Research on Curing Agents for Low-Viscosity, Slow-Curing Epoxy Resins (I)

Thread Content

Research on Curing Agents for Low-Viscosity, Slow-Curing Epoxy Resins (I) Epoxy resins are a class of linear polymer compounds containing epoxy groups, and they exhibit excellent adhesion to almost all types of construction materials such as concrete, metals, glass, fibers, and rigid plastics. Among thermosetting resins, epoxy cures have the lowest shrinkage rate, which can be as low as below 0.2%. Furthermore, the cured product of epoxy resin exhibits excellent resistance to aging and chemical agents, making it the best among thermosetting resins; as a result, it meets the special requirement that construction adhesives should have a service life of over 50 years. However, epoxy resin can only meet the standard requirements for construction reinforcement adhesives when it is used in combination with a suitable curing agent. In room-temperature curing systems, the common slow-curing agents that can cure at room temperature include polyamides, imines, alicyclic amines, polyether amines, aromatic amines, and imidazoles. Polyamides belong to traditional curing agents; they cure slowly at temperatures between 15 and 25°C, and a large amount of adhesive is required for curing. However, when the temperature exceeds 35°C, their working time decreases rapidly, making them difficult to use. Additionally, their high viscosity prevents the inclusion of more fillers, which limits their use in construction adhesives. Like imine curing agents, they are of the latent type; although their viscosity is appropriate, moisture or amines are required during the curing process, and their strength does not meet the standards for construction adhesives, which prevents the widespread use of this type of agent. Alicyclic amines and polyether amines cure slowly at temperatures above 35°C, but their high cost also limits their use. Aromatic amines are solids that are not convenient to prepare at room temperature, and their adoption is also limited. Although imidazole compounds can extend the setting time at room temperature, their degree of curing is too low to enable their use in the construction adhesive industry. Taking into account both price and performance factors, this paper selects aromatic amines for liquefied chemical modification to produce low-viscosity curing agents for epoxy resins, and experiments are conducted in accordance with the project standards for impregnation adhesives used in building reinforcement. 1 Experimental Section 1.1 Main Raw Materials: Epoxy resins CYD128 and EPG660, produced by Yuehua Resin Factory ； Gas-phase silica, Cabot, USA ； Coupling agent KH-550, Wuhan University New Materials Co., Ltd ； Curing agent HD-MG, accelerator DMP-30, Hubei University Chemical Plant. 1.2 Testing equipment: Inston electro-hydraulic servo material testing machine, model 1341. 1.3 Performance testing: The steel-to-steel shear strength is determined in accordance with GB/T7124-1986, the method for determining the tensile and shear strength of adhesives (metal to metal) ； Determine the steel-to-steel uneven tear strength in accordance with GB/T94-1986 ； The tensile strength, elastic modulus under tension, and elongation of the colloid are determined in accordance with GB/T2568-1981 ； Determine the flexural strength of colloids in accordance with GB/T2570-1981 ； The compressive strength of the colloid is determined in accordance with GB/T2569-1981. 1.4 Sample preparation: Process the sample pieces in accordance with the requirements of GB/T50367-2006, manufacture molds, and carry out curing as specified before testing. 2 Results and Discussion 2.1 Adhesive formulation The formulation consists of two components, Component A and Component B. Component A is CYD128/EPG660/vapor-phase silica/KH-550=100/10–15/appropriate amount/1. Component B is HD-MG (containing an appropriate amount of DMP-30). A:B = 100:33 (by mass). 2.2 Basic properties of HD-MG: Amine value, mgKOH/g: 600±20; viscosity, mpa·s (25°C): 1200±200. At 29°C, the working time for 100 g is 1 hour 50 minutes, which makes it highly suitable for on-site use where a working time of 30–50 minutes is required. (For ordinary polyamides, the viscosity at temperatures below 40°C is around 3000–30000 MPa·s; too high a viscosity makes handling difficult) ....................... ...........................