THERMOSET FOAMS AND MANUFACTURING PROCESS

Abstract

A process for the manufacture of a solid thermoset foam includes the following successive stages: (a) making available an expandable and thermosetting composition containing a sugar and an acid catalyst chosen from strong acids, phosphoric acid and acidic inorganic salts, (b) introducing the expandable and thermosetting composition into a mold or applying the expandable composition to a support as a film with a thickness at least equal to 1 mm, and (c) heating the expandable and thermosetting composition to a temperature at least equal to 140 C., so as to form a block of solid thermoset foam.

Claims

1. A process for manufacturing a solid thermoset foam comprising the following successive stages: (a) making available an expandable and thermosetting composition containing: a sugar, and an acid catalyst chosen from strong acids, phosphoric acid and acidic inorganic salts, a concentration of strong acids being at least equal to 0.1 N, a concentration of phosphoric acid being at least equal to 0.1 mol/l and a concentration of acidic inorganic salts being such that the pH of the composition is less than or equal to 3, the acidic inorganic salts being chosen from aluminum, gallium, copper, zinc, silver, nickel, iron and lead sulfates, nitrates, chlorides and bromides, (b) introducing the expandable and thermosetting composition into a mold or applying the expandable composition to a support as a film with a thickness at least equal to 1 mm, and (c) heating the expandable and thermosetting composition to a temperature at least equal to 140 C., so as to form a block of solid thermoset foam.

2. The process as claimed in claim 1, wherein, when the acid catalyst is chosen from a group formed by strong acids and phosphoric acid, the acid/sugar molar ratio is less than .

3. The process as claimed in claim 1, wherein the thickness of the film is at least equal to 2 mm.

4. The process as claimed in claim 1, wherein the block of solid thermoset foam is a slab.

5. The process as claimed in claim 1, wherein the expandable composition contains at most 60% by weight of water.

6. The process as claimed in claim 1, wherein the sugar represents at least 70% of the dry weight of the expandable composition.

7. The process as claimed in claim 1, wherein the sugar is chosen from reducing sugars and nonreducing sugars.

8. The process as claimed in claim 7, wherein the sugar is a reducing sugar chosen from glucose and starch hydrolysates.

9. The process as claimed in claim 1, wherein the concentration of strong acid is between 0.1 and 1.5 N.

10. The process as claimed in claim 1, wherein the expandable composition additionally contains up to 20% by weight, with respect to the dry weight of the total expandable composition, of one or more inorganic or organic fillers.

11. A solid foam produced by the process as claimed in claim 1.

12. The solid foam as claimed in claim 11, wherein the solid foam exhibits a density of between 30 and 60 kg/m.sup.3.

13. The solid foam as claimed in claim 11, wherein the solid foam exhibits a closed porosity.

14. The solid foam as claimed in claim 11, wherein a mean diameter of pores of the solid foam, determined by X-ray tomography, is between 100 and 800 nm.

15. A composition containing: a sugar, and an acid catalyst chosen from strong acids, phosphoric acid and acidic inorganic salts, wherein the composition is an expandable and thermosetting composition for manufacturing an insulating product of foam type.

16. The process as claimed in claim 1, wherein, when the acid catalyst is chosen from a group formed by strong acids and phosphoric acid, the acid/sugar molar ratio is between 1/34 and 1/10.

17. The process as claimed in claim 1, wherein the thickness of the film is at least equal to 10 mm.

18. The process as claimed in claim 1, wherein the expandable composition contains at most 5% by weight of water.

19. The process as claimed in claim 1, wherein the sugar represents at least 90% of the dry weight of the expandable composition.

20. The process as claimed in claim 1, wherein the sugar is chosen from reducing sugars.

Description

EXAMPLE 1

[0054] Inorganic Salts

[0055] Several expandable and thermosetting compositions are prepared by adding an aqueous solution of the acid catalyst (acidic inorganic salt) to a glucose monohydrate powder. The mixture is stirred at ambient temperature in order to disperse the powder.

[0056] The respective amounts of sugar and of acidic inorganic salt, expressed as dry matter, the concentration of the acid catalyst in mol/l and also the total solids content of the compositions prepared are shown in table 1a.

[0057] Each of the compositions is introduced into a flat-bottomed aluminum dish (diameter of 5 cm) as a film having a thickness of approximately 1 mm. The dishes are introduced into a drying oven heated to 200 C. After 20 minutes, they are removed and allowed to cool at ambient temperature and the thickness of the foam formed is observed:

Grading Scale:

