GB1593383A - Production of vermiculite suspension - Google Patents

Description

(54) PRODUCTION OF VERMICULITE SUSPENSION (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London, SW1P 3JF, a British Company, 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: This invention relates to the treatment of a phyllosilicate mineral in order to produce an aqueous suspension of the mineral such that articles may be produced therefrom.

It is known that many phyllo-silicate minerals may be swollen by means of aqueous solutions of various salts. Vermiculite (as hereinafter defined) is an example of one such material and it has been proposed to form flexible sheets of swollen vermiculite after it has been delaminated to reduce the size of the individual particles or lamellae to colloidal dimensions; see for example the specifications of British Patent Nos 1,016,385 and 1,119,305. The term vermiculite is used to cover materials described mineralogically or commercially as vermiculite, and includes other phyllosilicate minerals such as hydrobiotites or chlorite-vermiculites which contain a proportion of vermiculite-like layers and can be expanded in the same or similar' manner.

According to the present invention we provide a process for production of an aqueous suspension of vermiculite comprising swelling by treating vermiculite ore consecutively with solutions of two different salts, namely an aqueous solution of a salt of sodium and subsequently an aqueous solution of a salt of an organo-substituted amonium cation and washing or soaking the ore with water after each treatment with a salt so that the ore swells to at least twice its original volume.

A further aspect of the invention also comprises delamination of the swollen vermiculite by subjecting the particles in the aqueous suspension attained after swelling to a shearing action.

It is preferred to allow the swelling of the ore to proceed to at least four times its original volume and often best results are obtained when the swelling ratio is more than six to one.

The anions in the salts of sodium or substituted ammonium are preferably inert anions commonly found in stable salts of these cations; anions which will not chemically decompose during the swelling process; for example, halide ions and preferably chloride.

The swelling may be carried out by soaking the ore in aqueous solutions of the salts at a variety of temperatures; usually temperatures above ambient produce a result more quickly, and therefore it is preferred to reflux the aqueous solution with the ore. The maximum extent of the swelling is only achieved by washing the ore with pure water and optionally soaking in water subsequent to the contact with solutions of the salts.

The delamination of the swollen vermiculite particles in the suspension occurs fairly easily provided some degree of shearing action is imparted. It may be imparted by means of a mill, mixer, or macerator which contains a shearing element for example a rotary paddle or blade working in a confined volume or a counter-rotating roller in a multi-roll mill.

Alternatively it may be imparted by suitable vibratory treatment for example ultrasonic agitation of the suspension.

The desired product of the delamination step is a suspension of small lamellae or platelets of vermiculite having one dimension very much smaller than the other two and accordingly we prefer not to impart a vigorous grinding action or a percussive action to the suspension which would tend to equalise the three dimensions of the particles. Suitably the preferred milling or maceration of the suspension may be performed by a high-speed rotary mixer for example a laboratory mixer contaning a rotary paddle (such as 'Greaves HS' Mark III) (Greaves is a Registered Trade Mark) or a liquidiser used for domestic or culinary purposes.Some high intensity mills for example a colloidal mill or a 'Polytron' (Registered Trade Mark) mixer should be used with caution because they tend to break lamellae quickly after the required delamination has occurred and they should be used only for the minimum time necessary to achieve a desired flocculated viscosity value.

The flocculated viscosity is defined for the purposes of this specification as the maximum viscosity, which a suspension, containing 3.5% by weight vermiculite solids, after the flocculation with dilute hydrochloric acid, will exhibit at a shear rate of 58 see-l. After shearing the suspension the value should not be less than 100 centipoise, but we prefer the value to be at least 400 centipoise.

The viscosity test provides a method whereby the delamination step may be monitored.

