The FM6DD-MUL is perfectly capable of processing both paper and cardboard. However, cardboard can take the edge off the blades quicker than when using the mulcher to process standard green waste. If you see a drop in performance in the machine after processing cardboard, it's likely because the sharp edge has been removed from the blades.
These blades can be sharpened using an angle grinder or you can purchase spare replacement blades directly from ourselves. Remember that the blades are also reversible so once one side dulls, you can simply reverse the blades over and use a fresh set.