Lignin-based polyurethane supercritical foaming material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biomass foaming material preparation, in particular to a lignin-based polyurethane supercritical foaming material as well as a preparation method and application thereof. The lignin-based polyurethane supercritical foaming material is prepared from the following components in parts by weight: 1 to 25 parts of reactive lignin, 32 to 70 parts of long-chain polyol, 20 to 40 parts of isocyanate, 5 to 10 parts of a chain extender and 0.1 to 0.5 part of a catalyst. The lignin-based polyurethane base material capable of being used for supercritical foaming is directionally designed, a dynamic cross-linked network structure is designed, and an adaptive supercritical foaming process is developed. According to the present invention, the diffusion behavior of the supercritical fluid in the polyurethane structure is improved by using the reversible behavior of the dynamic crosslinking of the lignin-based polyurethane, the problems of green and efficient foaming of the crosslinking type lignin-based polyurethane in the background technology are solved by regulating the supercritical foaming process parameters, and the prepared lignin-based polyurethane has characteristics of excellent thermal stability, good thermal stability and good thermal stability. The invention relates to biomass polyurethane foam with high resilience.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass foaming material preparation, and particularly to a lignin-based polyurethane supercritical foaming material, a preparation method thereof, and an application thereof. Background Art

[0002] Biomass polyurethane is a polyurethane material produced by using renewable biomass resources (such as vegetable oil, lignocellulose, natural rosin, etc.) to replace petrochemical raw materials, and has environmental optimization, sustainability, and versatility. Due to its unique benzene ring structure and rich reaction sites, lignin is expected to be used as a polyol to prepare bio-based polyurethane foam, thereby increasing the compressive strength, compressive modulus, water resistance, and heat resistance of the foam, which is of great significance for promoting the green and sustainable development of polyurethane foam. Currently, lignin-based polyurethane foam is mainly prepared by chemical foaming. The patent "CN201710893984.4" uses lignin as a polyol, and polyol / polyamine reacts with isocyanate under the action of auxiliaries such as foaming agents, catalysts, and foam stabilizers to synthesize lignin-based polyurethane foam. Although chemical foaming has high efficiency, the use of organic solvents and a large number of auxiliaries does not conform to the concept of green development.

[0003] Supercritical foaming is a new foaming method for polyurethane materials. It uses the unique physical properties (low viscosity and high diffusivity) of supercritical fluids to promote polymerization foaming, and has the advantages of good foam controllability, environmental protection, and high efficiency. Currently, traditional polyurethane supercritical foaming materials represented by patents "CN117986846A", "CN113736048B", and "CN109501030B" all use TPU with a linear molecular structure for foaming. However, thermosetting polyurethane with a crosslinked structure cannot be foamed by supercritical foaming due to its high hardness and poor molecular chain mobility. However, the existing lignin-based polyurethane structure is generally a crosslinked structure, and lignin acts as a crosslinking agent or chain extender to form a three-dimensional crosslinked network, resulting in high material hardness and poor molecular chain segment mobility. Therefore, in the supercritical state, it is difficult for supercritical fluids to diffuse into the lignin-based polyurethane matrix, resulting in low foaming ratio, uneven cell structure, poor mechanical properties of the material, and even ineffective foaming and molding. Therefore, there is currently no technical practice of supercritical foaming of crosslinked lignin-based polyurethane. Summary of the Invention

[0004] To solve the above problems, the present invention provides a lignin-based polyurethane supercritical foaming material, its preparation method and application. The present invention directionally designs a lignin-based polyurethane substrate for supercritical foaming, designs a dynamic cross-linking network structure, and develops an adapted supercritical foaming process. Utilizing the reversible behavior of the dynamic cross-linking of lignin-based polyurethane, the diffusion behavior of supercritical fluid in the polyurethane structure is improved, and the supercritical foaming process parameters are regulated to solve the problems of green and efficient foaming of cross-linked lignin-based polyurethane in the background technology, and a biomass polyurethane foam with excellent thermal stability and high resilience rate is prepared.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a lignin-based polyurethane supercritical foaming material, which is prepared from components including the following parts by weight:

[0007] 1-25 parts of reactive lignin, 32-70 parts of long-chain polyol, 20-40 parts of isocyanate, 5-10 parts of chain extender, and 0.1-0.5 parts of catalyst.

[0008] Preferably, the reactive lignin includes one or more of hydroxyl lignin, phenolic lignin, oximated lignin, and amino lignin.

[0009] Preferably, the long-chain polyol includes one or more of polyethylene glycol, polycaprolactone, polyester polyol, polycaprolactone polyol, polycarbonate polyol, polyfuran diol, castor oil-based polyol, and soybean oil polyol.

