A method for preparing a bio-based polyester polyol and its application in cast polyurethane elastomers

Abstract

The application discloses a preparation method of a bio-based polyester polyol and application of the bio-based polyester polyol in a cast polyurethane elastomer. The method comprises the following steps: using polylactic acid diol and bio-based isocyanate as raw materials, and performing green polycondensation reaction under the action of a catalyst to obtain a bio-based polyol with high hydroxyl value; uniformly dispersing nano-enhanced fillers in the polyol through ultrasonic-assisted intercalation technology; and introducing a compound system of a benzotriazole light stabilizer and a hindered amine antioxidant, and improving solvent resistance and anti-aging performance through formation of a dynamic hydrogen bond network. After the obtained polyol, a chain extender and a catalyst are mixed, cast vulcanization is performed, and a cast polyurethane elastomer is prepared. The elastomer has high bio-based content, low VOC emission, high environmental protection and excellent comprehensive performance, and is suitable for high-end industrial elastomer products.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of polymer materials and green chemistry, specifically relating to a method for preparing a bio-based polyester polyol, and the application of the polyol in cast polyurethane elastomers. Background Technology

[0002] In the field of polymer materials, the research and development of bio-based polyester polyols and related products is an important development direction. With the increasing attention people pay to environmental protection and sustainable development, bio-based materials, due to their renewable and degradable properties, are gradually becoming ideal substitutes for traditional petroleum-based materials. As an important type of bio-based polymer material, bio-based polyester polyols have broad application prospects in many fields such as coatings, adhesives, and elastomers. Their development is of great significance to promoting the greening process of the polymer materials industry. Traditional cast polyurethane elastomers (CPUs) are widely used in tires, seals, industrial rollers and other fields, but they mainly rely on petrochemical-based polyols (such as polyethylene adipate, PEA) and aromatic isocyanates (such as MDI, TDI) for synthesis, which has the following problems: (1) the raw materials are non-renewable and have a high carbon footprint; (2) the curing process releases volatile organic compounds (VOCs); (3) the solvent resistance is poor, and the tensile strength retention rate is usually less than 70% after long-term immersion in oils or polar solvents.

[0003] In recent years, bio-based polyurethanes have become a research hotspot. For example, CN120647885A discloses a waterborne polyurethane using lignin and castor oil as raw materials. Although it improves hydrophobicity and mechanical strength, it is a water-dispersed system and is not suitable for high-performance CPUs. Furthermore, it does not solve the problem of nanofiller agglomeration and does not introduce a solvent-resistant modification mechanism. Other studies have attempted to prepare polyols using polylactic acid (PLA), but PLA has high crystallinity and low reactivity, and its direct application to CPUs leads to poor compatibility and decreased mechanical properties. In addition, among existing nanocomposite polyurethanes, nanoclay (MMT) or carbon nanotubes (CNTs) are prone to agglomeration due to their high surface energy, and their dispersion is generally below 80%, weakening the reinforcing effect.

[0004] Therefore, there is an urgent need to develop a polyurethane system that combines high bio-based content, excellent solvent resistance, good mechanical properties, and suitability for casting. Summary of the Invention

[0005] The purpose of this application is to provide a green, efficient, and scalable method for preparing bio-based polyester polyols, and to use it to prepare high-performance castable polyurethane elastomers, thereby solving the problems of low bio-based content, poor solvent resistance, and poor dispersion of nanofillers in the prior art.

[0006] To achieve the above-mentioned objectives, this application adopts the following technical solution: A method for preparing a bio-based polyester polyol includes the following steps: (a) Polylactic acid glycol is prepolymerized with vegetable oil-derived isocyanate to obtain terminal isocyanate prepolymer; (b) Adding a bimetallic catalyst ZnO / TiO2 to the prepolymer to perform a polycondensation reaction to obtain a bio-based polyester polyol; (c) Dispersing nanoparticles in an organic solvent to obtain a nano-dispersion; (d) Add the nano-dispersion to the polyol obtained in step (b) to make the nanoparticles dispersed evenly; (e) Add a compound of benzotriazole light stabilizer and hindered amine antioxidant, stir and mix evenly to obtain modified bio-based polyester polyol.

