PROCESS FOR THE PREPARATION OF MODIFIED SILICA, MODIFIED SILICA AND ITS USES, IN PARTICULAR FOR THE REINFORCEMENT OF POLYMERS

Abstract

The invention relates to a process for the preparation of a modified silica comprising the step of adsorbing at least one polycarboxylic acid on precipitated silica.

Claims

1. A process for the production of modified silica, the process comprising: adsorbing at least one polycarboxylic acid on a precipitated silica.

2. The process according to claim 1, wherein the precipitated silica has a BET between 45 and 700 m.sup.2/g.

3. The process according to claim 1, wherein the at least one polycarboxylic acid is selected from the group consisting of linear or branched, saturated or unsaturated, aliphatic polycarboxylic acids having from 2 to 20 carbon atoms and aromatic polycarboxylic acids.

4. The process according to claim 1, wherein the at least one polycarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, methyladipic acid, methylsuccinic acid, ethylsuccinic acid, methylglutaric acid, dimethylglutaric acid, citric acid, isocitric acid, and tartaric acid.

5. The process according to claim 1, wherein the amount of the at least one polycarboxylic acid adsorbed on the silica is such that the total content (C) of the at least one carboxylic acid and/or of its corresponding carboxylate, expressed as total carbon, is of at least 0.15% by weight with respect to the amount of silica, expressed as SiO.sub.2.

6. The process according to claim 1, which is carried out by impregnation.

7. The process according to claim 1, which comprises the step of preparing a precipitated silica by a precipitation reaction between a silicate and an acidifying agent, to obtain a silica suspension, recovering the silica from the suspension and drying the silica.

8. A modified silica comprising at least 0.15% by weight expressed as total carbon with respect to the amount of silica, expressed as SiO.sub.2 of at least one adsorbed polycarboxylic acid and/or of its corresponding carboxylate obtainable by the process of claim 1.

9. The modified silica of claim 8, wherein the at least one adsorbed polycarboxylic acid and/or carboxylate is selected from the from the group consisting of linear or branched, saturated or unsaturated, aliphatic polycarboxylic acids having from 2 to 20 carbon atoms and aromatic polycarboxylic acids and their carboxylates.

10. The modified silica of claim 8, wherein the at least one adsorbed polycarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, methyladipic acid, methylsuccinic acid, ethylsuccinic acid, methylglutaric acid, dimethylglutaric acid, citric acid, isocitric acid, and tartaric acid.

11. A method for reinforcing a polymer, the method comprising mixing a polymer with the modified silica of claim 8.

12. A polymer composition comprising the modified silica of claim 8.

13. An article comprising at least one composition as claimed in claim 12.

14. The article of claim 13, 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.

Description

EXAMPLES

Examples 1 and 2

[0106] Zeosil 1165MP (commercially available form Solvay) having a BET specific surface of 153 m.sup.2/g; a CTAB specific surface of 160 m.sup.2/g; a Al content of 0.33% by weight; a dispersive component of the surface energy y.sub.s.sup.d of 48 mJ/m.sup.2 and a ratio V2/V1 of 60 was used as a starting material for the preparation of a modified silica.

[0107] A solution in water (at 34 wt %) of a polycarboxylic acid mixture was prepared by dissolving (at 35 C.) a mixture of polycarboxylic acids having the following composition: 94.8 wt % of 2-methylglutaric acid, 4.9 wt % of ethylsuccinic anhydride, and 0.2 wt % of adipic acid and 0.1 wt % of others and then adjusting the pH to 6.5 with a 10M solution of NaOH.

[0108] 400 g of Zeosil 1165MP were placed in a blade mixer (WAM MAP MLH 631002, internal volume 2 I). The solution of the polycarboxylic acid mixture was injected into the mixer operating at 150 rpm through a nozzle at a pressure of 1 bar and at room temperature. The injection operation was carried out over a period 5 minutes at an injection rate of 3.3 ml/min to obtain a polycarboxylic acid/SiO.sub.2 weight ratio of 1.0%.

[0109] Following a similar procedure a modified silica having a polycarboxylic acid/SiO.sub.2 weight ratio of 1.5% was obtained by injecting a polycarboxylic acid mixture prepared by dissolving (at 35 C.) a mixture of polycarboxylic acids having the following composition: 94.8 wt % of 2-methylglutaric acid, 4.9 wt % of ethylsuccinic anhydride, and 0.2 wt % of adipic acid and 0.1 wt % of others at an injection rate of 3.6 ml/min for 5 minutes.

