Evolution Of The Properties Of An Epoxy Resin Submitted To Water And Alkaline Immersion And The Molecular Dynamic Simulation

Fiber reinforced polymer(FRP) composites are widely used in reinforcement, repair and reconstruction of civil engineering structures due to lightweight, high strength, corrosion resistance, ease of processing, etc. Since the complex service environment in civil engineering structures(such as water or alkaline solution immersion), FRP will absorb the moisture during, causing degraded performance and lead to long-term structural problems of the security service. FRP is mainly composed of fiber(such as carbon fiber) and resin matrix,while the resin matrix are more prone to occur erosion. Therefore, the study of the mechanism of the deterioration of the performance of the resin matrix in water or alkali solution immersion conditions have great significance to understand FRP’s durability and performance improvements, which will promote security applications of FRP.In this paper, combine experimental testing with molecular dynamics simulations to study the degradation of the epoxy matrix submitted to water and alkaline immersion includes: 1) water absorption and diffusion law(p H = 12.5, simulated concrete exudate) 、thermodynamic properties、fractional free volume and chemical composition change of epoxy resin at 20 oC, 40 oC and 60 oC water or alkaline solution; 2) based fiber grating monitoring techniques to study the swelling effect of the epoxy resin matrix due to the water absorption; 3) through molecular dynamic to simulate the absorption and diffusion processes and plasticizing effect of water molecules in the resin matrix.The results showed that water absorption process of epoxy resin corresponded to the classical model of Fick; equilibrium water absorption and diffusion coefficient of the resin increase with soaking temperature which shows significant plasticizing effect.Infrared analysis showed that long-term immersion in water or alkaline solution has little effect on the chemical structure of epoxy, and did not occur significant hydrolysis reaction.Monitoring results show that the fiber Bragg grating, within one month’s water absorption, the resin expansion strain(swelling effect) grew rapidly, then maintain a subsequent balance.Through the establishment of a molecular model of epoxy resin with molecular dynamics, author simulated glass transition of the resin matrix and the plasticizing effect of water absorption of the resin; at a lower water absorption, the system has a greater hydrogen energy with density increasing, With the improved water absorption, density decreases, the diffusion coefficient of water molecules increased, which speeds up the local chain movement, indicating that the hydrogen has great significance for the performance of the resin.