CA1046873A

CA1046873A - Hardenable sheet materials

Info

Publication number: CA1046873A
Application number: CA214,818A
Authority: CA
Inventors: Robert S.R. Parker
Original assignee: National Research Development Corp of India
Current assignee: National Research Development Corp of India
Priority date: 1973-11-29
Filing date: 1974-11-28
Publication date: 1979-01-23
Also published as: AU7561474A; AU499410B2; FR2252837B1; IT1024928B; JPS5089458A; SE7414956L; IL46121A0; IL46121A; DE2456145A1; DE2456145C2; IN143637B; FR2252837A1; ES432446A1; JPS5511139B2; ZA747391B; SE417844B; BR7409973A

Abstract

ABSTRACT
A water-hardenable sheet material comprising a flexible web having deposited thereon an intimate mixture of a water soluble poly(carboxylic acid) or a precursor thereof and an ion leachable inorganic particulate material.

Description

-This inventiou relates to hardenable sheet materials and more particularly to sheet materials which harden on contact with water. ~ater-hardenable sheet materials have a variety of applications, for example, in orthopaedic surgery they are widely used as splinting materials. Traditionally, bandages comprising plaster-of-Paris are soaked in water and then applied to the affected limb. The plaster-of-Paris hardens within a - few minutes to form a rigid casing. Although plaster-of-Paris casts are adequate for some applications, they are heavy, not wholly resistant to water, and partially opaque to x-rays. In addition, plaster-of-Paris casts usually take at least twenty four hours to develop their maximum strength, and thi~ time may be considerably longer in high humidity environments. If a plaster-of-Paris cast is stressed whilst in the "green" state, that is to say before it has reached its maximum strength, it i9 liable to delaminate, leading to incipient failure of the cast.
In some applications these disadvantages can be quite serious, and for this reason many attempts to find an alternative to plaster-of-Paris have been tried. For example, it has been suggested to use a polymerisable resin system which i~ polymsrised by ultraviolet light. ~owever, this requires the use of specialised techniques, and of course involves the expense of a suitable ultraviolet light source. For many surgical applications there i~ a need for a splinting material which is simple to u~e, hardens at room temperature without the evolution qk :- . . - . .
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of substantial amounts of heat, has a high green strength, develops its maximum strength as rapidly as possible, is non-toxic, resistant to hot and cold water, and transparent to x-rays.
In recent years, a range of dental cements have been developed known as the poly(carboxylate) cements and these are described and claimed in British Patent~ Nos. 1,139,430 and 1,316,129. The~e materials normally comprise an ion-leachable powder and an a~ueous soluti-Dn of a poly(carboxylic acid) which when mixed together form a cement of great mechanical strength and water resistance.
The present invention provides a water-hardenable sheet material in which the hardening reaction involves the formation of a poly(carboxylate) cement~
According to the present invention, a water-hardenable sheet material comprises a flexible web having deposited thereon an intimate mixture of a water soluble poly(carboxylic acid) or a precursor thereof and an ion-leachable inorganic particulate material.
The term "sheet" is used in the sense of a body whose breadth i8 large in comparison with its thickness. The flexible web may be woven, laid down as a non-woven fabric, cast, or extruded.
It is preferred that the web be permeable in order to aid the deposition thereon of the water soluble poly(carboxylic acid) or precursor thereof and the ion-leachable inorganic particulate material. For surgical applications, a permeable web has the further advantage that it can allow access of air to the encased limb. The web most preferably has a porous structure, and in the case of woven or non-woven fabrics, the poro~ity of the web-may be conditioned by the method of manufacture, so ; 2 ~, ~ ' ' - .. : , .. . ., .,: ~- .. ~ .
-104ti873 that this particular characteristic may be predetermined to suit anyspecial requirements.
; The flexible web may ccmprise an or~anic natural or synthetic polymeric material, and particularly a cellulosic fibrous material such -`
as cotton or other vegetable fibres, animal fibres such as wool, and synthetic polymeric fibrous material such as polyamides, polyesters, and cellulose acetates. The flexible web desirably has sufficient mechanical strength to enable it to act as a reinforcement for the sheet material.
For surgical aPplications very good results have been obtained using a cotton bandage fabric, for example of leno weave. The cotton fibres may be reinforced with glass fibre if desired. Although less preferred, the flexible web may also be in the form of an impermeable film or foil of plastic or other suitable material.
me preferred poly(carboxylic acids) are those prepared by the homopolymerisation and copolymerisation of unsaturated aliphatic carboxylic acids for example acrylic acid, itaconic acid, mesaconic acid, citraconic acid, and aconitic acid, and copoly~meris~tion of these acids with other unsaturated aliphatic monomers, for example, acrylamide and acrylonitrile. Particularly preferred are the homopolymers of acrylic acid, and its copolymers, particularly with itaconic acid for example as described and claimed in ~ritish Patent Specification No. 1,~84,454.
Good results have also been obtained using a copolymer of vinyl methyl ether and maleic acid. Any suitable route may be used for the preparation of the poly(carboxylic acid) and for example, polyacrylic acid may be B