[0007] Furthermore, the degree of dispersion of the nano-dispersion is ≥95%.

[0008] Step a is the prepolymerization reaction, which is carried out at 80–120℃ for 1–3 hours under an inert atmosphere; Step b is the polycondensation reaction, which is carried out at 180–220℃ under a vacuum of less than -0.09 MPa for 2–4 hours to obtain a bio-based polyester polyol; Step c is the dispersion, which is obtained by ultrasonic treatment at 200 W for 20–40 minutes to obtain a nano-dispersion.

[0009] By employing the above technical solutions, prepolymerization of polylactic acid glycol and vegetable oil-derived isocyanate at a specific temperature under an inert atmosphere can yield terminal isocyanate prepolymers. Using a bimetallic catalyst to carry out a polycondensation reaction at a specific temperature and vacuum level can produce bio-based polyester polyols. Dispersing nanoparticles in an organic solvent and ultrasonically treating them to obtain a nano-dispersion, followed by further ultrasonication in a polyol, can achieve a nanoparticle dispersion uniformity exceeding 95%. Adding a compound of benzotriazole light stabilizers and hindered amine antioxidants and stirring until homogeneous yields modified bio-based polyester polyols. Through the synergistic design of bio-based raw materials, nano-dispersion, and dynamic hydrogen bond stabilizers, polyester polyols with high bio-based content, high solvent resistance, and uniform dispersion are obtained.

[0010] Furthermore, the polylactic acid glycol has a hydroxyl value of 140–160 mg KOH / g, and the vegetable oil-derived isocyanate is soybean oil-based isophorone diisocyanate (IPDI).

[0011] Using aliphatic / alicyclic isocyanates derived from vegetable oils improves the renewability of raw materials and avoids the yellowing and toxicity problems associated with aromatic isocyanates.

[0012] Furthermore, the molar ratio of ZnO to TiO2 in the bimetallic catalyst is 1:1 to 3:1.

[0013] Using ZnO / TiO2 bimetallic oxide catalysts to replace traditional tin-based catalysts achieves green catalysis with no heavy metal residues, while promoting efficient polycondensation.

[0014] Furthermore, the nanoparticles are selected from montmorillonite (MMT), carbon nanotubes (CNTs) or graphene, and their amount is 0.5–5% of the mass of the polyol.

[0015] By introducing specific nano-reinforcing fillers, the mechanical strength, abrasion resistance, and dimensional stability of polyurethane can be significantly improved even with low addition amounts.

[0016] Furthermore, the benzotriazole light stabilizer is UV-1180, the hindered amine antioxidant is GW-540, and the benzotriazole light stabilizer and the hindered amine antioxidant are compounded in a 1:1 ratio, with the total amount of the compound being 0.5–2% of the mass of the polyol.

[0017] Benzotriazole and hindered amines are combined in a 1:1 ratio to form a dynamic hydrogen bond network, which synergistically inhibits photo-oxidative aging and solvent erosion, significantly reduces yellowing (ΔE<1.5) and improves strength retention.

[0018] A method for preparing a castable polyurethane elastomer, wherein the bio-based polyester polyol obtained by the preparation method of the bio-based polyester polyol is mixed with a chain extender and a catalyst, and after vacuum degassing, it is cast into a mold and vulcanized at 80–100°C for 0.5–2 hours to obtain a castable polyurethane elastomer.

[0019] The polyol is used in the casting process to achieve green, low-VOC, one-step molding preparation of high-performance CPUs.

[0020] Furthermore, the chain extender is 1,4-butanediol, and the catalyst is dibutyltin dilaurate.

[0021] Furthermore, the bio-based content is ≥60%, the tensile strength retention rate is >85% after soaking in organic solvent for 500 hours, and the yellowing index ΔE is <1.5.

[0022] The resulting CPU has a high bio-based content (≥60%), excellent solvent resistance (strength retention rate >85%), and long-term stability, meeting the needs of high-end industrial applications.

