WO1998037018A1 - Procede de preparation de silicagels hydrophobes plus stables a la chaleur - Google Patents

Procede de preparation de silicagels hydrophobes plus stables a la chaleur Download PDF

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WO1998037018A1
WO1998037018A1 PCT/US1998/003156 US9803156W WO9837018A1 WO 1998037018 A1 WO1998037018 A1 WO 1998037018A1 US 9803156 W US9803156 W US 9803156W WO 9837018 A1 WO9837018 A1 WO 9837018A1
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silica hydrogel
hydrophobic silica
silica
heat
hydrogel
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PCT/US1998/003156
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English (en)
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Gary T. Burns
James R. Hahn
Charles W. Lentz
Clifford C. Reese
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Dow Corning Corporation
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Priority to AU66589/98A priority Critical patent/AU6658998A/en
Publication of WO1998037018A1 publication Critical patent/WO1998037018A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3081—Treatment with organo-silicon compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/16—Preparation of silica xerogels
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/22—Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/90—Other properties not specified above

Definitions

  • the present invention is a method for the preparation of hydrophobic silica gels with improved heat stability which are useful as reinforcing fillers in silicone rubber compositions.
  • the method comprises two steps, where in the first step a silica hydrosol is heat treated in the presence of a strong mineral acid at a pH less than 1 to form a silica hydrogel.
  • the silica hydrogel is contacted with an organosilicon compound and a water soluble compound of cerium or iron in the presence of a catalytic amount of a strong acid to effect hydrophobing of the silica hydrogel thereby forming a heat-stabilized hydrophobic silica hydrogel having a surface area within a range of 100 m.2/g to 750 rn ⁇ /g as measured in the dry state.
  • the hydrophobic silica hydrogel is contacted with a sufficient quantity of a water-immiscible organic solvent to convert the hydrophobic silica hydrogel into a hydrophobic silica organogel.
  • the organic solvent can then be removed from the organogel to form a hydrophobic silica gel having a surface area within a range of 100 m ⁇ g to 750 m ⁇ g as measured in the dry state.
  • hydrophobic silica gels prepared by the present method are useful in many applications such as thermal insulation, reinforcing and extending filler in natural rubbers and as filler in floatation devices, they are particularly useful as reinforcing fillers in silicone rubber compositions. It is well known that silicone rubbers formed from the vulcanization of polydiorganosiloxane fluids or gums alone generally have low elongation and tensile strength values. One means for improving the physical properties of such silicone rubbers involves the incorporation of a reinforcing silica filler into the fluid or gum prior to curing.
  • silica reinforcing fillers have a tendency to interact with the polydiorganosiloxane fluid or gum causing a phenomenon typically referred to as "crepe hardening."
  • a great deal of effort has been made in the past to treat the surface of reinforcing silica fillers with organosilanes or organosiloxanes to make the surface of the silica hydrophobic. This surface treatment reduces or diminishes the tendency of the compositions to crepe harden and improves the physical properties of the cured silicone rubber.
  • the method comprises:
  • Step (A) of the present method a silica hydrosol comprising from 0.02 g to 0.5 g of Si ⁇ 2 per ml can be used.
  • the method used to prepare the silica hydrosol is not critical and can be any of those known in the art.
  • the silica hydrosol may be prepared by deionizing sodium silicate by a method such as the use of an ion exchange resin.
  • the silica hydrosol may be prepared by hydrolyzing a silane at a low temperature. Useful methods for preparing the silica hydrosol are provided in the examples herein.
  • the silica hydrosol must comprise a sufficient concentration of a strong mineral acid such that the pH of the silica hydrosol is less than pH 1.
  • a strong mineral acid such that the pH is essentially 0, that is so that the pH cannot be measured.
  • any strong mineral acid can be used.
  • strong mineral acid refers to those acids which ionize to the extent of at least 25 percent in 0.1 N aqueous solution at 18°C.
  • the strong mineral acid may be hydrochloric, hydroiodic, sulfuric, nitric and phosphoric acid.
  • step (A) the silica hydrosol is heated at a temperature within a range of 20 to 250°C. Preferred is when the silica hydrosol is heated at a temperature within a range of 75 to 150°C. Even more preferred is when, in step (A), the silica hydrosol is heated at a temperature within a range of 90 to 110°C.
