Investigation and Prevention of the Aging Mechanism of Silicone Molds for Vacuum Casting
Silicone casting molds are mainly used in the vacuum casting process for the production of prototypes made of polyurethane. However, due to lifetime limitation of these casting molds to few production cycles, this production process is rarely considered for an extensive use in small batch production . In the presented work, the chemical and physical mechanisms of the aging effects in silicone molds have been studied by using a wide variety of characterization methods. It has been shown that an anomalous diffusion process of the diisocyanate component of the polyurethane casting resin into the silicone surface leads to the formation of interpenetrating polymer networks of polyurea derivatives in the poly(dimethylsiloxane) matrix . This has been proven by extracting and analyzing polyurea of low molecular weights from the silicone. The development of an appropriate barrier layer system for the protection of silicone molds from the diisocyanate would result in an improved economic efficiency for the applied production processes in industry. With this, the gap in plastic processing between very small (rapid prototyping) and very large quantities (injection molding) might be closed. Therefore, we have grown several combinations of thin films onto plane silicone samples, including carbon nanomembranes  prepared via spin-coating and silicon dioxide deposited by reactive radio-frequency magnetron sputtering. Subsequently, the samples were characterized in terms of the films’ individual growth and their ability to prevent the aging mechanisms in silicone.
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