GB2103224A - Cellulose sulfate gel composition - Google Patents

Abstract

The physical properties of aqueous gels comprising cellulose sulfate and one or more inorganic alkali metal salts are improved by the addition of one or more other water soluble polymers. The water soluble polymers are typically natural polysaccharides or cellulose derivatives other than cellulose sulfate. The gel can be obtained by dissolving the cellulose sulfate and water-soluble polymer components in water, adding an aqueous solution of the alkali metal salt to form a precipitate, redissolving the precipitate by heating, and then cooling the resulting solution. The thus obtained gel, in comparison with a corresponding composition containing no other water soluble polymer, has a higher gel strength and is a thermally reversible gel. The gel composition has various useful applications such as in the food, toiletry and medical arts, and as a slow-releasing carrier for perfumes or insecticides.

Description

SPECIFICATION Cellulose sulfate gel composition The present invention relates to gel compositions. Aqueous gelled products are useful in fields such as the food, toiletry or medicine fields, for example, in chilled confectionery, an aromatic, or an agent for forming tooth shape. However, such materials with sufficient processability, gel strength and resistance to syneresis have not been obtained.

Recently, a new method of preparing cellulose sulfate was disclosed (R. G. Schweiger, Carbohydrate Research, Vol. 70, page 185 (1979) and Japanese Laid-Open Patent Application 51-16392) and commercial production and uses of cellulose sulfate have attracted attention due to the unique properties thereof.

It is known that cellulose sulfate is a strong anionic, water-soluble polymer having many specific properties not observed in other cellulose derivatives. For example, cellulose sulfate is stable in electrolytes despite being an ionic polymer, is stable in strong alkalis and acids despite being a cellulose ester, and it forms thermally reversible gel. A gel obtained from a cellulose sulfate aqueous solution by adding a potassium or sodium salt, heating and then cooling does not, however, exhibit high strength and elasticity, and exhibits syneresis, and it cannot be effectively used in the applications of interest described above.

It has also been reported that cellulose sulfate aqueous solutions gel under the influence of physical energy such as vibrations, shock or shear (Japanese Patent Publication 53-28070). However, it is believed such procedures are not suitable for use in gel preparation methods as they would result in poor product properties as well as requiring special means to provide such physical energy. Further, a gel prepared in such a way would not have thermally reversible properties.

An anionic cellulose derivative, such as carboxymethyl cellulose, is gelled by the addition of polyvalent cations (Japanese Laid-Open Patent Application 51-112782). However, the use of polyvalent cations is deleterious in food and medical supplies.

As the result of extensive research, we have found that a thermally reversible gel with high strength, elasticity and low yielding rate of syneresis water is obtained when the gel is produced from an aqueous solution of cellulose sulfate in the presence of one or more alkali metal salts and at least one other water-soluble polymer.

In the accompanying drawings Figure 1 is a sketch illustrating an instrument for the measurement of gel strength.

Figure 2 is a sketch showing a gel under storage for the measurement of water releasing rate, wherein: 1: weight 2: plate for weight loading 3: piston with scale 4: glass tube 5: glass cylinder 6: gel for strength measurement 7: beaker 8: polyethylene film 9: gel for water releasing rate measurement Our invention relates to an aqueous gel composition comprising cellulose sulfate, one or more alkali metal salts (such as a potassium or a sodium salt), and one or more other water-soluble polymers.

In this invention, the term "cellulose sulfate" means an alkali salt (e.g., potassium salt or sodium salt) of cellulose sulfate half ester, i.e., a compound obtained by the following reaction scheme:

0 H-O\ O )I Cellulose-OH + / S < NaOH > Cellulose-O-S-ONa II 0 There are no limitations on the degree of substitution and polymerization of the cellulose sulfate so long as the cellulose sulfate is soluble in water However, the cellulose sulfate used in this invention preferably has the degree of substitution of 0.2 to 2.5 and the viscosity of 1 to 3,000 cps at 200C (1 wt% solution in water).

A first group of "other" water soluble polymers used together with cellulose sulfate herein are natural polysaccharides, e.g., locust bean gum, guar gum, tragacanth gum, agar-agar, carrageenan, arabic gum, pectin, dextran, pullulan, curdlan, or xanthan gum. Among these, agar-agar and carrageenan are self-gelling which forms a thermally reversible gel so that the addition thereof remarkably increases strength and elasticity and decreases the yield rate of syneresis water. Even polysaccharides, which do not have any thermally reversible gelling property, give considerable additional effects. Especially remarkable effects are obtained with polysaccharides having a branch in their molecule, such as locust bean gum, guar gum or xanthan gum.

