Foams based on polylysine

Abstract

The present invention relates to a method for producing a foam comprising foaming a mixture comprising one or more poly (amino acids) (A), one or more components (B) capable of reacting with said poly (amino acids) (A), and one or more blowing agents (F) wherein component (B) is selected from the group consisting of reducing sugars, 1, 2, 3, 3, 3-tetrafluoropropene, 1, 2, 3, 3-tetrafluoropropene, 1, 2, 3, 3-tetrafluoropropene, 1, 2, 3-tetrafluoropropene, 1, 2, 3-tetrafluoropropene, 1, 2, 3-tetrafluoropropene, 1, 2, 3-tetrafluoropropene, 1, 2, 3 and 2, 3-dihydroxyacetone, glycolaldehyde, glyceraldehyde, or any mixture thereof.

Description

[0001] The present invention relates to a method for producing a foam and a foam obtainable by this method, the method comprising foaming a mixture comprising one or more poly(amino acids) (A), one or more components (B) capable of reacting with said poly(amino acids) (A) and one or more blowing agents (F), wherein component (B) is selected from reducing sugars, 1,3-dihydroxyacetone, glycolaldehyde, glyceraldehyde or any mixture thereof.

[0002] Related prior art

[0003] Reactive non-thermoplastic (thermosetting) polymer foams are used in many applications. In the case of flexible non-thermoplastic polymer foams, the products are applied to sound absorption, cushioning, cleaning, packaging and many other applications.

[0004] To obtain these foams, three techniques are known. Flexible polyurethane foams can be foamed using water. Water undergoes an exothermic reaction with the isocyanate groups of the corresponding isocyanate (e.g. TDI or MDI) to form a disubstituted urea and CO2. CO2 acts as an inherent blowing agent in foam formation. The final foam shows high flexibility and good sound absorption. Sometimes, the foaming reaction is supported by a physical blowing agent (e.g. pentane). However, the use of isocyanates results in high safety inputs in terms of safe transportation, storage, processing and disposal. Flexible polyurethane-based foams are described in many sources, such as DE 10226414 A1.

[0005] Another example of obtaining a flexible non-thermoplastic foam is the melamine resin foam described in DE 09929A1. These foams are produced from melamine-formaldehyde condensates, surfactants, salts, curing agents and physical blowing agents (e.g. pentane or hydrofluoroolefins). Due to the low exothermicity, the foaming process must be supported by hot air and / or microwaves and / or steam. The resulting foams are lightweight and show very good sound absorption properties, good heat insulation and good cleaning properties. However, due to the potential emission of formaldehyde during the production process and in applications, the use of these foams is limited.

[0006] Another example of obtaining a flexible foam is described in DE 2950289 A1. These foams are based on urea-formaldehyde condensates, which provide flexible foams with a density of 8 - 40 kg / m 3 by the oven method and pentane as a blowing agent. Here too, due to the potential emission of formaldehyde during the production process and in applications, these applications are limited.

[0007] WO 2016 / 009062 and WO 2011 / 138458 disclose an adhesive which comprises the reaction product of a carbohydrate reactant and a polyamine and can be used for consolidating loosely assembled materials such as fibres. Foams using such an adhesive are not disclosed.

[0008] WO 2022 / 136613 discloses an adhesive composition and its use for manufacturing lignocellulosic composite articles, the adhesive composition comprising polylysine having a total weight average molecular weight Mw of at least 800 g / mol as component A and 1,3-dihydroxyacetone, glycolaldehyde, glyceraldehyde or a mixture thereof as component B. Foams using such an adhesive composition are not disclosed.

[0009] WO 2022 / 136614 relates to an adhesive composition for composite articles comprising a polyamine and hydroxyacetone. Foams using such an adhesive composition are not disclosed.

[0010] US2011 / 0257284 A1 describes a method for producing flame-retardant polyurethane foams which uses hyperbranched nitrogen-containing polymers (in particular hyperbranched polylysine, hyperbranched polyisocyanurate and hyperbranched polyesteramide) to impart flame retardancy to the polyurethane foams. Summary of the Invention

[0011] The present invention has been made in view of the above prior art, and the object of the present invention is to provide a flexible foam having good mechanical properties, free of formaldehyde and isocyanates, which can be obtained from bio-based and water-based raw materials.

