I am trying to make rubber films from Natural rubber. Unfortunately, I don't have access to extruders or similar equipment and therefore work with solvents. As for my curing system, I am using Sulphur, DPG, Zinkoxide and Stearic Acid. I dissolve/disperse everything and then cast the solution into containers. Once the films are completely dry, I vulcanise them in an oven at 160 °C. However, the films look inhomogenious, are easy to break and are extremely sticky and tacky.
I hope someone can tell me what might be happening during cross-linking and how I can improve my process. I am grateful for any suggestions.
Jan, natural rubber will undergo rapid thermo-oxidative degradation at 160°C if the films are exposed to air during curing. Adding an antioxidant could help prevent this. Additionally, DPG is slow acting and inherently gives a relatively poor state of cure. It would probably be better to use a much faster accelerator, for example ZDMC (Zinc dimethyldithiocarbamate), as this would allow curing over shorter times and at lower temperatures, reducing the risk of degradation.
Thanks Mike for the very helpful answer!
Based on your response I could additionally perform the curing in a vacuum? The oven can go down as low as 10 mbar. That way less oxygen should be present which would then be in my favor.
I would anyways switch to the Accelerator you recommended. But just to check the Hypothesis you suggested I could check the curing with DPG under Vacuum.
Question is, how well have you mixed/dispersed components? How your non homogenity look like ? If you can share more info I can try to help you. [email protected] Kind regards Jirka
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