WO2022101015A1

WO2022101015A1 - Whitening oral care compositions

Info

Publication number: WO2022101015A1
Application number: PCT/EP2021/079827
Authority: WO
Inventors: M. Cédric FERAL-MARTIN; Caroline FAYOLLE
Original assignee: Rhodia Operations
Priority date: 2020-11-10
Filing date: 2021-10-27
Publication date: 2022-05-19
Also published as: EP4243759A1; CN116437893A

Abstract

A precipitated silica characterised by low density of silanol groups per surface area and by good abrasion properties. The precipitated silica allows for the preparation of peroxide- based whitening oral care compositions having improved stability over time.

Description

WHITENING ORAL CARE COMPOSITIONS

Technical Field

[0001] The present invention relates to precipitated silica suitable for the use in whitening oral care compositions having improved stability over time.

Background Art

[0002] Everyday activities, including eating or drinking, cause undesirable staining of surfaces of teeth. There are a variety of compositions described in the art for preventing or treating the discoloration of teeth. The materials most commonly used in teeth whitening today are peroxides. Peroxides are generally deemed safe from a physiological standpoint, and can be effective to whiten teeth.

[0003] Oral care compositions comprising peroxides or peroxide-releasing compounds are known. One drawback of the use of peroxides is their high reactivity, which leads to decomposition of the peroxide during storage hence to lower whitening activity of the composition. In addition to that, it has been observed that the presence of precipitated silica in the formulation may induce the decomposition of peroxide or peroxidereleasing compounds. Precipitated silica is used extensively in oral care formulations as abrasive and/or thickening agent.

[0004] For instance, precipitated silica abrasives provide controlled mechanical cleaning, plaque removal and polishing of teeth. Such silica abrasives are known to interact not only with peroxide or peroxide-releasing compound but also with other active ingredients of the compositions, such as certain antimicrobial agents, fluorides and zinc compounds. Such interactions have the consequence that these active ingredients are no longer available to elicit their beneficial effects.

[0005] It would thus be advantageous to obtain oral care compositions, comprising a peroxide or peroxide-releasing compound and precipitated silica, characterised by a reduced decomposition of the peroxide or peroxide-releasing compound, hence by a longer shelf-life.

Summary of invention [0006] Object of the invention is a precipitated silica characterised by:

- a CTAB surface area SCTAB from 5 to 45 m²/g; and

- a number of OH groups per surface area equal to or lower than 2.00 OH/nm².

[0007] The expression “silica” is used herein to refer to silicon dioxide, SiO . The term “silica” is used throughout the text to refer to precipitated silica. The expression “precipitated silica” is used to refer to a synthetic amorphous silica obtained by a process wherein a silicate is reacted with an acid causing the precipitation of SiO .

[0008] The inventive silica is characterised by a number of OH groups per surface area, expressed as number of OH/nm², which is equal to or lower than 2.00 OH/nm², even less than 1.50 OH/nm², preferably less than 1.00 OH/nm². The number of OH groups per surface area is typically equal to or greater than 0.05 OH/nm², even equal to or greater than 0.10 OH/nm², preferably equal to or greater than 0.20 OH/nm². The inventive silica is advantageously characterised by a number of OH groups per surface area of 0.10 to 2.00 OH/nm², preferably of 0.15 to 1.00 OH/nm², more preferably of 0.15 to 1.00 OH/nm².

[0009] The determination of the silanol density, i.e. the number of OH groups per surface area, is determined using the ATD-ATG technique detailed hereafter.

[0010] The CTAB surface area SCTAB is at least 5 m²/g, typically at least 10 m²/g. The CTAB surface area SCTAB may be greater than 15 m²/g.

[0011] The CTAB surface area does not exceed 45 m²/g, the CTAB surface area is preferably lower than 42 m²/g, even lower than 40 m²/g.

[0012] For applications as an abrasive in toothpaste formulations, advantageous ranges of CTAB surface area SCTAB are from 15 to 42 m²/g, preferably from 15 to 40 m²/g.

[0013] The CTAB surface area is a measure of the external specific surface area as determined by measuring the quantity of N-hexadecyl-N,N,N- trimethylammonium bromide adsorbed on the silica surface at a given pH. The CTAB surface area can be determined according to the standard NF ISO 5794-1 , Appendix G (June 2010). [0014] The BET surface area SBET of the inventive silica is not particularly limited but it is at least 5 m²/g, typically at least 10 m²/g. BET surface area SBET may in certain instances be greater than 15 m²/g, even greater than 20 m²/g. BET surface area SBET is generally at most 60 m²/g. The BET surface area may advantageously be from 5 to 50 m²/g, even from 10 to 45 m²/g, preferably from 15 to 45 m²/g.

