GB2303383A

GB2303383A - Water-repellent polysaccharides

Info

Publication number: GB2303383A
Application number: GB9615018A
Authority: GB
Inventors: John Prince; Gary Baker
Original assignee: Rhone Poulenc Chimie de Base SA
Current assignee: Rhone Poulenc Chimie de Base SA
Priority date: 1995-07-19
Filing date: 1996-07-17
Publication date: 1997-02-19
Anticipated expiration: 2016-07-17
Also published as: GB9514750D0; GB2303383B; AU6466496A; GB9615018D0; WO1997004022A1

Description

WATER-REPELLENT TREATMENT OF POLYSACCEARIDES This invention relates to water-repellent polysaccharides and provides a method for making a watersoluble polysaccharide such as starch or gum waterrepellent.

In our British specification 2236122 and our European specification 0491773 we have described aqueous compositions which are water-repellent when dried, comprising the reaction product of (i) at least one carboxylic acid containing from 3 to 22 carbon atoms; (ii) at least one unsubstituted or substituted aliphatic amine or polyfunctional aromatic amine, containing from 2 to 25 carbon atoms; and (iii) a water-soluble metal complex crosslinking agent comprising one or more metals from groups Ia, IIa, IIIa, IVa and the first and second rows of transition metals from the Periodic Table of Elements. These compositions are used to impart water-repellency to various substrates including wood, paper and other cellulosic materials.

It has now been found that these compositions can advantageously be applied to water-soluble polysaccharides such as starches and gums to impart water-repellency. The term "water-soluble polysaccharide" as used herein means a polysaccharide which dissolves or at least swells substantially on contact with hot or cold water.

It has also been found that aqueous dispersions of water soluble polysaccharides treated by the method of the present invention have a stabilized viscosity. Solutions of untreated polysaccharide, such as untreated starch, thicken with time and temperature.

The present invention accordingly provides a method of treating a water-soluble polysaccharide, e.g. a starch or gum, to render it water-repellent which comprises applying thereto an aqueous composition as aforesaid.

The said aqueous compositions can also be used in the preparation of water-soluble polysaccharides, aqueous dispersions of which have a stabilized viscosity.

Preferred crosslinking agents contain zinc, aluminium, titanium, copper, chromium, iron, zirconium and/or lead.

The crosslinking agent may be a salt or complex of the metal(s). The salts may be acid, basic or neutral.

Suitable salts include halides, hydroxides, carbonates, nitrates, nitrites, sulphates, phosphates etc.

The preferred crosslinking agents are zirconium complexes, for example those described in GB-1002103, which are salts of the zirconyl radical with at least two monocarboxylic acids, one acid group having from 1 to 4 carbon atoms, the other having more than 4 carbon atoms, which may be made by refluxing the carboxylic acid of 1 to 4 carbon atoms with a zirconyl carbonate paste and then adding the carboxylic acid having more than 4 carbon atoms.

Water-soluble inorganic metal compounds may also be used.

Ammonium zirconium carbonate is particularly preferred.

The carboxylic acid is an optionally substituted, e.g.

by hydroxy, straight or branched chain, saturated or unsaturated C3 - C22 preferably C10 - Cls, fatty acid, e.g.

oleic, isostearic, stearic, ricinoleic or tall oil fatty acid.

The unsubstituted or substituted aliphatic amine or polyfunctional aromatic amine is preferably water-soluble in order that a water-dispersible compound is produced when it is reacted with the carboxylic acid. It may be a primary, secondary or tertiary amine optionally substituted, e.g. by one or more hydroxyls, or in the form of an amide, e.g. an amide of the formula R-C(O)-NR1R2 where R, R1 and R2 each represent hydrogen, or an optionally substituted alkyl group of 1 to 5 carbon atoms.

Suitable substituents for the above optionally substituted groups include halogen, hydroxy or an alkyl group preferably with from 1 to 5 carbon atoms.

Examples of suitable amines and substituted amines include: ethylamine, 2-amino-2-methyl-propan-l-ol, diethylamine, triethylamine, 2-amino-2-ethyl-propane-1,3diol, 3-amino-l,2-propane-diol, formamide, acetamide, Nethyl-acetamide, N,N-dimethyl-butyranrride, hydrazine, hexamethylene-diamine and tris -hydroxy-methyl-amino methane.

