Coatings prepared from polyurethane soft foam recycling polyols.
Recycling polyols are derived from polyurethane soft foams by the combination of glycolysis and aminolysis. In this process the cleavage of the urethane bonds results in urea groups and the hydroxyl compounds. The polyureas from the water reaction of the polyisocyanate are in general not cleaved due to short reaction times and moderate temperatures.
By this process homogenous polyols of low glycol content are obtained, the hydroxyl number of which is adjusted to the properties of the coatings aimed at and is in the range of 180 to 300 mg KOH/g depending on the Shore hardness to be produced. The primary amine content, a limiting parameter for distribution in Europe, is lower than one percent leading to no limitations in this respect. The viscosity of the recycling polyols is in the range of 3000 to 6000 mPas (25[degrees]C) with some influence of the amount of dissolved polyureas originating from the reaction mentioned above.
Coatings are produced by simple mixing of the recycling polyols plus additives in low concentrations with a di- or polyisocyanate. The coating is either sprayed by gun onto the surface like concrete, paper, sheet metal or plastic films or by applying a knife for thin film techniques using the Mathis LabDryer for knife coating and hardening.
The films of 0.2 to 4 mm thickness thus produced are hardened either at room temperature being tack-free after 30 to 120 minutes depending on catalysis or by applying warm air of 70[degrees]C in the LabDryer for five to 30 minutes.
Hardness and elasticity of the coatings can be adjusted by simply varying the isocyanate index. The coatings thus produced have better tensile strength than current trade products, an optimal elongation behavior and can be used in the temperature range of -20 to +60[degrees]C.
At present, most of the polyurethane soft foam waste from production or car disassembly is burned or brought to landfills. The possibilities of recycling this type of condensation polymer consist only in direct recycling of the material, e.g. direct use of the foam flakes, combustion or chemical degradation of the macromolecules, e.g. by pyrolysis, hydrolysis, solvolysis or hydrogenation. Chemical degradation procedures have the advantage of converting the macromolecules to oligomers or monomers which can be brought to another application.
The object of our work is the synthesis of new raw materials for the production of specialty polyurethanes plastics. Our ecological aim is to recycle hitherto not used wastes without any depreciation by using a new synthesis route and new technologies. The environmental impact is reduced by decreasing the necessity of landfill or combustion. The amount of primary raw material can be reduced by using recycling polyols so that material and energy resources are saved. Considered economically, new application fields are opened by the inexpensive production of specialty products from the recycled materials.
Our work was directed to a modified solvolysis procedure which enables us to produce new polyols from polyurethane soft foams which, according to the aim mentioned above, can be processed to high-grade polyurethanes, especially coatings, adhesives and sealants as well as composites, by formulation with polyisocyanates. In this way, polyurethane soft foams are recycled not to give the original products but to new materials having an essentially higher value.
This aim shall be approached by a modified solvolysis consisting in the
conversion of the polyurethane soft foams with a reaction mixture of higher glycols (molecular weight > 100 g/mole) and aliphatic primary and/or secondary amines within the temperature range of 120 to 180[degrees]C.
The recycling polyols thus produced have a set of fitting properties (hydroxyl number, viscosity, reactivity) for the proposed application and are converted to the desired polyurethanes by specially developed formulations, processed to coatings as the basic example in the laboratory with a Mathis LabDryer and characterized by physical measurements and mechanical tests.
New Pathways of Polyurethane Foam Recycling
The authors studied three new pathways of the material recycling of polyurethane foams in co-operation with partners in small and medium-sized enterprises:
1. Low molecular weight wastes from the polyester synthesis (so-called oligoester condensates) are used in the glycolysis instead of the glycols in order to lower the costs of the procedure as well as to recycle another, not used waste stream .
2. A combination of glycolysis and aminolysis is applied to the polyurethane foams. With this procedure, di- and/or tri-substituted ureas are formed which are soluble in the polyol mixture, and polyether alcohols originating of the waste of soft foams.
3. The soft foams react with dicarboxylic acids (acidolysis) forming acylureas and the polyether alcohols in their original form. As for expensive diisocyanates, the separation of the acylureas and the cleavage of them to diamine is recommended. Acylureas based on common diisocyanates should be kept in the polyol mixture.
Excess carboxylic acid groups are esterified after reaction. This reaction is, for instance, carried out with phthalic anhydride and provides rigid foam polyols.
