Polyester polyol and polyurethane foam system containing the same

Technical Field

The present disclosure relates to a polyester polyol having a functionality larger than 6, a polyurethane system containing the same, a polyurethane article produced from the same, and use thereof.

Background

Polyurethane (Pll) foams are suitable for many applications, for example cushioning materials, thermal insulation materials, packaging, automobile-dashboards, or construction materials.

In most cases a polyurethane foam with a high mechanical strength is desired. To produce such polyurethane foam, usually a polyester polyol with a high functionality is employed in the A component. Polyester polyols with high functionality are difficult to synthesize and handle as their viscosity increases significantly when the functionality increases.

CN103724598A describes a polyester polyol comprising in parts by weight: 5 to 25 parts of trimellitic anhydride, 5 to 20 parts of pyromellitic dianhydride, 65 to 70 parts of recycled polyhydric alcohol, 2 to 5 parts of glycerol and 0.01 to 0.025 part of a catalytic agent.

Summary

An objective of the present disclosure is to overcome the problems of the prior art discussed above and to provide a polyester polyol having a functionality of hydroxyl groups larger than 6 for producing polyurethane foam. The polyester polyol has a processable viscosity and is easy to handle.

Surprisingly, it has been found by the inventors that the above object can be achieved by a polyester polyol which comprises the product of at least one selected from the group of a carboxylic acid containing at least three carboxylic groups and a derivative thereof; a carboxyl- reactive compound containing at least two functional groups reactive towards the carboxylic acid and a side chain with at least 10 carbon atoms; and a polyhydroxy alcohol with at least three hydroxyl groups.

According to another aspect of the present disclosure, provided is a polyurethane foam system comprising: a polyol component; and an isocyanate component, wherein the polyol component comprises the polyester polyol; one or more catalysts; and at least one blowing agent.

In a further aspect, the present disclosure provides a polyurethane foam produced from the polyurethane foam system according to the present disclosure.

In another further aspect, the present disclosure provides a composite comprising the polyurethane foam according to the present disclosure.

In still another further aspect, the present disclosure provides usage of the composite as a board or a panel in a cleanroom or a cold storage, a reefer, a roof panel, a laminate; or as a pipe insulation in a spray pipe or an injection pipe.

It has been surprisingly found in this application that, the polyester polyol provided has a relatively low viscosity and is processable for polyurethane compositions. The polyurethane foam produced therefrom has a high mechanical strength and is easy to demold.

Detailed description

Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which the present disclosure belongs. As used herein, the following terms have the meanings ascribed to them below, unless specified otherwise.

As used herein, the articles "a" and "an" refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

Unless otherwise identified, all percentages (%) are “percent by weight".

Carboxyl refers to the carboxyl group (-C(O)OH), the functionality in organic carboxylic acids.

Unless otherwise identified, “polyether segment” refers to any bi-valent segment consisting of one or more repeating units of alkylene oxide. The alkylene oxide may include without limitation to tetramethylene oxide, ethylene oxide, propylene oxide, butylene oxide, pentylene oxide, hexylene oxide, or styrene oxide. Polyether segments include without limitation to, e.g.,

-[CH ₂ CH ₂ CH ₂ CH ₂ O] _a -, -[CH ₂ CH ₂ O] _b -, -[CH ₂ CH(CH ₃ )O] _c -, - [CH ₂ CH ₂ O]d[CH ₂ CH(CH3)O] _e -, and/or any other combination of alkylene oxides, wherein a through e are independently an integer not less than 1 .

Tetramethylene oxide is -CH ₂ CH ₂ CH ₂ CH ₂ O-

Ethylene oxide (EO) is -CH ₂ CH ₂ O-

Propylene oxide (PO) is -CH(CH ₃ )CH ₂ O-, or -CH ₂ CH(CH ₃ )O-

Butylene oxide (BO) is -CH(C ₂ H ₅ )CH ₂ O-, -C(CH ₃ ) ₂ CH ₂ O-, -CH ₂ C(CH ₃ ) ₂ O-, - CH(CH ₃ )CH(CH ₃ )O-, or -CH ₂ CH(C ₂ H ₅ )O-.

Pentylene oxide is -CH(C ₃ H ₇ )CH ₂ O-, -CH ₂ CH(C ₃ H ₇ )O-, -CH(C ₂ H ₅ )CH(CH ₃ )O-, - CH(CH ₃ )CH(C ₂ H ₅ )O-, -C(CH ₃ )(C ₂ H ₅ )CH ₂ O-, -CH ₂ C(CH ₃ )(C ₂ H ₅ )O-, -C(CH ₃ ) ₂ CH(CH ₃ )O-, or - CH ₂ (CH ₃ )C(CH ₃ ) ₂ O-. Hexylene oxide is -CH(C ₄ H ₉ )CH ₂ O-, -CH ₂ CH(C ₄ H ₉ )O- -C(C ₃ H ₇ )(CH ₃ )CH ₂ O-, - CH ₂ C(C ₃ H ₇ )(CH ₃ )O- -CH(C ₃ H ₇ )CH(CH ₃ )O, -CH(CH ₃ )CH(C ₃ H ₇ )O-, -C(C ₂ H ₅ )(C ₂ H ₅ )CH ₂ O- - CH ₂ C(C ₂ H ₅ ) ₂ O-, -CH(C ₂ H ₅ )CH(C ₂ H ₅ )O- -C(CH ₃ ) ₂ CH(C ₂ H ₅ )O- -CH(C ₂ H ₅ )C(CH ₃ ) ₂ O- or - CH(CH ₃ ) ₂ C(CH ₃ ) ₂ O-.

