Polyurethanes

Muhammad Shafiq Randhawa

Technical Consultant Polyurethane Emailmsrandhawa87@hotmail.com

Cell #00923334114187Skyep=taha.shafiq87

Polyurethanes

History of Polyurethanes

• Dr. Otto Von Bayer (1937)

•IG Farben Industries•Rigid and flexible foams•TDI and polyols

•Attempts to reduce natural rubber use

What are Polyurethanes?

•Polyurethane

•Polyurethane polymers are traditionally and most

commonly formed by reacting a di- or

polyisocyanate with apolyol. Both the isocyanates

and polyols used to make polyurethanes contain on

average two or more functional groups per molecule.

•Types of polyurethane•1.Flexible Polyurethane Foam•2.Rigid Polyurethane Foam•3.Coating,Adhesives,Sealants and Elastomers(CASE)•4.Thermoplastic polyurethane (TPU)•5.Reaction Injection Molding (PIM)•6.Binders•7.Waterborne Polyurethane Dispersions (PUDs)

Polyurethane Structure

Polyurethane Monomers

• Polyurethanes consist of different block co-polymers•MDI- 4 4'-diphenylmethane diisocyanate• TDI- Toluene-2,4-diisocyanate

Polyurethane Monomers

Polyols- hydroxy terminated polyether, polyester, polyolefins, and glycols

Polyurethane Reactions

•Multiple types of reactions make up different end products of polyurethanes•Polyurea reactions are important for spandex production

Raw Materials

Components of Polyurethanes • Isocyanates• Polyol • Catalysts• Silicon surfactant• Fire retardant• blowing agent

Isocyanates;

Different Isocyanates are used for the

synthesies of polyurethane. Toluene

diisocyanate (TDI) was the first mass produced

isocyanate. It was used for rigid and flexible

products before the development of Methyl

phenyl diisocyanate (MDI) in the early 1960s.

TDI is still used in most flexible foam and many

elastomers and coatings. The TDI production

process yields two difunctional isomers

. The series of multifunctional aromatic or aliphatic isocyanates are used in polyurethane foams. The detail information about synthesis and reactions of isocyanates can be studied in the literature. Polyurethane is commercially produced by the phosgenation of amines. The solution of amine and phosgene are mixed to form a slury of amine hydrochloride and carbamic chloride then by heating the amine salts react with excess phosgene.

Parameter Value

Colour Dark brown

Viscosity (CPS) 170-250

Specific Gravity at 25

degree centigeade

1.24

NCO content 32

Specification of Crude MDI

Molecular Weight 174.163

Density (g. per cm3) @20°C (68°F)

1.21

Viscosity (cs) @100°C (212°F) 0.8

Freezing/Melting Point Range T100 (°C)

21.5-22.0

Freezing Point 2,4-isomer (°C)

15.0

Boiling Point @10mm Hg (°C) 121

Flash Point, COC (°C) 132

Acidity, as HCI (%) T100 <0.0130

Specification of TDI

Polyols

During the initial development of polyurethanes, polyesters were the most commonly used type of Polyols. Since unsaturated polyesters were found unstable for use in polyurethanes, completely saturated polyesters containing terminal hydroxyl groups rather than carboxyl groups are used many Polyols are available to the polyurethane formulator. The size, functionality, and starting materials determine the properties of the final product.

Rigid polyurethanes are formed by low molecular weight polyol.

Flexible polyurethane are make from the higher molecular weight polyols, castor oil, trihydroxy fatty triglyceride, is an example of naturally occurring polyol.

Polyester polyols are prepared by step growth or condensation polymerization. Formation of polyester chains is a random process and leads to broad distribution of molecular weights. Bifunctional monomer make the linear polymers.

Adipic acid used where flexibility is required, The Phthalic anhydride is used for those requiring rigidity, Dioles include ethylene glycol, 1.4 butandiol. And 1,6- hexandiol The polymerization has the characterstics of a chain reaction, whose chemistry is presented by initation, propagation and termination steps. Propylene oxide (PO) and ethylene oxide(EO) , are low price epoxides produce by the oxidation of proplylene and ethylene.

