In the introduction, I mentioned that polyurethanes are chemically different. Perhaps, it is worth briefly mentioning the chemistry of polyurethanes used in our production in conjunction with their physical and mechanical properties.
Well, first of all, the isocyanate component. In our production we always use MDI – methylene diphenyl diisocyanate, this is one of the three most common sources of isocyanate groups.
The second is TDI, which is extremely poisonous in processing and is not very technological, nevertheless, some brands (such as SKUPFL) have been based on it since Soviet times. It is cheaper, but we decided that it would be better to have healthy experienced workers than cheap savings on raw materials. Again, TDI is basically banned for processing in civilized countries, and maybe in Russia it will eventually be banned, so it’s risky.
The third option is NDI, compositions based on it have a number of unique characteristics (for example, residual deformation is minimal and can withstand very high impact and compressive loads), but it is extremely difficult to process.
There are dozens of other options for isocyanate components, from obsolete IDIs and HDIs to experimental aromatic triisocyanates, but these are all exotic: according to Wikipedia, they all together occupy a few percent of the market.
The second component of polyurethanes is polyol, and options are also possible here. In general, polyols can be divided into polyols based on simple and complex polyesters, while polyurethane of the same hardness on the basis of simple ones will be more elastic and frost-resistant, and on the basis of complex ones – more durable.
We produce auto parts from both, depending on the applicability: if the part undergoes constant large deformations and has a small thickness, as a result of which it bursts in harsh Siberian conditions (for example, a boot or a snowmobile hood mount), we take a composition based on a simple one, if the part experiences high loads – on the basis of the complex, if you want a little of everything, and extreme properties are irrelevant – we take a mixture.
The third component is a crosslinker, a polyhydric alcohol capable of bridging the chains of the base polymer. This is what determines the hardness of the material, more bridges – more hardness. Unfortunately, the most common crosslinker in the world – 1,4-butanediol (BDO) – is also a precursor, so its distribution in Russia is limited and most processors never meet it in its pure form, but get ready-made polyol mixtures from European manufacturers with a crosslinker, losing the ability to vary the hardness of the resulting product. We have permission to use BDO, and we use it, so we can theoretically make polyurethane of any hardness within reasonable limits (from 40 to 99 Shore A).
There are also a number of auxiliary components – catalysts, inhibitors, plasticizers, copolymers, pigments, and so on, but perhaps it makes no sense to consider them.