Preparation method of polyurethane-modified phenolic aerogel and polyurethane-modified phenolic aerogel prepared thereby

Abstract

The present invention provides a preparation method of a polyurethane-modified phenolic aerogel and the prepared polyurethane-modified phenolic aerogel. The preparation method includes: S1, preparing a polyurethane prepolymer terminated with a phenolic ring; S2, mixing the polyurethane prepolymer terminated with a phenolic ring with a phenolic resin to obtain a mixed solution, adding a curing agent to carry out a gel reaction to obtain a polyurethane-modified phenolic resin gel; S3, removing the liquid phase in the polyurethane-modified phenolic resin gel to obtain a polyurethane-modified phenolic resin aerogel. The preparation method of the present invention introduces a phenolic ring as an end group into the polyurethane prepolymer to obtain a polyurethane prepolymer terminated with a phenolic ring, and then mixes it with a phenolic resin to prepare an aerogel, solving the problem that polyurethane cannot be effectively introduced into the phenolic resin system, and having the characteristics of simple process, short cycle and suitability for industrial production. The prepared aerogel has good mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerogel materials, and particularly relates to a preparation method of polyurethane-modified phenolic aerogel. Background Art

[0002] Aerogel is a material with low density and high specific surface area, having a three-dimensional network structure of continuous pores composed of interconnected particles. Due to its unique physical and chemical properties, aerogel has attracted extensive attention from scientists in various fields. With the rapid development of aerogel, various high-performance aerogel materials have emerged continuously, and have shown attractive application prospects in the fields of environmental protection, energy storage and conversion, and biomedicine. Phenolic resin is a traditional industrial material, and its raw materials are economically available. The aerogel made from phenolic resin has excellent thermal and chemical stability, heat insulation and fire prevention, and high char yield and other characteristics. Therefore, phenolic resin aerogel has good application prospects in thermal insulation materials.

[0003] However, due to the poor toughness of phenolic aerogel, brittle solids are obtained, with low mechanical strength, and the aerogel is prone to fragmentation under external force, which restricts the application of phenolic aerogel. In order to improve the mechanical properties of phenolic aerogel, the currently common method is to use fiber blending for modification. However, due to the introduction of fibers, the density of the aerogel is increased, and the process is complex. How to develop a phenolic aerogel with simple preparation process and excellent performance through the regulation of the intrinsic structure of aerogel, such as the pore structure and the molecular structure of the aerogel skeleton, to achieve high strength of phenolic aerogel has important application value.

[0004] Polyurethane is a class of block copolymers synthesized by the reaction of polyisocyanate and polyol. Among them, polyol is used as the soft segment and polyisocyanate constitutes the hard segment. The structural characteristics of the soft segment endow the material with good impact resistance and elasticity. The soft segment in polyurethane can be used to modify the rigidity brought by the structure of phenolic resin itself. Introducing polyurethane into the skeleton structure of phenolic aerogel is expected to achieve a strengthening effect. However, since polyurethane is prepared by the reaction of isocyanate group and active hydrogen, and in the preparation process of phenolic aerogel, solvents with low toxicity and low cost such as water and alcohol are mostly selected. These solvents themselves can react with the isocyanate group, and a stable sol cannot be obtained, so that the polyurethane component cannot be effectively introduced into the skeleton structure of phenolic aerogel, and the modification effect cannot be achieved. Therefore, how to design the molecular structure of polyurethane so that it can form a stable sol with phenol, and further introduce the polyurethane component into the phenolic aerogel skeleton through the gelation and curing of the sol to achieve a strengthening effect and match the preparation process of the aerogel is extremely important for the preparation of high-strength phenolic aerogel.

