METHOD FOR PRODUCING AN EXPANDED RIGID FOAM WITH SEALED PORES

Abstract

A method for producing an expanded rigid foam with sealed pores includes at least the following steps: a) a mixture is prepared containing at least: an anionic polymer suited for ionotropic gelation; a foaming agent; a source of multivalent cations, said multivalent cations not being released in the mixture a); and a solvent; b) the mixture is stirred so as to obtain a foam; c) a compound capable of releasing protons in a sufficient amount to release said multivalent cations is added to the foam such that the anionic polymer gels ionotropically; d) the foam is dried. A foam is obtained in this manner and an object (for example a package, a heat-insulating or flame-retardant material) is made from this foam.

Claims

1. A method for producing an expanded rigid foam with sealed pores (1), wherein it comprises at least the following steps: a) a mixture is prepared containing at least: an anionic polymer suited for ionotropic gelation; a foaming agent; a source of multivalent cations, said multivalent cations not being released in the mixture a); and a solvent; b) the mixture is stirred so as to obtain a foam; c) at least one compound capable of releasing protons in a sufficient amount to release said multivalent cations is added to the foam obtained on completion of step b) such that the anionic polymer gels ionotropically; d) the foam obtained on completion of step c) is dried so as to obtain said expanded rigid foam with sealed pores (1).

2. The method according to claim 1, wherein the mixture a) comprises at least one amongst a sequestering agent, a stabilizing agent and a charge.

3. The method according to claim 1, wherein the anionic polymer suited for anionic gelation is a polymer that is naturally anionic or made anionic by chemical modification and is selected from alginates, kappa and iota carrageenans, pectins, starch and derivatives thereof, cellulose carboxymethyl, dextrane sulfate, xanthan, chondroitin sulfate, hyaluronate, N-acyl chitosans, acrylic polymers, methacrylic polymers, polylactic polymers, polyglycolic polymers, copolymers of acrylic and methacrylic acid, proteins and carbomers.

4. The method according to claim 1, wherein the foaming agent is selected from anionic surfactants.

5. The method according to claim 4, wherein the foaming agent is selected from sodium lauryl sulfate, ammonium lauryl sulfate, sodium stearate and sodium dodecylbenzenesulfonate and polysorbates.

6. The method according to claim 1, wherein the source of multivalent cations is selected from calcium carbonate, calcium sulfate, calcium citrate, calcium fluoride, calcium glycerophosphate, calcium hydroxide, calcium oxalate, dibasic calcium phosphate (or calcium hydrogen phosphate), monobasic calcium phosphate, tribasic calcium phosphate, calcium pyrophosphate, calcium saccharate, calcium succinate, and calcium tartrate.

7. The method according to claim 1, wherein the solvent is selected from water and aqueous solvents.

8. The method according to claim 1, wherein the compound capable of releasing protons in a sufficient amount to solubilize the multivalent cations is selected from lactones of carboxylic acid and boric acid.

9. The method according to claim 2, wherein the sequestering agent is selected from sodium hexametaphosphate, polyphosphates and sodium or potassium phosphate (or trisodium phosphate).

10. The method according to claim 2, wherein the charge is selected from activated carbon, clays, silica, titanium dioxide, cork, plant barks and colorants.

11. The method according to claim 1, wherein at step b), at least one mechanical reinforcing agent which consists of fibers selected from cellulose, wood, hemp, silk, cotton, coco, textile and linen fibers is added to the mixture.

12. The method according to claim 1, wherein the mixture a) comprises, in weight percent expressed with respect to the total mass of said mixture: between 0.77% and 4.6% of the anionic polymer suited for ionotropic gelation; between 0.02% and 0.08% of the foaming agent; between 0.1% and 3% of the source of multivalent cations; q.s. 100% of solvent.

13. The method according to claim 1, wherein the mixture comprises in weight percent expressed with respect to the total mass of said mixture, between 0.00005% and 0.001% of the sequestering agent and/or 0.02% and 0.15 of the stabilizing agent and/or 0.05% and 8% of the charge and/or 0.05% and 8% of the mechanical reinforcing agent.

