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Polyurea spray coatings - Huntsman Corporation

Polyurea spray coatings The technology and latest developments Marc Broekaert Application and Product Development Manager - Coatings Huntsman Polyurethanes




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Polyurea spray coatingsThe technology and latest developmentsMarc BroekaertApplication and Product Development Manager - CoatingsHuntsman PolyurethanesEverslaan 45B3078 Everberg, BelgiumTel. +32 2 758 spray coatings technology is one of the new developments of the last 20 technology combines fast curing, even at very low temperatures, and waterinsensitivity with exceptional mechanical properties, chemical resistance and development of new raw materials and improved spray equipment has made itpossible to overcome the initial problems of this technology such as substrate wetting,intercoat adhesion and surface finish latest development programs are focussing on the extension of the application fieldsthrough the introduction of MDI-prepolymers combining low viscosity with low NCO-content, resulting in slower reactivity and/or higher flexibility. Alternatively,prepolymers with higher NCO-content produce coatings with superior paper details the technology, eradicates the misconceptions and provides an updateon the latest developments in the field of raw materials, formulation and applicationperformance for polyurea IntroductionPolyurea spray coatings technology is a recent development in the polyurethane coatingsindustry. The polyurethane chemistry is about 60 years old. Since the 1970s elastomericurethane coatings have been available. The polyurea elastomer technology wasintroduced some 10 years later. Two main application areas are Reaction InjectionMoulding (RIM) and sprayable coatings combine extreme application properties such as rapid cure, even attemperatures well below 0 C, and insensitivity to humidity, to exceptional physicalproperties such as high hardness, flexibility, tear strength, tensile strength, chemical andwater resistance. The result is good weathering and abrasion resistance. The systems are100 percent-solids, making them compliant with the strictest VOC regulations. Due toits specific curing profile and exceptional film properties, the polyurea spray coatingtechnique developed into various areas, including corrosion protection, containment,membranes, linings and DefinitionThe term polyurea has been wrongly used in the past. The urethane coatings chemistrycan be divided into three sub segments: i/ polyurethane coatings, ii/ polyurea coatings,and iii/ hybrid polyurethane/polyurea coatings, all linked to different isocyanatereactions (Figure 1). Each of these segments deals with systems, which can be aromatic,aliphatic, or a blend of both aromatic and aliphatic. Pigments, fillers, solvents and/oradditives can be introduced to all of A purely polyurethane coating is the result of a reaction between an isocyanatecomponent and a resin blend made with only hydroxyl-containing resins. The finalcoating film will contain no intentional urea groups. A polyurethane system will mostprobably contain one or more A polyurea coating is the result of a one-step reaction between an isocyanatecomponent and a resin blend component. The isocyanate can be monomer based, aprepolymer, a polymer or a blend. For the prepolymer, amine- and/or hydroxyl-terminated resins can be used. On the other hand, the resin blend should only containamine-terminated resins and/or chain extenders and not any hydroxyl reactive polymercomponents. All the polyurea coatings mentioned in the paper comply with 1: Isocyanate A polyurethane / polyurea hybrid coating has a composition which is acombination of the above-mentioned two coating systems. The isocyanate componentcan be the same as for the pure polyurea systems. The resin blend is a blend of amine-terminated and hydroxyl-terminated polymer resins and/or chain extenders. The resinblend may also contain additives, or non-primary components. To bring the reactivity ofthe hydroxyl-containing resins to the same level of reactivity as the amine-terminatedresins, the addition of one or more catalysts is water/isocyanate reaction also produces urea-groups at the end of the , this reaction should not be considered a polyurea reaction since themechanism is a two-step process, which is controlled by the much slowerisocyanate/water reaction, and produces carbon The polyurethane landscapeThe choice between the different polyurethane (PU) technologies is based upon differentparameters (Figure 2). Polyurethane presents the best compromise between cost andquality, but is limited by the application performance. The polyurethane system issusceptible to blistering when the substrate contains more than 5% humidity. This is dueto the competition between hydroxyl-polyols and water for the reaction with anisocyanate group. Humidity