[0005] In view of this, the present invention is particularly proposed. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a preparation method of a polyurethane-modified phenolic aerogel and the prepared polyurethane-modified phenolic aerogel in view of the above problems in the prior art. The present invention introduces a phenolic ring as a terminal group into a polyurethane prepolymer to obtain a phenolic-ring-capped polyurethane prepolymer, and then mixes it with a phenolic resin to prepare an aerogel, solving the problem that polyurethane cannot be effectively introduced into the phenolic resin system; by introducing a polyurethane structure into the phenolic aerogel framework structure, the mechanical strength of the phenolic aerogel is greatly improved.

[0007] By using the preparation method of the polyurethane-modified phenolic aerogel of the present invention, polyurethane can be successfully introduced into the phenolic aerogel, while improving the intrinsic mechanical properties of the phenolic resin, and it can be successfully prepared by the existing aerogel preparation method, and can be fully adapted to the existing aerogel preparation process.

[0008] To achieve the above objective, the first aspect of the present invention provides a preparation method of a polyurethane-modified phenolic aerogel, including the following steps:

[0009] S1. Prepare a phenolic-ring-capped polyurethane prepolymer;

[0010] S2. Mix the phenolic-ring-capped polyurethane prepolymer with a phenolic resin to obtain a mixed solution, and add a curing agent to carry out a gel reaction to obtain a polyurethane-modified phenolic resin gel;

[0011] S3. Remove the liquid phase in the polyurethane-modified phenolic resin gel to obtain a polyurethane-modified phenolic aerogel.

[0012] In the above solution, polyurethane is introduced into the phenolic aerogel system in the form of a phenolic-ring-capped polyurethane prepolymer. Since the isocyanate group has reacted with the phenolic ring, it will not react further after being introduced into the phenolic aerogel system, solving the problem of poor compatibility between the terminal isocyanate group in polyurethane and the phenolic aerogel preparation system, and will not affect the formation of the aerogel due to the introduction of polyurethane; since polyurethane contains a soft segment and hydrogen bonds, the elasticity and toughness of the phenolic resin are improved after being introduced into the phenolic aerogel system.

[0013] Further, step S1 specifically includes:

[0014] React a diol and a diisocyanate to obtain a polyurethane, and then use a phenolic compound to cap the polyurethane to obtain a phenolic-ring-capped polyurethane prepolymer;

[0015] The phenolic compound contains both a phenolic hydroxyl group and at least one functional group having reactivity with an isocyanate group.

[0016] In the above solution, it is specified that the phenolic compound has one phenolic hydroxyl group and at least one functional group capable of reacting with isocyanate groups. After the phenolic compound is end-capped with polyurethane through the functional group reactive with isocyanate groups, there is still one hydroxyl group on the phenolic ring at the end. Furthermore, the polyurethane can be connected to the phenolic resin molecule by reacting the end-capped phenolic ring with the phenolic resin, achieving an improvement in the intrinsic mechanical properties of the phenolic resin.

[0017] Furthermore, the functional groups reactive with isocyanate groups include hydroxyl groups, amino groups, phenolic hydroxyl groups, mercapto groups, hydroxymethyl groups, and aminomethyl groups. Regarding the differences in the reactivity of different functional groups, technical researchers have found that amino functional groups have high reactivity with isocyanate groups and can react rapidly at room temperature. At the same time, the position of the functional group on the phenolic ring can be ortho, meta, or para. Phenols with ortho functional groups such as salicyl alcohol, phenols with meta functional groups such as resorcinol and m-aminophenol, and phenols with para functional groups such as 4-mercaptophenol. Phenolic molecules with a meta functional group structure have higher reactivity at the reaction sites on the benzene ring, which is beneficial for further curing reactions.

[0018] Preferably, the phenolic compound is m-aminophenol.

[0019] In the above solution, m-aminophenol is selected as the phenolic compound, and a reaction is formed through the reaction of isocyanate groups and amino groups.

[0020] Furthermore, the diol has a molecular weight range of 250 - 2000.

