Precipitated silica and process for its manufacture
A chemically modified precipitated silica characterised by the presence of methyl moieties chemically bound to the silica and a process for its manufacture.
1. A precipitated silica comprising units of formula [SiO 4/2 ] and units of formula [(CH 3 )SiO 3/2 ], wherein the 13 C NMR spectrum of the precipitated silica exhibits two resonance peaks assigned to the methyl group: a first peak in the region between −2.0 and −5.0 ppm and a second peak in the region between −5.5 and −9.0 ppm and wherein the ratio (intensity of the second peak)/(intensity of the first peak) is greater than 0.40 and wherein the precipitated silica comprises a median particle size d50 and a CTAB (cetyltributylammonium bromide) surface area such that |d50|>164.5−0.3*|CTAB| wherein |CTAB| represents the numerical value of the CTAB surface area expressed in m 2 /g and |d50| represents the numerical value of the median particle size d50 measured by centrifugal sedimentation and expressed in nm, wherein the CTAB surface area ranges from 40 to 600 m2/g.
2. The precipitated silica of claim 1 wherein the ratio (intensity of the second peak)/(intensity of the first peak) is between 0.50 and 1.60.
3. The precipitated silica of claim 1 wherein the precipitated silica comprises a carbon content of from 0.2 wt % to 10.0 wt % with respect to the total weight of silica.
4. A process for preparing the precipitated silica of claim 1 , the process comprising: (i) providing a starting solution with a pH of between 2.0 and 5.0; (ii) simultaneously adding silicate and an acid to said starting solution, such that the pH of the resulting reaction medium is maintained between 2.0 and 5.0; (iii) stopping the addition of the acid, while continuing the addition of the silicate to the reaction medium until a pH value of the reaction medium of between 7.0 and 10.0 is obtained; (iv) simultaneously adding silicate and acid to the reaction medium obtained in (iii), such that the pH is maintained between 7.0 and 10.0; and (v) stopping the addition of the silicate while continuing the addition of the acid to the reaction medium until a pH value of the reaction medium of less than 6.0 is reached and a silica suspension is obtained; wherein at least one alkali metal methyl siliconate is metered into the reaction medium in step (iv) or (v).
5. The process according to claim 4 wherein step (v) comprises a first phase wherein the acid and the alkali metal methyl siliconate are simultaneously metered into the reaction medium at a pH between 7.0 and 10.0 followed by a second phase wherein the addition of the alkali metal methyl siliconate is stopped while the addition of the acid is continued and the pH of the reaction medium is allowed to decrease below 6.0.
6. The process of claim 4 wherein the at least one alkali metal methyl siliconate is sodium or potassium methyl siliconate.
7. A composition comprising the precipitated silica of claim 1 and at least one polymer.
8. An article comprising the precipitated silica of anyone of claim 1 .
9. The article of claim 8 , wherein the article is selected from the group consisting of a footwear sole, a floor covering, a gas barrier, a roller for cableways, a seal for domestic electrical appliances, a seal for liquid or gas pipes, a braking system seal, a pipe, and a sheathing.
10. The article of claim 8 , wherein the article is selected from the group consisting of a thermal insulation material, a resorcinol-formaldehyde/silica composite, concrete, and paper.
11. A tire or tire element comprising the precipitated silica of claim 1 .