[0015] The BET surface area is determined according to the Brunauer - Emmett - Teller method described in The Journal of the American Chemical Society, Vol. 60, page 309, February 1938, and corresponding to the standard NF ISO 5794-1 , Appendix D (June 2010).

[0016] The inventive silica is characterised by a good balance of abrasive properties, that is ability to remove the pellicle deposit of the teeth without damaging the enamel.

[0017] The silica is characterised by an abrasion depth value Hm, as determined using the PMMA abrasion test described hereafter, between 3.5 and 25.0 pm, even between 3.5 and 20.0 pm, preferably between 4.0 and 18.0 pm, more preferably between 4.0 and 15.0 pm.

[0018] The silica is further characterised by a Relative Dentin Abrasion (RDA), determined according to the method detailed hereafter, between 100 and 200, typically between 120 and 190.

[0019] The second object of the invention is an oral care composition comprising a peroxide-releasing compound and the precipitated silica which is the first object of the invention, that is a precipitated silica characterised by:

- a CTAB surface area SCTAB from 5 to 45 m²/g; and

- a number of OH groups per surface area equal to or lower than 2.00 OH/nm².

[0020] The expression “peroxide-releasing compound” is used herein to refer to hydrogen peroxide, peroxides as well as any compound capable to release hydrogen peroxide under the conditions of use in an oral care application. Notable, non-limiting examples of peroxide-releasing compounds are include hydroperoxides, hydrogen peroxide, peroxides of alkali and alkaline earth metals, organic peroxy compounds, peroxy acids, pharmaceutically-acceptable salts thereof, and mixtures thereof. Peroxides of alkali and alkaline earth metals include lithium peroxide, potassium peroxide, sodium peroxide, magnesium peroxide, calcium peroxide, barium peroxide, and mixtures thereof. Organic peroxy compounds include urea peroxide, glyceryl hydrogen peroxide, alkyl hydrogen peroxides, dialkyl peroxides, alkyl peroxy acids, peroxy esters, diacyl peroxides, benzoyl peroxide, and monoperoxyphthalate, and mixtures thereof. Peroxy acids and their salts include organic peroxy acids such as alkyl peroxy acids, and monoperoxyphthalate and mixtures thereof, as well as inorganic peroxy acid salts such as and perborate salts of alkali and alkaline earth metals such as lithium, potassium, sodium, magnesium, calcium and barium, and mixtures thereof. Preferred solid peroxides are sodium perborate, urea peroxide, and mixtures thereof.

[0021] The peroxide-releasing compound may be bound to a polymer such as polymers of poly(vinylpyrrolidone), polyacrylates, polymethacrylates.

[0022] The oral care composition typically contains from 1 to 50%, typically from 3 to 40%, preferably from 3 to 20 % by weight of the peroxide-releasing compound.

[0023] The oral care composition contains from 3 to 60%, typically from 5 to 50%, preferably from 5 to 30 % by weight of the inventive silica.

[0024] The composition of the invention may include other ingredients commonly used in oral care applications, in particular other water-insoluble inorganic abrasive agents, thickening agents, moisturizers, surfactants, and the like. Other abrasive agents which may be mentioned in particular are calcium carbonate, hydrated alumina, bentonite, aluminium silicate, zirconium silicate and sodium, potassium, calcium and magnesium metaphosphates and phosphates.

[0025] Among thickening agents mention may be made in particular of xanthan gum, guar gum, carrageenans, cellulose derivatives and alginates, in a quantity that can range up to 5 % by weight of the composition.

[0026] Among the moisturizers mention may be made, for example, of glycerol, sorbitol, polyethylene glycols, polypropylene glycols and xylitol, in a quantity of the order of 2 to 85 %, preferably of the order of 10 to 70 % of the weight of composition, expressed on dry basis. [0027] The inventive composition may additionally comprise surface-active agents, detergent agents, colorants, bactericides, fluorine derivatives, opacifiers, sweeteners, antitartar and antiplaque agents, sodium bicarbonate, antiseptics, enzymes, etc.

[0028] In a preferred embodiment of the invention, the composition further comprises antibacterial agent. Notable non-limiting examples of suitable antibacterial agents are chlorhexidine and chlorhexidine salts, such as bigluconate or diacetate, triclosan, cetylpyridinium chloride, benzalconium chloride and cetyltrimethylammonium bromide.