[0021] The molecular weight range specified in the above solution is a more suitable molecular weight range discovered by technical personnel based on a large number of studies and experiments. When the molecular weight is too low, the soft segment in the polyurethane is too short, and the toughening and strengthening effect on the aerogel is poor. The phenolic aerogel modified with polyurethane still exhibits the inherent brittleness of the phenolic aerogel and is prone to fragmentation. When the molecular weight of the diol is too large, the content of the introduced soft segment is too large, affecting the strength of the overall aerogel network framework. At the same time, a suitable molecular weight is beneficial for the refinement of the aerogel pore size, thereby ensuring that the aerogel has higher strength.

[0022] Furthermore, the diol in step S1 is selected from polyether diols or polyester diols.

[0023] Preferably, the diol is polytetramethylene ether glycol.

[0024] Preferably, the diisocyanate is selected from one of aliphatic diisocyanates, cycloaliphatic diisocyanates, and aromatic diisocyanates.

[0025] Preferably, the diisocyanate is toluene diisocyanate.

[0026] In the above solution, based on a large number of studies and experiments, the inventor found that polytetramethylene ether glycol has appropriate flexibility and an appropriate ether bond content; if polydimethyl ether glycol is selected, its hydrophilicity will increase the difficulty of water removal during the preparation process, resulting in an increase in side reactions and poor aerogel performance; if aliphatic diol is selected, it will lead to insufficient flexibility of the polyurethane modifier and poor mechanical properties.

[0027] Further, in step S2, the phenolic resin is selected from linear phenolic resin;

[0028] Preferably, the softening point range of the linear phenolic resin is 80 - 130 °C;

[0029] Preferably, the softening point range of the linear phenolic resin is 90 - 110 °C.

[0030] In the above solution, based on a large number of studies and experiments, the inventor found that if the softening point is less than 80 °C, its ablation performance and char yield will decrease significantly; at the same time, if the softening point is higher than 120 °C, heating is required for dissolution when preparing the resin solution, which is not conducive to the simplicity of the overall preparation process. Considering the comprehensive performance and processability, the preferred softening point temperature of the resin is 90 - 110 °C.

[0031] Further, in step S2, the mass ratio of the phenol - ring - capped polyurethane prepolymer to the phenolic resin in the mixture is (5 - 50):100.

[0032] In the above solution, the mixing ratio of the polyurethane prepolymer to the phenolic resin is an excellent ratio range obtained by the inventor based on a large number of experiments and studies. The polyurethane prepolymer within the above range can significantly improve the mechanical properties, compression modulus and strength of the phenolic aerogel. If the amount of the polyurethane prepolymer is too large, the cross - linking density of the phenolic aerogel will decrease significantly, resulting in a large decrease in the modulus and attenuation of the compressive strength; if the amount of the polyurethane prepolymer is less than 5, the aerogel still shows brittleness and powdering characteristics, and its lack of toughness has not been improved.

[0033] Further, the curing agent is selected from at least one of hexamethylenetetramine, formaldehyde or paraformaldehyde.

[0034] In the above solution, the selection of hexamethylenetetramine is an excellent choice of curing agent obtained by the inventor. Its raw materials are easily available, it has lower toxicity than formaldehyde and does not volatilize, and its decomposition rate is related to temperature, which is beneficial to controlling the curing reaction rate.

[0035] Further, in step S2, the gel reaction is carried out in a closed reactor, the reaction temperature is 70 - 110 °C, and the reaction duration is 12 - 48 h.

[0036] Preferably, the reaction temperature of the gel reaction is 90 °C and the reaction duration is 24 h.

[0037] Further, in step S3, the liquid phase in the polyurethane-modified phenolic resin gel is removed by high-temperature drying, the temperature is 50-90°C, and the normal-pressure drying time is 12h-48h;

[0038] Preferably, the drying temperature is 90°C and the drying time is 12h.

