A polylactic acid-based polyurethane, and a preparation method and application thereof

Abstract

The application discloses a kind of polylactic acid-based polyurethane and its preparation method and application, the polyurethane is with polyester polyol and L-lactide ring-opening polymerization to obtain diblock prepolymer, again with dicyclohexyl methane diisocyanate reaction and be prepared multi-block polyurethane;Wherein, the polyester polyol is PriplastTM 3238.The polyurethane body of the application has superior mechanical properties and excellent hydrophobic capacity, has excellent bonding performance after being used as adhesive and can be maintained bonding ability underwater.Solve the contradiction that existing polyurethane adhesive pollutes environment, the mechanical properties and adhesion of body cannot be taken into account, effectively prolong the service period of adhesive, make it show great application potential in many fields.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a polylactic acid-based polyurethane, its preparation method, and its application. Background Technology

[0002] Polyurethane (PU) is an important class of polymer materials, produced by the reaction of isocyanates and polyols. Its molecular structure contains repeating urethane groups (-NHCOO-). Its discovery can be traced back to the early 1930s, when it was first synthesized by German scientist Otto Bayer and his team. After World War II, with technological advancements and the expansion of its applications, polyurethane gradually became an important commercial product, widely used in various industries due to its excellent physical and chemical properties.

[0003] Polyurethane is mainly produced through the addition reaction of isocyanates (such as MDI and TDI) with polyols (such as polyether polyols and polyester polyols) under the action of a catalyst. During the reaction, auxiliary components such as chain extenders, crosslinking agents, and foaming agents can be added to regulate the performance of the final product. Adhesives are media that can tightly bond the surfaces of the same or different solid materials together. Polylactic acid (PLA) is an environmentally friendly material derived from plants. It possesses good biocompatibility and safety, is easy to process and mold, and produces products with good gloss and mechanical strength, making it widely applicable in many fields. Traditional adhesives are made from non-renewable chemical raw materials such as petroleum, highly dependent on limited fossil resources and solvent-based polymerization methods, resulting in adhesive materials containing volatile organic compounds (VOCs). The core advantage of bio-based polyurethane adhesives lies in their green environmental protection; they utilize renewable resources such as vegetable oils and straw to replace petroleum raw materials, significantly reducing carbon emissions. Their performance is also excellent, with their natural long-chain structure providing outstanding hydrophobicity and hydrolysis resistance. These materials are widely available, green, and renewable, with excellent biodegradability and biocompatibility. Furthermore, bio-based adhesives are safer, containing no toxic or harmful components and not releasing volatile organic compounds during use, making them safer for both humans and the environment. In addition, they possess excellent bonding properties and a wide range of applications, suitable for bonding various materials to meet the needs of different fields.

[0004] Chinese patent application CN116855213A discloses a self-adhesive polylactic acid (PLA) adhesive and its applications. The raw materials for this PLA adhesive include polyols, lactide, caprolactone, and acrylates. Applying this PLA adhesive to common substrates results in high adhesion, manifested as high peel strength. The bulk polymerization method used in its preparation is simple, offering advantages such as low production cost, simple reaction process, controllable molecular weight, adjustable viscosity, and environmental friendliness. It allows for the directional design of pressure-sensitive adhesive components to meet different market demands, making it suitable for commercial promotion and showing great application potential. However, its bulk properties are weak, limiting its application scenarios. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to improve the mechanical and adhesive properties of polyurethane.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] A polylactic acid-based polyurethane is a multiblock polyurethane prepared by ring-opening polymerization of polyester polyol (DAEP) and L-lactide (LLA) to obtain a diblock prepolymer (PLDL), and then reacting it with dicyclohexylmethane diisocyanate (HMDI); wherein the polyester polyol is Priplast™ 3238.

[0008] The polyurethane matrix of this invention possesses superior mechanical properties and excellent hydrophobicity, exhibiting excellent adhesive performance when used as an adhesive and maintaining adhesion underwater. Simultaneously, the adhesive prepared from bio-based polyester polyols and lactide demonstrates outstanding adhesive properties, meeting the growing market demand for environmentally friendly bio-based adhesives and injecting new momentum into the industrialization of green adhesives. The precise construction of the adhesive structure not only overcomes the contradiction between the mechanical properties and adhesive properties of traditional adhesives but also effectively extends the service life of the adhesive, demonstrating its enormous application potential in multiple fields.

