TEMPERATURE-RESPONSIVE HYDROGEL AND METHOD FOR PRODUCING THE SAME

Abstract

A temperature-responsive hydrogel exhibiting a high viscosity at a high temperature, a low viscosity at a low temperature and a high ratio of the viscosity at a high temperature to the viscosity at a low temperature produced by mixing of an aqueous solution containing a polyalkylene glycol having an average molecular weight of 20,000 to 10,000,000 with an aqueous dispersion containing a silicate salt so as to achieve a specific compositional range of the components in the hydrogel, at a mass concentration of A of 0.01 to 1.5% by mass, at a mass concentration of A of 0.1 to 0.4% by mass and at a mass concentration of B of 0.5 to 10% by mass, at a mass concentration of B of 1 to 5% by mass, with the mass ratio R of A to B (R=(mass of A)/(mass of B)) within the range of 0.01 to 0.5.

Claims

1. A temperature-responsive hydrogel comprising a polyalkylene glycol A and a silicate salt (B) wherein the concentration by mass of the polyalkylene glycol A is 0.01 to 1.5% by mass in the hydrogel.

2. The temperature-responsive hydrogel according to claim 1, wherein the temperature-responsive hydrogel further comprises a dispersant (C) for the silicate salt.

3. The temperature-responsive hydrogel according to claim 1, wherein the polyalkylene glycol (A) is polyethylene glycol or polypropylene glycol having a weight average molecular weight of 20,000 to 10,000,000.

4. The temperature-responsive hydrogel according to claim 1, wherein the concentration by mass of the silicate salt (B) is 0.5 to 10% by mass in the hydrogel.

5. The temperature-responsive hydrogel according to claim 1, wherein the silicate salt (B) is water-swellable silicate salt particles.

6. The temperature-responsive hydrogel according to claim 5, wherein the water-swellable silicate salt particles are particles of a water-swellable silicate salt selected from the group consisting of smectite, bentonite, vermiculite, and mica.

7. The temperature-responsive hydrogel according to claim 1, wherein the mass ratio R of the polyalkylene glycol (A) to the silicate salt (B) (R=[the mass of A]/[the mass of B]) is 0.01 to 0.5.

8. The temperature-responsive hydrogel according to claim 2, wherein the dispersant (C) is at least one dispersant selected from the group consisting of sodium pyrophosphate, citric acid, and polyphosphoric acid.

9. The temperature-responsive hydrogel according to claim 1, wherein the viscosity of the hydrogel at a temperature of 50 to 100 C. is twice or more the viscosity of the hydrogel at a temperature of 0 to 25 C.

10. The temperature-responsive hydrogel according to claim 1, wherein the hydrogel exhibits a viscosity of 600 to 10,000 mPa.Math.s at a temperature of 50 to 100 C. and a viscosity of 100 to 580 mPa.Math.s at a temperature of 0 to 25 C.

11. The temperature-responsive hydrogel according to claim 1, wherein the hydrogel exhibits a viscosity of 3,000 to 10,000 mPa.Math.s at a temperature of 50 to 100 C. and a viscosity of 500 to 2,980 mPa.Math.s at a temperature of 0 to 25 C.

12. A method for producing a temperature-responsive hydrogel, the method comprising a step of mixing an aqueous solution containing a polyalkylene glycol (A) at a concentration by mass of 0.02 to 3.0% by mass with an aqueous dispersion containing a silicate salt (B).

13. The method for producing a temperature-responsive hydrogel according to claim 11, wherein one or more water-soluble organic solvents (D) are contained in either or both of the aqueous solution and the aqueous dispersion before mixing of the aqueous solution and the aqueous dispersion.

14. The temperature-responsive hydrogel according to claim 9, wherein the temperature-responsive hydrogel exhibits at least one reproducible change in viscosity of the hydrogel with respect to a change in temperature.

Description

EXAMPLES

[0059] The present invention will next be described in detail by way of examples, but the present invention is not limited to the following examples.