Polyols

•Polyols are the major component of rigid polyurethane. Rigid polyurethane foam can be manufactured by standard polyether base and polyester base polyol.

Type of PU average

molecular

weight

OH no(mg

KOH/gram)

Average

functionalit

y

Viscosity

at 25

degree

centigrate

(CPS)

Acid

number

Density(gm/cm)

Rigid foam 930 350-390 6.2 1500-

3000

1.0 1.1

Shoe sole 2000 58-62 2.1 700-1000 0.4 1.15

Elastomers 2000 50-58 2 500-800 1 1.17

Soft coating 2750 38-45 2 700-800 1 1.12

Hard coating 2450 250-270 11.3 17000 4 1.24

Flexible foam 2400 57-63 2.7 1000-

1200

1.3 1.15

Catalysts

Catalyst is the important additive. It is control the reaction rate and also control the balance between polyol and isocyante reactions. and blowing in order to attain the desired foam properties. Amine and Tin are two good catalyst used. Formation of transient complexes between polyol and isocyanate are formed due to catalyst.

Tertiary amines can catalyze both in gelling and blowing reaction and are usually called the blowing catalysts, Reaction rate of both gelling and blowing process depend on catalyst structure.Amine catalyst are control the both these parameter.Tin catalyst are more reactive and use in less quantity but it is use for gelling reaction, so it is called the gelling catalyst. .

Surfactant

•It is important additive in polyurethanes to get

homogenous foam with low density,

•Surfactant help in good mixing during foaming.it can

prevent bobbles from collapse and stabilize the cell

structure. Branching chains can be introduced to

either silicone or polyether and different end group

can be cooed in to chain end.

Blowing agent

Different blowing agents are used to form gas bubbles in the reaction mixture Firstly water was used as a blowing agent then it was rejected due to high boiling point and open cell foam is produced which was not good for insulation. In insulation we need low thermal conductivity material but the polyurethane which is manufactured by water has high thermal conductivity. Now CFCs, HCFCs, Pentanes, HFCs are use as blowing agent in rigid PU foam these gases are responsible for excellent insulation properties

CFCs gases were phased out due to environmental problems. In japan & Europe CFCs-11 was substituted by HCFCs 141b are Pentanes. middle East Asia and Africa CFCs-11 is still used.

Blowing

agent name

Molecular

weight

gm/mole

Boiling point

In centigrade

Liquid

Density at 20

degree C

Ozone

depletion

potential

CFC-11 137.4 23.8 1.49 1

HCFC-141b 116.9 32.2 1.24 0.11

HCFC-22 86.5 -40.6 1.21 0.055

HCFC-142b 100.5 -9.8 1.10 0.065

Physical properties of different blowing agents

Breakdown of the PU Industry

Economics

•The PU industry was estimated to produce 13.65 million tons of plastic in 2010 and is expected to grow to 17.95 million tons by 2016•The PU industry is expected to grow from $33

billion in 2010 to $55.5 billion in 2016.

Processing Machineries

Rigid PU processing machines1) Spray foam machine

2) Discontinuous PU panel

3) Continuous PU panel

Shoe Grade PU

Flexible PU

ApplicationsApplications

Building and Construction

PU Pipes

Wall insulation

Water cooler

Refrigerator

Appliances  and Hot pots

PU shoes

Bibliography

1.http://www.pslc.ws/macrog/urethane.htm

2.http://www.8linx.com/cnc/polyurethane_foam.htm

3. http://www.essentialchemicalindustry.org/polymers/polyurethane.html

4. http://sunilbhangale.tripod.com/pu.html 

5.http://www.poliuretanos.com.br/Ingles/Chapter1/132comercial.htm

6.http://www.plastemart.com/Plastic-Technical-Article.asp?LiteratureID=1674&Paper=global-polyurethane-market-PU-foams-thermoplastic-elastomers 

7.J.M. Buist.  Developments In Polyurethane-1;  Applied Science Publishers LTD, UK, 1978.