Chapter 1 - Reagents & Fundamentals

Since Otto Bayer developed the polyurethane's (PU's) in 1937, in modern times this product turned out to be a fantastic success story as well as a business of many billion dollars. They are produced by the polyaddition reaction of an isocyanate (Chapter 1) (which may be di or polyfunctional) with a polyol (Chapter 1) and other low molecular weight reagents as chain extenders or crosslinking agents (Chapter 1), containing two or more reactive groups. Additives such as catalysts (Chapter 2), blowing agents (Chapter 2), surfactants (Chapter 2), fillers (Chapter 2), etc. are also used. The isocyanate can be aromatic or aliphatic (Chapter 1). The molecular weight, chemical nature and functionality of the hydroxyl compounds may vary within wide limits. The polyols can be polyethers (Chapter 1), polyesters (Chapter 1), or a hydrocarbon (Chapter 1). The chemical nature as well as the functionality of the reagents should be chosen in agreement with the desired final properties. This flexibility makes possible to obtain materials of different physical and chemical properties. This is the reason why PU's occupy an important position in the world market of high performance synthetic polymers.

The commercial development of PU's began initially in Germany in the end of the thirties, with the production of rigid foams (Chapter 5), adhesives (Chapter 7.1), and coatings (Chapter 7.3). PU elastomers (Chapter 6) originated in the forties, in Germany and England. During Second World War the development of PU's was discontinued, however since 1946 enormous growth could be observed in this market. The fifties registered the commercial development of PU's as flexible foams (Chapter 3). During the sixties, the use of chlorofluorocarbons (CFC's) as blowing agents in rigid foams resulted in extended use of this material in thermal insulation. In the seventies the semi-flexible and semi-rigid molded foams (Chapter 4) covered with thermoplastic materials were broadly used in the automotive industry. In the eighties, a commercially relevant technique, reaction injection moulding (RIM) (Chapter 4.2) was developed, giving impulse to studies on the relationships between molecular structure and properties of PU's. Due to environmental concern, in the nineties and in the beginning of the present millennium, researches have been directed to the substitution of CFC's considered harmful to the layer of terrestrial ozone, so that systems have been developed which are free of volatile organic compounds (VOC's), as well as PU's recycling.

1.1 - Market

The market for PU's, initiate in the years 1930, it already reached in 2002 a world consumption of the order of 10 million tons, with forecast of 11,6 million tons, in 2006 (Table 1.1). Nowadays, PU's occupy the sixth position, with about 5% of the market of the plastics more sold in the world, proving to be one of the most versatile products used by the industry. The largest consuming centers are North America, Europe and the Asian Continent. The global growth is largely being driven by the Asian economies, though the best markups are obtained mainly in the traditional markets of Europe and North America, where the high properties of the PUs can be used in new applications in the medical, automobile and construction markets.

By combining different raw materials such as polyols, isocyanates and additives, it is possible to obtain infinite variations of foam products. Thus, the need to assist market segments led to the development of several applications. In the area of flexible foams, PU's were popularized in the segments of mattresses, upholstery and automotive seats; semi-rigid ones were applied in the automotive industry as rest-arms, panels, bumpers, etc; the microcellular elastomers were directed to footwear (Chapter 4.8); and the rigid foams, used for the thermal insulation of refrigerators, freezers and trucks, and in construction as sandwich panels, etc. In most of the areas, the volume growth was 3-5% from 1996 to 2001, being larger for the rigid foams. Otherwise, solid PU's are used as elastomers, paints & coatings, adhesives & sealants, fibers, electric encapsulation, etc. Although the fields of PU's application are diverse, several key segments can be identified (Figure 1.1 and Table 1.2). Nowadays, PU's as flexible and rigid foams, coatings, elastomers, fibers, etc. comprise about 20 kg of the bulk of passenger cars.

Figure 1.1 - World PU application areas

In regional bases, the demand of polyurethane foam is relatively close of the production because the trade is relatively small. Even inside of the United States, geographically the supply follows the demand very closely, especially for the flexible products. A lot of hundreds of producers in the world manufacture the polyurethane foam, frequently in plants in different places. Most the producing of foam concentrate the efforts in flexible foam (Chapter 3) or in rigid (Chapter 5) because the markets and technologies are quite different. In recent years, the industry testified a concentration process, mainly in the United States and West Europe. Now the capacity of production of flexible and PU rigid foams is enough to assist the demand. The PU flexible foam is used mainly as a stuffing material in furniture, transport and mattresses. The PU rigid foam is used mainly as a material of thermal insulation in construction and refrigeration. The automotive seats (Chapter 4) are a globalize area where the main producers operate in several regions of the world. Global producers of block flexible foams are also appearing, but with less intensity.

In terms of the analysis of the market through the type of final product, it is interesting to notice that although mattresses & upholstered represent the largest market now in terms of volumes, other markets are trying a larger growth tax. Especially the production of rigid foams used for construction. This tendency is in agreement with the current norm of to reduce the greenhouse effect and to improve the energy efficiency, as well as the continuous urbanization of many economies in development. Out of the refrigeration section, the global growth of the PU rigid foam is close to the 5-7% a year, during at least the next 4-5 years.

Different reagents are used in the production of PU's, such as polyols, isocyanates and chain extenders. Additives are also used as catalysts, blowing agents, surfactants, etc. Several polyol types are found in the world market as: poly (propylene/ethylene oxides) glycol (PPG's), polyester polyols, poly (tetramethylene oxide) glycols (PTMEG's or PTHF's), castor oil-based polyols, polycaprolactone glycols, hydroxyl terminated polybutadiene (HTPB), etc. However, the more heavily consumed polyols are polyethers of different structures (PPG's). Several aromatic and aliphatic isocyanates are commercially available, however 95% of the consumed isocyanates are based on toluene diisocyanate (TDI) and difenylmethane diisocyanate (MDI) that may be prepared from accessible low cost diamines. Table 1.3 presents the market of the main raw materials.

During the eighties and half of the nineties, the polyester polyols was considered the poor relatives of the polyols, answering for only 10% of the total market. Nowadays, the polyesters represent 25% of the market and it is waited that this tendency continues. In the flexible PUs (as synthetic leather, shoe soles, and elastomers), the aliphatic polyesters polyols (Chapter 1) are used whose market in 2001 was about 1.000 thousand tons, with forecast of 1.090 thousand tons in 2006. In the rigid PIR and PUR foams are used the aromatic polyesters polyols (Chapter 1), whose consumption in 2001 was about 310 thousand tons with forecast of 410 thousand tons in 2006.

1.2 - Isocyanates