Solvent resistant, recyclable, self-healing polyurethane elastomers and methods of making the same

Abstract

The application relates to a solvent-resistant, recyclable and self-repairing polyurethane elastomer and a preparation method thereof, and belongs to the technical field of high-performance polymers. Ascorbic acid is used as a chain extender, and a new crosslinking system is found. Compared with a common chain extender BDO, ascorbic acid can provide sufficient chemical crosslinking points, form a polyurethane elastomer with relatively optimal mechanical properties, and make the polyurethane elastomer only swell but not dissolve in various organic solvents at normal temperature. This enables the material to be applied to various complex environments. Due to the dynamic balance between the ketone and enol structures in ascorbic acid, the obtained polyurethane elastomer has a self-repairing function. After a test sample is pulled apart, the fracture is spliced, and the preliminary healing can be realized in a short time. After the repair is carried out at normal temperature for 1 day, the self-repairing efficiency is not less than 29%.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of solvent-resistant, recyclable, self-repairing polyurethane elastomer and its preparation method, belong to high-performance polymer technical field. BACKGROUND

[0002] Polyurethane elastomer is widely used in various fields such as national defense and military industry and civil construction due to its excellent performance. It is a macromolecular polymer obtained by chemical reaction between the hydroxyl group (-OH) of polyol and the isocyanate group (-NCO) of polyisocyanate in the molecular chain, which is a typical block polymer composed of alternating soft segments and hard segments. The interaction between soft and hard segments makes it exhibit microphase separation and supramolecular network. Among them, the soft segment is composed of flexible polyether polyol with long molecular chain, accounting for 50% to 90%, and the hard segment is composed of isocyanate and small molecule chain extender, accounting for about 10% to 50%. A large number of hydrogen bonds can be formed between the urethane groups in the hard segment corresponding to the isocyanate and the chain extender, which has the effect of physical crosslinking, forming hard segment micro area. The thermodynamic incompatibility between soft and hard segments leads to microphase separation structure in the aggregate state. These unique structures endow polyurethane elastomer with excellent performance. The soft segment endows polyurethane with good elasticity and low temperature resistance, and the hydrogen bond in the hard segment can make it have wear resistance, toughness and small tensile permanent deformation. Polyurethane elastomer has excellent comprehensive performance, low weight, corrosion resistance, simple processing, good sound insulation and shock absorption compared with metal materials; it has the advantages of cut resistance, ozone resistance, tear resistance, transparency, various preparation methods and wide hardness range compared with general rubber.

[0003] However, during use, the material will inevitably produce microcracks or macroscopic cracks due to mechanical, chemical, thermal and other factors, affecting the service life of the material, and even posing a safety hazard. The self-repairing ability of polymers has become a research hotspot in recent years. Self-repairing materials are materials that can repair damaged parts without intervention or under certain stimuli (light, heat, electricity, microwaves, etc.) to restore their original state. Self-repairing is significant for polymer materials in that it reduces maintenance costs while improving the durability, reliability and safety of the materials. From the principle, the self-repairing of materials is generally divided into external aid type and intrinsic type. The former relies on microcapsules or liquid core fibers containing repair agents pre-filled in the matrix to achieve repair, while the latter has repeatable self-repairing ability, which only relies on the physical and chemical properties (such as molecular diffusion, reversible covalent bond and reversible non-covalent bond) contained in the material itself to repair the material. Compared with external aid type self-repairing, intrinsic type self-repairing material is simple to prepare, and because of the dynamic recombination of internal dynamic bonds, it can also endow the material with recyclable and degradable properties.

[0004] However, the current common self-repairing polyurethane has many defects: it is easily corroded by organic solvents at room temperature, resulting in a large amount of swelling or even dissolution, and it is difficult to recycle after use, causing a lot of resource waste, which does not meet the current concept of sustainable development. SUMMARY

