| Using the scientific research methods of a combination of theoretical analysis, experimental research, and mathematical statistics, the feature of the epoxy resin matrix, the curing mechanism and the cure kinetics of the composite system were analyzed and represented for bisphenol A epoxy resin. By means of FTIR, DSC, GPC, and MATLAB technique, the epoxy value, the hydroxyl value, the chlorine content, the molecular weight and the molecular weight distribution of the matrix resin for bisphenol A epoxy resin system were studied. In addition, the curing mechanism and the cure kinetics of epoxy resin with amine, the component and the cure properties of the prepreg were investigated systematically.(1) By means of chemical analysis, the epoxy value, the hydroxyl value, the chlorine content, the molecular weight and the molecular weight distribution of different epoxy resin were characterized. The analysis results of the chemical titration for the ammonium bromide show that, the highest epoxy value is 0.578 mol/100 g of MY790-1, and the lowest was 0.408 mol /100 g of E-39 D among the known five brands epoxy resin measured. The analysis results of hydroxy potential titration method show that, the highest hydroxyl content is 0.4739 mol/100 g of DER331 and the lowest is 0.2516 mol/100 g of DER671-X75, the content of E-44 is close to that of DER671-X75. The results of chlorine content of hydrolytic extraction tests show that, the lowest chlorine content 0.015% in MY790, and the content is 0.019% both for DER383 and DER331. In addition, the highest chlorine content in domestic epoxy resin E-44 is 0.072%, which is approximately 5 times of that in MY790, and is 4 times of that in DER383 and DER331.(2) The molecular weight and the molecular weight distribution were characterized by GPC method for different brands epoxy resin produced by different manufacture factory. The testing results show that, there is only one molecular peak of MY790 Hengster, and the distribution index is controlled at 1.015, so it is a kind of polymer with narrow distribution of molecular weight. Three molecular peaks appear for MY0510 of Hengster’s another brand, and the molecular weight distribution of the basic peak is 1.113, and the distribution of the molecular is relatively large. Three-level peak values of molecular weight appear in DER331 and DER383 of DOW, and the distribution index is between 1.015 and 1.025, and the distribution index of molecular weight is relatively narrow. The four-level and five-level of molecular weight peak values appear in E-44 and E-39 D of Xinchen in Nantong, the distribution index of molecular weight is between 1.003 and 1.032, and the distribution of molecular weight is wider.(3) The epoxy value of different epoxy resin matrix was characterized by FTIR and the combination of chemical methods with FTIR, and the epoxy index of different epoxy resin was obtained by MATLAB data statistics. The standard curve of the epoxy index and the epoxy value of bisphenol A epoxy resin were obtained by the method of combination of chemical analysis with FTIR techniques, and the value range of the epoxy value of epoxy resin was determined using the curve. The hydroxyl index was obtained with the same method. However, due to the association of hydroxyl group, the mean error was so large that was not suitable for standard curve. For the same specifications of different batches of products, it can be compared to the hydroxyl value as a basis for judging the quality of its stability. The test results of infrared spectra of testing different prepreg by FTIR show that, the structure of resin matrix is similar for the four kinds of prepreg, and is all bisphenol A epoxy resin.(4) The reaction kinetics of epoxy resin curing system was investigated by dynamic FTIR spectra technique. The variation in the stretching vibration wave numbers, the bending vibration wave numbers, and swing vibration wave numbers of the epoxy group, the hydroxyl group, the C-N bond and C-O bond versus time was obtained by MATLAB data statistics technique. The reaction rate expressions of different groups were obtained, and the reaction process can be analyzed according to the reaction rate of different groups. Results show that, the curing reaction rate ratio of the epoxy group, the C-O bond and the C-N bond was about 18:16:4. The reaction rate of the corresponding groups is the highest in the start of reaction process, which is the typical n level reaction history, whereas not the self-catalysis reaction mechanism with the induction procedure.(5) DSC thermal analysis method was used to characterize the curing reaction mechanism of epoxy resin and its pre-impregnated materials, and to obtain the reaction kinetic data such as activation energy of curing reaction, reaction order n and so on. Using non-isothermal DSC technique, the curing reaction of bisphenol A epoxy resin DER331 system was investigated. The n order reaction model and Malek conversion method were used to determine the curing reaction kinetic equation, and initially to determine the relation curve of curing temperature and curing time. The results show that, the best ratio of DER331 epoxy resin and DEH622 curing agent is 100:30, activation energy EA is 46950J/mol, frequency factor A is 2.08×106/S-1, and isothermal cure temperature is 330.3K, reaction order is 0.89. The relationship between the curing time and the curing temperature is exponential. Three characteristic temperatures of curing reaction for bisphenol A epoxy resin DER331 and amine curing agent DEH622 are approximately: tgel =313.7K(40℃), Tpcure=329.3K(56℃) and Texpcure=330.3K(57℃).The activation energy of NSM epoxy prepreg is 83644 J/mol, the frequency factor A is 1.357 ×1011/S-1, the reaction order is 1.24, three characteristic temperatures of NSM epoxy prepreg material are approximately: Tgel =381.7K(108.6 ℃), Tpcure=399K(126℃) Texpcure=397K(124℃). The ctivation energy Ea of 100 AH epoxy prepreg is 74298J/mol, the frequency factor A is 4.719×109/S-1, the reaction order is 0.79, three characteristic temperatures of Epoxy prepreg materials are approximately: tgel =394.2K(121℃), Tpcure=405.1K(132℃),Texpcure= 404K(131℃), Ttreat=422.2 K(149 ℃).Through the research on the epoxy resins and prepregs, the technical parameters of the epoxy resin matrix, the composite system and its prepreg will be detected and characterized, and to provide theoretical and data support for quality control of epoxy resin. |
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