[0012] Technical Problem Solved

[0013] This object is solved by a foam and a method for producing the foam, the method comprising foaming a mixture which comprises one or more poly(amino acids) (A), one or more components (B) capable of reacting with said poly(amino acids) (A) and one or more blowing agents (F), wherein component (B) is selected from reducing sugars, 1,3-dihydroxyacetone, glycolaldehyde, glyceraldehyde or any mixture thereof.

[0014] The foaming of the mixture can be achieved by using an external heat source (such as a hot mould or hot air) and / or by using microwaves.

[0015] Preferably, the foam is not a polyurethane foam. Preferably, the foaming mixture is free of isocyanates and / or polyols. Preferably, the foaming mixture comprises poly(amino acids) (A) in an amount greater than 50 wt.-%, more preferably greater than 70 wt.-%, based on the sum of the reactive components (A) and (B).

[0016] Preferably, the method comprises foaming a mixture which comprises

[0017] 10 to 60 wt.-% of one or more poly(amino acids) (A)

[0018] 3 to 30 wt.-% of one or more components (B) capable of reacting with the poly(amino acid) (A)

[0019] 0.5 to 5 wt.-% of one or more salts (C) of an inorganic or organic carboxylic acid

[0020] 3 to 10 wt.-% of one or more surfactants (D)

[0021] 10 to 60 wt.-% of water (E)

[0022] 1 to 20 wt.-% of one or more physical blowing agents (F)

[0023] 0 to 82.5 wt.-% of one or more additional additives (G)

[0024] wherein the sum of the weight percentages of components (A) to (G) is 100 wt.-%.

[0025] More preferably, the method comprises foaming a mixture consisting essentially of the above amounts of components (A) to (F).

[0026] Most preferably, the method comprises foaming a mixture consisting of

[0027] 20 to 60 wt.-% of one or more poly(amino acids) (A)

[0028] 3 to 30 wt.-% of one or more components (B) capable of reacting with the poly(amino acid) (A)

[0029] 0.5 to 5 wt.-% of one or more salts (C) of an inorganic or organic carboxylic acid

[0030] 3 to 10 wt.-% of one or more surfactants (D)

[0031] 10 to 60 wt.-% of water (E)

[0032] 1 to 20 wt.-% of one or more physical blowing agents (F)

[0033] wherein the sum of the weight percentages of components (A) to (F) is 100 wt.-%.

[0034] Component (A)

[0035] Use poly(amino acids) (such as synthetic poly(amino acids), natural poly(amino acids), polypeptides, proteins, or mixtures thereof) as component (A). Poly(amino acids) are produced by the polymerization of amino acids. Poly(amino acids) can be obtained by chemical synthesis or by biosynthesis in living organisms. In particular, proteins can be obtained by biosynthesis in living organisms. Polypeptides can be obtained by the hydrolysis of proteins.

[0036] According to the present invention, the term poly(amino acids) may also include poly(amino acid) derivatives that can be obtained by modifying poly(amino acids) after polymer synthesis.

[0037] Preferred amino acids for the polymerization reaction are di-amino acids containing two amine groups (-NH2) and at least one carboxyl (-COOH) functional group. Such di-amino acids can be ornithine, diaminopimelic acid, 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, and / or lysine, preferably lysine, more preferably L-lysine. Although they are sometimes named di-amino acids, according to the present invention, asparagine and glutamine are not included in the group of di-amino acids because the second functional group is an amide (CO-NH2) rather than an amine (-NH2).

[0038] Preferably, polylysine is used as the poly(amino acid). Polylysine can be produced by the polymerization of lysine. Lysine itself can be produced by fermenting corn starch, sugar, or other carbohydrates in the presence of suitable bacteria. The production of polylysine is generally known and can be carried out as described, for example, in WO 2016 / 062578 or from lysine salts as described in WO 2007 / 060119. Preferred methods for producing polylysine are described in WO 2022 / 136613.