[0110] The characteristics of the inventive silica S1 and S2 obtained (in the form of substantially spherical beads) were the following:

TABLE-US-00002 S1 S2 Content of carboxylic acid + 0.25 0.37 carboxylate (C) (%) BET (m.sup.2/g) 148 145 CTAB (m.sup.2/g) 153 157 .sub.s.sup.d (mJ/m.sup.2) 36 33 Water uptake (%) 9.5 8.9 V2/V1 (%) 59 60 pH 6.1 4.6

Examples 3 and 4 and Comparative Example 1

[0111] The following materials were used in the preparation of SBR-based elastomeric compositions:

[0112] SBR: SBR Buna VSL5025-2 from Lanxess; with 50+/4% of vinyl units; 25+/2% of styrene units; Tg in the vicinity of 20 C.; 100 phr of SBR extended with 37.5+/2.8% by weight of oil/

[0113] BR: oil Buna CB 25 from Lanxess

[0114] CS1: Silica Zeosil 1165 MP commercially available from Solvay

[0115] S1: Modified silica prepared according to the process present invention as described in Example 1

[0116] S2: Modified silica prepared according to the process present invention as described in Example 2

[0117] Coupling agent: Luvomaxx TESPT from Lehvoss France sari

[0118] Plasticizer: Nytex 4700 naphtenic plasticizer from Nynas

[0119] Antioxidant: N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine Santoflex 6-PPD from Flexsys

[0120] DPG: Diphenylguanidine; Rhenogran DPG-80 from RheinChemie

[0121] CBS: N-Cyclohexyl-2-benzothiazolesulfenamide; Rhenogran CBS-80 from RheinChemie

[0122] The compositions of the elastomeric blends, expressed as parts by weight per 100 parts of elastomers (phr), are shown in Table I below, were prepared in an internal mixer of Brabender type (380 ml) according to the following procedure.

[0123] The preparation the compositions was carried out in two successive preparation phases: a first phase consisting of a high-temperature thermo-mechanical working, followed by a second phase of mechanical working at temperatures of less than 110 C. This phase makes it possible the introduction of the vulcanization system.

[0124] The first phase was carried out using a mixing device, of internal mixer type, of Brabender brand (capacity of 380 ml). The filling coefficient was 0.6. The initial temperature and the speed of the rotors were set on each occasion so as to achieve mixture dropping temperatures of approximately 140-170 C.

[0125] During the first phase it was possible to incorporate, in a first pass, the elastomers and then the reinforcement filler (introduction in installments) with the coupling agent and stearic acid. For this pass, the duration was between 4 and 10 minutes.

[0126] After cooling the mixture (to a temperature of less than 100 C.), a second pass made it possible to incorporate zinc oxide and the protecting agents/antioxidant. The duration of this pass was between 2 and 5 minutes.

[0127] After cooling the mixture (to a temperature of less than 100 C.), the vulcanization system (sulfur and accelerators, such as CBS) was added to the mixture. The second phase was carried out in an open mill, preheated to 50 C. The duration of this phase was between 2 and 6 minutes.

[0128] Each final mixture was subsequently calendered in the form of plaques with a thickness of 2-3 mm.

TABLE-US-00003 TABLE I Composition Example 3 Example 4 Comparative Ex. 1 SBR 103.0 103.0 103.0 BR 25.0 25.0 25.0 S1 80.0 S2 80.0 CS1 80.0 Coupling agent 6.4 6.4 6.4 Plasticizer 7.0 7.0 7.0 Carbon black (N330) 3.0 3.0 3.0 ZnO 2.5 2.5 2.5 Stearic acid 2.0 2.0 2.0 Antioxidant 1.9 1.9 1.9 DPG 1.5 1.5 1.5 CBS 2.0 2.0 2.0 Sulphur 1.1 1.1 1.1

[0129] Subsequently, the mechanical and dynamic properties of the mixtures vulcanized at the curing optimum (T98) were measured according to the following general procedure.

[0130] Rheological Properties

[0131] Viscosity of the Raw Mixtures

[0132] The Mooney viscosity was measured on the compositions in the raw state at 100 C. using an MV 2000 rheometer. Mooney stress-relaxation rate was according to the standard NF ISO 289.

[0133] The value of the torque, read at the end of 4 minutes after preheating for one minute (Mooney Large (1+4)at 100 C.), is shown in Table II. The test was carried out on the raw mixtures after aging for 3 weeks at a temperature of 23+/3 C.

TABLE-US-00004 TABLE II Comp. Compositions Example 3 Example 4 Example 1 ML (1 + 4) - Initial 74 73 82 100 C. Mooney relaxation Initial 0.340 0.324 0.304 ML (1 + 4) - After 7 days 83 83 102 100 C. (23 +/ 3 C.) Mooney relaxation After 7 days 0.297 0.284 0.233 (23 +/ 3 C.) ML (1 + 4) - After 21 days 83 82 104 100 C. (23 +/ 3 C.) Mooney relaxation After 21 days 0.295 0.288 0.250 (23 +/ 3 C.)