14. The method according to claim 1, wherein, after step c) and before step d), the foam is casted into a mold.

15. An expanded rigid foam with sealed pores (1), wherein it is obtained with the production method according to claim 1 and has a compressive strength of 0.2 MPa or more.

16. An object wherein it is totally or partially made with a foam according to claim 15.

17. The object according to claim 16, wherein it is totally or partially made with a foam obtained by postforming of a foam.

18. The object according to claim 16, wherein it is selected from packages, horticultural containers, decorative objects, heat-insulating materials and flame-retardant materials.

Description

DESCRIPTION OF THE FIGURES

[0105] FIG. 1 represents a graph of the evolution of the temperatures measured within two glass vials filled with warm water one of which has been inserted in a pot made of a foam obtained according to the production method of the invention.

[0106] FIG. 2 represents a graph of the evolution over time of the mass loss of a foam according to the invention and of two comparative foams when these are subjected to an irradiation flux of 50 kW/m.sup.2 (cone calorimeter).

[0107] FIG. 3 represents a graph of the evolution over time of the heat output of these three foams.

[0108] FIG. 4 represents examples of foams obtained with the production method of the invention: plate (30 cm×20 cm×1.5 cm), and assemblies of plates by gluing.

[0109] FIG. 5 represents a graph of the evolution of strain as a function of stress of five foams, three foams of the invention and two commercial foams (polyurethane foam and expanded polystyrene foam).

[0110] FIG. 6 represents a photograph of three objects made from a foam obtained with a production method according to the invention: planar plate, cylindrical pot and postformed plate.

[0111] FIG. 7 represents a photograph of making of an object through a postforming operation.

[0112] Experiments have been carried out on foams obtained according to the production method and on comparative foams.

EXAMPLE 1

Preparation of a Foam According to the Method of the Invention and Illustration of its Heat-Insulation Properties

[0113] A mixture containing the following compounds has been prepared: [0114] 80 g of bipermuted water; [0115] 400 g of a sodium alginate solution at 4 weight %; [0116] 5 g of a polyvinyl alcohol solution at 10 weight %; [0117] 15 mL of a calcium carbonate suspension at 10 weight %; [0118] 0.1 mL of sodium hexametaphosphate at 5 weight %; [0119] 20 mL of a sodium lauryl sulfate at 1 weight %.

[0120] The mixture has been stirred in a mixer with whip-type paddles with 8 branches commercialized by the company Kenwood under the commercial name Cooking Chef for 18 minutes at a speed of 80 rpm and at a temperature of 20° C. A foam has been obtained.

[0121] At the 18.sup.th minute, 8 g of glucono-delta-lactone have been added to the mixture. Stirring of the foam has been carried on for 2 minutes.

[0122] The foam has been casted in a polypropylene mold which has been disposed afterwards in an oven set at 40° C., for 5 days.

[0123] The foam obtained in this manner had a density of 43 kg/m.sup.3.

[0124] The heat-insulation capability of this gelled foam has been determined. For this purpose, two cylindrical-shaped glass vials with a 500 mL volume have been half-filled with warm water at 90° C. and closed using a plastic plug. One amongst the vials has been inserted in a pot made of the foam. In each vial, a probe measured the evolution of the temperature over time.

[0125] FIG. 1 is a graph of the evolution of the temperatures measured within two vials over time: [0126] within the vial inserted in a foam pot (the upper curve denoted «T1»); [0127] within the 2.sup.nd vial (the lower curve denoted «T2 »).

[0128] The appearance of the two curves demonstrates the heat-insulation properties obtained with a foam obtained with the manufacturing method according to the invention. Indeed, the vial inserted in a pot made of a foam according to the invention cools down more slowly over time than the 2.sup.nd vial.