In order to perform the flocculated viscosity test the particles larger than 50 should be removed and it is convenient to filter off the particles larger than 50 llm from an aliquot of the suspension to flocculate by adding dilute hydrochloric acid and to transfer this sample suspension to a viscometer such as a Haake Rotovisko RV3 viscometer. Varying amounts of dilute hydrochloric acid are added to different aliquots of the suspension, the viscosity of each is determined and from the results, the maximum viscosity attainable is determined.

For example, from a graphical relation constructed for aliquots of 50 ml of suspension, it was observed that 20-30 ml of NA() hydrochloric acid (or 1-5 ml of N.HCI) were required to give the maximum viscosity.

For the de!amination process the concentration (measured by weight of vermiculite in a given volume of the suspension) may be suitably in the range 1% to 50% most conveniently in the range 5% to 25% by weight of vermiculite.

The particles in the suspension after delamination, are mainly those having particle dimensions of less than 50 Rm. These are the large dimensions of the particles and because the particles are in the form of small platelets or lamellae they all have one very small dimensions (the thickness of the plate), typically of the order of one thousandth or even one ten thousandth of the large dimensions.

Articles which may be produced from the suspensions of vermiculite lamellae after drying include sheet, film, papers, coatings, crepe, capsules, sachets, castings and mouldings, composed substantially wholly of vermiculite lamellae adhering together by mutually attractive forces.

Laminated or sandwich structures of vermiculite sheet or film with other materials, for example papers or plastics, may be made from suspensions of this invention.

The articles produced from the suspensions of the invention are affected by liquid water but they may be made water-resistant by an ion exchange process after shaping for example a process described in British Patent No. 1,016,385 or in the provisional specification accompanying our copending application no 14551/77. (Serial No.

Corrugated sheet may be prepared by either depositing the vermiculite suspension against a suitably contoured substrate or by impressing the dry sheet between shaped press platens or rollers. The corrugations may be produced in two directions, e.g. longitudinally and transversely and sheet so produced is not only decorative but also has improved mechanical properties e.g. elongation to break. Additionally, a large sheet so creped has improved handleability and drape. A plurality of layers of corrugated sheets may be cemented together to form a honeycomb, three dimensional structure.

Water may be removed whilst the article is being shaped either by evaporation with or without applied heat, or alternatively by absorption into an absorbent material of the shaping surface, e.g. a mould using a method similar to the slip-casting process used in the pottery industry. Electrophoretic methods of deposition of the lamellae from the suspension may be used advantageously when rapid removal of water is required. After the bulk of the water has been removed by any of the aforementioned methods the vermiculite layer may be stripped from the surface against which it is shaped or alternatively left in place as a non-combustible coating on the surface; a coating which has the added advantage of low water vapour permeability.

It has been observed that vermiculite of American origin, which tends to delaminate more efficiently than that of South African origin when made into sheet gives a much lower permeability to water vapour. For example a value has been obtained for water permeability of vcrmiculite twice as good as that normally found for polypropylene film.

The vermiculite suspension may be applied to a substrate for example a plastics material by any of the known surface coating techniques including spraying.

Materials such as wood, fibreboard and hardboard may be faced with vermiculite sheet by either using a suitable adhesive or by forming the vermiculite sheet in situ on the matcrials. The vermiculite coating enables such materials to obtain an improved rating on British Standard Fire Tests e.g. an indicative Class I in the small scale surface spread of flame whereas the materials without the vermiculite coating would only obtain Class III to IV.

Vermiculite sheet or paper may usefully be applied as a facing or liner to an organic polymer foam e.g. polyurethane foam panels, using conventional lamination techniques in order to improve the fire resistance of such panels as described in the provisional specification accompanying our copending application No 14764/76 (Serial No. 1585104).

Vermiculite sheet has been shown to withstand temperatures of at least 1000"C without cracking, the sheet maintaining its physical integrity although certain physical properties may be modified.

Vermiculite sheet may be used for example in the following applications: A To provide a fire-proof barrier to control the burning of organic foams or of wood and other inflammable products.