[0134] Compositions comprising the modified silicas S1 and S2 of the present invention have a significantly reduced initial raw viscosity with respect to compositions comprising a precipitated silica of the prior art (Comp. Ex. 1). The reduced viscosity of the compositions comprising the silica S1 and S2 with respect to reference compositions is maintained more constant even after ageing. A satisfactory Mooney relaxation over time is also observed.

[0135] Rheometry Testing

[0136] The measurements were carried out on the compositions described above in the raw state. Rheology testing was carried out at 160 C. using a Monsanto ODR rheometer according to standard NF ISO 3417. According to this test, the composition was placed in the test chamber (completely filling the chamber) regulated at the temperature of 160 C. for 30 minutes, and the resistive torque opposed by the composition to a low-amplitude) (3) oscillation of a biconical rotor included in the test chamber was measured.

[0137] The following parameters were determined from the curve of variation in the torque as a function of time: [0138] the minimum torque (Tmin), which reflects the viscosity of the composition at the temperature under consideration; [0139] the maximum torque (Tmax); [0140] the delta torque (T=TmaxTmin), which reflects the degree of crosslinking brought about by the action of the crosslinking system and, when needed, of the coupling agents; [0141] the time T98 necessary to obtain a degree of vulcanization corresponding to 98% of complete vulcanization (this time is taken as vulcanization optimum); and [0142] the scorch time TS2, corresponding to the time which is required increase the torque of 2 points above the minimum torque at the temperature under consideration (160 C.) and which reflects the time during which it is possible to process the raw mixture at this temperature without having initiation of vulcanization.

[0143] The results obtained for the compositions of Examples 3 and 4 and Comparative Example 1 are shown in Table III.

TABLE-US-00005 TABLE III Comparative Example 3 Example 4 Example 1 Tmin (dN .Math. m) 15.5 14.8 17.9 Tmax (dN .Math. m) 59.3 59.5 59.2 Delta torque (dN .Math. m) 43.8 44.7 41.3 TS2 (min) 5.4 5.9 4.0 T98 (min) 23.6 24.4 26.7 T98 T2 (min) 11.1 12.0 14.0

[0144] It was found that the compositions comprising the modified silica of the invention (Examples 3 and 4) exhibit a satisfactory combination of rheological properties.

[0145] In particular, while having a reduced raw viscosity (as discussed above), they showed a lower minimum torque value, which reflects a greater processability of the composition.

[0146] The higher scorch time of the compositions of Examples 3 and 4 also indicate that said compositions are easier to process with respect to the compositions using non-modified silica of the prior art.

[0147] Determination of the Mechanical Properties

[0148] The measurements were carried out on the optimally vulcanized compositions (T98) obtained at a temperature of 160 C.

[0149] Uniaxial tensile tests were carried out in accordance with standard NF ISO 37 with test specimens of H2 type at a rate of 500 mm/min on an Instron 5564 device. The x % moduli, corresponding to the stress measured at x % of tensile strain, were expressed in MPa.

[0150] A reinforcing index (RI) was determined which is equal to the ratio of the modulus at 300% strain to the modulus at 100% strain.

[0151] The Shore A hardness measurement on the vulcanisates was carried out according to standard ASTM D 2240, using a measurement time of 15 seconds. The properties are reported in Table IV.

TABLE-US-00006 TABLE IV Comp. Compositions Example 3 Example 4 Example 1 10% Modulus (MPa) 0.4 0.4 0.5 100% Modulus (MPa) 2.1 2.1 2.1 300% Modulus (MPa) 12.1 11.6 11.6 Resistance at break (MPa) 19.2 18.1 18.4 Deformation at break (%) 407 401 406 RI 5.8 5.5 5.5 Shore A hardness - 15 s (pts) 57 57 59

[0152] It was found that the compositions comprising the modified silica of the invention (Examples 3 and 4) exhibit a good compromise in mechanical properties, with respect to what is obtained with the reference composition.

[0153] Determination of the Dynamic Properties

[0154] The dynamic properties were measured on a viscosity analyser (Metravib VA3000) according to standard ASTM D5992.

[0155] The values for loss factor (tan ) and compressive dynamic complex modulus (E*) were recorded on vulcanized samples (cylindrical test specimen with a cross section of 95 mm.sup.2 and a height of 14 mm). The sample was subjected at the start to a 10% pre-strain and then to a sinusoidal strain in alternating compression of plus or minus 2%. The measurements were carried out at 60 C. and at a frequency of 10 Hz. The data obtained for the compositions of Examples 3 and 4 and Comparative Example 1 are reported in Table V.

