High cohesive strength composite materials and, E.G., cigarette filters shaped therefrom

Abstract

Composite materials having high cohesive strength, formed from at least one polymer and from at least one compound selected from among mineral oxides, aluminosilicates and active carbon, are characterized by a mean particle size of at least 100 mm, a pore volume (Vd1) formed by pores having a diameter ranging from 3.6 to 1,000 nm, equal to at least 0.2 cm.sup.3/g, a cohesive strength such that its content of particles having a size of less than 100 mm, obtained after being subjected to an air pressure of 2 bar, of less than 1.5%, preferably 0.0%, by volume; such composite materials are formed into useful liquid supports, catalyst supports, additives, or liquid or gas filters, in particular into cigarette filters.

Claims

1. A composite material comprised of at least one polymer (P) selected from celluloses, starches, and derivatives thereof and at least one compound (C) selected from mineral oxides, silicoaluminates and activated carbon, wherein the composite material has: a median particle size of at least 100 μm; a pore volume (Vd1), made up of pores of diameters ranging from 3.6 to 1,000 nm, of at least 0.2 cm.sup.3/g; and a cohesion such that the amount of particles thereof having a size of less than 100 μm, obtained after an air pressure stress of 2 bar, is less than 1.5% by volume.

2. The composite material as defined by claim 1, wherein said at least one polymer (P) is selected from celluloses and derivatives thereof.

3. The composite material as defined by claim 1, wherein said at least one polymer (P) comprises cellulose acetate.

4. The composite material as defined by claim 1, wherein said at least one compound (C) is selected from silicas, aluminas, zirconium oxides, titanium oxides, iron oxides, cerium oxides, aluminosilicates and activated carbon.

5. The composite material as defined by claim 1, wherein said at least one compound (C) comprises precipitated silica.

6. The composite material as defined by claim 1, wherein said at least one compound (C) comprises activated carbon.

7. The composite material as defined by claim 1, wherein said at least one compound (C) comprises a mixture of precipitated silica and activated carbon.

8. The composite material as defined by claim 1, having a median particle size of at least 200 μm.

9. The composite material as defined by claim 1, having a pore volume (Vd1), made up of pores of diameter ranging from 3.6 to 1,000 nm, of at least 0.3 cm.sup.3/g.

10. The composite material as defined by claim 1, having a pore volume (Vd1), made up of pores of diameter ranging from 3.6 to 1,000 nm, of at least 0.5 cm.sup.3/g.

11. The composite material as defined by claim 1, having a cohesion such that the amount of particles thereof having a size of less than 100 μm, obtained after an air pressure stress of 2 bar, is less than 1.0%.

12. The composite material as defined by claim 1, having a cohesion such that the amount of particles thereof having a size of less than 20 μm, obtained after an air pressure stress of 2 bar, is equal to 0.0% by volume.

13. The composite material as defined by claim 1, having an average pore diameter, for pores of diameter ranging from 3.6 and 1,000 nm, of greater than 11 nm.

14. The composite material as defined by claim 1, having a BET specific surface area of at least 50 m.sup.2/g.

15. The composite material as defined by claim 1, having a median particle size of at least 300 μm, a BET specific surface area greater than 300 m.sup.2/g and a cohesion such that the amount of particles thereof having a size of less than 100 μm, obtained after an air pressure stress of 2 bar, is equal to 0.0% by volume.

16. The composite material as defined by claim 1, having a polymer (P) content of from 10% to 95%, and a compound (C) content of from 5% to 90%.

17. The composite material as defined by claim 1, shaped into cylindrical form or in the form of granules.

18. The composite material as defined by claim 1, further comprising at least one aroma and/or at least one plasticizer.

19. A process for preparing a composite material as defined by claim 1, comprising the following successive steps: 1) adding at least one compound (C), selected from among mineral oxides, aluminosilicates and activated carbon, into a polymer (P) solution, optionally with stirring; 2) forming the mixture obtained, by granulation or by extrusion; 3) introducing, into a liquid that is not a solvent for the polymer (P) and that is at least partially miscible with the solvent comprising the polymer (P) solution, the product formed, in order to render said polymer (P) insoluble; 4) washing the product obtained in order to eliminate, at least partially, the solvent comprising the polymer (P) solution; and 5) drying same.

20. The process as defined by claim 19, said polymer (P) being selected from among the following polymers: a cellulose, a starch, an alginate, a polyethylene, a guar, and a polyvinyl alcohol.

21. The process as defined by claim 19, wherein said polymer (P) comprises cellulose acetate.

22. The process as defined by claim 21, wherein the cellulose acetate solution employed in step 1) contains acetic acid as a solvent.

23. The process as defined by claim 21, wherein the liquid, which is not a solvent for cellulose acetate, employed in step 3) is water or an aqueous solution of acetic acid.