EXAMPLE 2

Preparation of a Foam According to the Method of the Invention and Illustration of its Fire-Resistant Properties

[0129] A mixture containing the following compounds has been prepared: [0130] 150 g of bipermuted water; [0131] 10 g of orange barks; [0132] 400 g of a sodium alginate solution at 4 weight %; [0133] 5 g of a polyvinyl alcohol solution at 10 weight %; [0134] 15 mL of a calcium carbonate suspension at 10 weight %; [0135] 0.1 mL of sodium hexametaphosphate at 5 weight %; [0136] 20 mL of a sodium lauryl sulfate at 1 weight %.

[0137] The mixture has been stirred in the same mixer as that of Example 1 over 18 minutes at a speed of 80 rpm and at a temperature of 20° C. A foam has been obtained.

[0138] At the 18.sup.th minute, 8 g of glucono-delta-lactone have been added to the mixture. Stirring of the foam has been carried on for 2 minutes.

[0139] Afterwards, the foam has been casted in a polypropylene mold which has been disposed afterwards in an oven set at 40° C., for 5 days.

[0140] The fire behavior of this foam has been compared with that of the following two foams: [0141] a 1.sup.st comparative polystyrene foam commercialized by the company BASF under the commercial name STYRODUR®; [0142] a 2.sup.nd comparative polyurethane foam commercialized by the company SOPREMA under the commercial name EFIGREEN® ALU+ from which the outer aluminum film has been removed, in order to keep only the polyurethane core that includes a flame retardant.

[0143] The fire behavior of the three foams has been studied with a cone calorimeter which is a measuring instrument for fire tests in the laboratory. In particular, it allows measuring for a given material during the combustion thereof: [0144] the ignition time; [0145] the mass loss rate; [0146] the heat output.

[0147] The ignition time corresponds to the time after which a continuous flame remains at the surface of the tested material.

[0148] The mass loss is characterized as being the variation of mass of the tested sample over time, for a given temperature or temperature profile. The derivative of the mass loss over time corresponds to the mass loss rate.

[0149] The cone calorimeter that has been used during this 2.sup.nd experiment is a test apparatus developed in the NIST (namely the acronym of «National Institute of Standards and Technology»).

[0150] The three foams have been subjected to a heat flux of 50 kW/m.sup.2, corresponding to a fully developed fire.

[0151] FIG. 2 represents a graph of the evolution over time of the mass loss of the three foams. The major datum that is obtained is the residues level c at the end of combustion. For the foam according to the invention, this level amounts to 61%. For the 1.sup.st and 2.sup.nd comparative foams, this level amounts to 0 and 26%, respectively. These results show that the foam according to the invention has the capability of extinguishing the flame more rapidly than the two comparative foams.

[0152] FIG. 3 represents a graph of the evolution over time of the heat output of the three foams.

[0153] It is noticed that the foam according to the invention releases less heat than the two comparative foams. Indeed, the foam according to the invention has a lower heat output peak, as well as a lower total heat output (namely equivalent to the surface area under the curve of the heat output over time) than those of the two comparative foams.

[0154] Table 1 details hereinbelow for each of the three foams: [0155] the ignition time; [0156] the heat output peak; [0157] the total heat output; [0158] the residues level at the end of combustion.

TABLE-US-00001 TABLE 1 Residues Heat Total level at the Ignition output heat end of time peak output combusion (s) (kW/m.sup.2) (kJ/g) (%) Foam 12 17 0.6 61 according to the invention 1.sup.st 38 100 7.8 0 comparative foam 2.sup.nd 8 80 4.5 26 comparative foam Table 1 detailing the fire behavior parameters of the three tested foams

[0159] In light of the results detailed in Table 1 hereinabove and in FIGS. 2 and 3, the foam according to the invention has good fire properties which could compete with those of the heat-insulating foams known from the prior art such as the 1.sup.st and 2.sup.nd comparative foams. Unlike these comparative foams, the foam according to the invention further has the advantage of being free of fireproof chemical additives harmful to the health during the combustion thereof. It should be added that the production of these foams does not incorporate any toxic product (in comparison with the mentioned commercial foams), that these are biodegradable (biodegradability index close to cellulose; i.e., COD/BOD5=chemical oxygen demand/5-day biochemical oxygen demand=1.05, close to that of cellulose). These foams are compostable (including in household composting).