content of the environment and the application temperatureare limiting factors for polyurethanes and other chemically reacting systems already have a larger scope of application conditions, but the presenceof catalysts in hybrids makes them more sensitive to humidity than pure polyureasystems. Moreover, because the catalysed polyol/isocyanate reaction behaves differentlyfrom the amine/isocyanate reaction to changing application temperatures, the systembecomes less can be used in extreme conditions. When it is used on substrates almostsaturated with water, polyurea will not provoke blistering nor will blistering occur whenthe air contains high amounts of humidity. Even at very low temperatures (as low asminus 20 C) the polyurea coating will still cure. Polyurea coatings combine highflexibility with hardness. They are the most suitable coatings when the following isrequired: high curing speed, application under high humidity and/or at low temperatures, extreme abrasion resistance, impermeable membranes, high thickness build up, chemical 2: Applicability of the different PU chemistries3- The Applications for Polyurea CoatingsTo be able to define the right applications, a good understanding of the properties ofpolyurea spray coatings is needed. Table 1 provides a general overview of the physicaland chemical properties that can be expected of polyurea spray products. Polyureasystems are known to be very tough. They combine high elasticity with high surfacehardness, resulting in very good abrasion : Typical physical properties of polyurea and their specificationsPropertyUnitSpecificationR esultsReactivityGel timesecondsManual1 - 20Tack free timesecondsManual3 - 120Physical PropertiesShore A-DIN 5350560 100Shore D-DIN 5350525 75TensileN/mm2DIN 5350410 - 30Elongation%DIN 5350420 - 800Angle TearN/mmDIN 5351550 - 125Trouser TearN/mmDIN 5350720 - 60AbrasionmgASTM D 4060-90150 - 500Cold Impact ResistancekJ/m2ISO 18050 100 at -20 CThe market development started in the US, followed by Asia, with a very strong growthduring the second half of the 1990s. In a first stage, polyurea was used as a protectivelayer over polyurethane insulation foam for roofing applications. In Europe, thepolyurea spray coatings market only started to develop in the last few broad window of application conditions, with a high tolerance for humidity, bothfrom the environment and from the substrate, and temperature, makes polyurea a verysuitable coating for concrete in construction applications like roof repair, containmentliners, membranes, car park decks, bridges and offshore. The high abrasion resistanceleads to its application in liners for truck, bulk transport wagons, freight ships andconveyor belts. Table 2 represents an overview of the application fields where polyureais chosen based on one or more of the unique application and/or film 2: Polyurea application fields Roof Coatings Flat Roof Repair Pipe Protection Inner pipe repair Secondary containment Tank coatings Truck bed liners Freight ship liners Bulk transport wagon liners Conveyer belts Car park decks Bridges Offshore4- Raw materialsA polyurea spray coating formulation consists of five different elements:1. isocyanate component;2. (reactive) diluent;3. polyetheramines;4. chain extenders;5. additives and On the isocyanate side:1. IsocyanateSince the most commonly used isocyanate is diphenylmethane diisocyanate (MDI), thispaper focuses on MDI-based products. Aliphatic systems can be used where UV-stability is an polyurea spray coatings use MDI-prepolymers with a NCO-content of 15% to16%. In this NCO-range, a good compromise between viscosity of the material and thereactivity of the system is obtained. Lower NCO-prepolymers have a higher viscosity,but give higher elasticity and slower reactivity. Higher NCO-prepolymers are lower inviscosity, which is good for an effective mix of the two components. However, theybecome much more reactive, with the risk of building up more internal stress. HigherNCO-prepolymers will be used if higher surface hardness is needed. More details aboutthe new generation of products can be found in the chapter on the latest 3 provides an overview of the main properties of the MDI-prepolymers used forpolyurea spray coatings in 3: Properties of the MDI-prepolymers used in Europe for Polyurea Spray Coatings% NCO2 ,4-MDI contentViscosity, Typicalvalue at 20 C, DiluentPropylene carbonate is a reactive diluent for polyurea. Propylene carbonate has a highflash point, low toxicity and should not be considered as a volatile organic compound(VOC)The main advantages of using propylene carbonate are: improved shelf life of the isocyanate-prepolymer; a compatibiliser for the mixing of the two components in the mixing chamber of thespray gun; a viscosity reducer for isocyanate-prepolymers; improved levelling of the applied carbonate reacts with an amine to give a carbamate structure containing asecondary hydroxyl