CA2164490A1 - Lignin-containing isocyanate prepolymer mixtures, their preparation and their use for producing polyurethanes and also the production of the polyurethanes - Google Patents

Abstract

Lignin-containing isocyanante prepolymer mixtures are obtainable by reacting (b1) diphenylmethane 4,4'-, 2,4'-and 2,2'-diisocyanate, an isomer mixture of diphenylmethane 4,4'- and 2,4'- or 4,4'-, 2,4'- and 2,2'-diisocyanates or a mixture of diphenylmethane diisocyan-ates and polyphenyl-polymethylene polyisocyanates with a suspension (b2) comprising at least one polyoxyalkylene glycol (b2i) having a molecular weight of from 400 to 6000, preferably from 1000 to 3000, selected from the group of polyoxypropylene glycols, polyoxypropylene-polyoxyethylene glycols and mixtures thereof, and lignin (b2ii).

Description

2164!~Q

Lignin-cont~; n~n~ isocyanate prepolymer mi~tures, their preparation and their use for producing polyurethanes and also the production of the polyurethanes The present invention relates to lignin-contain-ing isocyanate prepolymer mixtures. The invention also relates to a process for preparing such isocyanate pre-polymer mixtures. Finally, the invention also re~ates to the use of the isocyanate prepolymer mixtures of the invention for producing polyurethanes (PU), in particular foamed shaped bodies based on polyurethane, and also a process for this purpose.
Polyoxyalkylene polyols prepared using lignin and tannin as initiator molecules are known. According to US-A-3,546,199 and US-A-3,654,194, lignin or tannin can be alkoxylated in the presence or absence of solvents using alkylene oxides, for example 1,2-propylene oxide, at from 20 to 250C and at atmospheric or elevated pressure. The polyoxyalkylene polyols prepared pos~ess hydroxyl numbers in the range from 50 to 1000, preferably from 200 to 800, and are suitable for producing flexible to rigid PU foams by reaction with organic polyiso-cyanates.
EP-A-0 342 781 describes the use of lignin in PU
production. Solutions of lignin in tetrahydrofuran (THF) or polyoxyethylene glycol (PEG) are reacted with di-phenylmethane diisocyanates (MDI) at 60C or at room temperature. The films obtained therefrom have a good mechanical strength, foams have a good elasticity ac~ord-ing to the publication. No comparative examples without lignin are given. The lignin forms the rigid phase, the PEG the soft phase.
Lignin can also be dissolved in polyoxyethylene 216~49Q

glycols (PEG~ and be reacted from this solution with isocyanates to give polyurethane parts, as d~scribed in U5-A-3,515,581. For this purpose, the lignin is disso~ved in a polyoxyethylene glycol (PEG) or a mixture of PEG and polyoxypropylene glycol ~PPG) and is treated, if desi~ed at temperatures above 100C, for esterifying the carboxyl groups of the lignin. The lignin/polyoxyalkylene glycol solutions obtained are advantageously left to cool to below 100C before they are reacted with the polyisocyan-ates to form polyurethanes. The reaction always takes place in the presence of a surface-active compound.
US-A-3,577,358 describes dissolving the lignin either in PEG or in dioxane for the purposes of the reaction. Curing occurs over a nl~her of hours at room temperature or else at elevated temperature (~ 80C). The polyurethane is isolated by removing the solvent. Lignin and isocyanate react when they are mixed at 120C. The IR
spectrum shows that all OH and -N=C=O groups have react-ed.
However, obstacles to the direct use of lignin in polyurethane systems are not only insufficient reactivity of the solid and even dissolved lignin, e.g. lignin dissolved in tetrahydrofuran or dioxane, towards isocyan-ates under the conditions of polyurethane production, but also a series of other disadvantages. Their high salt content very strongly influences the sensitive catalysis of the PU systems, particularly when the lignins are used as solution and not as solid. Industrially, lignins are used predominantly as thickeners, and in higher concen-trations they also have a similar viscosity-increasing effect in water-containing polyetherol components.
Incompatibility of the lignin with other PU polyol compo-nents is also frequently to be observed, which result8 in the lignin particles, which in themselves are very fine, coalescing after making up the polyol mixture, 80 that it is no longer processable. Some of the lignin 0~ groups are phenolic in nature, 80 that the polyurethane bonds 21 64~90 obtained from them are thermolabile. For the reasons given, lignin polyurethanes have not had 6atisfactory processing and product properties. In general, incorpora-tion of lignin even in polyurethane foams impair~ the mechanical properties. To obtain PU parts having good properties at all, u~e is often made of specifically fractionated lignins or lignins which have been obtained by a specific process (e.g. organosolv lignins).
Usual disadvantages of lignin in PU production are insufficient reactivity and insufficient incorpora-tion of the lignin in the PU matrix. Lignin solutions are usually highly viscous and are not readily miscible with organic polyisocyanates; in addition, the foams have pcor mechanical properties. Separation of the high molecular weight fractions of the lignin and carrying out the reaction in solution gives PU parts for which a series of advantages is reported. For example, a lower index is required, cf. CA-A-2,052,487. With kraft lignin itself, the PU polyaddition reaction in a PEG solution cannot be carried out. The molecular weight of the lignin and the viscosity of the lignin solution in PEG are too high and the miscibility with the isocyanate component is too poor. Special, modified lignin, e.g. one having a low molecular weight of from 300 to 2000 and better solubili-ty, gives more homogeneous foams having good mechanical properties. A one-shot or else a prepolymer method may be used. In the latter case, lignin/polyols/isocyanates are used to prepare a prepolymer which can then be cast into films or can also be foamed by mixing with water/catalysts/stabilizers.
To circumvent the above difficulties associated with the direct proce~ing of the lignin, alkoxylation of the lignin ha~ also been proposed, but this iq compli~
cated. In general, owing to the (processing) difficultie~
mentioned, lignins or lignin derivatives are not current-ly used on an industrial scale for producing polyur-ethanes. US-A-3,546,199 and US-A-3,654,194 describe ~16~

