Biodegradable melamine resin foam

Abstract

The present invention provides a method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave irradiation, wherein the mixture M comprises at least one melamine-formaldehyde pre-condensate having a melamine:formaldehyde molar ratio in the range of 1:1.3 to 1:2.5, at least one curing agent, at least one surfactant, at least one blowing agent, and at least one polyhydric alcohol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol, as well as a biodegradable melamine resin foam obtainable by the method.

Description

[Technical Field]

[0001] The present invention relates to a method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave irradiation, wherein the mixture M comprises at least one melamine-formaldehyde pre-condensate having a melamine:formaldehyde molar ratio in the range of 1:1.3 to 1:2.5, at least one curing agent, at least one surfactant, at least one blowing agent, and at least one polyhydric alcohol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol, as well as to biodegradable melamine resin foams obtainable by the method.

[0002] Related Prior Art Melamine resin foam is used for various purposes, such as sound absorption in rooms, thermal insulation in buildings, and pipe insulation. Another important application is the use of melamine resin foam as a cleaning sponge for consumer / household use. In particular, in household applications, such as cleaning sponges, there is a strong demand for biodegradable materials used.

[0003] Several methods are available for investigating the biodegradation of polymers in various media, such as soil, seawater, freshwater, and sludge water. The OECD 301F biodegradation test is one of the most important for testing the biodegradability of polymer foams used in household applications. The OECD 301F test investigates biodegradation in activated sludge for wastewater treatment. To date, no results have been reported in the literature for the biodegradation of melamine resin foams using the OECD 301F test.

[0004] EP 4001350 A1 provides a thermoformable melamine foam and a method for producing the same, the thermoformable melamine foam containing a condensate of a melamine-formaldehyde compound having a low molecular weight ratio M:F in the range of 1:1.3 to 1:1.8 so as to have a low formaldehyde content and excellent thermal stability. To improve the heat resistance of the thermoformable melamine foam, a predetermined amount of isosorbide is added to the dispersion.

[0005] WO 2018 / 095760 relates to a process for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave irradiation, the mixture M comprising at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant, at least one blowing agent, and a polyethylene glycol having a number average molecular weight Mn in the range of 500 to 10,000 g / mol, as well as to the melamine-formaldehyde foam obtained by the process and its uses.

[0006] WO 2014 / 170243 relates to melamine-formaldehyde foams containing microspheres with a core containing at least one active and / or effective substance selected from the group consisting of foam glass, sodium sulfate, sodium lauryl sulfate, polyethylene glycol, cocoamide, fatty alcohols, quaternary ammonium salts, latent heat storage agents, flame retardants, blowing agents, hydrophobizing agents, adhesives, substances that influence soil release behavior, formaldehyde scavengers, substances that improve indoor air quality, skin care products and formulations, abrasives, and mixtures thereof, and a shell containing at least one melamine-formaldehyde resin. Sorbitol may be used as a formaldehyde scavenger.

[0007] EP-A-0 688 852 relates to aqueous expanding solutions containing polyhydric alcohols for the impregnation of porous carrier materials and for the impregnation of composites of glass and mineral fiber plates, nonwovens, mats, plastic drainage mats, metal fiber nonwovens and / or metal mats, and of open-pore thermosetting synthetic resin foams produced in this way, and their use in fire and sound protection of buildings.

[0008] Cleaning implements comprising active agents, such as biocides and / or glycol solvents, impregnated in erodible foams, such as melamine-formaldehyde resin foams, are known, for example, from US Patent Application Publication No. 2014 / 0230847.

[0009] CN107903578 discloses a modified melamine-formaldehyde resin foam with improved toughness using diethylene glycol and propylene glycol.

[0010] Chinese Patent Publication No. 113185745 discloses a lightweight melamine-formaldehyde foam having surface-treated glass fiber as an inorganic filler, which has flame retardancy, high temperature resistance, and aging resistance, and is produced by mixing melamine resin with the surface-treated glass fiber in an extruder in the presence of diethylene glycol and polycarbonate.

[0011] US Patent Application Publication No. 2018 / 140158 discloses a cleaning tool comprising a melamine-formaldehyde foam produced in the presence of polyethylene glycol that has improved durability.

[0012] Summary of the Invention The present invention has been made in view of the above-mentioned prior art, and an object of the present invention is to provide a practical method that enables the production of melamine-formaldehyde foam with enhanced biodegradability while maintaining sufficient flexibility and low brittleness.

