GB1559644A - Method for the water resistance of pullulan - Google Patents

Description

(54) A METHOD FOR IMPROVING THE WATER-RESISTANCE OF PULLULAN (71) We, SUMITOMO CHEMICAL COMPANY LIMITED, a Corporation organised under the laws of Japan, of 15, Kitahama-5-chome, Higashi-ku, Osaka, Japan, and HAYASHIBARA BIOCHEMICAL LABORATORIES INC., a Corporation organise under the laws of Japan, of 2-3, Shimoishii-1-chome, Okayamashi, Okayama-ken, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : .- The present invention relates to a process for manufacturing improved pullulan articles. More particularly, the invention pertains to a method for enhancing the water-resistance of pullulan articles, while retaining the excellent properties of pullulan.

Pullulan, which is a linear high polymer representable by the following structural formula:

wherein n is an integer indicating the polymerization degree, has recently bcen proved to have various useful properties and be usable for many purposes. For example, pullulan is easily soluble in cold water and forms an aqueous solution which has a very low viscosity and is very stable without gelation or degradation on standing for a long period. Pullulan also has an excellent film-forming ability and the resulting film is superior in transparency, hardness and strength, and has a very low permeabilitv to gases such as oxygen and nitrogen. Further, pullulan is non-toxic and edible.

A number of useful articles can be prepared from pullulan. Films and sheets, for example, are prepared by casting an aqueous pullulan solution on a flat plate and evaporating water. Pullulan can also be converted to other useful shaped bodies (e. g. capsules, bottles, etc.), or to fibers.

However, the application of pullulan is limited co areas where a high resistance against water or humidity is not required because the solubility of pullulan in water is too high and hence products made of pullulan are not resistant to water or humidity and are liable to become tacky in a humid atmosphere.

It is known that the water-resistance of pullulan can be increased by introducing lipophilic groups into its molecule or cross-linking it with cross-linking agents such as aldehydes, epoxy compounds or polycarboxylic acids (see U. S. Patent No. 3,870, 537 and German Patent No. 2,508,857).

However, some practical properties of pullulan are spoilt when said hitherto known methods are applied. For example, gas impermeability of pullulan is deteriorated when pullulan is water-insolubilized by introducing lipophilic groups into its molecule. Edibility, which is the most characteristic and advantageous property of pullulan, is ruined by the introduction of lipophilic groups or the cross-linking.

It is known to water-insolubilize polyuronides by treating with an aqueous divalent metalic ion solution [A. HAUG et al. Acta Chem. Scand. 19 341-351 (19655].

As the result of studies made by the present inventors, it has now been ound that pullulan articles having increased water-resistance can be prepared without loss of the excellent properties of pullulan such as gas impermeability and edibility.

According to the present invention, there is provided a process for manufacturing pullulan articles having increased water-resistance, which comprises bringing a mixture or shaped composition of (a) pullulan or a water-soluble derivative thereof and (b) polyuronide or a water-soluble salt thereof in contact with an aqueous and/or alcoholic solution of a di-or polyvalent metallic ion.

As disclosed in U. S. Patent No. 3,827,937, pullulan is prepared by the biosynthetic process using a strain belonging to the genus Pullularia, and the physical properties of pullulan vary somewhat depending on the strain used. In the present invention, however, pullulan obtained from any strain can be used.

Further, water-soluble derivatives of pullulan may also be employed in the present invention so far as their properties are suited to desired pullulan articles.

Examples of such water-soluble pullulan derivatives are carboxymethyl ethers, methyl ethers, hydroxypropyl ethers, and hydroxyethyl ethers of pullulan, each of which has D. S. of 2 or less, preferably 1 or less. D. S. refers to the number of etherified hydroxyl groups per glucose residue of pullulan, the highest possible D. S. being 3.

The water-soluble pullulan derivatives are suitably prepared by the process disclosed in U. S. Patent No. 3,873, 33, 3.

The molecular weight of the pullulan and its water-soluble derivatives used in the present invention are not particularly limited, but a number average molecular weight of 10,000 to 3,000,000, preferably 30,000 to 1,000,000 is suitable.

The polyuronides used in the present invention include, for example, alginic acid, pectic acid, heparin, hyaluronic acid, chondroitin sulfates, gum arabic and xanthan gum. In case of water-insoluble polyuronides, they are used in the form of watersoluble salts such as the alkali metal (e. g. of sodium, potassium, lithium, etc.), silver or ammonium salts.

In the present invention, the most preferable polyuronide is alginic acid or its water-soluble salts because its properties are the most suitable for the pullulan articles of the present invention and it is edible.