[0023] This invention successfully prepared a high-performance polyester polyol with a bio-based content ≥60% and low VOC emissions by using polylactic acid glycol and bio-based isocyanate as raw materials, combining non-tin bimetallic catalytic green synthesis, ultrasonic-assisted high uniform dispersion of nanoparticles, and a dynamic hydrogen bond network solvent-resistant modification system formed by benzotriazole / hindered amine compound. When applied to cast polyurethane elastomers, the material maintains excellent mechanical properties while significantly improving solvent resistance (tensile strength retention rate >85% after solvent immersion for 500 hours), wear resistance, and anti-aging stability. It effectively overcomes the technical bottlenecks of traditional bio-based polyurethanes, such as easy agglomeration, poor solvent resistance, and easy yellowing, and has both environmental friendliness and engineering practicality. Detailed Implementation

[0024] The present application will be further illustrated by the following embodiments, but the scope of protection of the present application is not limited to the embodiments.

[0025] Raw material description Polylactic acid diol (PLA-diol): number average molecular weight Mn=1000–3000 g / mol, hydroxyl value 140–160 mgKOH / g, prepared by ring-opening polymerization of lactide with hydroxyl end capping, bio-based carbon content ≥95% (as determined by ASTM D6866).

[0026] Bio-based isocyanates: including soybean oil-based isophorone diisocyanate (IPDI), castor oil-derived hexamethylene diisocyanate (HDI), etc., with an NCO content of 30–40% and a bio-based content of ≥50%.

[0027] Non-tin bimetallic oxide catalysts: ZnO / TiO2 composite oxides, with a molar ratio of Zn:Ti of 1:1 to 3:1 and a specific surface area ≥80 m². 2 / g, activated by calcination at 500℃.

[0028] Nano-reinforced filler: Montmorillonite (MMT, Na) + The types of materials used include carbon nanotubes (CNTs, diameter 10–20 nm, length 1–5 μm) and graphene oxide (GO, sheet size 0.5–2 μm).

[0029] Solvent-resistant synergistic stabilizer composition: benzotriazole light stabilizer UV-1180 and hindered amine antioxidant GW-540 are mixed in a mass ratio of 1:1, and the total addition amount is 0.5%–2% of the mass of the polyol. Example 1:

[0030] The preparation of bio-based polyester polyols and castable polyurethane elastomers includes the following steps: 1. Prepolymerization reaction: In a 2L three-necked flask equipped with a stirrer, condenser and nitrogen inlet, add 1000g of polylactic acid glycol (PLA-diol) (Mn=2000, hydroxyl value 150mgKOH / g) and 300g of soybean oil-based isophorone diisocyanate. Purge with nitrogen for 10min to replace the air, heat to 100℃ and react for 2h to obtain terminal isocyanate prepolymer (NCO content about 4.2%).

[0031] 2. Catalytic polycondensation: Add 5g of ZnO / TiO2 catalyst (Zn:Ti=2:1), heat to 200℃, turn on the vacuum pump, control the vacuum degree ≤-0.09MPa, and carry out the polycondensation reaction for 2.5h. During the reaction, remove volatile by-products to obtain a light yellow bio-based polyester polyol (hydroxyl value 152mgKOH / g, viscosity 850mPa·s, 25℃).

[0032] 3. Nanodispersion: Add 20g of montmorillonite to 100mL of acetone, place it in an ultrasonic cleaning tank, and sonicate at 200W for 30min to form a stable dispersion; slowly add it dropwise to the above polyol, and continue to sonicate for 10min (200W). TEM observation showed that MMT was well exfoliated and the dispersion uniformity reached 96%.

[0033] 4. Solvent resistance modification: Add 5g each of UV-1180 and GW-540 (total addition 1%), stir at 60℃ for 30min to form a dynamic hydrogen bond network structure.

[0034] 5. Preparation of polyurethane elastomer: Take 100g of the above polyol, add 5g of 1,4-butanediol and 0.05g of dibutyltin dilaurate, and degas under vacuum at 80℃ for 30min; pour into an aluminum mold preheated to 80℃, place in an oven and vulcanize at 100℃ for 1h, cool and demold to obtain a transparent elastomer sample.