  • step (A) the heating time required varies with the temperature and acid concentration. Generally, the higher the temperature and the greater the acid concentration the shorter the heating time needed.
  • the heating of step (A) must be continued until the silica hydrogel acquires a structure such that the final product after hydrophobing has a surface area in the dry state within a range of 100 myfyg to 750 m ⁇ /g as determined by the Brunauer Emmett and Teller (BET) method described in the Jour. Am. Chem. Soc. 60:309 (1938) and as further described in U.S. Patent No. 3,122,520.
  • BET Brunauer Emmett and Teller
  • the surface area of the silica hydrogel at the conclusion of step (A) is immaterial provided it is such that the surface area of the dried product after the hydrophobing of step (B) is within the above described range.
  • the surface area of the silica hydrogel is reduced by the hydrophobing reaction, since the organosilyl groups which become attached to the surface of the silica hydrogel increase the average particle size.
  • the surface of the silica hydrogel can be above 750 m ⁇ /g provided that the hydrophobing treatment brings it within a range of 100 rn ⁇ /g to 750 rn ⁇ /g.
  • step (A) it is necessary to proceed with the hydrophobing of step (B) and then measure the surface area of the resulting product in the dry state. If the surface area of the resulting product in the dry state is above 750 m ⁇ /g, then the acid heating conditions of step (A) were too mild. If the surface area of the resulting product in the dry state is below 100 m ⁇ /g, then the acid heating conditions of step (A) were too severe. Examples of suitable acid concentrations, temperatures and times for conduct of step (A) are provided in the Examples herein. If the surface area of the hydrophobic silica gel in the dry state is above or below the described range, the hydrophobic silica gels have diminished reinforcing properties in silicone elastomers.
  • the silica hydrogel of step (A) may be subjected to a shearing force to reduce aggregate particle size and to improve the uniformity of the particle size distribution prior to conduct of step (B).
  • the shearing force may be applied to the silica hydrogel by any of those methods known in the art.
  • the shearing force may be applied by a mechanical means such as a high-speed mixer or by ultrasound. This reduction in aggregate particle size and improved uniformity of the particle size can provide for hydrophobic silica gels which when compounded into silicone elastomer compositions provide for lower viscosity compositions, more stable compositions and for cured silicone elastomers having improved clarity and physical properties.
  • step (B) of the present method the silica hydrogel of step (A) is contacted with one or more of the defined organosilicon compounds described by formulas (1) and (2) in the presence of a catalytic amount of a strong acid and a water soluble compound of cerium or iron.
  • the strong acid can be the same acid used in step (A).
  • the silica hydrogel can be washed free of acid and a catalytic amount of strong acid added either prior to, simultaneously with or subsequent to, the addition of the organosilicon compound.
  • the catalytic amount of the strong acid can be generated in situ by hydrolysis of the chlorosilane or the reaction of the chlorosilane directly with hydroxyls of the silica hydrogel.
  • the limitations on pH as described for step (A) do not apply. It is only necessary that a catalytic amount of a strong acid be present in an amount sufficient to effect reaction of the organosilicon compound with the silica hydrogel. Examples of useful acids include hydrochloric, sulfuric and benzene sulfonic. It is preferred that in step (B) the strong acid catalyst provide a pH less than 2.5.
  • the temperature at which the hydrophobing of step (B) is conducted is not critical and can be from 20 to 250°C. Generally, it is preferred that the hydrophobing of step (B) be conducted at a temperature within a range of 30 to 150°C. The hydrophobing of step (B) can be conducted at the reflux temperature of the water-immiscible organic solvent when present.
  • step (B) the silica hydrogel of step (A) is reacted with an organosilicon compound described by formula (1) or (2).
  • each R! can be independently selected from hydrocarbon radicals comprising 1 to 12 carbon atoms and organofunctional hydrocarbon radicals comprising 1 to 12 carbon atoms, R! can be a saturated or unsaturated hydrocarbon radical.
  • R* can be a substituted or non-substituted hydrocarbon radical.