[0005] In view of the defects existing in the technical field, the application provides a solvent-resistant, recyclable and self-repairing polyurethane elastomer and a preparation method thereof. The polyurethane elastomer uses ascorbic acid as a chain extender, and has a dynamic transformation of ketone and enol structure inside. The four hydroxyl groups of ascorbic acid provide enough chemical crosslinking points, and the unique chemical structure gives the polyurethane material the ability of self-repairing. At the same time, the crosslinking structure improves the structural stability of the polyurethane, and the solvent resistance is better than that of general polyurethane materials. The swelling rate in various organic solvents at room temperature is very small or even no swelling. It can be dissolved in general organic solvents at high temperature, and can be re-formed after evaporation of the solvent. The mechanical properties of the sample can be restored after recycling, and it has a very high elongation at break. The recyclable performance can effectively reduce resource waste. Polytetrahydrofuran diol (PTMG) is used as a soft segment, isophorone diisocyanate (IPDI) and ascorbic acid are used as hard segments, and a solution polymerization method is used for polymerization. DMF is used as a solvent to reduce the viscosity of the reaction system. The prepolymer method is used for polymerization, and PTMG needs to be dehydrated before use. First, the measured PTMG and IPDI are mixed and added to a three-necked flask, a small amount of DBTDL is added as a catalyst to accelerate the polymerization reaction, and the isocyanate-terminated polyurethane prepolymer is obtained after the reaction is completed. After the temperature drops, DMF is added as a solvent for the reaction, a measured amount of ascorbic acid powder is added, and the final product is obtained after continuous reaction. The product is cast in a preheated polytetrafluoroethylene mold, and after curing, it is used for subsequent testing.

[0006] To achieve the above purpose, the technical scheme of the application is as follows.

[0007] A solvent-resistant, recyclable and self-repairing polyurethane elastomer, the raw materials of the polyurethane elastomer include ascorbic acid chain extender, polytetrahydrofuran diol (PTMG), isophorone diisocyanate (IPDI), N,N-dimethylformamide (DMF) solvent, and dibutyltin dilaurate (DBTDL).

[0008] The percentage content of each component is as follows, based on the mass of ascorbic acid chain extender, polytetrahydrofuran diol (PTMG), isophorone diisocyanate (IPDI) and dibutyltin dilaurate (DBTDL) being 100%:

[0009] Ascorbic acid chain extender 3%-4%;

[0010] Polytetrahydrofuran diol (PTMG) 75%-80%;

[0011] Isophorone diisocyanate (IPDI) 15-20%;

[0012] Dibutyl tin dilaurate (DBTDL) 0.1-0.3%;

[0013] The ratio of N,N-dimethylformamide (DMF) solvent to polytetramethylene glycol is 10-30 mL: 15 g;

[0014] The molecular weight of the polytetramethylene glycol is 2000 g / mol.

[0015] A preparation method of a solvent-resistant, recyclable, self-repairing polyurethane elastomer, the steps of the method comprising:

[0016] First, the polytetramethylene glycol (PTMG) is dehydrated;

[0017] Second, the polytetramethylene glycol (PTMG) after the dehydration treatment in the first step, isophorone diisocyanate (IPDI) and dibutyl tin dilaurate (DBTDL) are mixed and stirred to react, the mixing temperature is 80-90℃, the stirring speed is 220-300r / min, the stirring time is 2-4h, and the isocyanate-terminated polyurethane prepolymer is obtained after the reaction is completed;

[0018] Third, the ascorbic acid chain extender and N,N-dimethylformamide (DMF) solvent are mixed to obtain a mixture;

[0019] Fourth, the mixture obtained in the third step is mixed with the prepolymer obtained in the second step, and the mixture is stirred to react, the mixing temperature is 80-90℃, the stirring speed is 220-300r / min, the stirring time is 4-6h, and the product is dried after the reaction is completed, the drying temperature is 75-85℃, the drying time is 1-2 days, and the solvent-resistant, recyclable, self-repairing polyurethane elastomer is obtained.

[0020] After the solvent-resistant, recyclable, self-repairing polyurethane elastomer is obtained, if damage occurs, etc., the recycling method is as follows:

[0021] The used solvent-resistant, recyclable, self-repairing polyurethane elastomer is cut into pieces and mixed with N,N-dimethylformamide (DMF) solvent to obtain a mixture A, which is sealed with plastic wrap and placed in an oven, the temperature is set to 80-100℃, after the sample is completely dissolved, the plastic wrap is pierced with several small holes, part of the solvent is evaporated, and a mixture B is obtained, the mass of the mixture B is 10%-15% of the mass of the mixture A, then the mixture B is dried, the drying temperature is 75-85℃, the drying time is 1-2 days, and the solvent-resistant, recyclable, self-repairing polyurethane elastomer is obtained again.