[0039] Another object of the present invention is to provide a polyurethane-modified phenolic resin aerogel prepared by the above preparation method;

[0040] Preferably, the compression modulus of the polyurethane-modified phenolic resin aerogel is ≥60 MPa, the compression strength is ≥10 MPa, and the compression strain is ≥50%.

[0041] The beneficial effects of the present invention are as follows:

[0042] 1. The present invention designs and synthesizes a polyurethane prepolymer capped with a phenolic ring, and introduces the polyurethane component into the phenolic resin through the phenolic ring, realizing the intrinsic modification of the phenolic aerogel. By using the soft segment in the polyurethane component and the abundant hydrogen bonds, the mechanical properties of the phenolic aerogel are significantly improved.

[0043] 2. By limiting the molecular weight of the diol in the polyurethane prepolymer, the length of the polyurethane soft segment is controlled. With an appropriate soft segment length, while improving the brittleness of the phenolic aerogel, it will not cause a decrease in the strength of the phenolic aerogel network skeleton. At the same time, it can also refine the pore size in the aerogel, which is beneficial to the improvement of the strength of the phenolic aerogel.

[0044] 3. Since the polyurethane prepolymer is capped with a phenolic ring, the polyurethane prepolymer can directly enter the phenolic aerogel preparation system without reacting with the solvent. That is, without changing the preparation process of the phenolic aerogel, the aerogel is prepared by the existing conventional sol-gel-normal pressure drying process, which is easy to realize industrial production. Description of the Drawings

[0045] Figure 1 It is the compression stress-strain curves of the polyurethane-modified phenolic aerogel and the pure phenolic aerogel prepared by using the preparation method of the present invention in Example 1.

[0046] Figure 2 It is the pore size distribution diagrams of the polyurethane-modified phenolic aerogel and the pure phenolic aerogel prepared by using the preparation method of the present invention in Example 1.

[0047] Figure 3 It is the char residue rate results of the polyurethane-modified phenolic aerogels prepared in Example 1, Example 6 and Comparative Example 2;

[0048] Figure 4It is the compression stress-strain curve graph of the uncapped polyurethane-modified phenolic aerogel in Comparative Example 3. Detailed implementation manners

[0049] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Those skilled in the art can understand that the following embodiments are only used to explain the technical principle of the present invention and are not intended to limit the protection scope of the present invention.

[0050] It should be noted that:

[0051] In the present invention, the compression tests are all carried out on an Instron universal material testing machine (model instron5567) at a compression rate of 1 mm / min. The specimens are cut into cylindrical blocks with a diameter of 17 mm and a height of 17 mm. The aerogel compression test method refers to "High polymer porous elastic materials - Determination of compression stress-strain characteristics" (GB / T 18942.1-2003).

[0052] The compression modulus is determined according to the slope of the initial linear part of the stress-strain curve. The compression stress is taken from the measured value when the specimen is crushed during compression, and the compression strain is taken from the corresponding value of the compression stress.

[0053] The pore structure of the aerogel sample is analyzed by mercury porosimetry. The mercury intrusion amount within the pressure range of 0.1 to 37500 Psia is measured by a mercury porosimeter MicroActive AutoPore (model: V9600), and the pore size and distribution of the aerogel are calculated and fitted according to the Washburn equation.

[0054] By measuring the mass, diameter, and height of the aerogel block that is completely dried at normal pressure, the volume of the aerogel is calculated, and the density is obtained by the ratio of mass to volume (all measurements are carried out at room temperature).