[0010] Preferably, the chain extender is one or more of 1,4-butanediol, ethylene glycol, 1,4-butanediamine, diethyltoluenediamine, and hydroquinone dihydroxyethyl ether.

[0011] Preferably, the catalyst is one or more of stannous octoate, triethyltin amine, diethyltin ester, and dibutyltin dilaurate.

[0012] The present invention also provides a preparation method of the lignin-based polyurethane supercritical foaming material described in the above technical solution, including the following steps:

[0013] 1) Mix the reactive lignin, long-chain polyol, isocyanate, chain extender, and catalyst, and then carry out a polymerization reaction to obtain a lignin-based polyurethane material;

[0014] 2) Thermally press the lignin-based polyurethane material obtained in step 1) to obtain a shaped lignin-based polyurethane material;

[0015] 3) Carry out supercritical foaming on the lignin-based polyurethane material obtained in step 2) to obtain a lignin-based polyurethane supercritical foaming material.

[0016] Preferably, the conditions for the polymerization reaction in step 1) include: temperature of 105 °C and time of 8 h.

[0017] Preferably, the conditions for the hot pressing in step 2) include: temperature of 150 °C and time of 10 min.

[0018] Preferably, the conditions for the supercritical foaming in step 3) include: pressure of 10 - 20 MPa, temperature of 140 - 180 °C, time of 0.5 - 2.5 h, and the supercritical fluid is nitrogen and / or carbon dioxide;

[0019] When the supercritical fluid is nitrogen and carbon dioxide, the volume ratio of nitrogen to carbon dioxide is 0.2 - 0.8:0.2 - 0.8.

[0020] The present invention also provides the application of the lignin - based polyurethane supercritical foaming material described in the above technical solution in improving the foaming performance of foaming materials.

[0021] To solve the problem of supercritical foaming of cross - linked lignin - based polyurethane, the present invention uses lignin with polyhydroxy, phenolic hydroxyl, oxime or amino groups as polyols to construct reversible covalent cross - linked structures such as urethane, phenol - urethane, oxime - urethane or urea - urethane. By utilizing the molecular rearrangement behavior of the dynamic cross - linked structure of lignin - based polyurethane in the high - temperature supercritical state, the molecular segment mobility of lignin - based polyurethane is improved, making it soften, thereby promoting the diffusion of supercritical fluid into the cross - linked polyurethane chain, preparing lignin - based polyurethane supercritical foam, and solving the problem that traditional cross - linked thermosetting polyurethane has a low foaming ratio or even cannot foam under supercritical conditions, and realizing the preparation of high - elasticity, high - resilience and high - strength lignin - based polyurethane foam.

[0022] The beneficial effects of the present invention:

[0023] 1. Through the dynamic cross - linked lignin - based polyurethane structure design, the physical and chemical properties and molecular movement ability of cross - linked materials in the supercritical foaming state are improved, promoting the diffusion behavior of supercritical fluid. For the first time, a supercritical cross - linked lignin - based polyurethane foam material is developed, solving the problem that cross - linked lignin - polyurethane materials cannot be used for supercritical foaming;

[0024] 2. By regulating supercritical fluid and optimizing foaming parameters to induce the formation of a micro - porous foaming structure, a porous biomass foam with low density, uniform hardness distribution, good uniformity and excellent mechanical properties is prepared. The developed dynamically cross - linked lignin - based polyurethane foam has a stable covalent structure, high resilience rate, and its compression modulus, thermal stability and chemical stability are all superior to those of ordinary supercritical TPU foam;

[0025] 3. No foaming aids, surfactants, or organic solvents are used during the foaming process, making the foaming process green and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments.

[0027] Figure 1 It is an infrared spectrogram of the lignin-based polyurethane foam substrate;

[0028] Figure 2 It is the crosslinking density of the lignin-based supercritical foam;

[0029] Figure 3 It is the Tg curve of the lignin-based polyurethane supercritical foam;

[0030] Figure 4 It is the compression and rebound curve of the supercritical lignin-based polyurethane foam;

[0031] Figure 5 It is the SEM image of the pore structure of the supercritical lignin-based polyurethane foam;

[0032] Figure 6 It is a physical photo of the supercritical lignin-based polyurethane foam. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention provides a lignin-based polyurethane supercritical foaming material, which is prepared from components including the following parts by weight: 1-25 parts of reactive lignin, 32-70 parts of long-chain polyol, 20-40 parts of isocyanate, 5-10 parts of chain extender, and 0.1-0.5 parts of catalyst.

