CN114736488B

CN114736488B - Preparation method of high-compression-resistance fireproof composite epoxy foam

Info

Publication number: CN114736488B
Application number: CN202210558314.8A
Authority: CN
Inventors: 贾晓龙; 吉早明; 黎何丰; 还献华; 郭天乐; 朱家宝; 杨小平
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2022-05-20
Filing date: 2022-05-20
Publication date: 2023-08-08
Anticipated expiration: 2042-05-20
Also published as: CN114736488A

Abstract

The invention relates to the technical field of preparation of epoxy foam materials, and mainly relates to a preparation method of high-pressure-resistance and fire-resistance composite epoxy foam. The invention is based on the principle of controllable benzyl hydroxyl activity, reduces the benzyl hydroxyl activity in the process of synthesizing the boron phenolic epoxy resin by taking ammonia water as a catalyst and adopting a step heating method, solves the problems of epoxy value reduction and boric acid surplus caused by overhigh benzyl hydroxyl activity in the resin synthesis, and successfully prepares a boron-containing high-temperature-resistant foaming resin matrix; by adding the difunctional foaming agent with synergistic curing effect in the foaming process, the problem of mismatch between resin gel and foaming agent decomposition is solved; the epoxy foam material integrating compression resistance, heat insulation and flame resistance is finally prepared by adding the boron phenolic epoxy resin grafted modified graphene oxide into the epoxy foam, so that the cell size is reduced, the cell wall is enhanced, the stable graphitized carbon layer is formed on the surface of the epoxy foam in flame, and the heat conductivity is reduced.

Description

Preparation method of high-compression-resistance fireproof composite epoxy foam

Technical Field

The invention relates to the technical field of epoxy foam, and mainly relates to a preparation method of high-pressure-resistance and fire-resistance composite epoxy foam.

Background

With the rapid development of the industries of aerospace, rail transit, automobiles and the like, the problem of mass consumption of energy becomes increasingly severe, and the use of light-weight high-strength materials is an important way to reduce energy consumption. Compared with metal materials, the foam materials prepared from the polymer are widely paid attention to in industry due to the characteristics of high specific strength, low density, low thermal conductivity and low cost, however, due to the poor heat resistance of the polymer foaming matrix, the polymer foam materials cannot maintain excellent compression resistance in flame, and how to maintain high mechanical strength while improving the flame resistance of the polymer foam materials is a scientific problem which is needed to be solved at present.

While the conventional flame-resistant resin-based foam materials are mostly prepared by foaming with phenolic resin as a matrix, epoxy foam materials obtained by foaming high-performance epoxy resins are gradually developed in recent years. Because phenolic resin has good heat resistance and high carbon residue rate, the foam material prepared by foaming the phenolic resin has good flame resistance, but the compression resistance of the foam is poor. Issaoui H et al (Issaoui H, de Hoyos-Martinez P L, pellerin V, et al Effect of Catalysts and Curing Temperature on the Properties of Biosourced Phenolic Foams [ J ]. ACS Sustainable Chemistry & Engineering,2021,9 (18): 6209-6223) prepared a bio-based phenolic foam from lignin lye and tannin, which had a mass loss rate of at least 60% and good flame resistance when flame tested, but had a compressive strength of only 1.7MPa, which has failed to meet the current demand. The epoxy resin has excellent mechanical property, so that the foam material prepared by foaming the epoxy resin has high compression strength, but the flame resistance of the foam is poor. The Chinese patent (application number 202110383936.7) takes isocyanate modified epoxy resin as a foaming matrix and modified graphene oxide nano particles are added, an epoxy foam material is prepared through two-step foaming, the compression strength is up to 13.4MPa, but the prepared foam does not have flame resistance performance due to the limitation of the foaming matrix, in the foaming process, the size of a foam hole is optimized by reducing the post-curing temperature, the compression strength is improved, but when the post-curing temperature is reduced, the variation amplitude of the resin gel time and the decomposition time of a foaming agent is inconsistent, the matching property between the resin and the foaming agent is influenced, and the great improvement of the compression strength is difficult to realize. Therefore, in order to simultaneously improve the compression resistance and flame resistance of the epoxy foam, it is necessary to develop a novel high temperature resistant epoxy resin which can be used for foaming. The phenolic epoxy resin is an epoxy resin with excellent mechanical property and high temperature resistance, has the basis for preparing high-performance epoxy foam materials, and can introduce inorganic hetero elements such as boron, molybdenum, phosphorus and the like into the molecular structure of the resin in order to further improve the high temperature resistance of the resin. The Chinese patent (application number 202110135593.2) uses phenol, aldehyde substances and modifier to react to obtain inorganic hybrid modified phenolic resin, then reacts with epoxy chloropropane, and finally is refined to obtain the inorganic hybrid modified phenolic epoxy resin. Chinese patent (application No. 202110254467.9) uses bisphenol A to react with formaldehyde and phosphoric acid to obtain phosphorus-containing phenolic resin, then reacts with epoxy chloropropane, and finally is refined to obtain the phosphorus-containing phenolic epoxy resin. The method for preparing the modified phenolic epoxy resin in the two patents can be summarized as that firstly, salicyl alcohol is prepared through the addition reaction of phenol and aldehyde, then, the modifier containing inorganic hetero elements and the salicyl alcohol are subjected to polycondensation reaction to generate phenolic resin containing hetero elements, and finally, the modified phenolic epoxy resin is obtained through the ring-opening etherification reaction of epichlorohydrin and the modified phenolic resin. The method has complicated steps and needs to consume a large amount of epoxy chloropropane which is a toxic reagent, and the problems can be avoided by directly adopting bisphenol A diglycidyl ether (DGEBA) to react with formaldehyde and a modifier, but benzyl hydroxyl introduced on benzene rings of the DGEBA through addition reaction has extremely high reactivity, can react with epoxy groups to reduce the epoxy value, or can directly react with active hydrogen on benzene rings of other DGEBA molecules to generate polycondensation reaction to cause that modified inorganic hetero elements cannot be introduced into a resin structure, so that the activity of benzyl hydroxyl needs to be reduced in order to prepare the modified phenolic epoxy resin through the DGEBA. In addition, the high viscosity of the phenolic epoxy resin can lead to higher melt strength in the foaming process, which is beneficial to reducing the cell size and improving the compression strength of the foam, but can lead to higher apparent density of the foam, and becomes a disadvantageous factor for reducing the heat conductivity of the foam, so that the problem of balance between compression resistance and heat insulation performance needs to be solved.

