Introduction To Polyurethane Foam Engineering Essay

Introduction To polyurethan froth applied science Essay polyurethanes be broad class of tangibles apply wide in many applications. Polyurethanes ar in any fact written as PUR. Polyurethanes also called as urethanes argon characterized by urethane linkage -NH- C (=O) O . This linkage is form due to the chemical reaction of isocyanate group with hydroxyl group as shown in the following equation. 2Equation 1.1 Equation showing the reaction of urethane linkage in polyurethanes. 2Polyurethanes ar discover by Otto Von Bayer co workers in 1937. 3 The sign social organization of urethanes is given asAnd they rat be con officered as esters or amide esters of carbonic acid. 3 The polyurethanes be also sometimes called as urethanes but and they ar also called as isocyanate polymers. They atomic number 18 synthesized by the reaction of polyfunctional hydroxyl compounds with polyfunctional isocyanates. 3 The twist of polyurethane formed from di hydroxyl compound and di isocya nate is given asPolyurethane is widely apply in diverse fields much(prenominal) as making of plastics, cushions, form bubbless, rubber goods, synthetic leathers and fibres. The total annual production of urethanes in the world is estimated to be 8 million tons per year and is change magnitude 4-5 % yearly. 4 Polyurethane is a versatile polymer having unique chemistry with excellent mechanistic and optical properties and have good solvent resistance. 5 Polyurethanes argon materials with many applications solely major applications are in furniture industry, form bubbles industry, twist anatomical structure and shoe industry and also polyurethanes can be utilise in medicinal and agricultural applications. 6 Polyurethanes have humongous number of applications and uses in disparate areas due to their versatility but most important application of polyurethane which has covered almost 29% of the total market of polyurethane is polyurethane effervesce. 71.2 Polyurethane FoamThe major application of polyurethane is polyurethane sparkles which are extensively utilise in many applications. They are referred as PUR scintillates and they are inclined(p) by the reaction of addition, condensation or cyclotrimerization. 2 spare-time activity defer shows the typecast of reaction in the form bubbles arrangement and the resulting effervesce property fork over in the fizz produced by that respective reaction.FoamReactionFoam PropertyPolyurethanePoly additionFlexible and strongPolyisocyanuratePoly cyclo trimerizationRigid polymeric amidePoly condensationFlexible and pissedPolyimidePoly condensationSemi rigid and rigidPolyureaPoly additionFlexible and rigidPoly CarbodiimidePoly condensationSemi rigidPoly Oxazolid champion work party opening Poly additionRigid and semi rigid give in 1.1 Table showing antithetical types of foam base on their synthesis reaction 2Mainly PUR foams are class into two types which is elastic and rigid foam and then limber an d rigid foam are classified into various sub types depending upon the opposite type of applications in which they are utilise.Polyurethane structure consist of a polyol and polyisocyanate luck we can say that polyols are the edifice blocks and isocyanates are jointing federal agents. So polyurethane foam chemistry is called as building block chemistry. All kinds of polyurethane foams are active with the proper excerpt of polyol and isocyanate luck with respect to chemical structure, equivalent weight and functionality. 2 Following table shows the classification of PU foam with respect to polyol comp unmatchablent and functionality.PolyolRigid foamSemi rigid foamFlexible foamOH No.350-560100-2005.6-7.0OH equal No.160-100560-28010,000-80Functionality3.0-8.03.0-3.52.0-3.1Table 1.2 Classification of polyurethane foam w.r.t polyol and functionality 21.3 Foam expression TechnologyPolyurethane foams are watchful by mixture isocynate component in polyol having throttle, fillers , additives, surfactants and other chemicals in it. No heating is required at room temperature. 21.3.1 foamy SystemsFoaming strategys are classified into three types based on the type of chemicals used in the synthesis dish up. These types are unmatchable step unmatchable slash dodgeQuasi Pre polymer system total Pre Polymer systemOne step system and Quasi system are mostly used in sparkly industries now in which one step process is used majorly while pre polymer system was used alone in the early times of urethane industry. 