[0013] Technical problem solved In order to solve the above problems, the present invention provides a method for producing biodegradable melamine-formaldehyde foam obtainable by the method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave irradiation, wherein the mixture M comprises at least one melamine-formaldehyde pre-condensate having a melamine:formaldehyde molar ratio in the range of 1:1.3 to 1:2.5, at least one curing agent, at least one surfactant, at least one blowing agent, and at least one polyhydric alcohol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol.

[0014] Surprisingly, it has been found that melamine resin foams have improved biodegradability when low functionality melamine resins having a melamine:formaldehyde molar ratio in the range of 1:1.3 to 1:2.5 are co-condensed with polyhydric alcohols.

[0015] Suitable polyhydric alcohols include organic compounds having multiple hydroxyl groups (-OH groups), preferably 2 to 8, more preferably 2 to 6 hydroxyl groups, such as ethylene glycol (2 carbon atoms), glycerol (3 carbon atoms), erythritol (4 carbon atoms), xylitol (5 carbon atoms), and sorbitol (6 carbon atoms). Other suitable polyhydric alcohols include pentaerythritol and trimethylolpropane.

[0016] Polyhydric alcohols are co-condensed in melamine-formaldehyde (MF) resins. The polyhydric alcohol (e.g., ethylene glycol) reacts with the methylol groups of the melamine-formaldehyde (MF) resin to form an ether bridge structure upon H2O decomposition.

[0017] The polyhydric alcohol is preferably selected from polyhydric alcohols having 2 to 6 hydroxyl groups, and most preferably selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol.

[0018] The melamine-formaldehyde precondensate has a molar ratio of melamine:formaldehyde ranging from 1:1.3 to 1:2.5, most preferably from 1:1.5 to 1:1.8.

[0019] Preferably, the melamine-formaldehyde precondensate has a number average molecular weight M in the range of 200 g / mol to 1000 g / mol. n It has.

[0020] Anionic, cationic and nonionic surfactants and mixtures thereof may also be used as dispersants / emulsifiers.

[0021] Useful anionic surfactants include, for example, diphenylene oxide sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkane sulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl and alkyl ether sulfonates. Useful nonionic surfactants include alkylphenol polyglycol ethers, fatty alcohol polyglycol ethers, fatty acid polyglycol ethers, fatty acid alkanolamides, ethylene oxide-propylene oxide block copolymers, amine oxides, glycerol fatty acid esters, sorbitan esters, and alkyl polyglycosides. Useful cationic surfactants include, for example, alkyltriammonium salts, alkylbenzyldimethylammonium salts, and alkylpyridinium salts.

[0022] The dispersant / emulsifier may be added in an amount of 0.2% to 5% by weight based on the melamine-formaldehyde precondensate.

[0023] Preferably, mixture M comprises a surfactant mixture comprising a mixture of 50-90% by weight of at least one anionic surfactant and 10-50% by weight of at least one nonionic surfactant, where each weight percentage is based on the total weight of the surfactant mixture.

[0024] As the curing agent, an acidic compound that catalyzes the further condensation of the melamine resin can be used. The amount of these curing agents is generally in the range of 0.01% to 20% by weight, preferably 0.05% to 5% by weight, based on the precondensate. Useful acidic compounds include organic and inorganic acids, such as those selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalic acid, toluenesulfonic acid, amidosulfonic acid, acid anhydrides, and mixtures thereof.

[0025] Preferably, formic acid is used as the hardening agent.

[0026] Depending on the selection of the melamine-formaldehyde precondensate, the mixture may contain a blowing agent. The amount of blowing agent in the mixture generally depends on the desired density of the foam. Preferably, the amount relative to the melamine-formaldehyde precondensate is such that the foam density is between 6 and 12 kg / m. 3 , more preferably 6.5 to 11 kg / m 3 The amount is selected.

[0027] In principle, the method of the present invention can use both physical and chemical blowing agents, with "physical" or "chemical" blowing agents being preferred (Encyclopedia of Polymer Science and Technology, Vol. I, 3rd ed., Additives, pages 203 to 218, 2003).

[0028] Useful "physical" blowing agents include, for example, hydrocarbons such as pentane, hexane, halogenated hydrocarbons, more preferably chlorinated and / or fluorinated hydrocarbons, such as methylene chloride, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFCs), alcohols such as methanol, ethanol, n-propanol or isopropanol, ethers, ketones and esters, such as methyl formicate, ethyl formicate, methyl acetate or ethyl acetate, in liquid form or as gases, such as air, nitrogen or carbon dioxide.