In general, the current preparation of foam materials having both high compression and flame resistance has the following problems: 1. the common foaming resin matrix has poor high temperature resistance and flame resistance, and is difficult to meet the requirements of preparing flame-resistant foam materials; 2. when the post-curing temperature is reduced, the gel time of the resin is inconsistent with the decomposition time variation amplitude of the foaming agent, so that the improvement effect of the compressive strength of the foam is limited; 3. when the high-temperature resistant phenolic epoxy resin is prepared, the benzyl hydroxyl activity is higher, so that the epoxy value is reduced and boric acid remains; 4. the increase in apparent cell density adversely affects the thermal insulation properties of the foam. Therefore, in order to prepare a high pressure resistant fire resistant foam material, it is necessary to develop an easy to prepare, high heat resistant phenolic epoxy resin which can be used for foaming, and solve the problem of mismatch between resin gel and foaming agent decomposition, and reduce the adverse effect on the heat insulation performance of the foam due to the improvement of the apparent density of the foam.

Disclosure of Invention

In order to solve the problems, the invention modifies the structure of phenolic epoxy resin based on the principle of controllable benzyl hydroxyl activity, introduces boron-oxygen bond into the molecular structure of the resin, effectively improves the decomposition temperature and carbon residue rate of the resin, provides a foaming matrix for preparing the fire-resistant foam material, reduces the benzyl hydroxyl activity in the resin synthesis process by adopting weak alkaline ammonia water as a catalyst and a step heating method, and solves the problems of epoxy group loss and boric acid residue caused by overhigh benzyl hydroxyl activity in the resin synthesis process; by adding a difunctional foaming agent with synergistic curing effect in the foaming process, the problem of mismatch between resin gel and foaming agent decomposition is solved; the multifunctional graphene oxide reinforced particles are obtained by modifying the graphene oxide grafting of the boron phenolic epoxy resin and used as a modifier of the epoxy foam, so that the cell size is effectively reduced, the cell wall is reinforced, a stable and firm graphitized carbon layer is formed on the surface of the foam in the flame combustion process, the thermal conductivity is reduced by utilizing the thermal resistance effect and the thermal infrared absorption effect of the graphene oxide particles, and finally, the composite epoxy foam material with high compression strength, excellent heat insulation performance and strong dimensional capability in flame is prepared by a two-step foaming method, and the problem that the current epoxy foam material cannot have both high compression resistance and flame resistance due to insufficient heat resistance of a foaming resin matrix is solved.

In order to achieve the above purpose, the invention provides a preparation method of high compression-resistant fire-resistant composite epoxy foam, which comprises the following specific technical contents:

(1) The synthetic procedure of the boron phenolic epoxy resin comprises the following steps: 1) Addition reaction: dissolving bisphenol A diglycidyl ether and formaldehyde in an organic solvent according to a molar ratio of 1:1.0-1.5, mechanically stirring for 5-10min, then adding 28wt% of catalyst ammonia, wherein the mass ratio of the ammonia to the bisphenol A diglycidyl ether is 1:20-100, and heating to 80-90 ℃ for reacting for 2-3h; cooling to 50-60 ℃ after the reaction is finished, and distilling under reduced pressure until the solution becomes clear, thus obtaining a low-activity benzyl hydroxyl-epoxy intermediate; 2) Polycondensation reaction: adding boric acid into the low-activity benzyl hydroxyl-epoxy intermediate obtained by addition reaction, mechanically stirring, wherein the molar ratio of boric acid to bisphenol A diglycidyl ether is 1:2-10, then heating the reaction solution in a stepped temperature rising mode, namely, the reaction is divided into three sections, the reaction temperatures of the three sections are 65-70 ℃ and 75-80 ℃ and 85-90 ℃ respectively in sequence, each section of the first two sections of the reaction is subjected to normal pressure heat preservation for 5-15min and reduced pressure distillation for 5-15min, the last section of the reaction is subjected to normal pressure heat preservation for 5-15min, and the reaction is finished after the reduced pressure distillation until the resin is changed into a wiredrawing state, so that colorless transparent viscous liquid, namely the boron phenolic epoxy resin, is finally obtained.

