Manufacturing Of Pu Foams

Manufacturing of PU foams

1. INTRODUCTION The term “cellular plastics” encompasses a range of materials with widely varying properties and fields of application. Virtually most polymers, thermoplastic or thermoset can be made into a cellular or foamed form with resulting products having wide range of densities. Foams can be rigid, semi rigid or flexible. In general, cellular plastics can be produced in the form of slabs, blocks, boards, sheets, molded shapes and sprayed coatings. Today it is possible to arrange the cells so that a product may have an essentially solid skin surface and a cellular core. There are various techniques for the production of cellular materials. A range of polymers can be processed either by physical or chemical expansion system in the production of cellular plastics. Foams are used because 1. They have increased strength to weight ratio than conventional injection molded solids. 2. They are used because reduction of sinkmarks in areas opposite to thick sections. 3. Reduction in manufacturing costs due to lower injection pressure encountered. 4. Can be used and thrown for ex. EPS 5. They can offer cushioning effect.

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Manufacturing of PU foams

2. BLOWING AGENTS Over the years many methods have been devised for producing cellular plastics of which most important are 1. Incorporation of a chemical compound which decomposes at processing temp to yield volatile reaction products. 2. In corporation of Low boiling liquids which volatilise during processing temp. 3. Diffusion of Gases into the polymer under pressure with subsequent expansion of composition all elevated temp. 4. Incorporation of powdered solid CO2 which volatilises at Elevated Temp. 5. Water produced in exothermic chemical reaction is volatilised within the mass by the heat of Reaction. 6. Chemical reactions of polymer intermediates during polymerization. This is important with polyurethanes. 7. Mechanical whipping of polymers in liquid form and subsequent ‘setting’ in whipped state. 8. Incorporation of hollow or expandable spheres of resin or of glass.

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Manufacturing of PU foams

CURRENT EXAMPLES OF THE BLOWING AGENTS Blowing Agent

Volatiles

Decomposition

1. Azocarbonamide

produced N2 , CO, CO2

range (oC) 190-230

2. Dinitrosopenta-

N2 , NO, H2O, 160-200

Used in Natural & synthetic

methylenetetramine

CH3NH2

Rubbers and some use in

3. Benzenesulphono-

N2 , H2O

150

Comments Used for PVC & polyolefins

polyolefins. This powder is affected by

hydrazide

phthalate

4. 4, 4'-oxybis

plasticisers. Faster decomposition rate than

N2 , H2O

150

(benzenesulphonohydrazide) 5.

and

phosphate

azodicarbonamide N2 ,

95-98

Decomposition products are toxic. Low cost and used for Rubber

Azoisobutyronitrile 6. NaHCO3 (Sodium

CO2

100-130

bi-carbonate) 7. Terephthalazide 8.

N2 , N2 , NH3

85-112 275

and for most plastics.

Trihydrazinotriazine

Due to its high Decomposition temp,

it

can

successfully

for

Polycarbonate, 9. Chloroflurocarban

be

used Nylons,

&

most

thermoplastics. Use For PU foam.

CFCl3 & CHFCl2 & CF2Cl2

3. SELECTION CRITERIA Requirements for blowing agents

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Manufacturing of PU foams

1. The Gases should be evolved within narrow but clearly defined temp range & in controlled manner. 2. The Decomposition temp range for a blowing agent should not be above the maximum processing temp if significant degradation is not to occur. 3. Gases should not corrode the processing equipment/mould plates, mixing equipment. 4. Low cost. 5. Ease of Availability. 6. Should not be toxic.

4. PU FOAMS Chemistry and Manufacture C.O.E. & T;Akola

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Manufacturing of PU foams

For Polyurethanes only a few Isocyanates are used commercially and they are 1) 80: 20 TDI i.e. 80:20 mixtures of 2, 4 – tolylene diisocyanate with 2, 6 – tolylene diisocyanate.

CH3 |

CH3 | NCO

OCN

NCO

| NCO 2,4 isomer

2,6 isomer

2) 65:35 mixtures of the above. 3) Diphenylmethane diisocyanales (M D I) 4) Naphthylene diisocynate NCO |

| NCO 1,5

Naphthylene diisocynate

5) Hexametheylene diisocyanate and its Derivatives.

Chemistry Polyurethane foams are prepared by reacting hydroxyl-terminated compounds called polyols (usually of polyster or polyether Family) with a polyisocyanate.