[0022] Advantages

[0023] The application provides a preparation method of a solvent-resistant, recyclable and self-repairing polyurethane elastomer. The end groups of diisocyanate in raw materials are isocyanate groups, and the end groups of polyether polyol are hydroxyl groups. After mixing and reaction, a prepolymer of isocyanate-terminated polyurethane is obtained. The prepolymer can be reacted with various small molecular chain extenders such as alcohols and amines, and the method can be flexibly adjusted according to the experimental formula design. The method is simple to operate and can be used for laboratory preparation and industrial production.

[0024] The application provides a preparation method of a solvent-resistant, recyclable and self-repairing polyurethane elastomer. Ascorbic acid is used as a chain extender, and a new crosslinking system is found. Compared with a common chain extender BDO, ascorbic acid can provide sufficient chemical crosslinking points, and form a polyurethane elastomer with relatively optimal mechanical properties, so that the polyurethane elastomer only swells but does not dissolve in various organic solvents at room temperature. This enables the material to be applied to various complex environments.

[0025] The application provides a preparation method of a solvent-resistant, recyclable and self-repairing polyurethane elastomer. Due to the dynamic balance between the ketone and enol structure inside ascorbic acid, the obtained polyurethane elastomer has a self-repairing function. After the test sample is broken, the fracture is spliced, and the preliminary healing can be realized in a short time. The self-repairing efficiency is not less than 29% after the repair at room temperature for 1 day.

[0026] The application provides a recycling method of a solvent-resistant, recyclable and self-repairing polyurethane elastomer. After the original sample is dissolved at high temperature, the sample is poured again to form a polyurethane elastomer, and the mechanical properties can be recovered to a certain extent. Meanwhile, the polyurethane elastomer exhibits super tensile properties, can effectively reduce resource waste and is conducive to sustainable development. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The infrared spectrum of the polyurethane obtained in the comparative example;

[0028] Figure 2 The infrared spectrum of the solvent-resistant, recyclable and self-repairing polyurethane elastomer;

[0029] Figure 3 The self-repairing result graph of the solvent-resistant, recyclable and self-repairing polyurethane elastomer;

[0030] Figure 4 The mechanical property comparison graph of the solvent-resistant, recyclable and self-repairing polyurethane elastomer before and after self-repairing;

[0031] Figure 5 The cyclic tensile graph of the solvent-resistant, recyclable and self-repairing polyurethane elastomer;

[0032] Figure 6 Figure for the swelling rate test of solvent-resistant, recyclable and self-repairing polyurethane elastomer in three organic solvents;

[0033] Figure 7 Figure for the mechanical property test of the remolded solvent-resistant, recyclable and self-repairing polyurethane elastomer. DETAILED DESCRIPTION

[0034] The application will be described in detail below with reference to the accompanying drawings, which are not intended to limit the patent.

[0035] Example

[0036] A preparation method of a solvent-resistant, recyclable and self-repairing polyurethane elastomer, comprising the following steps:

[0037] 1. Dehydration of raw materials: The water in polytetramethylene glycol (PTMG) will react with isocyanate, so as to exclude the interference of water by dehydration treatment. 100 g of PTMG is weighed and poured into a 250 ml three-necked flask, a magnetic rotor is added, the oil bath temperature is set to 105°C, the rotation speed is 250 r / min, a vacuum pump is connected for dehydration for 2 hours, and then poured into a tetrafluoroethylene bottle for standby after dehydration.

[0038] 2. Preparation of prepolymer: 7.5 mmol (15.00 g) of PTMG and 15 mmol (3.3348 g) of IPDI are weighed and added to a 250 ml three-necked flask, 0.04 g of DBTDL is added as a catalyst, the temperature is set to 85°C, the rotation speed is 250 r / min, and the reaction is carried out for 4 hours. The isocyanate-terminated polyurethane prepolymer is obtained.

