Processing recycled silicone powder in liquid silicone rubber injection molding and its influence on mechanical properties

Liquid silicone rubber (LSR) is characterized by a wide range of advantageous properties and is therefore used in many branches and industries. However, the material is difficult to recycle due to the non-reversible cross-linking reaction. A promising approach to recycle the already cross-linked (post-industrial) waste is the mechanical recycling of LSR via grinding and addition of the powder as filler in virgin material. This research focused on the processing of such LSR-powder-compounds via injection molding and the influence of the powder content on mechanical properties. Compounds of virgin LSR and ambient ground powder were prepared and injection molded. Both the processability and the mechanical properties were analyzed. Compounds of up to 40 wt% powder content could be processed with standard injection molding machine equipment without any noticeable issues. The results show a similar compression set for the virgin as for the recycled compounds. Hardness decreases slightly but constantly. Tensile strength and elongation at break are at similar levels for all powder added compounds and drop only by 16.6% and 12.6% compared with the virgin LSR. The results are promising and should be the basis for further and more detailed investigations to industrialize the mechanical recycling of LSR.Highlights Processing on standard injection molding machine with standard parameters. Up to 40 wt% recycled silicone powder content. Using recycled silicone particles has no effect on compression set. Tensile strength and elongation at break decrease only by 16.6% and 12.6%. Schematic representation of the processing of mechanical recycled liquid silicone rubber powder via injection molding. image