24. The process as defined by claim 19, wherein said at least one compound (C) is selected from among silicas, aluminas, zirconium oxides, titanium oxides, iron oxides, cerium oxides, aluminosilicates and activated carbon.

25. The process as defined by claim 19, wherein said at least one compound (C) comprises precipitated silica.

26. The process as defined by claim 19, wherein said at least one compound (C) comprises activated carbon.

27. The process as defined by claim 19, wherein said at least one compound (C) comprises a mixture of precipitated silica and activated carbon.

28. The process as defined by claim 19, wherein said at least one compound (C) has a BET specific surface area of at least 100 m2/g.

29. The process as defined by claim 19, wherein the step 2) is carried out by granulation, in a granulator equipped with blades or pins.

30. The process as defined by claim 19, wherein the step 2) is carried out by low-pressure or high-pressure extrusion.

31. The composite material as defined by claim 1, shaped as a liquid support.

32. The composite material as defined by claim 1, shaped as a solid support, as an additive or for liquid or gas filtration.

33. A cigarette filter comprising a composite material as defined by claim 1.

34. The cigarette filter as defined by claim 33, comprising precipitated silica and activated carbon.

Description

EXAMPLES 1-5

(1) In Examples 1 to 3, as compound (C), a precipitated silica in powder form is used as the starting material, having the following characteristics: BET specific surface area: 550 m.sup.2/g; oil uptake (DOP): 200 ml/100 g; median particle size: 23 μm; and moisture (ISO 787/2 standard, 105° C., 2 h): 7%.

(2) In Example 4, as compound (C), coconut activated carbon in powder form is used as the starting material, sold by Pica (containing 0.5% water, having a median particle size less than 80 μm and a BET specific surface area of 821 m.sup.2/g).

(3) In Examples 1 to 4, as polymer (P), cellulose acetate in solution in acetic acid is used as the starting material. More specifically, the solution of cellulose acetate used contains 18% of cellulose acetate, 11% of water and 71% of acetic acid.

Example 1

(4) Firstly, a mixture was prepared by adding 139 g of precipitated silica to 300 g of cellulose acetate solution.

(5) In order to do this, the precipitated silica was added gradually to the cellulose acetate solution, this addition being carried out with stirring (stirrer motor equipped with a frame paddle), so as to obtain a homogeneous mixture.

(6) Next, the mixture obtained was introduced into the bowl of a Rotolab Zanchetta granulator and granulation was carried out under the following conditions: temperature: room temperature; rotor speed of the granulator: 500 rpm; and granulation time: 25 minutes.

(7) The granules obtained at the end of the granulation were then poured into water, preheated to 60° C., in which they were left for 15 minutes, the water being subjected to stirring.

(8) After having removed them from the water, the granules were washed 5 times with cold water (duration of each wash: 15 minutes) in order to remove the residual acetic acid.

(9) After wiping, the granules were dried in a ventilated oven for 12 hours, at a temperature of 95° C.

(10) The characteristics of the composite material thus obtained (reference CM1) are given in Table 1.

Example 2

(11) Firstly, a mixture was prepared by adding 139 g of precipitated silica to 300 g of cellulose acetate solution.

(12) In order to do this, the precipitated silica was added gradually to the cellulose acetate solution, this addition being carried out with stirring (stirrer motor equipped with a frame paddle), so as to obtain a homogeneous mixture; the product obtained was placed in the bowl of a Rotolab Zanchetta granulator, in which it was subjected to stirring (rotor speed: 500 rpm) at room temperature for 5 minutes.

(13) Then the mixture obtained was introduced into the cylindrical screen of a Fuji Paudal extruder, the screen being pierced with 500 μm diameter orifices, and the extrusion was carried out by rotating the rotor that pushes the mixture through the screen, thus generating 500 μm diameter cylindrical extrudates. The application of an airstream made it possible to limit bonding between several cylindrical extrudates.

(14) The extrudates obtained were then poured into water that had been preheated to 60° C., in which they were left for 15 minutes, the water being subjected to stirring.

(15) After having removed them from the water, the extrudates were washed 5 times with cold water (duration of each wash: 15 minutes) in order to remove the residual acetic acid.

(16) After a light wiping, the extrudates were dried in a ventilated oven for 12 hours at a temperature of 95° C.

(17) The characteristics of the composite material thus obtained (reference CM2) are given in Table 1.

Example 3

(18) Firstly, a mixture was prepared by adding 13.9 g of precipitated silica to 30.0 g of cellulose acetate solution.

(19) In order to do this, the precipitated silica was added gradually to the cellulose acetate solution, this addition being carried out with stirring (stirrer motor equipped with a frame paddle), so as to obtain a homogeneous mixture.

(20) Then the mixture obtained was introduced into the ram body of a ram extruder and the extrusion was carried out by passing the mixture through a disc pierced with 800 μm diameter orifices, thus generating 800 μm diameter cylindrical extrudates.