[0055] The drugs and their sources used in the following examples are shown in the following table:

[0056] Table 1

[0057] Drug Name / Commercially Available Product Name Drug Specification (parameters such as purity) Manufacturer Polytetrahydrofuran diol 500 mL, Mn = 1000 g / mol InnoChem Co., Ltd. Polytetrahydrofuran diol 1000 g, Mn = 2000 g / mol BASF Polypropylene glycol 500 g, Mn = 2000 g / mol InnoChem Co., Ltd. Toluene 2,4 - diisocyanate 500g，98％ Energy Chemical Diphenylmethane diisocyanate 500g，97％ Energy Chemical Tetrahydrofuran AR 500 ml Beijing Chemical Works m - Aminophenol 500g，99％ InnoChem Co., Ltd. Salicyl alcohol 500g，99％ InnoChem Co., Ltd. Linear phenolic resin Industrial grade, grade number 8020 Shandong Jinan Shengquan Group Co., Ltd. Hexamethylenetetramine Analytical reagent grade Sinopharm Chemical Reagent Co., Ltd. Ethanol AR 500 ml Beijing Chemical Works

[0058] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples:

[0059] Example 1

[0060] (1) Preparation of polyurethane prepolymer

[0061] Dissolve 10 g of polytetrahydrofuran diol (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4 - diisocyanate (2,4 - TDI) in 20 g of tetrahydrofuran, react at 75 °C for 2 hours, then add 2.1 g of m - aminophenol and react at 50 °C for 1 hour. Remove the solvent tetrahydrofuran by vacuum distillation to obtain a phenol - ring - capped polyurethane prepolymer.

[0062] (2) Preparation of polyurethane - modified phenolic aerogel

[0063] Mix the phenol - ring - capped polyurethane prepolymer, linear phenolic resin (softening point 105 °C), hexamethylenetetramine, and ethanol in a mass ratio of 10:90:15:300, stir well to dissolve to obtain a stable and homogeneous polyurethane / phenolic sol. Cure the sol at 90 °C for 24 hours under closed conditions to obtain a polyurethane - modified phenolic wet gel, and then dry the wet gel at 90 °C for 12 hours to obtain a polyurethane - modified phenolic aerogel.

[0064] This polyurethane - modified phenolic aerogel has good mechanical properties. Figure 1 The compression stress - strain curve of this aerogel and pure phenolic aerogel (control example) is shown. It can be seen that compared with phenolic aerogel, the compressive strength, compressive modulus, and compressive strain of the polyurethane - modified phenolic aerogel have been greatly improved.

[0065] Figure 2 The pore size distribution diagram (measured by mercury intrusion method) of this aerogel and pure phenolic aerogel is shown, and its pore size is also significantly reduced compared with pure phenolic aerogel.

[0066] Figure 3 The char residue rate of the aerogel prepared in this example is shown in.

[0067] Example 2

[0068] (1) Preparation of polyurethane prepolymer

[0069] Dissolve 10 g of polytetrahydrofuran diol (molecular weight 2000 g / mol) and 1.74 g of toluene 2,4 - diisocyanate (2,4 - TDI) in 20 g of tetrahydrofuran, react at 75 °C for 2 hours, then add 0.92 g of m - aminophenol and react at 50 °C for 1 hour. Remove the solvent tetrahydrofuran by vacuum distillation to obtain a phenol - ring - capped polyurethane prepolymer.

[0070] (2) Preparation of polyurethane - modified phenolic aerogel

[0071] A polyurethane prepolymer with a phenol ring end group, linear phenolic resin (softening point 120 °C), hexamethylenetetramine, and ethanol were mixed in a mass ratio of 10:90:15:300, and stirred thoroughly to dissolve, obtaining a stable and homogeneous polyurethane / phenolic sol. The sol was cured and gelled at 90 °C for 24 hours under closed conditions to obtain a polyurethane-modified phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, a polyurethane-modified phenolic aerogel was obtained.

[0072] Example 3

[0073] (1) Preparation of polyurethane prepolymer

[0074] 10 g of polytetrahydrofuran diol (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran, and reacted at 75 °C for 2 hours. Then, 2.1 g of m-aminophenol was added, and the reaction was carried out at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a polyurethane prepolymer with a phenol ring end group.