[0160] FIG. 4 represents a photograph of 3 objects (plate and 2 blocks with different thicknesses) which have been made from a foam with sealed pores produced according to the operating method of Example 1. The 2 blocks have been obtained by gluing plates of said foam.

EXAMPLE 3

Preparation of a Foam According to the Method of the Invention and Illustration of its Mechanical Properties

[0161] Experiments covering the assessment of the mechanical properties have been carried out on foams obtained according to the production method of the invention (with the formulations described hereinbelow), as well as on commercial foams for comparison purposes.

[0162] A mixture containing the following compounds has been prepared: [0163] 400 g of bipermuted water; [0164] 1000 g of a sodium alginate solution at 4 weight %; [0165] 7.5 g of a polyvinyl alcohol solution at 10 weight %; [0166] 35 mL of a calcium carbonate suspension at 10 weight %; [0167] 0.2 mL of sodium hexametaphosphate at 5 weight %; [0168] 40 mL of a sodium lauryl sulfate at 1 weight %.

[0169] The mixture has been stirred in a mixer with whip-type paddles with 8 branches commercialized by the company Kenwood under the commercial name Cooking Chef for 20 minutes at a speed of 80 rpm and at a temperature of 20° C.

[0170] At the 20.sup.th minute, X g of fibers hydrated beforehand (cf. the table hereinbelow detailing the type of fibers as well as the used amounts) are added and stirring is maintained until the 28.sup.th minute. An expanded foam has been obtained.

[0171] At the 28.sup.th minute, 12.5 g of glucono-delta-lactone have been added to the mixture.

[0172] Stirring of the foam has been carried on for 2 minutes.

[0173] The foam has been casted in a polypropylene mold which has been disposed afterwards in an oven set at 40° C., for 5 days.

[0174] The dry foam obtained in this manner had a density of 40 kg/m.sup.3.

TABLE-US-00002 Fibers type (Fibers supplied by the company Fibers J.RETTENMAIER & mass Dimensions of Volumetric SÖHNE) Reference (X, g) the tested plates mass LIGNOCEL PF Serie L 5 g 1.5 × 10 × 10 cm 40 kg/m.sup.3 (200 à 300 μm) 10% (Wood fibers) ARBOCEL B400 Serie M 5 g 1.5 × 10 × 10 cm 40 kg/m.sup.3 (900 μm) 10% Cellulose fibers Without added fibers Serie K 0 g 1.5 × 10 × 10 cm 40 kg/m.sup.3

[0175] The mechanical strength tests (compressive stress) of these foams have been compared with those of the following two foams:

[0176] a 1.sup.st comparative polystyrene foam commercialized by the company BASF under the commercial name STYRODUR®;

[0177] a 2.sup.nd comparative polyurethane foam commercialized by the company SOPREMA under the commercial name EFIGREEN® ALU+ from which the outer aluminum film has been removed, in order to keep only the polyurethane core.

[0178] The tests have been carried out according to the standard ISO 844 Standard with a Preload: 50 N and Rate 10%/min.

[0179] FIG. 5 represents a graph of the evolution of strain as a function of stress of the five foams.

[0180] These results show that the foams according to the invention have mechanical properties close to those of synthetic materials commonly used in heat-insulation of buildings.

[0181] The applications of a foam produced in this manner are illustrated in FIGS. 6 and 7 showing objects obtained from this foam. The planar plate and the cylindrical pot of FIG. 6 have been produced by casting the foam into suitable molds and then drying. The curved plate of FIG. 6 and the object of FIG. 7 have been produced by postforming of the foam; the obtained foam according to Example 3 is rehydrated to become soft again and then molded and dried.