Compositions suitable for use in the invention may be prepared for example by the following method. The acid is added to a hot agitated solution of the amino compound in water. The mixture is agitated for 15 minutes, allowed to cool e.g. below 500C, and the metal crosslinking agent is then added to give the composition.

The said aqueous composition is generally applied to the water-soluble polysaccharide by intimately mixing the two together. The aqueous compositions can be applied to an aqueous solution of polysaccharide, or, preferably, to a dry or substantially dry polysaccharide. The mixing is preferably carried out with sufficient mechanical shear and thermal energy to produce a dispersed phase which is finely divided and homogeneously dispersed. Conventional mixing equipment, such as a high speed mixer (Henschel or Kunkle mill), a mill, or a Banbury mixer, may be used. The mixture is then dried to give the water-repellent product.

The temperature at which the mixture is dried affects the colour of an aqueous solution of the treated polysaccharide. Pale colours are preferred when the polysaccharide is used as a filler for a particle board or to form a hydrophobic layer on paper. Typically, the mixture is dried at from 30 to 1500C, preferably from 30 to SOOC, especially about 400C.

The compositions used in the invention are generally used at a concentration suitable to achieve a dispersed phase as described above and avoid the formation of a paste. Preferably they contain 1 to 10%, more preferably 3% to 5%, most preferably about 1.4%, by weight of solids.

Higher concentrations of composition can be achieved by preparing the composition at the time of use from a pack in which the water-soluble metal complex (iii) is separate from components (i) and (ii). In such circumstances, a concentration of about 5.5% by weight is typical.

In an embodiment of the invention aqueous acrylic polymers are added to the composition to increase the stability of the complexed compositions and give improved water-repellency. An example of an aqueous acrylic polymer suitable for use in the compositions used in the invention is Glascol LS12 (Trade Mark).

Other preferred additives to the compositions used in the invention are a saturated hydrocarbon wax (preferably a paraffin wax having a melting point in the range of about 50 to 700C) and/or an alkyd resin. From 25 to 150 weight % of wax may be included without the need for an organic solvent. These additives improve the water-repellency of the dried composition. Solubilising agents such as sodium hydroxide or ammonia may also be included.

An example of a composition suitable for use in the invention comprises 10% by weight of Glascol LS12, 1% by weight of an aqueous solution of the stearate derived from 2-amino-2-methyl-propan-1-ol (AMP), and 1% by weight of Zircomplex PN (a product described in GB 1002103).

The method of the invention may be applied to any water-soluble polysaccharide and especially to a starch or gum. The starch may, for example, be modified, unmodified or a starch derivative. Examples of starch include maize, wheat, oats, potato and rice starch. Examples of gums include alginate, arabic, carrageenin, guar, locust bean, tragacanth and xanthan gums.

Aqueous dispersions of water-soluble polysaccharides treated by the method of the present invention have a stabilized viscosity. A stabilized viscosity means a viscosity which does not increase with time and/or temperature as much as the viscosity of an aqueous solution of untreated polysaccharide.

Water-soluble polysaccharides treated by the method of the present invention may show a small initial increase in viscosity. However, the method of the present invention causes subsequent increases in viscosity with time and temperature to be reduced. Typically, reductions of up to 50%, preferably up to 85%, can be achieved. The initial increase in viscosity upon application of the said aqueous compositions is minimised when the treated polysaccharide is dried at from 30 to 500C, especially so at about 40"C.

The method of the present invention is particularly effective in stabilizing the viscosity of a cold starch solution. A cold starch solution is typically at less than about 300C and is preferably at about room temperature, such as is used in the manufacture of particle boards.

In addition, aqueous dispersions of water-soluble polysaccharides treated by the method of the present invention undergo less foaming than aqueous solutions of corresponding untreated polysaccharides.

In the method of the present invention, the said aqueous compositions are typically used in an amount of up to 5%, preferably up to 2%, more preferably up to 0.8% by weight composition based on the weight of water-soluble polysaccharide. The minimum amount of composition is typically about 0.1, preferably about 0.25% by weight based on the polysaccharide.

Preferably, the polysaccharides treated in the method of the present invention are not cationic in nature.

The water-soluble polysaccharide treated by the method of the invention may be used in numerous applications for example as a low cost filler for particle boards such as chip-board or medium density fibre board or as an absorbent for controlling oil spillages. It may also be used to impart a hydrophobic layer to paper.