[0029] It has been observed that the use of a the inventive silica not only increases the stability of the inventive composition towards the loss of peroxide activity but it also increases the stability of antibacterial agents, and in particular antibacterial agents containing chlorhexidine.

[0030] Thus, in this embodiment of the invention, the oral care composition comprises a peroxide-releasing compound, an antibacterial agent containing chlorhexidine and the inventive precipitated silica.

[0031] The inventive silica may further exhibit a good compatibility with respect to cations which are customarily present in oral care compositions. Notable non limiting examples of said cations are for instance, calcium, strontium, barium, manganese, indium, nickel, zinc, titanium, zirconium, silver, palladium, ammonium or amino cations. These cations may be in the form of mineral salts, for example chloride, fluoride, nitrate, phosphate, sulfate or in the form of organic salts such as acetates, citrates.

[0032] In a further embodiment of the invention, the oral care composition comprises a peroxide-releasing compound, an antimicrobial agent containing chlorhexidine, a Zn containing salt and the inventive precipitated silica.

[0033] Advantageously, the inventive composition has a compatibility with zinc, as determined using the Zn compatibility method described hereafter, of at least 50%.

[0034] In preferred embodiments of this invention, the oral composition is a dentifrice. Such dentifrices may include toothpaste (dental cream), tooth powders, or gel, or any other form known to one skilled in the art. [0035] In a preferred embodiment of the invention the dentifrice is characterised by a Relative Dentine Abrasion (RDA), measured on the formulation as detailed hereafter, of 90 to 200, typically of 100 to 160.

[0036] The dentifrice is characterised by a Pellicle Cleaning Ratio (PCR), measured on the formulation as detailed hereafter, between 75 and 110, typically between 80 to 100.

[0037] The inventive oral care composition may be used for the cleaning of teeth.

[0038] A further object of the invention is a process for the preparation of the inventive precipitated silica, said process comprising the steps of: providing a precipitated silica, hereinafter defined as the “Starting Silica”; and submitting said precipitated silica to a thermal treatment at a temperature of 400 to 650°C for 1 to 180 minutes.

[0039] The Starting Silica may be in any form, such as a powder, granules, or substantially spherical beads.

[0040] The Starting Silica is characterised by a number of OH groups per surface area higher than 2.00 OH/nm². The Starting Silica is characterised by a number of OH groups per surface area higher than 10.00 OH/nm², typically higher than 20 OH/nm², even higher than 40 OH/nm², in some instances higher than 50 OH/nm².

[0041] The thermal treatment may be carried out using any suitable equipment. Notable non-limiting examples of suitable equipment for the thermal treatment is for instance a rotating oven.

[0042] In a further embodiment, the process for the preparation of the modified silica comprises the steps of:

- providing a Starting Silica;

- heating said Starting Silica to a temperature of 400 to 650°C;

- holding said Starting Silica at a temperature of 400 to 650°C for 1 to 150 minutes; and

- cooling the resulting precipitated silica.

[0043] The thermal treatment is preferably performed at a temperature of 500 to 650°C, more preferably at a temperature of 550 to 650 °C. [0044] The precipitated silica is preferably held at the thermal treating temperature for 30 to 150 minutes, preferably for 30 to 120 minutes. The duration of the thermal treatment is adjusted so that the number of the OH groups per surface area are reduced from the initial value of the Starting Silica to a value below 2.0 OH/nm².

[0045] The Starting Silica may be any precipitated silica which is suitable for use as an abrasive silica in oral care application.

[0046] The Starting Silica typically has a surface area CTAB of less than 50 m²/g, typically between 5 and 50 m²/g.

[0047] Notable non-limiting examples of suitable commercially available precipitated silicas which can be used as Starting Silica are for instance : Tixosil® 73, Tixosil® 63, Tixosil® SoftClean, all available from Solvay SA.

[0048] A further object of the present invention is a method for reducing the decomposition of peroxide-releasing compounds in an oral care composition comprising a peroxide-releasing compound and precipitated silica, said method characterized in that the precipitated silica is a precipitated silica characterised by:

- a CTAB surface area SCTAB from 5 to 45 m²/g; and

- a number of OH groups per surface area equal to or lower than 2.0 OH/nm².

[0049] The use of the inventive precipitated silica as above detailed allows obtaining peroxide-containing compositions which retain their peroxide activity over a long period of time.

[0050] Additionally the use of the inventive precipitated silica allows at the same time to maintain high over time the availability of both chlorhexidine based antibacterial agents as well as zinc based compounds.