  • R* can be alkyl radicals such as methyl, ethyl, propyl, tert-butyl, hexyl, heptyl, octyl, decyl and dodecyl; alkenyl radicals such as vinyl, allyl and hexenyl; substituted alkyl radicals such as chloromethyl, 3,3,3-trifluoropropyl and 6-chlorohexyl; and aryl radicals such as phenyl, naphthyl and tolyl.
  • R ⁇ can be an organofunctional hydrocarbon radical comprising 1 to 12 carbon atoms where the functionality is mercapto, disulfide, polysulfide, arnino, carboxylic acid, carbinol, ester or amido.
  • a preferred organofunctional hydrocarbon radical is one having disulfide or polysulfide functionality.
  • each X is independently selected from halogen and alkoxy radicals comprising 1 to 12 carbon atoms.
  • halogen it is preferred that the halogen be chlorine.
  • X is an alkoxy radical, X may be methoxy, ethoxy and propoxy. Preferred is where each X is selected from chlorine atoms and methoxy.
  • the viscosity of the organosiloxanes described by formula (2) is not limiting and can range from that of a fluid to a gum. Generally, higher molecular weight organosiloxanes will be cleaved by the acidic conditions of the present method allowing them to react with the silica hydrogel.
  • the organosilicon compound may be provided to the present method as a single compound as described by formula (1) or (2) or as a mixture of two or more organosilicon compounds described by formulas (1) and (2).
  • organosilicon compounds include diethyldichlorosilane, allylmethyldichlorosilane, methylphenyldichlorosilane, phenylethyldiethoxysilane, 3,3,3- trifluoropropylmethyldichlorosilane, trimethylbutoxysilane, sym- diphenyltetramethyldisiloxane, trivinyltrimethylcyclotrisiloxane, hexaethyldisiloxane, pentylmethyldichlorosilane, divinyldipropoxysilane, vinyldimethylchlorosilane, vinylmethyldichorosilane, vinyldimethylmethoxysilane, trimethylchlorosilane, hexamethyldisiloxane, hexenylmefhyldichlorosilane, hexenyldimethylchlorosilane, dimethylchloros
  • the organosilicon compound be hexamethyldisiloxane or dimethyldichlorosilane.
  • the amount of organosilicon compound added to the method is that sufficient to adequately hydrophobe the silica hydrosol to provide a hydrophobic silica gel suitable for its intended use.
  • the organosilicon compound should be added to the method in an amount such that there is at least 0.04 organosilyl unit per Si ⁇ 2 unit in the silica hydrogel.
  • the upper limit of the amount of organosilicon compound added to the process is not critical since any amount in excess of the amount required to saturate the silica gel will act as a solvent for the method.
  • Step (B) of the present method requires the presence of an effective amount of a heat stabilizing agent selected from water soluble compounds of cerium and iron.
  • a heat stabilizing agent selected from water soluble compounds of cerium and iron.
  • a heat stabilizing agent selected from water soluble compounds of cerium and iron.
  • Such compositions can include silicone rubber, natural rubber and synthetic rubber. Generally, 0.01 percent weight/volume (% Wt. Vol.) to 10 %Wt./Nol. of the water soluble compound of cerium or iron in relation to the volume of components in step (B), excluding solvents, is considered useful in the present process.
  • water soluble compound of cerium or iron comprises 0.1 %Wt./Nol. to 1 %Wt./Vol. on the same basis.
  • water soluble compounds which may be useful in the present method include FeCl3, FeBr2, FeBr3.6H2 ⁇ , FeCl 2 .4H2 ⁇ , Fel2.4H2 ⁇ , Fe(NO3)3.6H2O,
  • a preferred water soluble compound of cerium and iron for use in the present method is selected from FeCl3 and CeCl3.9H2O.
  • the hydrophobic silica hydrogel of step (B) may be used as is or may be recovered for use by such methods as centrifugation or filtration.
  • the hydrophobic silica hydrogel may be dried by the use of such methods as heating or reducing pressure or a combination of both heating and reducing pressure.
  • a water-immiscible organic solvent in sufficient amount to convert the silica hydrogel or hydrophilic silica hydrogel to the corresponding organogel is added.
