The chemical reclamation of crushed waste tires was investigated by using a mixing mill. The effect of various conditions such as roll nip, roll temperature, size of rubber crumb, type of reclaiming oil etc. on the Mooney plasticity of the reclaimed rubbers and physical properties of the revulcanizates was studied. The results showed the following facts; (1) Mooney plasticity of the reclaimed rubbers was affected mainly by roll temperature during mastication, (2) Tall oil, processing oil and alloocymene were excellent reclaiming oils, (3) Increase in quantity of reclaiming oil did not improve the plasticity further, (4) Tensile properties of revulcanizates had close correlation to those of original materials, (5) The smaller was the size of rubber crumb and the more improved was the Mooney plasticity, the higher tensile properties the revulcanizates had.
As the model experiments, vulcanizates of SBR/NR blend were reclaimed with p-toluene sulfinic acid-DBU* system. Increase in contents of SBR caused the slower rate of reclamation, the lower molecular weight of the soluble fraction and the inferior physical properties of the revulcanizates.
Pulse NMR measurements suggest that molecular motion of the revulcanizates was less active than that of the original materials. Accordingly, the degradation in this reclaiming system may be considered to proceed mainly through the scission of the main chain in rubber molecules.
*1, 8-diaza-bicylo[5, 4, 0]undecene-7 (DBU)

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Discontinuity of crosslink density due to diffusion of sulfur near the interface between comminuted and matrix rubber has been assumed to be dependent on the vulcanization speed in the rubber matrix. The discontinuity has been studied by X-ray microprobe analysis (XMA) and freezing point depression of solvent for a model specimen with layered vulcanized rubber and unvulcanized rubber filled with various kinds of accelerators. Crosslink density in the vulcanized and the unvulcanized rubber after curing is highly dependent on the vulcanization speed in the latter or in the matrix rubber. The higher the vulcanization speed in the matrix rubber the discontinuity becomes the smaller. The tensile strength of vulcanizates filled with comminuted vulcanizates is found to increase with a decrease in the discontinuity.

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