Styrene oxide is -CH(C ₆ H ₅ )CH ₂ O- or -CH ₂ CH(C6H ₅ )O-

Hydroxyl number is defined as the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize the acetic acid taken up on acetylation of one gram of a polyol or a blend of polyols.

Functionality (shortened as “Fn”) of a polyol (including polyester polyols, polyether polyols, or other kinds of polyols) is defined as the number of hydroxyl groups per molecule. For a blend of several polyols, the functionality is defined as the molar average of the functionality of all the component polyols.

Isocyanate index or NCO index is defined as the ratio of number of NCO groups over number of isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage:

Isocyanate index = [NCO] x 100 (%) I [isocyanate-reactive hydrogen]

[NCO] is the number of NCO groups.

[active hydrogen] is the number of isocyanate-reactive hydrogen atoms.

In other words, the isocyanate index expresses the percentage of isocyanate actually used in a formulation with respect to the amount of isocyanate theoretically required for reacting with the amount of isocyanate-reactive hydrogen used in a formulation.

Unless otherwise identified, the temperature refers to room temperature and the pressure refers to ambient pressure.

Unless otherwise identified, the solvent refers to all organic and inorganic solvents known to the persons skilled in the art and does not include any type of monomer molecular.

Polyester polyol

The polyester polyol in the present disclosure has a functionality larger than 6. The polyester polyol comprises a product of: at least one selected from the group consisting of a carboxylic acid containing at least three carboxylic groups and a derivative thereof; a carboxyl- reactive compound containing at least two functional groups reactive towards the carboxylic acid and a side chain with at least 10 carbon atoms; and a polyhydroxy alcohol with at least three hydroxyl groups.

The reaction is an esterification reaction or transesterification reaction in which the hydroxyl groups in the polyhydroxy alcohol and/or the carboxyl- reactive compound react with carboxylic acid. The carboxylic acid containing at least three carboxylic groups can be carboxylic acid is hemimellitic acid, trimellitic acid, prehnitic acid, trimesic acid, pyromellitic acid, berberonic acid, citric acid, isocitric acid, aconitic acid, propane-1 , 2, 3-tricarboxylic acid, or any mixture thereof.

In some embodiments, the carboxylic acid is a mixture of two or more carboxylic acids.

The carboxylic acids can be used either as such, in the form of derivatives, or in the form of a mixture of one carboxylic acid, its own derivative, and/or derivative of another species of carboxylic acid.

Derivatives of carboxylic acid are defined as: the corresponding anhydrides in monomeric or polymeric form, monoalkyl, dialkyl, trialkyl, or higher alkyl esters, preferably mono- or di-C1-C4 alkyl esters, more preferably monomethyl or dimethyl esters or the corresponding monoethyl or diethyl esters, monovinyl and divinyl esters, and also mixed esters, preferably mixed esters with different C1-C4 alkyl components, more preferably mixed methyl ethyl esters.

The carboxyl- reactive compound contains at least two functional groups reactive towards the carboxylic acid and a side chain with at least 10 carbon atoms. The side chain is different from the backbone of the carboxyl-reactive compound. The backbone is the chain that carries the at least two functional groups reactive towards the carboxylic acid. The two functional groups may be the same or different, both independently selected from hydroxy, amino, or mercapto (-SH) groups.

Exemplary carboxyl-reactive compounds include without limitation to, di-alkoxylated monoalkylamine, which can be prepared as product of monoalkylamine and excessive alkoxides, or di-alkoxylated monoalkylglycerol, which can be prepared as product of monoalkylglycerol and excessive alkoxides.

In some embodiments, the di-alkoxylated monoalkylamine is an alkoxylated dodecylamine, an alkoxylated hexyldecylamine or an alkoxylated octyldecylamine.

Taking N-polyoxyethylated-N-octadecylamine shown in Formula (1) as an example, the backbone of the compound is the chain constituted by ethylene oxide and the central nitrogen atom. The side chain is the octadecyl group connected to the nitrogen atom.

In Formula (1), the sum of m and n equals to 12. The side chain can include at least 10 carbon atoms, preferably at least 12 carbon atoms, still preferably at least 14 carbon atoms. The side chain can be saturated or unsaturated. The side chain can be linear, branched, or include one or more ring structures.

