Dear mr. Juan,
During the last week of my stay, after talking with other manufacturers, I am putting together all my thoughts on milling herbal materials.
Using a roller compactor as they use in the pharmaceutical industry for granulation, or a type of roller / squeezer that they use for sugar cane, or a kind of vertical roller mill as they use in the concrete industry, would crush your leaves without causing too much dust. However, as your leaves also contain twigs, the twigs will be squeezed but not broken. They are tough. To get a manageable product for mixing, you would need to screen the product and then put the twigs in your cutter. All together, it would make the operation in your factory too complicated. Also, it would not be easy to organize a trial with such equipment. Therefore, I did not even propose it too you.
Another solution, at first sight, seems rather exotic, but on a second sight is said to be also used for your type of application, is cryogenic grinding: cooling your material with liquid nitrogen to -196 Centigrade before and during milling.
See the following site : http://www.chunnant.com/InfoProductView.asp?id=2322 . If they do use it for old tyres, it cannot be too expensive!
You can always reach me by mail.
Wishing you all the best,
Met vriendelijke groet, Kind regards,
Ries de Winter
Sector Coordinator Pharmaceutical & Cosmetic Products