A method for preparing degradable rubber using liquid rubber as raw material

Abstract

The application discloses a method for preparing degradable rubber by using liquid rubber as raw material, and is characterized by using hydroxyl-terminated liquid rubber and / or carboxyl-terminated liquid rubber as raw material, and preparing degradable rubber through polycondensation and ester exchange reaction. The rubber synthesized by the method has excellent mechanical properties and degradation and recycling performance, and has important significance for realizing green synthesis and economic circulation of rubber.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials and rubber synthesis technology, specifically to a method for preparing biodegradable rubber using liquid rubber as a raw material. Background Technology

[0002] Rubber products are made from natural or synthetic rubber as raw materials, with the addition of additives such as vulcanizing agents, vulcanization accelerators, antioxidants, and reinforcing fillers, through processing procedures. Currently, the production of synthetic rubber far exceeds that of natural rubber, with styrene-butadiene rubber (SBR) being the most produced. Rubber products have wide applications in people's production and daily life, and with the continuous development of my country's industry, agriculture, transportation, and oil extraction, the demand for them is constantly increasing. However, this has also brought about the pollution problem of waste rubber. Because nitrile rubber, butadiene rubber, and SBR are not biodegradable, the "black pollution" problem caused by waste rubber is becoming increasingly serious. Therefore, the recycling of waste rubber and the development of biodegradable rubber are of great significance.

[0003] Common methods for biodegradable modification of rubber include: First, blending decomposition accelerators such as PGA and glycolide into the rubber matrix. However, these accelerators produce large amounts of rubber residue, hindering subsequent recycling and leading to a decrease in the mechanical properties of the rubber composite. Second, constructing dynamic and reversible covalent bonds between rubber molecules for crosslinking, followed by decomposition under specific conditions to achieve recycling and reuse. This method requires stringent degradation conditions and also results in a decrease in the mechanical properties of the rubber composite. Third, copolymerizing small-molecule bio-based diacids and diols in different ratios to obtain biodegradable polyester rubber to replace traditional rubber. However, this method relies on limited raw materials and finding suitable ratios is challenging. Summary of the Invention

[0004] To overcome the problems of poor degradation and recycling capacity, high degradation difficulty, and large differences in mechanical properties compared with traditional rubber, the present invention provides a method for preparing biodegradable rubber using liquid rubber as raw material. By periodically introducing ester bonds into the rubber main chain, the inherent hydrolytic property of ester bonds is utilized to enable multiple depolymerization pathways, thereby giving the biodegradable rubber better mechanical properties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention first discloses a method for preparing biodegradable rubber from liquid rubber, comprising the following steps:

[0007] Step 1: Mix the hydroxyl-terminated liquid rubber with a dicarboxylic acid, add a catalyst, and heat and stir the mixture under an argon atmosphere until it cools to room temperature to obtain a carboxyl-terminated rubber; or, mix the carboxyl-terminated liquid rubber with a diol, add a catalyst, and heat and stir the mixture under an argon atmosphere until it cools to room temperature to obtain a hydroxyl-terminated rubber.

[0008] Step 2: Add the catalyst again to the carboxyl-terminated rubber or hydroxyl-terminated rubber obtained in Step 1, and carry out a heating and stirring reaction under vacuum conditions to obtain biodegradable rubber.

[0009] Furthermore, the molecular weight of the hydroxyl-terminated liquid rubber or the carboxyl-terminated liquid rubber is between 400 and 10,000.

[0010] Further: the dicarboxylic acid is selected from one of the following: substituted or unsubstituted aliphatic dicarboxylic acids with 2-10 carbon atoms, 2,5-furandicarboxylic acid, and carboxyl-terminated liquid rubber; the diol is selected from one of the following: substituted or unsubstituted aliphatic diols with 2-10 carbon atoms, 2,5-furandiethanol, polylactic acid diol, and hydroxyl-terminated liquid rubber.