[0009] Preferably, the polyester polyol is purchased from Cargill Biochemicals Co., Ltd., and its real name is Priplast™ 3238. It is a bio-based amorphous polyester polyol; its structural formula is approximately as follows: .

[0010] Preferably, the number average molecular weight of the polyester polyol is 2000.

[0011] Preferably, the mass ratio of the polyester polyol to L-lactide is 5-10:5-10; more preferably, it is one of 10:5, 7.5:7.5, or 5:10.

[0012] Preferably, the mass ratio of the polyester polyol to L-lactide is 1:1.

[0013] Preferably, the molar ratio of the diblock prepolymer to dicyclohexylmethane diisocyanate is 1:1.

[0014] Preferably, the preparation process also includes adding a catalyst to catalyze the reaction.

[0015] The present invention also proposes a method for preparing the polylactic acid-based polyurethane, comprising the following steps: removing water from polyester polyol and L-lactide, mixing with a catalyst, and heating under an inert gas atmosphere to carry out a copolymerization reaction to obtain a diblock prepolymer PLDL; after the reaction is completed, adding a solvent and passing an inert gas through it, then adding dicyclohexylmethane diisocyanate and a catalyst and heating to carry out the reaction; and after the reaction is completed, post-treatment is performed to obtain the polylactic acid-based polyurethane.

[0016] Preferably, in the process of preparing the diblock prepolymer, the reaction includes reacting at 110-115℃ for 1-2 hours, then heating to 125-135℃ for 1-2 hours, then heating to 140-150℃ for 1-2 hours, then heating to 155-160℃ for 1-2 hours, and then heating to 165-170℃ for 1-2 hours; the temperature for adding dicyclohexylmethane diisocyanate and catalyst and heating for reaction is 70-75℃ for 1-3 hours.

[0017] Preferably, in the process of preparing the diblock prepolymer, the reaction includes reacting at 110°C for 1 hour, then heating to 125°C for 1 hour, then heating to 140°C for 1 hour, then heating to 155°C for 1 hour, and then heating to 170°C for 1 hour; the reaction is carried out by adding dicyclohexylmethane diisocyanate and catalyst at 70°C for 3 hours.

[0018] Preferably, the catalyst used in the preparation of the diblock prepolymer is stannous isooctanoate (SnOct2), and the catalyst used in the reaction of the diblock prepolymer with dicyclohexylmethane diisocyanate is dibutyltin dilaurate (DBTDL); the solvent is N,N-dimethylformamide (DMF).

[0019] Preferably, in the process of preparing the diblock prepolymer, the mass of the catalyst added is three per thousand of the sum of the masses of the polyester polyol and L-lactide; and in the process of reacting the diblock prepolymer with dicyclohexylmethane diisocyanate, the mass of the catalyst added is five per ten thousand of the mass of the diblock prepolymer.

[0020] Preferably, the inert gas atmosphere of the polyester polyol, L-lactide, and catalyst is maintained by sealing the container after feeding the materials into a nitrogen glove box.

[0021] The present invention also proposes an application of the polylactic acid-based polyurethane as an adhesive.

[0022] The present invention also proposes an adhesive containing the aforementioned polylactic acid-based polyurethane.

[0023] Preferably, the polylactic acid-based polyurethane is the sole effective component of the adhesive.

[0024] The adhesive body of this invention possesses superior mechanical properties and excellent hydrophobicity. When used as an adhesive, it exhibits excellent bonding performance and can maintain bonding ability underwater. This resolves the contradictions inherent in existing polyurethane adhesives, namely environmental pollution, incompatibility between robust mechanical properties and adhesive performance, effectively extending the service life of the adhesive and demonstrating significant application potential in multiple fields.