1~46873 prepared by hydrolysis of polyacrylonitrile. It is also possible to use a precursor of a poly(carboxylic acid) which will be transformed into the poly(carboxylic acid) on contact with water, for example, a poly(car-boxylic acid anhydride) or other suitable polymer. The poly(carboxylic acid anhydride) may be a hcmopolymer of an unsaturated carboxylic acid anhydride, or a copolymer with a vinyl monomer, and particularly a vinyl hydrocarbon m~nomer. Particularly good results may be obtained using ; homopolymers of maleic anhydride, and copolymers thereof with ethylene, propene, butene and styrene.
The poly(carboxylic acid) or precursor thereof is preferably linear, although branched polymers may also be used, and preferably has an average molecular weight of from 1,000 to 1,000,000 and most preferably from 10,000 to 100,000. In this specification the average molecular weight is defined as being that measured by gel permeation chromatography.
The poly(carboxylic acid) is preferably in fine particulate form, and most preferably with a degree of fineness such that it will pass through a 150 BS mesh sieve.
The ion-leachable inorganic particulate material may for example comprise a di- or polyvalent metal oxide, preferably one that has been deactivated, for example by heat treatment as described in Eritish Patent No. 1,139,430, or by partially coating the surface of the metal oxide particles with an organic acid such as stearic acid.
A preferred metal oxide is zinc oxide, to which there may be -1(~46873 added up to about 10% by weight of other metal oxides such as, for example magnesium oxide. The di- or polyvalent metal oxide may if desired be replaced by a salt of the di- or polyvalent metal with a weak acid,the weak acid being capable of an exchange reaction with the poly(carboxylic acid) used, for example zinc oxide may be wholly or partially replaced by zinc borate. Alternatively, the ion-leachable inorganic particulate material may comprise a fused oxide made by heating a mixture of simple oxides to fusion temperature or an oxide glass, for example a glass comprising calcium or sodium oxide with alumina and silica. The preferred ion-leachable inorganic materials for use in the present invention are aluminosilicate glasses, wherein the ratio by weight of acidic to basic oxides in the glass is such that the glass will react with a poly(carboxylic acid) in the presence o$ wàter to produce a poly(carboxylate) cement. It has been found that the rate of reaction increases with increasing basicity of the aluminosilicate gla~s and thus the ratio of the oxides in the glass composition can be chosen in order to allow adequate working time to form the water-hardenable sheet material into a desired shape before it has set. For many applications it is preferable to attain a working time of about 5 minutes, or less, and then to have the shortest possible setting time in which the sheet material hardens and attains an appreciable rigidity and mechanical strength. Suitable aluminosilicate glasses may, for example, be prepared by fusing mixtures of alumina, silica, and calcium oxide in the