obtained can also be thermoformed and injected into molds in order to manufacture various parts or elements advantageously usable in non-limiting fields such as building, aeronautics, automotive, medical and transport. These polyurethane polymers are also recyclable, since these polymers can be first manufactured and then granulated to be remelted later. The modulus of elasticity of these polyurethane polymers according to the invention is further increased, due to the presence of the inorganic or hybrid component. The polymer obtained can therefore be rigid or be an elastomer.

According to an advantageous embodiment of the invention, the polyurethane prepolymer comprising functional groups complexing the metal of the precursor is obtained by a reaction implemented between monomers derived from polyols and monomers derived from di-isocyanates, the monomers derived polyols carrying complexing groups and being chosen from the group consisting of a carboxylic acid, an amine, an alcohol and a β-diketone, or any combination.

The hybrid polyurethane polymer obtained comprises macromolecular chains with pendent and/or terminal functions, part of the functions being linked to metal centers, and another part of the functions remaining free.

Preferably, the number of functions carried by the polyol monomers is greater than the number of inorganic precursors or inorganic/organic hybrid precursors. Advantageously, the functions of the polyol monomers are pendent and/or terminal.

Advantageously, the hybridization rate is less than 3. The applicant has shown that the best effects of the invention are obtained for this range of values. These values make it possible to obtain the best compromise between the mechanical characteristics and the repairability of the material.

The polyol derivatives bearing the complexing groups can preferably be compounds of the dimethylolpropionic acid type (whose trade name is “ ^DMPA® ”), and/or polypropylene glycol (whose acronym is “PPG”). Advantageously, other compounds of the diol type known to those skilled in the art can be used.

The di-isocyanate derivative monomer can be diphenylmethane di-isocyanate (whose acronym is "MDI"), toluene di-isocyanate (whose acronym is "TDI"), or aliphatic, such as di -hexamethylene isocyanate (whose acronym is "HDI") and isophorone di-isocyanate (whose acronym is "IPDI").

According to an advantageous mode of the invention, the inorganic precursors and/or inorganic/organic hybrids are capable of reacting with the monomers derived from functional polyols bearing the complexing functions.

According to an advantageous embodiment of the invention, the inorganic or inorganic/organic hybrid precursors are chosen from the group consisting of metal alkoxides, metal oxoalkoxides, metal oxides, or any combination.

According to an advantageous mode of the invention, the metal is chosen from the group consisting of titanium, zirconium, aluminum, iron, zinc or any combination.

The starting products, therefore the pre-polymer and the precursors, can be dissolved, if necessary, in a solvent of the dimethylformamide type (whose acronym is "DMF"), tetrahydrofuran (whose acronym is "THF") or any other suitable solvent, such as chlorinated solvents (chloroform and methylene chloride), or aromatic solvents, such as toluene and xylene.

The quantities, by mass, of polyurethane prepolymer and of precursor are respectively y ₁ (g) and y ₂ (g), y ₂ being calculated according to the rate of pendant functions of the prepolymer and the rate of desired hybridization X, according to the following equation:

where Mm = molecular mass of the polyol presenting the complexing function, Me = Metal, and X = hybridization rate.

Although the method can be implemented at ambient temperature, it is advantageous to carry out the method at temperatures between 40° C. and 70° C., and preferably between 50° C. and 70° C., for times which may up to 8 hours if the processing temperature is close to room temperature, up to about 4 hours for typical temperatures of 50°C to 70°C. Preferably, for a temperature of 60° C., the reaction time is approximately 1 hour. The reaction temperatures and times are advantageously chosen for the complete implementation of the reaction. The higher the temperature, the faster the reaction.

According to an advantageous embodiment of the invention, the process for preparing the hybrid polyurethane polymer comprises a step for preparing the functionalized polyurethane prepolymer, comprising the following sub-steps:

1. dissolving a _3x amount (g) of a first polyol-derived monomer in a solvent, such as DMF or THF;
2. introduction into a container of a quantity x₁(g) of a monomer derived from di-isocyanate, then the quantity x₃(g) the first monomer derived from polyol dissolved in the solvent and optionally an amount x₂ (g) a second polyol-derived monomer different from the first polyol monomer;
3. heating of the container, preferably under an inert atmosphere, for example under nitrogen or under argon, at temperatures typically comprised between 70° C. and 100° C., with mechanical stirring.