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Manufacturing of PU foams

In production of urethane foam two reactions occur. The first is a reaction of polyisocyanate, which is present in excess with the hydroxyl groups of polyol NCO

+

HO -

NHCO

(Diisocyanate) + (Polyol)

O A urethane

Ex. O = C = N – R – N = C = O + *HO-R ...... R-OH* O = C = N – R - N = C = O + *HO-R...... R-OH* (Polyisocyanate)

+ polyol

O || OCN – R – N – C – OR ...... + | H O O || || R – O – C – N – R – N – C – OR ....... R – OH* | | H* H* ( Polyurethane ) The IInd Reaction which generates the blowing Gas & produces the Expanded foam structure. For Low Density flexible foam, The blowing agent is CO2 produced during the reaction of excess Isolyanate and water.

NCO + H2O NCO ( Excess icocyanate ) C.O.E. & T;Akola

NH | C=O | NH

+ CO2

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Manufacturing of PU foams

The Density of product depends on amount of CO 2 evolved and can be reduced by increasing the isocyanate content of the reaction mixture and by corrospondingly increasing H2O to react with excess isocyanate. As a rule of Thumb, high molecular weight, low functionality polyols produce molecules with a low amount of cross-linking and consequently form a flexible foam. Conversely low molecular weight polyols of high functionality produce a structure with a high degree of cross linking and therefore the rigid foam.

5. MODIFIERS AND ADDITIVES Certain other ingredients are 1. Catalysts primarily tertiary amines are added to accelerate the rate of Reaction. 2. Surfactants for Ex – Silicone copolymers are used to develop a fine and uniform cell structure. 3. flame Retardants for Ex halogenated and Phosphorous compounds to reduce combustibility. 4. Dyes and pigments to colour the PU foam. 5. Filler = strength is increased. Mechanical and physical properties are increased & cost is reduced, Ex barytes, CaCO3 , talc & Kaolin.

6. FLEXIBLE FOAMS

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Manufacturing of PU foams

Polyurethane foams may be rigid, semirigid or flexible. They may be made from polyesters, polyethers or Natural polyols. This section deals with only flexible foams 1. One shot polyesters. 2. Polyether prepolymers 3. One shot polyethers. 1. One shot polyester foams Foams can be made from polyester resins by addition of 65:35 TDI, water, a catalyst, an Emulsifier, a structure modifier and paraffin oil which helps to control pore size and prevents splitting of the foams. Among the catalysts described in literature include Dimethylbenzamine, Dimethyl cyclohexylamine, Diethylaminoethanol & Adipic acid ester of N-diethyl amino ethanol. Emulsifiers includes sulphonated caster oil and structure modifiers such as Ammonium oleate and silicone oils. The bulk of flexible foam is produced in block (Slab stock) form using machines of the Henecke type or some simple modification of it. In this machine polyester and isocyanate are fed to a mixing head which oscillates in a horizontal plane. The other ingredients known as the ‘Activator Mixture’ are then injected or bled into the isocyanate polyester blend & the whole of mixture is vigoursly stirred and forced out of the base of mixing head.

The Emergent Reacting mixture runs into a trough which is moving

backwards at right angles to the direction of traverse of reciprocating Head. In this way whole of the trough is evenly covered with the reacting mass which has frequently foamed within a minute or so of issuing from the mixing head. The principle of Henecke Machine is illustrated in fig. Because of the Drag Effect of the side walls of the trough on the expanding and cross linking foam, the process gives a domed block. ( i.e. Dome shaped block ). Hence when the block is sliced up into sheet & slab, there is an undesirable level of scrap. To some extent, the fraction of scrap is reduced by increasing the block size. Over the years block sizes have been increased and widths of 2.20 m & heights of 1.2 m are produced although this is more common with polyether rather than polyester foams. 2. Polyether prepolymers C.O.E. & T;Akola

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Manufacturing of PU foams

In this process polyether is reacted with an excess of isocyanate to give an isocyanate terminated prepolymer which is reasonabaly stable if kept in sealed tins in dry conditions. If water, catalysts & other ingredients are added to the product a foam will result. Where linear polyethers are used, it is found that this foam has rather poor load bearing & cushioning properties and where this is important, a low molecular weight triol such as glycerol or trihydroxymethylpropane, is added to the polyether before reaction with isocyanate. This will then provide a site for chain branching. Alternatively a small amount of water could be added to the system. This would react with terminal isocyanate groups which link up to produce a urea link. This urea group is more reactive than a urethane link and reacts with isocyanates to give a biuret link as a site for chain branching. It is important that CO2 evolved in water- isocyanate reaction be allowed to escape & also that the reaction is kept down so that premature foaming does not occur. Advantages : Because there is exotherm, large blocks of foams can be produced. There is often a flexibility an Design of compounds, the reduced amount of free isocynate reduces handling hazards & foams will have better cushioning properties.