To prepare the carboxyl-terminated blowing agent, the polyhydroxy alcohol with at least three hydroxyl groups can include one or more triols, tetraols, pentaols or even higher polyols.

Suitable triols include triethanolamine, glycerin or trimethylolpropane or modifications of the before mentioned components with an alkoxylation degree of up to 10. Suitable tetraols include without limitation to threitol, erythritol, pentaerythritol, hexane-2,3,4,5-tetraol, or modifications of the before mentioned components with an alkoxylation degree of up to 10. Suitable pentaols and higher polyols include without limitation to fucitol, xylitol, glucose, sorbitol, or modifications of the before mentioned components with an alkoxylation degree of up to 10.

In some embodiments, the polyhydroxy alcohol is selected from the group consisting of diglycerol, alkoxylated diglycerol, triglycerol, alkoxylated triglycerol, erythritol, alkoxylated erythritol, pentaerythritol, alkoxylated pentaerythritol, dipentaerythriol, alkoxylated dipentaerythriol, tripentaerythriol, alkoxylated tripentaerythriol, or any mixture thereof.

When preparing the polyester polyol, the stoichiometry needs to be controlled so that the carboxylic groups in the carboxylic acid are totally or nearly exhausted during the esterification process.

In some embodiments, the molar ratio of the carboxylic acid containing at least three carboxylic groups and the carboxyl- reactive compound containing at least two functional groups reactive towards the carboxylic acid and a side chain with at least 10 carbon atoms is between 1:1 to 3:1.

In some embodiments, the molar ratio of the carboxylic acid containing at least three carboxylic groups and the polyhydroxy alcohol with at least three hydroxyl groups is between 1:2 to 2:1.

In some embodiments, the polyester polyol has a hydroxyl number of 100 to 300 mgKOH/g.

In some embodiments, the molecular weight of the polyester polyol is from 1 ,000 to 5,000 g/mol, preferably from 1 ,200 to 4,000 g/mol, more preferably from 1,500 to 3,500 g/mol.

In some embodiments, the viscosity of the polyester polyol is less than 35,000 mPa s at 30 °C, as measured in accordance with DIN EN 3219. In view of the functionality larger than 6, his viscosity is relatively low. It makes the polyester polyol according to the present disclosure processable for producing polyurethane foams.

Polyurethane foam system

To prepare a polyurethane foam, the polyester polyol according to the present disclosure is present in a polyurethane foam system. In various embodiments, the polyurethane foam system comprises a polyol component and an isocyanate component, wherein the polyol component comprises polyester polyol according to the present disclosure; one or more catalysts; and at least one blowing agent.

Preparation of the polyurethane foams has been described elsewhere, and basically involves reaction of polyol and a catalyst with an isocyanate in the presence of a blowing agent.

Polyol component

The polyol component comprises the polyester polyol according to the present disclosure; one or more catalysts; and at least one blowing agent.

In some embodiments, the polyol component comprises 5 wt. % to 30 wt. %, preferably 6 wt. % to 25 wt. %, still preferably 7 wt. % to 20 wt. %, of the polyester polyol, based on a total weight of the polyol component.

In some embodiments, the polyol component further comprises one or more polyester polyol, polycarbonate polyol, or polyether polyol.

Optionally, the polyol component may further comprise a chain extender or crosslinking agent; a flame retardant; and one or more additives and/or auxiliaries.

Other polyester polyols, polycarbonate polyol, and polyether polyols

In further embodiments, the polyester polyol provided in the present disclosure could be used in combination with other polyols. The other polyols include small molecule polyols, polyether polyols, polyester polyols, or polycarbonate polyols.

Small molecule polyols include without limitation to glycol, diethylene glycol, dipropylene glycol, glycerol, pentaerythritol, sucrose, etc.

Polyester polyols, polycarbonate polyols, and polyether polyols are collectively known as polyols. Polyol refers to a polyhydroxy compound. Preferably, polyhydroxy compounds having a functionality of 2 to 8, more preferably 3 to 6, and a hydroxyl number of 150 to 850 mg KOH/g, more preferably 200 to 600 mg KOH/g are examples of higher molecular weight compounds having at least two reactive hydrogen atoms.

For example, polythioether polyols, polyester amides, polyacetals containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl groups, and preferably, polyester polyols and polyether polyols. In addition, mixtures of at least two of the aforesaid polyhydroxy compounds can be used as long as these have an average hydroxyl number in the aforesaid range.