(2) The preparation process of the multifunctional graphene oxide reinforced particles comprises the following steps: adding graphene oxide into 100ml of organic dispersing agent to prepare a dispersing liquid with the concentration of 0.001-0.003g/ml, then carrying out ultrasonic treatment on the dispersing liquid for 1-2 hours, wherein the ultrasonic power is 80-120W, then adding 5-10g of boron phenolic epoxy resin, mechanically stirring for 5-10 minutes, then slowly adding alkaline catalyst, and carrying out heat preservation reaction for 4-8 hours at 50-80 ℃; and after the reaction is finished, washing the dispersion liquid with an organic dispersing agent for 3-5 times, and then centrifuging and drying to obtain the multifunctional graphene oxide reinforced particles.

(3) Preparation procedure of foaming precursor: mixing the multifunctional graphene oxide reinforced particles prepared in the step (1) with boron phenolic epoxy resin according to the mass ratio of 0.1-1:100, carrying out ultrasonic mechanical stirring for 1-2 hours to obtain a dispersion liquid, then carrying out mechanical stirring treatment on the dispersion liquid and an amine curing agent according to the molar ratio of epoxy groups to amine groups, wherein the stirring temperature is 90-110 ℃, the stirring speed is 50-100r/min, when the system viscosity reaches 2-4 times of the initial viscosity, adding a bifunctional foaming agent sulfonyl hydrazine with a synergistic curing effect, a surfactant and a toughening agent component, and carrying out mechanical stirring for 5-10 minutes to obtain a foaming precursor, wherein the mass ratio of the boron phenolic epoxy resin, the bifunctional foaming agent, the surfactant and the toughening agent is 100:2-3:0.2-0.3:2-3.

(4) And (3) a post-curing procedure of the foaming agent and the epoxy foam: pouring the foaming precursor into a foaming mold preheated in advance for mold closing foaming, and adopting stepped heating and curing, wherein the temperature of the first section is 120-140 ℃ and the time is 1-3h; the temperature of the second stage is 150-170 ℃ and the time is 4-6h; and (5) demoulding after the sample is cooled, and finally preparing the high-pressure-resistant and fire-resistant composite epoxy foam.

Wherein the organic solvent is one or more of n-butanol, toluene, xylene and cyclohexanol; the organic dispersing agent is one or more of N, N-dimethylformamide, N-butanol, toluene and N-methylpyrrolidone; the alkaline catalyst is one or more of sodium hydroxide, potassium hydroxide and barium hydroxide; the amine curing agent is one or more of diethyl toluene diamine, m-xylylenediamine, diaminodiphenylmethane and isophorone diamine; the surfactant is one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether and sorbitol ester; the toughening agent is one or more of carboxyl-terminated nitrile rubber, epoxy nitrile rubber and nano core-shell rubber.

Effects of the invention

(1) According to the invention, the problems of epoxy group loss and boric acid residue caused by higher activity of benzyl hydroxyl are effectively solved by adopting ammonia water as a catalyst, and the condensation dehydration reaction of benzyl hydroxyl and boron hydroxyl is promoted by reduced pressure distillation at a lower reaction temperature by a step heating method, at the moment, the reactivity of benzyl hydroxyl and epoxy group is low, the influence of epoxy group is smaller, after the temperature is raised, the residual benzyl hydroxyl in the solution can continue the condensation dehydration reaction, at the moment, the content of benzyl hydroxyl is smaller, the influence on the epoxy group is very limited, and finally, most of benzyl hydroxyl is used for the condensation reaction, so that the boron-containing phenolic epoxy resin with uniform texture and high epoxy value (0.47 mol/100 g) is successfully synthesized.

(2) According to the invention, boric acid modified synthesized phenolic epoxy resin is used as a foaming resin matrix, a boron-oxygen bond with high bond energy is introduced into a crosslinking network of the epoxy foam, the initial decomposition temperature of the epoxy foam material is improved, boron element in the foam generates glassy diboron trioxide to cover the surface of the foam when being burnt by flame, so that the decomposition of the inside of the foam can be effectively slowed down, and simultaneously, boron hydroxyl in the boron-phenolic epoxy resin structure can be subjected to condensation dehydration reaction at high temperature, so that the secondary crosslinking solidification of the foam is realized, and finally, the flame resistance of the foam is improved.

(3) According to the invention, the difunctional foaming agent with the synergistic curing effect is added into the epoxy foam, so that the gel time of the epoxy resin in the post-curing process is shortened, and the resin and the foaming agent have good matching property.

(4) According to the invention, the multifunctional graphene oxide reinforced particles are added into the epoxy foam, so that quadruple effects are generated: 1) The particles have heterogeneous nucleation in the foaming process, so that more foaming agent is used for nucleation rather than growth of cells, and the size of the cells is reduced; 2) Epoxy groups on the surfaces of the particles can react with amine groups in the foaming matrix, and a stable interface is constructed between the graphene and the foaming matrix through chemical bonds, so that the wall of the foam hole is enhanced, and the pressure resistance of a single foam hole is improved; 3) The particles have good carbon fixation effect in the combustion process of the epoxy foam, the carbon layer after flame burning is enhanced, the quality loss of the carbon layer caused by the fact that the carbon layer is flushed by flame airflow is reduced, the foam shape is maintained, and meanwhile, the stable graphitized carbon layer structure is formed on the surface of the epoxy foam; 4) The thermal resistance effect and the thermal infrared absorption effect of the particles can reduce the thermal conductivity, and make up for the adverse effect on the heat insulation performance of the foam due to the higher apparent density of the foam.

