CN109705353B - Curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system and preparation method and application thereof - Google Patents
Curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a modified benzoxazine and a preparation method thereof, and the preparation method comprises the following steps: (1) mixing N-allyl benzoxazine and a modified additive at room temperature by taking tetrahydrofuran as a solvent; (2) adding 0.1-2% mercaptan molar equivalent DMPA photoinitiator, and then placing the sample in an ultraviolet curing machine to irradiate for 1-5 minutes; (3) and then, the product is subjected to rotary evaporation to remove the solvent, and is dried in a vacuum drying oven to obtain the modified benzoxazine product. And adding the modified benzoxazine into an epoxy resin and benzoxazine system according to a certain proportion for thermosetting to prepare a curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system. The invention particularly optimizes the curing temperature and curing time in the thermosetting process, so that the blended cured product prepared by the invention has higher curing degree, better thermal stability and better flame retardant property.
Description
Technical Field
The invention relates to the field of high-temperature resistant materials, in particular to a curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system and a preparation method and application thereof.
Background
Benzoxazine is a six-membered heterocyclic compound containing oxygen atoms and nitrogen atoms, and is a novel phenolic resin. The benzoxazine resin keeps the excellent electrical, mechanical and flame retardant properties of the traditional phenolic resin, and overcomes the defect that the traditional phenolic resin volatilizes micromolecule byproducts in the polymerization process. In addition, the benzoxazine can be subjected to polymerization reaction only by heating or Lewis acid catalysis in the curing process, and a strong acid catalyst is not needed, so that the benzoxazine is very environment-friendly. The polybenzoxazine also has higher thermo-oxidative stability and glass transition temperature, and products meeting different actual requirements can be obtained when raw materials with different structures are used for preparation.
Epoxy resins are also an important class of thermosetting resins. The epoxy resin is a polymer oligomer which contains two or more epoxy groups, has an aliphatic, alicyclic or aromatic organic compound as a skeleton, and can form a three-dimensional network thermosetting product through reaction of the epoxy groups. The epoxy resin has the advantages of excellent mechanical property, good processing technology, good cohesiveness, good electrical property and the like, can form a three-dimensional network structure with high crosslinking density under the action of a curing agent, and is widely applied to various fields.
However, with the rapid development of the manufacturing industry and the industrial field, the cured products of common epoxy resins and common curing agents have the defects of cured product shrinkage, unstable high-temperature dielectric property, insufficient heat resistance, easy stress cracking and the like, and thus the technical requirements of packaging high-heat-resistance and high-insulation materials cannot be met. Therefore, in order to meet higher performance requirements, it is necessary to modify an epoxy resin curing system to improve flame retardancy and heat resistance of the epoxy resin curing system.
Therefore, blending modification of benzoxazine with epoxy resin occurs. This is because benzoxazine resins possess a high TgAnd modulus, but low crosslink density, while general purpose epoxy resins generally have a higher crosslink density, but TgThe content of the benzoxazine is low, so that the blending modification of the benzoxazine and the epoxy resin has good complementary action. In addition, the benzoxazine and the epoxy resin have good compatibility, and the benzoxazine and the epoxy resin have good operation manufacturability during blending modification. However, in the actual production process, the thermal stability and flame retardancy of the product modified by blending benzoxazine with epoxy resin are not good, and the analysis reason is probably caused by the low melt viscosity of benzoxazine monomer.
In general, in a curing system modified by blending benzoxazine and epoxy resin, curing temperature and curing time are important process parameters, and have a significant influence on the properties of the material after molding. In practical applications, the curing temperature is often increased to accelerate the curing reaction, so as to reduce the reaction time and the reaction cost. However, as for epoxy resin, the curing process is an exothermic reaction, and the thermal conductivity is poor, if the curing temperature is too high, heat accumulation is easy to occur during curing, so that a significant thermal shock phenomenon occurs, and finally, the obtained product is easy to have the problems of stress cracking, pressure resistance level reduction, life reduction and the like. Therefore, proper curing temperature and curing time are selected to obtain a product with better performance. Usually we use extrapolation to obtain the cure temperature, while another important cure parameter, cure time, is generally empirical. This situation is very disadvantageous in improving the product performance.
In order to overcome the defects of the prior art, the invention provides a curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system and a preparation method thereof, and particularly improves the curing temperature and curing time in the thermosetting process. A series of analysis experiments prove that the flame-retardant system prepared by the invention has higher curing degree, better thermal stability and better flame-retardant property.