[0029] Useful "chemical" blowing agents include, for example, isocyanates mixed with water, which release carbon dioxide as the active blowing agent. Furthermore, carbonates and bicarbonates mixed with acids can also be used, in which case carbon dioxide is again produced. Azo compounds, such as azodicarbonamide, are also suitable.

[0030] The mixture further comprises at least one blowing agent. The blowing agent is present in the mixture in an amount of 0.5% to 60% by mass, preferably 1% to 40% by mass, more preferably 1.5% to 30% by mass, based on the melamine-formaldehyde precondensate. It is preferred to add a physical blowing agent having a boiling point of 0 to 80°C. Preferably, pentane is used as the blowing agent.

[0031] The mixture may further comprise at least one additive selected from the group of dyes, fragrances, optical brighteners, UV and heat stabilizers, flame retardants, formaldehyde scavengers, and pigments, which additive is preferably uniformly dispersed within the foam.

[0032] The precondensate is generally foamed to obtain a foamed material by heating a suspension of the melamine-formaldehyde precondensate.

[0033] The energy is introduced by electromagnetic radiation at a frequency in the range of 0.2 to 100 GHz, preferably 0.5 to 10 GHz, for example by high-frequency radiation of 5 to 400 kW, preferably 5 to 200 kW, more preferably 9 to 120 kW per kilogram of mixture used. Magnetrons are a useful source of inductive radiation; one magnetron may be used or two or more magnetrons may be used simultaneously.

[0034] The resulting foamed material is finally dried to remove residual water and blowing agent from the foam.

[0035] The described method provides blocks / slabs of foam material that can be cut to size in any desired shape.

[0036] In a preferred embodiment, the method comprises the following steps: a) The following: 100 parts by weight of at least one melamine-formaldehyde precondensate, 2 to 4 parts by weight, preferably 2.2 to 3.8 parts by weight, and more preferably 2.7 to 3.3 parts by weight of at least one curing agent; 0.2 to 5 parts by weight, preferably 0.5 to 3 parts by weight, and more preferably 1.25 to 2.3 parts by weight of a surfactant mixture; 0.1 to 5 parts by mass, preferably 0.5 to 4 parts by mass, and more preferably 1.1 to 3.6 parts by mass of at least one salt of an inorganic acid and / or an organic carboxylic acid; 1 to 40 parts by weight, preferably 10 to 35 parts by weight, and more preferably 15 to 21 parts by weight of at least one blowing agent; 0.1 to 50 parts by mass, preferably 5 to 25 parts by mass, of at least one polyhydric alcohol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol; 0 to 20 parts by weight of one or more additives selected from the group consisting of dyes, fragrances, optical brighteners, UV and heat stabilizers, flame retardants, formaldehyde scavengers, and pigments; 25 to 60 parts by weight, preferably 30 to 50 parts by weight, and more preferably 36 to 44 parts by weight of water preparing an aqueous mixture M comprising: b) heating and foaming said mixture M using microwave radiation; c) annealing the foam using hot air and / or nitrogen at a temperature in the range of 150°C to 290°C.

[0037] The present invention further relates to melamine-formaldehyde foams obtainable by the process according to the invention described above.

[0038] The melamine-formaldehyde foam preferably contains 1 to 30 parts by weight, more preferably 5 to 25 parts by weight, of at least one polyhydric alcohol per 100 parts of dry melamine-formaldehyde foam.

[0039] The at least one polyhydric alcohol is preferably incorporated into the open-cell structure melamine-formaldehyde resin crosslink, where incorporated means that the polyhydric alcohol does not wash out.

[0040] The foam blocks or slabs may optionally be hot-pressed in a further process step. Hot-pressing per se is known to those skilled in the art and is described, for example, in WO 2007 / 031944, EP 451535, EP 111860 and U.S. Pat. No. 6,608,118.

[0041] The foams obtainable by the process of the present invention preferably have an open cell structure with an open cell content of more than 50%, more particularly more than 95%, measured according to DIN ISO 4590. Preferably, the density of the foam is between 6 and 12 kg / m 3 , more preferably 6.5 to 11 kg / m 3 is.

[0042] The melamine-formaldehyde foams according to the invention can be used for acoustic and / or thermal insulation in aircraft, ship and car construction, in mechanical engineering, building construction, or for cleaning, grinding or polishing sponges. [Example]

[0043] The present invention will be described in more detail and specifically below with reference to examples, but the present invention is not limited to these examples.

[0044] Measurement method: Ram pressure value [N]: Ram pressure measurements for evaluating the mechanical quality of melamine resin foams were all carried out as follows: a cylindrical ram with a diameter of 8 mm and a height of 10 cm was pressed against a cylindrical sample with a diameter of 11 cm and a height of 5 cm at an angle of 90% in the foaming direction until the sample broke. The tear force [N] (hereinafter also referred to as the ram pressure value) provides information about the quality of the foam.