[0039] Preferably, component (A) comprises at least one polylysine or consists of one or more polylysines that are polymerization products of monomeric lysine, preferably L-lysine, and optionally other monomers selected from the group consisting of

[0040] a) amino acids, which preferably contain at least two amino groups,

[0041] b) amines containing at least two amino groups, where these amines are not amino acids, and

[0042] c) dicarboxylic acids and / or tricarboxylic acids, which are preferably not amino acids,

[0043] where lysine is used as the monomer for the polymerization reaction in an amount of at least 50 wt.-%, preferably at least 75 wt.-%, most preferably 100 wt.-% based on the total amount of monomers.

[0044] The weight-average molecular weight Mw of the poly(amino acid) (A) affects the mechanical properties of the foam. Preferably, the poly(amino acid) (A) has a weight-average molecular weight Mw in the range of 500 to 20,000 g / mol, more preferably in the range of 800 to 3,500 g / mol. The weight-average molecular weight of the hydroxylated polymethacrylate is determined by size-exclusion chromatography (SEC) using 0.1% (w / w) trifluoroacetate as the solvent and 0.1 M NaCl in distilled water as the eluent, and calibrated with poly(2-vinylpyridine) standards. Most preferably, polylysine with a molecular weight in the range of 800 to 3,500 g / mol in an aqueous formulation is used as component (A) for producing foams with suitable Shore hardness and compressive load.

[0045] Component (B)

[0046] One or more components (B) capable of reacting with the poly(amino acid) (A) selected from reducing sugars, 1,3-dihydroxyacetone, glycolaldehyde, glyceraldehyde, or any mixture thereof are used in the foaming mixture. Preferably, hydroxyacetone or 1,3-dihydroxyacetone is used as component (B).

[0047] Preferably, the weight ratio of the poly(amino acid) (A) to component (B) is in the range of 2:1 to 5:1.

[0048] Poly(amino acids) and reducing sugars from natural sources can be used as raw materials to produce substantially bio-based foams.

[0049] It is assumed that components A and B undergo the Maillard reaction. In the first step, the free amine group of the (poly)amino acid (component (A)) is added to the carbonyl group of the reducing sugar (ketose / aldose) (component (B)). The formed glycosylamine is unstable and undergoes the Heyns / Amadori rearrangement to form a Heyns / Amadori compound (aldamine / ketamine), with the loss of a water molecule.

[0050] In the case of the reaction of polylysine with (di)hydroxyacetone, a crosslinked thermosetting light brown solid material is formed.

[0051] Component (C)

[0052] One or more salts of inorganic acids and / or one or more salts of organic carboxylic acids are added as component (C) to stabilize the foam. Particularly suitable are one or more salts of oxygen or sulfur, especially sodium salts and / or potassium salts, such as formic acid, acetic acid, and citric acid. Also particularly suitable are chlorides, bromides, nitrates, and dihydrogen phosphates, especially in the form of sodium salts and / or potassium salts. Preferably, the salts of inorganic acids and / or the salts of organic carboxylic acids are especially sodium formate and potassium formate or more compounds selected from sodium acetate and potassium acetate, sodium citrate and potassium citrate, sodium chloride and potassium chloride, sodium bromide and potassium bromide, sodium sulfate and potassium sulfate, sodium sulfite and potassium sulfite, sodium nitrate and potassium nitrate, and sodium dihydrogen phosphate and potassium dihydrogen phosphate. Very particularly suitable salts of inorganic acids and / or salts of organic carboxylic acids are formates, citrates, and mixtures thereof.

[0053] Preferably halogen-free salts are used to obtain halogen-free foam.

[0054] Component (D)

[0055] Component (D) of the system comprises one or more surfactants for forming and stabilizing the foam. Anionic, cationic, nonionic, or amphoteric surfactants are available.

[0056] Suitable anionic surfactants are diphenyl ether sulfonates, alkane sulfonates, and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, alkyl sulfates, alkyl ether sulfates, α-sulfo fatty acid esters, acylaminoalkane sulfonates, acylhydroxyethyl sulfonates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl phosphates, and alkyl ether phosphates.