Chemistry of Polyurethane Recycling
The degradation of polyurethanes is a series of reaction steps based on the special properties of the reaction products contained in them. Depending on the nature of the reagent, different reaction products are formed by the conversion of the products with the solvolysis agents. In the simple glycolysis with excess glycol(s) the urethane groups are simply transesterified as is shown in Figure 1.
[FIGURE 1 OMITTED]
In this reaction, urethanes containing the glycol used as the solvolysis agent as esterification component and polyester or polyether alcohols, resp., which were used as the polyol component in the polyurethane, are formed. As a side reaction the urea groups can be cleaved by the glycols (Figure 2).
[FIGURE 2 OMITTED]
In this reaction, primary aromatic amines are produced compulsory, being undesired because of their toxicological, especially carcinogenic properties. In the case of using aliphatic amines in combination with glycols, the urethane groups are preferably reacted with the amine providing araliphatic ureas (Figure 3), which are, depending on the structure of the selected amine, di- or tri-substituted. In this reaction no primary aromatic amines are formed.
[FIGURE 3 OMITTED]
Method and Procedures
The recycling of polyurethane soft foams using a combination of glycolysis and aminolysis providing a polyol mixture is carried out as a one-step reaction in a four-necked flask (0.75, 2.5 or 6 l) or in a heated stirring vessel (high-alloyed steel, 90 or 160 l). The apparatus units are fitted with a demister, cooler (which can be switched between refluxing and descending operation), inside thermometer and stirrer. The reactors are flushed with nitrogen. The raw materials are polyurethane soft foams which are provided by car recycling enterprises or from test productions.
The general procedure was the following : The weighed amount of the glycol component is filled into the vessel and heated with stirring. During the heating a part of the calculated amount of the amine is added. At a temperature of 160[degrees]C the addition of the polyurethane soft foam flakes begins. As soon as the temperature reaches 180[degrees]C, the residual amount of amine is added and heating of the mixture is continued. The foam flakes are added continuously at the defined temperature or temperature program until the calculated amount is added. The reaction mixture is stirred for another 0.2 to 5 hours at the defined temperature.
Eventually, heating is stopped and the mixture stirred until a temperature of 120[degrees]C is reached. Finally, the liquid product is filled into the prepared containers. The characteristic data (viscosity, hydroxyl number, amine number, amine content by GC, water content) of the polyols are determined.
The polyurethanes are synthesized from the recycling polyols according to Behrendt and Pohl. For the manufacture of films a component A is prepared and reacted with component B, which have the following composition:
Component A: recycling polyol 97.66 parts acetylacetone 2.20 parts Vinycene 400 0.14 parts
Component B: Lupranat M 20 A 90 to 17 parts
The amount of Lupranat M 20 A used depends on the hydroxyl number of the recycling polyol as well as on the defined isocyanate index. The essential mechanical properties, e.g. hardness of the coating, are adjusted mainly by the isocyanate index.
Analysis of hydroxyl and amine numbers, resp., was carried out according to standard methods. Viscosities were measured by using a Hoppler viscosimeter. Amine determinations were performed using a Hewlett Packard HP 5890 Series II with MSD 5970 instrument. Mechanical tests were made using a tensile tester FPG 7/20 of Kogel GmbH, Leipzig, with automatic recording of force and elongation. Relaxation spectra were obtained by an automatic torsion pendulum of Myrenne GmbH, Aachen (stepwise temperature program with 5 K per step and frequency 1 Hz).
The polyisocyanate Lupranat M 20 A was kindly provided by BASF AG and is based on aniline formic aldehyde condensates with an average isocyanate functionality of about 3.9.
Cleavage of polyurethane soft foams is a series of reactive steps which proceed in the case of reacting them with the solvolysis mixture glycol and amine as competing consecutive reactions. The faster reaction is the cleavage of the urethane group by the aliphatic amine resulting in the formation of substituted ureas in which the degree of substitution depends on the amine used. Because of the functionality of the polyisocyanate branched ureas are formed including those originally present in the foams from the reaction with water. The high-molecular weight polyureas thus formed are slightly soluble in the polyols originally forming the soft segments as well as in the polyols used for glycolysis with different ratios. Their solubility depends on their degree of branching and their molecular weight and further on the type and chain length of the glycol. Glycols based on propylene oxide dissolve the polyureas better than those based on ethylene oxide. Hence, the homogeneity of the recycling polyols is substantially determined by the choice of the glycols used.