When the polyuronides are used in the form of their salts, sodium and potassium salts are desirable.

Since polyuronides are mostly obtained from plant or animal tissues by extraction, they vary to some extent in chemical structure and physical properties. In the present invention, however, any such natural polyuronide can be used regardless of its source.

For example, alginic acid can be extracted from seaweed and its structure and physical properties vary somewhat depending upon the seaweed used. In the present invention, any such extracted alginic acid may be used, but excellent pullulan articles can be obtained when alginic acid whose viscosity at 1% aqueous solution is 5 to 1500 cps, preferably 10 to 500 cps when measured with B-type rotational viscometer (25 C, 60 rpm.).

The di-or polyvalent metallic ions used in the present invention include, for example, ions of metals which belong to group Ib, TIa, II ; S, lIIb, IVb, VIIa or VIII of the Periodic Table of'Elements according to Mendeleef, preferably, calcium, barium, palladium, copper, strontium, cadmium, zinc, nickel, cobalt and manganese. Among the metals, calcium is the most preferable.

The aqueous and/or alcoholic solution of a di-or polyvalent metallic ions used in the present invention can, for example, be prepared by dissolving a halide (e. g. chloride, bromide, iodide), hydroxide, oxide, sulfate, nitrate, carbonate, or organic acid salt (e. g. citrate) of the metals in water, alcohol (e. g. ethanol), or a mixture thereof so that the concentration of the metallic ions becomes 0. 0001 to 10 N (normality).

The pullulan articles of the present invention can be prepared by forming a mixture of pullulan or a water-soluble derivative thereof, water and at least one polyuronide or a water-soluble salt thereof in or into a desired shape, dipping or immersing the resultant shaped article in the metallic ion solution, or applying, painting or spraying the metallic ion solution to the shaped article, and then drying the pullulan article.

The pullulan articles of the present invention can also be prepared by extruding said mixture as a shaped article into the metallic ion solution and then drying the pullulan article.

Before molding, the polyuronide or its water-soluble salt and pullulan or its water-soluble derivative are homogeneously mixed with water.

The enhancement of the water-resistance of pullulan can suitably be effected by treating pullulan containing at least 0.1% by weight of polyuronide with the metallic ion solution. The ratio of polyuronide or salt thereof to pullulan or derivative thereof is suitably from 0. 1 : 99. 9 to 1: 1, preferably 0. 5 : 95. 5 to 3: 7, by weight. 7lis mixture can then be further mixed with water. The concentration of the mixture in water generally varies from 1 to 90% by weight depending upon the molding process used. Films and sheets, for example, are generally prepared by casting a 1 to 25% by weight aqueous solution of a mixture of pullulan and sodium alginate onto a drum, and passing the resulting article through a 1 to 20% by weight aqueous solution of calcium chloride, or guiding it to a roll, where it comes in contact with the calcium chloride solution. Shaped bodies of pullulan can also be prepared by extruding a mixture of pullulan and sodium alginate, which contains 10 to 40% by weight of water, into the metallic ion solution.

In a preferred process, the pullulan or derivative thereof is contacted in the form of a mixture (or a shaped composition formed from such a mixture) which contains 99.5 to 70 parts by weight of a pullulan or derivative thereof of number average molecular weight 30,000 to 1,000,000,0.5 to 30 parts by weight of sodium alginate and 10 to 99% by weight of water, and the metallic ion is calcium.

In the present invention, various types of pullulan articles (e. g. films, sheets, fibres, bottes, pipes, tubes and rods) can be prepared by using conventional molding processes such as casting, extrusion, compression-molding, injection-molding and blowmolding.

The pullulan articles of the present invention may also be a part of combinationproducts such as laminates, multilayered products or impregnated products.

In manufacturing the pullulan articles, conventional plasticizers may be added, if desired. Examples of suitable plasticizers are polyalcohols (e. g. ethylene glycol, propyl- ene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol and glycerine), sucrose fatty acid esters (e. g. sucrose monolaurate and sucrose monopalmitate), sorbitan fatty acid esters (e. g. sorbitan mono laurate and sorbitan monopalmitate) amines (e. g. ethanolamine, diethylene triamine, diethylene tetramine and prepylamine) and dimethyl sulfoxide. If desired, other agents such as dyes, anti-oxidants, thermostabilizers, U. V. ray-absorbers and lubricants may also be added.

The following Examples are given to illustrate the present invention more precisely.

Examples 1 to 3.

