Some Polyurethane Calculation Formulas

To facilitate everyone's learning and understanding, I will briefly introduce some essential calculation formulas and basic concepts that individuals engaged in polyurethane technology must grasp and understand.

1. Hydroxyl Groups

Hydroxyl Equivalent: The weight of resin equivalent to one hydroxyl group, calculated as:

E(OH)=Weight of Resin/Number of Hydroxyl Groups in the Resin Molecule

Hydroxyl Content: The weight percentage of hydroxyl groups in every 100 grams of resin, calculated as:

OH% =(N*17/ Weight of Resin)*100%

where N is the number of hydroxyl groups.

Hydroxyl Value: The number of milligrams of potassium hydroxide equivalent to the hydroxyl content per gram of sample, calculated as:

Hydroxyl Content=1700 / Hydroxyl Equivalent

Hydroxyl Value=56100 / Hydroxyl Content= Hydroxyl Equivalent*33

2. Isocyanate Index

TDI Index: The ratio of the actual amount of TDI used to the theoretical amount of TDI, calculated as:

TDI Index=Actual TDI Amount Used / Theoretical TDI Amount

Equivalent: Calculated as:

Equivalent=Molecular Weight / Functionality

For TDI:

TDI Equivalent=4200 / NCO%

TDI Amount: Calculated as:​

TDI Amount=(TDI Index / 100)*TDI Equivalent*(100 / Polyol Equivalent+Water Content / Water Equivalent)

where Polyol Equivalent=56100 / Hydroxyl Value, Water Equivalent=9.

For MDI, the formulas are the same, substituting TDI with MDI.

NCO Content: The content of isocyanate groups (NCO), usually expressed as a percentage.

3. Reaction Rate

The reaction rate refers to the rate at which the concentration of substances in a chemical reaction system changes over time, indicating the speed of the chemical reaction. During a chemical reaction, when external conditions (such as temperature and volume) are fixed, the concentration of substances in the reaction system changes over time: the concentration of reactants gradually decreases, while the concentration of products gradually increases. However, the reaction rate changes over time. The reaction rate at a specific moment is called the instantaneous reaction rate, typically expressed in moles/(dm³·s). The average reaction rate is usually referred to as the chemical reaction rate. Factors affecting the reaction rate include pressure, temperature, catalyst, concentration, solvent, etc.

4. Tensile Strength

Tensile strength refers to the stress at which a material exhibits maximum uniform plastic deformation. In tensile testing, the maximum tensile stress a sample withstands until it breaks is the tensile strength, expressed in MPa. It is also referred to as tensile strength or tensile resistance.

When testing tensile strength with instruments, data such as tensile fracture stress, tensile yield stress, and elongation at break can also be obtained.

Tensile Strength: Calculated as:​

Tensile Strength=Maximum Load / (Sample Width*Sample Thickness)

Elongation at Break: Calculated as:

Elongation at Break=(Length at Break−Initial Length) / Initial Length*100%

Peel Strength: The maximum destructive load per unit bonding area, representing the force required to peel the bonded surfaces per unit width of the sample. It is expressed in N/cm, N/m, or kN/m.