Biodegradable melamine resin foam

Abstract

The invention provides a method for producing a melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave radiation, and a biodegradable melamine resin foam obtainable by the method, the mixture M comprises at least one melamine-formaldehyde precondensate having a molar ratio of melamine: formaldehyde in the range of from 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 polyol, the polyol is selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol.

Description

[0001] The present invention relates to a method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave radiation, the mixture M comprising at least one melamine-formaldehyde precondensate 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 polyol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol, and a biodegradable melamine resin foam obtainable by the method.

[0002] Related prior art

[0003] Melamine resin foams are used in various applications, such as sound absorption in interior acoustics, thermal insulation in buildings, and pipe insulation. A more significant application is the use of melamine resin foams in consumer / household applications as cleaning sponges. In particular, in household applications, such as cleaning sponges, there is a strong demand for biodegradable materials.

[0004] Several methods are available for studying the biodegradation of polymers in various media (e.g., soil, seawater, freshwater, sewage sludge). The OECD 301F biodegradation test is one of the most important methods for testing the biodegradation of polymer foams used in domestic applications. The OECD 301F test studies biodegradation in activated sludge used for wastewater treatment. To date, no results have been reported in the literature for the biodegradation of melamine resin foams according to the OECD 301F test.

[0005] EP 4 001 350 provides a thermoformable melamine foam and a method for producing the same, wherein the thermoformable melamine foam comprises a condensate of a melamine-formaldehyde-based compound having a low molecular weight ratio (M:F) in the range of 1:1.3 to 1:1.8, thereby reducing the formaldehyde content and exhibiting excellent thermal stability. In order to improve the heat resistance of the thermoformable melamine foam, a predetermined amount of isosorbide is added to the dispersion.

[0006] WO 2018 / 095760 A1 relates to a method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave radiation, 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 g / mol to 10.000 g / mol, as well as to a melamine-formaldehyde foam obtainable by this method and its use.

[0007] WO 2014 / 170243 relates to a melamine-formaldehyde foam comprising microspheres having a core comprising at least one active and / or effective substance selected from the group consisting of foamed glass, sodium sulfate, sodium lauryl sulfate, polyethylene glycol, cocamide, fatty alcohols, quaternary ammonium salts, latent heat storage agents, flame retardants, swelling agents, hydrophobic agents, adhesives, substances influencing dirt release behavior, formaldehyde scavengers, substances improving indoor air quality, skin care products and preparations, abrasives, and mixtures thereof, and a shell comprising at least one melamine-formaldehyde resin. Sorbitol can be used as a formaldehyde scavenger.

[0008] EP 0 688 852 A1 relates to aqueous swelling solutions containing polyols for impregnating porous carrier materials and for impregnating glass fiber boards and mineral fiber boards, nonwovens, matt plastic drainage mats, nonwovens and / or metal mats of metal fibers, open-cell thermosetting synthetic resin foam composites produced in this way, and their use for fire protection and sound insulation in buildings.

[0009] Cleaning tools contain active agents such as biocides and / or glycol solvents impregnated in an erodible foam such as melamine-formaldehyde resin foam, as is known from US 2014 / 0230847 A1.

[0010] CN 107 903 578 A discloses a modified melamine formaldehyde resin foam having improved toughness using diethylene glycol and propylene glycol.

[0011] CN 113 185 745A discloses a lightweight melamine formaldehyde foam with surface-treated glass fiber as an inorganic filler, which has flame retardancy, high temperature resistance and aging resistance and is prepared by mixing melamine resin with surface-treated glass fiber in an extruder in the presence of diethylene glycol and polycarbonate.

[0012] US2018 / 140158 A discloses a cleaning tool comprising a melamine-formaldehyde foam with improved durability, which is produced in the presence of polyethylene glycol. Summary of the Invention

[0013] 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 capable of preparing melamine-formaldehyde foam having increased biodegradability while maintaining sufficient flexibility and low brittleness.

