Weldability of Dissimilar Thermoplastics-Experiments in Heated Tool Welding

In the welding of thermoplastics, there are various effects that contribute to the adhesion, such as flow processes, viscoelastic contact and diffusion. Where different thermoplastics are welded together, the heat applied has to suit both materials, and this can be done with two separate heating elements. For the different heating required for the two pieces being joined, it would not be possible to fix the temperatures of the heated tools with the viscosities and surface tensions of the melts. Characteristic for the adhesion is the polar part of the surface tensions of the solids. However, during cooling, stresses are formed in the weld zone which means that the ratio of the coefficients of thermal expansion must also be considered when assessing the weldability.