The invention is illustrated by the following Examples.

EXAMPLE 1 The water repellent composition used was prepared by the following method. A reaction vessel was charged with 91.42g of water, 1.47g of stearic acid and 0.63g of 2 amino-2-ethyl-propane-l, 3-diol i.e. in approximately equimolar amounts giving a total concentration of 2.25% by weight. The mixture was then heated to 70 to 750C with gentle stirring. When this temperature was reached, the stirring rate was increased to 2000 rpm and these conditions were maintained for 15 minutes. The reactor contents were then cooled rapidly to below 30"C while maintaining a stirring rate of 2000 rpm. The stirring was then reduced prior to the addition of 6.48g of ammonium zirconium carbonate at a concentration of 7.5 weight % of zirconium i.e. an equimolar ratio of zirconium to amine salt.The water repellent composition thus obtained, which had a total solids content of 3.0% by weight, was used to treat maize starch as follows: 20g of maize starch was placed in the mixer head of a high shear mixer (Kunkle Mill). The water-repellent system was then added at various loadings (see Table below) prior to being mixed at high speed for three 5 seconds bursts.

When thoroughly mixed the resulting powders were dried at 400C. The resistance to water wetting was then determined visually after placing the treated starch in a beaker of cold continually agitated water.

TABLE 1

Test Amount of Water- Water Resistance repellent composition g % by 1 minute 5 minutes weight water repellent solids on starch 1 10 1.5 NON NON WETTING WETTING 2 6.7 1.0 NON NON WETTING WETTING 3 3.3 0.5 NON NON WETTING WETTING UNTREATED - - TOTAL TOTAL STARCH WETTING WETTING Thus the application of the composition to maize starch rendered it water-repellent.

CONPARATIVE EXAMPLE 1 600g of a 10% solution of untreated starch in distilled water was heated to 1000C in a water bath. It was then allowed to cool. The total cooling time was 30 minutes (950C-300C). The following results were obtained on cooling: TABLE 2

Temperature (OC) | Average viscosity from 2 tests (Centipoise) 80 30.5 30 38.3 60 45.0 50 55.5 40 72.3 30 121.0 EXAMPLE 2 Cationic acid-thinned starch, referred to as type A, was treated with 0.25% and 0.5% on a solid/solids basis by weight, of the aqueous water repellent composition obtained in Example 1. The aqueous water repellent composition was used at a concentration of 1.4% by weight.A Steele & BR< Cowlishaw mixer was used. The starch was mixed dry for 5 minutes, then the water repellent was added over 3 minutes before being mixed for a further 5 minutes.

In order to assess the effect of drying temperature on appearance, samples of the mixture were then dried at 40, 80 and 1300C together with a sample of untreated starch.

After being allowed to dry for two days each sample was used in turn to produce a 10% starch solution. The solutions were assessed for any colour change. The results are shown in Table 3.

TABLE 3

Amount of Drying Appearance of final Appearance of water water Temp. of 10% starch solution final 10% repellent Starch (hot) starch based on the ( C) solution starch (cold) solids (%) 40 Yellow/brown slightly Buff coloured opaque liquid opaque liquid 0 (control) 80 Yellowish/brown II slightly opaque liquid 130 Yellowish/brown slightly opaque liquid 40 Lemon slightly opaque Pale lemon liquid opaque liquid 0.25 80 Yellow/buff slightly Buff coloured opaque liquid opaque liquid 130 Orange/brown slightly ..

opaque liquid 40 Lemon coloured Whitish lemon slightly opaque opaque liquid 0.50 liquid 80 Yellow/lemon slightly Buff coloured opaque liquid opaque liquid 130 Orange/yellow slightly opaque liquid The drying temperature of the untreated starch was found not to have any adverse effects on the colour of the hot or cold solution. The treated starches dried at 400C, when used to produce solutions, were found to be paler than the untreated control when hot or cold. Drying the treated starch at 800C gave solutions similar in appearance to the undried untreated starch. Drying starch samples at 1300C was found to cause the solutions produced with the treated starch to be darker then those produced with the untreated starch.

EXAMPLE 3 Samples of treated starch were prepared in the same way as Example 2 except that all the samples were dried at 400C and that the amount of aqueous water repellent was varied as set out in Table 4 below.

To avoid paste formation, the aqueous water repellent composition was used at a concentration of 2.8% by weight in order to add a water repellent solids loading of 1.25%.