[0034] In the present invention, the reactive lignin preferably includes one or more of hydroxy lignin, phenolic lignin, and oxime lignin. Among them, hydroxy lignin includes de-alkali lignin, hydroxyethylated lignin, hydroxypropylated lignin, etc. sold by Macklin, and its reactive group is an aliphatic hydroxyl group; phenolic lignin is prepared by demethylation modification of multi-lignin using an acidic proton solution, and lignin mainly uses phenolic hydroxyl groups as reactive groups; oxime lignin uses lignin as a raw material, and is modified with acrylonitrile and hydroxylamine hydrochloride in sequence, and then heat-treated in a proton solution to prepare lignin with oxime hydroxyl groups as reactive groups. Amino lignin is prepared using lignin as a raw material, with lysine and glyoxal as modification reagents, through the Manich reaction. For all reactive lignins, their molecular weights are below 5000 Da, and the content of reactive groups is higher than 2 mmol / g.

[0035] In the present invention, the types of the long-chain polyols preferably include one or more of polyethylene glycol, polycaprolactone, polyester polyol, polycaprolactone polyol, polycarbonate polyol, polyfuran diol, castor oil-based polyol, and soybean oil polyol. In the present invention, the function of the long-chain polyol is to serve as the soft segment of the polyurethane material, endowing the material with flexibility and elasticity. In the present invention, the types of the chain extender preferably include one or more of 1,4-butanediol, ethylene glycol, 1,4-butanediamine, diethyl toluene diamine, and hydroquinone bis(2-hydroxyethyl) ether. In the present invention, the function of the chain extender is to extend the molecular chain length of the lignin polyurethane and form a molecular network with a high degree of polymerization. In the present invention, the catalysts preferably include one or more of stannous octoate, triethyltin amine, diethyltin ester, and dibutyltin dilaurate. In the present invention, the function of the isocyanate is to polymerize with the hydroxyl group and the reactive groups of lignin to construct a dynamically crosslinked molecular network.

[0036] The present invention also provides a preparation method of the lignin-based polyurethane supercritical foaming material according to the above technical solution, comprising the following steps:

[0037] 1) Mix the reactive lignin, long-chain polyol, isocyanate, chain extender, and catalyst, and then carry out a polymerization reaction to obtain a lignin-based polyurethane material;

[0038] 2) Thermally press the lignin-based polyurethane material obtained in step 1) to obtain a shaped lignin-based polyurethane material;

[0039] 3) Carry out supercritical foaming on the shaped lignin-based polyurethane material obtained in step 2) to obtain a lignin-based polyurethane supercritical foaming material.

[0040] In the present invention, the reactive lignin, long-chain polyol, isocyanate, chain extender, and catalyst are mixed and then subjected to a polymerization reaction to obtain a lignin-based polyurethane material. In the present invention, the conditions of the polymerization reaction preferably include: the temperature is 105 °C and the time is 8 h. After the polymerization reaction, a lignin-based polyurethane material with a dynamically crosslinked structure is obtained.

[0041] In the present invention, the obtained lignin-based polyurethane material is thermally pressed to obtain a shaped lignin-based polyurethane material. In the present invention, the conditions of the thermal pressing preferably include: the temperature is 150 °C and the time is 10 min. In the present invention, the size of the shaped lignin-based polyurethane material is preferably 10 cm × 10 cm × 0.1 cm. In the present invention, the lignin-based polyurethane material is directly thermally pressed or processed into particles and then thermally pressed.

[0042] The lignin-based polyurethane material obtained in the present invention is subjected to supercritical foaming to obtain a lignin-based polyurethane supercritical foaming material. In the present invention, the conditions for the supercritical foaming preferably include: a pressure of 10 to 20 MPa, a temperature of 140 to 180 °C, a time of 0.5 to 2.5 h, and the supercritical fluid is nitrogen and / or carbon dioxide; when the supercritical fluid is nitrogen and carbon dioxide, the volume ratio of nitrogen to carbon dioxide is 0.2 to 0.8:0.2 to 0.8. In the present invention, when the supercritical fluid is nitrogen and carbon dioxide, the volume ratio of nitrogen to carbon dioxide is 0.5:0.5.

[0043] The present invention also provides the application of the lignin-based polyurethane supercritical foaming material described in the above technical solution in improving the foaming performance of the foaming material.

