Extensive research on the gel behavior of the hott

Extensive research on epoxy resin gel behavior at home and abroad

extensive research on epoxy resin gel behavior at home and abroad

August 10, 2007

[China paint information] gel behavior of epoxy resin has been widely studied at home and abroad, and the behavior of polyimide gel has been reported at least in the literature at home and abroad. This is mainly because the oligomer resin after acylation is solid at room temperature, and the next step of acylation crosslinking at high temperature is very high temperature and viscosity, so the experiment is quite difficult. Beijing Institute of Aeronautical Materials recently studied a new method for the gel behavior of epoxy polyimide resin: Based on the optimization of the curing process of two-component epoxy resin and PMR polyimide resin, the DMA disk compression fixture was used to determine the gel behavior of the two resins by isothermal mode, the mathematical model of gel dynamics was given, and the activation energy of gel of the resin was calculated to be 75.68kj/g

advanced thermosetting resin matrix composites have been successfully used as structural materials for military aircraft and civil airliners for more than 20 years. For this kind of composite material, thermosetting resin exists in liquid state before gel, which is convenient for flow molding and quality control. Therefore, the gel behavior of resin is an important reference for formulating process system, and its research is of great practical significance in the national famous professional market. The gel behavior of epoxy resin has been widely studied at home and abroad, mainly by testing the gel time at different constant temperature through different methods, and then fitting the relationship between gel time and temperature through appropriate kinetic models, so as to provide a scientific basis for process control (such as the selection of pressure time). The methods of testing gel to build an aluminum based new material industrial base with core competitiveness include rheometer, gel disk, gel timer, DMA, sol ability test, TMA, TBA, DDA, etc

the gel behavior of polyimide has not been reported in the literature at home and abroad, mainly because the oligomer resin after amidation is solid at room temperature, and the next step of amidation crosslinking at high temperature has high temperature and viscosity, so the experiment is quite difficult. There are many common judgment methods in the literature of testing gel points with DMA: Beihang academy selects the intersection of storage modulus E 'and loss modulus E "as the gel point, and the corresponding time is the gel time corresponding to the temperature. For the first time in China, they used DMA discs to hold the samples vertically and tested the gel behavior of two-component epoxy resin and PMR polyimide for composites. Through the kinetic model, the relationship between the gel time and temperature of the two resins was given, and according to the experimental results, it was speculated that there might be different curing reaction mechanisms of the polyimide system around 310 ℃

the raw materials used in the experiment are: the two-component epoxy (be) is a blend of e-54 epoxy resin (bisphenol A diglycidyl ether epoxy) and AG-80 epoxy resin (tetraglycidylamine epoxy), and the curing agent is 4,4 '- diaminodiphenylsulfone (DDS). The blending procedure is to mix the three components according to the ratio of M (e-54):m (AG-80):, m (DDS) =40:60:40, dissolve them in tetraradon furan and vacuum for 72h until no volatile matter is discharged from the rubber solution to obtain a two-component epoxy system. The PMR polyimide selected by the researchers is terminated by norbornene, and its imide prepolymer is self-made by Beijing Institute of aeronautical materials. In order to ensure that the liquid epoxy resin and polyimide octyl ester at high temperature will not yield during the test, so that the experiment is forced to stop, fine glass fiber cloth is selected as the necessary support to prepare the prepreg. The preparation of epoxy resin prepreg is carried out in an oven at 80 ℃, and the two-component epoxy resin to be used is evenly brushed on the glass cloth for constant temperature for 30min. After the resin umbrella is soaked in the fiber, the required prepreg is obtained; The polyimide prepreg is prepared at room temperature. The solution of the prepolymer is directly brushed onto the glass cloth, and can be used after the solvent volatilizes completely

researchers first analyzed the theory of gel model through experiments. Gel point is of great significance in the processing of thermosetting resin. When the curing reaction of the resin reaches a certain degree, the molecular chains will suddenly connect to form a three-dimensional complex structure, resulting in the phenomenon of gel; The biggest macroscopic feature of gel phenomenon is the sudden increase of viscosity, and the resin changes from liquid state to rubber colloidal state. The gel behavior of epoxy resin was measured at 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃ and 180 ℃ as constant temperature points for DMA test. At different temperatures, with the extension of constant temperature time, the storage modulus E 'and loss modulus E "decreased first, and then increased after a platform; The gel behavior of polyimide was measured by DMA at 260 ~ 350 ℃ every 10 ℃ as the constant temperature point. With the increase of temperature, the temperature at which the storage modulus E 'and loss modulus E "deviated from the baseline was advanced to varying degrees, indicating that the curing reaction of the resin was very sensitive to temperature

from the experimental data, it can be seen that the response time of gel is short at high temperature and long at low temperature, which conforms to the general principle of chemical reaction; The activation energy of the high temperature section is much greater than that of the low temperature section, indicating that the chemical crosslinking reaction of the resin system is more sensitive to temperature in the high temperature section than in the low temperature section. The late curing and crosslinking mechanism of polyimide prepolymer terminated by norbornene is very complex, and there is no clear conclusion at home and abroad so far. However, from the above analysis, it can be seen that the late crosslinking and curing of PMR polyimide takes 310 ℃ as the dividing point, there are two different gel response time periods and reaction activation energy, and there may be two different curing samples, and the said changing torque also changes the mechanism, But the specific mechanism is not clear. In this experiment, DMA disc compression fixture was used to measure the gel behavior of two-component epoxy resin, and the gel kinetic model of the resin system was given. The gel activation energy of the resin was calculated to be 75.68kj/g; The gel behavior of a PMR polyimide resin was measured, and the gel kinetic model of the resin system was given at 310 ℃, and the gel activation energy at two temperature ranges was calculated respectively; According to the experimental results of polyimide resin gel behavior, it is speculated that there may be two different assimilation reaction mechanisms in the system around 310 ℃