In the early 1900s, there were very few of the synthetic polymers we have grown accustomed to now. During succeeding years, polymer science experienced explosive growth with the invention of polyvinyl chloride (PVC, 1913), polyethylene (1933), polyvinylidene chloride (Saran, 1933), polyamides (nylon, 1934), and polytetrafluo-roethylene (Teflon, 1938). In addition, during the 1930s, the polymer family known as polyurethanes was invented. Now, of course, polyurethanes, and all the polymers developed during this period, have become an integral part of modern life. As you read this, you may not be aware of how many ways polyurethanes surround you. They are present in the shoes you stand in, the seat cushion you sit upon, the carpet backing and foam pad underlay you walk upon, the fibers of your clothing, insulation of your walls and roof, your refrigerator, dishwasher, water heater, automotive seating, automotive structural foam, automotive paints and coatings, furniture coatings, your bed mattress, and the adhesive holding this book together—the list just goes on. This book's purpose is to explain polyurethane science, technology, applications, trends, and markets in virtually all of its forms and relate those structures to the properties that make them so suited for so many uses. It is not an overstatement to say that polyurethanes are, if not the most versatile class of materials, then certainly one of the most versatile polymer categories in existence.
Discovery of polyurethane chemistry is attributed to the efforts of Otto Bayer and the research team he led at the now defunct I.G. Farben AG chemical company. The first patent associated with polyurethanes was filed in 1937, and numerous other patents, most notably the production of flexible foams resulting from isocyanate-water reactions, were filed thereafter. I.G. Farben was broken up following World War II for complicity in war crimes, and the company's top leaders were convicted for crimes against humanity (exploitation of slave labor and production of nerve gas). The largest surviving components of I.G. Farben, Bayer AG and BASF SE, remain very large and respected global chemical concerns and very large producers of polyurethane chemicals.
After the initial discovery and expositions of basic chemistry, mostly based on short-chain diols and polyester polyols, industrial polyurethanes saw immense growth following the development of polyether polyols by E.I. DuPont de Nemours and Co. and The Dow Chemical Co. While Dow Chemical remains one of the world's largest manufacturers of polyurethane chemicals, DuPont has exited its polyurethane businesses that were primarily textile and coating related. While polyesters remain prominent components of polyurethane chemistry, it was the superior processing, low-temperature flexibility, and hydrolytic stability of polyether polyols that expanded polyurethane polymers into their current acceptance in every aspect of modern life.
As ubiquitous as polyurethanes are, it is perhaps surprising that they represent a relatively minor (but still significant) fraction of the overall volume of plastics global consumption (Fig. 1.1). Structures of the listed commodity polymers are relatively simple repeating units (Fig. 1.2). Their simplicity is in part responsible for their high level of utility and low-cost positions. The plastics industry has generated variants of the structures shown in Figure 1.2 by introducing branching, for instance, but those complexities do not fundamentally alter the basic polymer structure.
Polyurethane is the largest volume commodity polymer that cannot be characterized by a simple structure such as shown in Figure 1.2. Instead, polyurethane represents a class of polymers, and any polymer with a urethane repeat unit is classified as a polyurethane regardless of the other functional or polymer structures incorporated (Fig. 1.3).
FIGURE 1.1 Percentage global consumption of plastics in 2012. Polyethylene encompasses all densities; styrenics includes all copolymers along with atactic polystyrene.
FIGURE 1.2 Illustrative structures of high volume commodity polymers.
FIGURE 1.3 The urethane unit within a polyurethane polymer chain.
Specific polyurethane structures used for making mattress foam, or insulation foam, or shoe foam, can be significantly different from one another and cannot be neatly represented like the structures in Figure 1.2. In fact, even structures of different insulation foams can vary so widely that they also cannot be easily represented by a single structure. Another difference with other commodity polymers is that large
FIGURE 1.4 Chemical structures of isocyanate, polyester, and polyethers. To make a polyurethane, the R' of the isocyanate structure must also have an isocyanate function. Reprinted with permission from Ref. . © John Wiley and Sons, Inc.
FIGURE 1.5 Structures of urea, ester, amide, and urethane functionalities.
volume polyurethane applications require the mixing of two reactive liquid components rather than the processing of a pellet into a molded or extruded object. Given these complexities, it is remarkable that polyurethanes have developed into a commodity plastic category and is a testament to polyurethane versatility and performance that polyurethanes are so difficult to replace in their favored applications.
Polyurethane polymers as a class are made from commodity building block reagents and short-chain polymers (or oligomers). These building blocks include categories: polyisocyanates, polyethers, polyesters, water, and amines, for example (Fig. 1.4). As building block categories, they also cannot be represented by unique structures and are denoted "R" to allow designers to insert any conceivable chemically allowable unit.