Drawings

FIG. 1 is a photograph of the foam prepared in example 1 after flame combustion, (a) being the side and (b) being the upper surface.

FIG. 2 is a photograph of the foam prepared in comparative example 4 after flame combustion, (a) being a side face and (b) being an upper face.

FIG. 3 is a photograph of the foam prepared in comparative example 5 after flame combustion, (a) being a side face and (b) being an upper face.

Detailed Description

In the examples, the compressive strength of the foam was measured according to the method for measuring the compressive properties of GB/T8813-2020 rigid foam; the flame resistance of the epoxy foam was tested using a butane flame, with a flame burn test time of 60 seconds.

Example 1

The organic solvent is n-butanol, the mol ratio of bisphenol A diglycidyl ether to formaldehyde is 1:1.2, and the mass ratio of ammonia water to bisphenol A diglycidyl ether is 1:50; the molar ratio of boric acid to bisphenol A diglycidyl ether is 1:5; the preparation method comprises the following specific operation steps of:

(1) The synthetic procedure of the boron phenolic epoxy resin comprises the following steps: 1) Addition reaction: dissolving bisphenol A diglycidyl ether and formaldehyde in n-butanol, mechanically stirring for 10min, adding 28wt% ammonia water as a catalyst, heating to 80 ℃ and reacting for 2.5h; cooling to 60 ℃ after the reaction is finished, and distilling under reduced pressure until the solution becomes clear, thus obtaining a low-activity benzyl hydroxyl-epoxy intermediate; 2) Polycondensation reaction: adding boric acid into the low-activity benzyl hydroxyl-epoxy intermediate obtained by the addition reaction, mechanically stirring, and then heating the reaction solution in a stepped temperature rising mode, wherein the reaction is divided into three sections, the reaction temperature of the three sections is respectively 70 ℃, 80 ℃ and 90 ℃ according to the sequence, each section of the first two sections of the reaction is subjected to normal pressure heat preservation for 10min and reduced pressure distillation for 10min, the last section of the reaction is subjected to normal pressure heat preservation for 10min, and the reaction is ended after the reduced pressure distillation until the resin is changed into a wiredrawing state, so that colorless transparent viscous liquid, namely the boron phenolic epoxy resin, is finally obtained.

(2) The preparation process of the multifunctional graphene oxide reinforced particles comprises the following steps: adding graphene oxide into 100ml of N, N-dimethylformamide to prepare a dispersion liquid with the concentration of 0.002g/ml, then carrying out ultrasonic treatment on the dispersion liquid for 1.5 hours, wherein the ultrasonic power is 100W, then adding 7g of boron phenolic epoxy resin, carrying out mechanical stirring for 10 minutes, then slowly adding sodium hydroxide, and carrying out heat preservation reaction for 5 hours at 70 ℃; and after the reaction is finished, washing the dispersion liquid with an organic dispersing agent for 4 times, and then centrifuging and drying to obtain the multifunctional graphene oxide reinforced particles.

(3) Preparation procedure of foaming precursor: mixing the multifunctional graphene oxide reinforced particles prepared in the step (2) with boron phenolic epoxy resin according to the mass ratio of 1:200, carrying out ultrasonic mechanical stirring for 1h to obtain a dispersion liquid, then carrying out mechanical stirring treatment on the dispersion liquid and an amine curing agent according to the molar ratio of epoxy groups to amine groups, wherein the stirring temperature is 90 ℃, the stirring speed is 70r/min, adding a bifunctional foaming agent sulfonyl hydrazide, a surfactant and a toughening agent component when the system viscosity reaches 3 times of the initial viscosity, and carrying out ultrasonic stirring treatment to obtain a foaming precursor, wherein the mass ratio of the boron phenolic epoxy resin, the bifunctional foaming agent, the surfactant and the toughening agent is 100:2:0.2:2.

(4) And (3) a post-curing procedure of the foaming agent and the epoxy foam: pouring the foaming precursor into a foaming mold preheated in advance for mold closing foaming, and adopting a step heating and curing mode, wherein the temperature of the first section is 130 ℃ and the time is 2 hours; the temperature of the second stage is 160 ℃ and the time is 5 hours; and (5) demoulding after the sample is cooled, and finally preparing the high-pressure-resistant and fire-resistant composite epoxy foam.

The boron phenolic epoxy resin synthesized in the embodiment is colorless, uniform and transparent liquid, boric acid added in the reaction is completely reacted, the epoxy value of the resin is 0.47mol/100g, the photo of the prepared foam after butane flame combustion is shown in figure 1, the original shape of the foam can be still found after flame test, and a solid carbon layer is formed on the surface after flame test.

The epoxy value, product state and average cell size of the foam, thermal conductivity, compressive strength and mass loss rate of the foam after flame combustion test of the obtained resin are shown in Table one.

