Method for preparing precipitated silicas, novel precipitated silicas, and uses thereof, particularly for polymer reinforcement
The invention relates to a process for preparing a precipitated silica, to precipitated silicas, and to uses thereof. The process of the invention generally includes reacting a silicate with an acidifying agent, so as to obtain a suspension of precipitated silica; filtering the precipitated silica to obtain a filter cake; subjecting the filter cake to a liquefaction operation to form a second filter cake; and drying the second filter cake. In the process of the invention, at least one polycarboxylic acid is added to the filter cake, during or after the liquefaction operation
1. A precipitated silica, characterized in that it has:
a BET specific surface area of between 100 and 240 m 2 /g,
a CTAB specific surface area of between 100 and 240 m 2 /g,
a content (C) of polycarboxylic acid+corresponding carboxylate, expressed as total carbon, of at least 0.15% by weight,
an object size distribution width Ld ((d84 d16)/d50), measured by XDC particle size analysis after ultrasound deagglomeration, of at least 0.70, and
a pore distribution width ldp of less than 0.65, and optionally
an aluminum (Al) content of at least 0.20% by weight;
wherein the precipitated silica comprises a mixture of polycarboxylic acids, and wherein the mixture of polycarboxylic acids comprises methylglutaric acid, ethylsuccinic acid and adipic acid.
2. The precipitated silica as claimed in claim 1 , wherein the precipitated silica has a pore distribution such that the pore volume generated by the pores whose diameter is between 175 and 275 Å represents at least 55% of the pore volume generated by the pores with diameters of less than or equal to 400 Å.
3. The precipitated silica as claimed in claim 1 , wherein the precipitated silica has a dispersive component of the surface energy γ s d of less than 52 mJ/m 2 .
4. A process for preparing the precipitated silica of claim 1 , the process comprising:
precipitating a silicate and an acidifying agent by:
(i) forming an initial feedstock comprising part of a total amount of alkali metal M silicate engaged in the reaction, the concentration of silicate, expressed as SiO 2 , in said initial feedstock being less than 20 g/l,
(ii) adding acidifying agent to said initial feedstock, until at least 50% of the amount of M 2 O present in said initial feedstock is neutralized, to form a reaction medium,
(iii) simultaneously adding alkali metal M silicate and acidifying agent to the reaction medium, such that the ratio of the amount of silicate added expressed as SiO 2 /amount of silicate present in the initial feedstock expressed as SiO 2 is greater than 4 and not more than 100,
(iv) discontinuing the addition of the silicate while continuing the addition of the acidifying agent to the reaction medium, until a value of the pH of the reaction medium of between 2.5 and 5.3 is obtained, thus providing a silica suspension
filtering the silica suspension to form a filter cake,
subjecting the filter cake to a liquefaction operation to form a second filter cake,
drying the second filter cake,
wherein the mixture of polycarboxylic acids is added to the filter cake, either during the liquefaction operation, or after the liquefaction operation and before the drying step.
5. The process as claimed in claim 4 , wherein, during the liquefaction operation, the mixture of polycarboxylic acids is added to the filter cake.
6. The process as claimed in claim 4 , wherein the mixture of polycarboxylic acids is added to the filter cake after the liquefaction operation.
7. The process as claimed in claim 4 , wherein the liquefaction operation comprises the addition of at least one aluminum compound.
8. The process as claimed in claim 7 , wherein, during the liquefaction operation, the mixture of polycarboxylic acids and at least one aluminum compound are simultaneously added to the filter cake.
9. The process as claimed in claim 7 , wherein, during the liquefaction operation, at least one aluminum compound is added to the filter cake prior to the addition of the mixture of polycarboxylic acids.
10. The process as claimed in claim 7 , wherein the mixture of polycarboxylic acids is added to the filter cake after the liquefaction operation.
11. A polymer composition comprising a precipitated silica as claimed in claim 1 .
12. A method for reinforcing a polymer, the method comprising adding a precipitated silica as claimed in claim 1 to the polymer as a reinforcing filler.
13. A precipitated silica, characterized in that it has:
a BET specific surface area of between 100 and 240 m 2 /g,
a CTAB specific surface area of between 100 and 240 m 2 /g,
a content (C) of polycarboxylic acid+corresponding carboxylate, expressed as total carbon, of at least 0.15% by weight,
a pore distribution width ldp of less than 0.49, and optionally
an aluminum (Al) content of at least 0.20% by weight;
wherein the precipitated silica comprises a mixture of polycarboxylic acids, and wherein the mixture of polycarboxylic acids comprises methylglutaric acid, ethylsuccinic acid and adipic acid.
14. An article comprising at least one composition as claimed in claim 11 , wherein the article is selected from a footwear sole, a floor covering, a gas barrier, a flame-retardant material, a roller for cableways, a seal for domestic electrical appliances, a seal for liquid or gas pipes, a braking system seal, a pipe, a sheathing, a cable, an engine support, a battery separator, a conveyor belt, a transmission belt and a tire.
15. The article as claimed in claim 14 , wherein the article is a tire.
16. A method for reducing the viscosity of a polymer composition, the method comprising adding the precipitated silica as claimed in claim 13 to the polymer composition.