PROPERTIES AND STRUCTURE OF SILICAS 509 1,000 9OO 8OO 700 600 5OO 40( 30( 2O0 100 70 -- SILICA STRUCTURE INDEX (SI) -- VERSUS OIL ABSORPTION -- LOG SI • 0.012 (OIL ABSORPTION) +3.93 I i i i I i I 90 110 130 150 170 190 210 OIL ABSORPTION Figure 9. Plot of silica structure versus oil absorption Experience of producing a wide variety of precipitated silicas has led us to the conclu- sion that VHS silicas exhibit oil absorption values above 200 ml oil/100 g silicas. The precipitated silicas between the oil absorption range of 125 to 175 ml/100 g silica are classified as MS silicas. Products with oil values below 200 and above ! 75 are called HS silicas. Products below 75 ml oil/100 g silica are called VLS silicas and the LS silicas range between the values 75 to 125 ml oil/100 g silica. Note that in Table IV we have referred to the product "C" as MS silica due to its WCM and SI values even though its oil absorption is slightly above the 175 ml oil/100 g silica cut-off range for the MS structure silica. D. GLYCERINE, MINERAL OIL AND $ORBITOL ABSORPTION VERSUS THE SILICA STRUCTURE Figure 10 shows the relationship between the % WCM of silica samples and their cor- responding mineral oil absorptions. Figure 11 is a plot of log SI versus the humectant absorption values of the various controlled-structure silicas. The mineral oil absorption values are relatively higher than the glycerine/sorbitol absorptions obtained with the same silica samples (see Table IV). This may be due to the nonhydrogen-bonding na- ture of the mineral oil. Note, also that the sorbitol absorption values are higher than the corresponding glycerine absorption values. The mathematical relationships be- tween the silica structure and various liquid absorption values are predicted by the regression program. These equations are listed in Table VII as well as in Figures 10 and 11.

510 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 9O 8O 7O 6O 5O 200 190 170 150 130 110 90 , I SILICA % WET CAKE MOISTURE {WCM) VERSUS MINERAL OIL ABSORPTION % WCM = 0.26 (MINERAL OIL ABSORPTjß+33.0 ß ß ß I t 80 100 120 140 160 180 200 MINERAL OIL ABSORPTION Figure 10. Plot of silica structure versus mineral oil absorption - SILICA STRUCTURE INDEX (SI) VERSUS HUMECTANT ABSORPTION - LOG SI = 0.014 (SORBITOL ABSORPTION) +3.59 LOG SI -- 0.019 (GLYCERINE ABSORPTION) +3.24 - E) 99.5% GLYCERINE [] 70.0% SORBITOL lOO 500 STRUCTURE INDEX Figure 11. Plot of silica structure versus humectant absorption J 22O I lOOO