[0051] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0052] The invention will be now described in more detail with reference to the following examples whose purpose is merely illustrative and not limitative of the scope of the invention. [0053] ANALYTICAL METHODS

[0054] The physicochemical properties of the precipitated silica of the invention were determined using the methods described hereafter.

[0055] Determination of CTAB surface area

[0056] CTAB surface area (SCTAB) values were determined according to an internal method derived from standard NF ISO 5794-1 , Appendix G.

[0057] Determination of BET surface area

[0058] BET surface area SBET was determined according to the Brunauer - Emmett - Teller method as detailed in standard NF ISO 5794-1 , Appendix E (June 2010) with the following adjustments: the sample was pre-dried at 200°C±10°C; the partial pressure used for the measurement P/P° was between 0.05 and 0.3.

[0059] Silanol density determination

[0060] The samples were analyzed using ATD-ATG technique on Mettler's

LF1100 thermobalance and a Tensor 27 Bruker spectrometer equipped with a gas cell, with the following program: Temperature rise from 25°C to 1100°C at 10°C/min, under air (60 mL/min), in AI2O3 crucible of 150 pL. The silanol density is directly related to the loss of mass between 200°C and 800°C. The loss of mass (%) between 200°C and 800°C is identified as AW% this value.

[0061] The silanol ratio (mmol/g) is defined by:

TsiOH = AW*2*1000 / (18.015*100) = 1.11 *AW

[0062] Silanol density (OH/nm²) is calculated by :

D = TsiOH*Na I 10²¹*SBET ⁼ TsiOH*602.2/ SBET wherein Na : Avogadro’s number

[0063] Determination of peroxide stability

[0064] The compatibility of silica with a hydrogen peroxide solution was determined by the method described below.

[0065] A solution of URECO HC L17 (molecular weight = 277.18 g/mol; 17 wt% in hydrogen peroxide), an organic peroxide-releasing compound, at 2 wt% was prepared by dispersion of the solution into water. The hydrogen peroxide solution used was (solution A). [0066] Starting from solution A, a suspension containing 10 wt% of silica, 2 wt% of hydrogen peroxide was prepared. The suspension thus obtained was stirred for 7 days at 25°C (suspension B).

[0067] Between 3 and 4 g of the suspension maintained under agitation were placed in a bottle which can be closed. After sampling, 2 g of KI and 5 mL of acetic acid (99 wt%) were added to the suspension. The bottle was closed and protected from light and the reaction between hydrogen peroxide and the iodide allowed to proceed for 25 minutes.

[0068] A iodometry dosing was then performed on suspension B. The unreacted iodine was dosed using a sodium thiosulfate solution at 0.1 mol/L with a Pt titrode.

[0069] The hydrogen peroxide compatibility was calculated as the ratio of peroxide hydrogen available in suspension B with respect to the initial value according to the following formula:

H2O2 in suspension B H2O2 compatibility (%) = — . - - — - - — x 100

H2O2 in solution A

[0070] Determination of abrasion depth Hm

[0071] Abrasivity of silica was determined according to an internal method using poly(methyl methacrylate) (PMMA) plates as a substrate. Method is correlated to state of the art abrasivity test Relative Dentine Abrasion (RDA) (F. Peditto et al. “Which Alternatives to ISO11609 RDA? PMMA Abrasion Test with Silicas”, IADR GA Seattle, 2013).

[0072] Cast PMMA plates (Altuglas CN, Atoglas, Shore D hardness 60-70) 89 x 20 x 7.5 mm were used as substrate. On each plate a 3 mm wide zone for brushing (Testing area) was defined using adhesive tape and then sumitted to brushing for 10000 cycles using toothbrushes Brosserie Franpaise, held at 15° angle and under a 240 g load, in the presence of slurries of abrasive silica prepared according to ISO11609:2010 protocol. The abrasion depth (Hm, expressed in pm) at the end of the brushing cycles was measured across a 20 x 10 mm area including the Testing area by optical profilometry (Altimet Altisurf 500) on rinsed plates. The area around the Testing area was used to define the baseline for the optical profilometry determination. [0073] Determination of Relative Dentine Abrasion (RDA) on toothpaste formulation or on powder

[0074] The Relative Dentin Abrasions (RDA) of the toothpaste compositions obtained as described above or on the precipitated silica of the invention (in powder form) were determined according to the method set forth by Hefferen, Journal of Dental Res., July-August 1976, 55 (4), pp. 563-573, and recommended by ISO norm 11609. RDA values are unitless.

