New epoxy resin composite material for composite gas cylinders was successfully developed
In resin matrix composites, the resin serves as a critical component that binds the fibers together and transfers mechanical stress throughout the structure. As such, the quality of the resin has a direct impact on the overall performance of the composite material. The properties of the resin are influenced by various factors, including the selection of raw materials, the mixing ratio, the molding process, and the curing conditions. Among these, the curing process is particularly important, as it involves a cross-linking reaction that transforms the resin from a linear molecular structure into a three-dimensional network. This structural change significantly affects the physical and mechanical properties of the final product.
When the same resin system is heat-cured, differences in curing time and temperature can lead to significant variations in the resulting material's characteristics. In recent years, Chinese industry experts have conducted extensive research on the curing behavior of composite gas cylinders using E-51/DDM epoxy resin systems under different curing conditions. By employing analytical techniques such as infrared spectroscopy, dynamic mechanical analysis (DMA), and mechanical testing, they have gained valuable insights into how resin properties influence the performance of epoxy-based composites.
The development process for this product begins with the careful selection of raw materials. For instance, the mixed epoxy resin is homemade, while the aromatic amine curing agent is chemically pure and commercially available. An accelerator is also used, which is readily available on the market. The mixture follows a specific ratio: epoxy resin : curing agent : accelerator = 110:35:0.5. A glue solution is prepared, and the exothermic reaction during curing is measured at various heating rates using a German-made PE-7 series differential scanning calorimeter (DSC). The DSC analysis reveals that the exothermic peak starts around 80°C, and at a heating rate of 1°C/min, the peak temperature is approximately 128°C. Based on these findings, the experiment sets 80°C and 130°C as the upper limits for the curing temperature. Two distinct curing schedules are then developed, and corresponding casting bodies are produced for further evaluation.
The casting test involves pouring the prepared glue solution into steel molds that have been coated with a release agent and preheated to remove air bubbles. The samples are then cured according to the two different temperature profiles. After cooling and demolding, the resulting castings—designated as FH80 and FH130—are ground and subjected to performance testing. The tests include measuring the degree of cure using the solvent extraction method, as per GB/T 2576-1989. Molecular structure analysis is performed using infrared spectroscopy, while mechanical properties are evaluated through tensile and bending tests according to GB/T 2568-1995 and GB/T 2570-1995, respectively. Additionally, the glass transition temperature is determined via dynamic modulus analysis, with a heating rate of 5°C/min, a dynamic test stress of 8.0×10ⴠPa, a static test stress of 1.0×10ⵠPa, and a test frequency of 1.0 Hz.
The equipment used in the testing is advanced and includes a German-made PE-7 thermal analyzer, a PEKIN-ELMER 2000 FT-IR infrared spectrometer, and an INSTRON 4505 universal testing machine from the UK. The results from these rigorous tests indicate that at 130°C, the degree of cure and mechanical strength do not improve further, and in some cases, the mechanical properties slightly decrease. However, when the maximum curing temperature is set at 80°C, the curing process still achieves a high degree of cure with good mechanical performance. Moreover, the use of an appropriate curing accelerator in the right quantity can effectively lower the activation energy of the epoxy resin system, enabling full curing at lower temperatures. The overall performance of the material is excellent, cost-effective, and meets the design requirements for high-pressure gas cylinders made from composite materials.
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