Silicone rheological behavior modification for 3D printing: Evaluation of yield stress impact on printed object properties

Silicone-based materials are commonly used in medical applications such as pre-surgery models or implants, leading to interesting biomimetic mechanical properties. Emergence of 3D printing and particularly liquid deposition modelling (LDM) has shown that specific rheological behaviors, particularly yield stress characters, were required to achieve efficient LDM. Unfortunately, standard silicone formulations seldom present such behaviors and are then proved to have low applicability in LDM-based 3D printing. In the present study, polyethylene glycol of different lengths were added as yield stress agents in a bi-component silicone and were demonstrated to operate a drastic improvement of the material rheological behaviors, without significant impact on the final mechanical properties of the material. An interesting relationship was demonstrated between dynamic yield stress values and reachable 3D geometries (the higher sigma(s)(y), the more complex the 3D printed shape can be) but the study also revealed that it is not the only key factor to ensure the printability of viscoelastic materials when highly complex geometries are seek; tack and melt strength have also to be investigated.