Diffusivities of Dialkyl Phthalates in Plasticized Poly(vinyl butyral): Impact on Binder Thermolysis

Hot-stage/Fourier transform infrared microspectroscopy (FTIR-M) was used to determine the diffusivities of a series of dialkyl phthalates in poly(viny1 butyral) (PVB) spin-coated films. The diffusivities ranged from lo-'' to lo-'' cmz/s for the isotherms investigated (60" to 150°C). In their respective temperature regimes, dimethyl phthalate and diethyl phthalate exhibited nonlinear diffusion behavior, while dibutyl phthalate (DBP) and dioctyl phthalate (DOP) exhibited Fickian behavior in PVB. The activation energies for DBP and DOP diffusion in the PVB-based films were calculated to be 76.3 and 114.7 kJ/mol, respectively. The diffusivity of DBP was used to compare the relative importance of diffusion and capillary migration in the thermolysis of PVB-DBP binders from ceramic greenware. Comparison of the calculated DBP loss due to diffusion alone could not account for the observed removal rates. A characteristic diffusion length is calculated from the experimental observations. [