Understanding Polyurethanes

Polyurethane products first made their appearance in the market place in the late 1930’s. This was after an intensive investigation by Dr Otto Bayer who was looking for a synthetic fibre to replace nylon. Once the basic technology was understood, new applications for foams (1941) and elastomers (1943) were developed. In the early 1950’s, commercial applications appeared.

The variety of raw materials as well as the range of different manufacturing techniques enabled pioneers to make a seemingly endless range of tailor-made products with different physical properties. These included soft foams, rigid structural and insulation foams, soft and hard elastomers and coatings.

Processing techniques include casting, spraying, foaming, reaction injection moulding, injection moulding, extrusion and painting.


How are they applied?

There are many grades of polyurethane, as well as a number of different ways to process it. The correct grade must be selected according to the properties required in the end product as well as the process to be used

  • Polyurethane can be cast by pouring into an open mould, or cast using rotational moulding, centrifugal moulding or vacuum moulding techniques. It can be weighed and mixed by hand, or a casting machine could be used.
  • Polyurethane can be sprayed using either single or two component machines.
  • Polyurethane can be used to coat the inside of pipes by using spinning techniques.
  • It can be used to coat floors or roofs.
  • It can be brush applied as a paint.
  • It can be used as a sealant.

Selecting a polyurethane

There are many ways to formulate polyurethane, and as the formulator develops different systems using the different properties of the different raw materials, a wide range of resins to suit different applications have evolved.

The following table demonstrates the influence that different raw materials have on the end products:

Tensile strength Ester Ether
Tear strength Ester Low cost ether
Compression set TDI MDI
Rebound MDI ether TDI ester
Low temp properties MDI ether TDI ester
High temp properties TDI MDI
Abrasion: sliding Ester Low cost ether
Hydrolysis resistance* MDI ether TDI ester
Oil resistance Ester Ether
Heat aging Ester Low cost ether
Abrasion: impingement MDI ether Low cost ether
UV resistance Aliphatic iso Aromatic iso
Solvent resistance Ester Ether


Building & Construction Moulds for concrete / gate seals / mastic shuttering / waterproofing systems / joint sealants / flooring systems / primers / structural wood adhesives / tyre fill / thatching material / crack injection systems / crack repair -depression repair systems/ buckets.
Coated Fabrics Textile adhesives / conveyor belt coatings / fuel storage tanks / power transmission belts / fabric -backed sheeting
Electrical Encapsulation ,insulation ,potting systems/cable jointing resins.
Engineered Components Gears / sprockets / wire guides / rail draft gears /stripper plates / press brake pads / textile yarn guides / cutting boards / belts /couplings.
Food Chute linings / grain buckets/ seamless flooring systems / joint sealants / primers/scrapper blades / conveyor guides.
Mining & Quarrying Tyre fill / rock consolidation materials[thin skin liners ] / fissure sealers / bunker lines / conveyor rollers / scraper blades / flotation cell impellers / pump linings / grading screens / lined pipe / cross over pads / acid resistant coatings[spray and brush coat] / abrasion resistant spray on liners / corrosion resistant paint coatings /acid resistant coatings and casting systems/blast barricades.
Oil , Chemical & Marine Bushings / bearings / hydrocyclones / buoys / pipeline pigs and scrapers / fenders / valves /corrosion resistant pipeline coatings / abrasion resistant pipe coatings.
Rollers Board rollers / nip rollers / metal forming / paper machine rollers[hydrophobic spray ] / printing / conveyor / can coating / paper mill.
Seals & Gaskets Pneumatic and oil seals / diaphragms.
Water & Sewage Potable water rigid polyurethane primeless coatings /sewage works coatings [pipes and tanks ] /flooring systems / waterproofing systems / pipe joint systems.
Recreational Nursery school play areas floor coatings. / wave pool linings / athletic track rubber binders [EPDM/shredded car tyres]
Shoe Industry Shoe soles / bottom moulding diaphragms / wear plates / energy -absorbing insoles.
Wheel & Tyres Pallet truck tyres / heavy duty caster wheels / escalator wheels / roller skate wheels / tyre fill.
Advertising Digital print protective coatings / doming resins.
Furniture Non-structural adhesives / coatings
Motor Home Building Single and two component adhesives / coatings.



Amine - chemical terminology: NH2, different types used as curatives or catalysts.

Angle of parallax - make sure that the point of observation is correct or errors may occur.


Cheesiness - cheesy-like feel of a casting.

Combustible - will burn.

Curative - substance used to react with the prepolymer to gel it.


Diamine - molecule with two amine (NH2) groups.

Diisocyanate - molecule with two isocyanate (NCO) groups.

Dimer - chemical reaction: two isocyanate groups reacted together.

Diol - molecule with two hydroxyl (OH) groups on it.


Flammable - will burn.

Flash point - lowest temperature at which a substance gives off combustible vapour to produce a flash of fire if a small flame / spark is near.


Gel - irreversible solidification of substance; solid / reacted casting after curative is added.

Glycol - 1,2-ethanediol; a type of diol.


Isocyanate - molecule with an NCO- group on it.

Inflammable - same as flammable; will burn.


MDI - chemical name: diphenylmethane diisocyanate. There are many grades.

Meniscus - curved upper surface of a liquid at the sides where in contact with the mould / container. This curve will remain after gellation. Measurements are read at the central flat portion.

Mix ratio - the constant proportions in which the substances are mixed.

MOCA/ MBCA - amine curative: 4,4-methylene-bis orthochloroaniline.


Plasticizer - ingredient which can be added to urethane systems to modify systems but weakens the properties considerably; also used for flushing machinery or testing ratios.

Polycaprolactone - chemical term: similar to polyester, but with better hydrolysis resistance.

Polyester - chemical term: high molecular weight substances containing the ester group –O-CO.

Polyether - chemical term: high molecular weight substances containing the ether group –O- There are two types: PPG (POPG) & PTMG (PTMEG).

PPG / POPG - chemical term: polypropylene glycol; low cost polyether.

Pressure - force applied to a surface, which is measured as force per unit area e.g. psi or bars or pascals or Kg per square meter.

PTMEG / PTMG - chemical term: polytetramethylene ether glycol; high cost ether.


Release agent - silicone based substance / surfactant applied to mould to prevent sticking.

Resin - refers to blends and partially reacted urethanes, esters, ethers, isocyanates.


Shore A/D - measurements of hardness; shore A being the softer range, D the harder.

Shot size - size / weight of each dose of resin.

Solvent - liquid used to dissolve a substance; often used to clean machinery, often flammable.

Stoichiometry - the science of calculating the quantities of substances to be mixed together based on their reactivity.

Substrate - the object or surface one is casting on.


Tear resistance - force necessary to tear a sample of urethane. Test results may vary according to the method used.

Temperature - the measurement of ‘hotness’ or ‘coldness’ of a substance.

Tensile strength - the breaking strength of a sample when subjected to tensile / stretching force which is measured in force per unit area.


Vacuum - the absence of air, usually in a sealed container

Vapour - gaseous phase of a liquid.

Viscosity - The resistance of fluid to flow.


Wet spots - parts on the surface of a casting that are ‘wet’ usually due to poor mixing.