A rubber compound for the preparation of pneumatic tyre parts comprising at least a crosslinkable unsaturated-chain polymer base, a filler, a vulcanization system and a dispersing agent comprising, in turn, a functionalized lignin having a plurality of functionalizations of the general formula I wherein R and R′ are different from each other and chosen from —OH and —OArLig and n is an integer between 1 and 6.