[0014] Technical problems solved

[0015] In order to solve this problem, the present invention provides a method for producing a biodegradable melamine-formaldehyde foam, which can be obtained by a method for producing a melamine-formaldehyde foam by heating an aqueous mixture M using microwave radiation and foaming it, wherein the mixture M comprises at least one melamine-formaldehyde precondensate 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 polyol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol.

[0016] Surprisingly, it has been found that melamine resin foams can show increased biodegradation if low-functionality melamine resins having a molar ratio of melamine:formaldehyde in the range of 1:1.3 to 1:2.5 are co-condensed with polyols.

[0017] Suitable polyols include organic compounds having a plurality of hydroxyl (-OH) groups, preferably in the range of 2 to 8, more preferably in the range of 2 to 6 hydroxyl groups, such as ethylene glycol (2-carbon), glycerol (3-carbon), erythritol (4-carbon), xylitol (5-carbon), sorbitol (6-carbon). Other suitable polyols are, for example, pentaerythritol, trimethylolpropane.

[0018] The polyols are cocondensed in a melamine-formaldehyde (MF) resin.

[0019] The above-mentioned polyols - such as ethylene glycol - react with the methylol groups of the melamine-formaldehyde (MF) resin to form ether bridge structures with H2-cleavage.

[0020] The polyol is preferably selected from polyols having 2 to 6 hydroxyl groups.Most preferably, the polyol is selected from the group of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose and sorbitol.

[0021] The molar ratio of melamine:formaldehyde (M / F) of the melamine-formaldehyde precondensate is in the range of 1:1.3 to 1:2.5, most preferably 1:1.5 to 1:1.8.

[0022] Preferably, the number average molecular weight M of the melamine-formaldehyde precondensate is n In the range of 200 g / mol to 1000 g / mol.

[0023] Anionic, cationic and nonionic surfactants and mixtures thereof can be used as dispersants / emulsifiers.

[0024] Useful anionic surfactants include, for example, diphenyl oxide sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfo fatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl and alkyl ether phosphates. 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 emulsifiers include, for example, alkyltriammonium salts, alkylbenzyldimethylammonium salts, and alkylpyridinium salts.

[0025] Dispersants / emulsifiers may be added in amounts of 0.2% to 5% by weight, based on the melamine-formaldehyde precondensate.

[0026] Preferably, 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 the weight percentages are each based on the total weight of the surfactant mixture.

[0027] As curing agent, the acidic compound that catalyzes the further condensation of melamine resin can be used.All based on precondensate meter, the amount of these curing agents is usually in the scope of 0.01 weight % to 20 weight %, and preferably in the scope of 0.05 weight % to 5 weight %. Available acidic compound comprises organic acid and the inorganic acid that for example is selected from the group of being made up of following item: hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalic acid, toluenesulfonic acid, sulfamic acid, acid anhydride and their mixture.

[0028] Preferably, formic acid is used as curing agent.

[0029] Depending on the choice of melamine-formaldehyde precondensate, the mixture contains a blowing agent. The amount of blowing agent in the mixture generally depends on the desired foam density. Preferably, the amount relative to the melamine-formaldehyde precondensate is selected so that the foam density is 6 kg / m 3 Up to 12kg / m 3 , more preferably 6.5 kg / m 3 Up to 11kg / m 3 amount.

[0030] In principle, the method of the present invention can use both physical and chemical blowing agents. "Physical" or "chemical" blowing agents are suitable (Encyclopedia of Polymer Science and Technology, No. 1, 3rd edition, Additives, pp. 203 to 218, 2003).

[0031] Useful "physical" inflating agents include, for example, hydrocarbons such as pentane, hexane, halogenated hydrocarbons, more particularly chlorinated and / or fluorinated hydrocarbons, for example methylene chloride, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFCs), alcohols such as methanol, ethanol, n-propanol or isopropanol, ethers, ketones and esters such as methyl formate, ethyl formate, methyl acetate or ethyl acetate, in liquid form or as gas.

[0032] Useful "chemical" blowing agents include, for example, isocyanates mixed with water to 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 generated. Azo compounds are also suitable, for example azodicarbonamide.