[0057] Useful nonionic surfactants include alkylphenol polyglycol ethers, fatty alcohol polyglycol ethers, fatty acid polyglycol ethers, fatty acid alkanolamides, EO-PO block copolymers, amine oxides, glycerol fatty acid esters, sorbitan esters, and alkyl polyglucosides. Useful cationic surfactants include alkyltriammonium salts, alkylbenzyl dimethylammonium salts, and alkylpyridinium salts.

[0058] Particularly preferably, a mixture of an anionic surfactant and a nonionic surfactant is used.

[0059] Preferably, a mixture of an anionic surfactant and a nonionic surfactant is used as surfactant (D). More preferably, a mixture of the sodium salt of (C12-C14) fatty alcohol ether sulfate, (C12-C14) alkylpolyglycoside, or a mixture thereof is used as surfactant (D).

[0060] Preferably, the weight ratio of the anionic surfactant to the nonionic surfactant is in the range of 50:50 to 90:10.

[0061] Component (E)

[0062] Water is used as component (E). Preferably, components (A), (B) and (D) are used in the form of an aqueous solution or dispersion. Additional water may be added to achieve the above composition of the mixture and to adjust the viscosity.

[0063] Component (F)

[0064] In principle, both physical blowing agents and chemical blowing agents can be used in the process of the present invention. "Physical" or "chemical" blowing agents are suitable (Encyclopedia of Polymer Science and Technology, Volume I, Third Edition, Additives, pages 203 to 218, 2003).

[0065] Physical blowing agents useful as component (F) include, for example, hydrocarbons such as butane, n-pentane, isopentane or cyclopentane, hexane, halogenated, more particularly chlorinated and / or fluorinated hydrocarbons (e.g., dichloromethane, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFC)), hydrofluorocarbons (HCF) such as methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, hydrofluoroolefins (HFO) such as hexafluorobutene, alcohols (e.g., methanol, ethanol, n-propanol or isopropanol), ethers, ketones and esters (e.g., methyl formate, ethyl formate, methyl acetate or ethyl acetate). Preferred physical blowing agents are those having a boiling point between 0 °C and 80 °C.

[0066] Useful chemical blowing agents include, for example, isocyanates mixed with water, which release carbon dioxide as the active blowing agent. Carbonates and bicarbonates mixed with acids can also be used, in which case carbon dioxide is again produced. Also suitable are azo compounds such as azodicarbonamide.

[0067] Preferably, the physical blowing agent (F) is a C4-C8 hydrocarbon, more preferably n-pentane, isopentane or cyclopentane, and most preferably an 80:20 mixture of n-pentane and isopentane.

[0068] Preferably, 1 to 20 wt.-% of one or more physical blowing agents are used to obtain a foam having a density in the range of 10 to 250 kg / m 3 range.

[0069] Component (G)

[0070] Flame retardants, fillers can be used as additional component (G). Preferably, flame retardants are used as additive (G).

[0071] The subject of the present invention is also a method for producing a foam by preparing an aqueous solution or dispersion of components (A) to (G) of the above system and foaming the aqueous solution or dispersion by heating (i.e., with hot air or microwaves).

[0072] The introduction of energy can preferably be achieved by electromagnetic radiation, for example by high-frequency radiation in the frequency range of 0.2 to 100 GHz, preferably 0.5 to 10 GHz, with a power of 5 to 400 kW, preferably 5 to 200 kW, and more preferably 9 to 120 kW / kg of the mixture. Magnetrons are useful sources of dielectric radiation, and one magnetron or two or more magnetrons can be used simultaneously.

[0073] The production of the polylysine foam is preferably carried out after a one-shot method, for example by means of high-pressure or low-pressure techniques. The foam can be produced discontinuously in an open or closed mold, or can be formed by continuously applying the reaction mixture to a conveyor belt to produce a foam block.

[0074] Operating according to the so-called two-component method is particularly advantageous in the case of preparing and foaming the polylysine component and the reducing sugar component as described above. These components are preferably mixed and introduced into the mold or applied to the conveyor belt at a temperature in the range of 15°C to 120°C, preferably between 20°C and 80°C. The temperature in the mold is generally in the range between 15°C and 120°C, preferably between 30°C and 80°C.