Disclosure of Invention
The invention aims to provide modified benzoxazine and a preparation method thereof; it is a further object of the present invention to provide a curing agent-free flame retardant benzoxazine and epoxy resin flame retardant system and a method for preparing the same, particularly optimizing the curing temperature and curing time during the thermal curing process.
Polyhedral oligomeric silsesquioxane (POSS) is a novel nano hybrid filler with a cage-shaped structure, and the special cage-shaped structure enables the filler to have higher thermal stability and good flame retardant property. In addition, the molecular mechanism has a size effect, and the movement capacity of the molecular chain segment of the material can be reduced by inhibiting the active movement of the whole molecular chain segment in the composite material. In the invention, the Benzoxazine (BOZ) and POSS containing sulfydryl are subjected to thiol-ene click chemical reaction under the ultraviolet curing condition to obtain a corresponding modified product POSS-BOZ, and the obtained product is subjected to infrared analysis and characterization. And then adding the modified product POSS-BOZ into a mixed system of benzoxazine and epoxy resin for blending and curing to obtain a curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system.
The purpose of the invention is realized by the following technical scheme:
the invention provides a preparation method of modified benzoxazine, which comprises the following steps:
(1) mixing N-allyl benzoxazine and a modified additive at room temperature by taking tetrahydrofuran as a solvent;
(2) adding 0.1-2% mercaptan molar equivalent DMPA photoinitiator, and then placing the sample in an ultraviolet curing machine to irradiate for 1-5 minutes;
(3) and then, the product is subjected to rotary evaporation to remove the solvent, and is dried in a vacuum drying oven to obtain the modified benzoxazine product.
Preferably, the modifying additive in step (1) is selected from: mercapto-containing POSS (silsesquioxanes) which, in the most preferred embodiment of the present invention, is available under the trade name TH 1550.
More preferably, the molar ratio of benzoxazine to mercapto in the mercapto-containing POSS is from 1:1 to 2: 1.
The reaction is a homolytic cleavage reaction, and the ring-opening reaction of the benzoxazine ring which may occur is an heterolytic cleavage reaction, i.e., a sulfur atom on the modified additive first abstracts a negative charge to form an ionic form, and then further causes the ring opening of the benzoxazine ring, but because the electron-donating structure of the modified additive itself provides enough electrons for the mercapto group, and the sulfur atom has little attraction to the electrons, the reaction hardly occurs as a side reaction.
A modified benzoxazine prepared according to the above method.
Preferably, the modified benzoxazine has the structure shown in formula I:
wherein R is selected from C1-8Straight chain alkyl, C3-10Branched alkyl or C3-8A cycloalkyl group; preferably, R is selected from C3-5Straight chain alkyl, C4-6A branched alkyl group; most preferably, R is selected from C4A branched alkyl group; in a preferred embodiment of the invention, R is
In the present invention, the formula I is named: POSS-BOZ.
In a preferred embodiment of the present invention, the modified benzoxazine has the following structure:
the benzoxazine reacts with POSS TH1550 to generate POSS TH1550-BOZ, and the reaction formula is as follows:
the invention provides a preparation method of a curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system, which comprises the following steps:
(1) adding benzoxazine and epoxy resin into an oil bath pan at 70-90 ℃ and stirring, adding modified benzoxazine at the same time, uniformly mixing, and stirring for 5-15 min;
(2) carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process;
(3) and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, and demolding after curing is finished to obtain the required blended cured product sample strip.
Preferably, in the step (1), 30-45 parts of benzoxazine and 50-55 parts of epoxy resin are added into an oil bath pan at 70-90 ℃ and stirred, and 5-20 parts of modified benzoxazine is added and mixed uniformly.
More preferably, the mass ratio of the modified benzoxazine to the epoxy resin E-44 is 5-20:30-45: 50.
In a preferred embodiment of the invention, the modified benzoxazine is present in the curing system in a mass fraction of 5-20%, such as 5%, 10%, 15%, 20%.
Most preferably, the modified benzoxazine is present in the curing system at a mass fraction of 20%.
In the most preferred embodiment of the present invention, the epoxy resin is E-44 and the modified benzoxazine is selected from: POSS-BOZ.
According to the previous research experience of the inventor, the following results are found: the ratio of benzoxazine in the benzoxazine/epoxy resin curing system has no obvious influence on the initial temperature and the peak temperature of the curing reaction, but the curing temperature is slightly high, and the combination of the appropriate curing temperature and the curing time is various within a certain temperature range, so the preferable thermal curing condition of the step (3) is 60-80 ℃/1h +110 ℃/1h + 130-.
More preferably, the thermosetting conditions are 60 ℃/1h +110 ℃/1h +130 ℃/1h +160 ℃/1h +180 ℃/1h (process 1 for short) or 80 ℃/1h +110 ℃/1h +140 ℃/1h +200 ℃/1h +220 ℃/0.5h (process 2 for short).