[0045] Shore hardness: Measurements were carried out according to ASTM D 2240. For measurements on low density foams, a scale of 000 was used (sphere diameter 2.4 mm, spring force 1.111 N).

[0046] Biodegradable: Biodegradability was measured in percent after 28 days according to OECD 301F: Manometric Respirometry Test (Organization for Economic Co-operation and Development Chemicals Testing - Guidelines. Adopted 17.07.1992).

[0047] Sludge: Mannheim Water Treatment Plant For the Manometric Respirometry (301F) method, activated sludge must be taken from treatment plants receiving primarily domestic sewage or from laboratory-scale plants when used. Inocula from other sources, which usually result in low cell densities, have been found to produce highly variable results.

[0048] [Table 1]

[0049] To confirm the chemical bonding of the co-condensed polyhydric alcohols, the following washing test was carried out: 10 g of the final foam was washed twice with hot (60 °C) demineralized water, after which the foam was dried (8 h, 100 °C) and weighed.

[0050] Materials used: Melamine-formaldehyde precondensate: HF-MF: High Functionality MF Melamine-Formaldehyde Precondensate HF-MF is a spray-dried melamine-formaldehyde precondensate with an average molecular weight (number average) Mn of 350 g / mol, with a melamine:formaldehyde molar ratio of 1:2.8.

[0051] LF-MF: Low Functionality Melamine-Formaldehyde Precondensate LF-MF is a spray-dried melamine-formaldehyde precondensate with an average molecular weight (number average) Mn of 320 g / mol, with a melamine:formaldehyde molar ratio of 1:1.6.

[0052] SM-1: A surfactant mixture of 80% by weight of an alkanesulfonate mixture and 20% by weight of an alkyl polyethylene glycol ether mixture.

[0053] Co-condensation additives (polyhydric alcohols, polyols): Ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, sorbitol, glucose, fructose, galactose, maltose, all obtained from Sigma-Aldrich.

[0054] Comparative Example C1 100 parts by weight of spray-dried melamine / formaldehyde precondensate HF-MF was dissolved in 30 parts by weight of water. To this mixture were added 2.75 parts by weight of sodium formate, 3.1 parts by weight of formic acid, 1.5 parts by weight of surfactant mixture SM-1, and 17.8 parts by weight of a blowing agent mixture of 80% by weight of n-pentane and 20% by weight of isopentane. The mixture was vigorously stirred and foamed in a polypropylene mold by irradiating with 2.54 GHz microwave energy. The foam was then oven-cured at 100°C for 8 hours and annealed at 240°C for 10 minutes.

[0055] Comparative examples C1.1~C1.16 100 parts by weight of spray-dried melamine / formaldehyde precondensate HF-MF was dissolved in 30 parts by weight of water. To this mixture were added 2.75 parts by weight of sodium formate, 3.1 parts by weight of formic acid, 1.5 parts by weight of surfactant mixture SM-1, and 17.8 parts by weight of a blowing agent mixture of 80% by weight of n-pentane and 20% by weight of isopentane. Next, 10 to 20% by weight of a polyol listed in Table 1, based on the dry melamine / formaldehyde precondensate, was added. The mixture was vigorously stirred and foamed in a polypropylene mold by irradiating with 2.54 GHz microwave energy. The foam was then oven-cured at 100°C for 8 hours and annealed at 240°C for 10 minutes.

[0056] Comparative Example C2: 100 parts by weight of spray-dried melamine / formaldehyde precondensate LF-MF was dissolved in 30 parts by weight of water. To this mixture were added 2.75 parts by weight of sodium formate, 3.1 parts by weight of formic acid, 1.5 parts by weight of surfactant mixture SM-1, and 17.8 parts by weight of a blowing agent mixture of 80% by weight of n-pentane and 20% by weight of isopentane. The mixture was vigorously stirred and foamed in a polypropylene mold by irradiating with 2.54 GHz microwave energy. The foam was then oven-cured at 100°C for 8 hours and annealed at 240°C for 10 minutes.