A second group of "other" water soluble polymers used in this invention are water soluble cellulose derivatives. Such cellulose derivatives include hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl propyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, carboxymethyl hydroxyethyl cellulose, carboxymethyl hydroxypropyl cellulose, methyl cellulose and carboxymethyl cellulose. Generally, the effect of addition is large with such derivatives having hydroxyalkyl or alkoxy groups.

Even though the addition of one water soluble polymer provides remarkable effects, the use of a polysaccharide and a water soluble cellulose derivative gives superior combined effects to produce a strong gel. Particularly excellent combinations are polysaccharides such as agar-agar, carrageenan, locust bean gum, guar gum, or xanthan gum with water soluble cellulose derivatives having hydroxyethyl, hydroxypropyl or methoxy groups.

The alkali metal salts used in this invention include a potassium salt and a sodium salt. Examples thereof include potassium chloride and sodium chloride. Preferably in the gel composition according to this invention, the cellulose sulfate is used in an amount of 0.5 to 10 wt% based on the weight of the gel composition, the other water soluble polymer is used in an amount of 0.5 to 10 wt% based on the weight of the gel composition, and the alkali metal salt is used in an amount of 0.5 to 10 wt% based on the weight of the gel composition. However, the total weight of the solid matter (i.e., total weight of the cellulose sulfate, the other water soluble polymer and the alkali metal salt) is used in an amount of 1.5 to 20 wt% based on the weight of the gel composition.

The mechanism of obtaining such a stable gel from cellulose sulfate is still under investigation. It is presumed that a network structure is formed by entanglement of the molecules in the water solution.

The gel composition of the present invention is suitable for use as a slow-releasing carrier for perfumes or insecticide, in toiletries as well as in food or medicines or as a cooling or heating medium.

The following detailed examples further illustrate this invention. All examples were carried out at room temperature and atmospheric pressure.

In the examples, gel strength and yield rate of syneresis water were measured by the following methods: Gel Strength A hundred grams of gel was prepared in a glass cylinder (280 ml) and kept at room temperature (about 200 C) for 24 hours. The piston device illustrated in Figure 1 is then fitted to the gel-containing cylinder. Gel strength is expressed as the loaded weight required to press the piston (19 mm in diameter) 5 mm into the gel.

Yield Rate ofSyneresis Water A gel was prepared in a glass beaker of known weight and kept at room temperature for 24 hours.

The gel was then cut into two pieces of equal volume. By removing one piece and weighing the remaining piece with the beaker, the original weight of the gel was calculated. The beaker containing the gel was covered with a polyethylene film to prevent the evaporation of water and was kept at room temperature-see Figure 2. After a designated time, water release from the gel was wiped off with blotting paper and the weight of the beaker and the remaining gel measured. Yield rate of syneresis water was expressed as the percentage of the reduced weight of the gel to the original weight of the gel.

Example 1 and Comparative Examples 1 to 3 Three grams of cellulose sulfate (SCS/LV, made by Kelco Co., U.S.A.; substitution degree: 2.2, viscosity of 1% aqueous solution at 250C: 5 cps) and one gram of locust bean gum (EMCO--GUM FLOUR M-1 75, made by Meypro Co., Switzerland) were dissolved in 86 grams of deionized water. An aqueous solution of potassium chloride was prepared by dissolving 1.5 grams of KCI in 8.5 grams of deionized water. When the KCI solution was added to the cellulose sulfate solution, a white precipitate appeared in the mixture. The precipitate redissolved upon heating the mixture at 60 to 700C to yield a uniform, clear solution.

After standing for 24 hours, the solution wholly gel led. The gel was allowed to stand for 24 hours and was then subjected to gel strength measurement at room temperature. The gel strength was 75 grams.

For comparison, gels from cellulose sulfate with KCI were prepared in the same manner except for leaving out the locust bean gum and the strength of the gels was also measured. The compositions and strength of the gels are shown in Table 1.

Table 1 Example Comparative Example 1 1 2 3 Composition of gel (g) Cellulose sulfate 3 3 4 5 Locust bean gum 1 0 0 0 KCI 1.5 1.5 2 2.5 Deionized water 94.5 95.5 94 92.5 Gel strength (g) 75 - - * 9. 1 5 *Piston penetrated into gel without weight loading It is apparent from the results shown in Table 1 above that the gel composition according to this invention had a much higher strength that that of the comparative gel compositions.