[0011] Further, the catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, antimony trioxide, antimony glycolate, antimony acetate, stannous octoate, stannous chloride, and stannous oxide in any proportion.

[0012] Further: In step 1, the molar ratio of hydroxyl-terminated liquid rubber to diacid is 1:1-1.5, and the molar ratio of carboxyl-terminated liquid rubber to diol is 1:1-1.5; the amount of catalyst added in step 1 is 1×10 of the molar amount of either hydroxyl-terminated or carboxyl-terminated liquid rubber raw material. -4 -5×10 -4 In step 2, the amount of catalyst added is 0.5 × 10⁻⁶ of the molar amount of the hydroxyl-terminated liquid rubber or carboxyl-terminated liquid rubber raw material. -4 -2.5×10 -4 The molar amount of hydroxyl-terminated liquid rubber or carboxyl-terminated liquid rubber is measured as the ratio of its weight to its molar mass.

[0013] Further: In step 1, the heating and stirring reaction method is as follows: adjust the heating rate to gradually raise the temperature of the reaction system to 150-180℃ over 1.5-2.5 hours, and maintain the temperature for 8-12 hours. In step 2, the heating and stirring reaction method is as follows: adjust the heating rate to gradually raise the temperature of the reaction system to 200-230℃ over 1.5-2.5 hours, and maintain the temperature for 4-6 hours. By controlling the heating rate, excessively vigorous internal exothermic reactions can be avoided, thereby preventing cross-linking of the product due to the reaction of double bond groups in the rubber with the catalyst.

[0014] The general structural formula of the biodegradable rubber obtained by the above preparation method can be expressed as:

[0015]

[0016] Wherein: R1 comes from hydroxyl-terminated liquid rubber or diol, and R2 comes from carboxyl-terminated liquid rubber or dicarboxylic acid.

[0017] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0018] 1. This invention utilizes macromolecular hydroxyl-terminated liquid rubber and / or carboxyl-terminated liquid rubber to prepare biodegradable rubber. A wide variety of raw materials can be selected, such as hydroxyl-terminated cis-butadiene rubber, hydroxyl-terminated nitrile butadiene rubber, hydroxyl-terminated natural rubber, or hydroxyl-terminated styrene-butadiene rubber for hydroxyl-terminated liquid rubber, and carboxyl-terminated cis-butadiene rubber, carboxyl-terminated nitrile butadiene rubber, carboxyl-terminated natural rubber, or carboxyl-terminated styrene-butadiene rubber for carboxyl-terminated liquid rubber. Different types of liquid rubber can be used to prepare biodegradable rubbers with various block structures, resulting in a wide range of adjustable properties and broad application areas for the obtained rubber.

[0019] 2. The biodegradable rubber synthesized in this invention has similar mechanical properties to traditional rubber and exhibits good degradation and recycling performance. Degradation can be achieved by adding the rubber to an alkaline or acidic mixture of water and alcohol (such as methanol or ethanol) and heating it. Furthermore, the resulting small molecules can be reused sustainably. Therefore, the biodegradable rubber prepared in this invention is a green and sustainable polymer, which is of great significance for realizing green rubber synthesis and economic recycling. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The NMR spectrum is shown for the biodegradable polyester rubber obtained in Example 1 of this invention.

[0022] Figure 2 The infrared image is of the biodegradable polyester rubber obtained in Example 1 of this invention.

[0023] Figure 3 The NMR spectrum of the biodegradable polyester rubber obtained in Example 2 of this invention;

[0024] Figure 4 The infrared image is of the biodegradable polyester rubber obtained in Example 2 of this invention.