group. Because of the quick reaction between isocyanate and amine,the secondary hydroxyl does not get a chance to react with an isocyanate group. Thepropylene carbonate molecule should, therefore, be considered as a mono-functionalmolecule (Figure 4).Figure 4: Carbamate StructureIn applications where contact with water cannot be avoided, the use of propylenecarbonate should also be limited since propylene carbonate is completely miscible withwater and unreacted propylene carbonate could be extracted, increasing the waterpermeability of the solvents or viscosity reducers can be used if they are compatible with theisocyanate component. They may be considered as a VOC. However, they will increasethe shrinkage On the resin blend or amine blend side:The amine blend used in polyurea spray coatings is a mixture of polyetheramines andchain PolyetheraminesThe main component of the resin blend is a mixture of amine terminated ethylene oxideand/or propylene oxide polyether with molecular weights varying from 200 to 5000g/mole. The primary amine groups provide a very fast and reliable reaction with theNCO-groups of the isocyanate component. Table 4 represents the properties of thepolyetheramines commonly used in 4: PolyetheraminesMolecular WeightFunctionalityViscosity, Typicalvalue at 25 C, 150003820Amine 220002250Amine 3400370Amine 4400221Amine 520029RONOCH3CH3OOH2. Chain extendersDiethyl-toluenediamine or DETDA is the standard chain extender used in aromaticpolyurea spray coatings. DETDA contributes to the hard block and improves the heatresistance of the cured film. It is the most reactive amine in the resin blend but, becauseof the phase separation during the curing, it controls the reaction mechanism and makesit possible to spray a polyurea chain extenders like dimethylthio-toluenediamine (DMTDA), N,N -di( )-amino-biphenyl methane (DBMDA) or 4,4'-methylenebis-(3-chloro, 2,6-diethyl)-aniline(MCDEA) slow down the reaction significantly. Table 5 lists various chain extendersand their 5: Chain extendersMolecular WeightFunctionalityViscosity, Typicalvalue, Extender 11782280 at 20 CChain Extender 22142691 at 20 CChain Extender 331028 at 38 CChain Extender 43792Solid at 20 CSlowing down the reaction also means that the competition with the water reactionbecomes more important and precautions need to be AdditivesDepending on the application, additives, pigments and/or fillers are introduced to theformulation. The addition of pigment and/or fillers is limited because the viscosity of thetwo components at the application temperature has to be kept under control. Higheramounts of fillers and reinforcement fillers can be added to the system as a Product application specificsThe most important element of handling polyurea coatings is the mixing. Good mixingwill be obtained in a suitable mixing module by impingement with mechanical pressure and temperature of the products will also help to optimise themixing of the high cure speed of polyurea and the short mixing time, the products aremixed by impingement at high pressure. Certainly for field applications, it is preferableto formulate the products on a fixed 1:1 volume-mixing ratio. The pressure used in thefield will vary between 150 and 250 bar. The viscosity of the products at applicationtemperature ideally needs to be lower than 100 and the viscosity of the twocomponents needs to be of the same level. Figure 5 shows the viscosity of the MDI-prepolymers at different temperatures. The properties of these prepolymers can be foundin table viscosity of the resin blend at 25 C is of approximately 900 , dropping below100 at application have proven that polyurea films produced at 65 C, 70 C and 80 C havedifferent properties and that these improve with increasing temperature. The new sprayequipment allows different temperature settings for the two components, ensuring anoptimum mixing in the spray 5: Effect of temperature on the viscosity of the isocyanatesThe spraying equipment has improved significantly. New features are: the separate temperature setting for both components; easier variable ratio settings; easy output control; easy monitoring of application index of a polyurea system is typically kept at a slight over-index of the isocyanatein the range of As the isocyanate-group reacts to humidity, the excessisocyanate compensates for the loss of isocyanate-groups during storage and/orapplication. The film properties for 1:1 volume ratio sprayed system were measured foran index variation between and The test results indicate that the film performsbest at an index of and higher. Below an index of the results can varysignificantly and become unpredictable, even for an index shift of [ C]Iso 1Iso 2Iso 3Iso 4Iso 5Iso 66- Misconception/past problemsThe application of polyurea has known some problems during the initial start up phase,which are at the origin of the misconception still existing about polyurea problems can be