reacting solid pulverulent lignin or lignin dissolved in reactive or unreactive solvents to give lignin polyether-018, both in the ab~_nce of catalyst and with ROH/aniline catalysis. The OH numbers of the polyols obtained enable the OH numbers of the lignins to be back-calculated. They are from about 600 to 1300. Tannin can also be used like lignin. The OH numbers of the lignin polyether-polyols are from 50 to 1000.
It i8 an object of the present invention to prepare isocyanate prepolymer mixtures which can be readily processed. A further ob~ect of the invention is to indicate such isocyanate prepolymer mixtures which in further processing give polyurethane products, in part-icular polyurethane foams, which possess improved phy~i-cal properties, in particular with regard to elongation at break, tensile strength and/or tear propagation resistance. It is also an object of the present invention to devise a process for preparing such isocyanate pre-polymer mixtures and also a process for producing polyur-ethanes having the improved mechanical properties.
We have found that this object is achieved byisocyanate prepolymer mixtures as defined in the claims.
The process of the invention for preparing such poly-isocyanate prepolymer mixtures and their use for produc-ing polyurethanes and polyurethane products and a process for this purpose are likewise defined in the claims.
Preferred embodiments of the invention are given in the following description and the subclaims.
According to the invention, use is advantageously made of a natural material, i.e. a regenerable poly-hydroxyl compound.
According to the invention, the synthetically prepared polyhydroxyl compounds are advantageously completely or at least partially replaced by lignin as a hydroxyl-containing natural material. The use of this regenerable hydroxyl-containing natural material requires no complicated technical syntheses. It is also ~164490 advantageous that lignin formed as waste product in other areas can be industrially utilized, if appropriate after slight technical troatment and/or purification. The use of novel starting materials enables, according to the invention, the production of polyisocyanate polyaddition products having different mechanical properties which in turn open up new application opportunities.
The isocyanate prepolymer mixtures provided according to the invention, which contain urethane groups and reactive isocyanate groups in bound form, are obtained by reacting bl) at least one organic polyisocyanate based on diphenylmethane diisocyanate with b2) at least one polyhydroxyl component.
According to the invention, the polyhydroxyl component consists at least partially of a suspension of lignin in a polyoxyalkylene glycol containing oxypropyl-ene groups. The isocyanate prepolymer mixture of the invention has an NC0 content of from 2.5 to 30% by weight, based on the total weight of the isocyanate prepolymer mixture, and is obtainable by reacting bl) diphenylmethane 4,4'-, 2,4'- and 2,2'-diisocyanate, an isomer mixture of diphenylmethane 4,4'- and 2,4'-or 4,4'-, 2,4'- and 2,2'-diisocyanates or a mixture of diphenylmethane diisocyanates and polyphenyl-polymethylene polyisocyanates with b2) a suspension comprising b2i) at least one polyoxyalkylene glycol having a molecular weight of from 400 to 6000, prefer-ably from 1000 to 3000, selected from the group of polyoxypropylene glycols, polyoxy-propylene-polyoxyethylene glycols and mix-tures thereof and b2ii) lignin.
The ratio of lignin to hydroxyl-containing compound is here preferably such that from 1 to 70% by weight of lignin and from 99 to 30% by weight of poly-216~490 hydroxyl component (b2) containing polyoxypropylene and/or polyoxypropylene-polyoxyethylene glycol together form 100% by weight of the suspension. The lignin 6uspension preferably comprises from 70 to 30% by weight, in particular from 60 to 50% by weight, of the polyoxypropylene-polyoxyethylene glycols and/or, in particular, a polyoxypropylene glycol, while the amount of lignin makes up from 30 to 70% by weight, in particular from 40 to 50~ by weight, of the suspension.
The reaction of the lignin suspension with the polyisocyanate is preferably carried out in the absence of a surfactant.
The lignins used are preferably ones which h2ve not been subjected to any special chemical treatment for their further processing. Rraft lignins are particularly preferred. Such lignins preferably have an acid nl~her of less than 10.
The preferred suspension media for the lignin are polyoxypropylene glycols having a molecular weight of from 1000 to 3000.
The isocyanate prepolymer mixture is preferably a fluid mixture having an -N=C=0 content of from 5 to 25~, based on the isocyanate prepolymer mixture. The particularly preferred isocyanate prepolymer mixture has an -N-C=0 content of from 9 to 15% by weight.
In the process of the invention for preparing the isocyanate prepolymer mixtures, the abovementioned components are reacted with one another to form the isocyanate prepolymer mixture. The lignin can be at least partially esterified on the surface by the hydroxyl groups of the polyoxypropylene and/or polyoxypropylene-polyoxyethylene glycols and any further polyhydroxyl compounds of the polyhydroxyl component (b2) and be thus chemically bonded to the latter. The chemical incorpora-tion of the lignin into the isocyanate prepolymer mixture occurs via the hydroxyl groups present on the lignin, and indeed out from the suspension with reaction with the ~164490 i60cyanate groups of the polyisocyanate component.
The bonding of the lignin into the isocyanate prepolymer mixture- enables any other relatively high molecular weight compounds having at least two reactive hydrogens to be used for the production of polyurethane.
Owing to its viscosity and good suitability for prepolymer preparation, it is easy to suspend lignin as solid in polyoxypropylene-polyoxyethylene glycols, preferably polypropylene glycols, to remove water adher-ing to the lignin (about 5~ by weight) and to react thewater-free lignin suspension thus obtained with isocyan-ates to give lignin-containing prepolymers.
Suspending in polyoxypropylene-polyoxyethylene glycol~ and/or polyoxypropylene glycols readily enables up to about 70% by weight of lignin to be introduced into the ~uspension and up to about 30~ by weight of lignin to be introduced into the isocyanate prepolymer mixture. The viscosity of the i60cyanate prepolymer mixtures of the invention is low despite the high lignin content and these are readily processable.
The lignin-containing isocyanate prepolymer mixtures based on lignin ~u~pensions are storage stable.
Even after standing for a prolonged period at room temperature, viscosity and -N=C=O content are essentially unchanged.
The use of the lignin-containing isocyanate prepolymer mixtures of the invention enable polyurethane parts to be produced without processing difficulties. The mechanical properties of the parts obtained are good.
Unmodified lignins, e.g. standard kraft lignin, standard organosolv lignins or lignins isolated via other digestion processes can also be used and are readily processable under the conditions according to the invention to give high performance polyurethanes.
In the process of the invention for producing compact or cellular polyurethanes, preferably PU foams, 21644~Q