Suitable polyester polyols can be produced, for example, from organic dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic acids with 4 to 6 carbons, and multivalent alcohols, preferably diols, with 2 to 12 carbons, preferably 2 to 6 carbons. Examples of dicarboxylic acids include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, and terephthalic acid. The dicarboxylic acids can be used individually or in mixtures. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives may also be used such as dicarboxylic acid mono- or di-esters of alcohols with 1 to 4 carbons, or dicarboxylic acid anhydrides. Dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid in quantity ratios of 20-35:35-50:20-32 parts by weight are preferred, especially adipic acid. Examples of divalent and multivalent alcohols, especially diols, include ethanediol, diethylene glycol, 1,2- and 1 ,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1 ,6-hexanediol, 1 ,10- decanediol, glycerin, and trimethylolpropane. Glycol, diethylene glycol, 1,4-butanediol, 1,5- pentanediol, 1 ,6-hexanediol, or mixtures of at least two of these diols are preferred, especially mixtures of 1,4-butanediol, 1 ,5-pentanediol and 1,6-hexanediol.

The polyester polyols can be produced by polycondensation of organic polycarboxylic acids, e.g., aromatic or preferably aliphatic polycarboxylic acids and/or derivatives thereof and multivalent alcohols in the absence of catalysts or preferably in the presence of esterification catalysts, preferably in an atmosphere of inert gases, e.g., nitrogen, carbon dioxide, helium, argon, etc., in the melt at temperatures of 150°C to 250°C, preferably 180°C to 220°C, optionally under reduced pressure, up to the desired polymerization degree, which is preferably less than 10, especially less than 5. In a preferred embodiment, the esterification mixture is subjected to polycondensation at the temperatures mentioned above up to an acid value of 80 to 30, preferably 40 to 30, under normal pressure and then under a pressure of less than 500 mbar, preferably 50 to 150 mbar. Examples of suitable esterification catalysts include iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the form of metals, metal oxides or metal salts. However, the polycondensation may also be per formed in liquid phase in the presence of diluents and/or entraining agents such as benzene, toluene, xylene or chlorobenzene for azeotropic distillation of the water of condensation.

To produce the polyester polyols, the organic poly carboxylic acids and/or derivatives thereof and multi valent alcohols are preferably polycondensed in a mole ratio of 1:1-1.8, preferably 1 :1.05-1.2.

The resulting polyester polyols preferably have a functionality of 2 to 3, and a hydroxyl number of 150 to 500, and especially 200 to 400.

Polyether polyols, which can be obtained by known methods, may also be used as the polyhydroxy compounds. For example, polyether polyols can be produced by anionic polymerization with alkali hydroxides such as sodium hydroxide or potassium hydroxide or alkali alcoholates, such as sodium methylate, sodium ethylate or potassium ethylate or potassium isopropylate as catalysts and with the addition of at least one initiator molecule containing 2 to 8, preferably 3 to 8, reactive hydrogens or by cationic polymerization with Lewis acids such as antimony pentachloride, boron trifluoride etherate, etc., or bleaching earth as catalysts from one or more alkylene oxides with 2 to 4 carbons in the alkylene radical. Suitable cyclic ethers and alkylene oxides include, for example, tetrahydrofuran, 1,3- propylene oxide, 1,2- and 2,3-butylene oxide, styrene oxide, and preferably ethylene oxide and 1 ,2-propylene oxide. The alkylene cyclic ethers and oxides may be used individually, in alternation, one after the other or as a mixture. Examples of suitable initiators include water, multivalent alcohols, organic dicarboxylic acids such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optionally N-mono-, N,N-, and N, N'-dialkyl substituted diamines with 1 to 4 carbons in the alkyl radical, such as optionally mono- and dialkyl-substituted ethylenediamine, diethylenetriamine, triethylenetetramine, 1,3- propylenediamine, 1,3- and 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5-, and 1,6- hexamethylenediamine, phenylenediamines, 2,3-, 2,4- and 2,6-toluenediamine and 4,4'-, 2,4'-, and 2,2'-diaminodiphenylmethane.

Multivalent alcohols, especially divalent, trivalent, and/or tetravalent alcohols are preferred such as ethanediol, 1 ,2-propanediol and 1,3-propanediol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerin, trimethylolpropane, erythritol, pentaerythritol, sorbitol, and sucrose.

Suitable initiators also include alkanolamines such as ethanolamine, diethanolamine, N- methyl- and N-ethyl ethanolamine, N-methyl- and N-ethyl diethanolamine and triethanolamine plus ammonia.

The polyether polyols have a functionality of preferably 3 to 8 and especially 3 to 6 and have a hydroxyl number of 300 to 850, preferably 350 to 800.

Also suitable as polyether polyols are melamine polyether polyol dispersions according to U.S. Pat. No. 4,293,657; polymer polyether polyol dispersions prepared from polyepoxides and epoxide resin hardeners in the presence of polyether polyols according to U.S. Pat. No. 4,305,861; dispersions of aromatic polyesters in polyhydroxy compounds according to U.S. Pat. No. 4,435,537; dispersion of organic and/or inorganic fillers in polyhydroxy compounds according to U.S. Pat. No. 4,243,755; polyurea polyether polyol dispersions according to DE A 31 2 402, tris-(hydroxyalkyl)isocyanurate polyether polyol dispersions according to U.S. Pat. No. 4,514,526 and crystallite suspensions according to U.S. Pat. No. 4,560,708, whereby the details in the aforesaid patents are to be regarded as part of the patent disclosure, and are herein incorporated by reference.