Comparative example 1

In this comparative example, sodium hydroxide was used instead of the catalyst for preparing the boron novolac epoxy resin in step (1), and the other conditions were the same as in example 1, and as a result, it was found that the resin synthesized in step (1) was in an insoluble solid state, because strong basicity of sodium hydroxide can promote nucleophilic addition reaction between an epoxy group and a benzyl hydroxyl group, DGEBA had both a benzyl hydroxyl group and an epoxy group per molecule after reaction with formaldehyde, crosslinking reaction easily occurred in a heated state, and the final product was in an insoluble solid state, so that an epoxy foam material was not prepared in this example.

The product state of the obtained resin is shown in Table one.

Comparative example 2

In the comparative example, zinc acetate is used for the catalyst for preparing the boron phenolic epoxy resin in the step (1), other conditions are the same as those in the step (1), and as a result, the resin synthesized in the step (1) is in a turbid state, and a large amount of boric acid remains unreacted, because zinc acetate is a weak acid catalyst, benzyl hydroxyl generated after DGEBA reacts with formaldehyde has extremely high activity in an acidic environment, condensation reaction can be carried out on the benzyl hydroxyl with active hydrogen on benzene rings of other DGEBA molecules before boric acid is added, only a small amount of residual benzyl hydroxyl can react with boric acid, so that the boron content of the resin is extremely low, the product is turbid, benzene dissolution, filtration, water washing, liquid separation, reduced pressure distillation and other operations are needed after reduced pressure distillation for further purification, the process is complicated, and the boron content is low, so that the high temperature resistance of foam cannot be effectively improved, so that the epoxy foam material is not prepared in the example.

The epoxy value and the product state of the obtained resin are shown in Table one.

Comparative example 3

In this comparative example, the addition reaction temperature for preparing the boron novolac epoxy resin in the step (1) was changed to 100℃and the other conditions were the same as in the example 1, and as a result, it was found that the epoxy value of the resin synthesized in the step (1) was 0.39, because the reaction temperature could affect the reactivity of the benzyl hydroxyl group and the epoxy group as well, and the higher the temperature, the more the loss of the epoxy group, so the reaction temperature should be reduced as much as possible, and the epoxy foam material was not prepared because the epoxy value of the resin was low in this example.

Comparative example 4

The comparative example was not added with the multifunctional graphene oxide reinforcing particles, and the other conditions were the same as in example 1, and the final foam cell size was higher than that of example 1, because after heterogeneous nucleation of reinforcing particles was absent, the blowing agent in the foam was used for cell growth more than nucleation, and the final resulting cell size was higher.

The photo of the obtained foam after butane flame burning is shown in fig. 2, the foam can be basically kept in the original shape after flame testing, but an expanded and loose carbon layer is formed on the surface after flame burning, and the carbon layer structure is slightly stressed and falls off, so that the carbon layer is very easy to be flushed by air flow in practical application.

Comparative example 5

In this comparative example, no multifunctional graphene oxide reinforcing particles were added, and a commercially available bisphenol a type epoxy resin (epoxy value of 0.51) was used as the foaming resin matrix, and the foam cells obtained by the same procedure as in example 1 were larger than those obtained by the procedure of example 1. This is because commercial bisphenol a epoxy resins have lower melt strength at high temperature foaming than boron novolac epoxy resins, while lacking heterogeneous nucleation of multifunctional graphene oxide, ultimately resulting in a foam with a higher cell size than in example 1.

The photograph of the produced foam after burning with butane flame is shown in fig. 3, and it can be found that the upper half of the foam after flame test is lost due to flame burning and cannot resist flame.

The average cell size, thermal conductivity, compressive strength and mass loss rate of the foam after flame burn testing of the resulting foam are shown in table one.

Example 2

Toluene is selected as the organic solvent, the mol ratio of bisphenol A diglycidyl ether to formaldehyde is 1:1.0, and the mass ratio of ammonia water to bisphenol A diglycidyl ether is 1:20; the molar ratio of boric acid to bisphenol A diglycidyl ether is 1:2; the preparation method comprises the following specific operation steps of:

(1) The synthetic procedure of the boron phenolic epoxy resin comprises the following steps: 1) Addition reaction: dissolving bisphenol A diglycidyl ether and formaldehyde in toluene, mechanically stirring for 5min, adding 28wt% ammonia water as a catalyst, heating to 90 ℃ and reacting for 2h; cooling to 50 ℃ after the reaction is finished, and distilling under reduced pressure until the solution becomes clear, thus obtaining a low-activity benzyl hydroxyl-epoxy intermediate; 2) Polycondensation reaction: adding boric acid into the low-activity benzyl hydroxyl-epoxy intermediate obtained by the addition reaction, mechanically stirring, and then heating the reaction solution in a stepped temperature rising mode, wherein the reaction is divided into three sections, the reaction temperature of the three sections is 65 ℃ and 75 ℃ respectively, the reaction temperature of the three sections is 85 ℃ in sequence, each section of the first two sections of the reaction is subjected to normal pressure heat preservation for 5min and reduced pressure distillation, the last section of the reaction is subjected to normal pressure heat preservation for 5min, and the reaction is ended after the reduced pressure distillation until the resin is changed into a wiredrawing state, so that the colorless transparent viscous liquid, namely the boron phenolic epoxy resin, is finally obtained.