[0044] In order to further illustrate the present invention, the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0045] Example 1

[0046] A preparation method of a lignin-based polyurethane supercritical foaming material, the steps are as follows:

[0047] 1) 50 parts of isocyanate, 50 parts of polyethylene glycol (long-chain polyol) (molecular weight 1066 Da), 0.5 part of stannous octoate, 5 parts of polyhydroxy lignin extracted by deep eutectic solvent (lignin) (prepared with reference to the literature [Wang D, Liu L, Shen R, et al. Fascinating polyphenol lignin extracted from sawdust via a green and recyclable solvent route[J]. International Journal of Biological Macromolecules, 2023, 234: 123780.]) and 10 parts of 1,4-butanediol are subjected to a polymerization reaction in a reactor, cured at 105 °C for 8 h to prepare a urethane-crosslinked lignin-based polyurethane;

[0048] 2) Subsequently, the polymerized lignin-based polyurethane is cut into granules, poured into a molding die and hot-pressed at a temperature of 150 °C for 10 min to prepare a 10 cm × 10 cm × 0.1 cm lignin-based polyurethane sheet;

[0049] 3) Subsequently, the above-mentioned sheet is placed in a high-pressure reactor, carbon dioxide is introduced to increase the pressure of the reaction kettle, and it is kept warm at a temperature of 160 °C and a pressure of 15 MPa for 1 h, and the pressure is released within 30 s to obtain a lignin-based polyurethane supercritical foaming material.

[0050] The infrared spectrum of the prepared lignin-based polyurethane foam is as Figure 1 shown, where the infrared absorption peaks at 2280 cm -1 and 3400 cm -1 disappear, indicating that the isocyanate and polyol have reacted successfully. Among them, the absorption bands at 1685 - 1715 cm -1 , 1540 cm -1 and 1610 cm -1 are respectively attributed to the absorption vibration of the carbonyl group, the stretching vibration of the N-H bond, and the skeletal vibration of the benzene ring, indicating that lignin has successfully polymerized into the polyurethane skeleton structure. Since lignin serves as the reaction center, it increases the crosslinking density of the polyurethane, promoting its transformation into a thermosetting material with thermoprocessing properties ( Figure 2 ). In addition, the increase in crosslinking degree and the rigid benzene ring structure of lignin significantly improve the thermal stability of the lignin-based polyurethane. Its initial thermal decomposition temperature is raised to around 288 °C, which provides the necessary thermal stability for the ultra-high temperature and high-pressure process of the present invention process. Figure 4 The cyclic compression curve of the lignin-based polyurethane supercritical foam shown indicates that the material of the present invention has excellent compression performance and resilience.

[0051] It can be seen from the scanning electron micrograph of the lignin-based polyurethane supercritical foam ( Figure 5 ) that the prepared foam has uniform cell pores and regular shapes. Its cell pores are smaller than those of chemically foamed pores, with an average pore diameter of about 42 μm, and the pore walls are thicker, which is the key to its good compression resilience.

[0052] The lignin-based polyurethane supercritical foam is cut into a specification of 50 mm × 15 mm × 3 mm. Using a universal testing machine, the fracture strength of the material is measured to be 2.0 MPa. Based on the volume ratio of lignin-based polyurethane before and after foaming, the foaming ratio of the lignin-based polyurethane foam is calculated to be as high as 12.7 times, and its density is 0.081 g / cm 3 .

[0053] Examples 2 - 5

[0054] The weight parts of lignin in Example 1 are changed to 10, 15, 20, 25, and the parts of long-chain polyol are changed to 45, 40, 35, 30 accordingly, and the remaining conditions are the same as in Example 1.

[0055] Table 1 Influence of lignin content on foam properties

[0056]

[0057] Examples 6 - 9

[0058] Change the supercritical pressure in Example 1 to 10, 12.5, 17.5, 20 MPa, and keep the other conditions the same as in Example 1.

[0059] Table 2 Influence of Supercritical Foaming Pressure on Foam Properties

[0060]

[0061]

[0062] Examples 10 - 13

[0063] Change the supercritical foaming temperature in Example 1 to 140, 160, 180, 200 °C, and keep the other conditions the same as in Example 1.

[0064] Table 3 Influence of Supercritical Foaming Temperature on Foam Properties

[0065] Supercritical temperature Average pore size / μm Tensile strength / MPa Foaming ratio <![CDATA[Density / g·cm -3 > 140 28 2.5 5.8 0.124 160 32 2.3 8.1 0.098 180 41 1.8 9.4 0..84 200 35 1.5 10.2 0.098

[0066] Examples 14 - 17

[0067] Change the supercritical fluid in Example 1 to N2, N2 / CO2 volume ratio of 0.8 / 0.2, N2 / CO2 volume ratio of 0.5 / 0.5, N2 / CO2 volume ratio of 0.2 / 0.8, and keep the other conditions the same as in Example 1.

