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What Is Polyurethane?

Nov 26, 2025 Leave a message

What Is Polyurethane?
 

Contents
  1. Polyurethane
    1. Isocyanates
    2.  
    3. Polyols
    4. Key numbers we watch on the shop floor every shift:
    5.  
    6. Main physical blowing agents we switched to in the last years (China Phase-out HCFC-141b):
    7. Typical additives we must dose accurately:
    8. Reaction temperature control:
    9. Polyol side 22–28 °C, isocyanate side 22–28 °C, mould temperature 40–65 °C depending on product.

Polyurethane

 

My name is Lao Zhang. I have been handling molding systems at ABIS Mold since 2007, first in the injection workshop in Shenzhen for prototypes, then in the main production line for automotive and electronics parts. Here is what polyurethane actually is when you have to mix and pour it every day in a precision mold setup.

 

polyurethane

 

Polyurethane (full chemical name polyurethanes or PUR/PU) is a polymer formed by the reaction between two liquid groups:

 

Isocyanates


Most common types we use:

TDI (Toluene Diisocyanate) – 80/20 or 65/35 mixture

MDI (Diphenylmethane Diisocyanate) – crude MDI, polymeric MDI, or pre-polymers

Sometimes HDI or IPDI when yellowing resistance is required

 

polyurethane

 

Polyols

 

Polyether polyols (PPG, functionality 2–6, MW 200–8000)

Polyester polyols (higher strength, higher cost)

Special polyols (PTMEG, polycaprolactone, etc. for elastomers)

When the two sides meet, they form urethane linkages (-NHCOO-). Depending on formulation you get different structures:

Flexible foam → long-chain polyols + high water level → CO₂ blowing → open cells

Rigid foam → short-chain polyols + low water + physical blowing agent (245fa, cyclopentane, HFO) → closed cells

Elastomers → 1000–4000 MW polyol + chain extender (BG, HQEE, MOCA) + no blowing agent → solid rubber-like material

CASE (Coatings, Adhesives, Sealants, Elastomers) → different NCO/OH ratios and additives

 

Key numbers we watch on the shop floor every shift:

 

NCO % of the B-component (isocyanate side): usually 18–32%
OH value of the A-component (polyol side): 28–1000 mgKOH/g
Index: normally 0.95–1.10 (100 means stoichiometric)
Cream time, gel time, tack-free time – measured with a stopwatch on every new batch
Density: flexible foam 15–60 kg/m³, rigid foam 30–200 kg/m³, elastomer 1000–1250 kg/m³

 

Main physical blowing agents we switched to in the last years (China Phase-out HCFC-141b):

 

Cyclopentane / iso-pentane blend

HFC-245fa (still used in some export refrigerators)

HFO-1233zd / 1336mzz (new low-GWP, expensive)

 

polyurethane

 

Typical additives we must dose accurately:

 

Water (chemical blowing, 0.1–5.0 phr)

Amine catalysts (A33, A1) and tin catalysts (T9, Kosmos-19)

Silicone surfactants (B8xxx series) for cell opening/stabilisation

Flame retardants (TCPP, DMMP, melamine, APP) for rigid foam

 

Reaction temperature control:


Polyol side 22–28 °C, isocyanate side 22–28 °C, mould temperature 40–65 °C depending on product.

That is polyurethane in real production. Two liquids go in, heat and gas come out, five minutes later you have a part that can be softer than a sponge or harder than many plastics. Everything else – colour, hardness, flame rating, abrasion resistance – is just formulation work.

At ABIS Mold we keep every polyol and isocyanate as separate raw materials, record the exact index and catalyst levels per batch, so when a customer wants the same part six months later we can repeat it 100 %.