[0075] Preferred methods include the following steps:

[0076] (a) Preparing an aqueous solution or suspension containing components (A) to (F),

[0077] (b) Transferring the aqueous solution or suspension obtained in step (a) to a mold, and

[0078] (c) Foaming the aqueous solution or suspension by raising the temperature to a temperature in the range of 35°C to 100°C or by exposure to microwaves.

[0079] The subject of the present invention is also a foam obtainable by the above method.

[0080] Preferably, the foam has a density in the range of 10 to 250 kg / m 3 determined according to DIN 53420. The preferred density depends on the application. The density can be adjusted by the amount of the blowing agent (F). The higher the density, the higher the Shore hardness and the compressive load can be. For foams with higher flexibility, a lower density is preferred.

[0081] Compared with melamine-formaldehyde foam, the foam according to the invention has a lower Shore hardness and higher flexibility at comparable densities.

[0082] Preferably, the foam has a Shore hardness 000 in the range of 20 to 100 as determined according to ASTM D 2240.

[0083] Preferably, the foam has a compressive stress value (compressive load deflection) in the range of 0.3 to 90 kPa according to DIN EN ISO 3386.

[0084] The foam according to the invention is water-based, solvent-free and free of formaldehyde and isocyanates, can be obtained from biobased raw materials such as reducing sugars and can be produced in a wide density range. The foam shows high flexibility as evidenced by a low Shore hardness, has good cleaning properties, high water absorption, moderate heat insulating properties and good sound absorption properties in a wide frequency range as well as low air flow resistance.

[0085] Determined by optical microscopy, the open cell content is preferably greater than 95%.

[0086] The foam according to the invention can be used in building and construction, i.e. for buffers and furniture in leisure or office environments (such as seats, sofas, mattresses) or in seats, headrests, armrests of means of transport such as trains, aeroplanes and motor vehicles. Further applications are in packaging (i.e. as packaging material for protecting goods in transit), as a filtration medium in cleaning applications (such as cleaning sponges, floor mats, hand pads), or in acoustic applications in building and construction (such as indoor acoustic absorbers for acoustic elements in offices, schools, restaurants, anechoic chambers, furniture, partition walls, walls and ceilings), and in mufflers in air conditioning or transport applications (such as mufflers in motor vehicles, underhood engines for noise reduction or as headliners, sun visors, hat racks indoors). Further applications include thermal insulation in industrial applications (such as pipe insulation or insulation of air conditioning units), or for wall and roof insulation in building and construction. Applications in agriculture include growth substrates and flower foams.

[0087] Examples

[0088] Hereinafter, the invention will be described in more detail and specifically with reference to examples, however, these examples are not intended to limit the invention.

[0089] Raw materials used:

[0090] Surfactant 1: Anionic surfactant SAS 93 (sodium C14-C17 secondary alkyl sulfonate), WeylChem

[0091] Surfactant 2: Non-ionic surfactant AT80 (C16-C18 fatty alcohol ethoxylate (approx. 80 units), BASF SE)

[0092] Surfactant 3 A surfactant mixture of Hostapur SAS93 / Lutensol AT80 in a weight ratio of 6:4

[0093] Water: Deionized water;

[0094] Polylysine-1: Having a weight-average molecular weight Mw of approximately 1,200 g / mol (50 wt.-% in water);

[0095] Polylysine-2: Having a weight-average molecular weight Mw of approximately 2,000 g / mol (50 wt.-% in water).

[0096] Polylysine-3: Having a weight-average molecular weight Mw of approximately 3,000 g / mol (50 wt.-% in water);

[0097] Polylysine-4: Having a weight-average molecular weight Mw of approximately 4,000 g / mol (50 wt.-% in water);

[0098] Polylysine-1 to polylysine-4 are prepared by heat-treating L-lysine according to Example 1 of WO 2022 / 136612

[0099] Crosslinking agent: 1,3-dihydroxyacetone (80 wt.-% in aqueous solution).