  • the organic solvent can be added prior to, simultaneously with or subsequent to, the addition of the organosilicon compound. That is the silica hydrogel can be first converted into an organogel by replacement of the water with the organic solvent.
  • the organosilicon compound and the organic solvent can be added simultaneously to the silica hydrogel. Under these conditions, the reaction of the silica hydrogel with the organosilicon compound and the replacement of the water in the silica hydrogel with the organic solvent may occur simultaneously.
  • organosilicon compound can be added prior to the organic solvent, in which case the silica hydrogel reacts with the organosilicon compound and the resulting product is then converted into an organogel by an addition of an organic solvent.
  • the conversion to an organogel is accomplished by a phase separation in which the hydrophobic silica gel passes into the organic solvent phase.
  • a preferred method is where a water-immiscible organic solvent is added after formation of the hydrophobic silica hydrogel thereby effecting formation of a hydrophobic silica organogel.
  • any organic solvent immiscible with water can be employed.
  • suitable solvents include low molecular weight siloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, diphenyltetramethyldisiloxane and trimethylsilyl endblocked dimethylpolysiloxane fluids.
  • siloxane When a siloxane is employed as a solvent, it may serve both as a solvent and as a reactant with the silica hydrogel.
  • suitable solvents include aromatic hydrocarbons such as toluene and xylene; heptane and other aliphatic hydrocarbon solvents; cycloalkanes such as cyclohexane; ethers such as diethylether and dibutylether; halohydrocarbon such as methylene chloride, chloroform, ethylene chloride and chlorobenzene; and ketones such as methylisobutylketone.
  • the amount of water-immiscible organic solvent is not critical so long as there is sufficient solvent to convert the silica hydrogel into a silica organogel.
  • the solvent should have a boiling point below 250°C. to facilitate its removal from the hydrophobic silica organogel, however the boiling point is not critical since the solvent may be removed from the hydrophobic silica organogel by centrifuging or other suitable means.
  • hydrophobic silica organogel may be used directly as a reinforcing agent in silicone rubber or in any other uses for which this type of product can be used.
  • the solvent may be removed from the hydrophobic silica organogel and the resulting dry material used.
  • a surfactant or water-miscible solvent to facilitate the reaction of the organosilicon compound with the silica hydrogel.
  • the surfactant of water-miscible solvent may be added in the presence or absence of any water-immiscible organic solvent added to the method.
  • Suitable surfactants can include anionic surfactants such as dodecylbenzene sulfonic acid, nonionic surfactants such as polyoxylene(23)lauryl ether and (Me3SiO)2MeSi(CH2)3(OCH2CH2)7OMe where
  • Me is methyl and cationic surfactants such as N-alkyltrimethyl ammonium chloride.
  • Suitable water miscible solvents can include alcohols such as methanol, ethanol, propanol, n-butanol and tetrahydrofuran.
  • a silica gel hydrophobed with hexamethyldisiloxane and containing no heat stabilizing metal additive was prepared.
  • 750 ml of PQ N Clear Sodium Silicate (PQ Corporation, Valley Forge, PA) was diluted with 1350 ml of deionized water. This solution was added at a rate of 420 ml per minute to a rapidly stirred solution comprising 280 ml of concentrated hydrochloric acid (HCl) (Fisher
  • silica hydrosol prepared as described above was deionized by pumping through a 1.5 m x 5 cm column packed with 1500 ml of Dowex 50WX8-100 ion exchange resin in the acid form (The Dow Chemical Company, Midland, MI) at a rate of 60 ml minute.
  • the pH of the column effluent was monitored until the pH dropped below 0.5, at which point the remaining 2000-2400 ml of deionized silica hydrosol effluent was collected.
  • the deionized silica hydrosol was agglomerated by placing 2000 ml of the deionized silica hydrosol in a 5 L flask and while stirring adding 626 ml of concentrated HCl (Fisher Certified).
  • the silica hydrogel which formed within a few minutes of addition of the HCl was broken-up by additional stirring to form an agglomerated silica hydrogel suspension.
  • the silica hydrogel suspension was heat treated at 100°C. for 3 hours and then cooled to 40°C.