Most preferably, the thermal curing conditions are process 2.
A curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system prepared according to the method.
The invention provides a curing system formed by modified benzoxazine and epoxy resin, which has a structure shown in a formula II and comprises the following components:
wherein R is selected from C1-8Straight chain alkyl, C3-10Branched alkyl or C3-8A cycloalkyl group; preferably, R is selected from C3-5Straight chain alkyl, C4-6A branched alkyl group; most preferably, R is selected from C4A branched alkyl group; in a preferred embodiment of the invention, R is
When the modified benzoxazine is POSS-BOZ, the reaction formula of a cured product formed by the modified benzoxazine and the epoxy resin is as follows:
an application of a condensate formed by modified benzoxazine and epoxy resin in preparing a flame-retardant polymer.
In the present invention, unmodified benzoxazine is represented by BOZ.
According to the invention, the thermal stability, the combustion performance and the like of the prepared cured product are researched through thermal loss analysis, dynamic thermomechanical analysis (DMA), limited oxygen index analysis or vertical combustion analysis tests.
The analysis operation method and the flow in the invention are conventional technologies, wherein the analytical instruments and parameters are as follows:
infrared spectroscopy (IR) analysis: the instrument is a Nicolette 6700 type infrared spectrometer, the scanning frequency is 32, and the resolution ratio is 4cm-1。
Thermogravimetric analysis: the instrument is a NETZSCH TG 209F1 type thermogravimetric analyzer, the test temperature is 40-600 ℃, the heating rate is 10K/min, the test is carried out under the nitrogen atmosphere, the gas flow rate is 50ml/min, and the sample dosage is 2-3 mg.
DMA analysis, the instrument is an SDTA861 instrument of METT L ER TO L EDO company, the frequency is 1HZ, the maximum load is 5N, the heating rate is 4K/min, and the test temperature range is-70-200 ℃.
And (3) analyzing a limiting oxygen index, namely, the instrument is an FTAII (1600)/WSBW804 type limiting oxygen index instrument of RS company in England, the test standard GB/T2406.2-2009, the specification of the sample strip is 100mm × 6mm × 3mm, and a group of 10-15 sample strips are arranged, and the sample strip is placed in an environment with the temperature of 23 +/-2 ℃ and the humidity of 50 +/-5% and is adjusted for more than 88h before testing.
U L-94 vertical burning test, wherein the test instrument is a CZF-5A horizontal vertical burning tester of Jiangning analytical instrument factory to perform U L-94 vertical burning test, the specification of the sample strip is 125mm × 13mm × 3.2.2 mm, a group of 5-10 strips, the test standard is ANSI/U L942013, and the sample strip is placed in an environment with the temperature of 23 +/-2 ℃ and the humidity of 50 +/-5% to be adjusted for more than 48h before the test.
Drawings
FIG. 1 is an infrared spectrum before and after POSS modified benzoxazine.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1 preparation of modified benzoxazine
Preparing POSS-BOZ: taking tetrahydrofuran as a solvent, and mixing N-allyl benzoxazine with sulfydryl-containing POSS at room temperature, wherein the molar ratio is 1: 1; adding 1% mercaptan equivalent DMPA photoinitiator, and then placing the sample in an ultraviolet curing machine for irradiation for 1 minute; and then, the product is subjected to rotary evaporation to remove the solvent, and is dried in a vacuum drying oven to obtain the modified benzoxazine POSS-BOZ.
Performance test 1: infrared analysis
Because the POSS structure has sulfydryl, the sulfydryl can appear 2700cm in the infrared spectrum-1The right and left absorption peaks are shown in FIG. 1, and in FIG. 1, the peak is 2700cm after POSS modified benzoxazine-1The thiol peak on the left and right disappears, indicating that POSS has successfully modified benzoxazines.
EXAMPLE 2 preparation of curing agent free flame retardant benzoxazine and epoxy flame retardant System
According to the mass ratio of 5: 45:50 percent of POSS-BOZ with the mass fraction of 5 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 1, and demolding after curing is finished to obtain the required blending cured product sample strip 1.
POSS-BOZ and BOZ-epoxy resin E-44 are mixed according to the mass ratio of 10: 40: 50 percent of POSS-BOZ with the mass fraction of 10 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 1, and demolding after curing is finished to obtain the required blending cured product sample strip 2.
According to the mass ratio of 15: 35: 50 percent of POSS-BOZ with the mass fraction of 15 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 1, and demolding after curing is finished to obtain the required blending cured product sample strip 3.