[0058] : less than 0.5 cm

[0059] +: 0.5 to 1 cm

[0060] ++: 1.1 to 2 cm

[0061] +++: 2.1 to 3 cm

[0062] ++++: 3.1 to 4 cm

[0063] +++++: more than 4 cm

TABLE-US-00001 TABLE 1a Acidic inorganic salts Acid Acid catalyst Solids Thickness Sugar catalyst concentration content of the foam 85 parts of 15 parts 0.6 mol/l 60% +++++ D-glucose Al.sub.2(SO.sub.4).sub.3 monohydrate 92.5 parts of 7.5 parts 0.3 mol/l 60% +++++ D-glucose Al.sub.2(SO.sub.4).sub.3 monohydrate 98.5 parts of 1.5 parts 0.06 mol/l 60% +++++ D-glucose Al.sub.2(SO.sub.4).sub.3 monohydrate 99.85 parts of 0.15 parts 0.006 mol/l 60% +++++ D-glucose Al.sub.2(SO.sub.4).sub.3 monohydrate 85 parts of 15 parts of 1.4 mol/l 60% +++++ D-glucose CuSO.sub.4 monohydrate 85 parts of 15 parts of 1.2 mol/l 60% +++++ D-glucose Cu(NO.sub.3).sub.2 monohydrate

[0064] The foams formed are all brown to black in color.

[0065] By way of comparison, similar compositions are prepared, either by omitting the acid catalyst or by replacing the acidic inorganic salts (Al.sub.2(SO.sub.4).sub.3, CuSO.sub.4 and Cu(NO.sub.3).sub.2) with inorganic salts which do not make it possible to acidify the composition down to a pH of less than 3.

[0066] The results are presented in table 1b below.

TABLE-US-00002 TABLE 1b Comparative inorganic salts Acid Acid catalyst Solids Thickness Sugar catalyst concentration content of the foam 100 parts of 60% D-glucose monohydrate 85 parts of 15 parts of 1.9 mol/l 60% D-glucose MgSO.sub.4 monohydrate 85 parts of 15 parts of 1.3 mol/l 60% D-glucose CaSO.sub.4 monohydrate 85 parts of 15 parts of 1.8 mol/l 60% D-glucose AlPO.sub.4 monohydrate 85 parts of 15 parts of 3.9 mol/l 60% D-glucose NaCl monohydrate

[0067] These samples are from yellow to caramel in color after curing for 20 minutes. No formation of foam is observed.

EXAMPLE 2

[0068] Strong Acids and Phosphoric Acid

[0069] Several expandable and thermosetting compositions are prepared by adding, to 9 g of a glucose monohydrate powder, 6 ml of an aqueous solution of the acid catalyst (strong acid or phosphoric acid) having the concentration shown in tables 2a and 2b. The mixture is stirred at ambient temperature in order to disperse the powder therein.

[0070] The concentration of mol/l of the acid catalyst used and also the total solids content of the compositions prepared are shown in table 2a.

[0071] Each of the compositions is introduced into a flat-bottomed aluminum dish (diameter of 5 cm) as a film having a thickness of approximately 1 mm. The dishes are introduced into a drying oven heated to 200 C. After 20 minutes, they are removed and allowed to cool at ambient temperature and the thickness of the foam formed is observed. The grading scale is identical to that of example 1.

TABLE-US-00003 TABLE 2a Strong acids and phosphoric acid Acid Thick- Acid catalyst ness Acid catalyst concen- Solids of the Sugar catalyst weight tration content foam 100 parts of HCl 219 mg .sup.1 mol/l 60% +++++ D-glucose monohydrate 100 parts of H.sub.2SO.sub.4 164 mg 0.28 mol/l 60% +++++ D-glucose monohydrate 100 parts of H.sub.2SO.sub.4 59 mg 0.1 mol/l 60% +++++ D-glucose monohydrate 100 parts of HNO.sub.3 453 mg 1.2 mol/l 60% ++ D-glucose monohydrate 100 parts of H.sub.3PO.sub.4 118 mg 0.20 mol/l 60% ++++ D-glucose monohydrate

[0072] Hydrochloric acid, sulfuric acid and phosphoric acid used at a concentration greater than or equal to 0.1 mol/l give voluminous foams from brown to black in color. Inexplicably, nitric acid, even at a high concentration, foams to a relatively lesser extent than the other acids.

[0073] By way of comparison, the same acids are used in a concentration of 0.01 mol/l. The results are presented in table 2b below.

TABLE-US-00004 TABLE 2b Strong acids and phosphoric acid (comparative) Acid Thick- Acid catalyst ness Acid catalyst concen- Solids of the Sugar catalyst weight tration content foam 100 parts of HCl 2 mg 0.01 mol/l 60% D-glucose monohydrate 100 parts of H.sub.2SO.sub.4 6 mg 0.01 mol/l 60% D-glucose monohydrate 100 parts of HNO.sub.3 4 mg 0.01 mol/l 60% D-glucose monohydrate 100 parts of H.sub.3PO.sub.4 6 mg 0.01 mol/l 60% D-glucose monohydrate

[0074] No foam is formed.

[0075] The applicant company has also carried out a series of tests by bringing D-glucose into contact with increasing amounts of acetic acid (weak acid) and by heating the mixture under the same conditions. Even in a concentration of acetic acid of greater than 15 mol/l, no formation of foam is observed.