[0025] The advantages of this invention are: This invention utilizes the ring-opening polymerization of bio-based amorphous polyester polyol (DAEP) and L-lactide (LLA) to obtain a diblock prepolymer (PLDL), which is then reacted with dicyclohexylmethane diisocyanate (HMDI) to synthesize a polylactic acid-based biodegradable polyurethane adhesive. The core technical approach is based on the synergistic modification of polyester polyol and L-lactide through copolymerization: through stannous isooctanoate-catalyzed ring-opening copolymerization, the flexible long chains of polyester polyol are introduced into the rigid segments of L-lactide, disrupting the regularity of the PLA molecular chain and improving toughness and processability. Furthermore, by changing the ratio of polyester polyol to L-lactide, the molecular chain structure is optimized to find the optimal ratio for improving adhesive performance. Finally, the chain extension reaction of dicyclohexylmethane diisocyanate is used to construct urethane bonds (-NHCOO-), enhancing intermolecular hydrogen bonding and interfacial chemical bonding capabilities. Simultaneously, the hydrophobic alkyl segments effectively inhibit water penetration, significantly improving the water resistance of the adhesive.

[0026] In this invention, polylactic acid is introduced into the polyurethane chain structure to regulate its composition. A polylactic acid-based biodegradable polyurethane adhesive is prepared by reacting a diblock copolymer polyol with isocyanate. With increasing L-lactide mass ratio, the mechanical properties of the polyurethane adhesive are significantly altered, with fracture stress gradually increasing, fracture strain gradually decreasing, and fracture toughness reaching 37.61 MJ / m. 3 Furthermore, its shear strength on wood substrates reaches up to 6.5 MPa. In addition, the polymer exhibits excellent surface hydrophobicity and water stability, maintaining its adhesive properties even in aquatic environments.

[0027] The main raw material of this adhesive comes from biomass resources, which are environmentally friendly and readily available. It conforms to the current green chemistry synthesis concept and provides a certain theoretical basis and data support for the synthesis and preparation of bio-based polyurethane adhesives. Attached Figure Description

[0028] Figure 1 The above is the 1H NMR spectrum of the prepolymer PLDL in Example 2 of this invention; Figure 2 The infrared spectrum of the polylactic acid-based biodegradable polyurethane adhesive prepared in Example 2 of this invention; Figure 3 This is a synthetic route diagram of the polylactic acid-based biodegradable polyurethane adhesive prepared in Examples 1-3 of the present invention; Figure 4 The stress-strain curves of the adhesives prepared in Examples 1-3 and Comparative Example 1 of this invention are shown. Figure 5 The image shows a sample prepared from the polylactic acid-based biodegradable polyurethane adhesive in Example 2 of this invention, lifted to a weight of 10 pounds. Figure 6 This is a graph showing the overlap strength data of overlap specimens prepared using different substrates with polylactic acid-based biodegradable polyurethane adhesive in Example 2 of the present invention. Figure 7 This is a graph showing the lap strength data of a steel substrate used to prepare an lapped specimen of polylactic acid-based biodegradable polyurethane adhesive in Example 2 of the present invention, after multiple detachments and repeated lapping experiments. Figure 8 The water contact angle diagrams are shown for the adhesives prepared in Examples 1-3 and Comparative Example 1 of this invention. Figure 9 This image shows the polylactic acid-based biodegradable polyurethane adhesive prepared in Example 2 of the present invention after being soaked underwater after adhering to items of different materials. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0031] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0032] The bio-based amorphous polyester polyol described below was purchased from Cargill Biochemicals Ltd. and is named Priplast™ 3238.