[0075] (2) Preparation of polyurethane-modified phenolic aerogel

[0076] A polyurethane prepolymer with a phenol ring end group, linear phenolic resin (softening point 105 °C), hexamethylenetetramine, and ethanol were mixed in a mass ratio of 30:70:15:300, and stirred thoroughly to dissolve, obtaining a stable and homogeneous polyurethane / phenolic sol. The sol was cured and gelled at 90 °C for 24 hours under closed conditions to obtain a polyurethane-modified phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, a polyurethane-modified phenolic aerogel was obtained.

[0077] Example 4

[0078] (1) Preparation of polyurethane prepolymer

[0079] 10 g of polypropylene glycol (molecular weight 2000 g / mol) and 2.5 g of diphenylmethane diisocyanate (MDI) were dissolved in 20 g of tetrahydrofuran, and reacted at 75 °C for 2 hours. Then, 0.97 g of m-aminophenol was added, and the reaction was carried out at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a polyurethane prepolymer with a phenol ring end group.

[0080] (2) Preparation of polyurethane-modified phenolic aerogel

[0081] A polyurethane prepolymer with a phenol ring end group, linear phenolic resin (softening point 105 °C), hexamethylenetetramine, and ethanol were mixed in a mass ratio of 30:70:15:300, and stirred thoroughly to dissolve, obtaining a stable and homogeneous polyurethane / phenolic sol. The sol was cured and gelled at 100 °C for 24 hours under closed conditions to obtain a polyurethane-modified phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, a polyurethane-modified phenolic aerogel was obtained.

[0082] Example 5

[0083] (1) Preparation of polyurethane prepolymer

[0084] Dissolve 10 g of polytetrahydrofuran diol (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4 - diisocyanate (2,4 - TDI) in 20 g of tetrahydrofuran, react at 75 °C for 2 hours, then add 2.43 g of salicyl alcohol, react at 50 °C for 1 hour, and remove the solvent tetrahydrofuran by vacuum distillation to obtain a phenol - ring - capped polyurethane prepolymer.

[0085] (2) Preparation of polyurethane - modified phenolic aerogel

[0086] Mix the phenol - ring - capped polyurethane prepolymer, linear phenolic resin (softening point 105 °C), hexamethylenetetramine, and ethanol in a mass ratio of 30:70:15:300, stir and dissolve thoroughly to obtain a stable and homogeneous polyurethane / phenolic sol. Cure the sol at 90 °C for 24 hours under closed conditions to obtain a polyurethane - modified phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, a polyurethane - modified phenolic aerogel is obtained.

[0087] Example 6

[0088] The difference between this example and Example 1 is that the softening point of the linear phenolic resin used is 90 °C, and other conditions are the same. The results are as Figure 3 shown.

[0089] Comparative Example 1

[0090] (1) Preparation of pure phenolic aerogel

[0091] Mix linear phenolic resin (softening point 105 °C), hexamethylenetetramine, and ethanol in a mass ratio of 100:15:300, dissolve to obtain a stable and homogeneous phenolic sol. Cure the sol at 90 °C for 24 hours under closed conditions to obtain a phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, a pure phenolic aerogel is obtained.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is that the softening point of the linear phenolic resin used is 60 °C.

[0094] (1) The preparation of the polyurethane prepolymer is the same as that in Example 1;

[0095] (2) Preparation of polyurethane - modified low - softening - point phenolic aerogel

[0096] A phenol-ring-capped polyurethane prepolymer, linear phenolic resin (softening point: 60 °C), hexamethylenetetramine, and ethanol were mixed at a mass ratio of 10:90:15:300 and stirred thoroughly to obtain a stable and homogeneous polyurethane / phenolic sol. The sol was cured and gelled at 90 °C for 24 hours under closed conditions to obtain a polyurethane-modified phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, a polyurethane-modified low-softening-point phenolic aerogel was obtained.

[0097] The results are as Figure 3 shown.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that an uncapped polyurethane prepolymer was used.