a) relatively high molecular weight compounds having at least two reactive hydrogens, preferably polyhydroxyl compounds, are reacted with b) liquid polyi60cyanate compositions containing urethane groups in bonded form.

This is carried out in the presence or absence of c) chain extenders and/or crosslinkers, d) blowing agents, e) catalysts and f) auxiliaries.

According to the invention, the polyisocyanate composition (b) consists at least partially of an i80-cyanate prepolymer mixture as defined above.
In the process of the invention for producing polyurethanes, it is preferred that the relatively high molecular weight compounds (a) have a functionality of from 2 to 8 and an amine or hydroxyl number of from 25 to 500 and are advantageously selected from the group of polyalkylene polyamines and/or polyhydroxyl compounds, in particular polyhydroxyl compounds having a functionality of from 2 to 8 and a hydroxyl number of from 25 to 500, which in turn are preferably selected from the group of polythioether polyols, polyester amides, hydroxyl-con-taining polyacetals, hydroxyl-containing aliphatic polycarbonates, polyester polyols, polymer-modified polyether polyols, preferably polyether polyols and mixtures of at least two of the specified polyhydroxyl compounds.
Suitable relatively high molecular weight poly-hydroxyl compounds as are used in (a) advantageously possess, as already mentioned, a functionality of from 2 to 8 and a hydroxyl number of from 25 to 500, with preference being given to using polyhydroxyl compounds having a functionality of preferably from 2 to 3 and a ~16~90 g hydroxyl number of preferably from 30 to 80 for the production of flexible PU foams and preference being given to using polyhydroxyl compounds having a functionality of preferably from 3 to 8 and in particular from 3 to 6 and a hydroxyl number of preferably from 100 to 500 for the production of rigid PU foams. The polyhydroxyl compounds used are preferably linear and/or branched polyester polyols and in particular linear and~or branched polyoxyalkylene polyols, with polyhydroxyl compounds from regenerable natural materials and/or chemically modified regenerable natural materials being particularly preferred. Suitable lignin-free polyhydroxyl compounds (a) are also polymer-modified polyoxyalkylene polyols, polyoxyalkylene polyol dispersions and other hydroxyl-containing polymers and polycondensates having the abovementioned functionalities and hydroxyl numbers, for example polyesteramides, polyacetals and/or polycarbonates, in particular those which are prepared from diphenyl carbonate and 1,6-hexanediol by transesterification, or mixtures of atlea6t two of the specified relatively high molecular weight polyhydroxyl compounds (a).
Suitable polyester polyols can be prepared, for example, from organic dicarboxylic acids having from 2 to 12 carbon atoms, preferably aliphatic dicarboxylic acids having from 4 to 6 carbon atoms and polyhydric alcohols, preferably alkane diols having from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms, dialkylene glycol~
and/or alkanetriols having from 3 to 6 carbon atoms.
Suitable dicarboxylic acids are, for example: succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid and tereph-thalic acid. The dicarboxylic acids can here be used either individually or in admixture. In place of the free carboxylic acids, it is also possible to use the corre-sponding carboxylic acid derivatives such as dicarboxylic esters of alcohols having from 1 to 4 carbon atoms or dicarboxylic anhydrides. Preference is given to using dicarboxylic acid mixtures of succinic, glutaric and adipic acid in weight ratios of, for example, 20 to 35:35 to 50:20 to 22, and in particular adipic acid. Examples of dihydric and polyhydric alcohols, in particular alkane diols and dialkylene glycols, are: ethanediol, diethylene glycol, 1,2- or 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decane-diol, glycerol and trimethylolpropane. Preference iBgiven to using ethanediol, diethylene glycol, 1,4-butane-diol, 1,5-pentanediol, 1,6-hexanediol, glycerol or mixtures of at least two of the specified alkane polyo's, in particular, for example, mixtures of 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol. Also usable are polyester polyols from lactones, e.g. ~-caprolactone, or hydroxycarboxylic acids, e.g. w-hydroxycaproic acid.
The polyester polyols can be prepared by polycon-densing the organic, for example aromatic and preferably aliphatic dicarboxylic acids and/or their derivatives with the polyhydric alcohols and/or alkylene glycols in the absence of catalyst or preferably in the presence of esterification catalysts, advantageously in an atmosphere of inert gases, for example nitrogen, helium, argon, etc., in the melt at from 150 to 250C, preferably from 180 to 220C, under atmospheric or reduced pressure, to the desired acid number which is advantageously less than 10, preferably less than 2. According to a preferred embodiment, the esterification mixture is polycondensed at the abovementioned temperatures to an acid number of from 80 to 30, preferably from 40 to 30, under atmospher-ic pressure and subsequently under a pressure of less than 500 mbar, preferably from 50 to 150 mbar. Suitable esterification catalysts are, for example, iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the form of metals, metal oxides or metal salts. However, the polycondensation can also be carried 216 l i~O