[0025] Figure 5 The NMR spectrum of the degradation product of the biodegradable polyester rubber obtained in Example 2 of this invention;

[0026] Figure 6 The image shows the infrared spectrum of the degradation product of the biodegradable polyester rubber obtained in Example 2 of this invention. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below through specific embodiments. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0028] Example 1

[0029] This embodiment prepares biodegradable rubber according to the following steps:

[0030] (1) Hydroxyl-terminated butadiene-acrylonitrile rubber (8.0 g, 6 mmol, 1350 g / mol) and succinic acid (1.1 g, 9 mmol) were added to a three-necked reaction flask, along with tetraisopropyl titanate (170 μg, 0.6 μmol). A stirrer was attached to the middle neck, and 90° vacuum fittings were attached to the two side necks. The flask was then filled with an argon atmosphere. A continuous flow of argon gas was maintained through the three-necked flask. The flask was placed in a sand bath, and the temperature was slowly increased to 150 °C (total heating time 2 h). The reaction was maintained at this temperature for 10 h, then cooled to room temperature to obtain a yellow, low-molecular-weight carboxyl-terminated rubber product.

[0031] (2) Add 5g of low molecular weight carboxyl-terminated rubber to a three-necked reaction flask, along with 100μg (0.35μmol) of tetraisopropyl titanate. Attach a stirrer to the middle neck and 90° vacuum fittings to the two side necks. Replace the gas atmosphere in the flask with argon. Place the reaction flask in a sand bath and slowly heat it. When the temperature reaches 100°C, begin vacuuming until the temperature stabilizes at 200°C (total heating time 2 hours). Continue the vacuum reaction for 5 hours to obtain a light yellow biodegradable rubber. The structure of this product is shown below:

[0032]

[0033] Figure 1 and Figure 2 The NMR and IR spectra of the biodegradable polyester rubber are shown below. In the NMR spectrum, a new signal peak appears at a chemical shift of 4.10 ppm, representing the methylene signal linked to the ester group in the product, indicating the presence of the ester group and successful synthesis. In the IR spectrum, a peak appears at 1735 cm⁻¹. -1 The appearance of a strong signal peak, which is the signal peak of the C=O double bond in the ester group, further proves that the product was successfully synthesized.

[0034] Example 2

[0035] This embodiment prepares biodegradable rubber according to the following steps:

[0036] (1) Carboxyl-terminated butadiene-acrylonitrile rubber (5.0 g, 1.5 mmol, 3250 g / mol) and 1,5-pentanediol (0.234 g, 2.25 mmol) were added to a three-necked reaction flask, along with tetraisopropyl titanate (4.26 mg, 0.15 μmol). A stirrer was attached to the middle neck, and 90° vacuum fittings were attached to the two side necks. The flask was then filled with an argon atmosphere. A continuous flow of argon gas was maintained through the three-necked flask. The flask was placed in a sand bath, and the temperature was slowly increased to 150 °C (total heating time 2 h). The reaction was maintained at this temperature for 10 h, and then cooled to room temperature to obtain a yellow, low-molecular-weight hydroxyl-terminated rubber product.

[0037] (2) Add 5g of low molecular weight hydroxyl-terminated rubber to a three-necked reaction flask, along with tetraisopropyl titanate (2.13mg, 0.075μmol). Attach a stirrer to the middle neck and 90° vacuum fittings to the two side necks. Replace the gas atmosphere in the flask with argon. Place the reaction flask in a sand bath and slowly heat it. When the temperature reaches 100°C, begin vacuuming until the temperature stabilizes at 200°C (total heating time 2h). Continue vacuuming for 5 hours. A light yellow biodegradable rubber is finally obtained. The structure of this product is shown below:

[0038]

[0039] Figure 3 and Figure 4 The NMR and IR spectra of the biodegradable polyester rubber are shown below. In the NMR spectrum, a new signal peak appears at a chemical shift of 4.09 ppm, representing the methylene signal linked to the ester group in the product, indicating the presence of the ester group and successful synthesis of the product. In the IR spectrum, a peak appears at 1735 cm⁻¹. -1 The appearance of a strong signal peak, which is the signal peak of the C=O double bond in the ester group, further proves that the product was successfully synthesized.