21.3.1.1 One step one shot SystemIn one step system Component A and Component B are taken separately. Component A contains completely polyisocyanate component while component B contains polyol, surfactant, blowing agent and catalyst. Both components are miscellaneous which led to the formation of foam.1.3.1.2 Quasi Pre polymer SystemIn this system in component A polyisocyanate component is taken with polyol and in component B recumb of the ingredients are taken with polyol which allow ins catalyst, blowing agent etc. immix forms a foaming product.1.3.1.3 Full Pre polymer SystemIn full prepolymer system in component A poly isocyantae component is taken and polyol is also added in it while in component B polyol is not added while the rest of chemicals like blowing agents, surfactants and catalyst are taken. Components A B are composite and foam is formed.These foaming systems show only two component system however in industrial processes there are modifications. For example in s science lab sway process three or four streams are employed carrying different reactants. 21.3.2 Foaming ProcessesMainly three types of foaming processes are used, which are loving cupful foaming, corner foaming and mechanism foaming. Machine foaming is further classified into various foaming processes. 21.3.2.1 Cup FoamingThis foaming process is also known as hand change integrity. This method is mostly used for lab scale synthesis of foaming prod ucts. In this process mixture is through with(p) in paper or plastic cups thats why called as cup foaming. In cup foaming poly isocyanate component is taken in a cup and rest of the reactants are also taken in a separate cup which includes polyols, catalysts etc. Then both the components are involved apply electric balance or by hand mixing and a foaming material is formed in the shape of a cup. This is the simple and cheap foaming process thats why used widely on lab scale.1.3.2.2 boxwood FoamingBox foaming is give way than cup foaming to obtain sufficient amount of samples for evaluating foam properties for machine foaming. The sizes of the box range from 15x15x15 cm and 30x30x30 cm. The inside of the box is lined with workmanship paper. The procedure is almost similar to that of cup foaming and mixing is through with(p) through electric drill equipped with mixer. Immediately after mixing system is poured into the box and allowed to rise to obtain foam. Foam is vulcanised at room temperature after some time. 2 This method is also used largely on lab scale to produce foam.1.3.2.3 Machine FoamingIn machine foaming variety of machine processes are available which are one by one described as under. 21.3.2.3.1 Large Box FoamingIt is a dis invariable process used to produce micro foam blocks with smaller volumes. The size can be 1x1x2 meters. Due to exo caloric conditions small modification is required in the process as compared to the box foaming process.1.3.2.3.2 Slabstock FoamingSlabstock foam is made by the continuous gushing of foamable suaves on a moving conveyer. A cut-off segment of the continuously produced foam loaf is called a block or bun 2. In the case of polyether-based flexible urethane foam, a slabstock foam size can be most 1 meter postgraduate and 2 meters wide, with a foam denseness of 1.6 to 2.0 pound/ft3. The shroud section is rectangular with a crown- make top surface. The higher(prenominal) the crown, the less the yield o f available foam. Two techniques canto used to reduce the crown. One method is to pull vertical sides of rising foam. Another technique is to reduce the top of crown surface. Equipment for doing this is commercially available. 21.3.2.3.3 Pour-in-Place FoamingThis process includes pouring of foaming ingredients into a void space to form an integral part of the foam and substrates. Products which use this process are household refrigerators and deep freezers.1.3.2.3.4 Sandwich Foaming and MoldingSandwich foaming is used to produce sandwich panels from foam malls. It can be produced continuously victimization conveyers or discontinuously using jigs. Surfaces material can be craft paper in it. Molding is used to produce shaped foam products such as car seating room and furniture. Reactants are placed in mold cavity and cured in the mold. After curing molded foam is removed. 