[0100] (1) Preparation of uncapped polyurethane prepolymer

[0101] 10 g of polytetrahydrofuran diol (molecular weight: 1000 g / mol) and 3.48 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran and reacted at 75 °C for 2 hours. The solvent tetrahydrofuran was removed by vacuum distillation to obtain an uncapped polyurethane prepolymer.

[0102] (2) Preparation of uncapped polyurethane-modified phenolic aerogel

[0103] The uncapped polyurethane prepolymer, linear phenolic resin (softening point: 105 °C), hexamethylenetetramine, and tetrahydrofuran were mixed at a mass ratio of 10:90:15:300 and stirred thoroughly to obtain a stable and homogeneous polyurethane / phenolic sol. The sol was cured and gelled at 90 °C for 24 hours under closed conditions to obtain an uncapped polyurethane-modified phenolic wet gel. After drying the wet gel at 90 °C for 12 hours, an uncapped modified low-softening-point phenolic aerogel was obtained.

[0104] Figure 4 The compression stress-strain curve of Comparative Example 3 is shown. It can be seen that the uncapped polyurethane-modified phenolic aerogel has a small compression strain and a low compression stress. At the same time, a large shrinkage occurred during the preparation process of Comparative Example 3, so its density is significantly higher than that of other examples (see Table 2). The uncapped polyurethane has extremely high reactivity and a too fast rate during the curing reaction process, making the overall process uncontrollable, resulting in an inability to form a uniform network with phenol-formaldehyde, severe shrinkage, and low mechanical properties.

[0105] Experimental Example 1

[0106] The properties of the aerogels prepared in Examples 1-5 and Comparative Examples 1-3 were tested, and the results are shown in the following table:

[0107] Table 2

[0108]

[0109]

[0110] Result analysis:

[0111] As can be seen from the above table, compared with Comparative Example 1, the compression modulus, compression strength and compression strain of the polyurethane-modified phenolic aerogel prepared by the method of Examples 1-5 are significantly improved compared with those of pure phenolic aerogel; and from the comparison between Example 1 and Example 3, it can be seen that the difference between Example 1 and Example 3 lies in the different ratio of the phenolic ring-capped polyurethane prepolymer to the linear phenolic resin. The proportion of linear phenolic resin in Example 1 is higher than that in Example 3, corresponding to a larger compression strain and lower compression modulus and compression strength. This shows that within the ratio range defined in the present invention, as the amount of the phenolic ring-capped polyurethane prepolymer increases, the brittleness of the aerogel gradually decreases, showing better deformation ability.

[0112] From the comparison between Example 3 and Example 4, it can also be seen that the proportion of the soft segment in the phenolic ring-capped polyurethane prepolymer prepared in Example 3 is larger, and the molecular weight of the diol forming the soft segment is higher. The compression strain of Example 4 is improved to a certain extent compared with that of Example 3, indicating that the increase in the soft segment content is beneficial for the aerogel to show better deformation ability.

[0113] Furthermore, Examples 1 to 5 show higher compression modulus and compression strength compared with Comparative Example 1, which fully confirms that the phenolic ring-capped polyurethane prepolymer can not only improve the deformation ability of phenolic aerogel, but also lead to the refinement of the internal pore diameter of the aerogel and improve the overall strength of the aerogel, which can also be clearly seen from Figure 2 it.

[0114] In Examples 1, 6 and Comparative Example 2, only the softening point of the linear phenolic resin is different, and other conditions are the same. As can be seen from the Figure 3 results, the char residue rate is 52.86% when the softening point is 105 °C (Example 1), 52.42% when the softening point is 90 °C (Example 6), and 47.61% when the softening point is 60 °C (Comparative Example 2). The thermal stability of the aerogels of Example 1 and Example 6 is much higher than that of Comparative Example 2. Therefore, Example 1 shows better thermal stability and char residue rate under nitrogen compared with Comparative Example 2, which fully proves the importance of preferably selecting a linear phenolic resin with a softening point of 90-105 °C. As can be seen from Figure 3 it, the low softening point linear phenolic resin (60 °C) has a faster thermal decomposition weight loss and a low char residue rate.