EXAMPLE 2 Cellulose sulfate having substitution degree of 0.3 and a viscosity of 1,200 cps at 200C (1 wt% solution in water) was prepared according to Schweiger's method (Carbohydrate Research, Vol. 70, page 185 (1 979)) using cotton linter as a raw material. One gram of such cellulose sulfate and 0.5 grams of hydroxyethyl cellulose (QP09H made by Union Carbide Co., U.S.A.; viscosity of 5 wt% aqueous solution at 200 C: 113-150 cps) was dissolved in 48.5 grams of deionized water. A potassium chloride solution prepared by dissolving 2 grams of KCI in 48 grams of deionized water was added to the cellulose sulfate solution.A white precipitate resulted was redissolved by heating the mixture at 60 to 700 C. The mixture gelled completely after cooling to room temperature After standing for 24 hours, gel strength was measured and it was found to be 450 grams. The gel strength of an identical gel prepared without using hydroxyethyl cellulose was 50 grams.

EXAMPLES 3 to 10 The same cellulose sulfate and procedure as were used in Example 1 were used to produce gels in combination with various water soluble polymers as shown below.

Guar gum: EMCO-GUM CSAA, Meypro Co., Switzerland Hydroxyethyl cellulose: same as Example 2 Hydroxypropyl cellulose: Nisso HPC-L, Nihon Soda Co., viscosity of 2 wt% aqueous solution at 200C: 4--10 cps Methyl hydroxypropyl cellulose: Metrose 90SH--100, Shinetsu Chemical Co., methoxy content: 1 9 to 24 wt%: hydroxypropyl content: 4 to 12 wt%; viscosity of 2 wt% aqueous solution at 200 C: 80-120 cps Agar-agar: food grade Carrageenen: GENUGEL WG, Copenhagen Pectinfactory Co., Denmark Xanthan gum: Keltrol, Kelco Co., U.S.A.

Compositions and test results are summarized in Table 2.

Table 2 Example 3 4 5 6 7 8 9 10 Composition of gel (g) Cellulose sulfate 3 3 3 3 3 3 3 3 Guargum 1 -- -- -- -- -- - - - Hydroxyethyl -- 1 -- -- -- -- -- - cellulose Hydroxypropyl - -- -- 1 -- -- -- - cellulose Methyl hydroxypropyl -- -- -- 1 -- -- -- -- - cellulose Methyl cellulose -- -- -- -- 1 -- -- - Agar-agar -- -- -- -- -- 1 -- - Carrageenan -- -- -- -- -- -- 1 - Xanthangum -- -- -- -- -- -- -- 1 KCI 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Deionized water 94.5 94.5 94.5 94.5 94.5 94.5 94.5 94.5 Gel strength (g) 50 190 120 90 60 30 350 100 It is apparent from the results shown in Table 2 that the gel compositions according to this invention had excellent strength.

EXAMPLES 11 to 18 Runs were repeated using same cellulose sulfate, KCI and polysaccharides as in Example 1, 3, 8, and 10 to produce gels with water soluble cellulose derivatives as follows.

Hydroxyethyl cellulose (a): QP4400H, Union Carbide Co., U.S.A.; viscosity of 2 wt% aqueous solution at 25 C:4,800-6,000 cps Hydroxyethyl cellulose (b): same as Example 2 Hydroxyethyl cellulose (c): synthesized by ourselves; molar substitution degree: 4, viscosity of 1 wt% aqueous solution at 250C: 1,470 cps Hydroxypropyl cellulose (a): same as Example 5 Hydroxypropyl cellulose (b): Nisso HPC-M, Nihon Soda Co.; viscosity of 2 wt% aqueous solution at 2O0C: 150 400 cps Gel compositions and strengths are shown in Table 3.

Table 3 Example 11 12 13 14 15 16 17 18 Composition of gel (g) Cellulose sulfate 3 3 3 3 3 3 3 3 Locust bean gum 0.5 0.5 0.5 0.5 0.5 - - - - - - Guam gum -- -- -- -- -- 0.5 -- - - Agar-agar -- -- -- -- -- -- 0.5 - Xanthangum -- -- -- -- -- -- -- 0.5 Hydroxyethyl cellulose (a) 1 -- -- -- -- -- -- - cellulose (b) -- 1 -- -- -- 1 1 1 cellulose (c) -- -- 1 -- -- -- -- - Hydroxypropyl cellulose (a) -- -- -- 1 -- -- -- - cellulose (b) -- -- -- -- 1 -- - KCI 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Deionized water 94.5 94.5 94.5 94.5 94.5 94.5 94.5 94.5 Gelstrength(g) 210 240 130 150 260 110 210 110 It is apparent from the results shown in Table 3 that the gel compositions according to this invention had excellent strength.