21.3.2.3.5 sprayer and frothingSpraying is a unique process used for urethane and iso cyanurate foams .It crea tes insulation layers not only on savorless surfaces like roofs but also on non flat surfaces such as spherical tanks and pipes and building structures such as frames. form bubbles process in urethane systems is similar to that of shaving cream. There are different types of frothing processes which are conventional frothing processes, chemical frothing and thermal frothing etc. Frothing process usage depends upon the reactants and conditions and which type of foaming product is required. 21.4 Types of Polyurethane foamsmajor(ip) classes of polyurethane foams are flexible and rigid foam further these two types are more classified tally to their extensive applications.1.4.1 Flexible Polyurethane foamFlexible polyurethane foams are synthesized by slabstock process or by boundary line process and they are also classified further on the basis of technique used for their synthesis. They are also classified on the basis of polyol in polyether and polyester foams. Slabstock foams includ e conventional polyether foam, high-resilience (HR) foam, visco-elastic foam, super- softening foam, vital force- entrancing (EA) foam, semi flexible foam, and flexible polyester foam. molded foams are classified in two classes hot molded foam and frigid molded foam. 2 All classes of flexible foams are explained one by one as follows .1.4.1.1 Slab stock foamThe contionous piece of foam by the continuous pouring of foaming ingredients on a continuously moving conveyer is called slab stock foam. A cut off segment of slab stock foam is called as bun foam. Slab stock process is widely used in industry in production of flexible polyurethane foam. 2In slab stock foam process inclined conveyer is used from the beginning of urethane industry. Following figure shows the production line of contionuous slab stock machine.Figure1.1 Continuous slabstock machine 2The cross section of slabstock foams produced by the inclined conveyer process is not precisely rectangular and has crown shape. A c rown-shaped cross section of foam bun results in a lower yield of fabricated foams. Accordingly, some modify processes to obtain rectangular cross sections have been proposed. One step process is widely used in these foaming systems. All ingredients are pump into the mixing base on balls through several streams and are poured from the mixing head onto the moving conveyer. From the standpoint of viscosity and metering accuracy, some ingredients are preblended. These blends include a blend of water and amine catalyst, a blend of tin catalyst and polyol, and a blend of physical blowing agent and polyol. The reaction temperatures in event foam usually reach about 160 to 170C. The exothermal heat is importantly a function of the water-isocyanate reaction. The reaction temperatures are affect by the isocyanate index, water level, and catalyst concentration.2Poly ether slab-stock foam is important in slab-stock flexible PU foams and it is produced by this slab-stock process widely in industries.1.4.1.2 wrought Flexible foamsMolded flexible foams are used for making shaped products such as automotive seats, child seats, head restraints, vibration damping for automobiles, build rests, furniture cushions and mattresses. The dumbness distribution of molded foams is composed of high density throw together foam and low density core foam. In the molding process mixed foaming ingredients are poured through a mixing head into a preheated mold made of aluminum, steel, or epoxy resin. The mixed ingredients flow and expand in the mold, and then the molded foams are unploughed at the required curing temperature for a limited time, which is followed by de-molding.2Molded flexible foams are further classified into hot molded and rimy molded flexible polyurethane foams.1.4.1.2.1 tempestuous Molded flexible foamsHot molded foam is produced using conventional polyether polyol with TDI 80/20. In 1961 hot-molded urethane foam mattresses was commercialized that provided bet ter sleeping comfort than slabstock foam mattresses and greater durability. Because of the comparatively higher cost, however, the molded mattress was not competitive with slabstock foam mattresses, and production was discontinued. 21.4.1.2.2 refrigerant Molded flexible foamsCold molded flexible foam is prepared at very(prenominal) low mold temperatures of 60 to 70 C with mold retention time of 10 minutes and then cured in a separate oven or at room temperature. In this type mostly isocyante components used are blends of TDI MDI and polyol used is polymer or graft polyol. Dual hardness automotive seats are made by this process using graft polyols. 