Like the polyester polyols, the polyether polyols may be used either individually or in the form of mixtures. Furthermore, they can be mixed with the aforesaid dispersions, suspensions, or polyester polyols as well as the polyester amides containing hydroxyl groups, the polyacetals, and/or polycarbonates.

Examples of hydroxyl group-containing polyacetals that can be used include, for example, the compounds that can be produced from glycols such as diethylene glycol, triethylene glycol, 4,4'-dihydroxyethoxydiphenyldimethylmethane, hexanediol and formaldehyde. Suitable polyacetals can also be produced by polymerization of cyclic acetals. Suitable hydroxyl group-containing polycarbonates include those of the known type such as those obtained by reaction of diols, e.g., 1,3-propanediol, 1 ,4-butanediol, and/or 1 ,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol and diaryl carbonates, e.g., diphenyl carbonate, or phosgene.

The polyester amides include the mainly linear condensates obtained from multivalent saturated and/or unsaturated carboxylic acids and their anhydrides and amino alcohols, or mixtures of multivalent alcohols and amino alcohols and/or polyamines.

Catalysts

The catalyst used in the present disclosure may include one or more selected from metalbased catalyst and amine-based catalysts. The catalysts can greatly accelerate the reaction of the hydroxyl group containing compounds of components and optionally with the polyisocyanates.

The metal-based catalyst may include an organic tin compound such as tin (II) salts of organic carboxylic acids, e.g., tin (II) acetate, tin (II) octanoate, tin (II) ethylhexanoate and tin (II) laurate, and dialkyltin (IV) salts of organic carboxylic acids, e.g., dibutyltin diacetate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, and dioctyltin diacetate. The metal-based catalyst may include a potassium compound selected from a group consisting of potassium hydroxide, potassium carbonate, potassium bicarbonate, potassium benzoate, potassium formate, potassium acetate, potassium propionate, potassium butyrate, potassium valerate, potassium caproate, potassium caprylate, potassium 2-ethylhexanoate, potassium neodecanoate, potassium caprate, potassium salicylate, potassium laurate, potassium oleate, potassium maleate, potassium citrate, potassium oxalate, potassium methoxide, potassium cellulose, potassium carboxymethylcellulose, potassium hyaluronate, potassium alginate, potassium gluconate and any combination thereof.

Examples of the amine-based catalysts may include amines such as 2,3-dimethyl-3,4,5,6- tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methylmorpholine, N-ethylmorpholine, N-cyclohexylmorpholine, N,N,N'N'- tetramethylethylenediamine, N,N,N',N'-tetraymethylbutanediamine, or -hexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1 ,2-dimethylimidazole, 1-azabicyclo[3.3.0]octane and preferably 1 ,4-diaza- bicyclo[2.2.-2]octane and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine.

Suitable catalysts include tris-(dialkylamino-s-hexahydrotriazines, especially tris(N,N- dimethylaminopropyl)-s-hexahydrotriazine, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, alkali hydroxides such as sodium hydroxide and alkali alcoholates such as sodium methylate and potassium isopropylate as well as alkali salts of long chain fatty acids with 10 to 20 carbon atoms and optionally OH dependent groups. A particular catalyst or combination of catalysts may be chosen by one skilled in the art.

Blowing agents

Blowing agents which can be used are physical blowing agents and chemical blowing agents.

The compounds known as physical blowing agents can preferably also be used in combination with water or preferably instead of water. These are compounds inert with respect to the starting components, mostly liquid at room temperature, and evaporating under the conditions of the urethane reaction. The boiling point of these compounds is preferably below 500 °C. Among the physical blowing agents are also compounds which are gaseous at room temperature and which are introduced or dissolved into the starting components under pressure, examples being carbon dioxide, low-boiling alkanes, and fluoroalkanes.

The physical blowing agents are mostly selected from the group consisting of alkanes and/or cycloalkanes having at least 4 carbon atoms, dialkyl ethers, esters, ketones, acetals, fluoroalkanes having from 1 to 8 carbon atoms, and tetraalkylsilanes having from 1 to 3 carbon atoms in the alkyl chain, in particular, tetramethylsilane. Examples which may be mentioned are propane, n-butane, isobutane, cyclobutane, n-pentane, isopentane, cyclopentane, cyclohexane, dimethyl ether, methyl ethyl ether, methyl butyl ether, methyl formate, acetone, and also fluoroalkanes which can be degraded in the troposphere and therefore do not damage the ozone layer, e.g., trifluoromethane, difluoromethane, 1 ,1 ,1 ,3,3-pentafluorobutane, 1 , 1 ,1 , 3,3- pentafluoropropane, 1 ,1 ,1 ,2-tetrafluoroethane, difluoroethane, and heptafluoropropane. The physical blowing agents mentioned may be used alone or in any desired combinations with one another.