The level of isocyanate functions can be monitored by back assay according to the ISO-14896 standard, in order to determine the end of the reaction. The percentage of isocyanate functions in the pre-polymer is determined by the following formula:

where Mm = molecular weight.

Once this percentage has been obtained, the step of preparing the functionalized polyurethane prepolymer of the process may comprise a sub-step d) of adding a quantity x ₄ (g) of a product allowing the neutralization of the ends of chains, such as primary amines, for example butylamine, tertiary amines, for example dimethylcyclohexylamine or diaza-1,4-bicyclo[2.2.2]octane (whose acronym is “DABCO”). The quantity of product for neutralizing the chain ends is calculated according to the return dosage of the isocyanate functions previously determined. The end of the synthesis is also determined by the back dosing, when the content of isocyanate functions becomes zero. A rate, defined by the Math 3 formula, is preferably chosen with a value between 1.1 and 1.3.

The choice of this reference range, between 1.1 and 1.3, is intended to avoid reactions between the isocyanates at the end of the chain and the titanates.

A subject of the invention is also a hybrid polyurethane polymer comprising macromolecular chains with pendent and/or terminal functions, a part of said functions being linked to metal atoms and another part of said functions remaining free, the polymer further comprising , a hybridization rate, defined by the number of complexing functions on the number of metal atoms, greater than 1.

According to an advantageous mode of the invention, the polymer is in the form of granules.

The invention also relates to a process for manufacturing parts by injection of hybrid polyurethane polymer, noteworthy in that the hybrid polyurethane polymer is according to the invention, and/or is prepared according to a preparation process according to the invention. .

Advantageously, the injection of the hybrid polyurethane polymer is carried out directly after the synthesis of said polymer.

Preferably, the polymer obtained according to the invention has a glass transition temperature (whose acronym is "Tg") of between -20°C and -55°C, and more preferably between -30°C and -50°C . Preferably, the elasticity (or Young's) modulus at 1% of the polymers obtained is between 1 MPa and 50 MPa. These values depend on the hybridization rate and the quantity of polyols deposited in the solution.

Other features and advantages of the present invention will be better understood from the description and the drawings.

represents tensile curves obtained with specimens made of hybrid polyurethane polymer. These specimens are either undamaged or have been cracked and repaired under the conditions described in Table 3;

represents tensile curves obtained with specimens made of hybrid polyurethane polymer. These specimens are either undamaged or have been cracked and repaired seven times in a row under the conditions described in Table 3;

represents tensile curves obtained with specimens made of hybrid polyurethane polymer. These specimens are either undamaged or they are cut and repaired in order to simulate recycling conditions, under the conditions described in Table 3.

detailed description

The invention relates to a self-assembling and heat-repairing hybrid polyurethane polymer, and to a method of manufacturing said polymer. This polymer is also injectable and thermoformable, polyurethane being synthesized from an alcohol and an isocyanate. In the context of the invention, the manufacture of the polyurethane polymer preferably takes place in two stages.

The first step consists in synthesizing a polyurethane prepolymer from monomers derived from isocyanates, and, more preferentially, from di-isocyanates, and from monomers derived from polyols. The monomers derived from polyols are functional monomers which bear groups chosen from the following list: carboxylic acid, amine, alcohol and β-diketone, or a mixture of said groups. The polyols can also be molecules with a functionality greater than or equal to 2. For example, the polyols can be dimethylolpropionic acid (whose trade name is “ ^DMPA® ”), and/or polypropylene glycol (whose acronym is “PPG”). The diisocyanate derivative monomer is advantageously chosen from diphenylmethane diisocyanate (whose acronym is "MDI"), toluene diisocyanate (whose acronym is "TDI"), or aliphatics, such as hexamethylene di-isocyanate (whose acronym is “HDI”) and isophorone di-isocyanate (whose acronym is “IPDI”), more preferably toluene di-isocyanate.