[0057] Examples 2.1 to 2.8, 2.13 to 2.16 and Comparative Examples C2.9 to C2.12 100 parts by weight of spray-dried melamine / formaldehyde precondensate LF-MF was dissolved in 30 parts by weight of water. To this mixture were added 2.75 parts by weight of sodium formate, 3.1 parts by weight of formic acid, 1.5 parts by weight of surfactant mixture SM-1, and 17.8 parts by weight of a blowing agent mixture of 80% by weight of n-pentane and 20% by weight of isopentane. Next, 10 to 20% by weight of a polyol listed in Table 2, based on the dry melamine / formaldehyde precondensate, was added. The mixture was vigorously stirred and foamed in a polypropylene mold by irradiating with 2.54 GHz microwave energy. The foam was then oven-cured at 100°C for 8 hours and annealed at 240°C for 10 minutes.

[0058] To confirm the chemical bonding of the co-condensed polyhydric alcohols, the following washing test was carried out: 10 g of the final foam was washed twice with hot (60 °C) demineralized water. The foam was then dried (8 h, 100 °C) and weighed. The mass loss should be approximately 0%.

[0059] For example, the combination of reducing sugars such as glucose, fructose, galactose, maltose, lactose, etc. with low functionality MF resin formulations does not demonstrate increased biodegradability.

[0060] The use of polyhydric alcohols ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol as co-condensation additives in low-functionality formulations (M / F 1:1.6) improves biodegradability without compromising flexibility and brittleness (Table 2). The decrease in Shore hardness is less than 20% and the loss in ram pressure is less than 50%.

[0061] To confirm the chemical bonding of the co-condensed polyhydric alcohols, the following washing test was carried out: 10 g of the final foam was washed twice with hot (60 °C) demineralized water. The foam was then dried (8 h, 100 °C) and weighed. The mass loss observed for Comparative Examples 1.1 to 1.16, Examples 2.1 to 2.8, 2.13 to 2.16, and Comparative Examples C2.9 to C2.12 was within the range of mass loss observed for Comparative Examples C1 and C2.

[0062] [Table 2]

[0063] [Table 3]

Claims

1. 1. A method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate having a molar ratio of melamine:formaldehyde in the range of 1:1.3 to 1:2.5, at least one curing agent, at least one surfactant, at least one blowing agent, and at least one polyhydric alcohol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol.

2. 2. The method of claim 1, wherein the polyhydric alcohol is selected from polyhydric alcohols having 2 to 8 hydroxyl groups.

3. 3. The process according to claim 1, wherein a melamine-formaldehyde precondensate is used having a molar ratio of melamine:formaldehyde in the range of 1:1.5 to 1:1.

8.

4. 4. The method of any one of claims 1 to 3, wherein the mixture M comprises a surfactant mixture comprising a mixture of 50 to 90% by weight of at least one anionic surfactant and 10 to 50% by weight of at least one nonionic surfactant, wherein each weight percentage is based on the total weight of the surfactant mixture.

5. 5. The method according to claim 1, wherein formic acid is used as the curing agent.

6. 6. The method according to claim 1, wherein pentane is used as the blowing agent.

7. Steps below: a) The following: 100 parts by weight of at least one melamine-formaldehyde precondensate having a molar ratio of melamine:formaldehyde in the range of 1:1.3 to 1:2.5, 2 to 4 parts by weight of at least one curing agent; 0.2 to 5 parts by mass of surfactant mixture, 0.1 to 5 parts by mass of at least one salt of an inorganic acid and / or an organic carboxylic acid, 1 to 40 parts by weight of at least one blowing agent; 0.1 to 50 parts by mass of at least one polyhydric alcohol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol; 0 to 20 parts by weight of one or more additives selected from the group consisting of dyes, fragrances, optical brighteners, UV and heat stabilizers, flame retardants, formaldehyde scavengers, and pigments; Water 25-60 parts by mass preparing an aqueous mixture M comprising: b) heating and foaming said mixture M using microwave radiation; c) annealing the foam using hot air and / or nitrogen at a temperature in the range of 150°C to 290°C.

7. The method of any one of claims 1 to 6, comprising:

8. A melamine-formaldehyde foam obtainable by the process according to any one of claims 1 to 7.

9. Density 6 to 12 kg / m 3 9. The melamine-formaldehyde foam of claim 8, wherein the viscosity of the foam is in the range of

10. 10. Melamine-formaldehyde foam according to claim 8 or 9, having an open cell content according to DIN ISO 4590 of more than 95%.

11. A melamine-formaldehyde foam according to any one of claims 8 to 10, having a biodegradability according to OECD 301F of more than 10% after 28 days.

12. 12. Use of the melamine-formaldehyde foams according to any one of claims 8 to 11 for acoustic and / or thermal insulation in aircraft, ship and motor vehicle construction, in mechanical engineering or in building construction, or for cleaning, grinding or polishing sponges.

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