Bi‐phasic water diffusion in sheet molding compound composite

Abstract

Sheet molding compound (SMC) composite has been studied under humid-aging conditions. Diffusion of water within the material, as measured by gravimetry, was found to be in good agreement with the "Langmuir-type" diffusion model developed by Carter and Kibler. In their theory, Carter and Kibler consider the existence of two types of water molecules in the material, «mobile» and «bound». In this study, these two types have been considered separately. Furthermore, Infrared spectroscopy (FTIR) analysis has been performed by decomposition of signals to study the fraction of free (mobile) and hydrogen-bounded water. Thermal analysis and microscopic observations were put forward to explain the two types of water molecules. In this contribution, we found a "bi-phasic" water diffusion. We suggest that the «mobile» water corresponding to the diffusion in the micro-porosities follows a Fickien kinetic, which turns to sigmoidal one at a specific time of immersion τ. Whereas the kinetic of «bound» water, referring to crosslinking and plasticization, follows a sigmoidal kinetic, which turns to Fickien behavior when the overall network is saturated.

Microstructure investigation of hydrothermal damage of aged SMC composites using Micro-computed tomography and scanning electron microscopy

“…5 where the normalized water uptake data (as mass uptake/mass at saturation) are plotted versus the normalized time given by t 0.5 /e (where e is the sample thickness). Similar trends were obtained for samples aged at 25, 50 and 70 • C and can be found here [22]. It was found that the «mobile» water corresponding to the diffusion in the micro-porosities.…”

“…9, cross sections of the 90 • C aged composite after different water uptake are shown. Overall, the damage development in the aged SMC composite proceeded faster which is in line with the evolution in water uptake properties as discussed in the previous work [22].…”

“…• An increase in the number of porosities caused by the phenomena of the chalks particules leaching; i.e this phenomena was discussed and analysed in the previous work [22].…”

“…The kinetic of water sorption was analysed in the previous study [22]. It was found that water diffusion in SMC composites follows the "Langmuir type diffusion" based on Carter and Kibler's theory [23].…”

“…In this study, we are interested to discuss the effect of mobile water molecules diffusion in the SMC microstructure. The effect of hydrogen-bounded molecules were discussed in the previous work [22].…”