Fractional diffusion model for emission and adsorption prediction of TXIB from wallpaper

Mercury injection test shows that wallpaper is a porous building material with a complex fractal mass transfer channel. Therefore, fractional Fick's law is employed to investigate sub-diffusion of 2,2,4 trimethy1-1,3-pentanediol diisobutyrate (TXIB) from wallpaper. In view of the fact that a small amount of TXIB has been released from the wallpaper before the environmental chamber experiment, the non-uniform initial concentration is introduced. Based on fractional Fick's law, both fractional convective mass transfer equation and fractional mass balance equation have been firstly proposed. Combining the finite difference method and L1 algorithm, the fractional diffusion model is solved numerically. Numerical simulation results show that the present model matches well with the experimental data. Compared with the previous model based on Fick's law, the present model is in better agreement with experimental data of di-2-ethylhexyl phthalate (DEHP) released from polyvinyl chloride (PVC) flooring. The influence of key parameters on the concentration of TXIB is analyzed graphically. In addition, the absorption amount and absorption rate of TXIB on the environmental bulkhead are numerically simulated for the first time.