[0068] Table 4 Influence of Supercritical Fluid on Foam Properties

[0069]

[0070] Examples 18 - 20

[0071] Change the lignin in Example 1 to phenolic lignin, oximated lignin, and aminated lignin, and construct phenolic - urethane, oximated - urethane, and urea - urethane dynamic cross - linked structures, and keep the other conditions the same as in Example 1.

[0072] Among them, hydroxy lignin includes de-alkali lignin, hydroxyethylated lignin, hydroxypropylated lignin, etc. sold by Maclean, and its reactive group is aliphatic hydroxyl; phenolic lignin is prepared by demethylation modification of multi-lignin using acidic proton solution, and the lignin mainly uses phenolic hydroxyl as the reactive group; oximated lignin uses lignin as the raw material, and is modified with acrylonitrile and hydroxylamine hydrochloride in sequence, and then heat-treated in a proton solution to prepare lignin with oxime hydroxyl as the reactive group. Amino lignin is prepared from lignin as the raw material, using lysine and glyoxal as modifying reagents through the Mannich reaction, and is lignin with amino as the reactive functional group. The mentioned phenolic lignin, oximated lignin and amino lignin are not limited to the above modification methods, and their characteristics are that they use phenolic hydroxyl, oxime hydroxyl and amino as reactive groups respectively, and their molecular weights are all below 5000 Da, and the content of reactive groups is higher than 2 mmol / g.

[0073] The mentioned phenolic lignin, oximated lignin and amino lignin are not limited to the above modification methods, and their characteristics are that they use phenolic hydroxyl, oxime hydroxyl and amino as reactive groups respectively, and their molecular weights are all below 5000 Da, and the content of reactive groups is higher than 2 mmol / g.

[0074] Table 5 Influence of lignin-based dynamic cross-linked structure on foam properties

[0075]

[0076] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A lignin-based polyurethane supercritical foaming material, characterized in that: Prepared from the following components in parts by weight: 1-25 parts of reactive lignin, 32-70 parts of long-chain polyol, 20-40 parts of isocyanate, 5-10 parts of chain extender and 0.1-0.5 parts of catalyst.

2. The lignin-based polyurethane supercritical foaming material according to claim 1, characterized in that: The reactive lignin includes one or more of hydroxyl lignin, phenolic lignin, oximated lignin and amino lignin.

3. The lignin-based polyurethane supercritical foaming material according to claim 1, characterized in that: The long-chain polyol includes one or more of polyethylene glycol, polycaprolactone, polyester polyol, polycaprolactone polyol, polycarbonate polyol, polyfurandiol, castor oil-based polyol and soybean oil-based polyol.

4. The lignin-based polyurethane supercritical foaming material according to claim 1, characterized in that: The chain extender includes one or more of 1,4-butanediol, ethylene glycol, 1,4-butanediamine, diethyltoluenediamine and hydroquinone dihydroxyethyl ether.

5. The lignin-based polyurethane supercritical foaming material according to claim 1, characterized in that: The catalyst includes one or more of stannous isooctanoate, triethyltinamine, diethyltin ester and dibutyltin dilaurate.

6. A method for preparing the lignin-based polyurethane supercritical foaming material according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) mixing the reactive lignin, long-chain polyol, isocyanate, chain extender and catalyst and performing polymerization reaction to obtain a lignin-based polyurethane material; 2) hot-pressing the lignin-based polyurethane material obtained in step 1) to obtain a molded lignin-based polyurethane material; 3) The lignin-based polyurethane material obtained in step 2) is subjected to supercritical foaming to obtain a lignin-based polyurethane supercritical foaming material.

7. The preparation method according to claim 6, characterized in that: The conditions of the polymerization reaction in step 1) include: temperature of 105° C. and time of 8 hours.

8. The preparation method according to claim 6, characterized in that: The conditions of hot pressing in step 2) include: temperature of 150° C. and time of 10 min.

9. The preparation method according to claim 6, characterized in that: The conditions of the supercritical foaming in step 3) include: a pressure of 10-20 MPa, a temperature of 140-180° C., a time of 0.5-2.5 h, and the supercritical fluid is nitrogen and / or carbon dioxide; When the supercritical fluid is nitrogen and carbon dioxide, the volume ratio of nitrogen to carbon dioxide is 0.2-0.8:0.2-0.

8.

10. Use of the lignin-based polyurethane supercritical foaming material according to any one of claims 1 to 5 in improving the foaming performance of foaming materials.

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