[0033] The mixture further comprises at least one expanding agent. The expanding agent is present in the mixture in an amount of 0.5 to 60 wt %, preferably 1 to 40 wt %, and more preferably 1.5 to 30 wt %, based on the melamine-formaldehyde precondensate. Preferably, a physical expanding agent having a boiling point between 0° C. and 80° C. is added. Preferably, pentane is used as the expanding agent.

[0034] The mixture may further comprise at least one additive selected from the group consisting of dyes, fragrances, optical brighteners, UV and heat stabilizers, flame retardants, formaldehyde scavengers and pigments. The additives are preferably uniformly distributed in the foam.

[0035] The foamed material is usually obtained by heating a suspension of the melamine-formaldehyde precondensate to foam the precondensate.

[0036] The energy is introduced via electromagnetic radiation, for example via high-frequency radiation in the frequency range of 0.2 GHz to 100 GHz, preferably 0.5 GHz to 10 GHz, at 5 kW to 400 kW, preferably 5 kW to 200 kW, more preferably 9 kW to 120 kW per kilogram of mixture used. A useful dielectric radiation source is a magnetron, and one magnetron or two or more magnetrons can be used simultaneously.

[0037] The resulting foamed material is finally dried to remove residual water and blowing agent from the foam.

[0038] The described method provides a block / board of foamed material which can be cut to size in any desired shape.

[0039] In a preferred embodiment, the method comprises the following steps:

[0040] a) producing an aqueous mixture M comprising

[0041] 100 parts by weight of at least one melamine-formaldehyde precondensate,

[0042] 2 to 4 parts by weight, preferably 2.2 to 3.8 parts by weight, more preferably 2.7 to 3.3 parts by weight of at least one curing agent,

[0043] 0.2 to 5 parts by weight, preferably 0.5 to 3 parts by weight, more preferably 1.25 to 2.3 parts by weight of a surfactant mixture,

[0044] 0.1 to 5 parts by weight, preferably 0.5 to 4 parts by weight, more preferably 1.1 to 3.6 parts by weight 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, more preferably 15 to 21 parts by weight of at least one swelling agent,

[0045] 0.1 to 50 parts by weight, preferably 5 to 25 parts by weight, of at least one polyol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose and sorbitol,

[0046] 0 to 20 parts by weight of one or more additives selected from the group of dyes, fragrances, optical brighteners, UV and heat stabilizers, flame retardants, formaldehyde scavengers and pigments,

[0047] 25 to 60 parts by weight, preferably 30 to 50 parts by weight, more preferably 36 to 44 parts by weight of water,

[0048] b) heating the mixture M using microwave radiation and causing it to foam,

[0049] c) annealing the foam using hot air and / or nitrogen in a temperature range of 150° C. to 290° C.,

[0050] The present invention further relates to a melamine-formaldehyde foam obtainable by the process according to the invention as described above.

[0051] The melamine-formaldehyde foam preferably comprises 1 to 30 parts by weight, more preferably 5 to 25 parts by weight, of at least one polyol per 100 parts of dry melamine-formaldehyde foam.

[0052] The at least one polyol is preferably incorporated into the melamine-formaldehyde resin bridges of the open-cell structure. Incorporation means that the polyol cannot be washed out.

[0053] The foam blocks or plates can optionally be hot pressed in a further process step.Hot pressing itself is known to the person skilled in the art and is described, for example, in WO 2007 / 031944, EP-A 451 535, EP-A111 860 and US Pat. No. 6,608,118.

[0054] The foam obtainable by the process of the invention preferably has an open-cell structure with an open-cell content of greater than 50% and more particularly greater than 95% when measured according to DIN ISO 4590. Preferably, the foam has a density of 6 kg / m 3 Up to 12kg / m 3 , more preferably 6.5 kg / m 3 Up to 11kg / m 3 .

[0055] The melamine-formaldehyde foams according to the invention can be used for sound and / or heat insulation in aircraft, ship and motor vehicle construction, in mechanical engineering or in building construction, or as cleaning, grinding or polishing sponges. Example

[0056] Hereinafter, the present invention is described in more detail and specifically with reference to Examples, however, these Examples are not intended to limit the present invention.