[0040] (3) The obtained biodegradable rubber (0.5 g) was added to a 150 mL thick-walled pressure-resistant bottle, along with 50 mL of a mixed solution of ethanol and water (ethanol:water = 49:1), and then 2.5 g of potassium hydroxide. The mixture was placed in an oil bath at 80 °C and heated and stirred for 4 hours. After 4 hours, the mixture was cooled to room temperature, the supernatant was removed, the precipitated potassium hydroxide was removed, and the supernatant was evaporated to dryness using a rotary evaporator. The evaporated product was then analyzed for NMR and IR spectra. Figure 5 and Figure 6 The images show the NMR and IR spectra of the biodegradable polyester rubber after degradation. Figure 3 contrast, Figure 5The signal peak at a chemical shift of 4.09 ppm disappeared in the NMR spectrum. This signal peak represents the methylene signal connected to the ester group in the product. Its disappearance indicates the disappearance of the ester group, and the biodegradable rubber has been successfully degraded. Figure 6 In the infrared spectrum, the undegradable rubber has an infrared value of 1736 cm⁻¹ before degradation. -1 The appearance of a strong signal peak is the signal peak of the C=O double bond in the ester group. The disappearance of the signal peak after degradation indicates that the ester group has disappeared, proving that the ester bond of the degradable rubber has been broken and the degradation was successful.

[0041] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing biodegradable rubber from liquid rubber, characterized in that, Includes the following steps: Step 1: Mix hydroxyl-terminated liquid rubber with a diacid until homogeneous, add a catalyst, and under an argon atmosphere, adjust the heating rate to gradually raise the temperature of the reaction system to 150-180℃ over 1.5-2.5 h, maintain the temperature for 8-12 h, and then cool to room temperature to obtain carboxyl-terminated rubber; or, mix carboxyl-terminated liquid rubber with a diol until homogeneous, add a catalyst, and heat and stir the reaction under an argon atmosphere until cooled to room temperature to obtain hydroxyl-terminated rubber; wherein the molar ratio of hydroxyl-terminated liquid rubber to diacid is 1:1-1.5, and the molar ratio of carboxyl-terminated liquid rubber to diol is 1:1-1.

5. The dicarboxylic acid is selected from one of the following: a substituted or unsubstituted aliphatic dicarboxylic acid with 2 to 10 carbon atoms, 2,5-furandicarboxylic acid, and carboxyl-terminated liquid rubber; the diol is selected from one of the following: a substituted or unsubstituted aliphatic diol with 2 to 10 carbon atoms, 2,5-furandimethyl alcohol, polylactic acid diol, and hydroxyl-terminated liquid rubber; the catalyst is one or more of the following: tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, antimony trioxide, antimony glycolate, antimony acetate, stannous octoate, stannous chloride, and stannous oxide, mixed in any proportion. Step 2: Add the catalyst again to the carboxyl-terminated or hydroxyl-terminated rubber obtained in Step 1. Under vacuum conditions, adjust the heating rate so that the reaction system is gradually heated to 200-230℃ over 1.5-2.5 hours and kept at this temperature for 4-6 hours to obtain the biodegradable rubber.

2. The method according to claim 1, characterized in that: The molecular weight of the hydroxyl-terminated liquid rubber or the carboxyl-terminated liquid rubber is between 400 and 10,000.

3. The method according to claim 1, characterized in that, In step 1, the amount of catalyst added is 1 × 10⁻⁶ of the molar amount of the hydroxyl-terminated liquid rubber or carboxyl-terminated liquid rubber raw material. -4 -5×10 -4 In step 2, the amount of catalyst added is 0.5 × 10⁻⁶ of the molar amount of the hydroxyl-terminated liquid rubber or carboxyl-terminated liquid rubber raw material. -4 -2.5×10 -4 .

4. A biodegradable rubber prepared by the preparation method according to any one of claims 1 to 3.

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