New epoxy resin composite material for composite gas cylinders was successfully developed
In resin matrix composites, the resin acts as a binder that connects and transfers stress between the fibers. Therefore, the quality of the resin directly influences the overall performance of the composite material. The properties of the resin itself are affected by various factors, including the choice of raw materials, mixing ratios, molding processes, and curing conditions. Among these, the curing process is one of the most critical stages. During curing, the resin undergoes a cross-linking reaction, transforming from a linear molecular structure into a three-dimensional network. When the same resin system is heat-cured, differences in curing time and temperature can lead to significant variations in physical and mechanical properties.
Recently, industry experts in China have conducted research on the curing of composite gas cylinders using an E-51/DDM epoxy resin system under different curing conditions. They employed physical and chemical analysis techniques such as infrared spectroscopy, dynamic mechanical analysis (DMA), and mechanical testing to study the effects of resin properties on its application in composite gas cylinders.
The development process for this product begins with careful selection of raw materials. 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 commercially sourced. The ratio of epoxy resin: curing agent: accelerator is 110:35:0.5. A glue solution is prepared, and the exothermic behavior during curing is measured at different heating rates using a German-made PE-7 series differential scanning calorimeter (DSC). The DSC analysis revealed that the exothermic peak starts around 80°C, with a peak temperature of 128°C at a heating rate of 1°C/min. Based on this, the experiment sets 80°C and 130°C as the maximum curing temperatures. Two different curing temperature profiles are established, and corresponding casting bodies are produced.
Next, the casting test is performed. The preparation involves mixing the glue solution, vacuum degassing it, and pouring it into a steel mold that has been coated with a release agent and preheated to remove air bubbles. The two different temperature profiles are applied, and the material is allowed to solidify. After cooling and demolding, the two casting samples, FH80 and FH130, are ground for further performance testing.
The performance test includes evaluating the degree of cure using the solvent extraction method according to GB/T 2576-1989. Infrared spectroscopy is used to analyze the molecular structure, while tensile and bending tests are conducted following GB/T 2568-1995 and GB/T 2570-1995, respectively. The glass transition temperature is determined through dynamic modulus analysis, with a heating rate of 5°C/min, dynamic test stress of 8.0×10ⴠPa, static test stress of 1.0×10ⵠPa, and a test frequency of 1.0 Hz.
The testing equipment used is advanced, including a German-made PE-7 thermal analyzer, a PEKIN-ELMER 2000 FT-IR infrared spectrometer, and an INSTRON 4505 universal material testing machine from the UK. The results from the rigorous testing indicate that at a curing temperature of 130°C, the degree of cure and mechanical strength do not improve further, and in some cases, mechanical properties slightly decrease. However, when the maximum temperature is set at 80°C, the curing time can still achieve a high degree of cure with good mechanical properties. Using the right amount of curing accelerator effectively reduces the activation energy of the epoxy resin system, allowing for full curing at lower temperatures. The final product exhibits excellent overall performance, low cost, and meets the design requirements for high-pressure gas cylinders made from composite materials.
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