  • the heat-treated silica hydrogel suspension was hydrophobed as follows. To the heat-treated silica hydrogel suspension, with stirring, was added 872 ml of isopropanol followed by the addition of 112 ml of hexamethyldisiloxane. The resulting mixture was stirred for 45 minutes at room temperature. Then, 2.4 L of toluene were added to the mixture. This mixture was mildly stirred for an additional 5 minutes, stirring stopped and the aqueous phase drained from the bottom of the treatment flask. The toluene phase was washed with 1 L of deionized water. The treatment flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried overnight at 150°C. to remove residual toluene.
  • the yield of hydrophobic silica gel was 232 g.
  • the surface area of the dried hydrophobic silica gel was determined by the BET method as referenced, supra.
  • the iron and cerium content of the hydrophobic silica gel were determined by atomic adsorption. The results of these determinations are provided in Table 1A.
  • a silica gel hydrophobed with hexamethyldisiloxane and heat stabilized by the addition of FeCl3 was prepared.
  • a silica hydrosol comprising 0.1 g of Si ⁇ 2 ml was prepared and deionized as described in Example 1.
  • the deionized silica hydrosol was agglomerated and heat treated as described in Example 1 to form a heat-treated silica hydrogel suspension.
  • the heat-treated silica hydrogel suspension was hydrophobed and
  • FeCl3 incorporated therein as follows. To the heat-treated silica hydrogel suspension, with stirring, was added 872 ml of isopropanol, 452 ml of hexamethyldisiloxane and 5.4 g of FeCl3. The resulting mixture was stirred for 1 hour at room temperature. One liter of toluene was added to the mixture. This mixture was mildly stirred for an additional 5 minutes, stirring stopped and the aqueous phase drained from the bottom of the treatment flask. The toluene phase was washed with 500 ml of deionized water. The treatment flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried overnight at 150°C. to remove residual toluene.
  • the yield of hydrophobic silica gel was 210 g.
  • Example 3 The surface area of the dried hydrophobic silica gel and concentration of iron was determined by the methods described in Example 1.
  • the carbon and hydrogen content of the dried hydrophobic silica gel was determined by CHN analysis using a Perkin Elmer Model 2400 CHN Elemental Analyzer (Perkin Elmer Corporation, Norwalk, CT). The results of these analysis are reported in Table 1 A.
  • Example 3 The surface area of the dried hydrophobic silica gel and concentration of iron was determined by the methods described in Example 1.
  • the carbon and hydrogen content of the dried hydrophobic silica gel was determined by CHN analysis using a Perkin Elmer Model 2400 CHN Elemental Analyzer (Perkin Elmer Corporation, Norwalk, CT). The results of these analysis are reported in Table 1 A.
  • Example 3 The surface area of the dried hydrophobic silica gel and concentration of iron was determined by the methods described in Example 1.
  • the carbon and hydrogen content of the dried hydrophobic silica gel was determined by CHN analysis using a Perkin Elmer Model 2400 CHN Elemental Ana
  • silica hydrosol was filtered through a fritted glass filter funnel and the silica hydrosol poured into 40 by 60 cm pans.
  • the silica hydrosol gelled in approximately 35 minutes and was let set for an hour after gelation.
  • the silica hydrogel was cut into approximately 1 cm squares and washed with deionized water until the pH of the effluent was 3.7.
  • the silica hydrogel was adjusted to pH 6.8 with sodium hydroxide.
  • the silica hydrogel was hydrophobed and FeCl3 incorporated therein as follows.
  • the silica hydrogel was placed in a 5 L flask and, while stirring, 727 ml of concentrated HCl (Fisher Certified) added and the content of the flask refluxed for 5 hours. After refluxing, the silica hydrogel was mixed with 909 ml of isopropanol, 417 ml of hexamethyldisiloxane and 8.3 g of FeCl3. After stirring the flask content 1 hour at room temperature, 2 L of toluene were added. After stirring the flask content for an additional 5 minutes, the stirring was stopped and the aqueous phase drained from the bottom of the flask.
  • the toluene phase was washed with 500 ml of deionized water.
  • the flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was then distilled under reduced pressure leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried overnight at 150°C.
  • the dried hydrophobic silica gel was analyzed for surface area, iron content and carbon and hydrogen content as described in Example 2 and the results are reported in Table 1 A.