Advantageously, a product for neutralizing the ends of the chains, of the butylamine type, is added to the synthesis of the prepolymer to avoid co-reactions between the isocyanates and the titanates. Butylamine can also be a functional chain extender. The amount of butylamine added to the prepolymer depends on the isocyanate function dosage of the mixture measured by a back dosage (by techniques known to those skilled in the art). The percentage of isocyanate functions in the pre-polymer is determined by the following formula:

The %( _expected NCO) being the percentage of isocyanate functions in the mixture; x ₁ , x ₂ , and x ₃ the respective masses, in grams, of TDI, of PPG and of DMPA ^® . The values 174.16, 2000 and 134.13 correspond to the respective molecular masses of TDI, PPG and DMPA ^® .

Then, the amount of butylamine to add to the mixture is determined using the following formula:

With n(NH ₂ ), the quantity of amine functions, and n(NCO), the quantity of isocyanate functions. The polyurethane prepolymer can optionally be replaced by an elastomeric thermoplastic polyurethane.

By way of example, Table 1 below shows examples of quantities of products used to manufacture different prepolymers.

TDI (x ₁ ) GPP (x ₂ ) ^DMPA® (x ₃ ) Butylamine (x ₄ ) Pre-polymer A 29.06 33.27 12.69 9.29 Pre-polymer B 25.45 39.06 10.49 10.49 Pre-polymer C 27.28 52.19 10.5 8.42 Pre-polymer D 24.63 56.57 8.82 7.95 Pre-polymer E 22.47 60.13 7.45 6.92

The second step consists in dispersing, in the prepolymer, inorganic precursors or hybrid organic/inorganic precursors, these precursors being capable of reacting with the functions of the monomers derived from polyols. This step makes it possible to obtain the hybrid polyurethane polymer according to the invention. Advantageously, these precursors are metal alkoxides, metal oxoalkoxides, metal oxides, or mixtures thereof. Advantageously, the metals are selected from the group consisting of titanium, zirconium, aluminum, zinc, iron, or mixtures thereof. By way of example, the precursor can be polydibutyltitanate dissolved in tetrahydrofuran (whose acronym is “THF”), and the polyol can be ^DMPA® . The mass of polydibutyltitanate to be added is calculated according to the following formula:

With y ₂ , the mass of polydibutyltitanate, y ₁ the mass of pre-polymer and X the hybridization rate, determined by the following equation:

With n(complexing functions), the amount of matter of complexing functions in the pre-polymer, and n(Ti), the amount of matter of titanium atoms in the titanium oligomer. Examples of quantities y₁ of pre-polymer, y₂of polydibutyltitanate, as well as the hybridization rate X corresponding to these quantities, are reported in Table 2.

X 1 1.5 2 3 Pre-polymer A there ₁ 20.89 20.64 20.07 / there ₂ 4.93 3.29 2.40 / Pre-polymer B there ₁ 20.02 20.44 20.19 / there ₂ 3.99 2.72 2.02 / Pre-polymer C there ₁ 19.36 20.07 19.46 19.64 there ₂ 3.28 2.27 1.64 1.11 Pre-polymer D there ₁ 20.41 20.26 20.19 / there ₂ 2.91 1.93 1.44 / Pre-polymer E there ₁ 20.43 20.22 20.43 17.09 there ₂ 2.49 1.65 1.25 0.69

The preparation of a polyurethane polymer according to the invention can be carried out by the solvent route or by the molten route, but the molten route is preferably used. This consists of introducing the polyurethane pre-polymer, with the organic or organic/inorganic hybrid precursors, into the hopper or into the barrel of a single-screw or twin-screw extruder. The molten polymer leaving the extruder can then be injected directly into a mold in order to produce the desired part, or be split into granules, so that it can be subsequently remelted and injected into a mould.

First step: synthesis of a polyurethane prepolymer :

Preparation of a solution comprising 10.59g of DMPA ^® dissolved in 36g of DMF.

Then 27.28 g of TDI are added to a reactor with 52.21 g of PPG, and the previously prepared solution of DMPA ^® . The reactor is then placed under argon, or under a stream of nitrogen, and in an oil bath at 80° C. with mechanical stirring at 220 revolutions/min for 5 hours.

The level of isocyanate functions is then determined by a back assay (using methods known to those skilled in the art). For example, by taking a small quantity of product (which depends on the expected %NCO) to which the dibutylamine is added in excess. Propan-2-ol is then added. The titration of the amine functions is then carried out either using a hydrochloric acid solution at 0.1 mol/l, by the metric pH titration method; or by the colorimetric titration method using bromcresol green.