[0057] Measurement method :

[0058] Punching force value [N] :

[0059] Punch force measurements for evaluating the mechanical quality of melamine resin foams are performed as follows. A cylindrical punch with a diameter of 8 mm and a height of 10 cm is pressed into a cylindrical sample with a diameter of 11 cm and a height of 5 cm at a 90% angle in the direction of foaming until the sample ruptures. The tear force [N], also referred to as the punch force value below, provides information on the quality of the foam.

[0060] Shore hardness :

[0061] The measurements are carried out according to ASTM D 2240. For the measurement of low-density foams, a scale of 000 is used (sphere diameter 2.4 mm, spring force 1.111 N).

[0062] Biodegradation :

[0063] Biodegradation was determined as a percentage after 28 days according to: OECD 301F: Manometric Respirometry Test. Organisation for Economic Co-operation and Development - Testing of Chemicals - Guidelines. Adopted 17.07.1992.

[0064] sludge: Mannheim

[0065] For the manometric respirometry (301F) method, if activated sludge is used, it should be taken from a treatment plant or laboratory-scale unit that receives primarily domestic sewage. Inocula from other sources (which generally produce lower cell densities) have been found to give a higher scatter in results.

[0066]

[0067]

[0068] In order to confirm the chemical bonding of the cocondensate polyol, the following washing test was performed: 10 g of the final foam were washed twice with hot (60° C.) demineralized water. The foam was then dried (8 hours, 100° C.) and weighed.

[0069] Materials used :

[0070] Melamine-formaldehyde precondensate :

[0071] HF-MF: High functional MF melamine-formaldehyde precondensate HF-MF is the average molecular weight

[0072] A spray-dried melamine-formaldehyde precondensate having a (number average) Mn of 350 g / mol and a molar ratio of melamine:formaldehyde of 1:2.8.

[0073] 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 and a molar ratio of melamine:formaldehyde of 1:1.6.

[0074] SM-1: A surfactant mixture of 80 wt% of an alkane sulfonate mixture and 20 wt% of an alkyl polyglycol ether mixture.

[0075] Co-condensate additives (polyols) :

[0076] Ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, sorbitol, glucose, fructose, galactose, and maltose were all provided by Sigma-Aldrich.

[0077] Comparative Example C1

[0078] 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 a surfactant mixture SM-1, and 17.8 parts by weight of a blowing agent mixture consisting of 80% by weight of n-pentane and 20% by weight of isopentane. This mixture was vigorously stirred and then foamed in a polypropylene mold by irradiation with 2.54 GHz microwave energy. The foam was then cured in an oven at 100° C. for 8 hours and annealed at 240° C. for 10 minutes.

[0079] Comparative Examples C1.1-C1.16

[0080] The spray-dried melamine / formaldehyde precondensate HF-MF of 100 weight parts is dissolved in the water of 30 weight parts.In this mixture, add the sodium formiate of 2.75 weight parts, the formic acid of 3.1 weight parts, the surfactant mixture SM-1 of 1.5 weight parts and the swelling agent mixture of being made up of 80 weight % n-pentane and 20 weight % isopentane of 17.8 weight parts.Then, add 10 weight % to 20 weight % of the polyol as listed in Table 1 based on the melamine / formaldehyde precondensate of drying.This mixture is stirred vigorously and then foamed in a polypropylene mold by irradiating microwave energy at 2.54GHz.Then the foam is in 100 ℃ of curing 8 hours and in 240 ℃ of annealing 10 minutes in an oven.

[0081] Comparative Example C2 :

[0082] 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 a surfactant mixture SM-1, and 17.8 parts by weight of a blowing agent mixture consisting of 80% by weight n-pentane and 20% by weight isopentane. The mixture was vigorously stirred and then foamed in a polypropylene mold by irradiation with 2.54 GHz microwave energy. The foam was then cured in an oven at 100°C for 8 hours and annealed at 240°C for 10 minutes.