out in the liquid phase in the presence of diluents and/or entrainers such as benzene, toluene, xylene or chlorobenzene, for azeotropically distilling off the water of condensation.
The polyester polyols are advantageously prepared by polycondensing the organic dicarboxylic acids and/or their derivatives with the polyhydric alcohols in a molar ratio of 1:1 to 1.8, preferably l:l.OS to 1.2.
The polyester polyols obtained preferably have a functionality of from 2 to 4, in particular from 2 to 3, and a hydroxyl number of from 240 to 30, preferably from 180 to 40.
However, the polyhydroxyl compounds used are particularly preferably polyoxyalkylene polyols prepared by known methods, for example by anionic polymerization using alkali metal hydroxides such as sodium or potas6ium hydroxide, or using alkali metal alkoxides such as sodium methoxide, sodium or potassium ethoxide or potassium isopropoxide as catalysts and with addition of at least one initiator molecule containing from 2 to 8, preferably from 2 to 3, reactive hydrogens in bonded form for preparing polyoxyalkylene polyols for flexible PU foams and preferably from 3 to 8 reactive hydrogens in bonded form for preparing polyoxyalkylene polyols for semi-rigid and rigid PU foams, or by cationic polymerization using Lewis acids such as antimony pentachloride, boron fluo-ride etherate, etc., or bleaching earth as catalysts, from one or more alkylene oxides having from 2 to 4 carbon atoms in the alkylene radicals.
Suitable alkylene oxides are, for example, tetrahydrofuran, 1,3-propylene oxide, 1,2- or 2,3-butyl-ene oxide and preferably ethylene oxide and l,2-propylene oxide. The alkylene oxides can be used individually, alternately in succession or in admixture. Suitable initiator molecules are, for example: water, organic dicarboxylic acids such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and 2164~90 aromatic, unsubstituted or N-monoalkylated, N,N-dialkyl-ated or N,N'-dialkylated diamines having from 1 to 4 carbon atoms in the lkyl radical, such as unsubstituted or monoalkylated or dialkylated ethylenediamine, diethyl-ene triamine, triethylene tetramine, l,3-propylenedi-amine, 1,3- or 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, phenylene diamines, 2,3-, 3,4-, 2,4- and 2,6-tolylenediamine and 4,4'-, 2,4'-and 2,2'-diaminodiphenylmethane.
Also ~uitable as initiator molecules are: alkano-lamines such as ethanolamine, N-methylethanolamine and N-ethylethanolamine, dialkanolamines such as diethanol-amine, N-methyldiethanolamine and N-ethyldiethanolamine and trialkanolamines such as triethanolamine, and ammo-nia. Preference is given to using polyhydric, in particu-lar dihydric to octahydric alcohols and/or alkylene glycols such as ethanediol, 1,2- and 1,3-propanediol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, pentaeryth-ritol, sorbitol and sucrose and also mixtures of at lea~t 2 polyhydric alcohol~.
The polyoxyalkylene polyols, preferably polyoxy-propylene and polyoxypropylene-polyoxyethylene polyols, have a functionality of from 2 to 8 and hydroxyl numbers of from 25 to 500, with, as already stated, preference being given to using polyoxyalkylene polyols having a functionality of from 2 to 3 and a hydroxyl number of from 30 to 80 for flexible PU foams and polyoxyalkylene polyols having a functionality of from 3 to 8 and a hydroxyl number of from lOO to 500 for semi-rigid and rigid PU foams and suitable polyoxytetramethylene glycols having a hydroxyl number of from 30 to about 280.
Other suitable polyoxyalkylene polyols are polymer-modified polyoxyalkylene polyols, preferably graft polyoxyalkylene polyols, in particular those based on styrene and/or acrylonitrile, which are prepared by in-situ polymerization of acrylonitrile, ~tyrene or ~164490 preferably mixtures of styrene and acrylonitrile, for example in a weight ratio of from 90:10 to 10:90, prefer-ably from 70:30 to 30:70 advantageously in the above-mentioned polyoxyalkylene polyol~ using a method ~imilar to those given in the German Patents 11 11 394, 12 22 669 (US 3 304 273, 3 383 351, 3 523 903), 11 52 536 (GB 10 40 452) and 11 52 537 (GB 987618), and also polyoxyalkylene polyol dispersions containing as disper~e phase, usually in an amount of from 1 to 50~, preferably from 2 to 25~: for example, polyureas, polyhydrazides, polyurethanes containing tert-amino groups in bonded form and/or melamine and described, for example, in EP-B-011 752 (US-A-4,304,708), US-A-4,374,209 and DE-A-32 31 497.
The polyoxyalkylene polyols can, like the polyes-ter polyols, be used individually or in the form of mixtures. Furthermore, they can be mixed with the graft polyoxyalkylene polyols or polye~ter polyols and also the hydroxyl-containing polyester amides, polyacetals and/or polycarbonates.
Suitable hydroxyl-containing polyacetals are, for example, the compound~ which can be prepared from glycols 6uch as diethylene glycol, triethylene glycol, 4,4'-dihydroxyepoxydiphenyldimethylmethane, hexanediol and formaldehyde. Polymerization of cyclic acetals also allows ~uitable polyacetals to be prepared.
Suitable hydroxyl-containing polycarbonates are those of the type known per se which can be prepared, for example, by reacting diols such as 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol with diaryl carbonates, for example diphenyl carbonate, or phosgene.
The polyester amides include, for example, the predominantly linear condensates obtained from polybasic, ~aturated and/or unsaturated carboxylic acids or their anhydrides and polyhydric saturated and/or unsaturated amino alcohols or mixtures of polyhydric alcohols and 2~ 6A~90 amino alcohols and/or polyamines.
The relatively high molecular weight polyhydroxyl compounds (a) can, depending on the application of the isocyanate prepolymer mixtures (b), be completely or preferably partially replaced by low molecular weight chain extenders and/or crosslinkers. In the production of flexible PU foams, the addition of chain extenders, crosslinkers or, if desired, mixtures thereof can be advantageous for modifying the mechanical properties of the PU foams, for example the hardness. In the production of PU rigid foams, the use of chain extenders and/or crosslinkers can usually be omitted. Chain extenders which can be u~ed are difunctional compounds and suitable cros~linkers are trifunctional and higher-functional compounds, each having molecular weights less than 400, preferably from 62 to about 300. Examples of chain extenders are alkane diols, for example those having from 2 to 6 carbon atoms in the alkylene radical, such as ethane diol, 1,3-propane diol, 1,4-butane diol, 1,5-pentane diol and 1,6-hexane diol, and dialkylene glycols such as diethylene, dipropylene and dibutylene glycol, and examples of crosslinkers are alkanolamines, e.g.
ethanolamine, dialkanolamines, e.g. diethanolamine, and trialkanolamines, e.g. triethanolamine and triiso-propanolamine, and trihydric and/or higher-hydric alco-hols such as glycerol, trimethylolpropane and pentaeryth-ritol. Other suitable chain extenders or cros~linkers are the low molecular weight ethoxylation and/or propoxyl-ation products, for example those having molecular weights up to about 400, of the abovementioned polyhydric alcohols, alkylene glycols, alkanolamines and of aliphat-ic and/or aromatic diamines.
As chain extenders, preference is given to using alkanediols, in particular 1,4-butanediol and/or 1,6-hexanediol, alkylene glycols, in particular ethylene glycol and propylene glycol, and preferred crosslinkers are trihydric alcohols, in particular glycerol and ~164~90 trimethylolpropane, dialkanolamine, in particular dieth-anolamine, and trialkanolamine, in particular triethanol-amine.
The chain extenders and/or crosslinkers (c) which are preferably used in the production of flexible PU
foams can be used, for example, in amounts of from 2 to 60% by weight, preferably from 10 to 40~ by weight, based on the weight of the relatively high molecular weight compounds (a).
The isocyanate prepolymer mixtures of the inven-tion (b) can be mixed with further polyisocyanates for producing the PU. Specific examples are: alkylene diiso-cyanates having from 4 to 12 carbon atom~ in the alkylene radical, for example dodecane 1,12-diisocyanate, 2-ethyltetramethylenel,4-diisocyanate,2-methylpentamethy-lene 1,5-diisocyanate, 2-ethyl-2-butylpentamethylene 1,5-diisocyanate, tetramethylene 1,4-diisocyanate and prefer-ably hexamethylene 1,6-diisocyanate; cycloaliphatic diisocyanates, for example cyclohexane 1,3- and 1,4-diisocyanate and also any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (iRophorone dii~ocyanate), hexahydrotolylene 2,4- and 2,6-diisocyanate and also the corresponding isomer mixtures, dicyclohexylmethane 4,4'-, 2,2'- and 2,4'-diisocyanate and also the corresponding isomer mixtures, and preferably aromatic diisocyanates and polyiso-cyanates, for example tolylene 2,4- and 2,6-diisocyanate and the corresponding isomer mixtures, diphenylmethane 4,4'-, 2,4'- and 2,2'-diisocyanate and the corresponding isomer mixtures, mixtures of diphenylmethane 4,4'- and 2,4'-diisocyanates, polyphenylpolymethylene polyisocyan-ates, mixtures of diphenylmethane 4,4'-, 2,4'- and 2,2'-diisocyanates and polyphenylpolymethylene polyisocyanates (raw MDI) and mixtures of raw MDI and tolylene diisocyanates. The organic diisocyanates and polyiso-cyanates can be used individually or in the form of their mixtures.