[0035] The method for preparing bio-based polyester polyols provided in this application includes steps such as prepolymerizing polylactic acid glycol with vegetable oil-derived isocyanate, adding a bimetallic catalyst for polycondensation, dispersing nanoparticles, mixing the nano-dispersion, and adding a compound. Specifically, by precisely controlling the temperature, time, and vacuum level of prepolymerization and polycondensation under an inert atmosphere, using a bimetallic catalyst to effectively promote the reaction, ultrasonic treatment to ensure uniform dispersion of nanoparticles, and adding a compound containing light stabilizers and antioxidants to enhance the polyol's performance, the method achieves the beneficial effects of improving product purity and performance, ensuring reaction efficiency and quality stability, and enhancing the material's lightfastness and antioxidant properties. This is because an inert atmosphere avoids the introduction of impurities, precise reaction conditions reduce side reactions, the bimetallic catalyst has high catalytic activity, ultrasonic treatment facilitates nanoparticle dispersion, and the compound enhances the material's lightfastness and antioxidant capacity.

[0036] This embodiment optimizes the process through a series of precise steps and condition controls, from raw material selection and reaction condition setting to the use of additives. Reacting under an inert atmosphere avoids the introduction of impurities, and precise control of temperature, time, and vacuum improves reaction efficiency and product quality. The use of a bimetallic catalyst enhances the catalytic effect, ultrasonic treatment ensures uniform dispersion of nanoparticles, and the combination of light stabilizers and antioxidants improves the material's light resistance and antioxidant properties. Compared to existing technologies, this effectively solves problems such as incomplete reaction, numerous side reactions, uneven nanoparticle dispersion, and poor material performance, improving the quality and performance of bio-based polyester polyols and promoting the development of bio-based polymer materials. Example 2:

[0037] In Example 1, the MMT was replaced with multi-walled carbon nanotubes (CNTs, 10 g), and the remaining steps were the same. The resulting CPU exhibited electrical conductivity (volume resistivity 10). 4 Ω·cm), suitable for antistatic industrial rollers. Example 3:

[0038] Soybean oil-based isophorone diisocyanate was replaced with castor oil-based diisocyanate, and the rest was the same as in Example 1. Example 4:

[0039] The ZnO / TiO2 molar ratio was adjusted to 1:1, and the rest was the same as in Example 1.

[0040] Comparative Example 1 (Petrochemical-based polyols control) 1000g of polyethylene adipate (PEA, hydroxyl value 150mgKOH / g) was used to replace PLA-diol, and the rest was the same as in Example 1. The resulting CPU had a bio-based content of only 15%, and the tensile strength retention rate after soaking in toluene / DMF (1:1) for 500h was 68%, ΔE=2.3.

[0041] Comparative Example 2 (without ultrasonic dispersion) The ultrasonic step was omitted, and MMT (20g) was dispersed by mechanical stirring at 1000 rpm for 1 hour. TEM showed obvious agglomerates, dispersion uniformity <75%, abrasion resistance improved by only 3%, and tensile strength retention rate was 76%.

[0042] Comparative Example 3 (without solvent-resistant stabilizer) The steps for adding UV-1180 and GW-540 are omitted; the rest is the same as in Example 1. After aging for 500 hours, ΔE = 2.1, and the strength retention rate drops to 79%.

[0043] Experiment: Performance Testing Test method description: Bio-based content: Based on ASTM D6866 standard, using radiocarbon (RTO) content. 14C) Analytical methods are used to determine the proportion of renewable carbon in the material.

[0044] VOC emissions: Release tests were conducted on cured samples after 28 days at 23°C and 50% RH, according to ISO 16000-9. Unit: mg / m³ 3 .

[0045] Tensile strength and retention rate: Dumbbell-shaped specimens were prepared according to GB / T528, and the initial tensile strength was denoted as σ0. The specimens were completely immersed in a toluene:DMF mixed solvent of 1:1 (v / v) at 50℃ for 500h, then removed and dried. The tensile strength was measured as σ1, and the retention rate was (σ1 / σ0)×100%.

[0046] Nanoparticle dispersion uniformity: The polyol film sample was observed using transmission electron microscopy (TEM). 100 fields of view were randomly selected, and the proportion of nanoparticles dispersed in monolayer or isolated state was counted (aggregates with a diameter >100nm were considered undispersed).

