This work experimentally monitored the physical and mechanical properties of natural rubber/carbon black/reclaimed rubber blends vulcanized by microwave (MW) irradiation and conventional thermal (CT) systems, and the curing mechanisms are addressed in conjunction with the vulcanizate properties. The microwave oven for rubber blend vulcanization was specially designed and constructed in this work. The results suggested that the tensile modulus and the hardness of the vulcanizates could be enhanced by increasing the reclaimed rubber (RR) content, whereas the tensile stress, elongation at break, and tear strength decreased with the RR loading. The mechanical properties of the vulcanizates from the CT method were higher than those from the MW method. The vulcanizates from the MW method had higher resistance to toluene penetration than those from the CT method. The differences in the properties of the vulcanizates from the CT and MW methods became smaller at higher RR contents. The sensitivity in property changes of the vulcanizates due to addition of the RR content was greater for the CT method than for the MW method. The differences in the results between these two curing systems could be explained in terms of the density and the types of crosslinks present in the vulcanizates. (c) 2000 Wiley Periodicals, Inc.