Example 1

[0060] A transparent aqueous dispersion containing 4.0% by mass a water-swellable layered clay mineral (LAPONITE XLG: synthetic hectorite, manufactured by Wilbur-Ellis) as a silicate salt was prepared, and an aqueous PEG solution containing 0.2% by mass polyethylene glycol 500,000 (PEG) (molecular weight: about 500,000, manufactured by Wako Pure Chemical Industries, Ltd.) as a polyalkylene glycol was prepared. Subsequently, while the aqueous LAPONITE XLG dispersion was stirred, an equal amount of the aqueous PEG solution was added dropwise to the dispersion. After completion of the dropwise addition, the resultant mixture was further stirred for one hour, to thereby prepare an aqueous LAPONITE XLG/PEG dispersion having a LAPONITE XLG concentration of 2.0% by mass and a PEG concentration of 0.1% by mass.

Example 2

[0061] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous PEG solution was replaced with an aqueous PEG solution containing 0.4% by mass PEG. The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 2.0% by mass and a PEG concentration of 0.2% by mass.

Example 3

[0062] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous PEG solution was replaced with an aqueous PEG solution containing 0.8% by mass polyethylene glycol (PEG). The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 2.0% by mass and a PEG concentration of 0.4% by mass.

Comparative Example 1

[0063] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous PEG solution was replaced with water containing no polyethylene glycol (PEG). The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 2.0% by mass and a PEG concentration of 0% by mass.

Referential Example 1

[0064] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous PEG solution was replaced with an aqueous PEG solution containing 2.0% by mass polyethylene glycol (PEG). The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 2.0% by mass and a PEG concentration of 1.0% by mass.

Measurement of Viscosity

[0065] The viscosity of each of the aqueous LAPONITE XLG/PEG dispersions prepared in Examples 1 to 3, Comparative Example 1, and Referential Example 1 was measured at a temperature of 25 C. with a tuning-fork vibration viscometer (SV-100) manufactured by A&D Company, Limited. The viscosity was defined as the average of values obtained by five-minute measurement. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Composition (% by mass) Viscosity LAPONITE XLG PEG (mPa .Math. s) Example 1 2.0 0.1 460 Example 2 2.0 0.2 550 Example 3 2.0 0.4 380 Comparative Example 1 2.0 0 3 Referential Example 1 2.0 1.0 11

[0066] As shown in Table 1, the aqueous LAPONITE XLG/PEG dispersions of Examples 1 to 3 (PEG concentrations: 0.1, 0.2, and 0.4% by mass) were in the form of a hydrogel. In particular, the aqueous LAPONITE XLG/PEG dispersion of Example 2 (PEG concentration: 0.2% by mass) exhibited the highest viscosity of all aqueous LAPONITE XLG/PEG dispersions of the Examples. In contrast, the dispersion of Comparative Example 1 (containing no PEG) and the dispersion of Referential Example 1 (PEG concentration: 1% by mass) exhibited a very low viscosity and were in the form of a sol (aqueous solution).

Change in Viscosity with Temperature

[0067] The viscosity of the aqueous LAPONITE XLG/PEG dispersion prepared in Example 2 was measured with a tuning-fork vibration viscometer (SV-100) manufactured by A&D Company, Limited under repeated cycles of measurement temperature change (4 C..fwdarw.25 C..fwdarw.70 C..fwdarw.4 C.). The viscosity was defined as the average of values obtained by five-minute measurement. The cycle of measurement temperature change was repeated six times.

[0068] Table 2 shows the average of viscosities measured at each temperature in six repeated cycles of temperature change. In all the six repeated cycles of temperature change, the aqueous LAPONITE XLG/PEG dispersion exhibited a high viscosity at a high temperature and a low viscosity at a low temperature. As shown in Table 2, the aqueous LAPONITE XLG/PEG dispersion exhibited a temperature response such that the viscosity at a temperature of 70 C. was about six times the viscosity at a temperature of 4 C.

TABLE-US-00002 TABLE 2 Composition (% by mass) Viscosity (mPa .Math. s) LAPONITE XLG PEG 4 C. 25 C. 70 C. Example 2 2.0 0.2 204 460 1200

Example 4

[0069] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous LAPONITE XLG dispersion was replaced with a transparent aqueous dispersion containing 6.0% by mass LAPONITE XLG. The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 3.0% by mass and a PEG concentration of 0.1% by mass.

Example 5

[0070] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous LAPONITE XLG dispersion was replaced with a transparent aqueous dispersion containing 6.0% by mass LAPONITE XLG, and the aqueous PEG solution was replaced with an aqueous PEG solution containing 0.4% by mass PEG, The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 3.0% by mass and a PEG concentration of 0.2% by mass.