B To provide a flexible fire-proof packaging material able to prevent the spread of fire either by itself or when laminated to other materials e.g. polymer films or paper.

C To provide a combined fire and moisture resistant barrier for example an external facing for building materials.

D As a flexible container for thermal insulation material which is of a powdered or fibrous nature to prevent the dispersion of the insulation either at high temperatures or after prolonged use.

E To provide a flexible electrical insulation layer (e.g. a wrapping for cables) that will not disintegrate when exposed to fire or other high temperature conditions.

F As a flexible fire-proof membrane that will provide a protected enclosure during fire conditions to restrict the spread of smoke or gases or other contamination.

G As a protective flexible blanket or shield against sparks or flames e.g. from a welding torch.

H As separators for articles being treated in furnaces or kilns or as spacers for valuable documents e.g. to reduce the risk of complete destruction by fire.

I As a base structure for written records that will withstand high temperatures, and be relatively inert to chemical attack.

The invention is illustrated by the following Examples: Example 1 A 1 Kg sample of South African vermiculite (known as Mandoval "micron" grade) was refluxed for eight hours in 5 litres of a saturated solution of sodium chloride. Excess salt was then washed out of the product with water. The vermiculite was then refluxed for 8 hours in 5 litres of a solution of n-butylammonium chloride (made by diluting a mixture of 1250 ml of Normal hydrochloric acid and 120 ml of n-butylamine). After washing out excess salts, the product was left to swell in water. The fully swollen material (swelling ratio = 6.0) was divided into 2 equal portions.

Each portion was made up to 4 litres with water and milled for 1 hour with a "Greaves" high-speed mixer operating at 6000 rpm. Oversize material ( > 50 clam) was then removed from the product by a sedimentation procedure and the flocculated viscosity was measured as 500 centipoises.

Example 2 A 1 Kg of South African vermiculite (as used above) was refluxed in 5 litre of saturated sodium chloride solution for half an hour and subsequently washed thoroughly in distilled water. After draining out excess water, the vermiculite was refluxed for 2 hours in 5 litre of n-butylammonium chloride solution as prepared in Example 1. The vermiculite was then washed in distilled water and left to stand in water until the maximum swelling had taken place (swelling ratio = 4.8). A "Greaves" mixer was used to convert the swollen vermiculite into a suspension of suitably small lamellae (see Example 1).

On completion of the milling operation the oversize material ( > 50 um) was removed by passing the suspension through a 50 um stainless steel sieve and the flocculated viscosity was observed to be 500 centipoises. The solids content of the classified material was found to be 4.12% W/v (g./100 ml).

The suspension was dried overnight at room temperature in a well ventilated area, e.g. a fume cupboard, to form a sheet of thickness 0.13 mm. A failure stress and tensile modulus of 24,480 KNm-2 and 1929 MNm-2 respectively were recorded. Flexibility of the sheet under ambient conditions was good, giving more than 20 reverse folds without failing.

Example 3 1 Kg of North American vermiculite (Zonolite No 4) was subjected to the same processing conditions as in Example 2 (a swelling ratio of 5.6 was observed). The solids content of the filtered suspension ( < 50 um) was found to be 3.5% w/v.

Vermiculite sheets produced as in Example 2 had failure stress of up to 50,592 KNm-2 and tensile moduli of up to 6069 MNm-2. The flexibility of the sheets were similar to those in Examples 1 and 2.

Example 4 Two 3 Kg batches of South African vermiculite (Mandoval "micron" grade) were refluxed for half an hour in 15 litres of saturated sodium chloride solution and, then after thorough washing in distilled water, were refluxed for a further two hours in 15 litre of n-butylammonium chloride solution as prepared in Example 1. The vermiculite ore was again thoroughly washed in distilled water and swelling began to take place. When placed in 20 litres containers each batch reached a final swollen volume of 5.5 times the original volume of the ore. The two batches were then combined for the milling experiments. The solids content of the combined batch was adjusted to 9% w/w.