TABLE-US-00007 TABLE V Comparative Compositions Example 3 Example 4 Example 1 E*, 60 C., 10 Hz (MPa) 6.4 6.6 7.2 Tan , 60 C., 10 Hz 0.118 0.120 0.137

[0156] The use of the modified silica S1 and S2 of the present invention (Examples 3 and 4) makes it possible to improve the maximum value of the loss factor with respect to the control mixture.

[0157] The data in Tables II to V show that compositions comprising the modified silica of the invention are characterized by a good compromise among processing, reinforcement and hysteresis properties, with respect to reference compositions, in particular with a gain in raw viscosity, scorch time and vulcanization speed.

Example 5

[0158] Zeosil 165GR (commercially available form Solvay) having a BET specific surface of 154 m.sup.2/g; a CTAB specific surface of 150 m.sup.2/g and a Al content of 0.32% by weight was used as a starting material for the preparation of a modified silica.

[0159] A solution in water (at 34 wt %) of a polycarboxylic acid mixture was prepared by dissolving (at 35 C.) a mixture of polycarboxylic acids having the following composition: 94.8 wt % of 2-methylglutaric acid, 4.9 wt % of ethylsuccinic anhydride, and 0.2 wt % of adipic acid and 0.1 wt % of others.

[0160] 700 g of Zeosil 165GR were placed in a mixer. The solution of the polycarboxylic acid mixture was injected into the mixer through a nozzle at a pressure of 1 bar and at room temperature. The injection operation was carried out over a period 12 minutes at an injection rate of 2 ml/min to obtain a polycarboxylic acid/SiO.sub.2 weight ratio of 1.2%.

[0161] The characteristics of the inventive silica S3 obtained (in the form of substantially spherical beads) were the following:

TABLE-US-00008 S3 Content of carboxylic acid + 0.42 carboxylate (C) (%) BET (m.sup.2/g) 158 CTAB (m.sup.2/g) 160 .sub.s.sup.d (mJ/m.sup.2) 36 Water uptake (%) 8.7

Example 6 and Comparative Example 2

[0162] Following the procedure of Examples 3 and 4 and using the same materials the following SBR-based elastomeric compositions were prepared, wherein CS2 identifies Zeosil 165GR.

TABLE-US-00009 TABLE VI Composition Example 6 Comparative Ex. 2 SBR 103.0 103.0 BR 25.0 25.0 S3 80.0 CS2 80.0 Coupling agent 6.4 6.4 Plasticizer 7.0 7.0 Carbon black (N330) 3.0 3.0 ZnO 2.5 2.5 Stearic acid 2.0 2.0 Antioxidant 1.9 1.9 DPG 1.5 1.5 CBS 2.0 2.0 Sulphur 1.1 1.1

[0163] Subsequently, the mechanical and dynamic properties of the mixtures vulcanized at the curing optimum (T98) were measured according to the general procedure described above. The results are reported in Tables VII to X.

TABLE-US-00010 TABLE VII Comp. Compositions Example 6 Example 2 ML (1 + 4) - 100 C. Initial 75 80 Mooney relaxation Initial 0.336 0.322 ML (1 + 4) - 100 C. After 8 days 77 86 (23 +/ 3 C.) Mooney relaxation After 8 days 0.327 0.300 (23 +/ 3 C.)

[0164] Compositions comprising the modified silica S3 has a lower initial raw viscosity with respect to the composition comprising a precipitated silica of the prior art (Comp. Ex. 2).

TABLE-US-00011 TABLE VIII Comparative Example 6 Example 2 Tmin (dN .Math. m) 15.8 16.6 Tmax (dN .Math. m) 58.5 65.5 Delta torque (dN .Math. m) 42.7 48.9 TS2 (min) 5.8 4.4 T98 (min) 26.7 20.5 T98 T2 (min) 21.0 16.1

[0165] It was found that the compositions comprising the modified silica of the invention (Example 6) showed a lower minimum torque value, which reflects a greater processability of the composition.

TABLE-US-00012 TABLE IX Comp. Compositions Example 6 Example 2 10% Modulus (MPa) 0.6 0.6 100% Modulus (MPa) 2.5 2.4 300% Modulus (MPa) 12.9 11.9 Resistance at break (MPa) 21.4 20.9 Deformation at break (%) 433 450 RI 5.2 5.0 Shore A hardness - 15 s (pts) 57 58

TABLE-US-00013 TABLE X Comparative Compositions Example 6 Example 2 E*, 60 C., 10 Hz (MPa) 6.3 6.6 Tan , 60 C., 10 Hz 0.116 0.117

[0166] The data in Tables VII to X show that compositions comprising the modified silica S3 of the invention are characterized by a gain in raw viscosity and scorch time, while maintaining mechanical and dynamic properties.