[0039] 3. Chain extension: 3.75 mmol (0.66 g) of ascorbic acid powder is weighed in a glass beaker, 20 g of DMF is added, and after the ascorbic acid is dissolved, the solution is added to the above prepolymer, the polymerization temperature is set to 85°C, the rotation speed is 250 r / min, and the reaction is carried out for 4 hours. The reaction product is poured into a tetrafluoroethylene evaporating dish, the temperature is set to 80°C, the residual solvent is evaporated in an oven, and the solidification is carried out for two days.

[0040] The obtained product is a brownish red polyurethane elastomer, and the infrared spectrum test result is as shown in Figure 2 There is no characteristic absorption peak at 2271 cm -1 , indicating that -NCO has been completely reacted; 3325 cm -1 and 1110 cm -1 appear, which correspond to the stretching vibration peaks of N-H and C-O-C of the urethane group. The disappearance and appearance of the above peaks indicate that the polyurethane preparation is successful.

[0041] The sample was cut in the middle, then spliced along the fracture, and the healing was initially achieved, as shown in Figure 3 The cut dumbbell sample was used for mechanical tensile testing, as shown in Figure 4

[0042] The cyclic tensile test results are shown in Figure 5 The loading rate was set to 200 mm / min, and the deformation of each cycle gradually increased from 100% to 400%. The sample exhibited a hysteresis loop, and the hysteresis energy gradually increased as the strain increased to 400%. After several loading cycles, the sample could recover to its original length in a short time, exhibiting good resilience.

[0043] The sample was cut with a square cutter for swelling test to investigate the solubility of the polyurethane elastomer in three organic solvents, namely N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO). In the experiment, the sample weight was first measured in a dry state, then immersed in the solvent, and after reaching swelling equilibrium, the solvent was completely evaporated, and the weight was recorded again. The results showed that the prepared polyurethane elastomer only swelled but did not dissolve in the three organic solvents at room temperature, and had good solvent resistance. The test results are shown in Table 1 and Figure 6 The obtained polyurethane elastomer swelled most obviously in N,N-dimethylformamide with a swelling rate of 213.6%; N,N-dimethylacetamide was second with a swelling rate of 143.9%; and the swelling degree was smallest in dimethyl sulfoxide with a swelling rate of 54.1%.

[0044] Table 1 Swelling test results of polyurethane in organic solvents

[0045] Solvent class Initial mass (mg) Equilibrium mass (mg) Swelling ratio (%) N,N-dimethylformamide 175.8 551.4 213.6 N,N-dimethylacetamide 176.3 430.9 143.9 Dimethyl sulfoxide 173.6 264.2 52.1

[0046] The recycling method of the obtained polyurethane is as follows:

[0047] All the waste samples after testing were cut into pieces and poured into a 500 ml beaker. 250 g of DMF was added, and the beaker was sealed with plastic wrap and placed in an oven. The temperature was set to 100°C. After the sample was completely dissolved, several small holes were made in the plastic wrap, and the solution was evaporated to 75 g. Then the solution was poured into a tetrafluoroethylene mold and placed in an oven to evaporate the residual solvent. The temperature was set to 80°C, and the sample was cured for two days to obtain the remolded sample.

[0048] ​The dumbbell test sample was cut by a cutter for mechanical tensile test, the loading rate was 200 mm / min, and the test result was as shown in Figure 7 The breaking strength was 7.594 MPa, the breaking elongation reached 2588%, and the overall recovery efficiency reached 65.8%.

[0049] Comparative Example

[0050] A common chain extender 1,4-butanediol (BDO) was used for chain extension.

[0051] 1. Dehydration of raw materials: The water in polytetrahydrofuran diol (PTMG) can react with isocyanate, in order to exclude the interference of water, the dehydration treatment was carried out. 100 g of PTMG was weighed into a 250 ml three-necked flask, a magnetic rotor was added, the oil bath temperature was set to 105℃, the speed was 250 r / min, a vacuum pump was connected for dehydration for 2 hours, and then it was poured into a tetrafluoroethylene bottle for standby.

[0052] 2. Preparation of prepolymer: 7.5 mmol (15.00 g) of PTMG and 15 mmol (3.3348 g) of IPDI were weighed into a 250 ml three-necked flask, 0.04 g of DBTDL was added as a catalyst, the temperature was set to 85℃, the speed was 250 r / min, and the reaction was carried out for 4 hours. The isocyanate-terminated polyurethane prepolymer was obtained.