  • a dried silica gel hydrophobed with hexamethyldisiloxane and heat stabilized with FeCl3 was prepared.
  • Into a 5 L flask was placed 374 g of Amberlite IRC 50 resin (Rohm and Haas, Philadelphia, PA) in the hydrogen form. With stirring, 625 ml of PQ N Clear Sodium Silicate (PQ Corporation) diluted with 1875 ml of deionized water was added to the resin. When the resulting mixture reached pH 8.5, the resin was separated from the mixture by filtration. The resulting silica hydrosol was transferred to another 5 L flask, heated to reflux for two hours, cooled to 60°C, 900 ml of concentrated HCl (Fisher Certified) added.
  • This mixture was heated to reflux for 13 hours and then cooled to room temperature thereby forming a heat-treated silica hydrogel. After cooling, to the silica hydrogel was added 900 ml of isopropanol, 468 ml of hexamethyldisiloxane and 4.1 g FeCl3. The resulting mixture was stirred for 1 hour at room temperature and then 2 liters of toluene were added to the mixture. This mixture was stirred for an additional 5 minutes, then stirring stopped and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 500 ml of deionized water.
  • Example 5 The flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was distilled under reduced pressure leaving as product a hydrophobic silica gel. The hydrophobic silica gel was dried overnight at 150°C. to remove residual toluene. The yield of dried hydrophobic silica gel was 190 g. The surface area, iron content and carbon and hydrogen content of the dried hydrophobic silica gel were determined by the methods described in Example 2 and the results are reported in Table 1A. Example 5
  • a dried silica gel hydrophobed with hexamethyldisiloxane and heat stabilized by the addition of cerium trichloride hydrate was prepared.
  • a silica hydrosol comprising 0.1 g of Si ⁇ 2/ml was prepared and deionized as described in Example 1.
  • the deionized silica hydrosol was agglomerated and heat treated as described in Example 1 to form a heat-treated silica hydrogel.
  • the heat-treated silica hydrogel was hydrophobed and cerium trichloride incorporated therein as follows.
  • the resulting mixture was stirred for 45 minutes at room temperature and then 2.4 L of toluene were added to the mixture. This mixture was mildly stirred for an additional 5 minutes, stirring stopped and the aqueous phase drained from the bottom of the flask.
  • the toluene phase was washed with 1 L of deionized water.
  • Example 6 The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel. The hydrophobic silica gel was dried overnight at 150°C. to remove residual toluene. The yield of dried hydrophobic silica gel was 231 g. The surface area, cerium content and hydrogen and carbon content of the dried hydrophobic silica gel were determined by the methods described in Example 2 and the results are reported in Table IB. Example 6
  • a dried silica gel hydrophobed with hexamethyldisiloxane and vinyldimethylchlorosilane and heat stabilized by the addition of FeCl3 was prepared.
  • a silica hydrosol comprising 0.1 g of Si ⁇ 2 ml was prepared and deionized as described in
  • Example 1 The deionized silica hydrosol was agglomerated and heat treated as described in Example 1 to form a heat-treated silica hydrogel suspension.
  • the heat treated silica hydrogel suspension was hydrophobed and FeCl3 incorporated therein as follows.
  • the resulting mixture was stirred 45 minutes at room temperature and then 2.4 L of toluene were added. This mixture was mildly stirred for an additional 5 minutes, stirring stopped and the aqueous phase drained from the bottom of the flask.
  • the toluene phase was washed with 1 L of deionized water.
  • the treatment flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was distilled to remove 250 ml of the toluene.
  • the mixture was cooled to room temperature and 14.4 ml of vinyldimethylchorosilane added. This mixture was refluxed for one hour, cooled to 70°C. and 50 ml of deionized water were added. The resulting mixture was refluxed to remove the water and generated hydrochloric acid.
  • the toluene solution was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried overnight at 75°C. to remove residual toluene.
  • the yield of hydrophobic silica gel was 207 g.
  • the surface area, iron content and carbon and hydrogen content were determined by the methods described in Example 2 and the results are reported in Table IB.