Organic polyisocyanates which have been found to be very useful are mixtures of diphenylmethane diisocyan-ates and polyphenylp~lymethylene polyisocyanates, prefer-ably those having a diphenylmethane diisocyanate content of at least 35~ by weight, e.g. from 45 to 95~ by weight and in particular from 48 to 60% by weight, 80 that ~uch raw MDI compo6itions are particularly preferably used.
Suitable blowing agents (d) for producing the cellular polyurethanes are water and/or gases which are liquid at room temperature and liquids which are inert to the liquid isocyanate prepolymer mixtures and have boiling points at atmospheric pressure below 50C, in particular from -50C to 30C, and also mixtures of gaseous and liquid blowing agents. Examples of such ga~es and liquids which are preferably used are alkanes such as propane, n- and iso-butane, n- and iso-pentane, prefera-bly technical grade mixtures of n- and iso-pentane, and cycloalkanes such as cyclopentane, alkyl ethers such as dimethyl ether, diethyl ether and methyl isobutyl ether, alkyl carboxylates such as methyl formate, and halogenat-ed hydrocarbons such as dichlorofluoromethane, trifluoro-methane, l,l-dichloro-l-fluoroethane, monochlorotri-fluoroethane, monochlorodifluoroethane, difluoroethane, dichlorotrifluoroethane, monochlorotetrafluoroethane, pentafluoroethane, tetrafluoroethane and dichloromono-fluoroethane. The cellular polyurethanes, preferably PU
foams, are produced using, in particular, water, linear and cyclic alkanes having from 5 to 7 carbon atoms and mixtures thereof.
The blowing agents mentioned by way of example can be used individually or as mixtures. Blowing agents which are not used are chlorofluorocarbons which damage the ozone layer.
It is also possible to mix the liquids having boiling points below 50C with (cyclo)alkanes such as hexane and cyclohexane and alkyl carboxylates, such as ethyl formate having boiling points above 50C, as long as the blowing agent mixture advantageously has a boiling point below 38C. The amount of blowing agent or blowing agent mixture required can be experimentally determined in a ~imple manner as a function of the type of blowing agent or blowing agent mixture and on the mixing ratios.
The blowing agents are usually used in an amount of from 0.1 to 30 part~ by weight, preferably from 1 to 25 parts by weight, based on 100 parts by weight of the components a-c.
Catalysts (e) which can be used in the production of PU are preferably compounds which strongly accelerate the reaction of the hydroxyl-containing component ~a) with the isocyanate prepolymer mixtures of the invention (b) or the mixtures of isocyanate prepolymer mixtures (b) and further organic polyisocyanates. Suitable catalysts are, for example, organic metal compounds, preferably organic tin compounds such as tin(II) salts of organic carboxylic acids, e.g. tin(II) diacetate, tin(II) diocto-ate, tin(II) diethylhexanoate and tin(II) dilaurate, and the dialkyltin(IV) salts of organic carboxylic acids, e.g. dibutyltin diacetate, dibutyltin dilaurate, dibutyl-tin maleate, dioctyltin diacetate, and dibutyltin dimer-captide and strongly basic amines, for example amidines such as 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methylmorpholine, N-ethylmorpho-line, N-cyclohexylmorpholine, dimorpholino-diethyl ether, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetra-methylbutanediamine, N,N,N',N',tetramethylhexane-1,6-diamine, di(4-N,N-dimethylaminocyclohexyl)methane, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1,2-dimethylimidazole,l-azabicyclo[3.3.0~octane,alkano-lamine compounds such as triethanolamine, triisopropanol-amine, N-methyldiethanolamine and N-ethyldiethanolamine and dimethylethanolamine, tris(N,N-dialkylaminoalkyl)-s-hexahydrotriazine, in particular tris(N,N-dimethylamino-2164~0 propyl)-s-hexahydrotriazine,tetraalkylamoniumhydroxides such as tetramethylammonium hydroxide and preferably 1,4-diazabicyclo[2.2.2]o~tane. Preference i8 given to using from 0.001 to 5% by weight, in particular from 0.05 to 2~
by weight, of catalyst or catalyst combination, based on the weight of the component (a).
If desired, auxiliaries (f) can also be incorpo-rated into the reaction mixture for producing the compact or cellular polyurethanes, preferably PU foams. Examples are surface-acti~e substances, foam stabilizers, cell regulators, flame retardants, fillers, dyes, pigments, antistatic agents, hydrolysis inhibitors, fungistatic and bacterio6tatic sub6tances.
Suitable surface-active substances are, for example, compounds which serve to assist the homogeniza-tion of the isocyanate prepolymer mixtures and may also be suitable for regulating the cell structure of the PU
foams. Examples are emulsifiers such as the sodium salts of castor oil sulfates or of fatty acids, and also 6alts of fatty acids with amines, for example diethanolamine salts of oleic acid, stearic acid and ricinoleic acid, salts of sulfonic acids, for example alkali metal or ammonium salts of dodecylbenzenedisulfonic or dinaphthyl-methanedisulfonic acid, and ricinoleic acid; foam stabi-lizers such as siloxane-oxyalkylene copolymer~ and other organopolysiloxanes, ethoxylated alkylphenols, ethoxyl-ated fatty alcohols, paraffin oils, castor oil ester~ or ricinoleic esters, Turkey red oil and peanut oil, and cell regulators such as pyrogenic silica, paraffins, fatty alcohol~ and dimethylpolysiloxanes. Other suitable compounds for impro~ing the emulsifying action, the cell structure and/or stabilization of the foam are oligomeric polyacrylates having polyoxyalkylene and fluoroalkane radicals as side groups. The surface-active substances are usually used in amounts of from 0.01 to 5 parts by weight, based on 100 parts by weight of the component (a).