According to the return dosage of the isocyanate functions obtained (and the chosen rate of which was determined by formula Math 5), 8.42 g of butylamine are then added to the reactor. The reactor is then maintained under argon at 80° C. in an oil bath and with mechanical stirring at 220 rpm for 4 hours, this duration being adjusted according to the level of residual isocyanates.

The end of the synthesis is then determined by a level of isocyanate functions in the composition, by back dosing, equal to 0.

A stage of elimination of the DMF, by techniques known to those skilled in the art, is then carried out. For example, DMF can be eliminated by dissolving the material in tetrahydrofuran (whose acronym is “THF”), which is then placed in an oven at 80°C, leading to its evaporation. Or the material can be dissolved in THF and then precipitated in water, before vacuum filtration and drying in an oven.

Second step :s synthesis of polyurethane polymer hybrid :

19.46 g of dry prepolymer (obtained after elimination of the DMF) and 1.64 g of polydibutyltitanate are dissolved in 200 ml of THF. The mixture is left stirring at reflux for a maximum of 6 hours, in an oil bath at 60° C. and under a nitrogen stream. The mixture is then poured into a mould, and left under a hood for 3 days, then for 3 days in an oven at 60°C. After obtaining the hybrid polyurethane polymer material, dumbbell specimens (according to the ISO 527-2 standard) of this material are produced.

Thus, the hybrid polyurethane polymer obtained by the method described above has a rate of complexing functions of 21% mol, and a rate of hybridization (X) of 2.

Test s of damage s materials hybrid polyurethane polymers .

Two types of material damage are tested. The first type of damage consists in making a crack with a scalpel over the entire thickness of the material, in order to test the repairability of said material. The second type of damage consists of cutting the material into pieces before repairing it, so as to simulate recycling. The repair of the specimens is carried out under a compression press, with a variation of the duration, the pressure and the temperature to which the specimens are subjected. The results obtained are shown in Table 3. The “1% Modulus” in Table 3 corresponds to the modulus of elasticity of the sample, taken at 1% strain. The repair efficiency ŋ is defined by the following formula.

Damage Cracking Recycling Repair conditions in press 80°C/15min/60bar 110°C/15min/60bar Repair efficiency η Modulus at 1% 103±9% 62±8% Stress at break 103±5% 69±4% Elongation at break 96±7% 128±11%

Figures 1 through 3 illustrate the results obtained from the material damage tests described above. Thus, the mechanical behavior of the dumbbell specimens made in the hybrid polyurethane polymer and possibly damaged under the conditions described in the table above is represented.

In figure 1, the damage studied is the cracking of the specimens and then their repair. Two types of curves are shown in this figure: light gray curves (a), showing the results obtained on hybrid polyurethane polymer specimens cracked and then repaired; and dark gray curves (b), showing results obtained with undamaged hybrid polyurethane polymer specimens. It can be seen that, whether the specimens have been damaged or not, the stress and the tensile strain of the specimens are similar, demonstrating excellent repair conditions, therefore good durability of the polymer after repair.

Figure 2 shows the results obtained after 7 cycles of cracking and repair of dumbbell specimens made of hybrid polymer material according to the invention. Dark gray curves (c) show the results obtained with undamaged hybrid polyurethane polymer specimens; and light gray curves (d), show the results obtained on hybrid polyurethane polymer specimens cracked and then repaired 7 times. The tensile stress of the dumbbell specimens produced in the polymer according to the invention is studied. In this figure, the repair of the specimens is 100% after the 7 cycles of damage and repair, these results being similar to those obtained when the specimens made of polymer material according to the invention are not damaged.

Figure 3 shows the results obtained when recycling conditions are simulated, i.e. when the material is cut into pieces before being repaired. Thus, the dark gray curves (e) show the results obtained with undamaged hybrid polymer material specimens. The light gray curves (f) show the results obtained when the specimens of hybrid polymer material are cut into pieces and then repaired. The tensile strain of the repaired specimens is of excellent quality, but the tensile stress is significantly lower than the values obtained with undamaged specimens. Even if the quality of the repairs seems to be less effective under these conditions, the polymer shows good qualities in the case of recycling.

