In most daily activities we all use products in which polyurethanes were processed.

Polyurethanes play a large role in our daily life although we are not always aware of it. Polyurethanes are used among other places in our car, household appliances, furniture, beds, chairs, clothes, our shoes, foils, lacquers, skis, sports stadium linings and floor coverings, packing materials, sponges and many other ranges. Polyurethanes contribute to the improvement of our quality of life at home, in the working process and in our spare time.

Polyurethanes are plastics which can be used in most different applications. Charlotte Baur Formschaumtechnik GmbH has decided to specialize mainly in the area of the moulded foam materials to manufacture and supply.

Polyurethanes, shortened PUR, are manufactured by the polyaddition reaction by multi-functional polyisocyanaten and alcohols with two or higher order (Polyols).
For Polyurethanes the group of urethanes with the chemical structure of the urethane-linkage is characteristic:

Materials of this class usually also contain different bonding types, e.g. urea, amide, biuret, allophanate, ester and/or ether bondings. Therefore, the name polyurethane stands as comprehensive term for quite differently composed polymers.
The polyurethanes come to very different characteristics depending upon the varying raw materials used and the stoichiometric ratio of the basic materials. These materials are applied in adhesives and varnish (PUR resins), as thermoplastic material for storage parts like roles, tire, rollers, to be used as polyether and/or polyester urethane rubber, as duro-plastic casting resins and above all, as foamed plastics in various applications.

Polyurethane foams are produced from the polyaddition, if water and/or blowing agents are present. Water reacts with isocyanates to separate carbon dioxide which acts as propellant.
Depending on the raw materials, its stoichiometric ratio and chemical reaction conditions, it comes to Polyurethane soft foams, polyurethane rigid foams, integral foams and polyurethane composites.
 
Integral foams are foam materials, which are chemically identical over the entire cross section, their density decreases continuously from the outside in the core. They are characterized by a foamingly core and an almost solid skin. The set foaming process temperature gradient from inside to the skin of the part, causes a different expansion of the evaporating blowing agent, which condenses in the cold edge zone. Thus the described density variation in the foam material over the form cross section is received.
 
Additionally necessary auxiliary materials or additives with the polyaddition can be catalysts, emulsifying agents, foam surfactants, pigments, aging and fl

The polyaddition is a stepwise reaction of bi -, tri- or more-functional basic molecules (monomers) to large chain molecules (polymers). The polyaddition runs with no cleavage of molecules in contrast to the polycondensation.
A well-known example of a polyaddition is the reaction of diisocyanates with diols (more-functional alcohols) to polyurethanes. The isocyanate-group (-N=C=O) reacts with the hydroxyl group (-OH) to an urethane linkage (-NH-CO-O-).
Reaction scheme:

 

In chemistry all organic compounds are generally called alcohols, whose characteristic functional group is the hydroxy group (-OH). In polyurethanes mainly polymolecular polyetherole and/or polyesterole are used and are also briefly called polyole. E.g. in a two-component system the polyols is contained in the A-component.

Polyisocyanates (B-component) can be differentiated into aliphatic and/or cyclo-aliphatic and aromatic isocyanates. They can be summarized with the following general structural formula:
R-(N=C=O)n
The aromatic polyisocyantes have the greater economic importance. They are used with more than 90% of the applications of Polyurethanes. The two mainly used materials are 4,4'-methylenedi(phenylisocyanate) abbreviated MDI und toluolediisocyanate abbreviated TDI. Aliphatic and cyclo-aliphatic isocyanates are mainly used in varnishs due to their light resistance.
 
The production of the moulded polyurethane foams takes place by the injection of the liquid reaction mixture into the tool which is kept at a moderate temperature. The foam fills out the tool cavity completely after completion of the foaming reaction. The so called RIM (Reaction Injection Moulding) technology was developed in the 1970's for the production of also complicated polyurethane parts. The RIM procedure is based on rapid proportioning and mixing of the components (e. g. 2 components: A- und B-component) in the mixing chamber and injection of the whole reactive mixture e.g. in a tool (further steps for foams: rising / foaming of the reaction mixture and filling up the cavity and the fast cure of the part). The cycle time only takes a few minutes.

 

Photo (s) by: birgitH / pixelio.de
Small PUR Encyclopedia