Modeling temperature and time dependence of the wetting of tool steel surfaces by polymer melts

Beside the surface properties of the tool material, its temperature is an important parameter influencing the wettability of the tool surface by polymer melts in extrusion technology and injection molding. The temperature and time dependence of the contact angle of a polypropylene and a polymethylmethacrylate melt on polished tool steel was studied in this work at close to process conditions. The experiments were conducted by placing the polymeric sample on the hot tool material substrate in a high temperature chamber and recording the drop shape dependence on time. Based on the experimental results, a novel model was developed which allows a description of the contact angle dependent on temperature and time. The contact angle of the investigated polymer melts exhibits a linear decrease with rising temperature, which means that the wettability of the tool material by the polymer melt is improved with increasing temperature. Furthermore, the model proposed herein enables a complete mathematical description of the contact angle of polymer melts on the tool material dependent on temperature and time. The parameters of this function are the initial contact angle h 0, the contact angle when time approaches infinity h? and a characteristic material time B. The time dependency is incorporated by an exponential function. The characterizing contact angle parameters (h 0, h?) follow a linear decrease with rising temperature. The characteristic material time B obeys an exponential law dependent on the reciprocal value of temperature similar to Arrhenius’ law.