Optimization of the bake-on siliconization of cartridges. Part II: Investigations into burn-in time and temperature.

Combination products have become popular formats for the delivery of parenteral medications. Bake-on siliconization of glass syringes or cartridges allows good piston break-loose and gliding during injection at low silicone levels. Although widely implemented in industry, still little is known and published on the effect of the bake-on process on the silicone level, layer thickness and chemical composition. In this study, cartridges were bake-on siliconized in a heat-tunnel by varying both temperature from 200 to 350°C for 12min and time from 5min to 3h at 316°C. Furthermore, a heat-oven with air-exchange was established as an experimental model. Heat treatment led to a time- and temperature-dependent decrease in the silicone level and layer thickness. After 1h at 316°C lubrication was insufficient. The silicone levels substantially decreased between 250 and 316°C after 12min. After bake-on, the peak molecular weight of the silicone remained unchanged while fractions below 5000g/mol were removed at 316 and 350°C. Cyclic low molecular weight siloxanes below 500g/mol were volatilized under all conditions. Despite most of the baked-on silicone was solvent-extractable, contact angle analysis indicated a strong binding of a remaining, thin silicone film to the glass surface.