MD80 CREW RETURNED TO THE DEP STATION WITH BURNING RUBBER FUMES IN THE CABIN AT ORD.

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BURNING RUBBER SMELL AFTER TKOF. WE LEFT THE GATE AND USED BOTH ENGS FOR INITIAL TAXI THEN SHUT DOWN THE R TO CONSERVE FUEL AFTER LEAVING THE RAMP AREA. WE RESTARTED THE R ENG ABOUT 4 MINS BEFORE TKOF ON RWY 22L ORD. AT 5000 FT ON THE CLBOUT STILL MAINTAINING CLB PWR THE FLT ATTENDANT IN THE REAR OF THE ACFT CHIMED ME TO SAY THEY SMELLED BURNING RUBBER IN THE REAR OF THE ACFT. A QUICK SCAN OF THE ENGS REVEALED NOTHING. THEY SAID THERE WAS NO SMOKE BUT BELIEVE THE SOURCE WAS FROM THE R SIDE OF THE ACFT. I SHUT OFF THE R PACK; AND THE RECIRCULATING FAN AND LEVELED AT 9000 FT. ABOUT 1 MIN LATER THEY STILL SMELLED THE BURNING RUBBER BUT DIDN'T THINK IT WAS AS BAD. I DECIDED TO RETURN TO ORD AND ASKED FOR PRIORITY HANDLING. ABOUT ANOTHER MIN LATER THE FLT ATTENDANTS INFORMED ME THEY DEFINITELY SMELLED THE BURNING RUBBER AGAIN. I DECLARED AN EMER AS I WAS OVERWT; 132000 LBS; AND LANDED ON RWY 9R IN ORD AND HAD THE ARFF MEET THE ACFT. WE CLRED THE RWY AND AFTER A THOROUGH CHKOUT TAXIED TO THE GATE; WITH A FIRE TRUCK IN TRAIL. ONCE WE CLRED THE RWY I SHUT DOWN THE R ENG. WE COMPLETED OUR SINGLE ENG TAXI WITHOUT STARTING THE APU TO THE GATE AND NO FURTHER ACTION WAS REQUIRED.