The reaction of glycols with the urethane groups can be considered to be a transesterification in which the short chain diols (used in excess) replace the long chain polyether alcohols. This reaction, like every transesterification, is a balance reaction. As a side reaction, urea groups may be cleaved by the hydroxyl groups. Here the hydroxyl groups act as nucleophilic reagents and form by this slower cleavage reaction primary aromatic amines. Hence, a short reaction time with glycols of only low nucleophily is desired for the production of high-quality recycling polyols.
Our experimental series resulted in dipropylene glycol or a mixture from dipropylene and hexapropylene glycol to be optimal. Table 1 gives the formulations and some properties of recycling polyols. As is shown, recycling polyols could be produced having a wide range of hydroxyl numbers and viscosities useful for polyurethane production. The family of reactive polyols so far produced includes the range of hydroxyl numbers from 80 to 400. Table 2 shows a small group of selected polyols.
The combination of different glycols allows one to produce recycling polyols with properties advantageous for the requirements of specialty products. The amine number of the polyols is mainly a result of residues of the reactants used and can be reduced by subsequent degassing by a rotating evaporator (120[degrees]C/25 mPa/2 h). The reactivity of the recycling polyols against isocyanates is very high so that the starting times without any catalyst are 30 to 90 seconds. The reaction rate can be controlled by the addition of one to three weight percent of acetylacetone.
According to the present state of research, the recycling polyols may be used in several fields of polyurethane production such as rigid foams, semi-rigid foams or elastomeric products. Their main application field is now considered to be in elastic coatings using the polyols with hydroxyl numbers between 180 and 320 mg KOH/g. The polyols having hydroxyl numbers beyond 300 were used for the manufacture of rigid foams using the standard formulation. In this way, rigid foams could be produced from the polyol P 222 for instance. The following properties were achieved at an aimed raw density of 40 g/[dm.sup.3]:
raw density (g/[dm.sup.3]) 36.4 compression strength (kN/[mm.sup.2]) 2.87 dimension stability (24 h/140[degrees]C) +1.6%
From recycling polyols with lower hydroxyl numbers and isocyanate indices below 80 semi-rigid foams are obtained. These foams were first produced in the density range of about 60 g/[dm.sup.3] in order to demonstrate the polyols to be usual for this application.
Primarily, semi-rigid films are produced from the recycling polyols at the Mathis LabDryer in order to simulate reactive coatings. The films are drawn with a knife coater on silicone release paper according to the standard formulation with isocyanate indices between 90 and 75 and hardened at 90[degrees]C for 25 minutes. Two example formulations based on recycling polyols P 223 and P 224 (hydroxyl number 272 mg KOH/g) and their film properties are shown in Table 3.
The stress-strain curves of the two film materials described here (standard rods with 40 mm length and cross section of 4x4 mm) show Hook behavior by an almost linear ascent of the strain against the elongation in range up to an elongation of ca. 20%. After that a distinct plateau follows until break of the specimen (Figure 4). The Hook behavior in the range of low elongation is due to the structure of the polyurethane based on a long-chained polyether and short-chained diols. The relatively broad plateau range is assumed to be caused by the rearrangement of the polyether chains in the soft-segment and their sliding at each other. The hard-segment phase does not play any significant role. A reduction of the amount of short chain diol (P 224) results in further improvement of the elastic behavior (Figure 4).
[FIGURE 4 OMITTED]
The relaxation spectra of the polyurethanes made from the recycling polyols show some peculiarities compared to a typical polyurethane elastomer which are due to the composition of the polyols and the special procedure of their production. The new synthesis route of the polyols results in a composition of excess glycols from the glycolysis reaction, the polyether polyols originally used in the soft foams (molecular weight in the range of 5,000 to 6,000 g/mole and hydroxyl functionality 2.7 to 3.0), small amounts of hydroxyl reactive additives, e.g. chain prolongers (short-chained glycols), cell openers (in general polyethylene glycol 600 with two to five weight percent of the polyol component) and curing agents (frequently amine polyether alcohols having an OH-functionality of four to five). Besides the hydroxyl compounds, in the recycling polyols catalysts from the soft foam production (e.g. diethylenetriamine and other tertiary amines as well as tin-organic compounds as dibutyltindilaurate), which accelerate the polyurethane formation reaction, and finally dissolved or dispersed polyureas are present.