The chemical blowing agents include water, carboxylic acid such as formic acid, and/or carboxyl-terminated oligomers, these reacting with isocyanate groups with elimination of carbon dioxide and, respectively, carbon dioxide and carbon monoxide.

The amount of the blowing agent is from 1 to 55% by weight, preferably from 1 to 40% by weight, particularly preferably from 2 to 30% by weight, and in particular from 5 to 25% by weight, based on the total weight of the polyol component.

In some embodiments, the amount of water is preferred in a range of 0.1 to 5.0 % by weight, based on the weight of the polyol component.

Chain extenders and crosslinking agents

The polyurethane foams can be prepared with or without using chain extenders and/or crosslinking agents. Suitable chain extenders and/or crosslinking agents include preferably alkanolamines, more preferably diols and/or triols. Typical examples are alkanolamines such as ethanolamine and/or isopropanolamine; dialkanolamines, such as diethanolamine, N-methyl-, N-ethyldiethanolamine, diisopropanolamine; trialkanolamines such as triethanolamine, triisopropanolamine; and the addition products from ethylene oxide or 1,2-propylene oxide, and alkylenediamines having 2 to 6 carbon atoms in the alkylene radical such as N,N'-tetra(2- hydroxyethyl)-ethylenediamine and N,N'-tetra(2-hydroxypropyl)ethylenediamine, aliphatic, cycloaliphatic and/or araliphatic diols having 2 to 14, more preferably 4 to 10 carbon atoms such as ethylene glycol, 1,3-propanediol, 1 ,10-decanediol, o-, m-, p-dihydroxycyclohexane, diethylene glycol, dipropylene glycol, and preferably 1 ,4-butanediol, 1,6-hexanediol, and bis(2- hydroxyethyl)hydroquinone; triols such as 1,2,4- and 1,3,5-trihydroxycyclohexane, glycerin and trimethylolpropane; and lower molecular weight hydroxyl group containing polyalkylene oxides, based on ethylene oxide and/or 1,2-propylene oxide and aromatic diamines such as toluenediamines and/or diaminodiphenylmethanes as well as the aforesaid alkanolamines, diols, and/or triols as initiator molecules.

If chain extenders, crosslinking agents, or mixtures thereof are used in the preparation of polyurethane foams, then advantageously these are used in a quantity of from up to 20 wt. %, more preferably 2 wt. % to 10 wt. %, based on the weight of the polyol component.

Flame retardants

The polyol component may optionally include a flame retardant. Flame retardant comprises at least one phosphorus-containing flame retardant which is a derivative of phosphoric acid, polyphosphoric acid, phosphonic acid, and/or phosphinic acid.

Suitable flame retardants for the purposes of the present disclosure are preferably liquid organic phosphorus compounds such as halogen-free organic phosphates such as triethyl phosphate (TEP), halogenated phosphates, for example tris (1-chloro-2-propyl) phosphate (TCPP) and tris (2-chloroethyl) phosphate (TCEP), and organic phosphonates such as dimethyl methylphosphonate (DMMP), dimethyl propane phosphonate (DMPP), or solids such as ammonium polyphosphate (APP) and red phosphorus. Furthermore, besides the phosphorus- containing flame retardant, halogenated compounds, for example, halogenated polyols, as well as solids, such as expanded graphite and melamine are suitable as an auxiliary flame retardant.

Other additives and auxiliaries

Optionally other additives and/or auxiliaries may be incorporated into the polyol component to produce the polyurethane foam. Examples include surfactants, foam stabilizers, cell regulators, fillers, dyes, pigments, hydrolysis preventing agents, fungistatic and bacteriostatic agents.

Examples of suitable surfactants are compounds which serve to support homogenization of the starting materials and may also regulate the cell structure of the plastics. Specific examples are salts of sulfonic acids, e.g., alkali metal salts or ammonium salts of fatty acids such as oleic or stearic acid, of dodecylbenzene- or dinaphthylmethanedisulfonic acid, and ricinoleic acid; foam stabilizers, such as siloxane-oxyalkylene copolymers and other organopolysiloxanes, oxyethylated alkyl-phenols, oxyethylated fatty alcohols, paraffin oils, castor oil esters, ricinoleic acid esters, Turkey red oil and groundnut oil, and cell regulators, such as paraffins, fatty alcohols, and dimethylpolysiloxanes. The surfactants are usually used in amounts of 0.01 to 5 parts by weight, based on 100 parts by weight of the polyol component. Furthermore, the oligomeric acrylates with polyoxyalkylene and fluoroalkane side groups are also suitable for improving the emulsifying effect, the cell structure and/or for stabilizing the foam. These surfactants are generally used in amounts of 0.01 wt. % to 5 wt. % based on the weight of the polyol component. For example, fillers are conventional organic and inorganic fillers and reinforcing agents. Specific examples are inorganic fillers, such as silicate minerals, for example, phyllosilicates such as antigorite, serpentine, hornblendes, amphiboles, chrysotile, and talc; metal oxides, such as kaolin, aluminum oxides, titanium oxides and iron oxides; metal salts, such as chalk, baryte and inorganic pigments, such as cadmium sulfide, zinc sulfide and glass, inter alia; kaolin (china clay), aluminum silicate and coprecipitates of barium sulfate and aluminum silicate, and natural and synthetic fibrous minerals, such as wollastonite, metal, and glass fibers of various lengths. Examples of suitable organic fillers are carbon black, melamine, colophony, cyclopentadienyl resins, cellulose fibers, polyamide fibers, polyacrylonitrile fibers, polyurethane fibers, and polyester fibers based on aromatic and/or aliphatic dicarboxylic acid esters, and in particular, carbon fibers. The inorganic and organic fillers may be used individually or as mixtures and may be introduced into the polyol component or isocyanate side in amounts of from 0.5 to 40 percent by weight, based on the weight of components (the polyols and the isocyanate).