3. Polyether One-shot foams : The one-shot polyethers form the bulk of flexible polyurethane foam now being manufactured. This is a result of favorable economics of polyethers & because C.O.E. & T;Akola

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Manufacturing of PU foams

polyethers generally produce foams of better cushioning characteristics.

A typical

formulation for producing a one shot polyether foams will comprise polyol, isocyanate, catalysts, surfactants & blowing agent. A variety of polyethers have been used & may be enumerated in their order of development 1. Polymers of tetrahydrofuran 2. Polymers of Ethylene oxide, cheaper than the tetrahydrofroan polymers, too hydrophilic to use. 3. Propylene oxide polymers which are less hydrophilic. 4. Block copolymers of Ethylene oxide and propylene oxide. 5. To produce flexible foams of high resiliance, the so called polymer polyols can be used. 6. An alternative approach is to use a polyether containing a reactive organic filler such as (a) polyurea. (b) Isocyanate The second largest component of foam formation is the isocyanate, 80:20 TDI is found to be the most suitable of various isocyanates available & is most exclusively used. (c) Catalysts : one shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines were used with both polyesters and the newer polyethers. Examples include alkyl morpholines & triethylamine. More recent catalyst such as triethylenediamine is more powerful. Other examples include stannous Octoate. It was found that by the use of varying combinations of a tin catalyst with a tertiary amine, it was possible to produce highly active systems in which foaming and cross linking reactions can be properly balanced. (d) Surface Active Agents : They are important components of foam formulation. They decrease the surface tension of the system & facilitate the dispersion of water in the hydrophobic resin. They can stabilize the foam and control cell structure. A wide range of such agents both ionic & non-ionic has been used at various times. The water present reacts with isocyanate to produce CO2 & urea bridges. The more the water present, the more the gas evolved & the more the number of active C.O.E. & T;Akola

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Manufacturing of PU foams

urea points for cross linking. Thus the foams of lower density do not necessarily have inferior load bearing characteristics. When soft foams are required a volatile liquid such as fluorotrichloromethane may be used. This will volatile during exothermic reaction & will increase the total gas present but not increase the degree of cross linking. A typical formulation for the process is as follows – Contents

Parts by weight

Polyether triol

=

100

80 : 20 TDI

=

40

Water

=

3

Triethylene diamine (catalyst)

=

0.5

stannous Octoate (catalyst)

=

0.3

silicone block copolymer =

1.0

Additives : Commercial formulations may also include other additives. Prominant amongst these are antiaging additives, fillers, colourants , cell regulators. Flame Retardants have become increasingly important. Process : Most foam is produced an machines based in Henecke process, but in many cases it is necessary to have at least four streams to the mixing head; e.g. polyol, isocyanate, water, amine, silicone and tin catalyst. Reaction is carried out with slightly warmed components & foaming is generally complete within a minute of the mixture emerging from the head. Although slab stock flexible foam remains the largest single outlet for polyurethane materials, directly moulded foam now claims 30% of the market. Such direct moulding can be carried out for following reasons. 1. Where it is required to use metal or other inserts for fastening of upholstery elements or coverings. 2. Where shape of product is complex & it is difficult to cut this readily from slab stock. 3. Where it is uneconomic, because of scrap, to cut from slab stock, for ex , car industry where moulded foam is used for chair bucks, chair seats, kneestrips & head restraints. The foam components, mixed in a mixer are laid down onto a conveyer belt usually lined with sulphate paper or PE foil at the bottom and both sides. The conveyor belt is titled downward at an angle of 10 to prevent the growing foam from creeping back. C.O.E. & T;Akola

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Manufacturing of PU foams

Petzetakis – Draka process Another continuous method is the maxiform process in which the mixture is fed from bottom upward to overflow over a threshhold and on a belt lined with paper on which it is transported by a conveyer. As expansion proceeds the bottom foam layer is lowered so a to keep the top surface of foam as flat as possible. Then the expanded PUR foam passes through a heating tunnel where curing takes place at a temp not exceeding 1600C.