21.4.1.2.3 High Resilience HR foamsHR foams have higher resiliency than conventional flexible foams. These foams are prepared by cold molded process. The verbalism principle is to reduce intermolecular interactions such as hydrogen bonding of urethane linkages, irregular structures of polymeric molecule, and so on. High Molecular weig ht polyether polyols are used in the formulation of these foams. Polyisocyante components used are blends of TDI MDI with the weight ratio of 80/20. Also polymeric MDI alone can be used. HR foms are widely used in furniture and automotive applications. 21.4.1.2.4 Visco-elastic foamVisco-elastic VE foams are characterized by slacken recovery after coalescence. The foam is also called low-resiliency foam, slow-recovery foam, ergonomic foam, better-riding comfort foam, and temperature-sensitive foam. VE foams are used by NASA in early 1960 but they are highlighted commercially only in the recent years. VE foams are synthesized using polyol blend of high and low molecule weight polyols with TDI or MDI, and they can also be produced using blend of MDI TDI with polyether polyol. TDI-based VE foams are soft to the touch and have very low resilience and slow recovery. MDI-based foams are easier to process and can be produced in a wider range of isocyanate indexes. However, physical stre ngths of MDI-based foams are lower, resilience is higher, and compression set is better than TDI-based foams.The VE foam market includes seat cushions for people who top a long time sitting such as transport drivers, office workers, and airline pilots, as well as for NASAs space raspberry seats, wheelchair seats, and so on sporting goods that require energy absorption such as gym mats, helmet linings, leg guards for ice hockey, ski boots, and ice skates. 2Our main product is VE foam and it is further explained in the later chapters.1.4.1.2.5 Super soft slab-stock foamThis foam can be prepared by using a high molecular weight polyether triol with TDI 80/20. Blowing agent can be water alone or some physical blowing agent can be used with water. It is a low density foam. Major market of super soft foam is high quality tail end cushions for sofas. This foam also have low cross linking density. 21.4.1.2.6 Semi flexible slab-stock foamThese foams have high open cells, high load pram and high energy absorbing characteristics. These foams are used in large number of automotive applications such as bumper cores, interior knee bolsters, side impact absorbing door panels, and headliners under the automotive roof. Due to energy absorbing characteristics this foam may be called as Energy absorbing EA foam. 21.4.1.2.7 Reticulated foamIt is 100% open cell structure foam with no cell membranes. Removal of cell membranes for polyether foam is possible when membranes are change state with an alkaline solution. Reticulated foam find its applications in various mats, filters and pads.2 Mostly the foam used in floor mats is this type of foam and it is mostly used in making mats and filters because it is completely open celled foam.1.4.1.2.8 Integral skin flexible foamIntegral skin foam is also called self skin foam. It consists of high density skin foam and low density core foam that is sandwich structure. The mold temperature for integral skin foam is guardedly controlled at 40 to 70 C. Water can be used as a blowing agent but it produces thin skins. Integral skin foam is prepared by open mold process or by reaction injection molding. 21.4.1.2.9 Micro-cellular ElastomersThese are also called foamed urethane elastomers. The density is in the range of about 320 to 960 kg/m3. Micro-cellular foams are prepared by using aliphatic polyester diols with poly tetra methylene ether glycol (PTMEG). The poly isocyanate component used is TDI pre-polymer and liquid MDI. Also chain extenders and cross linkers are used. Water is used as a blowing agent. These elastomeric foams are used for various shock absorbing elements in vehicle suspensions, precision machines, shoe soles and sports shoes etc. 21.4.1.2.10 Shoe fillet of sole foamThe advantages of polyurethane foam in shoe soles include high slit resistance, high flexibility, low density, high cushioning, and solvent resistance. In addition, the take away molding of the sole with the upper part of shoe makes it possible to add-on production efficiency and lower production costs. Casual shoes are produced using polyether-based foam systems. Some sports shoes such as tennis shoes are produced by polyester foam systems, because polyester-based foam has higher abrasion resistance, tensile strength, and elongation at break in comparison with polyether-based foams. 2