~l6,l4sn Suitable flame retardants are, for example, diphenyl cre~yl phosphate, tricresyl phosphate, tris(2-chloroethyl) phosphate, tris(2-chloropropyl) phosphate, tris(l,3-dichloropropyl) phosphate, tris(2,3-dibromoprop-yl) phosphate and tetrakis(2-chloroethyl)ethylene diphos-phate.
Apart from the halogen-substituted phosphates mentioned, it is also possible to use inorganic flame retardants such as hydrated aluminum oxide, antimony 10 trioxide, arsenic oxide, ammonium polyphosphate, expanded graphite and calcium sulfate, or cyanuric acid deriva-tives such as melamine, or mixtures of at least two flame retardants such as ammonium polyphosphates and melam'ne and/or expanded graphite, and also, if desired, starch to make the PU foams produced from isocyanate prepolymer mixtures flame resistant. In general, it has been found to be advantageous to use from 5 to 50 parts by weight, preferably from 10 to 40 parts by weight, of the flame retardants or mixtures mentioned per 100 parts by weight 20 of the components (a) to (c).
For the purposes of the present invention, fillers, in particular reinforcing fillers, are the customary organic and inorganic fillers and reinforce-ments known per se. Specific examples are: inorganic fillers such as siliceous minerals, or example sheet silicates such as antigorite, serpentine, hornblendes, amphiboles, chrysotile, zeolites, talc; metal oxides such as kaolin, aluminum oxides, aluminum silicate, titanium oxides and iron oxides, metal salts such as chalk, barite 30 and inorganic pigments such as cadmium sulfide, zinc sulfide, and also glass particles. Examples of suitable organic fillers are: carbon black, melamine, rosin, cyclopentadienyl resins and graft polymers.
The inorganic and organic fillers can be used individually or as mixtures and are advantageously incorporated into the reaction mixture in amounts of from O.5 to 5096 by weight, preferably from 1 to 1096 by weight, based on the weight of the components (a) to (c).
Further details about the other customary auxil-iaries (f) mentioned above can be found in the 6pecialist literature, for example the monograph of J.H. Saunders and K.C. Frisch "High Polymers", Volume XVI, Polyureth-anes, part 1 and 2, Verlag Interscience Publishers 1962 and 1964, or the ~unststoff-Handbuch, Polyurethane, Volume VII, Carl-Hanser-Verlag, Munich, Vienna, 1st and 2nd edition, 1966 and 1983.
Further preferred features and embodiments of the invention are given in the following examples.