4) Rigid Polyurethane foam : They are obtained from polyfunctional oligomerols of high hydroxyl number (450-550). Polymeric isocyanates include crude TDI or MDI (Diphenylmethane diisocyanate) Blowing agent CFC-11, pentane and CO2.

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Manufacturing of PU foams

In pour technique, a liquid urethane chemical mixture is metered into cavity. The reactive liquid flows to the bottom of the cavity and starts to expand. Rigid PU foam has glass transition temp about 200C and their % elongation does not exceed 10%. They vary in density from 10 to 600 kg/m3 Laminates with rigid PUR foam are produced in a continuous process. The foaming mixture of PUR reactants are applied with a mixing of head onto the surface of one laminate board laced and belt conveyor. Another laminate board is placed on the expanded PUR layer before gelation is complete and the sandwich is passed through a conveyor press. The laminate linings are made from steel sheet, paper, Al foil, or glass fabrics. The PUR is cured for a few minutes by allowing it to pass through a furnace (tunnel). The use of lining has following advantages 1. Increased rigidity compared with PUR foam alone. 2. Barriers to gases & vapours. 3. Thermal barrier preventing ignition.

5. Spray Coating : Rigid fast curing foams are obtained from oligoetheramines, oligoetherols and MDI (Diphenyl methane diisocyanate) blown with water and physical blowing agents. Ex = CF2 Cl2 C.O.E. & T;Akola

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Manufacturing of PU foams

If physical blowing agent of boiling point below 00C ( for Ex = CF2 Cl2) is used, foaming of mixture undergoes expansion immediately on being released from the mixing head nozzle & a ready foam can be applied to a substrate. Such foams are reffered to as froths. They are used to apply to a vertical surface. The above system cure within 2 seconds at room temp. They can be applied by sprayings onto both horizontal and vertical surfaces & on to ceilings. The sprayings of PUR foam is used to make seamless joints in insulations. Portable mobile PURF spraying equipment comprises 1. Drums containing the PUR components. 2. A cylinder of dry N2 to keep the PUR components in an inert atmosphere. 3. A metering device made of pumps of 2 to 14 kg/min delivery & heating elements. 4. A set of hoses 60 to 120 m long to which PUR has low adhesion and a compressor that allows cleaning of the hoses by flushing with compressed air/solvent. 5. A spray gun. 6. A compressor for metering pumps and spraying equipment. The portable PUR foam spraying device is illustrated in fig The surface to be coated should be cleaned beforehand. Before spraying, the surface should be primed to ensure satisfactory adhesion of the foam-coat to the substrate. The foam coat is applied perpendicular to the surface not exceeding 10 to 20 mm in are operation. By repeated operations, insulating layer of foam 20 cm or more thick can be obtained. The adhesion between successive coats is excellent. Advantages : This insulating technique is good for the internal and external surfaces of concrete, metal, wood, paper, textiles etc.

6. Moulded PU foam : 1. Hot moulded Polyurethane foams :

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Manufacturing of PU foams

Moulded PUR foams are expanded in a closed mould under the slight self pressure of the foam. Composition : 1. Copolyoxypropylene – ethylene triols 2. TDI = 80 3. Catalyst ( Ex Organotin & Amines ) 4. Surface Active Agents 5. Physical blowing Agents 6. Water. Steel and Al molds are commonly used. As the mould is filled it is closed. The reactant mixture is foamed and fills the mould. After some time mould is opened and article is removed. Curing time is upto 40 min and extra heating is required for 1 hour at 120°C. The Effect of water content v/s hardness and density of hot molded flexible PUR foam is illustrated.

