LOW-TEMPERATURE DEBINDING KINETICS OF 2-COMPONENT MODEL SYSTEMS

Two component model binder systems composed low molecular weight stear ic acid (SA) and low density polyethylene (LDPE) or polypropylene (PP) were chosen to study the kinetics of conventional thermal debinding o f SA from a metal powder compact formed by spherical stainless steel p owder. The burnout temperatures of SA and the respective thermoplastic were widely different, so that the weight loss of the low molecular w eight component could be followed independently by thermogravimetric a nalysis. The experiment provides at constant temperature an exponentia l decrease of the SA weight with the debinding time. The debinding rat e is therefore controlled by diffusion of SA in the thermoplastic to t he inner surfaces of pores, which develop in the material during debin ding. Pore development considerably increases the debinding speed, bec ause the diffusion length of the SA molecules is much smaller than if they had to diffuse to the part surface. The kinetics of other possibl e rate controlling mechanisms are reviewed and compared with the exper imental results. The dependence of the debinding kinetics on temperatu re, sample thickness, porosity and tortuosity of the sample is quantif ied. It is suggested that removal of a low molecular weight component controlled by diffusion in the basic component may be only valid if th e interaction between the constituents is similar, as for the binder s ystems LDPE/SA or PP/SA.