attributed partly to the lack of experience at the time of theintroduction of this technology, partly to the lack of adequate application equipment, andpartly to the fact that this new technology could not be applied in the same way as theexisting coating polyurea was first presented, the initial misunderstanding started, as it simplylooked almost too easy to apply: Polyurea is very fast, the coating can be put in serviceimmediately after the application and the final properties of the coating are obtainedonly a few hours afterwards; it is not water or temperature sensitive, and is easy toformulate and produce. Below is a list of common concerns resulting from unsuccessfultrials and their solutions:1. The system is too fast, intercoat adhesion is therefore first systems on the market were indeed very fast with a gel time of maximum 2seconds. Lab tests with times between coats of several weeks have shown that intercoatadhesion is very good, also with these very fast systems. When problems occur withintercoat adhesion, most of the time they can be related back to problems with the rawmaterials, the manufacturing of the systems or the spray equipment problems or a disturbance of the feeding of one or both componentstowards the mixing module can cause poor mixing. Adapting the machine settings ofthe spray can solve Surface quality is very to the high reactivity of the systems, the surface quality of the sprayed film wasinitially very poor. The fine-tuning of the spraying equipment was a first improvementfor solving that problem. The use of non-VOC, reactive diluents and the development ofnew MDI-prepolymers with higher 2,4 -isomer content resulted in perfect surfacequality without compromising on working Too fast build up of layer initial applications of polyurea spray coatings resulted in high layer development of the spray equipment provided access to applications where onlya few hundred microns were needed. Industrial applications looking for 100 to 150microns will be available in the near Substrate wetting is very , this was a problem linked to the development phase of polyurea with the use ofextremely fast spray systems. Development programs focusing on adhesion on concrete,with polyurea systems presenting gel times of 3 to 4 seconds, resulted in cohesiveadhesion failure in the concrete. In practice, to limit the risks under variable fieldconditions, a multilayer system is applied, made of a primer and a Cost of the system (raw material cost versus project cost and product lifecycle). Pure polyurea systems are more expensive, when considering the raw materials costalone, but can be applied in areas where any other systems will fail. While estimatingthe capital for a project, polyurea is even more competitive, when both the processingtime and the waiting period are included, before putting the coated substrate back Equipment initial investment in equipment is rather costly. As highlighted above, the successof the project is very equipment and applicator dependent and we believe that the highentry barrier can only guarantee quality services from specialised and skilled Experienced experience and motivation of well-trained applicator teams is as important as thespray equipment, the choice of raw materials, the adequate personal protectiveequipment and the formulation of a suitable Latest developments1. Influence of the functionality of the coatings are known for their chemical resistance and toughness. For someapplication areas like primary containment and inside oil-pipe coatings, a high chemicalresistance is needed. A way to improve chemical resistance is by increasing the crosslinkdensity. The following conclusion results from one of our experimental programs:With increasing functionality of the polyurea system: the viscosity of prepolymer increases and the mixing becomes less efficient; the gel and tack free time decreases and the surface quality becomes very poor. Atprepolymer functionalities above the systems cannot be processed anymore; the physical properties improve until a functionality of about is reached; , the physical properties decrease with the increasing functionality of the polyureasystem; The flexibility of the system decreases; The abrasion resistance decreases; The chemical resistance expected improvements of physical and chemical resistance properties are notobtained because of the loss of crosslink efficiency with increasing functionality of thepolyurea system. In a typical formulation with a gel time of 2 to 4 seconds, afunctionality of or below should be 6: Film properties as a function of the functionality of the systemSystem12345678910Functionalityof the the time(seconds)43423442<1<1Tack freeTime(seconds)7896558522Surfacequality++++/--+++/---Tear (N/mm) (N/mm2) (%)3152251921361102851821509168Shore A93979595979295969594Shore D445145495046484545452. 