Urethane Glossary

Additive

Any substance that is added to a resin, usually in a relatively small percentage, to alter properties. Examples are slip additives, pigments, stabilizers and flame retardants.

Aliphatic

An organic substance which contains no aromatic rings.

Ambient Temperature Cure

Curing at room temperature without the benefit of a heated oven.

Aromatic

A class of organic compounds containing a resonant, unsaturated ring of carbon atoms. Included are benzene, naphthalene, anthracene and their derivatives.

Cast

A molding process, using little or no pressure, to fill an open mold cavity.

Catalyst 

A substance that causes or accelerates a chemical reaction when added to the reactants in a minor amount, and that is not consumed in the reaction.

Curative 

A compound (or mixture of compounds) that link long molecules together and thereby complete a polymer reaction. In polyurethane systems, the curative is comprised of hydroxyl (or amine) -terminated compounds which react with isocyanate groups present in the mixture.

Elastome

Polymers which resist and recover from deformation produced by force, similar in behavior to natural rubber. At room temperature they can be stretched repeatedly to at least twice their original length and, immediately upon release of the stress, return with force to their approximate original length.

Flame Retardants

An added substance that inhibits the initiation and/or spread of flame.

Gel Time

The “working time” from the initial mixing of the urethane raw material components to the solidification of the material.

Green Strength 

A term used to describe the strength of a polyurethane or rubber compound in the early stages of cure. To minimize damage to a molded part, a compound must attain adequate green strength prior to subjecting it to the demold process.

Index

The ratio of isocyanate groups to hydroxyl (or amine) groups in a reaction mixture. The index must be near 1 to achieve acceptable physical and mechanical properties.

Isocyanate

A compound containing the isocyanate group, -N=C=O.

MDI

An acronym for 4, 4′ diphenylmethane diisocyanate, a common raw material used in the production of polyurethane elastomers.

Mold

A cavity or structure used to produce a specific part shape.

NCO

An isocyanate chemical group. This designation refers to the nitrogen, carbon, and oxygen atom of the isocyanate group.

%NCO 

A measure of the isocyanate content of a prepolymer or other isocyanate-containing compound measured as the weight percent of unreacted isocyanate groups in the material. Value is used to determineproper mix ratio of polyurethane system components.

PPDI 

An acronym for para-phenylene diisocyanate, a raw material that imparts excellent temperature resistance to a polyurethane system.

PPG

An acronym for poly(propylene) glycol, a type of polyether polyol used in the manufacture of some polyurethane systems.

Plasticiser

An additive designed to soften or add pliability to a compound.

Polyester

A polymer containing the ester chemical group

Polyether

A polymer containing the ether chemical group

Polyol

A substance containing several hydroxyl groups. A diol, triol and tetrol contain 2, 3 and 4 hydroxyl groups respectively.

Post Curing

A secondary period of curing a cast part at elevated temperature, once it has reached its “green strength”. Post curing of polyurethane elastomers promotes completion of the chemical reaction and is oftennecessary to obtain optimum properties.

Prepolymer 

A substance formed by pre-reacting an isocyanate with some or all of a polyol. A final amount of polyol and / or extender (referred to as the “curative”) is added to the prepolymer to complete the reaction.

PTMEG

A specialized type of ether polyol primarily used to optimize the resilience of a polymer, as well as to achieve high impact resistance, low abrasion loss, and low rolling resistance.

Polycaprolactone

Any specialty ester polyol which provides improved hydrolytic stability over conventional polyesters and high cut, tear, and abrasion resistance when incorporated into a polyurethane compound.

Stoichiometry

Refers to the equivalence of reactive chemical groups in a mixture. In polyurethane chemistry,term is used to define the ratio of hydroxyl (or amine) groups to isocyanate groups in a reaction mixture (inverse of “Index”). This ratio is sometimes multiplied by 100% and referred to as “%Theory”.

TDI

An acronym for toluene diisocyanate, a common raw material used in the production of polyurethane elastomers.

Thermoplastic

A type of polymer that can be melted and reformed by application of heat.

Thermoset

A type of polymer that cannot be melted and reformed by application of heat.

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