Pullulan having an average molecular weight of 300, 000 and sodium alginate (a reagent produced by NAKARAI CHEMICAL CO.) were blended at the ratios as indicated in Table 1. The mixtures were further mixed with water. (The concentrations of the mixture in water are given in the Table 1). Thus obtained aqueous solutions of the mixtures were cast on a clean, flat and horizontal plate and dried at a room temperature. The resulting articles were dipped in a 5% aqueous solution of calcium chloride for about a half minute, washed with water and dried to give transparent, bright and strong films.

The tackiness of the films obtained as above were observed after they were allowed to stand for one day at 30 C and 90% of relative humidity, of which results are given in the Table 1.

The state of the films which were put into water at 20 C for I hour are indicated in the Table 1 to illustrate the solubility of the films in water.

TABLE 1

Mixing ratio 0 0 of the Sodium mixture Example Pullulan alginate in water No. (wt. %) (wt. %) (wt. %) Tackiness Solubility 1 95 5 20 No Slightly swelled 2 90 10 20 No Slightly swelled 3 50 50 10 No Slightly swelled Control * 100 0 20 Yes Dissolve in 1 minute Control * 0 100 4 No Slightly swelled Control : films were prepared from pullulan and sodium alginate separately in the same way as above. The film prepared from pullulan was not dipped in the calcium chloride solution because it dissolves easily in the solution.

Claims (15)

WHAT WE CLAIM IS :

1. A process for manufacturing a pullulan article having increased water-resist ance, which comprises bringing a mixture or a shaped composition of (a) pullulan or a water-soluble derivative thereof and (b) polyuronide or a water-soluble salt thereof, in contact with an aqueous and/or alcoholic solution of a di-or polyvalent metallic ion.

2. A process according to Claim 1, wherein the pullulan or derivative thereof has a number average molecular weight of 10,000 to 3,000,000.

3. A process according to Claim I or 2, wherein the pullulan derivative is. 1 carboxymethyl ether-, methyl ether-, hydroxypropyl ether-, or hydroxyerhyl ether-of pul ! ulan, each of which has D. S. of 2 or less.

4. A process according to any one cf the preceding c ! aims wherein the polyuronide is alginic acid, pectic acid, heparin, hyaluronic acid, chondroitin sulfates, gum arabic, or Xanthan gum.

5. A process according to any one of the preceding claims, wherein the water soluble salt of the polyuronide is an alkali metal, silver or ammonium salt.

6. A process according to any one of the preceding claims, wherein the polyuron ide is sodium alginate.

7. A process according to any one of the preceding claims, wherein the ratio of the polyuronide or salt thereof to the pullulan or derivative thereof is 0. 1 : 99.9 to 1: 1 by weight.

8. A process according to any one of the preceding claims wherein the di-or polyvalent metallic ion is an ion of a metal of Group Ib, IIa, IIb, IIIb, IVb, VIIa or VIII of the Periodic Table of Elements according to Mendeleef.

9. A process according to claim 8, wherein the metal is calcium, barium, pal ladium, copper, strontium, cadmium, zinc nickel, cobalt or manganese.

10. A process according to any one of claims 1 to 9 wherein a mixture of pullulan or derivative thereof, water and the polyuronide or salt thereof is formed into a desired shape and then dipped or immersed into a solution of metallic ion or the solution of metallic ion is applied, painted or sprayed on to the shaped article, and the shaped article is then dried.

11. A process according to any one of claims 1 to 9 wherein a mixture of pullulan or derivative thereof, water and the polyuronide or salt thereof is extruded as a shaped article into the solution of metallic ion and the shaped article is then dried.

12. A process according to any one of the preceding claims, wherein the pullulan or derivative thereof is contacted in the form of a mixture which contains 99.5 to 70 parts by weight of a pullulan or derivative thereof of number average molecular weight 30,000 to 1,000,000,0.5 to 30 parts by weight of sodium alginate and 10 to 99% by weight of water, and the metallic ion is calcium ion.

13. A process according to any one of the preceding claims wherein the pullulan or derivative thereof is contacted in the form of a shaped composition which is prepared from a mixture of 99.5 to 70 parts by weight of a pullulan or derivative thereof of number average molecular weight 30,000 to 1,000,000,0. 5 to 30 parts by weight of sodium alginate, and 10 to 99% by weight of water, and the metallic ion is calcium ion.

14. A proces for manufacturing a pullulan article of high water resistance, according to claim I substantially as hereinbefore described with reference to any one of the Examples.

15. A pullulan article of high water resistance obtained by a process according to any one of the preceding claims.