[0083] Examples 2.1-2.8, 2.13-2.16 and Comparative Examples C2.9-C2.12

[0084] 100 parts by weight of spray-dried melamine / formaldehyde precondensate LF-MF were 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 a surfactant mixture SM-1, and 17.8 parts by weight of an expanding agent mixture consisting of 80% by weight n-pentane and 20% by weight isopentane. Next, 10% to 20% by weight of a polyol as listed in Table 2, based on the dry melamine / formaldehyde precondensate, was added. The mixture was vigorously stirred and then foamed in a polypropylene mold by irradiation with 2.54 GHz microwave energy. The foam was then cured in an oven at 100° C. for 8 hours and annealed at 240° C. for 10 minutes.

[0085] To confirm the chemical bonding of the cocondensate polyol, the following washing test was performed: 10 g of the final foam was washed twice with hot (60° C.) demineralized water. The foam was then dried (8 hours, 100° C.) and weighed. The mass loss should be approximately 0%.

[0086] No increased biodegradation was observed for reducing sugars such as glucose, fructose, galactose, maltose, and lactose in combination with low-functionality MF resin formulations.

[0087] By using the polyols ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol as cocondensate additives in a low-functionality formulation (M / F 1:1.6), biodegradability was increased without compromising flexibility and brittleness (Table 2). The reduction in Shore hardness was less than 20%, and the loss in punch force was less than 50%.

[0088] To confirm the chemical bonding of the cocondensate polyol, the following washing test was performed: 10 g of the final foam was washed twice with hot (60°C) demineralized water. The foam was then dried (8 hours at 100°C) and weighed. The percent weight loss observed for Comparative Examples 1.1.-1.16 and Examples 2.1-2.8, 2.13-2.16, and Comparative Examples C2.9-C2.12 was within the range of the percent weight loss for Comparative Examples C1 and C2.

[0089] Table 1: From high-functionality MF precondensate (M / F 1:2.8) MF foam

[0090]

[0091] Table 2: From low-functionality MF precondensate (M / F 1:1.6) MF foam

[0092]

[0093]

Claims

1. A method for producing melamine-formaldehyde foam by heating and foaming an aqueous mixture M using microwave radiation, the mixture M comprising at least one melamine-formaldehyde precondensate 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 polyol selected from the group consisting of ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, xylitol, xylose, and sorbitol.

2. The method according to claim 1, wherein the polyol is selected from polyols having 2 to 8 hydroxyl groups.

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

8.

4. The process according to claim 1 , 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, the weight percentages being each based on the total weight of the surfactant mixture.

5. The method according to any one of claims 1 to 4, wherein formic acid is used as curing agent.

6. The process according to any one of claims 1 to 5, wherein pentane is used as the swelling agent.

7. The method according to any one of claims 1 to 6, comprising the steps of: a) producing an aqueous mixture M comprising 100 parts by weight of at least one melamine-formaldehyde precondensate having a molar ratio of melamine to 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 weight of a surfactant mixture, 0.1 to 5 parts by weight of at least one inorganic acid and / or organic carboxylic acid salt, 1 to 40 parts by weight of at least one swelling agent, 0.1 to 50 parts by weight of at least one polyol 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, and 25 to 60 parts by weight of water, b) heating the mixture M using microwave radiation and causing it to foam, c) Annealing the foam using hot air and / or nitrogen in a temperature range of 150°C to 290°C.

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

9. Melamine-formaldehyde according to claim 8, wherein the density is 6 kg / m 3 Up to 12kg / m 3 within the range. 10 . The melamine-formaldehyde foam according to claim 8 , wherein the open-cell content according to DIN ISO 4590 is greater than 95%.

11. Melamine-formaldehyde foam according to claims 8 to 10, having a biodegradation of more than 10% after 28 days according to OECD 301F.

12. Use of the melamine-formaldehyde foam according to claims 8 to 11 for sound and / or heat insulation in aircraft, ship and motor vehicle construction, in mechanical engineering or in building construction, or as a cleaning, grinding or polishing sponge.

Images