Preparation of the lignin-containing isocyanate prepoly-mer mixtures of the invention Lignin-containing prepolymers according to the invention were prepared using three different unmodified lignins: kraft lignin AT and two organosolv lignins. The lignin powders were first stirred into polyoxypropylene glycol having a molecular weight of 2000 and were treated while removing the water for 5 hours at 150C and under reduced pressure of 2mbar. The dewatered lignin suspen-sion obtained was subsequently slowly metered while stirring into the initially charged isocyanate heated to 80C and was stirred for 2 hours at 80C or 120C to complete the reaction.
This gave lignin-containing isocyanate prepolymer mixtures whose vi6cosity was strongly dependent on the lignin type and also on the structure of the polyisocyan-ate used. The viscosity was down to below 1000 mPas at 25C, measured using a rotation viscometer, at lignin contents in the prepolymer of > 20% by weight. The storage stability is evidenced by the testing of viscosi-ty and -N=C=0 content after 60 days (Table 1, experiment 1) and also the fact that the prepolymer formation at elevated temperature did not lead to increased viscosi-ties or significantly altered -N=C=0 contents (Table 1, experiments 1 to 3).

Table 1 -N=C=O prepolymers from lignin suspensions in polyoxypropylene glycols R2porim~nt Lignln Polyol Lig~in:polyol Ieocyanato (~oight ratio) 1 Llg PH41)PPG 20002) 42 : 58 M20W3) 2 Lig PH9 PPG 2000 48 : 52 M20W

3 Llg AT PP~ 2000 48 : 52 M20W

4 Llg AT PPG 2000 44 : 56 MI~) 0 ~xperlment Suspenslon:I~ocya- -N=C~O Re~arks nate ~ by (welght ratio) wt.)PreparationVl~co~ity te~peratureat 25C
C
1 1000 : 1050 13.2 80 42400 after 60 13.2 120 58500 day85) 13.3 80 370050 2 500 : 650 14.5 B0 4100 14.4 120 4200 3 500 : 650 16.9 80 6800 16.9 120 6500 4 280 : 320 16.4 80 725 (1) Lig AT: Kraftlignin Indulin AT from Westvaco, Charleston, SC, USA
Lig PH4 and Lig PH9: organosolv lignins from Organo-cell GmbH, Munich (2) A polyoxypropylene glycol having a molecular weight of 2000 (3) Mixture of diphenylmethane diisocyanates and poly-phenyl-polymethylene polyisocyanates (raw MDI) (4) Mixture of diphenylmethane 4,4'- and 2,4'-diisocyan-ate '~16 4490 (5) The measurements of the -N=C=O content and the viscosity using a rotation viscometer were carried out after storage of the suspension for 60 day~ at Table 1 shows that the isocyanate prepolymer mixtures of the invention are very stable both physically and chemically. This is a particular advantage of the invention.

Production of polyurethane parts Flexible polyurethane foams were produced using the lignin-containing isocyanate prepolymer mixtures of the invention as described in Example 1.
The base polyetherol used was a polyoxypropylene-polyoxyethylene block polyol initiated using a glycerol and having a content of primary hydroxyl end groups greater than 80%, a hydroxyl number of 35 mg of KOH/g of polyol and a viscosity of 850 mPas at 25C measured in accordance with DIN 51562 using an Ubbelohde viscometer.
The cell opening polyol used was a polyoxypropyl-ene-polyoxyethylene polyol initiated using glycerol and having an ethylene oxide content of 70% by weight, based on the alkylene oxide content, a hydroxyl number of 42 mg of KOH/g of polyol and a viscosity of 980 mPas at 25C
measured in accordance with DIN 51562 using an Ubbelohde viscometer.
The comparative substance used was a polyisocyan-ate mixture containing urethane groups and having an -N=C=O content of 24.5% by weight, obtained from diphenylmethane diisocyanates (40.7% by weight), polyphenyl-polymethylene polyisocyanates (30.4~ by weight), polyoxypropylene glycol having an average molecular weight of 2000 (10% by weight) and the abovementioned cell opening polyol (10~ by weight).
The flexible PU foams were produced by intensive-~164490 ly mixing the polyol and isocyanate components at an NCO
index = 80 (80 -N=C=O groups per 100 OH groups) and pouring the reaction mixture into an open beaker (deter-mination of the reaction times and the free-foamed bulk density) and into a heatable mold (mold temperature 50C) having the dimen6ions 400x400x100 mm (determination of the mechanical propertie~ of the foams) and allowed to foam therein.
Formulation for producing flexible polyurethane foams in parts by weight.

Component (A): mixture consisting of:

Ba~e polyetherol 54.55 Cell opening polyol 5.0 Water 3.00 Stabilizer1) 0.20 Diazabicyclo[2.2.2]octane 0.20 33% by weight in dipropyl-ene glycol N,N-dimethylaminopropylamine 0.30 N,N,N',N'-tetramethyl-4,4'-diaminodicyclohexylmethane 0.45 Glycerol 1.20 Tris(chloropropyl) phosphate 5.00 Foam stabilizer based on silicone, Tegostab B 8680 from Goldschmidt.

Component (B): Isocyanate mixture as de~cribed in Table In the experiments described in Table 2, the polyisocyanate mixture containing urethane groups used a~
comparative substance was replaced completely or partially as indicated by the lignin-containing iRocyanate prepolymer mixture of the invention.