[0047] Yellowing index ΔE: The color difference of the sample before and after aging in a QUV accelerated aging chamber (UV-A 340nm, 60℃, 500h) is measured using a colorimeter according to ISO7724-2.

[0048] Abrasion resistance improvement rate: DIN abrasion test (load 10N, stroke 40m) was conducted according to GB / T9867. The relative improvement rate was calculated based on the abrasion volume of Comparative Example 1.

[0049] Test Results Summary Table: Example 1 62 <0.1 87 96 1.2 +15 Example 2 61 <0.1 85 94 1.3 +18* Example 3 63 <0.1 84 95 1.1 +12 Example 4 62 <0.1 86 95 1.0 +14 Comparative Example 1 15 1.2 68 — 2.3 Benchmark (0) Comparative Example 2 62 <0.1 76 73 1.8 +3 Comparative Example 3 62 <0.1 79 96 2.1 +14 Results analysis: 1. Examples 1–4 all exhibited high bio-based content (≥61%), extremely low VOC, and excellent solvent resistance (retention rate ≥84%), which were significantly better than Comparative Example 1 (conventional petrochemical system). 2. Comparative Example 2 demonstrates that ultrasonic-assisted dispersion is crucial for improving the uniformity and performance of nanomaterials; 3. Comparative Example 3 demonstrates that the solvent-resistant synergistic stabilizer composition plays an irreplaceable role in inhibiting yellowing and maintaining strength; 4. Example 4 shows that even when the catalyst ratio is adjusted (Zn:Ti=1:1), high performance can still be maintained, indicating that the process of the present invention has good robustness.

[0050] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a bio-based polyester polyol, characterized in that, Includes the following steps: (a) Polylactic acid glycol is prepolymerized with vegetable oil-derived isocyanate to obtain terminal isocyanate prepolymer; (b) Adding a bimetallic catalyst ZnO / TiO2 to the prepolymer to perform a polycondensation reaction to obtain a bio-based polyester polyol; (c) Dispersing nanoparticles in an organic solvent to obtain a nano-dispersion; (d) Add the nano-dispersion to the polyol obtained in step (b) to make the nanoparticles dispersed evenly; (e) Add a compound of benzotriazole light stabilizer and hindered amine antioxidant, stir and mix evenly to obtain modified bio-based polyester polyol.

2. The method for preparing a bio-based polyester polyol as described in claim 1, characterized in that, The dispersion of the nano-dispersion is ≥95%.

3. The method for preparing a bio-based polyester polyol as described in claim 1, characterized in that, The polylactic acid glycol has a hydroxyl value of 140–160 mg KOH / g, and the vegetable oil-derived isocyanate is soybean oil-based isophorone diisocyanate (IPDI).

4. The method for preparing a bio-based polyester polyol as described in claim 1, characterized in that, The molar ratio of ZnO to TiO2 in the bimetallic catalyst is 1:1 to 3:

1.

5. The method for preparing a bio-based polyester polyol as described in claim 1, characterized in that, The nanoparticles are selected from montmorillonite (MMT), carbon nanotubes (CNTs) or graphene, and their amount is 0.5–5% of the mass of the polyol.

6. The method for preparing a bio-based polyester polyol as described in claim 1, characterized in that, The benzotriazole light stabilizer is UV-1180, and the hindered amine antioxidant is GW-540. The benzotriazole light stabilizer and the hindered amine antioxidant are compounded in a 1:1 ratio, and the total amount of the compound is 0.5–2% of the mass of the polyol.

7. A method for preparing a castable polyurethane elastomer, characterized in that, The bio-based polyester polyol obtained by the preparation method of the bio-based polyester polyol according to any one of claims 1-6 is mixed with a chain extender and a catalyst, and after vacuum degassing, it is poured into a mold and vulcanized at 80-100°C for 0.5-2 hours to obtain a castable polyurethane elastomer.

8. The method as described in claim 7, characterized in that, The chain extender is 1,4-butanediol, and the catalyst is dibutyltin dilaurate.

9. A castable polyurethane elastomer prepared by the method of claim 8, characterized in that, Bio-based content ≥60%, tensile strength retention rate >85% after soaking in organic solvent for 500 hours, yellowing index ΔE <1.5.