POSS-BOZ and BOZ-epoxy resin E-44 are mixed according to the mass ratio of 20: 30: 50 percent of POSS-BOZ with the mass fraction of 20 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 1, and demolding after curing is finished to obtain the required blending cured product sample strip 4.
POSS-BOZ and BOZ-epoxy resin E-44 are mixed according to the mass ratio of 5: 45:50 percent of POSS-BOZ with the mass fraction of 5 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 2, and demolding after curing is finished to obtain the required blending cured product sample strip 5.
POSS-BOZ and BOZ-epoxy resin E-44 are mixed according to the mass ratio of 10: 40: 50 percent of POSS-BOZ with the mass fraction of 10 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 2, and demolding after curing is finished to obtain the required blending cured product sample strip 6.
According to the mass ratio of 15: 35: 50 percent of POSS-BOZ with the mass fraction of 15 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 2, and demolding after curing is finished to obtain the required blending cured product sample strip 7.
POSS-BOZ and BOZ-epoxy resin E-44 are mixed according to the mass ratio of 20: 30: 50 percent of POSS-BOZ with the mass fraction of 20 percent, placing the mixture in an oil bath kettle at the temperature of 80 ℃, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 2, and demolding after curing is finished to obtain the required blending cured product sample strip 8.
Comparative example preparation of BOZ and epoxy resin blended cured product
Placing BOZ and epoxy resin E-44 in an oil bath kettle at 80 ℃ according to the mass ratio of 50:50, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, wherein the curing temperature and time are as in the process 1, and demolding after curing is finished to obtain a comparison sample strip 1.
Placing BOZ and epoxy resin E-44 in an oil bath kettle at 80 ℃ according to the mass ratio of 50:50, stirring for 10min, and uniformly mixing; carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process; and pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting at the same temperature and time as in the process 2, and demolding after the curing is finished to obtain a comparison sample strip 2.
Performance test 2DMA analysis
Tables 1 and 2 are DMA related data tables for the post-and post-POSS modification benzoxazine and epoxy curing systems cured according to process 1 and process 2, respectively. Comparing the data in table 1, it can be seen that the curing system added with POSS-BOZ has a slightly lower temperature corresponding to the original tan maximum (i.e. the glass transition temperature of the curing system), and the data in table 2 has the same trend as table 1, which indicates that the curing system of the present invention has a reduced crosslinking density to some extent after the POSS-BOZ is added. The preparation raw materials of the comparison sample strip 1 and the comparison sample strip 2 are BOZ and epoxy resin in a mass ratio of 1:1, but the tan maximum for comparative bar 2 increased from 106.2 ℃ to 124.5 ℃ by 18.3 ℃ as compared to comparative bar 1, indicating that process 2 gave a product with an increased glass transition temperature as compared to process 1. In the curing system added with POSS-BOZ, compared with the curing product with the same addition amount of POSS-BOZ under the two processes, the glass transition temperature of the product obtained under the process 2 is also obviously higher than that of the product obtained under the process 1, which fully indicates that the crosslinking degree of the curing product obtained under the process 2 is greater than that of the product obtained under the process 1.
TABLE 1 DMA Effect analysis of POSS-BOZ on curing System (Process 1)
TABLE 2DMA Effect analysis of POSS-BOZ on curing System (Process 2)
Performance test 3 thermogravimetric analysis
For the curing system which is obtained by curing in the process 1 and is added with the POSS-BOZ, when the adding amount of the POSS-BOZ is 10%, the mass residual rate of the system is the highest compared with the curing system with other POSS-BOZ adding proportions, and is increased by 2.46% and is 19.79% compared with the curing system before modification. For the curing system which is obtained by curing in the process 2 and is added with the POSS-BOZ, when the adding amount of the POSS-BOZ is 20 percent, the mass residual rate of the system is improved by 7.05 percent and is 29.45 percent compared with that before modification. And as can be seen from the comparison of table 3 and table 4, the initial decomposition temperature and the mass residual rate of the curing system prepared by the process 2 are obviously improved compared with those of the curing system prepared by the process 1 in the same proportion, and the initial decomposition temperatures of the curing system with the POSS-BOZ addition amounts of 5%, 10% and 15% are respectively improved by 8.9 ℃, 7.6 ℃, 22.3 ℃ and the mass residual rates at 800 ℃ are respectively improved by 6.64%, 8.14% and 9.73%. This shows that the curing system obtained in the process 2 has a higher crosslinking degree of the crosslinked network than that obtained in the process 1, a higher curing degree and better thermal stability of the product.
