Studies of Hard Rubber Reactions III. Changes in the Acetone Extract during Vulcanization

Abstract

Abstract In the former communications (Part I and Part II) the author dealt with the characteristic changes in some physical properties with time of cure of hard rubber compounds. The work has now been extended by chemical observations. In the first place, the author studied the acetone extract of the same compounds of the previous reports with a view to ascertaining the nature of the hard rubber reactions. Preliminary Examination of the Acetone Extract Samples were prepared for acetone extraction in two ways. In the case of soft rubber products, the material was sheeted out to thin crepe by passing between the tightly closed rolls of a laboratory mill and was then cut with scissors into fine strips. Hard rubber samples were prepared by buffing with an alundum grinder and sifting through a 100-mesh screen. In each case the sample taken for the extraction was 0.5–1.0 gram. The extraction apparatus was a new design, as illustrated in Fig. 1, which has the advantage of extracting the sample in the vapor of boiling acetone, and in many other respects is more efficient and convenient than the Cottle type of extractor. There has been considerable discussion as to a standard time of extraction for hard rubber. According to the specification of the Society of Rubber Industry of Japan, for example, extraction of at least 48 hours is recommended, while it is specified in the British Standard Specification No. 234 (1933) that only 8 hours of continuous extraction are necessary for ebonite for electrical purposes. Besides these, extraction periods of 72 hours, 20 hours, etc., have been advocated by various authors.