The swollen vermiculite was converted into a suspension using three different milling systems; (a) 4 1 batches were milled in a Greaves mixer at 6000 rpm.

(b) 2 1 batches were milled in a similar rotor-in-stator mill (known as an Ilado mill) at approximately 15,000 rpm.

(c) 1 1. batches were milled in a "Kenwood" liquidiser as used for culinary purposes.

The operating speed was 14,000 rpm. ("Kenwood" is a Registered Trade Mark).

The milled suspension in each case was classified by passing through a 50 llm sieve. To determine the maximum flocculated viscosity of each milled sample, increasing amounts of N HCI were added to 50 ml aliquots of the suspensions adjusted to 3.5% w/w solids content.

After mixing the acid and the vermiculite suspension using a magnetic stirrer the flocculated suspension was rapidly transferred to a viscometer and the maximum viscosity measured.

All viscosity determinations were made on a Haake Rotovisko RV3 viscometer running at a fixed shear rate of 5X sec-l and a temperature of 25"C. Vermiculite sheets were made from each of the suspensions (not flocculated) and the tensile strength measured on samples dried for 24 hours in a vacuum desiccator. The relationship between Failure Stress and flocculated viscosity is shown in the Table.

Type of Time of milling GX, convcrsion* Flocculated Failure mill (mins) to 50Mm viscosity (cp) stress suspension KNm Greaves 45 37 630 32,700 90 47 510 22,750 ll;ido 2 35 650 27,050 20 78 600 26,500 Kcnwood 5 30 470 23,000 30 68 440 16,200 * % conversion is that percentage of the total vermiculite solids in the suspension which is converted to particles of less than 50 Mm.

In this present application we make no claim to the subject matter claimed in our UK Application No. 41733/79 (Serial No. 1582121). In our copending application No. 39510/76 (Serial No. 1593382), from which the subject matter of this present application has been divided, a process for the production of shaped articles of vermiculite lamellae and an aqueous suspension used to make such articles are described and claimed: a characteristic of both the process and the suspension claimed in that the vermiculite lamellae have dimensions no greater than 50 um.

WHAT WE CLAIM IS: 1. A process for the production of an aqueous suspension of vermiculite comprising swelling, by treating vermiculite ore consecutively with solutions of two different salts, namely an aqueous solution of a salt of sodium and subsequently with an aqueous solution of a salt of an organo-substituted ammonium cation, and washing or soaking the ore with water after each treatment with a salt so that the ore swells to at least twice its original volume.

2. A process as claimed in claim 1 also comprising delamination of the swollen vermiculite by subjecting the particles in the aqueous suspension produced by the process of claim 1 to a shearing action.

3. A process as claimed in claim 1 or claim 2 wherein the salts are halide salts.

4. A process as claimed in any one of claims 1 to 3 wherein the organo substituted ammonium cation is the n-butyl ammonium cation.

5. A process as claimed in any one of claims 1-4 wherein the salts are contacted at

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Vermiculite sheets produced as in Example 2 had failure stress of up to 50,592 KNm-2 and tensile moduli of up to 6069 MNm-2. The flexibility of the sheets were similar to those in Examples 1 and 2.

   Example 4 Two 3 Kg batches of South African vermiculite (Mandoval "micron" grade) were refluxed for half an hour in 15 litres of saturated sodium chloride solution and, then after thorough washing in distilled water, were refluxed for a further two hours in 15 litre of n-butylammonium chloride solution as prepared in Example 1. The vermiculite ore was again thoroughly washed in distilled water and swelling began to take place. When placed in 20 litres containers each batch reached a final swollen volume of 5.5 times the original volume of the ore. The two batches were then combined for the milling experiments. The solids content of the combined batch was adjusted to 9% w/w.