2,4 -isomer content of the higher sterical hindrance of the 2,4 -isomer has an effect on the reaction time. Thelonger gel time and open time result in: less critical application conditions setting; better substrate wetting; superior adhesion on a variety of substrates; improved levelling behaviour resulting in a better surface quality, and enhanced physical properties (Table 7).Table 7: Influence of the 2,4 -contentSystem1112131415*2,4 content of the MDI2530405050Gel time(seconds)34566Tack freeTime (seconds)66788Surface quality-+/-+/-++Tear (N/mm) (N/mm2)9585626381Shore A9799979396Shore D5455525253* Slightly higher functionality3. Fast property coatings are mainly used in applications were fast curing is needed. When usedas a corrosion protection on pipes, storage of high volumes of coated pipes is difficultand, because of the weight, the coating needs to be fully cured before being used for pier protection needs to be fully cured before high polyurea coating builds up high internal stress during the initial phase of the curingdue to the high reactivity. The stress has a negative influence on the development of thephysical properties of the freshly applied polyurea film. By modifying the MDI-prepolymer, it is possible to improve the relaxation of the coating and thereby reduce thewaiting period before the applied coating can be put in service. The improved relaxationresults in: less stress build up; no deformation; improved adhesion, and faster physical properties this study the cold impact resistance was tested, along with standard physicalproperties (table 8a). Cold impact testing within the hour after application proved to be avery reliable measurement of property development as a function of time. The goal wasto develop the properties faster without compromising the end properties as shown intable 8a: Cold impact resistance at -20 C (kJ/m2)SystemTime in days* * Time between application and testingTable 8b: Physical Properties after 14 daysSystem161718Aspect+/-++Cold impact resistance at-20 C (kJ/m2) (N/mm) (N/mm2) (%)401373383Taber abrasion, H18, 1kg,1000 cycles (mg weight loss)2994202704. Flexibility and/or polyurea spray coatings are formulated with a MDI-prepolymer of approx. 15%NCO on one side and a blend of Polyetheramines and DETDA on the other side. Forfield applications, it is preferable to stick to an index of about for productconsistency and a 1:1 volume-mixing ratio for practical reasons. However, theselimitations always result in film properties with comparable physical properties. Slightmodifications could be made by adding secondary or sterically hindered diamines, or byintroducing additives like fillers, diluents or coatings combine surface hardness with flexibility and hence result in toughcoatings with good abrasion resistance. This combination of properties is the result of thesoft block-hard block balance in the system (table 9).Higher elasticity values up to 1000% can be obtained by lowering the hard block can be done by: using lower NCO-containing prepolymers; changing the mixing use of lower NCO-prepolymers is limited by the viscosity increase. The mixing ratiovariations will be limited by the mixing efficiency decrease at extreme coatings can be formulated in line with the physical property modifications formore flexibility. With higher NCO-prepolymers, additional hardblock can be built in,resulting in a higher surface hardness. Those high NCO-prepolymers are lower inviscosity, improving the mixing. However, the higher reactivity results in: higher internal stress, making those systems very brittle during the first 24 hoursafter the application; shorter gel times resulting in a limited flow and possibly a poorer surface 9: High flexibility/ high hardness systemsSystem1920Reference21*22MDI IsocyanateIso 1Iso 1Iso 2Iso 5Iso 6Gel time (seconds)713391Tack free time (seconds)21375222Surface quality++++-Tensile (N/mm2) (N/mm)534163113124Elongation (%)615750393273241Shore A7869959997Shore D2620466766Taber abrasion, H18, 1kg,1000 cycles (mg weightloss)386430356226139* Slow formulation for improved flow5. polyurea technology provides the opportunity to produce durable and high-performance coating films very rapidly, even in difficult conditions. However,experienced applicators have reported encountering undesirable side effects varying frompinholes even to delamination. In practice, the risks of failure can be limited by the useof a system consisting of a suitable primer/sealer combined with a polyurea general study was performed with an acrylic emulsion, a high solids epoxy, anemulsifiable MDI and a two component PU system on dry and wet concrete, steel,plywood and fiber cement board. Table 10 presents an overview of the obtained 10: Adhesion on different primers (N/mm2)NoprimerAcrylicEpoxyEmulsifiableMDI2-ComponentPolyurethaneDry * Cement * Time between primer application and polyurea spraying 2hours/24 hours The following conclusions can be made: on dry concrete all primers generated improved