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Nature volume 150, page 31 (04 July 1942) | Download Citation



ACCORDING to G. G. Winspear (Bell Lab. Rec., 20, No. 8, April, 1942) vulcanized rubber may have a wide variety of characteristics depending on the amount of sulphur, the period and temperature of vulcanization, and the other substances compounded with it. Identical rubber compositions, vulcanized for the same time and at the same temperature, do not always develop the same characteristics. One of the unsatisfactory conditions that sometimes appears is spottiness, indicating a lack of homogeneity in the product. Before the sulphur assumes a position in the rubber molecule, it dissolves, and to secure uniform solution the sulphur is first dispersed evenly throughout the rubber mass. When sulphur and rubber are mixed on a mill the sulphur is dispersed throughout the rubber mass but most of it is in particles of measurable size. Although the particles may be small, and perhaps even invisible to the unaided eye, they are still very large compared to the sulphur molecule, so that the mixture is far from being one where all the sulphur is in immediate contact with the rubber molecules, which is the theoretical state required to give a homogeneous solution of sulphur in rubber. Such an intimate mixture results from a diffusion of the sulphur of each particle following the dispersion on the mill.

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