[0075] Toothpaste formulations described in Table 1 were prepared in a GUEDll reactor (4.5 L) according to the protocol detailed Table 1 below. Silicas from the invention were used in the formulation in an amount of 11 wt%. Pre-gel was prepared in a RAYNERI mixer, adding ingredients at 1000- 1500 rpm, the day before mixing on the GUEDll reactor.

[0076] Inorganic fillers and other additives were incorporated when mixing was stopped and before mixing under vacuum (Pressure p=1 OOmbar). A final mixing under vacuum was performed after surfactant addition (p<50mbar) during at least 4 minutes.

Table 1

[0077] Determination of the Pellicle Cleaning Ratio (PCR) on toothpaste formulation

[0078] The cleaning performance of the silica materials in the toothpaste formulation obtained as above described was typically quantified in terms of the Pellicle Cleaning Ratio ("PCR") value. The PCR test measures the ability of a toothpaste composition to remove pellicle film from a tooth under fixed brushing conditions. The PCR test is described in "In Vitro Removal of Stain With Dentifrice" G K Stookey, et al., J. Dental Res., 61 , 1236-9, 1982, which is incorporated herein by reference for its teaching of PCR. PCR values are unitless.

[0079] EXAMPLES

[0080] Materials:

[0081] CS1 : Precipitated silica Tixosil® 73 commercially available from Solvay SA [0082] Thickening silica: Precipitated silica Tixosil®43 commercially available from Solvay SA

[0083] Example 1

[0084] Tixosil®73 (commercially available form Solvay, identified as CS1 in Table 1) was used as a starting material for the preparation of a modified silica. 100 g of Tixosil®73 were placed in an oven and heated from 25°C to the final temperature of 600°C at a ramp-up speed of 2°C/ min. The silica was the held at 600°C for 60 minutes. Finally the temperature was reduced from 600°C to 30°C with a speed of 10°C/min. At the end of the cool-down cycle the precipitated silica S1 was recovered and placed in a sampling bottle.

[0085] The properties of silica S1 and CS1 and of the formulations containing the two silicas are reported in Table 2.

Table 2

* Determined on a thermobalance, weight loss at 160°C.

[0086] The hydrogen peroxide compatibility data in Table 1 show that inventive silica S1 reduces the activity of the peroxide over time much less than silica CS1 having a much higher number of silanol (OH) groups per surface area..

[0087] Silica S1 exhibits higher cleaning performances (PCR) vs CS1 in toothpaste formulation, related to a higher abrasivity as shown by both RDA and PMMA methods.

Claims

1. A precipitated silica characterised by: a CTAB surface area SCTAB from 5 to 45 m²/g; and a number of OH groups per surface area equal to or lower than 2.00 OH/nm².

2. The precipitated silica of claim 1 wherein the number of OH groups per surface area is 0.15 to 1.00 OH/nm².

3. The precipitated silica of claim 1 or 2 characterised by an abrasion depth value Hm, as determined using the PMMA abrasion test, between 3.5 and 25.0 pm.

4. The precipitated silica of anyone of the preceding claims characterised by Relative Dentin Abrasion (RDA) between 100 and 200.

5. An oral care composition comprising a peroxide-releasing compound and the precipitated silica of anyone of claims 1 to 4.

6. The oral care composition according to claim 5 further comprising an antibacterial agent containing chlorhexidine and/or a Zn containing salt.

7. The oral care composition of claim 5 or 6 which contains from 3 to 60% by weight of the precipitated silica.

8. The oral care composition of anyone of claims 5 to 7 which is characterised by Relative Dentin Abrasion (RDA) between 90 and 200.

9. The oral care composition of anyone of claims 5 to 8 characterised by a Pellicle Cleaning Ratio (PCR) between 75 and 110.

10. A process for the manufacture of the precipitated silica of anyone of claims 1 to 4 said process comprising the steps of: providing a precipitated silica [Starting Silica]; heat treating said Starting Silica at a temperature of 400 to 650°C for 1 to 180 minutes.

11. The process of claim 10 comprising the steps of: providing a Starting Silica; heating said Starting Silica to a temperature of 400 to 650°C; holding said Starting Silica at a temperature of 400 to 650°C for 1 to 150 minutes; and cooling the silica.

12. The process of claim 10 or 11 wherein the Starting Silica is a precipitated silica having a number of OH groups per surface area greater than 2.00 OH/nm² The process of anyone of claims 10 to 12 wherein the Starting Silica has a

CTAB surface area SCTAB lower than 50 m²/g. Use of an oral care composition of anyone of claims 5 to 9 for the cleaning of teeth.