7. Integral – skin PU foam (Cold molding) : Integral skin PUR foams have cellular foamed structure of the core integral with the solid top skin. The principle of the method of manufacturing such foams is the C.O.E. & T;Akola

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Manufacturing of PU foams

use of halocarbons as blowing agents ( with no water) and moulding in cooled (chilled) wall metal moulds which make blowing agent condense on the cool walls at the molding pressure (0.1 to 0.4 Mpa) and the polymer to form a solid top skin, whereas bulk of the product remains hot and cures to a foam. A cross section of flexible integral skin PUR foam is shown in fig . Starting materials : 1. Oligomerols of RMM 3000-6500 2. MDI (Diphenylmethane diisocyanate) and Polymeric Isocyanates 3. halocarbon ( a blowing agent) [no water] 4. Catalyst (Amines) 5. Surface active agents Properties of Integral skin PUR foam v/s Isocyanate functionality (foam density 0.108 g/cm3) 1.

Property MDI functionality Tensile strength /105 Nm-2

2.8 1.1

2.2 1.1

2 2.1

2.

Elongation at break / %

80

150

250

3.

40% compression strength/105 Nm-2

2.5

1.2

1.0

HOT MOLDED FOAMS AND COLD MOLDED FOAMS Hot Molded foams Advantages 1. Higher load bearing capacity upto 30%

Cold Molded foams Advantages 1.Less power consumption in production

2. Higher hardness and hardness to density 2. Less manufacturing space required (as ratio is higher.

no external heating arrangement is made).

3. Lower raw material cost per kg of foam.

3. Lower capital cost.

4. Higher moisture resistence.

4. Less scrape. 5. Lower ignitability.

7. PROPERTIES PROPERTIES OF MELAMINE MODIFIED FLEXIBLE PUR FOAM Density (Kg/m3)

42 – 64

Tensile strength (Kpa)

48 – 76

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Manufacturing of PU foams

Elongation at break (%)

80 – 110

Abrasion Resistance (N/m)

158 – 228

Resiliance (%)

55 – 60

Properties of a fast cure high resiliance polyurethane foam. Sr.No Property 1 Core Density / kgm-3

Absolute values 47 – 51

2.

Tensile strength/Mpa

0.130 – 0.155

3.

Elongation at break / %

135 – 165

4.

Abrasion Resistance Nm-1

265 – 325

5.

Hardness / N (200 mm)-1

205 – 264

Selected properties of semi-rigid foam. Property 1. Density/Kgm

-3

2. Tensile strength/Kpa

One shot free foaming method. 55 – 65 130 – 170

3. Elongation at break %

50 – 60

4. Stress on 40 % compression/Kpa

14 – 18

Effect of Manufacturing parameters on properties of flexible PUR foam slabstock 1) The apparent density of PURF depends on the quantity of blowing agent.

With

increasing water conent and Isocyanate in reaction mixture, more CO2 is produced and therefore density decreases as well as tensile strength also decreases.

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Manufacturing of PU foams

2) Cell size and cell uniformity are mainly affected by mixing efficiency. If reaction mixture is mixed uniformly, cells of uniform structure are formed and hence tensile strength increases. 3) The hardness of flexible PU foam increases (1) with apparent density and with the degree of cross linking and (2) with increasing functionality of polyol. (3) With the presence of fillers.

Properties of oligooxyalkylene – styrene-acrylonitrile PUR foam. I NCO/OH

Density Kgm-3

1.00 1.00 1.10 1.10 1.15

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34 28 29 24 22

65% compre-

Property Tensile

Elongation at

sion strength

Strength

break %

Kpa 4.32 8.06 3.56 2.86 4.86

Kpa 123 128 154 164 265

150 137 73 100 117

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Manufacturing of PU foams

Effect of amount of water blowing agent on properties of polyurethane foam block 1. Density 2. Tensile strength 3. Elongation at break.

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Manufacturing of PU foams

Load bearing capacity of flexible PUR foam of varying density

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Manufacturing of PU foams

Hardness of PUR foam of density 20 kg/m3 v/s Polyol content at constant isocyanate index

4) Stress v/s strain curves for rigid PUR foams of varying density

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Manufacturing of PU foams

1) Low density rigid PUR foam 2) High density PUR foam

For same strain, the load beared by high density foam is more. High density PURFs provide better comfort for users and have a longer service life.

5) Stress Strain Behaviour

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Manufacturing of PU foams

Behaviour of PU foam of density 35 kg/m3 – 1) For polyesterurethane foam 2) Polyether hot foam 3) High resiliance polyetherurethane cold foam.

A higher degree of cross linking increases the load bearing capacity of PUR foam. Inert inorganic fillers confer a higher strength and makes their stress v/s Elongation behaviour more linear. Common fillers are barytes, calcium carbonate, talc and kaolin.

