Contents
1. Why these two raw materials define every PU system
Every polyurethane system in industry — rigid panel cores, flexible furniture foam, viscoelastic mattress layers, integral-skin steering wheels, spray insulation, cast elastomers — starts from the same two raw material classes: a polyol (a long-chain molecule carrying multiple hydroxyl groups, –OH) and an isocyanate (a molecule carrying reactive isocyanate groups, –N=C=O). When the two meet, each –NCO reacts with an –OH to form a urethane linkage. That single bond, repeated thousands of times across the mix, is what builds the polymer.
Everything else in a polyurethane formulation — catalysts, surfactants, blowing agents, flame retardants, colorants — exists to control how that base reaction unfolds. So the behavior of any finished foam, elastomer or coating is driven first by which polyol you pick, which isocyanate you pair it with, and the ratio between them. The rest is fine tuning, and that fine tuning is where formulation expertise sits.
2. The polyol — what it is
Polyols are oligomers carrying multiple –OH groups. Industrially, two families dominate: polyether polyols (made by adding propylene oxide and/or ethylene oxide onto a starter molecule — the most widely used class, with easier handling, lower viscosity and lower cost) and polyester polyols (made by polycondensation of acids with glycols — typically more viscous and more expensive, but producing polyurethanes with higher abrasion, cut and solvent resistance, and better high-temperature performance).
Beyond the chemistry family, the polyol's molecular weight, functionality (the number of –OH groups per molecule) and hydroxyl number largely set the behavior of the final foam. High-molecular-weight, low-functionality polyols bias the system towards flexible polymers; lower-molecular-weight, higher-functionality polyols bias it towards rigid, more crosslinked polymers. Specialised polyols — graft polyols, polymer polyols, natural-oil-based polyols, biomass-balanced grades — extend the range further for specific end uses.
3. The isocyanate — MDI, TDI and where each is used
Two aromatic isocyanates carry almost all industrial polyurethane volume worldwide. MDI (Methylene Diphenyl Diisocyanate) is the dominant isocyanate for rigid systems, panel cores, spray foam, microcellular elastomers and TPU. It is less volatile and easier to handle than TDI, and comes in several variants — pure 4,4'-MDI for elastomers and TPU, and especially polymeric MDI (pMDI), the workhorse for rigid foam, panel lines and spray applications.
TDI (Toluene Diisocyanate) is the dominant isocyanate for flexible slabstock foam — mattresses, furniture cushions — and many moulded flexible foams. It is more reactive than MDI, with faster rise kinetics, but also more volatile, with stricter exposure controls. A smaller set of aliphatic isocyanates (HDI, IPDI, H12MDI) is reserved for light-stable, non-yellowing applications such as automotive clear coats and premium leather coatings.
4. The isocyanate index — why balance matters
The "isocyanate index" expresses how much isocyanate is in the system relative to a perfect 1:1 stoichiometric match with the available –OH groups. An index of 100 is exact stoichiometry; values above or below shift the character of the final polymer. Real systems run at indices tuned for the application — slightly above 100 for most foams, much higher for PIR (polyisocyanurate) chemistry, occasionally below 100 for specific elastomer prepolymers.
In practice the index is one of the most important formulation levers. Two systems with the same polyol and the same isocyanate can behave very differently if their index is different — affecting hardness, dimensional stability, fire performance and surface quality. Setting the right index, choosing the right polyol-isocyanate pair, and tuning the catalyst and surfactant package for a given application is what a polyurethane system actually is. That work is the formulation expertise that goes into every JiTPOL product.
5. Safety and the REACH context
Polyols are generally classified as low-hazard chemicals. Isocyanates require more care: they are reactive towards moisture and amines, and exposure to NCO vapors or aerosols can cause respiratory sensitisation in untrained workers. The European trade association ISOPA publishes detailed product-stewardship and emergency-response guidelines for diisocyanate handling, transport and storage.
Since August 2023, the EU REACH restriction on diisocyanates has required industrial and professional users of any product containing more than 0.1% free diisocyanate to complete documented training. For exporters into European markets, downstream customers will expect aligned safety data sheets, packaging information and training documentation. In Türkiye, KKDIK and SEA regulations apply in parallel; safety data sheets must be in Turkish for domestic distribution.