[0115] The above are only the preferred embodiments of the present invention, and there is no restriction on the present invention in any form. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of this patent can make some changes or modifications to equivalent embodiments by using the technical content prompted above within the scope of the technical solution of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. However, as long as it does not depart from the technical content of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the present invention's solution.

Claims

1. A method for preparing polyurethane modified phenolic resin aerogel, characterized in that: The steps include: S1, preparing polyurethane by reacting diol and diisocyanate, and then end-capping the polyurethane with a phenolic compound to prepare a phenol ring-terminated polyurethane prepolymer; The phenolic compound contains a phenolic hydroxyl group and at least one functional group reactive with isocyanate; the functional group reactive with isocyanate includes a hydroxyl group, an amino group, a phenolic hydroxyl group, a thiol group, a hydroxymethyl group, and an aminomethyl group; The molecular weight range of the diol is 250-2000, and the diol is selected from polyether diol or polyester diol; S2, mixing a phenol ring-terminated polyurethane prepolymer with a linear phenolic resin to obtain a mixed solution, adding a curing agent to perform a gel reaction to obtain a polyurethane-modified phenolic resin gel; the linear phenolic resin has a softening point range of 80-130° C.; The mass ratio of the phenol ring terminated polyurethane prepolymer to the linear phenolic resin is (5-50):100; S3, removing the liquid phase in the polyurethane-modified phenolic resin gel to obtain the polyurethane-modified phenolic resin aerogel.

2. The method for preparing polyurethane modified phenolic resin aerogel according to claim 1, characterized in that: The phenolic compounds include salicyl alcohol, resorcinol, m-aminophenol and 4-mercaptophenol.

3. The method for preparing polyurethane modified phenolic resin aerogel according to claim 2, characterized in that: The phenolic compound is m-aminophenol.

4. The method for preparing the polyurethane modified phenolic resin aerogel according to any one of claims 1 to 3, characterized in that: The diisocyanate is selected from aliphatic diisocyanate, alicyclic diisocyanate and aromatic diisocyanate.

5. The method for preparing polyurethane modified phenolic resin aerogel according to claim 4, characterized in that: The diisocyanate is toluene diisocyanate.

6. The method for preparing the polyurethane modified phenolic resin aerogel according to any one of claims 1 to 3, characterized in that: The diol is polytetramethylene ether glycol.

7. The method for preparing the polyurethane modified phenolic resin aerogel according to any one of claims 1 to 3, characterized in that: In step S2, the softening point of the linear phenolic resin is in the range of 90-110°C.

8. The method for preparing the polyurethane modified phenolic resin aerogel according to any one of claims 1 to 3, characterized in that: The curing agent is selected from at least one of hexamethylenetetramine, formaldehyde or paraformaldehyde.

9. The method for preparing the polyurethane modified phenolic resin aerogel according to any one of claims 1 to 3, characterized in that: In step S2, the gel reaction is carried out in a closed reactor at a reaction temperature of 70-110° C. and a reaction time of 12-48 hours.

10. The method for preparing the polyurethane modified phenolic resin aerogel according to any one of claims 1 to 3, characterized in that: In step S3, the polyurethane modified phenolic resin gel is heated and dried at normal pressure to remove the liquid phase to obtain polyurethane modified phenolic aerogel, wherein the temperature of the normal pressure heating and drying is 50° C.-90° C. and the normal pressure drying time is 12 h-48 h.

11. A polyurethane modified phenolic resin aerogel prepared by the preparation method according to any one of claims 1 to 10.

12. The polyurethane modified phenolic resin aerogel according to claim 11, characterized in that: The compression modulus of the polyurethane modified phenolic resin aerogel is ≥60MPa, the compression strength is ≥10MPa, and the compression strain is ≥50%.

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