[0033] Example 1 A method for preparing a polylactic acid-based biodegradable polyurethane adhesive, the roadmap of which is shown below. Figure 3 As shown, it includes the following steps: By weight, 10 parts of bio-based amorphous polyester polyol (DAEP) with a number-average molecular weight of 2000, 5 parts of L-lactide (LLA) after dehydration, and 0.045 parts of stannous isooctanoate (SnOct2) were placed in a three-necked flask under a nitrogen atmosphere and sealed. The flask was removed from the glove box and placed in an oil bath at 110°C, 125°C, 140°C, 155°C, and 170°C for one hour each (heating time is not included), for a total reaction time of five hours to obtain the diblock prepolymer PLDL. The reaction system was cooled to 70°C, and N,N-dimethylformamide (DMF) at a mass ratio of 1:1 with PLDL was added, followed by nitrogen purging. Next, dicyclohexylmethane diisocyanate (HMDI) at a molar ratio of 1:1 with PLDL was slowly added dropwise to the reaction mixture under constant pressure, and dibutyltin dilaurate (DBTDL) at 0.05% by mass of PLDL was added as a catalyst. The reaction was carried out for 3 hours. After the reaction was completed, the white viscous polymer was transferred to a polytetrafluoroethylene mold, placed in a 100°C oven under negative pressure to remove the solvent, and polylactic acid-based biodegradable polyurethane adhesive was obtained.

[0034] The obtained product was fabricated into dumbbell-shaped specimens with an intermediate size of 0.2 mm × 2.05 mm. Tensile testing was performed using a mechanical testing machine with a length maintained at 10 mm and a tensile rate of 50 mm / min. The measured ultimate stress was 3.65 MPa. Figure 4 As shown.

[0035] Example 2 A method for preparing a polylactic acid-based biodegradable polyurethane adhesive differs from Example 1 only in that: 7.5 parts of a bio-based amorphous polyester polyol (DAEP) with a number-average molecular weight of 2000, 7.5 parts of L-lactide (LLA) after dehydration, and 0.045 parts of stannous isooctanoate (SnOct2) are added to a three-necked flask in a nitrogen-atmosphere glove box and sealed. All other steps are the same as in Example 1.

[0036] Figure 1 The 1H NMR spectrum of the diblock prepolymer PLDL: via Figure 1 The results show that DAEP and LLA have successfully copolymerized. The peak positions and proportions are accurate, and no extraneous peaks appear. These all demonstrate the successful preparation of the prepolymer PLDL. Fourier transform infrared spectroscopy characterization confirms that the isocyanate and hydroxyl groups react completely during the reaction process, and multiple characteristic peaks in the carbamate are clearly visible. The infrared spectrum of this embodiment is shown below. Figure 2 As shown, by Figure 2It can be seen that the preparation of polylactic acid-based biodegradable polyurethane adhesive is complete. The obtained product was made into dumbbell-shaped specimens with an intermediate size of 0.2 mm × 2.05 mm, and tensile tests were performed using a mechanical testing machine. The length was maintained at 10 mm, the tensile rate was 50 mm / min, and the ultimate stress was measured to be 6.91 MPa. Figure 4 As shown.

[0037] Example 3 A method for preparing a polylactic acid-based biodegradable polyurethane adhesive differs from Example 1 only in that: 5 parts of bio-based amorphous polyester polyol (DAEP) with a number-average molecular weight of 2000, 10 parts of L-lactide (LLA) after dehydration, and 0.045 parts of stannous isooctanoate (SnOct2) are added to a three-necked flask in a nitrogen-atmosphere glove box and sealed. All other steps are the same as in Example 1.

[0038] The obtained product was fabricated into dumbbell-shaped specimens with an intermediate size of 0.2 mm × 2.05 mm. Tensile testing was performed using a mechanical testing machine with a length maintained at 10 mm and a tensile rate of 50 mm / min. The measured ultimate stress was 10.38 MPa. Figure 4 As shown.

[0039] Comparative Example 1 A method for synthesizing an adhesive, comprising the following steps: One part by molar amount of dehydrated bio-based amorphous polyester polyol (DAEP) with a number-average molecular weight of 2000 was added to a three-necked flask. The mixture was heated to 70°C and purged with nitrogen. One part by molar amount of dicyclohexylmethane diisocyanate (HMDI) was dissolved in DMF at a mass ratio of 1:1 to HMDI and then slowly added dropwise to the reaction mixture under constant pressure. Dibutyltin dilaurate (DBTDL) at a mass ratio of 0.05% of DAEP was added as a catalyst, and the reaction was carried out for 3 hours. After the reaction was completed, the white viscous polymer was transferred to a polytetrafluoroethylene mold and placed in a 100°C oven under negative pressure to remove the solvent, thus obtaining the adhesive.