appropriate proportions, together with, if necessary, up to 30% by weight, ~0~6873 based on the total weight of the composition, of a flux which may be a fluoride, a borate, a phosphate, or a carbonate. Many suitable alumino- -silicate glasses are available. Most prefera~ly, however, the ion-leachable inorganic partic~ate material comprises a fluoroaluninosilicate glass, for example as described and claimed in British Patent No. 1,316,129, wherein the ratio by weight of silica to alumina is from 1.5 to 2.0 and the ratio by weight of fluorine to alumina is from o.6 to 2.5 or wherein ; the ratio by weight of silica to alumina is from 0.5 to 1.5 and the ratio by weight of fluorine to alumina is from 0.25 to 2Ø The fluoroalumino-silicate glasses may be prepared by fusing mixtures of silica, alumina, cryolite, and fluorite in the appropriate proportions at a temperature -above 950 C. Suitable methods for preparing the glasses are described in the aforementioned British Patent.
me degree of fineness of the ion-leachable inorganic particulate material should preferably be such that when the water-hardenable sheet material is contacted with water it sets in the desired shape within an , acceptable period. Preferably the degree of fineness of the ion-leachable } inorganic particulate material is such that it will pass through a 150 mesh B.S. sieve and most preferably such that it will pass through a 350 mesh B.S. sieve. Where the ion-leachable inorganic material comprises an aluminosilicate glass, this may be used in the form of glass fibres if desired.
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1~46873 In a preferred method of preparing the water-hardenable sheet materials of this invention, the ion-leachable inorganic particulate material is slurried in a dispersion or solution of the poly(carboxylic acid) or precursor thereof in a suitable organic solvent, Ifor example methyl ethyl ketone, cyclohexanone or methylene dichloride. The flexible web is then impregnated with the slurry by a coating technique, and the organic solvent removed, for example by evaporation. m e amount of slurry deposited on the flexible web may be varied within wide limits, but preferably the depo~ited ion-leachable inorganic particulate material and poly(carboxylic acid) or precursor thereof comprise from ahout 5 to about 95% by weight, preferably from 60 to 90% by weight, of the total weight of the water-hardenable sheet material. m e acid and the ion-leachable inorganic particulate material are preferably present in the ratio of 1 to 100 parts by weight of ion-leachable inorganic particulate material for each 10 parts by weight of the poly(carboxylic acid) or precursor thereof.
Preferably, the ~lurry comprises a binder to assist the adherence of the ion-leachable inorganic particulate material to the flexible web. Suitable binders include polyvinyl alcohol, polyvinyl acetate and partially hydrolysed polyvinylacetate.
Usually only small quantities of the binder are required, for example up to about 5% by weight based on the combined weight of the acid and the inorganic material, and preferably from 0.1 to 1%.

