Several factors, eg exposure to sunlight, there presence of pro-oxidants such as copper ions, and the subjecting of the rubber to extensive mastication, reduce the initial Wallace Plasticity (Po) of natural rubber. Studies conducted at RRII India showed that treatment of undried crumbs with solutions of tetraethylene pentamine of hydrazine increased Po and helped to impart better properties to the raw rubber without adversely affecting vulcanizate ageing resistance. Crumb rubber masticated at 60 C for 20 minutes had lower Po values than samples exposed to bright sunlight for about 35 hours. However, the former sample showed a higher rheometric torque, reflecting better vulcanizate properrties, than the latter, hence indicating that the performance of the vulcanizate was less dependent on Po. Infrared (IR) spectral studies showed that molecular level changes taking place under various conditions which reduce Po are different from one another. IR studies confirmed that oxidation intermediates that contain > C = CH are not formed during mastication, whereas they are formed during sunlight-ageing. Acetone extractable increased with the duration of sunlight-ageing. IR spectra of acetone extractable of sunlight-aged samples showed adsorption at 891 cm-1 corresponding to the formation of oxidation intermediates such as acids, aldehydes and ketones that contain > C = CH. IR spectra of pyrolyzates of both sunlight-aged and pro-oxidant treated samples showed adsorption at 118 cm-1 as well adsorption at 1716 cm-1, thus showing the presence of ketons, aldehydes etc, whereas no absorption at 1128 cm-1 was shown for the masticated samples.