(2) The preparation process of the multifunctional graphene oxide reinforced particles comprises the following steps: adding graphene oxide into 100ml of n-butanol to prepare a dispersion liquid with the concentration of 0.001g/ml, then carrying out ultrasonic treatment on the dispersion liquid for 2 hours, wherein the ultrasonic power is 80W, then adding 5g of boron phenolic epoxy resin, carrying out mechanical stirring for 5 minutes, then slowly adding potassium hydroxide, and carrying out heat preservation reaction for 8 hours at 50 ℃; and after the reaction is finished, washing the dispersion liquid with an organic dispersing agent for 3 times, and then centrifuging and drying to obtain the multifunctional graphene oxide reinforced particles.

(3) Preparation procedure of foaming precursor: mixing the multifunctional graphene oxide reinforced particles prepared in the step (2) with boron phenolic epoxy resin according to the mass ratio of 1:100, carrying out ultrasonic mechanical stirring for 2 hours to obtain a dispersion liquid, then carrying out mechanical stirring treatment on the dispersion liquid and an amine curing agent according to the molar ratio of epoxy groups to amine groups, wherein the stirring temperature is 110 ℃, the stirring speed is 100r/min, adding a bifunctional foaming agent sulfonyl hydrazide, a surfactant and a toughening agent component when the system viscosity reaches 2 times of the initial viscosity, and carrying out ultrasonic stirring treatment to obtain a foaming precursor, wherein the mass ratio of the boron phenolic epoxy resin, the bifunctional foaming agent, the surfactant and the toughening agent is 100:3:0.3:3.

(4) And (3) a post-curing procedure of the foaming agent and the epoxy foam: pouring the foaming precursor into a foaming mold preheated in advance for mold closing foaming, and adopting a step heating and solidifying mode, wherein the temperature of the first section is 130 ℃ and the time is 3 hours; the temperature of the second stage is 150 ℃ and the time is 6 hours; and (5) demoulding after the sample is cooled, and finally preparing the high-pressure-resistant and fire-resistant composite epoxy foam.

Comparative example 6

The mass ratio of the boron phenolic epoxy resin, the difunctional foaming agent, the surfactant and the toughening agent is changed to 100:5:0.3:3, the content of the foaming agent is only increased, and other conditions and steps are the same as those in the embodiment 2. As a result, it was found that although the apparent density of the foam was lowered, a large number of giant cells appeared in the foam and the cell diameter distribution was uneven, mainly due to excessive blowing agent to generate a large amount of gas, causing the cells to grow too fast before the resin gel, causing the cells to be enlarged and part of adjacent cells to merge, resulting in giant cells.

Example 3

The organic solvent is selected from dimethylbenzene, the mol ratio of bisphenol A diglycidyl ether to formaldehyde is 1:1.5, and the mass ratio of ammonia water to bisphenol A diglycidyl ether is 1:100; the molar ratio of boric acid to bisphenol A diglycidyl ether is 1:10; toluene is used as an organic dispersing agent, barium hydroxide is used as an alkaline catalyst, diaminodiphenyl methane is used as an amine curing agent, sorbitol ester is used as a surfactant, epoxy nitrile rubber is used as a toughening agent, and the concrete operation steps are as follows:

(1) The synthetic procedure of the boron phenolic epoxy resin comprises the following steps: 1) Addition reaction: dissolving bisphenol A diglycidyl ether and formaldehyde in dimethylbenzene, mechanically stirring for 10min, adding 28wt% ammonia water as a catalyst, and heating to 85 ℃ for reaction for 3h; cooling to 55 ℃ after the reaction is finished, and distilling under reduced pressure until the solution becomes clear, thus obtaining a low-activity benzyl hydroxyl-epoxy intermediate; 2) Polycondensation reaction: adding boric acid into the low-activity benzyl hydroxyl-epoxy intermediate obtained by the addition reaction, mechanically stirring, and then heating the reaction solution in a stepped temperature rising mode, wherein the reaction is divided into three sections, the reaction temperature of the three sections is respectively 70 ℃, 80 ℃ and 90 ℃ according to the sequence, each section of the first two sections of the reaction is subjected to normal pressure heat preservation for 15min and reduced pressure distillation for 15min, the last section of the reaction is subjected to normal pressure heat preservation for 15min, and the reaction is ended after the reduced pressure distillation until the resin is changed into a wiredrawing state, so that colorless transparent viscous liquid, namely the boron phenolic epoxy resin, is finally obtained.

(2) The preparation process of the multifunctional graphene oxide reinforced particles comprises the following steps: adding graphene oxide into 100ml of toluene to prepare a dispersion liquid with the concentration of 0.003g/ml, then carrying out ultrasonic treatment for 1h and the ultrasonic power of 120W, then adding 10g of boron phenolic epoxy resin, mechanically stirring for 10min, then slowly adding barium hydroxide, and carrying out heat preservation reaction for 4h at 80 ℃; and washing the dispersion liquid with an organic dispersing agent for 5 times after the reaction is finished, and then centrifuging and drying to obtain the multifunctional graphene oxide reinforced particles.