adhesion results; on wet concrete the primers produced inferior adhesion results with the acrylicemulsion performing better than the other primers; on steel the adhesion values with or without primer are of the same order ofmagnitude (cohesive failure of the epoxy adhesive between polyurea film and thepull-off adhesive test s dolly); also on plywood the adhesion with or without primer is similar; on fiber cement board all primers, except for the emulsifiable MDI, perform Adhesion on influence of temperature and humidity content on the adhesion performance onconcrete is summed up in table 11. The following conclusions can be made: for all systems applied at 23 C, a cohesive substrate failure is observed; without primer, the adhesion is insufficient at 8 C. A primer is recommended; at 8 C epoxy primer 1 performs better than epoxy primer 11: Adhesion on concrete (N/mm2)DryWet8 C23 C8 C23 CNo > * > primer 1> > > > primer > > * cohesive failure of the concrete8- ConclusionsPolyurea holds a unique position in the coatings industry as well as in the polyurethanecoatings industry. The new developments both for the raw material and the applicationequipment have enlarged the application portfolio considerably. The important advantagesof polyurea spray coatings are their reactivity, water insensitivity, low temperature curingand their unique physical and chemical its raw material cost, higher than for most other systems, polyurea can still be themost cost-effective system available at present for consequent and specific coatings will not replace all other systems, but have their place in high growthniche coatings markets. If one or more of the unique performance properties are met,polyurea can be the best or even the only suitable solution available depending on end-properties required or application ultimate success of a polyurea system for a project will always be dependent on theinvolvement of the four key players, namely the raw material supplier, the equipmentmanufacturer, the systems house and the Johan Van Tongelen, Untapped potential , guest editorial, European CoatingsJournal, January-February, 20012. Chris Godinich, Polyurea: a market overview , European Coatings Journal, October2000, p. 543. Dudley J. Primeaux II, Fast-curing polyurea spray elastomers rapidly spreading incommercial use , Urethanes Technology, October-November 2000, p. 374. Dudley J. Primeaux II, Spray polyurea versatile high performance elastomer for thepolyurethane industry , Polyurethanes 89 Proceedings of the 32nd annualtechnical/marketing conference, SPI, San Francisco, October 1989, p. 1265. Aureliano Perez, Jay A. Johnston, Performance and processing enhancements ofaromatic polyurea elastomer systems prepared from high 2,4 -MDI isocyanates ,Proceedings of the Polyurethanes Conference 2000, October 8-11, 2000, Boston6. Marc Broekaert, Wolfgang Pille-Wolf, The influence of isomer composition andfunctionality on the final properties of aromatic polyurea spray coatings ,Proceedings of the Utech 2000 Conference, The Hague7. Marc Broekaert, Modified MDI-prepolymers improve the initial physical propertiesand reduce the in-service time of aromatic polyurea coatings , Proceedings of the6th N rnberg Congress Creative advances in coatings technology, April 2-4 , 2001,N rnberg, p. 7618. Marc Broekaert, Profits in the pipeline , Polymer Paints Colour Journal, July 2001,p. 189. Aureliano Perez Jr., Calvin C. Shen, Performance enhancements of aromaticpolyurea spray coatings by the use of conventional primer systems , presented at thePolyurea Development Association in New Orleans, Louisiana, , November 29 December 1rst, 200010. Gusmer Corporation, Direct impingement mixing for the spraying of polyurea,1st Annual PDA meeting, 30/11-1/12/2000, New OrleansThe information and recommendations in this publication are to the best of ourknowledge, information and belief accurate at the date of publication. NOTHINGHEREIN IS TO BE CONSTRUED AS A WARRANTY, EXPRESS OR OTHERWISE. Inall cases, it is the responsibility of users to determine the applicability of suchinformation or the suitability of any product for their own particular IN THIS PUBLICATION IS TO BE CONSTRUED AS RECOMMENDINGTHE INFRINGEMENT OF ANY PATENT OR OTHER INTELLECTUAL PROPERTYRIGHT AND NO LIABILITY ARISING FROM ANY SUCH INFRINGEMENT ISASSUMED. NOTHING IN THIS PUBLICATION IS TO BE VIEWED AS A LICENCEUNDER ANY INTELLECTUAL PROPERTY sale of any products referred to in this publication is subject to the general termsand conditions of Huntsman International LLC or its affiliated Polyurethanes is an international business unit of Huntsman InternationalLLC. Huntsman Polyurethanes trades with Huntsman affiliated companies in therelevant countries such as Huntsman International LLC in the USA and HuntsmanHolland BV in Western 2002 Huntsman International LLC. All rights reserved. 01-2002.

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