Polyurethane systems

Concentrol constantly reviews its entire range of products to adapt it to the requirements of the industry and current regulations. Polyurethane systems have been the focus of the chemical company’s latest research, which is going to define the strategy for each of the lines.

Polyurethane systems consist of two components, one of which is a mixture of polyols with additives and the other a diisocyanate. When mixed homogeneously, they react forming polyurethane. Concentrol has focused its efforts on the system for the last 6 years, investing hours of research both in the laboratory and in the commercial field.

The first of the components of the system is the mixture of polyols with reactive -OH groups, containing catalysts, flame retardants, expansive agents and foam stabilizing agents. There are polyols of the polyester type (the most common), polyether (which provide good mechanical properties and high reactivity) or special polyols.

The second component of the polyurethane system is the Isocyanate, a bond of one or several NCO groups. The most common would be the aromatic types (MDI, TDI, PMDI), but there are also aliphatic types.

Each polyurethane system is adapted to the needs of the client. In this way, polyurethane can acquire various properties through additives:

• Catalysts
• Stabilizing Silicones
• Expansive agents
• Flame retardant agents
• Deaerating and antifoaming agents
• Antioxidants
• Cell openers
• Anti-separation additives
• Moisture absorbers
• Fungicides
• Dyes

The versatility of polyurethane systems, their composition and their additives means that they are used in many sectors. There are several types: flexible, viscoelastic, rigid, semi-rigid, integral, RIM, RRIM.

The production process

The production process is both continuous and discontinuous and is based on the mixture of raw materials (polyols or isocyanates, depending on the case) and other auxiliaries (catalysts, expansive agents, flame retardant agents, colorants and additives, depending on the case).

To manufacture the formulated polyol component (component A), different kinds of polyol are mixed together with other materials, such as catalysts, foaming agents, flame retardants, dyes, silicone stabilizers and other additives.

The polyol provides many of the final properties of the polymer, including flexibility, low temperature properties, processing characteristics, and stiffness. The most common polyols intended for the manufacture of polyurethanes are the polyethers synthesized from ethylene oxide, propylene oxide and tetrahydrofuran (C2, C3 and C4, respectively). There are also polymeric polyols.

On the other hand, the formulated isocyanate component (component B) is produced by mixing different types of MDI (4-4-diphenylmethane diisocyanate). In some cases, small doses of polyol are also added to the MDI, producing a prepolymerization chemical reaction that aims to modify the final characteristics of the product.

Within the isocyanates they are generally classified as aromatic and aliphatic. Within the aromatics we can mention the MDI, PMDI and TDI. Those who are of the aromatic type, one of their two main characteristics is that their aromaticity causes them to be prone to absorb UV radiation. This causes secondary oxidation reactions to take place, especially in the presence of atmospheric oxygen and water. This causes colorations from yellow to brown, depending on the degree of oxidation.

Another very important characteristic is that they are more reactive than the aliphatic types. These are more expensive and less reactive and are used when light stability is an important factor. To carry out the production, mixing reactors of different capacities are available. The dosing and mixing process is automated and managed by robots.

Technology

There are two types of polyurethane injection machines: low pressure and high pressure. These can be used for batch or continuous production.

• Low pressure machines: they are the least used, low production, small production volumes. In that case, the mixing heads, the components are mixed in separate chambers by means of a mechanical stirrer. More raw material is wasted and the head must be cleaned at each shot.
• High pressure machines: with these the working conditions are improved. The manufacture is more precise, since the components are mixed effectively. The heads clean themselves every time.

Sectors

The polyurethane market is divided into a dozen sectors, the most important being: construction and building, the automobile sector and electronics. It is also used in furniture, mattresses and packaging.

For construction and building, formulated and semi-formulated polyurethane systems are used to obtain rigid foams.

One of the relevant applications within this sector would be Sandwich panels, which are made up of an insulating core of rigid polyurethane (PUR) or polyisocyanurate (PIR) foam adhered to two metal profiles. These are usually made of steel or aluminum.

Rigid polyisocyanurate foam (PIR) is a variant of polyurethane foam (PUR) that maintains practically the same appearance, altering, instead, its mechanical and thermal properties, which differ mainly due to its better fire behavior. PIR foam reacts to fire safely by forming a carbonaceous surface layer that protects and prevents fire penetrating the internal layers.

Examples of applications of polyurethane systems within this sector are shown below:

• PUR and PIR Sandwich Panels with continuous technology, both with metallic and flexible coatings, used in enclosures (facades and roofs), cold rooms and insulation in construction.
• PUR and PIR Sandwich Panels with discontinuous technology used in the cold industry.
• Rigid PUR systems for on-site spray application in the construction sector.
• Rigid polyurethane systems to be applied by casting. Rigid polyurethane block for obtaining plates and shells for insulation.
• Rigid PUR systems for loads and shutters
• Rigid polyurethane systems for pipe insulation (pipe insulation)
• Rigid polyurethane systems for insulation in thermal solar collectors
• Elastomeric PU systems by coating (density 1000)
• Polyureas

Secondly, the automotive sector stands out. Below is a summary according to the polyurethane system which application we would have within the commented sector:

Another important sector for sales potential is furniture. Here we see the different possibilities:

As for another important sector, such as footwear, below we see the possibilities: