Low-viscosity solvent-free high-carbon phenolic resin and preparation method thereof

Abstract

The invention relates to low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof, belongs to the technical field of phenolic resin, and solves the problems that in the prior art, traditional phenolic resin is low in residual carbon rate, the viscosity is too high under a solvent-free system, and technological operation is difficult to carry out. The invention relates to a preparation method of low-viscosity solvent-free high-carbon phenolic resin, which comprises the following steps: (1) respectively heating at least two phenolic substances until the phenolic substances are molten, adding a first part of aldehyde substances, uniformly stirring and mixing, adding a composite catalyst, and carrying out a first reaction while heating and continuously stirring; after the first reaction is finished, adding a second part of aldehyde substances, and carrying out a second reaction under heating and continuous stirring; (2) after the second reaction is finished, cooling to room temperature, and adding a polymerization inhibitor to terminate the reaction to obtain a phenolic resin solution; and (3) removing the solvent through vacuum heating, and naturally cooling to room temperature to obtain the low-viscosity solvent-free high-carbon phenolic resin. The synergistic optimization of the processing performance and the heat resistance of the phenolic resin is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of phenolic resins, and particularly to a low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof. Background Art

[0002] Due to its excellent heat resistance and ablation resistance, phenolic resin has become a matrix of ablation-resistant materials widely used in the aerospace field. The structure of phenolic resin consists of long chains of phenol molecules bridged by methylene groups. However, the phenolic resin obtained by traditional preparation methods has too high a degree of polymerization, resulting in a relatively high viscosity, and usually a solvent needs to be introduced for dilution to improve the molding performance. During the curing and drying processes, the solvent will volatilize from the resin system, causing pores and defects inside the composite material, reducing the mechanical properties of the composite material, and having an adverse impact on its antioxidant and ablation resistance.

[0003] The char yield of phenolic resin is a key index to measure its thermal stability. The existing phenolic resins have a relatively low char yield, resulting in difficulty in forming a dense protective carbon layer during the ablation process of the composite material, being unable to effectively prevent oxidation erosion, and thus reducing its ablation resistance in extreme environments. Therefore, developing a phenolic resin with both low viscosity, solvent-free characteristics and a high char yield is of great significance for improving the ablation resistance of phenolic resin-based composite materials, and will also provide important material support for the technological progress in the aerospace field. Summary of the Invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof to solve at least one of the problems such as the relatively low char yield of traditional phenolic resins and the too high viscosity in a solvent-free system, making it difficult to carry out process operations.

[0005] On the one hand, the embodiments of the present invention provide a preparation method of a low-viscosity solvent-free high-carbon phenolic resin, and the specific steps are as follows: (1) Heat at least two phenolic substances to melting respectively, mix to obtain a mixed phenolic substance, add the first part of aldehyde substances, stir and mix evenly, then add a composite catalyst, and carry out the first reaction under heating and continuous stirring; after the first reaction ends, add the second part of aldehyde substances, and carry out the second reaction under heating and continuous stirring; (2) After the second reaction ends, cool to room temperature, add an inhibitor to terminate the reaction, and obtain a phenolic resin solution; (3) Remove the solvent from the phenolic resin solution prepared in step (2) by vacuum heating, and naturally cool to room temperature to obtain a low-viscosity solvent-free high-carbon phenolic resin.

[0006] Further, in step (1), the phenolic substances include phenol and aryl-substituted phenol.

[0007] Preferably, the aryl-substituted phenol is one or both of 2-phenylphenol and 2,4-diphenylphenol.

[0008] Further, in step (1), the first part of aldehyde substances and the second part of aldehyde substances are each one or a mixture of two of aqueous formaldehyde solution or furfural.

[0009] Specifically, the molar ratio of the sum of the first part of aldehyde substances and the second part of aldehyde substances to the mixed phenolic substances > 1.4.

[0010] Exemplarily, in step (1), the composite catalyst is a mixed solution of sodium hydroxide and barium hydroxide.

[0011] Specifically, the mass ratio of sodium hydroxide, barium hydroxide to the mixed phenolic substances is (0.02~0.1):(0.02~0.1):1.

[0012] Preferably, the mass ratio of sodium hydroxide to barium hydroxide in the composite catalyst system ≥ 1.0.

[0013] Further, in step (3), the process conditions for vacuum heating to remove the solvent are: temperature 80~90 °C, vacuum degree 200 mbar~300 mbar.

[0014] On the other hand, the embodiment of the present invention also provides a low-viscosity solvent-free high-carbon phenolic resin, the degree of polymerization of the low-viscosity solvent-free high-carbon phenolic resin is 3~5, the weight-average molecular weight < 400 g / mol, and the viscosity at 50 °C < 300 mPa•s.

[0015] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects: 1. In the preparation process of the phenolic resin of the present invention, the aldehyde substances are fed in segments, effectively avoiding the addition reaction at the para position of the phenolic hydroxyl group caused by the excessive aldehyde substances in the initial stage of the reaction, and improving the ortho selectivity of the phenolic resin; in addition, feeding in segments is beneficial to improving the reaction conversion rate and reducing the content of free phenol in the resin system.

[0016] 2. In the preparation of the phenolic resin of the present invention, through the efficient introduction of aromatic groups and the synergistic effect of the composite catalyst system, a high-carbon, high-ortho structure of the phenolic resin is constructed, improving its crosslinking density and the stability of the crosslinking network, and significantly enhancing the thermal stability of the phenolic resin; Using phenol and aryl-substituted phenol as reactants can introduce aromatic groups into the crosslinking network structure of the phenolic resin, enhance the stability of the overall structure, and at the same time promote the polycondensation process during high-temperature carbonization, significantly improving its thermal stability; By reasonably controlling the dosages and proportions of two catalysts, namely sodium hydroxide and barium hydroxide, the high ortho selectivity of phenolic resin is effectively promoted, which is conducive to the formation of a rigid three-dimensional network structure with high crosslinking density during the thermal polymerization process, thereby improving the thermal stability and ablation resistance of phenolic resin.

[0017] 3. The degree of polymerization of the liquid phenolic resin of the present invention is 3 - 5, the weight average molecular weight is < 400 g / mol, and the viscosity is < 300 mPa•s (50 °C), and it can achieve a viscosity of < 200 mPa•s (50 °C), fully meeting the requirements of the resin fluidity for liquid molding processes of composite materials such as RTM; it solves the technical problem that it is difficult to reconcile the process operability (low viscosity) and thermal stability (high carbon) of phenolic resin, and realizes the synergistic optimization of processing performance and heat resistance performance.

[0018] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can be made obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the description and the drawings. Description of the Drawings

[0019] The drawings are only for the purpose of showing specific embodiments, and are not considered as limitations of the present invention. Throughout the drawings, the same reference signs represent the same components; Figure 1 It is a physical photograph of the cured low-viscosity solvent-free high-residual-carbon phenolic resin of Example 2 of the present invention; Figure 2 It is the thermogravimetric curves of the low-viscosity solvent-free high-residual-carbon phenolic resins of Examples 1 - 9 and Comparative Examples 1 - 6 of the present invention; Figure 3 It is the molecular weight distribution curve of the low-viscosity solvent-free high-residual-carbon phenolic resin of Example 2 of the present invention; Figure 4 It is the viscosity-temperature curve of the low-viscosity solvent-free high-residual-carbon phenolic resin of Example 2 of the present invention. Detailed Embodiments

[0020] The following will specifically describe the preferred embodiments of the present invention with reference to the drawings. The drawings form a part of this application and are used together with the embodiments of the present invention to explain the principle of the present invention, and are not used to limit the scope of the present invention.

[0021] On the one hand, a specific embodiment of the present invention discloses a preparation method of a low-viscosity solvent-free high-carbon phenolic resin, and the specific steps are as follows: (1) Heat the phenolic substances to melting respectively, mix them to obtain a mixed phenolic substance, add the first part of aldehyde substances, stir well and mix evenly, then add a composite catalyst, and carry out the first reaction under heating and continuous stirring; after the first reaction is completed, immediately add the second part of aldehyde substances, and carry out the second reaction under heating and continuous stirring; (2) After the second reaction is completed, cool to room temperature, add an inhibitor to terminate the reaction, and obtain a phenolic resin solution; (3) Remove the solvent from the phenolic resin solution prepared in step (2) by vacuum heating, and naturally cool to room temperature to obtain a low-viscosity solvent-free high-carbon phenolic resin.

[0022] Specifically, in step (1), the phenolic substances include phenol and aryl-substituted phenols.

[0023] Further, the aryl-substituted phenol is one or both of 2-phenylphenol and 2,4-diphenylphenol.

[0024] Exemplarily, when the phenolic substances include 2,4-diphenylphenol, 2-phenylphenol and phenol, the components are mixed in any ratio; preferably, the molar ratio of 2,4-diphenylphenol, 2-phenylphenol to phenol is (0~0.5):(0~0.5):1.

[0025] Using phenol and aryl-substituted phenols as reactants can introduce aromatic groups into the cross-linked network structure of phenolic resin, enhance the stability of the overall structure, and at the same time promote the polycondensation process during high-temperature carbonization, significantly improving its thermal stability. When the proportion of aryl-substituted phenols is too high, the phenolic resin chain lacks sufficient active cross-linking sites, hindering the formation of a three-dimensional network structure with a high cross-linking density, and the integrity of the network structure becomes poor, thus affecting the mechanical properties and heat resistance of the resin.

[0026] Exemplarily, in step (1), the first part of aldehyde substances and the second part of aldehyde substances are both one or a mixture of two of aqueous formaldehyde solution or furfural, and the mass fraction of formaldehyde in the aqueous formaldehyde solution is 37%.

[0027] When the aldehyde substances are a mixed solution of aqueous formaldehyde solution and furfural, in the mixed solution, the molar ratio of furfural to formaldehyde is (0.1~0.5):1. When the proportion of furfural is low, the degree of aryl introduction on the phenolic resin cross-linked network is relatively small, and the thermal stability of the resulting phenolic resin decreases.

[0028] Further, in step (1), the molar ratio of the mixed phenolic substances, the aldehyde compounds in the first part of aldehyde substances and the aldehyde compounds in the second part of aldehyde substances is 1:(0.8~1.5):(0.1~0.5).

[0029] The staged feeding effectively avoids the addition reaction at the para-position of the phenolic hydroxyl group caused by the excessive amount of aldehyde substances in the initial stage of the reaction, improving the ortho-selectivity of phenolic resin; in addition, the staged feeding is beneficial to improving the reaction conversion rate and reducing the content of free phenol in the resin system.

[0030] Furthermore, the sum of the first part of aldehyde substances and the second part of aldehyde substances and the molar ratio of the mixed phenolic substances is the feeding ratio of aldehyde substances to phenolic substances. Increasing the proportion of aldehyde substances can accelerate the addition reaction rate, effectively reduce the content of free phenol, and improve the crosslinking density during curing; however, when the addition amount of aldehyde is too much (aldehyde / phenol > 1.6), a large amount of para-addition products will be generated, and these products hinder the formation of the crosslinking network due to large steric hindrance and high activation energy during the polycondensation process. Therefore, the molar ratio of aldehyde substances to phenolic substances should be > 1.4, such as 1.5, 1.6, 1.7, 1.9, and the preferred one is 1.6.

[0031] Preferably, in step (1), the composite catalyst is a mixed solution of sodium hydroxide and barium hydroxide, where the mass fractions of sodium hydroxide and barium hydroxide are both 5 - 20%.

[0032] Furthermore, the mass ratio of sodium hydroxide to barium hydroxide in the composite catalyst system is ≥ 1.0, such as 1, 1.2, 1.4, 1.5, 1.6, 1.7, 1.8, and the preferred ratio is 1.8.

[0033] Sodium hydroxide provides an alkaline environment: when the alkalinity is too low, the addition and condensation reaction activities of phenolic aldehyde are poor; when the alkalinity is too high, formaldehyde is prone to self-disproportionation reaction. Barium hydroxide can catalyze the ortho-addition reaction of formaldehyde on phenol and promote the ortho-polycondensation reaction between polymers. By reasonably controlling the dosages of the two catalysts, the efficient progress of the ortho-addition and polycondensation reactions can be ensured, obtaining a high-ortho phenolic resin, which is beneficial to forming a rigid three-dimensional network structure with a high crosslinking density during the thermal polymerization process, thereby improving the thermal stability and ablation resistance of phenolic resin.

[0034] Preferably, the mass ratio of sodium hydroxide, barium hydroxide in the catalyst to the mixed phenolic substances is (0.02 - 0.1):(0.02 - 0.1):1 to ensure high ortho-selectivity during the reaction process.

[0035] Furthermore, the inhibitor in step (2) is a non-oxidizing strong acid, preferably hydrochloric acid, and the mass fraction of the hydrochloric acid is 20 - 35%.

[0036] Specifically, the reaction process of step (1) is as follows:

[0037] It should be noted that in step (1), the termination points of the first reaction and the second reaction are determined by controlling the reaction duration; the process conditions of the first reaction are: stirring at 400 - 600 r / min at 50 - 90 °C for 0.5 - 1.5 hours; the process conditions of the second reaction are: stirring at 400 - 600 r / min at 50 - 90 °C for 0.5 - 1 hour.

[0038] The degree of polymerization and molecular weight of phenolic resin increase with the increase of reaction temperature and the prolongation of reaction time. By strictly controlling the reaction time and terminating the reaction in time, the degree of polymerization and molecular weight of phenolic resin can be effectively reduced, which is beneficial to maintaining a lower viscosity after solvent-free treatment. Exemplarily, the degree of polymerization of the phenolic resin prepared in the present invention is 3 - 5, the weight-average molecular weight is < 400 g / mol, and there is a linear correlation between the degree of polymerization and the weight-average molecular weight of the phenolic resin. The degree of polymerization can be deduced from the weight-average molecular weight and the molecular weight of the repeating unit.

[0039] Furthermore, the process conditions for vacuum heating to remove the solvent in step (3) are: temperature 80 - 90 °C, vacuum degree 200 mbar - 300 mbar. By controlling the vacuum heating temperature, the condensation reaction can be prevented from continuing at high temperature, thus avoiding too high viscosity of the phenolic resin.

[0040] On the other hand, a specific embodiment of the present invention also discloses a low-viscosity solvent-free high-carbon phenolic resin, the degree of polymerization of the low-viscosity solvent-free high-carbon phenolic resin is 3 - 5, the weight-average molecular weight is < 400 g / mol, the viscosity is < 300 mPa•s (50 °C), and the carbonization yield at 900 °C is ≥ 64.1%.

[0041] It should be noted that the carbonization yield of the phenolic resin of the present invention at 900 °C is ≥ 64.1%, the residual carbon rate is high, the thermal stability at high temperature is good, and it is not easy to decompose; the results of thermogravimetric analysis show that the mass retention rate at 800 °C is ≥ 68.8%, the mass retention rate at 1200 °C is ≥ 66%, the mass ablation rate is low, and the ablation resistance at high temperature is strong.

[0042] In summary, in the preparation process of the phenolic resin of the present invention, the aldehyde substances are added in segments, effectively avoiding the addition reaction at the para-position of the phenolic hydroxyl group caused by the excessive amount of aldehyde substances in the initial stage of the reaction, and improving the ortho-selectivity of the phenolic resin; through the efficient introduction of aromatic groups and the synergistic effect of the composite catalyst system, a high-carbon and high-ortho structure of the phenolic resin is constructed, improving its crosslinking density and the stability of the crosslinking network, and significantly enhancing the thermal stability of the phenolic resin; by reasonably controlling the dosage and ratio of the two catalysts, sodium hydroxide and barium hydroxide, the high ortho-selectivity of the phenolic resin is effectively promoted, which is beneficial to the formation of a rigid three-dimensional network structure with a high crosslinking density during the thermal polymerization process, thereby improving the thermal stability and ablation resistance of the phenolic resin. The liquid phenolic resin of the present invention has a degree of polymerization of 3-5, a weight average molecular weight of <400 g / mol, a viscosity of <300 mPa•s (50 °C), and a carbonization yield of ≥64.1% at 900 °C, fully meeting the requirements of the resin fluidity for composite liquid molding processes such as RTM; solving the technical problem that it is difficult to be compatible between the process operability (low viscosity) and thermal stability (high carbon) of phenolic resin, and realizing the synergistic optimization of processing performance and heat resistance performance.

[0043] The following is a description of the low-viscosity solvent-free high-carbon phenolic resin of the present invention and its preparation method in conjunction with specific examples.

[0044] Example 1 This example provides a low-viscosity solvent-free high-carbon phenolic resin and its preparation method.

[0045] Raw materials: The phenolic substances include 77.8 g of phenol, 70.3 g of 2-phenylphenol, and 101.8 g of 2,4-diphenylphenol. The first part of the aldehyde substances includes 71.5 g of formaldehyde aqueous solution and 42.4 g of furfural. The second part of the aldehyde substances includes 71.5 g of formaldehyde aqueous solution and 42.4 g of furfural. The mass fraction of formaldehyde in the formaldehyde aqueous solution is 37%.

[0046] Catalysts: Sodium hydroxide and barium hydroxide. Weigh 12.5 g of solid sodium hydroxide and 12.5 g of solid Ba(OH)2•H2O, dissolve them fully in 100 g of water, and use them as catalysts for standby.

[0047] The preparation process is as follows: (1) Heat the phenolic substances to melting respectively, mix them to obtain a mixed phenolic substance, add the first part of the aldehyde substances, stir well, and then add the catalyst. Heat and stir at 50 °C for the first reaction for 1.5 hours; when the first reaction ends and the system is still at a relatively high temperature, immediately add the second part of the aldehyde substances, and heat and stir at 80 °C for the second reaction for 40 minutes; After the second reaction, cool to room temperature, add 7.44 g of inhibitor to terminate the reaction, and obtain a phenolic resin solution; (3) Remove the solvent from the phenolic resin solution prepared in step (2) by vacuum heating, and naturally cool it to room temperature to obtain a low-viscosity solvent-free high-carbon phenolic resin; The dehydration process is as follows: temperature 80 °C, vacuum 200 mbar, time 90 minutes.

[0048] Performance test: Keep the low-viscosity solvent-free high-carbon phenolic resin obtained in step (3) at 110 °C for 8 hours for curing, and calculate the curing yield; conduct thermogravimetric tests in the range of 30 - 1200 °C and at a heating rate of 10 °C / min to obtain the mass retention rates at 800 °C and 1200 °C; conduct carbonization experiments in a tube furnace under N2 atmosphere in the range of 30 - 900 °C and at a heating rate of 5 °C / min to obtain the carbonization yield at 900 °C; the specific results are shown in Table 4, and the thermogravimetric curves are shown in Figure 2 .

[0049] Example 2 This example provides a low-viscosity solvent-free high-carbon phenolic resin and its preparation method.

[0050] The raw materials and catalyst conditions are shown in Tables 2 and 3 respectively. The difference from Example 1 is the different addition ratios of sodium hydroxide and barium hydroxide in the catalyst, as shown in Table 3 specifically.

[0051] The preparation process is the same as that of Example 1, as shown in Table 1 specifically.

[0052] The product performance test method is the same as that of Example 1, and the specific results are shown in Table 4, and the thermogravimetric curves are shown in Figure 2 .

[0053] The product photos are as Figure 1 shown, the molecular weight distribution curve is as Figure 3 shown, and the viscosity-temperature curve is as Figure 4 shown.

[0054] Examples 3 - 5 This example provides a low-viscosity solvent-free high-carbon phenolic resin and its preparation method.

[0055] The raw materials and catalyst conditions are shown in Tables 2 and 3 respectively. The difference from Example 2 is the different feeding ratios of aldehyde substances and phenolic substances, as shown in Table 3 specifically.

[0056] The preparation process is the same as that of Example 1, as shown in Table 1 specifically.

[0057] The product performance test method is the same as that of Example 1, and the specific results are shown in Table 4, and the thermogravimetric curves are shown in Figure 2 .

[0058] Example 6 This embodiment provides a low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof.

[0059] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The difference from Example 2 is that the phenolic raw material is a mixed phenol of phenol and 2-phenylphenol, as shown in Table 3 specifically.

[0060] The preparation process is the same as that of Example 1, as shown in Table 1 specifically.

[0061] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0062] Example 7 This embodiment provides a low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof.

[0063] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The difference from Example 2 is that the phenolic raw material is a mixed phenol of phenol and 2,4-diphenylphenol, as shown in Table 3 specifically.

[0064] The preparation process is the same as that of Example 1, as shown in Table 1 specifically.

[0065] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0066] Example 8 This embodiment provides a low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof.

[0067] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The difference from Example 2 is that both the first part of aldehyde substances and the second part of aldehyde substances are aqueous formaldehyde solutions, as shown in Table 3 specifically.

[0068] The preparation process is the same as that of Example 1, as shown in Table 1 specifically.

[0069] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0070] Example 9 This embodiment provides a low-viscosity solvent-free high-carbon phenolic resin and a preparation method thereof.

[0071] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The difference from Example 2 is that both the first part of aldehyde substances and the second part of aldehyde substances are furfural, as shown in Table 3 specifically.

[0072] The preparation process is the same as that of Example 1, as shown in Table 1 specifically.

[0073] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0074] Comparative Example 1 This comparative example provides a phenolic resin and a preparation method thereof.

[0075] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The main difference from Example 1 is that the catalyst is only sodium hydroxide, as shown in Table 3 specifically.

[0076] The preparation process is the same as that of Example 1. The specific process conditions and parameters are shown in Table 1.

[0077] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0078] Comparative Example 2 This comparative example provides a phenolic resin and a preparation method thereof.

[0079] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The main difference from Example 1 is that the catalyst is only barium hydroxide, as shown in Table 3 specifically.

[0080] The preparation process is the same as that of Example 1. The specific process conditions and parameters are shown in Table 1.

[0081] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0082] Comparative Example 3 This comparative example provides a phenolic resin and a preparation method thereof.

[0083] The raw materials and catalysts are shown in Tables 2 and 3 respectively, which are the same as those of Example 2.

[0084] The preparation process is basically the same as that of Example 2, except that the first reaction time in step (1) is too long, which is 2.5 hours. The specific process conditions and parameters are shown in Table 1.

[0085] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0086] Comparative Example 4 This comparative example provides a phenolic resin and a preparation method thereof.

[0087] The raw materials and catalysts are shown in Tables 2 and 3 respectively. The main difference from Example 1 is that the mass ratio of sodium hydroxide to barium hydroxide as the catalyst < 1, as shown in Table 3 specifically.

[0088] The preparation process is the same as that of Example 1, and the specific process conditions and parameters are shown in Table 1.

[0089] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0090] Comparative Example 5 This comparative example provides a phenolic resin and its preparation method.

[0091] The raw materials and catalysts are shown in Tables 2 and 3 respectively, which are the same as those of Example 2.

[0092] The preparation process is basically the same as that of Example 2, except that the aldehyde substances are added at one time in step (1). The specific process conditions and parameters are shown in Table 1.

[0093] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0094] Comparative Example 6 This comparative example provides a phenolic resin and its preparation method.

[0095] The raw materials and catalysts are shown in Tables 2 and 3 respectively, which are the same as those of Example 2.

[0096] The preparation process is basically the same as that of Example 2, except that the second reaction time in step (1) is too long, which is 2.5 hours. The specific process conditions and parameters are shown in Table 1.

[0097] The product performance test method is the same as that of Example 1. The specific results are shown in Table 4, and the thermogravimetric curve is shown in Figure 2 .

[0098]

[0099]

[0100]

[0101]

[0102] Compared with Example 2, in Example 1 and Comparative Examples 1-2, the ratio of sodium hydroxide to barium hydroxide in the composite catalyst system was mainly changed. Among them, in Comparative Example 1, only sodium hydroxide was used as the catalyst. Due to the lack of Ba 2+The catalytic promotion for ortho addition and polycondensation reactions results in a large accumulation of para addition products in the system. During the thermal polymerization process, due to steric hindrance limitations, the crosslinking degree is relatively low, which in turn affects the thermal stability of phenolic resin. On the contrary, in Comparative Example 2, only barium hydroxide is used as the catalyst. Due to insufficient alkalinity, the addition reaction proceeds incompletely, and there are not enough phenolic resin molecular chains participating in the reaction during the thermal polymerization process, resulting in a significant reduction in thermal stability performance. Compared with Example 2, the mass ratio of sodium hydroxide to barium hydroxide in Example 1 is relatively low, and the alkalinity of the system is slightly insufficient compared to the requirements for efficient catalytic addition reaction, resulting in lower thermal stability of phenolic resin than in Example 2. In Comparative Example 4, the mass ratio of sodium hydroxide to barium hydroxide < 1, which does not meet the requirements of the present invention, and the alkalinity of the system completely fails to meet the requirements for efficient catalytic addition reaction, resulting in poor thermal stability of phenolic resin. By constructing a composite catalyst system of barium hydroxide and sodium hydroxide and reasonably regulating the ratio of the two, the efficient generation of high ortho phenolic resin can be achieved, thereby significantly improving its crosslinking degree and thermal stability performance. The mass ratio of sodium hydroxide to barium hydroxide in the composite catalyst system should be ≥ 1.0, and the optimal ratio is 1.8.

[0103] Compared with Example 2, the reaction time of the first reaction in Comparative Example 3 is too long, and the reaction time of the second reaction in Comparative Example 6 is too long. The extension of the reaction time leads to the growth of the polycondensation product chain, which is more likely to break bonds and release small molecules at high temperatures, resulting in a decrease in the char yield.

[0104] Compared with Example 2, in Comparative Example 5, the aldehyde substances are not added in segments, resulting in poor ortho selectivity of the reaction, low crosslinking density and stability of the crosslinking network, and the thermal stability of phenolic resin is lower than that in Example 2.

[0105] Examples 2 to 5 mainly changed the feeding ratio of aldehydes to phenols. Increasing the proportion of aldehydes can accelerate the addition reaction rate, effectively reduce the content of free phenol, and increase the crosslinking density during curing. When the amount of aldehyde substances is relatively large (aldehyde / phenol > 1.6), more para addition products will be generated. These products have relatively large steric hindrance and high activation energy during the polycondensation process, which has a certain impact on the formation of the crosslinking network. The ratio of aldehydes to phenolic compounds should be greater than 1.4, and the optimal ratio is 1.6.

[0106] In Examples 2, 6, and 7, the proportions of three phenols in the phenolic substances were mainly changed. As can be seen from Table 4, aryl-substituted phenols can introduce aryl groups into the crosslinked network of phenolic resins. However, when the proportion of aryl-substituted phenols is too high, compared with the optimal example, the active crosslinking sites on the phenolic resin chain are relatively insufficient, resulting in certain limitations in the formation of a three-dimensional network structure with a high crosslinking density. Furthermore, the integrity of the network structure is slightly inferior. In this case, the mechanical properties and heat resistance of the resin are slightly different from those of the optimal example. The optimal molar ratio range of 2,4-diphenylphenol, 2-phenylphenol, and phenol is (0-0.5):(0-0.5):1.

[0107] In Examples 2, 8, and 9, the proportions of two aldehydes in the aldehyde substances were mainly changed. As can be seen from Table 4, when the proportion of furfural is low, the degree of aryl introduction into the crosslinked network of phenolic resin is relatively small. Compared with the optimal Example 2, its thermal stability performance is slightly different, but it still shows good performance overall.

[0108] In summary, in the preparation process of the phenolic resin of the present invention, the method of adding aldehyde substances in segments is adopted, effectively avoiding the addition reaction at the para position of phenolic hydroxyl groups caused by excessive aldehyde substances in the initial stage of the reaction, and improving the ortho selectivity of phenolic resins; through the efficient introduction of aromatic groups and the synergistic effect of the composite catalyst system, a high-carbon and high-ortho structure of phenolic resin is constructed, improving its crosslinking density and the stability of the crosslinked network, and significantly enhancing the thermal stability of phenolic resin; by reasonably controlling the dosage and proportion of two catalysts, sodium hydroxide and barium hydroxide, the high ortho selectivity of phenolic resin is effectively promoted, which is beneficial to the formation of a rigid three-dimensional network structure with a high crosslinking density during the thermal polymerization process, thereby improving the thermal stability and ablation resistance of phenolic resin. The polymerization degree of the liquid phenolic resin of the present invention is 3-5, the weight average molecular weight is <400 g / mol, the viscosity is <300 mPa•s (50 °C), and the carbonization yield at 900 °C is ≥64.1%, fully meeting the requirements of resin fluidity for composite material liquid molding processes such as RTM; solving the technical problem that it is difficult to reconcile the process operability (low viscosity) and thermal stability (high carbon) of phenolic resins, and realizing the coordinated optimization of processing performance and heat resistance performance.

[0109] The above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a low-viscosity solvent-free high-carbon phenolic resin, characterized in that The specific steps are as follows: (1) Heat phenol and at least one aryl-substituted phenol to melting respectively, mix them to obtain a mixed phenolic substance, add the first part of aldehyde substance, stir and mix evenly, then add a composite catalyst, and carry out the first reaction under heating and continuous stirring; after the first reaction is completed, add the second part of aldehyde substance, and carry out the second reaction under heating and continuous stirring; Both the first part of aldehyde substance and the second part of aldehyde substance are furfural or a mixture of aqueous formaldehyde solution and furfural; (2) After the second reaction is completed, cool to room temperature, add an inhibitor to terminate the reaction, and obtain a phenolic resin solution; (3) Remove the solvent from the phenolic resin solution prepared in step (2) by vacuum heating, and naturally cool to room temperature to obtain a low-viscosity solvent-free high-carbon phenolic resin.

2. The preparation method according to claim 1, characterized in that, The aryl-substituted phenol is one or two of 2-phenylphenol and 2,4-diphenylphenol.

3. The preparation method according to claim 2, wherein The molar ratio of 2,4-diphenylphenol, 2-phenylphenol to phenol is (0~0.5):(0~0.5):

1.

4. The preparation method according to claim 1, wherein, The molar ratio of the sum of the first part of aldehyde substance and the second part of aldehyde substance to the mixed phenolic substance > 1.

4.

5. The preparation method according to claim 1, characterized in that, When the aldehyde substance is a mixed solution of aqueous formaldehyde solution and furfural, in the mixed solution, the molar ratio of furfural to formaldehyde is (0.1~0.5):

1.

6. The preparation method according to claim 1, wherein In step (1), the composite catalyst is a mixed solution of sodium hydroxide and barium hydroxide.

7. The preparation method according to claim 6, characterized in that, The mass ratio of sodium hydroxide, barium hydroxide to the mixed phenolic substance is (0.02~0.1):(0.02~0.1):

1.

8. The preparation method according to claim 6, characterized in that, In the composite catalyst system, the mass ratio of sodium hydroxide to barium hydroxide ≥ 1.

0.

9. The preparation method according to claim 1, characterized in that, The process conditions for removing the solvent by vacuum heating in step (3) are: temperature 80~90 °C, vacuum degree 200 mbar~300 mbar.

10. A low-viscosity solvent-free high-carbon phenolic resin, characterized in that, Prepared by the method according to any one of claims 1~9, the polymerization degree of the low-viscosity solvent-free high-carbon phenolic resin is 3~5, the weight-average molecular weight < 400 g / mol, and the viscosity at 50 °C < 300 mPa•s.

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