Modeling the pyrolysis of 3D-printed tannin-based composites - A first approach

A two-dimensional axisymmetric finite element model of the pyrolysis of 3D-printed tannin-based composite was developed using COMSOL Multiphyics. The thermal degradation of such bio-based composites involves the interaction, in a porous medium, of heat, mass and momentum transfer with chemical reactions. Heat is transported by conduction and convection, and mass transfer is driven by pressure and concentration gradients. Using a simplified model to account for char and gas production, the predicted mass loss, shrinkage profile and gas generation as a function of temperature agreed well with experimental results obtained by TGA-MS and TMA. Varying the model parameters and process features highlighted that a longer residence time of volatiles leads, for the same final carbon yield, to a reduced overall pressure and therefore tends to limit cracking and deformations. Controlling and decreasing the rate of mass loss and reducing gas pressure have also been shown to be possible by adding isothermal stages at key pyrolysis temperatures such as 573 and 673 K.