Hygrothermal aging behavior and mechanism of multi-filler reinforced epoxy composites for steel structure coatings

• Published in: European polymer journal Vol. 184; p. 111780
• Main Authors: Tian, Jingwei, Li, Chenggao, Qi, Xiao, Xian, Guijun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 07.02.2023
• Subjects: Coating for steel structure; Degradation mechanism; Hygrothermal aging; Long-term life prediction; Mechanical properties; Moisture uptake; Mechanical properties; Coating for steel structure; Long-term life prediction; Degradation mechanism; Hygrothermal aging; Moisture uptake
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2022.111780

[Display omitted] •The MFREC for steel structure coatings were fabricated and its hygrothermal behavior was experimentally investigated.•The moisture uptake behavior of MFREC followed the two-stage model, an initial Fick’s diffusion-occupied stage and a subsequent relaxation-controlled degradation response.•Hygrothermal exposure led to the thermal and mechanical property degradation of MFREC due to the coupling effects of recoverable epoxy plasticization and irrecoverable fillers/epoxy interface debonding.•The long-term life prediction of MFREC for steel bridge coatings showed an additional strength degradation percentage up to 11.5% in a comparison of southern and northern environments. The long-term hygrothermal resistance of epoxy-based composites plays a key role as an anti-corrosion and anti-wear coating for steel structures when exposed to complex service environments. The hygrothermal aging will cause an irreversible damage to the service performances of composites. In the present paper, the multi-fillers reinforced epoxy composites (MFREC) had been successfully prepared and have been given higher expectations for steel coatings. Its hygrothermal aging behavior was experimentally investigated through the immersion in distilled water (DW) and saline water (SW) at 20, 40, and 60 °C as long as 120 days. The moisture uptake, thermal properties, mechanical properties and microstructure analysis were tested to evaluate the long-term hygrothermal evolution. The research results showed that the quasi-equilibrium moisture uptake content (3.72%) of MFREC in SW was lower than that (4.14%) in DW owing to the preferential permeation and occupation effects of small ions (Na+, Cl−). Hygrothermal exposure led to a maximum degradation of tensile strength, elongation at break and glass transition temperature of MFREC, up to 38.2%, 46.6% and 20.8% in DW, and 34.5%, 40.8% and 18.4% in SW, respectively. This was because the epoxy matrix had generated relaxation and reinforced-fillers/epoxy interfaces had been destroyed, which can be verified by hydrogen bond increasing (maximum 75.2%) from infrared test, fiber pulling out from epoxy matrix (morphology analysis), elastic modulus decreasing (maximum 37.8%) from micro-hardness measurement and pore volume increasing (maximum 53.9%) from N2 adsorption test compared to unaged samples. Based on the Arrhenius theory, the long-term life prediction of MFREC tensile strength under three typical bridge service environments was conducted to evaluate the service time as coatings. It can be found that the stable strength retentions were 63.19% and 66.03% in the simulated pure water and marine environments, respectively. Furthermore, an additional strength degradation percentage up to 11.5% can be found for MFREC exposed to steel bridge coatings in southern as long as 3 years compared to the northern environment.