[0040] The obtained product was fabricated into dumbbell-shaped specimens with an intermediate size of 0.2 mm × 2.05 mm. Tensile testing was performed using a mechanical testing machine with a length maintained at 10 mm and a tensile rate of 50 mm / min. The measured ultimate stress was 1.42 MPa. Figure 4 As shown.

[0041] Comparative Example 2 A method for synthesizing an adhesive differs from Example 2 only in that: 7.5 parts of a bio-based semi-crystalline polyester polyol with a number-average molecular weight of 2000 (Priplast™ 3294, purchased from Cargill Biochemicals Ltd.), 7.5 parts of L-lactide (LLA) after dehydration, and 0.045 parts of stannous isooctanoate (SnOct2) are added to a three-necked flask in a nitrogen-atmosphere glove box and sealed. All other steps are the same as in Example 2.

[0042] Since Priplast™ 3294 is a bio-based semi-crystalline polyester polyol, the polyurethane prepared by reacting it with L-lactide, which is also crystalline, has an excessively high degree of crystallinity. The resulting samples are too brittle, making it difficult to prepare dumbbell-shaped specimens for tensile testing, thus lacking practical value.

[0043] Comparative Example 3 A method for synthesizing an adhesive includes the following steps: 7.5 parts by weight of a bio-based amorphous polyester polyol (DAEP) with a number-average molecular weight of 2000, 7.5 parts by weight of L-lactide (LLA) after dehydration, and 0.045 parts by weight of stannous isooctanoate (SnOct2) are placed in a nitrogen-atmospheric glove box and sealed. The three-necked flask is removed from the glove box and placed in an oil bath at 110°C, 125°C, 140°C, 155°C, and 170°C for one hour each (heating time is not included), for a total reaction time of five hours to obtain a diblock prepolymer PLDL. After the reaction is complete, the prepolymer is transferred to a polytetrafluoroethylene mold, placed in a 100°C oven under negative pressure to remove the solvent, thus obtaining an adhesive.

[0044] Because no isocyanate was added, the sample was too soft to prepare dumbbell-shaped specimens for tensile testing, thus lacking practical value.

[0045] Data Analysis: Table 1. Characterization of the mechanical properties of adhesives

[0046] Table 1 shows that a series of polyurethane adhesives with varying mechanical properties can be obtained by controlling the differences in the content of polyester polyol and L-lactide. As the content of L-lactide increases, the stress of the elastomer increases and the strain decreases, with Example 2 exhibiting the highest toughness and optimal mechanical properties. This is because the flexible long chains of the polyester polyol and the rigid segments of L-lactide and isocyanate coordinate with each other to form a microphase separation structure, effectively controlling the rigidity and toughness of the material at the nanoscale, thus endowing the material with excellent mechanical properties (such as...). Figure 5As shown, a 45 mm × 4 mm × 1.75 mm spline successfully lifted a 10-pound weight. The interface between traditional homogeneous adhesives and the substrate is a smooth, clear plane, making it easy for cracks to propagate along this single interface. However, adhesives with microphase separation structures, after curing, exhibit differential interactions between their different micro-regions and the substrate surface, forming a nanoscale "interpenetrating / anchoring" transition zone. This transforms the clear macroscopic interface into a blurred, three-dimensionally interlocked nano-interface, effectively improving the adhesive's bonding performance. Figure 6 , Figure 7 ), Figure 6 The image shows a synthesized polyurethane sample film placed between two substrates, with an overlap area of ​​12.5 mm × 25 mm. The film was heat-melted in a vacuum oven at 120 ℃ for 2 h, then cured at room temperature for 12 h to prepare lap joint specimens. Different substrates were used, including wood, copper, iron, aluminum, and steel. Subsequent lap shear and tensile tests were performed, showing high lap strength across all substrates, far exceeding national standards. Figure 7 The image shows that the steel lap joint specimen can be re-attached after being damaged. After multiple adhesions, the lap strength decreases slowly but remains above 4 MPa.

