Effects Of Environments On Pultruded Carbon Fiber/Vinyl Ester Resin Composite

The environmental aging behaviors of the pultruded carbon fiber/vinyl ester (CF/VE) composite in distilled water, 3%NaCl aqueous solution, 5%H2SO4 aqueous solution and 10%NaOH aqueous solution were studied in laboratory. The absorption characteristics of the composite in these environments were investigated. Moreover, the effects of the environments on dynamic and static properties and aging mechanisms were analyzed. The aim of this paper is to provide theoretic base for the valuation of the durability of the continuous pultruded CF/VE composite used as sucker rods in oil industry.The results of moisture content measurement showed that the absorption characteristics of the pultruded CF/VE composite obeyed Fick's second law in distilled water and 3%NaCl aqueous solution, that is the moisture content of the composite increased rapidly at the early immersion and was linear with t1/2, after that the moisture content nonlinear increased slowly and then equilibrium moisture content was reached. In the 5%H2SO4 aqueous solution, the absorption behavior was similar to the Fick's second law at the early stage, but the moisture content decreased a little at last. While in 10%NaOH aqueous solution, at first the moisture content increased linearly and thereafter decreased a little and then increased with the prolongation of immersion time. Moreover, the increase of environmental temperature leaded to a quicker diffusion of water in the composite and a higher equilibrium moisture content.The effects of the environments on the dynamic mechanical properties of the pultruded CF/VE composite were studied by dynamic mechanical thermal analysis (DMTA). The results showed that the storage modulus (E') of pultruded CF/VE composite decreased with immersion time, while the loss factor (tanδ) increased. Furthermore, the higher the temperature was the more serious the effects were. The decrease in glass transition temperature (Tg) of the composite was relative to the increase in moisture content. In 10%NaOH aqueous solution, Tg of the composite kept on decreasing with the farther prolongation of immersion time. But in distilled water and 3%NaCl aqueous solution at 95℃, Tg of the composite had a little increase again after the minimum value reached because of the different bonding state between water and resin matrix. The flexural and shear properties of the pultruded CF/VE composite were measured on an universal testing machine to study the effects of the environments on the macroscopical mechanical properties of the composite. The results showed that environmental conditions induced the decrease in the flexural and shear properties of the pultruded CF/VE composite and the decrease was relative to the increase in moisture content. The results of DMTA, infrared spectrometer (IR) and scanning electron microscope (SEM) showed that the composite had the same aging mechanisms in distilled water and 3%NaCl aqueous solution. That is the environments caused the swell and plasticization of matrix, interfacial debonding and resultant microstructure changes of matrix and interface. No chemical aging were founded. The increase of temperature didn't change the aging mechanism of the composite, but the speed of water diffusion and the equilibrium moisture content were changed, so the changes of mechanical properties were different. But in 5%H2SO4 aqueous solution and 10%NaOH aqueous solution, hydrolysis with different degree was founded. And the hydrolysis was different with environmental temperature. In 10%NaOH aqueous solution, the ester bond and aether bond of vinyl ester resin both hydrolyzed at different extent. The residue found in 10%NaOH aqueous solution was almost micro-molecular aliphatic alcohol at 65℃ and the content of aromatic molecule increased at 95℃.