TABLE 3 analysis of the influence of POSS-BOZ on the thermal weight loss of the curing System (Process 1)
TABLE 4 analysis of the influence of POSS-BOZ on the thermal weight loss of the curing System (Process 2)
Performance test 4 limiting oxygen index analysis
Tables 5 and 6 show the limiting oxygen index data of the cured product of the epoxy resin before and after the POSS modified benzoxazine obtained by the process 1 and the process 2 respectively. As can be seen from the table, for the curing system obtained by the process 1, the limit oxygen index of the cured product is gradually increased along with the increase of the addition amount of POSS-BOZ, and when the addition amount of POSS-BOZ is 15%, the limit oxygen index of the system is the highest and reaches 27.6%; for the curing system obtained by the process 2, when the addition amount of POSS-BOZ is 5%, 10% and 15%, the limit oxygen index of the system is slightly lower than that before the addition of POSS-BOZ, but when the addition amount of POSS-BOZ is increased to 20%, the limit oxygen index of the system is increased by 0.4% and is 28.6% compared with that before the addition; this shows that the flame retardant property of the system is improved to a certain extent when the adding amount of POSS-BOZ reaches a certain value, presumably because the POSS-BOZ forms compact SiO during combustion2The layer can prevent the combustion from spreading to a certain extent, and the blow-out effect generated by the combustion of the product after the POSS-BOZ is added promotes the extinguishing of the combustion, thereby improving the flame retardant property of the product to a certain extent.
TABLE 5 analysis of the effect of POSS-BOZ on the limiting oxygen index of the curing System (Process 1)
TABLE 6 analysis of the effect of POSS-BOZ on the limiting oxygen index of the curing System (Process 2)
Performance test 5 vertical Combustion analysis
Shown in tables 7 and 8 are experimental result data obtained in the U L94 vertical burning test of the samples of benzoxazine and epoxy resin blended and cured before and after POSS modification under two curing processes, including vertical burning grade and average after-burning time t after first ignition1Average afterflame time t after second ignition2Whether molten drops exist or not, whether flame reaches the clamp or not and the vertical combustion grade. As can be seen from the table, for the POSS-BOZ added curing system obtained in the process 1, the vertical burning performance of the product is improved to a certain extent along with the increase of the adding amount of the POSS-BOZ. And when the addition amount of the POSS-BOZ is 15%, the vertical combustion performance of the system is optimal, which shows that the flame retardant property of the system is improved to a certain extent by adding the POSS-BOZ. For the curing system obtained by the process 2 and added with the POSS-BOZ, the vertical combustion grade of the cured product is V-1 grade, and is greatly improved compared with that before modification. The results show that the flame retardant effect of the cured product is remarkably improved by adding the POSS modified benzoxazine.
TABLE 7 POSS-BOZ vertical burn impact analysis of U L94 on curing System (Process 1)
TABLE 8 POSS-BOZ vertical burn impact analysis of U L94 on curing System (Process 2)
In conclusion, the POSS modified benzoxazine is added into a mixed system of benzoxazine and epoxy resin, and after the POSS modified benzoxazine is cured according to a certain process, the thermal stability of the mixed system can be increased, and the value of the limiting oxygen index and the U L94 vertical burning grade of the mixed system can be improved.
The above embodiments are merely illustrative of the present disclosure and do not represent a limitation of the present disclosure. Other variations of the specific structure of the invention will occur to those skilled in the art.
Claims (4)
1. A preparation method of a curing agent-free flame-retardant benzoxazine and epoxy resin flame-retardant system comprises the following steps:
(1) adding benzoxazine and epoxy resin into an oil bath pan at 70-90 ℃ and stirring, adding modified benzoxazine at the same time, uniformly mixing, and stirring for 5-15 min;
(2) carrying out vacuum defoaming on the obtained mixture in a vacuum oven, and removing residual solvent and air mixed in the stirring process;
(3) pouring the mixture subjected to vacuum defoaming into a preheated mold for thermosetting, and demolding after curing to obtain a required blending cured product; the thermosetting condition is 80 ℃/1h +110 ℃/1h +140 ℃/1h +200 ℃/1h +220 ℃/0.5 h;
the modified benzoxazine structure is shown as formula I:
wherein R is selected from
The mass fraction of the modified benzoxazine in the curing system is 20%.
2. A curing agent-free flame retardant benzoxazine and epoxy flame retardant system made according to the method of claim 1.
3. A curing system formed by modified benzoxazine and epoxy resin has a structure shown as a formula II, and contains a cured product shown as a general formula (II),
wherein R is selected from
The curing system is prepared by the method of claim 1.
4. Use of the curing system of claim 3 for the preparation of flame retardant polymers.
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