The two main components in a polyurethane formulation are polyol and toluene diisocyanate.

The polyol, which constitutes 60-70% of the initial mix, is a liquid similar in appearance to glycerine or oil, and is very low in toxicity. The isocyanate, which is usually toluene diisocyanate (TDI), is a toxic liquid of water-like appearance, which is irritating to skin, eyes and respiratory tract.  TDI constitutes 25-30% of the initial mix. An alternative isocyanate that can be used is methylene diphenyl diisocyanate (MDI), which is less volatile than TDI. There are many different types of MDI ranging from crude to purified ones. The two main materials (polyol and isocyanate), in combination with other ingredients such as water, silicone surfactant, amine, tin catalysts and auxiliary blowing agent, react together to produce inert resilient polyurethane polymer in the form of a cellular foam.

SIMPLE OVERVIEW OF POLYURETHANE CHEMISTRY

1.Foaming (blowing) reaction between water and TDI to produce an amine and CO2 gas (only one functional group shown).

R-N=C=O + H2O è RNH2 + CO2

  Isocyanate       Water         Amine     Carbon dioxide

2.Primary chain forming (polymerisation) reaction between a polyol and TDI to produce the urethane foam network.

R-N=C=O + R"OH è RNH-C(O)-OR'

Isocyanate      Polyol            Urethane

3.Secondary crosslinking reactions of the polymer products and TDI to strengthen the foam network (formation of biurets and allophanates).

     R-N=C=O = R'NH-C(O)-NHR" è RNH-C(O)-NR' - C(O)-NHR"

      Isocyanate            Urea                                     Biuret

R-N=C=O + R'NH-C(O)-R" è RNH-C(O)-NR' -C(O) - OR"

Isocyanate       Urethane               Allophanate

Immediately followed by the formation of a urea

R-N=C=O + R"NH2 è RNH-C(O)-NHR"

Isocyanate     Amine       Disubstituted Urea

A TYPICAL CHEMICAL COMPOSITION:

There are additional additives used in formulating urethane:

ADDITIVES - REASON  FOR  USE

• Dyestuffs and pigments - To colour the foam.
• Fillers
• inorganic eg. calcium carbonate-  To increase density and hardness.
• organic eg. melamine-  To impart fire retardance
• Flame Retardants (eg.)
• Trichlorethylphosphate - To impart fire retardance.
• Bacteriostats - To impart resistance to attack by microorganisms.
• Plasticisers - To soften the foam and give it a modified feel.
• Antistatic Agents - To reduce the electrical resistance of the foam making it more suitable for electronic parts.

There are many different types of polyurethane foams now available on the market. All foams are created for a specific application. The issue lies in the requirements of the particular foam with certain qualities one has in mind; e.g.: feel (comfort and support properties), endurance properties and most importantly durability.

FLEXIBLE:

• Conventional
• High Resilient (H.R. Foams)
• Low Resilient (L.R. Foams) or alternatively called Slow Recovery foams
• Polyester foams
• Moulded foams using either all MDI or TDI / MDI blends technology.
• Bonded crumb foams
• Prepolymers

RIGID:

• Rigid foams
• Polyester foams

Alternatively there is maybe a desire to create a new type of foam for a specific application. We have personally a vast knowledge is this area:

• Graphite filled foams
• True Low Resilient foams:
• Low density types
• High density types
• All MDI (Source 5) moulded foams
• Prepolymers

What ever the demand, PUTech can accommodate your needs