~154~9~

Table 2 Rrpari~unt 5 ~C~ p~rinon~ 6 lln-~ntion) 7 (ID~antio~
Comparatlve ~ub~tance 100 0 50 IRocy~n-t~ prepolymer mlxtur- from e~periment 4 in E~ample 1 0 100 50 Viscoaity at 25-C mPas c 100 980 790 5eaker tlme~-:
Start tim- ~eec] 12 10 10 1 0 S-ttlng tlma- [~cl 67 70 48 Rl~lng tlme [nec) 75 105 68 Free-foamed denelty [g/ll 48.37 54.46 50.93 Molded foame-:
Mold t~mp~rat~re [-C] 51.2 50.8 50.9 C~hlon w~lght [g] 824 692 Bl9 Core denPlty [g/l] 50.3 59.7 49.9 Proportlon of open celle [~] 3 2 3 Compre~slve hardnecR
[ kPal 20~ 1.8 1.0 1.7 40~ 3.0 2.3 2.7 60~ 6.0 5.7 5.1 Compre~ e ~-t [~] 7.7 44.0 13.3 Ela~ticlty [cm] 45.9 35.1 42.7 Elongatlon at break [~] 70 152 106 Ten~ etrength [kPa] 61 85 75 7ear propagatlon re~l~- 0.20 0.45 0.28 tance [N/mml 30 Notes on Table 2:

100 g of the components (A) (polyol) plus (B) (poly-i60cyanate), in the ratios given, were introduced into a beaker having a capacity of 1000 ml.

16 1 cu6hion mold, demolding time 5 min, Proportion of open cells: subjective evaluation after 5 min after demolding. Scale 1-5, 1: very open, 5: very closed.

~16449~

Foam tests were carried out as follows:
Den~ity determination DIN 53420 Elasticity measurem-=nt: Rebound resilience measured by an internal BASF method Compressive set DIN 53572 Compressive hardness DIN 53577 Tear propagation resistance DIN 53515 Tensile strength DIN 53571.

The figures in Table 2 show that the isocyanate prepolymer mixtures of the invention are suitable for producing polyurethane foam articles which have improved properties. In particular, the increased elongation at break, the increased tensile strength and the increased tear propagation resistance are notable and represent a surprising result.

Claims (12)

1. An isocyanate prepolymer mixture containing urethane groups and reactive isocyanate groups in bonded form, which has an NCO content of from 2.5 to 30% by weight, based on the total weight of the isocyanate prepolymer mixture, and is obtainable by reacting b1) diphenylmethane 4,4'-, 2,4'- and 2,2'-diisocyanate, an isomer mixture of diphenylmethane 4,4'- and 2,4'-or 4,4'-, 2,4'- and 2,2'-diisocyanates or a mixture of diphenylmethane diisocyanates and polyphenyl-polymethylene polyisocyanates with b2) a suspension comprising b2i) at least one polyoxyalkylene glycol having a molecular weight of from 400 to 6000, prefer-ably from 1000 to 3000, selected from the group of polyoxypropylene glycols, polyoxy-propylene-polyoxyethylene glycols and mix-tures thereof and b2ii) lignin.

2. An isocyanate prepolymer mixture as claimed in claim 1, wherein the suspension, based on the total weight of b2i) and b2ii) in the suspension, comprises or preferably consists essentially of b2i) from 99 to 30% by weight, preferably from 50 to 40% by weight, of at least one polyoxyalkylene glycol having a molecular weight of from 400 to 6000, in particular from 1000 to 3000, selected from the group of polyoxypropylene glycols, polyoxypropylene-polyoxyethylene glycols and mixtures thereof, and b2ii) from 1 to 70% by weight, preferably from 50 to 60% by weight, of lignin.

3. An isocyanate prepolymer mixture as claimed in any of the preceding claims, which has an -N=C=O content of from 5 to 25% by weight, based on the total weight of the isocyanate prepolymer mixture.

4. An isocyanate prepolymer mixture as claimed in any of the preceding claims, wherein the polyoxyalkylene glycol used is a polyoxypropylene-polyoxyethylene glycol having an oxypropylene group content of at least 60% by weight based on the polyoxyalkylene groups.

5. An isocyanate prepolymer mixture as claimed in any of the preceding claims, wherein the lignin used has not been subjected to a special chemical treatment for this further processing.

6. Use of an isocyanate prepolymer mixture as claimed in any of the claims pertaining to an isocyanate prepolymer mixture in the production of polyurethane.

7. A process for preparing an isocyanate prepolymer mixture containing urethane groups and reactive isocyan-ate groups in bonded form by reacting the organic poly-isocyanates (b1) and suspensions (b2) defined in the claims pertaining to an isocyanate prepolymer mixture.

8. A process as claimed in claim 7, wherein the suspension (b2) is, prior to the reaction with the polyisocyanates, treated at a temperature of from 60 to 130°C, preferably under a pressure of at most 30 mbar for a period of from 1 to 8 hours, particularly preferably in the presence of esterification catalysts.

9. A process for producing compact or cellular polyurethanes, preferably PU foams, by reacting a) relatively high molecular weight compounds having at least two reactive hydrogens, preferably polyhydroxyl compounds, with b) liquid polyisocyanate compositions containing polyurethane groups in bonded form.

in the presence or absence of c) chain extenders and/or crosslinkers, d) blowing agents, e) catalysts and f) auxiliaries, wherein the polyisocyanate compositions (b) used consist at least partially of an isocyanate prepolymer mixture as claimed in any of the claims pertaining to an isocyanate prepolymer mixture.

10. A process as claimed in claim 9, wherein the relatively high molecular weight compounds (a) have a functionality of from 2 to 8 and a hydroxyl number of from 25 to 500 and are preferably polyhydroxyl compounds, particularly those selected from the group of polythio-ether polyols, polyesteramides, hydroxyl-containing polyacetals, hydroxyl-containing aliphatic polycarbon-ates, polyester polyols, polymer-modified polyether polyols, preferably polyether polyols and mixtures of at least two of the specified polyhydroxyl compounds.

11. A process as claimed in claim 9 or 10, wherein the blowing agent (d) used is water, a linear or cyclic alkane having from 3 to 7 carbon atoms or a mixture thereof.

12. A process as claimed in any of the claims per-taining to the production of polyurethane, wherein the relatively high molecular weight compounds (a) and the polyisocyanate compositions (b) are reacted in a mold in the presence of a blowing agent (d) to form a polyure-thane foam article.