Isocyanate component

The isocyanate component in the present disclosure comprises one or more selected from the group consisting of aliphatic, cycloaliphatic, araliphatic, and aromatic isocyanates. For example, the isocyanate component may include alkylene diisocyanates with 4 to 12 carbons in the alkylene radical such as 1,12-dodecane diisocyanate, 2-ethyl-1,4-tetramethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, 1 ,4-tetramethylene diisocyanate and preferably 1 ,6-hexamethylene diisocyanate; cycloaliphatic diisocyanates such as 1,3- and 1,4- cyclohexane diisocyanate as well as any mixtures of these isomers, 1-isocyanato-3,3,5- trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), 2,4- and 2,6- hexahydrotoluene diisocyanate as well as the corresponding isomeric mixtures, 4,4'-2,2'-, and 2,4'-dicyclohexylmethane diisocyanate as well as the corresponding isomeric mixtures and preferably aromatic diisocyanates and polyisocyanates such as 2,4- and 2,6-toluene diisocyanate and the corresponding isomeric mixtures 4,4'-, 2,4'-, and 2,2'-diphenylmethane diisocyanate and the corresponding isomeric mixtures, mixtures of 4,4'- and 2,4'- diphenylmethane diisocyanates and polyphenylenepolymethylene polyisocyanates (polymeric M DI), as well as mixtures of polymeric MDI and toluene diisocyanates. The organic di and polyisocyanates can be used individually or in the form of mixtures. Preferably, the isocyanate component comprises monomeric and/or polymeric methylene diphenyl diisocyanate in a percentage of not less than 90 wt.%.

The polyurethane foams of the present disclosure can be prepared with the help of conventional mixing equipment. The method includes providing polyol component; providing isocyanate component; and reacting the polyol component and the isocyanate component in a weight ratio of such that the isocyanate index is from 100 to 500, preferably from 110 to 450, more preferably from 110 to 150.

It should be observed that the isocyanate index as used herein is considered from the point of view of the actual foaming process involving the isocyanate ingredients and the isocyanatereactive ingredients. Any isocyanate groups consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate-derivatives referred to in the art as prepolymers) or any active hydrogens consumed in a preliminary step (e.g., reacted with isocyanate to produce modified polyols or polyamines) are not taken into account in the calculation of the isocyanate index. Only the free isocyanate groups and the free isocyanatereactive hydrogens (including those of the water) present at the actual foaming process are taken into account.

Applications

The polyurethane foam according to the present disclosure may be included in a composite. The composite may be a sandwich panel. The sandwich panel may include the polyurethane foam as its core layer. The sandwich panel may include metal layer as outer layer(s).

The composite may be used in various fields, such as boards or panels in the application of cleanroom or a cold storage, reefer, roof panels, laminate, or insulation boards, or as pipe insulation in the field of spray pipe applications and injection pipes.

Examples

Measuring and test methods

The measuring and test methods are shown in Table 1.

Table 1 Measuring and test standards Demolding thickness (demoldability) was determined by measuring demolding thickness of post-expansion foam bodies produced using a 70x40x9 cm box mold at a mold temperature of 45±2 °C and demolding time of 3.5 min. Overpacking was 14.5%, i.e., 14.5% more reaction mixture than needed to completely foam out the mold was used. The post-expansion depicts the swelling of the foam block in mm. A poor demoldability is evident by significant post expansion of the rigid Pll foam, as shown by a demolding thickness significantly larger than 90 mm.

Materials

The materials used in the examples are as follows.

Polyol 1 , polyether polyol (PO based), with a molecular weight of ca. 1100, an OH value of

110 mg KOH/g and functionality of 2.

NJ4502, sucrose-based polyether polyol, from Jurong Ningwu New Material Development

Co., Ltd., an OH value of 450 mg KOH/g and functionality of 5.1.