Two examples show the characterization of the network structure by means of the dynamic-mechanical analysis: polyurethanes based on polyol P 15 or P 134, resp., the formulations and analytic data of which are given in Table 4. The relaxation spectrum of the film based on polyol P 15 shows four distinct maxima of the storage module G against temperature at -153.2, -88.2, -21.0 and 54.9[degrees]C (Figure 5).
[FIGURE 5 OMITTED]
The transition areas at -153[degrees]C and -88[degrees]C may be attributed to the onset of group mobility in the polyurethane chain. In these temperature areas the movement of the methylene groups of the chains as well as that of the oxygen atoms of the polyethers as can be seen from the maxima of the storage modules. The transition area at -21[degrees]C is caused by the onset of the segment mobility in the polyether elastic phase and marks in this way the first [alpha]-area of the phase-separated polyurethanes (for comparison: the transition areas of OH-functional high molecular weight polyether alcohols with an average molecular weight of ca. 5,000 reacted with 4,4'-diphenylmethanediisocyanate are at ca. -45[degrees]C). In the range of approximately 55[degrees]C the main relaxation is found showing the glass transition of the polyurethanes from the low molecular weight glycols (for comparison: the [alpha] relaxation of a polyurethane made of dipropylene glycol and methylene bis(4-phenyl-isocyanate) is found at +78[degrees]C). The relaxation of the hard segments derived from the polyisocyanate could not be determined because of thermal degradation beyond 200[degrees]C. It is established that the transition temperature of hard segments of aromatic polyisocyanates and short chain glycols or water (polyureas) are in the range of 240[degrees]C. The loose ends (OH groups) existing in the polymer because of the low isocyanate index act as an inner softener and cause lower glass transitions and lower strengths.
Compared to the relaxation spectrum of the film made from polyol P 15 that of the film from polyol P 134 is less structured in the temperature range beyond room temperature (Figure 6). It can be assumed that the composition of the polyether polyols made from soft foams is nearly the same in both cases. Obviously, the lower isocyanate index in the sample made of P 134 as well as the use of a single glycol in P 15 have an influence on the relaxation behavior of the polyurethane. The glass transition of P 134 polyurethane is broadened compared to that of polyol P 15 and increased by 30 K to 85[degrees]C, other transition may be found at about +50[degrees]C and +130[degrees]C. The relaxation spectrum indicates better mixed phases and a limited phase segregation caused by the composition of the recycling polyol and the isocyanate index.
[FIGURE 6 OMITTED]
Figure 7 shows the relaxation spectra of a series of polyurethanes produced from recycling polyols with increasing amount of soft polyurethane foam by the same solvolysis mixture of dipropylene glycol and di-n-butylamine (for composition, see Table 3). The glass transition of the soft segment phase at -45[degrees]C appears, explicitly indicating a well pronounced phase separation of the weakly crosslinked polyurethane network based on the high molecular weight polyether. The glass transition region in the temperature range of 75[degrees]C exhibits features related to the change in structure of the recycling polyol correlating to their composition: the polyurethane made from recycling polyol with the lowest amount of soft foam (P 221, 59.2 weight percent of soft foam) shows a single glass transition at 76.5[degrees]C with only little expressed shoulder at higher temperatures (at about 105[degrees]C). The higher the content of soft foam in the composition the higher the amount of high molecular weight polyether triol, but at the same time also that of polyureas resulting from the polyisocyanate-water reaction during soft foam production. The glass transition of the polyurethane of the recycling polyol P 222 (64.5 weight percent of soft foam) is found at 82.8[degrees]C, i.e., the increase in the glass transition temperature of 6.3 K suggests a better segregation into soft and hard phases of the polyurethane.
[FIGURE 7 OMITTED]
The high temperature shoulder is found in the range of 115[degrees]C and is more pronounced as in the polyurethane of P 221. The polyurethane from recycling polyol P 223 (65.6 weight-percent of soft foam) has its glass transition broadened and split into two maxima at 67.8[degrees]C and 83.9[degrees]C suggesting the appearance of a third phase in the polyurethane.
Further, an explicit shoulder may be seen at about 128[degrees]C. These data let us assume that the dissolved polyureas in the recycling polyols are reacted with the polyisocyanate and thus incorporated by chemical bonds into the polymer matrix. They are thus chemically bound reinforcing fillers in the nanometer range and exhibit properties of reinforcing nano particles. The shift of the transition temperatures to higher ranges implies that the nano particles support the phase segregation and form within themselves hydrogen bonds of higher density with the known higher bond energy in them. The breakdown of the physical structure of the rigid polyurea segments occurs because of these two reasons at higher temperatures.
