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«——[·Preface·] ——»
Epoxy resins usually react with curing agents under external stimuli to form thermosetting materials with a three-dimensional network structure.
Its cured performance is often affected by factors such as the degree of cross-linking of the network, the defect of the junction (such as etc.), the intermolecular force and other factors.
By introducing amino acids with different content and different structures to react with DADGEBA, four different CSC-EPs are obtained.
The optimal curing reaction process for four systems was also identified: 50C 3h+100C 3h+150C 3h. Under this curing condition, the four CSC-EP systems undergo self-curing reactions to obtain materials with different antelope/epoxy network structures.
Through the study of the curing behavior of different systems, the influence of group content and structure on the reactivity during the weekization process was obtained. We also believe that these two factors also have an impact on different base/epoxy network structures.
Therefore, in this chapter, different antelope/epoxy crosslinking networks are studied through infrared spectroscopy, thermodynamic properties, thermal stability, mechanical properties, and cross-sectional morphology after curing.
The influence of antelope content and structure on the overall network structure and performance was discussed. Due to the presence of bonds and groups in the cured system, the degradability and surface properties of the cured products of different CSC-EP systems were studied.
«——[Design of Experiments.]——»
Add the prepared CSC-EP and 1-MI, which accounts for 1% of its mass ratio, to Ming's medium stirring and mixing for 10min, and then mix in a three-dimensional blending testing machine for 2min, take it out and put it into a centrifuge and centrifuge at 3000r/min for 3min.
The mixed sample is evenly poured into the mold and put into the blast oven for curing according to the process of 50C 3+100C3h+150 3h. After curing, the splines are removed for testing. Performance testing of cured products of four systems.
In order to study the network differences of the four systems after curing, infrared spectroscopy was used to characterize the structure of the four cured materials. It is clear that the four systems are different at the base at 3700-3200cm".
The C2E2 system and the CE system can be observed with obvious broad peaks at 3700-3500cm, while the C22E system and C2; The E system has no peak at 3700-3500cm. However, there was no significant difference in the size of the basal peak in the antelope group at 3500-2500 cm in the four systems.
It shows that there are group-to-group reactions to form vinegar bonds in the CEa system, CE2 system, CE system and C2E system. The difference in the size of the base peak at 1735 cm' also indirectly indicates that the gazelle content of the four systems is different.
It was also found that the four systems still had weak peaks at the base of the 897 cm ring. This indicates that the cyclic groups in the system are not fully represented, and also indicates that the groups in the CE2 system and the CE system are not complete.
It can be clearly found that the cyclic group of the CnE2 system has the highest degree of reactivity, which is related to the single-group side chain in the system.
This is also related to the lower degree of epoxy group reaction of the C2oEa system than that of the CE system. The low degree of reaction of the groups of the C22E2 system and the C2E system is related to the excess antelope group of both. Excess antelope groups in the system and the antelope chain formed by hydrogen bond association will hinder the reaction of epoxy groups with neighboring antelope groups, reducing the degree of reaction of the system.
The contents of antelope, light and epoxy groups of the network structure of the solidified products of these four systems are different, which makes the networks obviously different, which in turn affects the performance of the solidified products.
The CE system and the CE2 system consume roughly the same epoxy groups and light groups during curing, and the content of the base chain in the cured product of the two systems is also about the same. The cool substrate content of the cured product of the C0E2 system is lower than that of the CE system and the CE system.
Among the four systems, the content of the base chain in the solidified product of the C20E2 system and the CnE2 system is roughly the same, but it is far less than the cured content of the CEa system and the C2E2 system.
DSC can determine the transition temperature (T) of a sample from the change in the specific heat capacity of the sample. Four kinds of CSC-EP system solidified products were T after DSC scanning test, of which 7 of C2E2 cured products was 5720CCzE system cured products were 47.23C, C2E system cured products were T 52.0C, and CE system cured products were 37.55C.
It can be clearly seen that T is related to the base content of the system. The higher the base content, the greater the density of the crosslinked network of the resulting solidified product, and thus the greater its T. But in the C20E system, the T is higher than the CE2 system. This is the opposite of the base content of both.
In the non-isothermal curing reaction kinetics in Chapter 3, it has been analyzed that the C2E2 system is the single-base side chain that first participates in the curing reaction, and the T of the combined CEa system is lower than that of the C22E2 system, and it can be considered that the monogale side chain that participated in the reaction first formed a sparse network.
Although the subsequent biantelope-based side chains are also involved in part of the reaction, the density of the crosslinked network is lower than that of the crosslinked network of the C20E2 system.
In order to further analyze the difference of the crosslinking network after curing of the four CSC-EP systems, the thermomechanical properties of the four cured products were analyzed and thermogravimetric analysis (TG) was used to study the thermal decomposition temperature of the cured resin to study the thermal stability of the resin.
It can be found that MSA has only one thermal decomposition temperature of 228C, and all solidified products of CSC-EP systems have two distinct thermal decomposition peaks, and both end thermal decomposition at 600C, where 253C should be the thermal decomposition temperature of the grafted group.
Because it is grafted to DADGEBA, the thermal stability of the base chain increases and the thermal decomposition temperature increases, which also indicates that there are remaining basal side chains in the four systems after curing, which is also consistent with the results of the residual epoxy groups of the four systems in the infrared spectrum.
Similarly, the level of the decomposition peak of the base side chain also indicates the amount of residual group content in the four systems.
The greater the network density, the greater its T. But in the C20E system, the T is higher than the CE2 system. This is the opposite of the base content of both.
Combined with the lower T of the CEa system than the C22E2 system, it can be considered that the monoantelyl side chain that first participated in the reaction formed a sparse network, although the subsequent biantelope side chain also participated in part of the reaction, but the density of its crosslinking network was lower than that of the crosslinking network of the C20E2 system.