[0100] Physical blowing agent: A mixture of n-pentane / isopentane 80 / 20 wt.-%

[0101] Salts: Sodium formate, sodium acetate, sodium citrate, sodium chloride

[0102] MF Melamine-formaldehyde precondensate having an average molecular weight (number average) Mn of 350 g / mol, wherein the molar ratio of melamine:formaldehyde is 1:3

[0103] Determine the weight-average molecular weight M of polylysine w

[0104] M w Determined by size exclusion chromatography under the following conditions:

[0105] ● Solvent and eluent: 0.1% (w / w) trifluoroacetate, 0.1 M NaCl in distilled water

[0106] ● Flow rate: 0.8 ml / min

[0107] ● Injection volume: 100 μl

[0108] ● The sample was filtered through a Minisart RC 25 (0.2 μm) filter from Sartorius

[0109] ● Column material: hydroxylated polymethacrylate (TSKgel G3000PWXL)

[0110] ● Column dimensions: inner diameter 7.8 mm, length 30 cm

[0111] ● Column temperature: 35 °C

[0112] ● Detector: DRI Agilent 1100 UVGAT-LCD 503 [232 nm]

[0113] ● Calibration was performed using poly(2-vinylpyridine) standards with a molar mass range of 620 to 2,890,000 g / mol (from Polymer Standards Service (PSS), Mainz, Germany) and pyridine (79 g / mol)

[0114] ● The integration upper limit was set to 29.01 mL

[0115] ● M w was calculated to include lysine oligomers and polymers as well as monomeric lysine.

[0116] Characterization of the foam

[0117] The foam density was determined according to DIN 53420.

[0118] The Shore hardness was measured according to ASTM D 2240. For the measurement of low-density foams, grade 000 was used (sphere diameter 2.4 mm, spring force 1.111 N). Sample conditioning: 23 °C, 50% relative humidity, 24 h.

[0119] The air flow resistance was measured according to ASTM C-522.

[0120] The compressive stress value (compressive load deflection) CV 40 was measured according to DIN EN ISO 3386-1.

[0121] Examples 1 - 45: Preparation of polylysine-based foams foamed with pentane

[0122] Polylysine, (di)hydroxyacetone, surfactant and optionally salt were dissolved in water and the mixture was processed with a high-shear mixer at high speed for 1 min. Next, a physical blowing agent (e.g., pentane) was added and stirred again for 10 s. Finally, the entire mixture was transferred to a heated mold or to a mold exposed to hot air (oven) or microwave (e.g., a cardboard box of 25×25×25 cm).

[0123] Program A: Microwave: 4 × 2.45 GHz, 60 s; subsequent oven: 50 °C, 24 h.

[0124] Program B: Oven: 80 °C and 100 °C, 24 h.

[0125] After cooling, the new solid foam with a fine and uniform cell structure was demolded.

[0126] The composition and mechanical properties of the obtained foams are shown in Tables 1 - 7.

[0127] Table 1 shows that the Shore hardness and compression load can be increased by using polylysine with a weight - average molecular weight in the range of 1,000 to 3,000 g / mol.

[0128] Tables 5 and 6 show the effect of density on mechanical properties (such as Shore hardness and compression load).

[0129] Table 1: Variation of the molecular weight of polylysine without salt, Program A

[0130] Example 1 2 3 4 Polylysine - 1, 1,200 g / mol, 50% aqueous solution / g 78 - - - Polylysine - 2, 2,000 g / mol, 50% aqueous solution / g - 78 - - Polylysine - 3, 3,000 g / mol, 50% aqueous solution / g - - 78 - Polylysine - 4, 4,000 g / mol, 50% aqueous solution / g - - - 78 Tenside mixture: Hostapur SAS93 / Lutensol AT80 6:4 / g 3.6 3.6 3.6 3.6 Dihydroxyacetone, 80% aqueous solution / g 15.8 15.8 15.8 15.8 Blowing agent pentane / g 8.0 8.0 8.0 8.0 Density / kg / m3 16.4 18.1 20.3 19.5 Shore hardness 000, after tempering at 23 °C / 50% relative humidity 42 60 69 <30 Compression load / kPa, after tempering at 23 °C / 80% relative humidity 1.0 3.3 17.5 <0.3

[0131] Table 2: Variation of salt in the formulation of polylysine foam, Program A

[0132]

[0133]

[0134] Table 3: Variation of surfactant without salt, Program A

[0135]

