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We present an in-depth investigation of the aging effects in silicone molds for vacuum casting processes. Their lifetime is limited to a few production cycles due to contamination with the diisocyanate component of polyurethane casting materials. Using thermogravimetric analysis measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and helium-ion-microscopy the chemical and physical mechanisms of the aging process have been identified. It has been shown that a diffusion process of diisocyanate into the cavity surface leads to the formation of interpenetrating polymer networks of polyurea derivatives in silicone rubber. This has been proven by extracting and analyzing polyurea of low molecular weights from the silicone. [ABSTRACT FROM AUTHOR]

We present an in-depth investigation of contaminated silicone molds by use of scanning electron microscopy, that provides additional insight into the aging process of the molds. The molds lifetime in vacuum casting processes of polyurethane is limited due to contamination with the diisocyanate compound of the PUR resin. SEM investigations, combined with FIB cross-sections and EDX measurements show that three different types of particles are distributed in the contaminated silicone matrix. The particles differ in shape and size, with a range from 50 nm to 50 µm. This explains the loss in transparency and the hardened haptics of contaminated molds. [ABSTRACT FROM AUTHOR]

In this work we present a new method to enhance the durability of silicone molds, which are used in industrial processes for small batch production. The goal is to reduce the aging effects of the molds that occur after a minor number of casting processes and therefore get a higher output of these molds. First the source of the aging effects is identified. It is shown that the molds are nourished with the low molecular components of the polyurethane mixtures during the casting process, and that the diisocyanate component is responsible for the aging effects. For the removal of these components, several solvents are used. Acetone is shown to be most effective; the regeneration leads to a 30% higher output. Because acetone also removed free silicone oil from the molds, a mixture of the solvent with new silicone oil as regenerating agent was applied, which led to an overall improvement of lifetime of 60%. [ABSTRACT FROM AUTHOR]