(21) The extrudates obtained were then poured into water that had been preheated to 60° C., in which they were left for 15 minutes, the water being subjected to stirring.

(22) After having removed them from the water, the extrudates were washed 5 times with cold water (duration of each wash: 15 minutes) in order to remove the residual acetic acid.

(23) After a light wiping, the extrudates were dried in a ventilated oven for 12 hours at a temperature of 95° C.

(24) The characteristics of the composite material thus obtained (reference CM3) are given in Table 1.

Example 4

(25) Firstly, a mixture was prepared by adding 109.7 g of activated carbon to 200 g of cellulose acetate solution.

(26) In order to do this, the activated carbon was added gradually to the cellulose acetate solution, this addition being carried out with stirring (stirrer motor equipped with a frame paddle), so as to obtain a homogeneous mixture.

(27) Then the mixture obtained was introduced into the ram body of a ram extruder and the extrusion was carried out by passing the mixture through a disc pierced with 1000 μm diameter orifices, thus generating 1000 μm diameter cylindrical extrudates.

(28) The extrudates obtained were then poured into water that had been preheated to 60° C., in which they were left for 15 minutes, the water being subjected to stirring.

(29) After having removed them from the water, the extrudates were washed 5 times with cold water (duration of each wash: 15 minutes) in order to remove the residual acetic acid.

(30) After a light wiping, the extrudates were dried in a ventilated oven for 12 hours at a temperature of 95° C.

(31) The characteristics of the composite material thus obtained (reference CM4) are given in Table 1.

(32) TABLE-US-00001 TABLE 1 CM1 CM2 CM3 CM4 Median particle size (μm) 700 715 860 790 Vd1 (cm.sup.3/g) 0.78 0.55 0.77 0.46 Cohesion (Amount of 0.0% 0.0% 0.0% 0.0% particles <100 μm (2 bar))* Average pore diameter (nm) 14.0 11.7 12.4 36.5 BET surface area (m.sup.2/g) 360 380 360 517 Silica content (%) 70 70 70 — Activated carbon content (%) — — — 75 Cellulose acetate content (%) 30 30 30 25 *measured by the cohesion test mentioned in the description (% by volume)

(33) In particular, it can be seen that the composite materials according to the invention (CM1, CM2, CM3 and CM4), for each of which the amount of particles with a diameter of less than 100 μm, obtained after an air pressure stress of 2 bar (measured by the cohesion test mentioned earlier in the description) is equal to 0.0%, have a higher cohesion than silica alone (for which this amount is 10%) and than activated carbon alone (for which this amount is 2.0%).

Example 5

(34) In order to evaluate their properties for adsorbing volatile and semi-volatile compounds in a stream of cigarette smoke, the composite materials obtained in Examples 1 and 3 were used, after screening between 400 and 800 μm, in cigarette samples made from the tobacco part of standard Coresta Monitor No. 4 samples with which a manually mounted cavity filter is associated.

(35) This filter is made from an 8 mm long cellulose acetate segment, a cavity completely filled (without dead volume) with the additive to be tested and from another 8 mm long cellulose acetate segment. The additive to be tested is made either from one of the composite materials from Examples 1 and 3, or from silica alone or from activated carbon alone (corresponding to those used as the starting material in the above examples) by way of reference; in these last two cases, the quantity of silica or of carbon used in the filter is equal to the quantity of silica present in the filter containing the composite material from Example 1 or 3. The length of the cavity containing the additive is about 9 mm.

(36) After manually mounting the filter, each cigarette sample was conditioned for 90 hours at 60% relative humidity and at a temperature of 22° C., then smoked in a Borgwaldt (RM20H) 20 position rotary smoking machine.

(37) The smoke exiting the filter passes into a “Cambridge” filter that only allows the vapour phase to pass, this then being recovered by cold traps filled with methanol.

(38) The volatile and semi-volatile compounds thus recovered were analysed by gas chromatography-mass spectrometry (GC-MS).

(39) The degrees of reduction of the volatile and semi-volatile species indicated in Table 2 below were determined relative to those obtained with cigarettes of the same type, but for which a 9 mm long cavity was left empty between the two cellulose acetate segments.

(40) TABLE-US-00002 TABLE 2 Activated CM1 CM3 Silica carbon Silica content (%) 70 70 100  — Activated carbon content — — — 100  (%) Quantity used (mg) 107  107  75 75 Degree of reduction (%) Pyridine 81 81 75 55 Crotonaldehyde 47 48 34 71 Acrolein 55 63 52 69 Acetone 72 70 64 68 Methyl ethyl ketone 84 87 79 71 Acetonitrile 65 63 52 61

(41) It can be seen that the composite materials CM1 and CM3 have very satisfactory adsorption properties. Thus, they make it possible to obtain degrees of reduction of the volatile and semi-volatile species greater than those obtained with silica alone and overall at least equivalent to, even greater than, those obtained with activated carbon alone, while having a better cohesion.