Thus, the hybrid polyurethane polymer according to the invention has a good level of repair, and can be easily recycled compared to previously known polymers. When recycled, this polymer is of good quality. The possibility of presenting the polymer in the form of granules, able to be molded in a second time in order to make finished parts is also possible, due to the good quality of the polymer after "recycling".

An embodiment of the invention is shown, but for each polymer, the properties of said polymer will be optimized according to the ratio between the quantity of complexing and/or terminal functions of the macromolecular chains according to the quantity of metal centers, the quantity of centers metal must always be in excess. This ratio will have to be determined according to the nature of the metal center and according to the bond strength between the metal and the available function of the polyurethane. Thus, the hybrid polyurethane polymer obtained will have the usage properties of a thermosetting polymer or an elastomer, while having the processability and recyclability properties of a thermoplastic.

The example described above for which the material damage tests were carried out correspond to the prepolymer C defined in Tables 1 and 2. This prepolymer comprises, in its composition, two polyols (DMPA ^® and PPG) and as precursor polydibutyltitanate. Its hybridization rate X is 2. Other syntheses of hybrid polyurethane polymers have been carried out and show interesting mechanical results. It has been demonstrated that a hybridization rate greater than 1 and less than 3 makes it possible to obtain the best compromise between the mechanical characteristics and the reparability of the material.

Claims (10)

Process for the preparation of a hybrid polyurethane polymer, comprising a step of reacting inorganic precursors and/or inorganic/organic hybrids, comprising a metal, with a polyurethane pre-polymer comprising functional groups complexing said metal, for obtaining the hybrid polyurethane polymer in which a hybridization rate (X), defined by the number of complexing functions over the number of metal atoms, is greater than 1. Process for the preparation of a polymer according to claim 1, characterized in that the polyurethane prepolymer comprising functional groups complexing the metal of the precursor is obtained by a reaction carried out between monomers derived from polyols and monomers derived from di-isocyanates, the monomers derived from polyols bearing complexing groups and being chosen from the group consisting of a carboxylic acid, an amine, an alcohol and a β-diketone, or any combination. Process for the preparation of a polymer according to Claim 2, characterized in that the inorganic precursors and/or inorganic/organic hybrids are capable of reacting with the monomers derived from functional polyols carrying the complexing functions. Process for preparing a polymer according to one of Claims 1 to 3, characterized in that the inorganic or inorganic/organic hybrid precursors are chosen from the group consisting of metal alkoxides, metal oxoalkoxides, metal oxides, or any combination. Process for preparing a polymer according to one of Claims 1 to 4, characterized in that the metal is chosen from the group consisting of titanium, zirconium, aluminium, iron, zinc or any combination. Process for preparing a polymer according to one of Claims 1 to 5, characterized in that the said process comprises a step for preparing the functionalized polyurethane prepolymer, comprising the following sub-steps:
a) dissolving an amount x ₃ (g) of a first monomer derived from polyol in a solvent;
b) introducing into a container an amount x ₁ (g) of a monomer derived from di-isocyanate, then an amount x ₃ (g) of the first monomer derived from polyol dissolved in the solvent and optionally an amount x ₂ (g) of a second polyol-derived monomer different from the first polyol monomer;
c) heating the container, preferably under an inert atmosphere, to temperatures between 70° C. and 100° C., with mechanical stirring. Process for preparing a polymer according to claim 6, characterized in that the step for preparing the functionalized polyurethane prepolymer comprises a sub-step d) of adding a quantity x ₄ (g) of a product allowing the neutralization of chain terminations. Hybrid polyurethane polymer comprising macromolecular chains with pendent and/or terminal functions, part of said functions being linked to metal atoms and another part of said functions remaining free, the polymer further comprising a hybridization rate (X ), defined by the number of complexing functions on the number of metal atoms, greater than 1. Hybrid polyurethane polymer according to Claim 8, characterized in that the said polymer is in the form of granules. Process for manufacturing parts by injection of hybrid polyurethane polymer, characterized in that the hybrid polyurethane polymer is according to one of Claims 8 and 9, and/or is prepared according to a preparation process according to one of Claims 1 at 7.