Further, beyond about 125[degrees]C there is a plateau region in any of the polymers up to the end of measurement at 200[degrees]C resembling the classical rubber plateau but depending on the composition in its absolute values. The higher this plateau region is the less the rigid domains are broken and support the structure to higher temperatures; in this respect the content of the polyureas supports the absolute altitude of this plateau. With higher polyurea concentration in the recycling polyols, the value of the mechanical loss in the plateau region increases.
The series of recycling polyols thus produced show a defined influence of composition on the mechanical properties. When mechanical or physical properties are known or the table of them corresponds to a certain field of application the formulation of the recycling polyol may adjusted directly to the desired properties.
The newly developed procedure of combined aminolysis and glycolysis of polyurethanes allows the production of recycling polyols with wide range properties which are useful for a great number of applications. The hitherto examined application spectrum includes rigid foams, semirigid foams, duromer foams, sheets, adhesives, coatings and binders for composites containing natural raw materials . The main properties of the recycling polyols are their adjustable hydroxyl numbers and viscosities. In general, for machining viscosities lower than 10,000 mPas (25[degrees]C) are required which can be achieved by this procedure. The polyols have to be homogenous and stable and their reactivity has to be suitable to the special application. The homogeneity is achieved by the composition of the solvolysis mixture, especially of the glycols. Low-molecular polypropylene glycols, in particular dipropylene glycol, but also propylene glycols of an average molecular weight of up to 600 g/mole, have proved to be suitable for this purpose.
The reactivity of the recycling polyols is essentially determined by the amine content and the type of the hydroxyl groups. If a secondary aliphatic amine like di-n-butylamine is used only a low residue of it may be contained in the polyol so that the reactivity may be too high for some applications.
It was found that the addition of acetylacetone in a certain ratio can mask the amine reactivity and control the pottime of polyurethane preparations. The properties of the polymers are not evidently influenced by the addition of acetylacetone.
The main area of application of these recycling polyols was in the field of sheet materials . During the development of these polyols it became evident that the solvolysis procedure developed provides polyurethanes with elastic properties without any necessity of the addition of longchained primary raw materials. Hence, for the production of semi-rigid or elastic polymers it is sufficient to react only recycling polyols with commercial polymer isocyanates.
Hardness and elasticity of the polyurethanes can be adjusted only by varying the isocyanate index. This represents an interesting method for the production of coatings with different properties made from the same polyurethane system.
The coatings for tanks, tubes or concrete surfaces developed on the basis of the recycling polyols, compared to current commercial products parallel machined, have a better strength and an optimal elongation behavior. The strength of the coatings manufactured as a film may be twice as high as that of a comparison product having at the same time a higher elongation and a broader application range with regard to temperature. The coatings can be used without any limitation in the temperature range of-20 to +60[degrees]C owing to a completely different structure of the polyol component and the broad transition area in the storage module resulting therefrom. After reaction with pure or raw 4,4'-diphenylmethanediisocyanate, the recycling polyol structure yields polyurethanes the segregation behavior of which can be controlled by the solvolysis mixture and the formulation so that it is possible to produce final products with a wide range of properties by the exclusive use of recycling polyols. Thus, new property spectra and new application fields have been opened to recycling polyols made from polyurethane soft foams.