   The swollen vermiculite was converted into a suspension using three different milling systems; (a) 4 1 batches were milled in a Greaves mixer at 6000 rpm.

   (b) 2 1 batches were milled in a similar rotor-in-stator mill (known as an Ilado mill) at approximately 15,000 rpm.

   (c) 1 1. batches were milled in a "Kenwood" liquidiser as used for culinary purposes.

   The operating speed was 14,000 rpm. ("Kenwood" is a Registered Trade Mark).

   The milled suspension in each case was classified by passing through a 50 llm sieve. To determine the maximum flocculated viscosity of each milled sample, increasing amounts of N HCI were added to 50 ml aliquots of the suspensions adjusted to 3.5% w/w solids content.

   After mixing the acid and the vermiculite suspension using a magnetic stirrer the flocculated suspension was rapidly transferred to a viscometer and the maximum viscosity measured.

   All viscosity determinations were made on a Haake Rotovisko RV3 viscometer running at a fixed shear rate of 5X sec-l and a temperature of 25"C. Vermiculite sheets were made from each of the suspensions (not flocculated) and the tensile strength measured on samples dried for 24 hours in a vacuum desiccator. The relationship between Failure Stress and flocculated viscosity is shown in the Table.

   Type of Time of milling GX, convcrsion* Flocculated Failure mill (mins) to 50Mm viscosity (cp) stress suspension KNm Greaves 45 37 630 32,700

   90 47 510 22,750 ll;ido 2 35 650 27,050

   20 78 600 26,500 Kcnwood 5 30 470 23,000

   30 68 440 16,200 * % conversion is that percentage of the total vermiculite solids in the suspension which is converted to particles of less than 50 Mm.

   In this present application we make no claim to the subject matter claimed in our UK Application No. 41733/79 (Serial No. 1582121). In our copending application No. 39510/76 (Serial No. 1593382), from which the subject matter of this present application has been divided, a process for the production of shaped articles of vermiculite lamellae and an aqueous suspension used to make such articles are described and claimed: a characteristic of both the process and the suspension claimed in that the vermiculite lamellae have dimensions no greater than 50 um.

   WHAT WE CLAIM IS: 1. A process for the production of an aqueous suspension of vermiculite comprising swelling, by treating vermiculite ore consecutively with solutions of two different salts, namely an aqueous solution of a salt of sodium and subsequently with an aqueous solution of a salt of an organo-substituted ammonium cation, and washing or soaking the ore with water after each treatment with a salt so that the ore swells to at least twice its original volume.
2. 2. A process as claimed in claim 1 also comprising delamination of the swollen vermiculite by subjecting the particles in the aqueous suspension produced by the process of claim 1 to a shearing action.
3. 3. A process as claimed in claim 1 or claim 2 wherein the salts are halide salts.
4. 4. A process as claimed in any one of claims 1 to 3 wherein the organo substituted ammonium cation is the n-butyl ammonium cation.
5. 5. A process as claimed in any one of claims 1-4 wherein the salts are contacted at

   temperatures above ambient.
6. 6. A process as claimed in claim 5 wherein the salts are contacted under reflux conditions.
7. 7. A process as claimed in any one of claims 1-6 wherein the swelling of the ore is allowed to proceed to at least four times its original volume.
8. 8. A process as claimed in any one of claims 2-7 wherein the delamination is continued until the flocculated viscosity is at least 100 centipoises.
9. 9. A process as claimed in claim 8 wherein the delamination is continued until the flocculated viscosity is at least 400 centipoises.
10. 10. A process as claimed in any one of the preceding claims wherein the solution of the sodium salt is a saturated solution.
11. 11. A process as claimed in claim 1 and substantially as described herein with reference to and as shown in any one of the foregoing examples.
12. 12. A suspension of vermiculite lamellae produced by a process as claimed in any one of claims 2-11.
13. 13. A suspension of vermiculite lamellae substantially as described herein and as shown in any one of the foregoing examples.