[0053] 3. Chain extension: 7.5 mmol (0.675 g) of BDO was weighed in a glass beaker, 20 g of DMF was added, after the BDO was dissolved, the solution was added to the above prepolymer, the polymerization temperature was set to 85℃, the speed was 250 r / min, and the reaction was carried out for 4 hours. The reaction product was poured into a tetrafluoroethylene evaporating dish, the temperature was set to 80℃, the residual solvent was evaporated in an oven, and solidification was carried out for two days.

[0054] The obtained product was slightly yellow and sticky, and was difficult to use for mechanical test, a small amount of sample was used for infrared spectrum test, and the result was as shown in Figure 1 .

[0055] In summary, the above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A solvent-resistant, recyclable, self-repairing polyurethane elastomer, characterized in that: the raw materials of the polyurethane elastomer include ascorbic acid chain extender, polytetrahydrofuran diol, isophorone diisocyanate, N,N-dimethylformamide, dibutyltin dilaurate; the percentage content of each component is: ascorbic acid chain extender 3%-4%; polytetrahydrofuran diol 75%-80%; isophorone diisocyanate 15%-20%; dibutyltin dilaurate 0.1%-0.3%; the ratio of N,N-dimethylformamide to polytetrahydrofuran diol is 10-30 mL: 15 g. 2.The solvent-resistant, recyclable, self-repairing polyurethane elastomer of claim 1, characterized in that: the molecular weight of the polytetrahydrofuran diol is 2000 g / mol.

3. A process for the preparation of solvent resistant, recyclable, self-healing polyurethane elastomers as claimed in claim 1, characterized by The steps of the method include: First, the polytetrahydrofuran diol is dehydrated; Second, the polytetrahydrofuran diol, isophorone diisocyanate and dibutyltin dilaurate after the first step of dehydration are mixed and stirred to react, and the isocyanate-terminated polyurethane prepolymer is obtained after the reaction is completed; Third, the ascorbic acid chain extender and N,N-dimethylformamide are mixed to obtain a mixture; Fourth, the mixture obtained in the third step is mixed with the prepolymer obtained in the second step to react, and the product is dried after the reaction is completed to obtain the solvent-resistant, recyclable, self-repairing polyurethane elastomer. 4.The preparation method of the solvent-resistant, recyclable, self-repairing polyurethane elastomer of claim 3, characterized in that: in the second step, the mixing temperature is 80-90℃, the stirring speed is 220-300 r / min, and the stirring time is 2-4h. 5.The preparation method of the solvent-resistant, recyclable, self-repairing polyurethane elastomer of claim 3, characterized in that: in the fourth step, the mixing temperature is 80-90℃, the stirring speed is 220-300 r / min, and the stirring time is 4-6h. 6.The preparation method of the solvent-resistant, recyclable, self-repairing polyurethane elastomer of claim 3, characterized in that: in the fourth step, the drying temperature is 75-85℃, and the drying time is 1-2 days. 7.A method for recycling the solvent-resistant, recyclable, self-repairing polyurethane elastomer of claim 1, characterized in that: after use, the solvent-resistant, recyclable, self-repairing polyurethane elastomer is cut into pieces and mixed with N,N-dimethylformamide to obtain a mixture A, which is sealed with plastic wrap and placed in an oven, and after the sample is completely dissolved, the plastic wrap is pierced with several small holes to evaporate part of the solvent, and a mixture B is obtained, the mass of the mixture B is 10%-15% of the mass of the mixture A, and then the mixture B is dried to obtain the solvent-resistant, recyclable, self-repairing polyurethane elastomer again.

8. The method for recycling the solvent-resistant, recyclable and self-repairing polyurethane elastomer according to claim 7, characterized in that: The ratio of the sheared self-repairing polyurethane elastomer and N,N-dimethylformamide is 25g:200-250mL.

9. The method for recycling the solvent-resistant, recyclable and self-repairing polyurethane elastomer according to claim 7, characterized in that: The oven temperature is 80-100℃.

10. The method for recycling the solvent-resistant, recyclable and self-repairing polyurethane elastomer according to claim 7, characterized in that: The drying temperature is 75-85℃, and the drying time is 1-2 days.

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