Table 1. Formulation and properties of recycling polyols. Component/Number P 311 P 17 P 117 P 338 Soft foam (g) 1720 430 26500 430 Diethylene glycol (g) 1120 140 9100 80 Hexapropylene glycol (g) 285 Di-n-butylamine (g) 64 16 1650 10 Hydroxyl number (mg KOH/g) 356 224 224 173 Viscosity (mPas, 25[degrees]C) 3370 8120 8100 9560 Amine number (mgKOH/g) 48 51 39 36 Table 2. Properties of recycling polyols. P 318 P 338 P 326 Hydroxyl number (mg KOH/g) 81 173 210 Viscosity (mPas, 25[degrees]C) 23,500 9,560 2,560 Amine number (mg KOH/g) 44 36 17 Water content (%) 0.06 0.07 0.07 P 223 P 225 P 222 Hydroxyl number (mg KOH/g) 283 328 382 Viscosity (mPas, 25[degrees]C) 7,860 7,700 1,950 Amine number (mg KOH/g) 43 43 31 Water content (%) 0.03 0.05 0.06 Table 3. Semi-rigid sheets from recycling polyols. P 221 P 222 P 223 P 224 Polyol (g) 135 135 135 135 Lupranol (g) 15 15 15 15 Lupranat M 20 A (g) 82.5 78.8 71 75 Tensile strength (kN/[mm.sup.2]) 32.3 18.2 16.9 16.5 Elongation at break (%) 22.8 18.2 72.8 78.7 Shore A hardness 95 95 91 95 Table 4. Polyols and polyurethanes made of them. P 15 P 134 Soft foam (g) 850 740 Dipropylene glycol (g) 290 119 Polyethylene glycol 400 (g) -- 119 Di-n-butylamine (g) 53 29.5 Hydroxyl number (mg KOH/g) 294 256 Viscosity (mPas, 25[degrees]C) 3,940 9,680 Amine number 17 46 Lupranat M 20 A (mixture ratio) 1:1 1.7:1 Isocyanate index 0.7 0.97 Additives: titanium dioxide (phr) 8 castor oil (phr) 6
[1.] Behrendt, G., and M. Pohl 1998. "Two Waste Streams--One New Technology--a New Family of Valuable Products, "paper presented at Purdue Industrial Waste Conference, West Lafayette, May 1998. * [2.] Behrendt, G., and M. Pohl. 1999. "Verfahren zur Herstellung von Polyolen und diese Polyole," German Offenlegungsschrift 199 17 932, April 16, 1998 / October 21, 1999. * [3.] Behrendt, G., and M. Pohl. 1999. "Verfahren zur Herstellung von Polyurethanen," German Offenlegungsschrift 199 17 934, April 16, 1998 / December 9, 1999. * [4.] Behrendt, G., Pohl, M., Lehrack, U. and J. Volk. 1999. "Verbundstoffe und Verfahren zu ihrer Herstellung, " German Offenlegungsschrift 198 17 541, April 16, 1998/October 28, 1999; Pohl, M., Behrendt, G., Lehrack, U. and J. Volk. 1999. "Polyurethan-Ceralith-Verbundwerkstoffe," presented at the 3rd Beckmann-Symposium, Wismar, June 5, 1999. * [5.] Behrendt, G., and H. Koch. 2001. "Entwicklung neuartiger Betonversiegelungsmaterialien," R&D-project of TAB GmbH and Technische Fachhochschule Wildau, 2001.
Rainer Langenstrassen joined the Institut fur Kreislaufwirtschaft in 1998 and is the project leader for development of polymer recycling procedures. Harald Goering works on nanostructures at the Federal Agency of Material Research and Testing in Berlin. Hannelore Huth is now the leader of the laboratory of polymer analytic at the Institut fur Kreislaufwirtschaft. Svetlana I. Ivanyi is Cand. Ing., studying chemical engineering at the University of Chemical Technology and Metallurgy at Sofia (Bulgaria). Martin Pohl was the project leader in polyurethane recycling and formulation at the Institut fur Kreislaufwirtschaft until 2000. Karl-Heinz Schmidt is the project leader for polyurethane application techniques at the Institut fur Kreislaufwirtschaft. Gerhard Behrendt is professor at Technische Fachhochschule Wildau and has been the manager of the Institut fur Kreislaufwirtschaft since 1995.
Rainer Langenstrassen, Hannelore Huth, Martin Pohl, Karl-Heinz Schmidt and Gerhard Behrendt Institut fur Kreislaufwirtschaft der Technischen Fachhochschule, Wildau, Germany Svetlana I. Ivanyi University of Chemical Technology and Metallurgy, Sofia, Bulgaria Harald Goering Bundesanstalt fur Materialforschung und -prufung, Berlin, Germany
This paper was originally presented at the Polyurethanes Expo 2001 in Columbus, OH. Polyurethanes Expo/Conference 2002, slated for Oct. 13-16 in Salt Lake City, UT, will examine technologies for polyurethane coatings, including a new coatings systems for automotive applications and performance testing results for military and polyurea elastomer coating applications. More info: Lisa Smith, (703) 741-5656.
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|Author:||Langenstrassen, Rainer; Huth, Hannelore; Pohl, Martin; Schmidt, Karl-Heinz; Behrendt, Gerhard; Ivany|
|Article Type:||Brief Article|
|Date:||Jun 1, 2002|
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