In order to further analyze the differences in the cured crosslinking networks of the four CSC-EP systems, the thermomechanical properties of the four cured products were analyzed.
The thermal stability of the resin is studied by thermogravimetric analysis (TG) to study the temperature of thermal decomposition of the resin after curing.
It can be found that MSA has only one thermal decomposition temperature of 228C, and all solidified products of CSC-EP systems have two distinct thermal decomposition peaks, and both end thermal decomposition at 600C, where 253C should be the thermal decomposition temperature of the grafted group.
Because it is grafted to DADGEBA, the thermal stability of the base chain increases and the thermal decomposition temperature increases, which also indicates that there are remaining basal side chains in the four systems after curing, which is also consistent with the results of the residual epoxy groups of the four systems in the infrared spectrum.
Similarly, the level of the decomposition peak of the base side chain also indicates the amount of residual group content in the four systems. In addition, the thermal decomposition process of the backbone of DADGEBA occurs at about 386C in the four CSC-EP systems.
In order to further compare and analyze the thermal stability of the solidified products of the four systems, some important parameters were calculated by quantitative analysis.
Among them, T% is the decomposition temperature of 5% weight loss, also known as the initial decomposition temperature, Ta30% is the decomposition temperature of 30% weight loss, and R60 is the residual weight of the solidified product at 600C. Based on these, the heat resistance index of the material can be calculated T.
The initial decomposition temperature of the four systems T5% is the same as the residual content in the four systems, indicating that the residual base side chain has undergone thermal decomposition at about 200C.
For each CSC-EP system, the content of residual groups in the solids is different, which affects the thermal stability of the material.
On the other hand, this secondary bond is more easily broken by heat than the heat of the primary cool bond (generated by the reaction of acids with epoxy groups)181) due to the reaction of the group to form a secondary bond with the light base of epoxy ringing.181) Analysis results of infrared spectroscopy showed that this secondary bond existed in all four systems. The higher the secondary bond content, the worse the heat resistance of the material.
Combined with thermogravimetric analysis and the characterization of infrared spectroscopy of the cured material, the results show that the grafted monogazelle side chain system is more reactive, the degree of epoxy group reaction is higher, the antelope residue is lower, and the thermal stability of the cured product is better.
A system with too high a gazelle content will have a large number of base chains remaining and forming a large number of secondary cool chains, and the thermal stability of the solidified product will be worse.
DMA is a technical means that can be used to characterize the properties of materials such as glass transition temperature (T), energy mode (E), loss factor (tand), crosslinking density (v). Generally, the peak of the loss factor (tan) is used as the glass transition temperature (T) of the material. The crosslinking network density (v) of the CSC-EP curing system is calculated according to the classical rubber elastic equation.
Key data such as Tve25E are now shown in Table 42. 42 can be to the Cz2Ea system solidified product T; It is 73.61C, the Tg of CE2 cured product is 63.23C, the 7 of CEa cured product is 67.49C, and the T of CEa cured product is 4709C.
This is the same size trend as the DSC measured by T. The difference in Tee size measured by the two test methods is due to the frequency effect T of DMA test; The size is related to the ability of the network to move and is therefore affected by the free volume, crosslinking density, and cohesive energy.
In the previous article, it has been confirmed that there are light-based cool chains, hanging chains, and cool base chains (antelope-based reactions with light groups) in the base-epoxy curing network.
Among them, the cool base chain will reduce the chain spacing, increase the local crosslinking density, and then increase the storage modulus, among which the hanging chain includes the antelope chain associated with hydrogen bonds, the normal base chain and the methyl propionate chain that does not participate in the reaction.
The base chains associated with these bonds will reduce the spacing of some molecular chains in the network, reduce the free volume, increase the density of the local cross-linked network, and increase the storage modulus.
These normal antelope-based chains and propionate formase chains that do not participate in the reaction will increase the free volume of the network, reduce the density of the cross-linked network, and then reduce the storage modulus C20E2 system and the CE system as systems with phase content.
«——[·Epilogue.]——»
This chapter tests the thermodynamic properties, thermogravimetric tests, mechanical properties, degradability, gel content, and cross-sectional morphology of the cured products of four different CSC-EP systems.
The detailed results are as follows: (1) The structural differences of different base/ring networks are studied. The results of infrared light characterization of the four solidified substances showed that the cool matrix structure after the reaction of antelope groups and groups existed in the network of the cured products of the four systems, while the C2E2 system and the C2E2 solidified products had high content chains.
The TG test results show that the higher the base content of the system, the worse the thermal stability of the solidified product. The results of DSC and DMA tests show that the grafted system with a bibase structure ve, T25 E is high, and the containing system e, T, 25 E is higher.
- The tensile performance test and cross-section decomposition results of the solidified products of the four systems showed that the higher the base content, the smoother the cross-section, the fewer the number of cracks, the simpler the crack hierarchy, and the lower the tensile strength.
The results of the degradable properties of the cured products of the four systems showed that the cured products of the CSC-EP system could be degradable in the alkaline aqueous solution, and could be completely degraded within 35min at the fastest.
At the same time, the cured products of these four systems have good acid resistance: no large amount of degradation occurs after 72h. The junction of the surface properties of the four system solids shows that the optimal water contact angle of the CSC-EP system cured products can reach 38.
Therefore, the side chain on the CSC-EP molecule is grafted with a biradical structure and the higher the group content, the higher the E of ve,T25°C, and its faster degradation rate and better hydrophilicity. The side chain is connected to a single-base structure system, which has better thermal stability, tensile strength and elongation at break.
«——[References] ——»
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- Design and preparation of nanofiber membrane for wound material and application of Geng Huan [D] Beijing:Beijing Hua University, 2017