In all other cases the aqueous water repellent concentration was used at a concentration of 1.4% by weight.

The viscosity of the starches were measured immediately at 800C and after 24 hrs at 300C. The results are shown in Table 4.

TABLE 4

Amount of water Viscosity repellent based on (Centipoise) the starch solids (%) Immediately 980 C After 24hrs 030 C Undried control 38 900 400C dried control 56 910 0.25% 43 650 0.50% 42 260 0.79% 75 160 1.25% 61 134 800C dried control 42 1590 0.25% 44 950 0.50% 59 326 1300C dried control 46 1700 0.25% 65 1080 0.50% 58 330 EXAMPLE 4 Samples of cationic acid-thinned starch, referred to as type B, were prepared in the same way as in Example 2, except that all the samples were dried at 400C and that the amount of aqueous water repellent was varied as set out in Table 5 below.

To avoid paste formation, the aqueous water repellent composition was used at a concentration of 2.84% by weight solids in order to add a water-repellent solids loading of 1.4%. In all other cases, the aqueous water repellent composition was used at a concentration of 1.42% by weight solids.

The results are shown in Table 5.

TABLE 5

Amount of water Viscosity repellent (Centipoise) composition based on the the starch solids 8800C After 24 brs 8300C Undried Control 58 1780 Control 76 2240 0.25 77 1550 0.50 196 900 0.80 89 440 1.40 129 364 From the results obtained it can be seen that as the loading of water repellent composition was increased the viscosity of the starch solutions &commat;300C were reduced.

EXAMPLE 5 Samples of acid-thinned cationic starch, referred to as types A and B, were treated with varying amounts of the water repellent composition obtained in Example 1, in the same way as in Example 3.

10% starch sclutions were produced in the same way as in Example 2. They were heated to 1000C in a water bath and allowed to cool to 800C, at which point their initial viscosity was measured. They were then placed in sealed bottles in an oven at 800C for 24hrs before having their viscosity measured again. After this point the samples were placed for a further 24hrs in a water bath at 300C before once again being measured for viscosity.

The results are shown in Table 6.

TABLE 6

Starch Starch % of Water Initial Viscosity Viscosity Type Repellent based Viscosity after 24hrs after 24hrs on starch solids @80 C &commat; ;800C @30 C A 0 37 47 1370 (control) A 0.25 43 59 740 A 0.50 74 88 320 A 0.79 62 61 215 A 1.25 63 70 120 B 0 75 84 2430 (control) B 0.25 127 122 1410 B 0.50 156 157 850 B 0.80 127 137 I~ 540 B 1.40 132 138 380

Claims

1. A method of treating a water-soluble polysaccharide to render it water-repellent which comprises applying thereto an aqueous composition which is waterrepellent when dried, comprising the reaction product of (i) at least one carboxylic acid containing from 3 to 22 carbon atoms; (ii) at least one unsubstituted or substituted aliphatic amine or polyfunctional aromatic amine, containing from 2 to 25 carbon atoms; and (iii) a water-soluble metal complex crosslinking agent comprising one or more metals from Groups Ia, IIa, IIIa, IVa and the first and second rows of transition metals from the Periodic Table of Elements.

2. A method according to claim 1 wherein the metal is zinc, aluminium, titanium, copper, chromium, iron, zirconium or lead.

3. A method according to claim 1 wherein the crosslinking agent is ammonium zirconium carbonate.

4. A method according to claim 1, 2 or 3 wherein the carboxylic acid is stearic acid or tall oil fatty acid.

5. A method according to any one of claims 1 to 4 wherein the amine is 2-amino-2-methyl-propan-1-ol, 2-amino2-ethyl-propane-1,3-diol, or 3-amino-1,2-propane-diol, or tris-hydroxy-methyl-amino-methane.

6. A method according to any one of the preceding claims wherein the composition includes a saturated hydrocarbon wax.

7. A method according to any one of the preceding claims wherein the composition includes an alkyd resin.

8. A method according to any one of the preceding claims wherein the composition includes an aqueous acrylic polymer.

9. A method according to any one of the preceding claims wherein the composition includes a solubilising agent.

10. A method according to any one of the preceding claims wherein the composition contains 1 to 10% by weight of solids.

11. A method according to any one of the preceding claims wherein the water-soluble polysaccharide is starch, guar gum or xanthan gum.