[0136] Table 4: Variation of surfactant with salt, Program A

[0137]

[0138]

[0139] Table 5: Variation of foam density without salt, Program A

[0140]

[0141] 6: Variation of foam density with salt, Program A

[0142]

[0143]

[0144] Table 7: Variation of the foaming process: oven foaming without using microwaves, process B

[0145]

[0146]

[0147] Comparative examples C1 - Comparative examples C15

[0148] Preparation of melamine resin foam

[0149] 100 parts by weight of a melamine - formaldehyde pre - condensate MF, 38 parts by weight of water, 1.2 parts by weight of an anionic surfactant T1, 0.3 parts by weight of a non - ionic surfactant T2, 2.5 parts of sodium formate, 3.0 parts of formic acid and 19.5 parts by weight of pentane are mixed with each other at a temperature of 20 °C to 35 °C. The mixture is introduced into a foaming mold of polypropylene and irradiated with microwaves in a microwave oven. The foam obtained after microwave irradiation is annealed in a circulating air oven at 200 °C for 20 min. The blowing agent content, density and Shore hardness are summarized in Table 8.

[0150] Table 8: Comparative tests of flexible melamine foam:

[0151]

Claims

1. A method for producing a foam, the method comprising foaming a mixture comprising one or more poly(amino acids) (A), one or more components (B) capable of reacting with the poly(amino acids) (A), and one or more blowing agents (F), wherein the component (B) is selected from reducing sugars, 1,3-dihydroxyacetone, glycolaldehyde, glyceraldehyde, or any mixture thereof.

2. The method according to claim 1, wherein, the mixture comprises 10 to 60 wt.-% of one or more poly(amino acids) (A) 3 to 30 wt.-% of one or more components (B) capable of reacting with the poly(amino acids) (A) 0.5 to 5 wt.-% of one or more salts (C) of inorganic or organic carboxylic acids, 3 to 10 wt.-% of one or more surfactants (D), 10 to 60 wt.-% of water (E), 1 to 20 wt.-% of one or more physical blowing agents (F), 0 to 982.5 wt.-% of one or more additional additives (G), wherein the sum of the weight percentages of the components A) to G) is 100 wt.-%.

3. The method according to claim 1 or 2, wherein, the poly(amino acid) (A) is polylysine having a weight-average molecular weight Mw in the range of 800 to 20,000 g / mol determined by size exclusion chromatography (SEC).

4. The method according to any one of claims 1 to 3, wherein, 1,3-dihydroxyacetone is used as the component (B).

5. The method according to any one of claims 1 to 4, wherein, the salt (C) of inorganic or organic carboxylic acid is sodium formate, sodium acetate or sodium citrate.

6. The method according to any one of claims 1 to 5, wherein, the physical blowing agent (F) is a C4-C8 hydrocarbon.

7. The method according to any one of claims 1 to 6, wherein, a mixture of an anionic surfactant and a non-ionic surfactant is used as the surfactant (D).

8. The method according to any one of claims 1 to 7, wherein, a flame retardant is used as the additive (F).

9. The method according to any one of claims 1 to 8, wherein, the weight ratio of the poly(amino acid) (A) to the component (B) is in the range of 2:1 to 5:

1.

10. The method according to any one of claims 6 to 9, wherein, the weight ratio of the anionic surfactant to the non-ionic surfactant is in the range of 50:50 to 90:

10.

11. The method according to any one of claims 1 to 10, wherein, the method comprises the following steps: (a) preparing an aqueous solution or suspension comprising the components (A) to (G), (b) transferring the aqueous solution or suspension obtained in step (a) to a mold, and (c) foaming the aqueous solution or suspension by heating to a temperature in the range of 35°C to 100°C or by exposure to microwaves.

12. A foam obtainable by the method according to any one of claims 1 to 11.

13. The foam according to claim 12, having a density in the range of 10 to 250 kg / m 3 determined according to DIN 53420.

14. The foam according to claim 12 or 13, which has a Shore hardness 000 in the range of 20 to 100 as determined according to ASTM D 2240.

15. The foam according to claims 12 to 14, which has a compression stress value in the range of 0.3 to 90 kPa according to DIN EN ISO 3386-1.

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