(3) Preparation procedure of foaming precursor: mixing the multifunctional graphene oxide reinforced particles prepared in the step (2) with boron phenolic epoxy resin according to the mass ratio of 1:1000, carrying out ultrasonic mechanical stirring for 2 hours to obtain a dispersion liquid, then carrying out mechanical stirring treatment on the dispersion liquid and an amine curing agent according to the molar ratio of epoxy groups to amine groups, wherein the stirring temperature is 100 ℃, the stirring speed is 50r/min, adding a bifunctional foaming agent sulfonyl hydrazide, a surfactant and a toughening agent component when the system viscosity reaches 4 times of the initial viscosity, and carrying out ultrasonic stirring treatment to obtain a foaming precursor, wherein the mass ratio of the boron phenolic epoxy resin, the bifunctional foaming agent, the surfactant and the toughening agent is 100:2:0.2:2.

(4) And (3) a post-curing procedure of the foaming agent and the epoxy foam: pouring the foaming precursor into a foaming mold preheated in advance for mold closing foaming, and adopting a step heating and curing mode, wherein the temperature of the first section is 140 ℃ and the time is 1h; the temperature of the second stage is 170 ℃ and the time is 4 hours; and (5) demoulding after the sample is cooled, and finally preparing the high-pressure-resistant and fire-resistant composite epoxy foam.

Comparative example 7

The first stage temperature in the post-curing process of the epoxy foam was changed to 150℃and the other conditions and steps were the same as in example 3. As a result, it was found that the foam cell diameter was 314 μm, which is higher than 225 μm of example 3, because the melt strength of the epoxy foam prepolymer at a higher post-curing temperature was lower, the cell growth was less constrained, and the cells grew rapidly before the resin gel, resulting in a higher cell diameter.

Example 4

The organic solvent is cyclohexanol, the mol ratio of bisphenol A diglycidyl ether to formaldehyde is 1:1.2, and the mass ratio of ammonia water to bisphenol A diglycidyl ether is 1:50; the molar ratio of boric acid to bisphenol A diglycidyl ether is 1:5; the preparation method comprises the following specific operation steps of:

(1) The synthetic procedure of the boron phenolic epoxy resin comprises the following steps: 1) Addition reaction: dissolving bisphenol A diglycidyl ether and formaldehyde in cyclohexanol, mechanically stirring for 10min, adding 28wt% ammonia water as catalyst, heating to 80 ℃ for reaction for 2.5h; cooling to 60 ℃ after the reaction is finished, and distilling under reduced pressure until the solution becomes clear, thus obtaining a low-activity benzyl hydroxyl-epoxy intermediate; 2) Polycondensation reaction: adding boric acid into the low-activity benzyl hydroxyl-epoxy intermediate obtained by the addition reaction, mechanically stirring, and then heating the reaction solution in a stepped temperature rising mode, wherein the reaction is divided into three sections, the reaction temperature of the three sections is respectively 70 ℃, 80 ℃ and 90 ℃ according to the sequence, each section of the first two sections of the reaction is subjected to normal pressure heat preservation for 10min and reduced pressure distillation for 10min, the last section of the reaction is subjected to normal pressure heat preservation for 10min, and the reaction is ended after the reduced pressure distillation until the resin is changed into a wiredrawing state, so that colorless transparent viscous liquid, namely the boron phenolic epoxy resin, is finally obtained.

(2) The preparation process of the multifunctional graphene oxide reinforced particles comprises the following steps: adding graphene oxide into 100ml of N-methyl pyrrolidone to prepare a dispersion liquid with the concentration of 0.002g/ml, carrying out ultrasonic treatment on the dispersion liquid for 1.5 hours, wherein the ultrasonic power is 100W, adding 7g of boron phenolic epoxy resin, carrying out mechanical stirring for 10 minutes, slowly adding sodium hydroxide, and carrying out heat preservation reaction for 5 hours at the temperature of 70 ℃; and after the reaction is finished, washing the dispersion liquid with an organic dispersing agent for 4 times, and then centrifuging and drying to obtain the multifunctional graphene oxide reinforced particles.

(4) And (3) a post-curing procedure of the foaming agent and the epoxy foam: pouring the foaming precursor into a foaming mold preheated in advance for mold closing foaming, and adopting a step heating and curing mode, wherein the temperature of the first section is 120 ℃ and the time is 2 hours; the temperature of the second stage is 160 ℃ and the time is 5 hours; and (5) demoulding after the sample is cooled, and finally preparing the high-pressure-resistant and fire-resistant composite epoxy foam.