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The water-hardenable sheet m~terial may comprise additional components, for example chemically unreactive particulate fillers may be included, to effectively eliminate any slight contraction which may take place on hardening of the hardenable sheet material. It is also often found advantageous to add a water soluble chelating agent such as tartaric ; acid, as described and claimed in British Patent Specification No. 1,422,3~7, to the water-hardenable sheet material as this has been found to decrease the setting time of poly(carboxylate) cements and increase the strength of the set cement.
In low humidity environments, poly(carboxylate) cements tend to lose water and this may have a slight detrimental effect upon the strength of the hardened sheet material. This effect may be substantially overcome by including in the slurry to be applied to the flexible web a water insoluble polymer. Such a polymer may, for example, be dissolved or emulsified in the organic solvent so that after removal of the solvent the water insoluble polymer is in particulate form, intimately mixed with the other components. The water insoluble polymer preferably comprises pendant carboxylic acid groups which can take part in the hardening reaction, and for example it may comprise a copolymer of an unsaturated allphatic carboxylic acid for example acrylic acid, methacrylic acid and itaconic acid, and an unsaturated aliphatic ester, for example an acrylic ester such as methyl methacrylate, ethyl acrylate and ethyl methacrylate.
Good results E3y be obtained using a B

1~46873 copolymer of methacrylic acid and ethyl acrylate. Alternatively the water insoluble polymer may be applied to the water-hardenable sheet ~ -material as an aqueous emulsion at the time of use.
When used as splinting materlal-s~ the water-hardenable sheet materials of this invention are designed to be used by the practitioner in the same manner as the conventional plaster-of-Paris splinting materials.
m us the water-hardenable sheet material in the form of a roll may be contacted with water by, for example, dipping or spraying, and then wound around the limb which it is desired to encase, overlapping ad~acent turns as required. me sheet material is ~nitially flexible enabling it to be formed into a desired shape prior to hardening. Within a relatively short time, usually a few minutes, however, the hardening has proceeded to an extent sufficient to produce a hard tough cast. me hardening reaction may be accelerated by the use of warm water.
The water-hardenable sheet materials of the present invention may also find applications outside conventional surgical use, for ex~mple they may be used in forestry to repair damaged branches of young ~rees, ¦ and may find application as m~delling materials for children.
e inventlon is illustrated by the following Example:
EXAMPLE
This Example describes the production of a water-hardenable sheet material according to the present invention and its application to the manufacture of surglcal splints.

-80.0 gms. of a fluroaluminosilicate glass powder prepared as described in Example 2 of British Patent No. 1,316,129 and having a particle size of 350 B.S. mesh are intimately mixed with 24.4 gms. of finely powdered polyacrylic acid of average molecular weight 90000 and water content 8% by weight. This mixture is slurried in methylethyl ketone to give a suspension of about 40X
solids, and 0.5 gm. of poly(vinyl acetate) binder added. With the suspension in agitation, 50 mm width leno gauze bandage is passed through and the pick-up of solids controlled with a doctor blade. The methylethylketone is removed by drying under a hot air blower whereupon the gauze can be rolled up in the manner of a conventional bandage.
m e coated gauze is then sprayed with water, and wound around a cylindrical mandrel, smoothing the turns by hand. m e turns of the gauze are allowed to overlap so that on hardening, after 30 minutes, the gauze can be removed from the mandrel as a hollow cylindrical cast. After 48 hours the cast i8 cut up into rings, mounted in an Instron machine and subjected to compression at a rate of 5 mm.min 1 The stresses for strains of 5%, 10% and 12.5%
are calculated. For the purposes of comparison, a pla~ter-of-Paris ca~t i~ prepared in the same manner and similarly tested for compressive strength. The results are given below:

" 1¢146873 TABLE 1:

Specimen Rin~ Dimensions Poly(carboxylate) Plaster-of-Paris Length (mm) 15 15 Internal Diameter (mm) 14 14 External Diameter (mm) 15. 5 18 Weight of material (Kgm ) 0.183 0.398 Length of gauze bandage (mm) 225 225 TABLE 2:
. _ Strain (%) Average Stress (N) Poly(carboxylate) Plaster-of-Paris .
16.3 21.1 22.4 26.4 12.5 24.2 28.8 These results show that the water-hardenable sheet materials of the present invention have excellent compressive strength combined with a considerable reduction in weight. Although the poly(carboxylate) cast iY half the weight of the plaster-of-Paris 5 cast, its compressive strength is only slightly less. In addition, the poly(carboxylate) cast is not attacked by hot or cold water, is non-toxic and non-irritational, and is transparent to x-rays.
The average time taken for a poly(carboxylate) cast to reach its maximum strength is about 8 hours, in comparison with 2~ hours for a plaster-of-Paris cast.
Further tensile stress tests carried out on samples of comparable size show that a poly(carboxylate) cast i9 almost twice as strong as a cast made from plaster-of-Paris.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A sheet material hardenable in the presence of water with the formation of a poly(carboxylate) cement.

2. A sheet material according to claim 1 which comprises a flexible web.

3. A sheet material according to claim 2 in which the flexible web has a porous structure.

4. A sheet material according to claim 2 or 3 in which the flexible web comprises a cellulosic fibrous material.

5. A sheet material according to claim 2 in which the flexible web carries a water soluble poly(carboxylic acid) or a precursor thereof that will form the poly(carboxylic acid) on contact with water and an ion-leachable inorganic particulate material.