EXAMPLES 19 to 26 and COMPARATIVE EXAMPLE 4 The same cellulose sulfate, water soluble polymers and KCI as were used in Example 1 and Examples 3 to 8 were used in the same procedure as Example 1 to prepare gels and the yield rate of syneresis water thereof was measured. Gel compositions and results are summarized in Table 4.

Table 4 Example Comparative 19 20 21 22 23 24 25 26 Example 4 Composition of gel (g) Cellulose sulfate 3 3 3 3 3 3 3 3 5 Hydroxyethyl cellulose (b) 1 -- 1 -- -- 1 1 1 - Hydroxypropyl cellulose (a) -- 1 - Guam gum 0.5 - - - - - - - - - - - Locust bean gum -- 1 -- -- -- -- -- -- -- Carrageenan -- -- -- 1 -- -- 0.5 - Xanthangum -- -- -- -- 1 -- -- 0.5 - Agar-agar -- -- --. -- -- 0.5 - - - KCI 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2.5 Deionized water 94.5 93.5 94.5 94.5 94.5 94.5 94.5 94.5 92.5 Yield rate of syneresis water (%) (weight decreased) 2 Hours -- 6.4 0.0 0.5 0.0 1.4 1.4 or 11.9 4 Hours 8.1 10.3 1.3 1.2 0.0 2.0 2.3 0.8 19.4 1 Day --17.4 5.0 2.8 0.1 4.4 4.4 2.4 26.6 6 Days - - 24.1 11.0 3.7 0.9 6.9 6.6 5.0 32.8 It is apparent from the results shown in Table 4 above that the gel compositions according to this invention had remarkably lower yield rate of syneresis water as compared with that of comparative gel composition.

EXAMPLE 27 Two hundred ml of the gel prepared in Example 18 was placed in a polyethylene beaker and heated at 600C to obtain a homogeneous cellulose sulfate solution. One gram of lilac perfume commercially available was emulsified in 10 ml of a 1 wt% aqueous solution of sodium lauryl sulfate and mixed with the homogeneous cellulose sulfate solution using a conventional homogenizer. The mixture was cooled in a water bath to 200C to produce a gel containing the lilac perfume. The thusobtained gel did not show syneresis and provided excellent perfume tenacity. The gel structure did not change upon freezing and thawing.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims (9)

1. A gel composition comprising cellulose sulfate, an inorganic alkali metal salt and at least one other water soluble polymer.

2. A gel composition as claimed in Claim 1, wherein said other water soluble polymer is a natural polysaccharide and/or a water soluble cellulose derivative.

3. A gel composition as claimed in Claim 2, wherein said polysaccharide is at least one member selected from the group consisting of locust bean gum, guar gum, tragacanth gum, agar-agar, carrageenan, gum arabic, pectin, dextran, pullulan, curdlan and xanthan gum.

4. A gel composition as claimed in Claim 2, wherein said water soluble cellulose derivative is at least one member selected from the group consisting of hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl propyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, carboxymethyl hydroxyethyl cellulose, ca rboxymethyl hydroxypropyl cellulose, methyl cellulose and carboxymethyl cellulose.

5. A gel composition as claimed in Claim 1 , wherein the inorganic alkali metal salt is a potassium salt or a sodium salt.

6. A gel composition as claimed in Claim 5, wherein the inorganic alkali metal salt is potassium chloride or sodium chloride.

7. A gel composition as claimed in any preceding claim wherein the cellulose sulfate, the inorganic alkali metal salt and the other water soluble polymer are each used in an amount of 0.5 to 10 wt% based on the weight of the gel composition, with the proviso that the total amount of the cellulose sulfate, the inorganic alkali metal salt and the other water soluble polymer is 1.5 to 20 wt% based on the weight of the gel composition.

8. A gel composition as claimed in claim 7, wherein the balance of the gel composition is predominantiy water.

9. A gel composition as claimed in claim 1, substantially as hereinbefore described in any one of Examples 1 to 27.