[0047] The long alkane chains of polyester polyols provide low surface energy and nonpolarity, while the microphase-separated structure allows hydrophobic segments to dominate surface chemistry, and hard microregions create natural roughness. This synergistic effect results in excellent hydrophobicity of the adhesive, endowing it with stability in aquatic environments. Water contact angle tests were conducted on the films of Examples 1-3 and Comparative Example 1 to investigate the improvement in hydrophobicity and the effect of molar ratio on the hydrophobic properties of the samples. Figure 8 As shown, in Comparative Example 1, the water contact angle was 72.6°; after introducing L-lactide to form a microphase-separated structure, the water contact angle of Example 2 was 86.1°, exhibiting significant hydrophobic material properties. Figure 9 As shown, after placing the polyurethane sample film of Example 2 on the iron substrate, three drops of tetrahydrofuran solvent were added to it. Then, different materials (rubber, wood, plastic, iron, glass and stainless steel) were placed on it and gently pressed. After the solvent evaporated, they were successfully bonded. They did not detach even after being soaked in water for 12 hours.

[0048] This invention develops a polylactic acid-based biodegradable polyurethane adhesive and its preparation method. Through the synergistic effect of multiple soft and hard segments, the inherent contradiction between the mechanical and adhesive properties of the adhesive is balanced. By adjusting the molar ratio of polyester polyol and L-lactide, the degree of separation between the soft and hard microdomains is controlled, thereby achieving precise regulation of the overall performance of the polyurethane adhesive.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polylactic acid-based polyurethane, characterized in that: It is a multi-block polyurethane prepared by ring-opening polymerization of polyester polyol and L-lactide to obtain a diblock prepolymer, and then reacting it with dicyclohexylmethane diisocyanate; wherein the polyester polyol is Priplast™ 3238.

2. The polylactic acid-based polyurethane according to claim 1, characterized in that: The number average molecular weight of the polyester polyol is 2000.

3. The polylactic acid-based polyurethane according to claim 1, characterized in that: The mass ratio of the polyester polyol to L-lactide is 5-10:5-10.

4. The polylactic acid-based polyurethane according to claim 1, characterized in that: The molar ratio of the diblock prepolymer to dicyclohexylmethane diisocyanate is 1:

1.

5. The polylactic acid-based polyurethane according to any one of claims 1-4, characterized in that: The preparation process also includes adding a catalyst to catalyze the reaction.

6. A method for preparing polylactic acid-based polyurethane as described in any one of claims 1-5, characterized in that: Includes the following steps: Polyester polyol and L-lactide were dehydrated, mixed with a catalyst, and copolymerized under an inert gas atmosphere to obtain a diblock prepolymer. A solvent was added and an inert gas was introduced, followed by the addition of dicyclohexylmethane diisocyanate and a catalyst, and the mixture was heated to carry out the reaction. After the reaction was completed, the polylactic acid-based polyurethane was obtained through post-treatment.

7. The method for preparing polylactic acid-based polyurethane according to claim 6, characterized in that: In the preparation of the diblock prepolymer, the reaction includes reacting at 110-115℃ for 1-2 hours, then heating to 125-135℃ for 1-2 hours, then heating to 140-150℃ for 1-2 hours, then heating to 155-160℃ for 1-2 hours, and then heating to 165-170℃ for 1-2 hours; the reaction is carried out by adding dicyclohexylmethane diisocyanate and catalyst at 70-75℃ for 1-3 hours.

8. The method for preparing polylactic acid-based polyurethane according to claim 6, characterized in that: The catalyst used in the preparation of the diblock prepolymer is stannous isooctanoate, and the catalyst used in the reaction of the diblock prepolymer with dicyclohexylmethane diisocyanate is dibutyltin dilaurate; the solvent is N,N-dimethylformamide.

9. An application of polylactic acid-based polyurethane as an adhesive as described in any one of claims 1-5.

10. An adhesive, characterized in that: Contains polylactic acid-based polyurethane as described in any one of claims 1-5.

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