  • a silica gel hydrophobed with hexamethyldisiloxane and heat stabilized with FeCl3 was prepared where the aggregate particle size of the silica hydrogel was reduced by shearing prior to hydrophobing.
  • 400 ml of PQ N Clear Sodium Silicate (PQ Corporation) was diluted with 600 ml of deionized water. This solution was added at a rate of 420 ml per minute to a rapidly stirred solution comprising 400 ml of HCl (Fisher Certified) diluted with 400 ml of deionized water to form a silica hydrogel.
  • An additional 200 ml of concentrated HCl was added and the resulting mixture heat-treated by refluxing for 3 hours.
  • silica hydrogel was sheared for 1 minute in a Waring Blender (Model 7011 , Waring Products Division of Dynamics Corporation of America, New Hartford, CT) to reduce the aggregate particle size of the silica hydrogel.
  • the silica hydrogel was hydrophobed as follows. To the silica hydrogel, with stirring in a 5 L flask, was added 666 ml of isopropanol, 90.8 ml of hexamethyldisiloxane and 4.3 g of FeCl3. The resulting mixture was stirred for 30 minutes at room temperature. Then, 2 L of toluene were added to the mixture.
  • a silica gel hydrophobed with hexamethyldisiloxane and heat stabilized with FeCl3 was prepared using colloidal silica as a starting material. 1091 ml of Nalco 1115 colloidal silica (Nalco Chemical Co., Chicago, IL) was diluted with 909 ml of deionized water to give a silica hydrosol comprising 0.1 g Si ⁇ 2 ml. To this silica hydrosol was added
  • the cooled silica hydrogel was hydrophobed as follows. To the silica hydrogel, with stirring in a 5 L flask, was added 1 L of isopropanol, 530 ml of hexamethyldisiloxane and 4.55 g of FeCl3. The resulting mixture was stirred for 1 hour at room temperature. Then, 1.5 L of toluene were added to the mixture. This mixture was stirred for an additional 5 minutes, stirring stopped and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 1 L of deionized water. The flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • Example 9 The toluene phase was removed by vacuum stripping and the remaining hydrophobic silica gel was dried overnight at 150°C. to remove residual toluene.
  • the surface area, iron content and carbon content of the dried hydrophobic silica gel were determined by the methods described in Example 2 and the results are reported in Table IB.
  • a silica gel hydrophobed with bis ⁇ 3-(triethoxysilyl)propyl ⁇ tetrasulfide and hexamethyldisiloxane and heat stabilized by the addition of FeCl3 was prepared.
  • a silica hydrosol comprising 0.1 g of Si ⁇ 2 ml was prepared and deionized as described in Example
  • the deionized silica hydrosol was agglomerated and heat-treated by placing 2 L of the deionized silica hydrosol in a 5 L flask and, while stirring, adding 626 ml of concentrated HCl (Fisher Certified). This mixture was refluxed for 3 hours and then cooled to room temperature providing a heat-treated silica hydrogel.
  • the heat-treated silica hydrogel was hydrophobed as follows. To the heat- treated silica hydrogel, with stirring, was added 872 ml of isopropanol followed by the addition of 14.4 ml of bis ⁇ 3-(triethoxysilyl)-propyl ⁇ tetrasulfide. The resulting mixture was stirred for 5 minutes and then 5.41 g of FeCl3 and 112 ml of hexamethyldisiloxane were added. After stirring for 1 hour, 2 L of toluene were added to the mixture. This mixture was mildly stirred for an additional 5 minutes, stirring stopped and the aqueous phase drained from the bottom of the flask.
  • Example 10 Each of the dried hydrophobic silica gels prepared in Examples 1 through 8 were compounded into a silicone rubber composition, the composition cured and the physical properties determined.
  • Each of the dried hydrophobic silica gels was compounded at 38 parts per hundred (pph) into a polydimethylsiloxane gum containing 0.15 mole percent vinyl radicals substituted on silicon atoms and having a plasticity of 55 to 65.
  • Into this base composition was blended 0.7 pph of 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, based on the polydimethylsiloxane gum.
  • the catalyzed base composition was cured in appropriate configurations for physical property testing by hot pressing at 34.5 MPa for 15 minutes at 175°C.