Table epoxy value, product state and cell diameter of foam, thermal conductivity, compressive strength of the resin and mass loss rate of foam after flame combustion test in examples and comparative examples

Claims

1. The preparation method of the high-pressure-resistance fire-resistant composite epoxy foam is characterized by comprising the following preparation steps: 1) Preparing a low-activity benzyl hydroxyl-epoxy intermediate through an addition reaction, and obtaining the high-heat-resistance boron phenolic epoxy resin through a polycondensation reaction; 2) The grafting reaction of the boron phenolic epoxy resin on the graphene oxide is carried out to obtain a multifunctional graphene oxide reinforced particle; 3) Preparing a foaming precursor by adopting three raw materials of boron phenolic epoxy resin, multifunctional graphene oxide reinforced particles and a difunctional foaming agent sulfonyl hydrazide through a pre-curing method; 4) Finishing the post-curing process of the epoxy foam by means of the synergistic curing effect of the difunctional foaming agent;

the boron phenolic epoxy resin is prepared through the following steps: 1) Addition reaction: dissolving bisphenol A diglycidyl ether and formaldehyde in an organic solvent according to a molar ratio of 1:1.0-1.5, mechanically stirring for 5-10min, then adding 28wt% of catalyst ammonia, wherein the mass ratio of the ammonia to the bisphenol A diglycidyl ether is 1:20-100, and heating to 80-90 ℃ for reacting for 2-3h; cooling to 50-60 ℃ after the reaction is finished, and distilling under reduced pressure until the solution becomes clear, thus obtaining a low-activity benzyl hydroxyl-epoxy intermediate; 2) Polycondensation reaction: adding boric acid into a low-activity benzyl hydroxyl-epoxy intermediate obtained by addition reaction, mechanically stirring, wherein the molar ratio of boric acid to bisphenol A diglycidyl ether is 1:2-10, then heating a reaction solution in a stepwise heating mode, namely dividing the reaction into three sections, wherein the reaction temperature of the three sections is 65-70 ℃, 75-80 ℃ and 85-90 ℃ respectively in sequence, keeping the temperature of each section at normal pressure for 5-15min and distilling the temperature at reduced pressure in the first two sections, keeping the temperature of the last section at normal pressure for 5-15min, and finishing the reaction after distilling the pressure at reduced pressure until the resin becomes a wiredrawing state, thus obtaining colorless transparent viscous liquid, namely the boron phenolic epoxy resin;

the preparation method of the high-pressure-resistance fire-resistant composite epoxy foam comprises the following steps of; the method also comprises the following steps:

(1) Preparation process of multifunctional graphene oxide reinforced particles: adding graphene oxide into 100ml of organic dispersing agent to prepare a dispersing liquid with the concentration of 0.001-0.003g/ml, then carrying out ultrasonic treatment on the dispersing liquid for 1-2 hours, wherein the ultrasonic power is 80-120W, then adding 5-10g of boron phenolic epoxy resin, mechanically stirring for 5-10 minutes, then slowly adding alkaline catalyst, and carrying out heat preservation reaction for 4-8 hours at 50-80 ℃; washing the dispersion liquid with an organic dispersing agent for 3-5 times after the reaction is finished, and then centrifuging and drying to obtain multifunctional graphene oxide reinforced particles;

(2) Preparation procedure of foaming precursor: mixing the multifunctional graphene oxide reinforced particles prepared in the step (1) with boron phenolic epoxy resin according to the mass ratio of 0.1-1:100, carrying out ultrasonic mechanical stirring for 1-2 hours to obtain a dispersion liquid, then carrying out mechanical stirring treatment on the dispersion liquid and an amine curing agent according to the molar ratio of epoxy groups to amine groups, wherein the stirring temperature is 90-110 ℃, the stirring speed is 50-100r/min, when the system viscosity reaches 2-4 times of the initial viscosity, adding a bifunctional foaming agent sulfonyl hydrazine with a synergistic curing effect, a surfactant and a toughening agent component, and carrying out mechanical stirring for 5-10 minutes to obtain a foaming precursor, wherein the mass ratio of the boron phenolic epoxy resin, the bifunctional foaming agent, the surfactant and the toughening agent is 100:2-3:0.2-0.3:2-3;

(3) And (3) a post-curing procedure of the foaming agent and the epoxy foam: pouring the foaming precursor into a foaming mold preheated in advance for mold closing foaming, and adopting a step heating solidification mode, wherein the temperature of the first section is 120-140 ℃ and the time is 1-3h; the temperature of the second stage is 150-170 ℃ and the time is 4-6h; and (5) demoulding after the sample is cooled, and finally preparing the high-pressure-resistant and fire-resistant composite epoxy foam.

2. The method for preparing the high compression-resistant refractory composite epoxy foam according to claim 1, which is characterized in that: the organic solvent is one or more of n-butanol, toluene, xylene and cyclohexanol.

3. The method for preparing the high compression-resistant refractory composite epoxy foam according to claim 1, which is characterized in that: the organic dispersing agent is one or more of N, N-dimethylformamide, N-butanol, toluene and N-methylpyrrolidone.

4. The method for preparing the high compression-resistant refractory composite epoxy foam according to claim 1, which is characterized in that: the alkaline catalyst is one or more of sodium hydroxide, potassium hydroxide and barium hydroxide.

5. The method for preparing the high compression-resistant refractory composite epoxy foam according to claim 1, which is characterized in that: the amine curing agent is one or more of diethyl toluene diamine, m-xylylenediamine, diamine diphenyl methane and isophorone diamine.

6. The method for preparing the high compression-resistant refractory composite epoxy foam according to claim 1, which is characterized in that: the surfactant is one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether and sorbitol ester.

7. The method for preparing the high compression-resistant refractory composite epoxy foam according to claim 1, which is characterized in that: the toughening agent is one or more of carboxyl-terminated nitrile rubber, epoxy nitrile rubber and nano core-shell rubber.