6. A sheet material according to claim 5 in which the poly(car-boxylic acid) is a homopolymer or copolymer of acrylic acid.

7. A sheet material according to claim 5 in which the precursor is a poly(carboxylic acid anhydride).

8. A sheet material according to claim 5 in which the poly(car-boxylic acid) or precursor thereof has an average molecular weight of from 10,000 to 100,000.

9. A sheet material according to claim 5 in which the poly(car-boxylic acid) or precursor thereof is in fine particulate form, and has a degree of fineness such that it will pass through a 150 BS mesh sieve.

10. A sheet material according to claim 5 in which the ion-leachable inorganic particulate material comprises an oxide of a di- or higher polyvalent metal, or a salt of a weak acid (as herein defined) or a di-or higher polyvalent metal.

11. A sheet material according to claim 10 in which the oxide is zinc oxide.

12. A sheet material according to claim 5 in which the ion-leachable inorganic particulate material comprises an aluminosilicate glass.

13. A sheet material according to claim 12 in which the alumino-silicate glass has been prepared by fusing a mixture of alumina, silica, and calcium oxide optionally together with up to 30% by weight, based on the total weight of the mixture, of a fluoride, borate, phosphate, or carbonate flux.

14. A sheet material according to claim 12 or 13 in which the ion-leachable inorganic particulate material comprises a fluoroalumino-silicate glass.

15. A sheet material according to claim 12 in which the ion-leachable inorganic particulate material has a degree of fineness such that it will pass through a 150 BS sieve.

16. A sheet material according to claim 5 in which the combined weight of the ion-leachable inorganic particulate material and the poly(car-boxylic acid) or precursor thereof comprises from 60 to 90% of the total weight of the material.

17. A sheet material according to claim 5 in which the poly(car-boxylic acid) or precursor thereof and the ion-leachable inorganic particulate material are present in the ratio of 1 to 100 parts by weight of ion-leachable inorganic particulate material to every 10 parts by weight of the poly(carboxylic acid) or precursor thereof.

18. A sheet material according to claim 5 in which the water soluble poly(carboxylic acid) or precursor thereof and the ion-leachable particulate material are deposited on the flexible web as an intimate mixture.

19. A sheet material according to claim 5 that includes a binder to assist the adherence of the ion-leachable inorganic particulate material to the flexible web.

20. A sheet material according to claim 19 in which the binder is polyvinyl alcohol, polyvinyl acetate, or partially hydrolysed polyvinyl acetate.

21. A sheet material according to claim 19 in which the binder is present in an amount of from 0.1 to 1% by weight based on the combined weight of the acid and the inorganic material.

22. A sheet material according to claim 1 or 5 that comprises an inert particulate filler.

23. A sheet material according to any of the preceding claims that comprises a water soluble chelating agent.

24. A sheet material according to claim 1 or 5 that comprises a water insoluble polymer in particulate form.

25. A sheet material according to claim 24 in which the water insoluble polymer comprises pendant carboxylic acid groups.

26. A sheet material according to claim 24 in which the water insoluble polymer is a copolymer of an unsaturated aliphatic carboxylic acid and an unsaturated aliphatic ester.

27. A sheet material according to claim 24 in which the water insoluble polymer is a copolymer of methacrylic acid and ethyl acrylate.

28. A sheet material according to claim 1 or 5 which has been hardened by the formation of a poly(carboxylate) cement.

29. A sheet material according to claim 28 which comprises a flexible web and which is formed as a surgical splint.

30. A process for the production of a water-hardenable sheet material, which process comprises depositing on to a flexible web a water soluble poly(carboxylic acid) or a precursor thereof and an ion-leachable inorganic particulate material.

31. A process according to claim 30 in which the water soluble poly(carboxylic acid) or precursor thereof and the ion-leachable inorganic particulate material are deposited on the flexible web as an intimate mixture.