Example 6

[0071] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous LAPONITE XLG dispersion was replaced with a transparent aqueous dispersion containing 6.0% by mass LAPONITE XLG, and the aqueous PEG solution was replaced with an aqueous PEG solution containing 1.2% by mass polyethylene glycol (PEG). The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 3.0% by mass and a PEG concentration of 0.6% by mass.

Comparative Example 3

[0072] An aqueous LAPONITE XLG/PEG dispersion was prepared in the same manner as in Example 1, except that the aqueous LAPONITE XLG dispersion was replaced with a transparent aqueous dispersion containing 6.0% by mass LAPONITE XLG, and the aqueous PEG solution was replaced with an aqueous PEG solution containing 4.0% by mass polyethylene glycol (PEG). The aqueous LAPONITE XLG/PEG dispersion was found to have a LAPONITE XLG concentration of 3.0% by mass and a PEG concentration of 2.0% by mass.

Measurement of Viscosity

[0073] The viscosity of each of the aqueous LAPONITE XLG/PEG dispersions prepared in Examples 4 to 6 and Comparative Example 3 was measured at a temperature of 25 C. with a tuning-fork vibration viscometer (SV-100) manufactured by A&D Company, Limited. The viscosity was defined as the average of values obtained by five-minute measurement. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Composition (% by mass) Viscosity LAPONITE XLG PEG (mPa .Math. s) Example 4 3.0 0.1 2280 Example 5 3.0 0.2 2730 Example 6 3.0 0.6 1890 Comparative Example 3 3.0 2.0 167

[0074] The aqueous LAPONITE XLG/PEG dispersions prepared in Examples 4 to 6 were in the form of a hydrogel and exhibited a high viscosity of about 2,000 to 3,000 mPa.Math.s. In contrast, the aqueous LAPONITE XLG/PEG dispersion prepared in Comparative Example 3 exhibited a low viscosity of 167 mPa.Math.s despite a high PEG concentration.

[0075] The aqueous LAPONITE XLG/PEG dispersion prepared in Example 6 was evaluated for change in viscosity with temperature in the same manner as in Example 2. Consequently, the viscosity was 5,500 mPa.Math.s at a high temperature (70 C.) and 1,890 mPa.Math.s at a low temperature (25 C.). Thus, the aqueous LAPONITE XLG/PEG dispersion prepared in Example 6 also exhibited a temperature response such that the viscosity at a high temperature was higher than the viscosity at a low temperature.

Comparative Example 4

[0076] An aqueous solution containing 0.2% by mass polyethylene glycol 500,000 (PEG) (molecular weight: about 500,000) only was prepared.

Comparative Example 5

[0077] An aqueous dispersion containing 2% by mass Laponite XLG only was prepared.

Test for Temperature Dependence of Viscosity

[0078] The viscosities of the aqueous solution prepared in Comparative Example 4 and the aqueous dispersion prepared in Comparative Example 5 were measured under repeated cycles of temperature change (4 C..fwdarw.25 C..fwdarw.70 C..fwdarw.4 C.). Consequently, the aqueous solution and the aqueous dispersion exhibited a common temperature dependence of viscosity; i.e., a low viscosity at a high temperature (70 C.) (12.9 mPa.Math.s (Comparative Example 4) and 3.5 mPa.Math.s (Comparative Example 5)) and a high viscosity at a low temperature (4 C.) (15.7 mPa.Math.s (Comparative Example 4) and 4.6 mPa.Math.s (Comparative Example 5)).

TABLE-US-00004 TABLE 4 Composition (% by mass) Viscosity (mPa .Math. s) LAPONITE XLG PEG 4 C. 25 C. 70 C. Example 2* 2.0 0.2 204 460 1200 Comparative 0 0.2 15.7 12.9 Example 4 Comparative 2.0 0 4.6 3.5 Example 5 *Redescribed

INDUSTRIAL APPLICABILITY

[0079] The hydrogel of the present invention can be prepared only by mixing of inexpensive raw materials without use of a chemical reaction, such as radical polymerization. The hydrogel can be used as a temperature-responsive hydrogel by taking advantage of its characteristics.