  • Example 11 The following test methods were used to test the cured silicone rubber: Tensile, ASTM D412; Elongation, ASTM D412; 100% Modulus, ASTM D412; 50% Modulus, ASTM D412; Durometer (Shore A), ASTM 2240; Tear (Die B), ASTM D624; Tear (Die C), ASTM D624; Compression set (22 h at 177°C), ASTM D395. Plasticities of the uncured compositions were measured on samples weighing two times the specific gravity of the composition that were formed into balls and rested one hour before measurement by ASTM 926. The results of this testing are provided in Table 1A and IB. In Tables 1A, IB and 2, the heading "Example No.” refers to the dried hydrophobic silica gel made by the corresponding example method. Example 11
  • Example 10 The heat stability of cured silicone rubber compositions prepared as described in Example 10 was evaluated.
  • the cured silicone rubber compositions were stored in a hot air furnace at 250°C. for the times described in Table 2 and then selected physical properties tested by the test methods referenced in Example 10. The results are reported in Table 2.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Silicon Compounds (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

Cette invention concerne un procédé de préparation de silicagels hydrophobes plus stables à la chaleur qui sont utiles en tant que charges de renforcement dans des compositions de caoutchouc de silicone. Le procédé comprend deux étapes. Dans la première étape on fait subir à un hydrosol de silice un traitement thermique en présence d'un acide minéral fort à un pH inférieur à 1 pour former un hydrogel de silice. Dans la deuxième étape on met en contact l'hydrogel de silice avec un composé organosilicié et un composé hydrosoluble de cérium ou de fer en présence d'une quantité catalytique d'un acide fort pour rendre l'hydrogel de silice hydrophobe et former ainsi un hydrogel de silice hydrophobe stabilisé par la chaleur dont la surface active, mesurée à l'état sec, se situe entre 100 m2/g et 750 m2/g. Dans un procédé de préparation préféré on met en contact l'hydrogel de silice hydrophobe avec une quantité suffisante d'un solvant organique non miscible dans de l'eau pour transformer l'hydrogel de silice hydrophobe en un organogel de silice hydrophobe.
PCT/US1998/003156 1997-02-24 1998-02-18 Procede de preparation de silicagels hydrophobes plus stables a la chaleur WO1998037018A1 (fr)

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Cited By (1)

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Publication number Priority date Publication date Assignee Title
CN109627480A (zh) * 2018-11-06 2019-04-16 青岛科技大学 一种柔性橡胶基超疏水材料制备方法

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US4360388A (en) * 1980-02-12 1982-11-23 Degussa Aktiengesellschaft Cerium containing precipitated silica, process for its production
EP0721002A2 (fr) * 1995-01-03 1996-07-10 Dow Corning Corporation Procédé de fabrication d'un élastomère organosiloxane sous forme d'une poudre fine s'écoulant librement et ayant une faible déformation permanente
US5708069A (en) * 1997-02-24 1998-01-13 Dow Corning Corporation Method for making hydrophobic silica gels under neutral conditions

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US3122520A (en) * 1959-10-05 1964-02-25 Dow Corning Method of making silicone rubber fillers
SU369131A1 (fr) * 1969-11-12 1973-02-08
FR2085772A1 (fr) * 1970-04-01 1971-12-31 Bayer Ag
US4360388A (en) * 1980-02-12 1982-11-23 Degussa Aktiengesellschaft Cerium containing precipitated silica, process for its production
EP0721002A2 (fr) * 1995-01-03 1996-07-10 Dow Corning Corporation Procédé de fabrication d'un élastomère organosiloxane sous forme d'une poudre fine s'écoulant librement et ayant une faible déformation permanente
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GAJEWSKI M.: "Modification of the surface of silica and its reinforcing effect in diene elastomers.", INTERNATIONAL POLYMER SCIENCE AND TECHNOLOGY., vol. 5, no. 1, 1978, SHAWBURY GB, pages T/69 - T/74, XP002065810 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109627480A (zh) * 2018-11-06 2019-04-16 青岛科技大学 一种柔性橡胶基超疏水材料制备方法
CN109627480B (zh) * 2018-11-06 2021-05-18 青岛科技大学 一种柔性橡胶基超疏水材料制备方法

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