Polydo PN 560, a pentaerythritol-initated polyol based on propylene oxide from Kukdo

Chemical, with an average molecular weight of 400 g/mol, an OH value of 560 mg KOH/g, and a functionality of 4.

AC1812, N-polyoxyethylated-N-octadecylamine from Shanghai Jiahua Company Limited,

CAS No. 26635-92-7, with a molecular weight of 801 and functionality of 2.

AC1210, N-polyoxyethylated-N-dodecylamine from Shanghai Jiahua Company Limited,

CAS No. 26635-75-6, with a molecular weight of 645 and functionality of 2.

Trimitilic acid, also known as 1 ,2,4-benzenetricarboxylic acid, from Shanghai Guoyao

Company Limited, CAS No. 528-44-9.

1 ,2,4-Benzenetricarboxylic anhydride from Shanghai Guoyao Company Limited, CAS No.

552-30-7.

Trimesic acid, also known as 1 ,3,5-benzenetricarboxylic acid, from Shanghai Guoyao

Company Limited, CAS No. 554-95-0.

Cyclopentane, referred to as “c-pentane” from BASF, CAS No. 287-92-3.

PMDI, 4,4'-diphenylmethane diisocyanate (MDI) containing oligomers of high functionality and isomers from BASF.

Niax silicone L6900 copolymer from Momentive Performance Materials GmbH is a foam stabilizer used in manufacture of rigid polyurethane foams.

Dabco® BL-11 , 70% dipropylene glycol solution of bis(dimethylaminoethyl) ether from

Evonik, CAS No. 59948-21-9, used as catalyst.

Polycat® 8, N,N-dimethylcyclohexanamine from Evonik, CAS No. 98-94-2, used as catalyst.

Dabco® TMR-2, 2-hydroxypropyltrimethylammonium formate from Evonik, CAS No. 62314- 25-4, used as catalyst. Synthesis of the Polyester polyols

The chemical pathway to synthesize this chemical is an esterification of 1,3,5- benzenetricarboxylic acid and a mixture of two polyhydroxy alcohols. The synthesis may follow a stepwise approach or a one-pot approach.

In the stepwise approach, 1,3,5-benzenetricarboxylic acid was first mixed and heated with a dihydroxy alcohol. The reaction was catalyzed with 0.03wt. % of TTB, based on a total weight of the acid and the dihydroxy alcohol. The reactor was fitted with a Vigreux column and a Dean- Stark type condenser to collect the condensation product. During the first half of the synthesis, the setup was continuously flushed with nitrogen gas to limit oxidation and facilitate transport of water vapor. While stirring, the mixture was heated to 120 °C using a heating mantle. The catalyst was added when the temperature of the mixture reached 120 °C. The reaction temperature was increased stepwise to maintain distillation of the formed by-products. After 8 h at 230 °C the product was left to cool down to 60°C. At the second step, PN560 was added into the mixture. The same protocol was followed and after the final product was cooled to room temperature, it was discharged from the reactor.

In the one-pot approach, all reactants were mixed and heated in the beginning. The protocol according to which the synthesize was conducted was the same as that of the first step in the stepwise approach.

After the synthesis, the OH values and viscosity values were measured. The OH values were determined by titration. The viscosity values were tested under 30 °C except for the polyester polyol in Comparative Example 2 due to very high viscosity. Said polyester polyol was heated to 35 °C to lower its viscosity to the range measurable for the viscometer.

Table 2 Raw materials and properties of polyester polyol as synthesized The formulations of the polyurethane foam systems with the polyester polyols synthesized in Comparative Examples 1 and 2 and Examples 1 through 4 are shown in Table 3. From the comparison, it can be inferred that any of Example 1 through 4, despite a similar functionality, has a comparable or even lower viscosity at 30 °C than Comparative Example 1 or 2. By using AC1812 or AC1210 in the raw materials, the resultant polyester polyols have a workable viscosity at 30 °C. The existence of side chain on nitrogen atom may contribute to lowering the viscosity. Additionally, considering the similar raw materials between Comparative Examples 1 and 2, the viscosity increases significantly when the functionality increases. Example 4, having a shortened side chain of 12 carbon atoms compared to a long side chain of 18 carbon atoms in Example 3, has a slightly higher viscosity.

These six formulations were used to prepare a box mold foam with the size of 40cm*40cm*9cm. During the reaction, the temperature in the mold was controlled at 50 °C. 30 minutes after injecting the foam into the mold the cured foam was demolded. The properties of the foams are listed in Table 3.

Table 3 Recipes and properties of polyurethane foam systems

From Table 3, it is suggested that the formulation with polyester polyols synthesized in Examples 1 through 4 expressed a comparable compression strength to other high functionality polyester polyol in Comparative Example 1. The demoldability of the resultant polyurethane foam was also maintained or improved. Polyester polyol synthesized in Comparative Example 2 was too viscous and the foaming test failed due to difficulties in blending the polyol component and isocyanate component.