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Manufacturing of PU foams

Stress v/s Strain relation on compression of 41kg/m3 density rigid foam 1) For free foaming stock 2) For moulding stock

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Manufacturing of PU foams

Relation between compression strength and density for rigid PUR foam

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Manufacturing of PU foams

Hydrolytic stability of polyether type of PUR. Immersion in water at various temperature.

8. APPLICATIONS OF PU FOAM 1. Flexible PU Foams : 1.Measure interest of flexible PU foam is cushioning and other upholstery materials. 2. In addition to upholstery applications polyester foams are useful as foam backs, i.e. foambacking in order to stiffen or shape some softer fabrics, examples include car –door, roof-trim, quilting, shoulder pads and coat interlinings. 3. paint rollers, sponges and packaging for delicate equipments. C.O.E. & T;Akola

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Manufacturing of PU foams

4. Automobile Industry Widely used in Automobile industry for making chair backs, chair seats, head restraints etc. The market for cushioning materials is dominated by PU flexible foam. 2. Rigid PU foams 1. Semirigid and high molecular foams are useful in the manufacture of car-crash pads and in packaging equipments. 2. Construction : When sandwiched between metal, paper, plastic, wood, PU Rigid foam plays an important role in construction Industry.

Such composites can replace

conventional structure of bricks, cement, wood and metal. 3. Thermal Insulation : Rigid foam offer advantages in thermal insulation of building, refrigerators and domestic appliances and for heat exchanger- insulation, condensor- insulation. 4. Shoe manufacturing : Polyurethane coatings are used to improve the appearance and wear resistance of shoe uppers made from real leather and PVC leathercloth.

9. CONCLUSION The technique for PU foam manufacturing in the form of sheet, slab, board, moldings and sprayed coatings with varying level of flexibility offers various grades of foams with widely varying properties. More than 35 grades of PU foam are important and they are produced commercially.

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Manufacturing of PU foams

The low cost and Interesting properties of cellular PU make them a significant group of material for wide range of products ranging from packaging to insulation and structural foam sections, further improvements will widen its uses. The PU foams has opened the new area in plastic packaging and other works and have tremendous scope in future.

10. BIBLIOGRAPHY 1. Chemistry for thrmosets – J. B. Foreman, 1993.

Page no. 310-319.

2. Polymer materials

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Manufacturing of PU foams

J. A. Braidson,

Page no.709-720

3. P U Chemistry, Technology & Applications By Zygmunt Wirpssa –

Page no. 220 – 267.

4. S P I Hand Book. Page no. 540-580 5. www.google.com.

CONTENTS 1. Introduction

1

2. Foaming agents

2

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Manufacturing of PU foams

3. Selection criteria of foaming agents

4

4. Chemistry of forming of PU foams

6

5. Additives

7

6. Manufacturing of PU foams

8

i) One shot polyester foams. ii) Polyether prepolymers iii) Polyether one-shot foams iv) Rigid PU foams v) Sprayed coatings vi) Moulded PU foams vii) Integral skin PU foam 7. Properties of PU foams

17

8. Applications of PU foams

27

9. Conclusion

28

10. Bibliography

29

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Manufacturing of PU foams

Maxifoam system for continuous production of PUR foam blocks 1. Mixing head 2.Trough 3. Bottom paper feed 4. Conveyor belt 5. PURF

Petzetakis – Draka continuous system producing PUR foam blocks 1. Traversing mixing head 2. slide paper (or PE foil ) liner 3. Bottom paper feed 4. Conveyor belt 5. PURF

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Manufacturing of PU foams

Spray gun for application of PUR foam ( portable metering device in the background).

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Manufacturing of PU foams

Principle of the Henecke machine

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Manufacturing of PU foams

The effect of water content v/s hardness and density of hot molded flexible PUR foam 1. Density 2. Hardness

Manufacturing of hot molded PUR foam

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Manufacturing of PU foams

Manufacturing of Rigid PUR foam blocks by a batch process 1. Reaction mixture 2. Floating cover 3. Limiters

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Manufacturing of PU foams

Manufacturing of rigid PUR foam laminated boards laminated on both sides with a lining. 1. Sheet Metal roll 2. Shaping 3. Annealing 4. Mixing head 5. Belt press 6. Cutter 7. Laminating board

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