Further Electron Microscope Studies on Colloidal Carbon, and the Role of Surface in Rubber Reenforcement

(1) Based on preliminary electron microscope analysis, rubber carbons are assigned tentative surface values, ranging from one to upward of 12 acres per pound. (2) In all cases particles are of essentially spherical habit. (3) Indications of chain and network structure have appeared in acetylene carbon and lampblack plates (conclusion not final). (4) Physical properties of carbons in rubber are reviewed, and the advantages of “soft” carbons enumerated. (5) Differences in chemical compositions are found not to square with reënforcing differences in rubber. (6) When colloidal properties, tinctorial properties, and rubber properties are plotted against acres per pound, it is found, as anticipated, that surface is, in general, the dominating influence; subject, however, to important and sometimes controlling anomalies. (7) These anomalies appear to be largely resolved on the assumption that three broad types of carbon behavior exist. (I) Carbon-rubber complexes (reënforced rubber) are formed (examples— semireënforcing carbons, Statex and carbon blacks). (II) Carbon-carbon complexes or networks are formed in addition to (I). Examples, acetylene carbon and lampblack. (III) Carbons are inert—neither (I) nor (II) occurs. Examples—thermal carbons. These relations are brought together in Table 1.