The polyurethane unit is easily mistaken for the related polyester, polyurea, or polyamide (nylon) structures (Fig. 1.5). In fact, polyureas, polyesters, and polyurethanes are often joined into polyurethane materials and still broadly classified as polyurethane (polyamides are not a part of polyurethane chemistry due to vastly different processing characteristics).
As commodity products, polyurethanes have achieved a certain establishment status in academic science. However, activity in polyurethane science shows no sign of abating, due to its high potential for design and innovation [1-14]. Figure 1.6 shows total global publication activity including patents, journal articles, reviews, meeting abstracts, governmental documents, etc. for the years 2003-2014 for all commodity plastics named in Figure 1.1. While many plastics exhibit activity approximately in proportion to their production, polyurethane activity is more than double its production. Figure 1.7 shows the annual growth of polyurethane publishing for publications where a polyurethane polymer property is the focus of the document. The steady growth of activity appears independent of general global economic activity. Figure 1.8 quantifies the kinds of publications over this time period showing that open literature publications predominate but that patent activity is nearly as prevalent.
FIGURE 1.6 Publication activity focused on commodity plastics for the years 2003-2013. The total includes all public literature, patent filings, conference proceeding, and books where the subject focus is the plastic. The total number of publications for all listed plastics = 1,265,554.
FIGURE 1.7 Publication activity for the years 2003-2013 where the subject focus is polyurethane polymer properties. Graph shows steady increase and no apparent dip in the global recession years 2008-2010. Only publications in English are collated. Addition of other languages does not materially change the distribution but does change the number.
FIGURE 1.8 Type of publications where the focus of the work is polyurethane polymer properties for the years 2003-2013. The high level of open literature and patent activity demonstrates the continuing intellectual and commercial interest in these materials. The logarithmic scale may exaggerate the importance of items at the low end of the distribution. Only publications in English are collated, which partially skews the distribution. Addition of other languages would include a significant amount of work in Chinese.
This book also covers markets and commercial aspects of the polyurethane industry. The market and commercial activities overlap, but they are not synonymous. The overlap in how the words "marketing" and "commercial" are used reflects their conflation in meaning. Polyurethane market concepts are broader, more strategic, and more theoretical than commercial concepts. Marketing encompasses the equilibrium and nonequilibrium driving forces that make one material attractive to a consumer and another unacceptable. They take into consideration regional preferences, regional access to feedstocks, and the underlying cultural and societal influences that make a product useful or desirable or possess value. They also include the advantages a particular competitor in a market may possess from all facets including intellectual (i.e., patents).
The commercial aspects of an industrial product include those aspects that are important to specific customers or groups of customers such as advantages or value a product may have versus a competitive material or a competitive company. Probably the most prominent commercial aspect, especially for commoditized products, is price and price movement. Without doubt, thorough and confident knowledge of pricing in commerce is essential and can distinguish a profitable enterprise from one that fails. A commercial move to raise prices when there is excess capacity, or failure to raise prices when there are shortages or feedstock prices are rising, is common commercial failure, and the ability to shrewdly navigate price movements is the hallmark of well-run companies.
FIGURE 1.9 Percentage isocyanate plant capacity utilization. Projections are indicated by enhanced data points based on announced capacity increases and closings and growth extrapolations.
In recent years, the polyurethane industry has been subject to significant macroeconomic forces. The overriding force has been the expansion of polyurethane feedstock manufacturing capacity in China. In particular, this capacity growth has injected chemical production during a period of global economic stagnation (especially in Europe) and slow growth environments in North America. Figure 1.9 shows the extent of isocyanate overproduction. The deteriorating demand/capacity ratio can have a very material impact on price expectations and influence decisions on additional capacity expansions. It is not always the case that manufacturers flee a market in response to temporary price declines resulting from overexpansion. It has occurred in the past that manufacturers with a strong financial base will wait out the failure of financially weaker producers. The closure of these weak assets will reduce production volumes, called "tightening the market." It has also occurred in the past that manufacturers with a particularly strong financial position and a strong commitment to the market will increase production in the face of overcapacity to further drive down prices and drive weak manufacturers into untenable production economics. The anticipated response is for weak producers to shutter poorly performing manufacturing assets or sell their business to one of their competitors. Following these closings, production can regain a capacity/demand balance and prices can rise. This kind of "game" is not seen very often now in the chemical industry. In part, this is due to the relatively small number of global manufacturers and their similar financial strengths, maturity, and experience. Additionally, regulation of monopolistic behavior has become more stringent, and the potential gain by this kind of predatory practice may not be worth the potential reputational risk. Lastly, many manufacturers see the benefit of strong and rational competition in the marketplace. Rational and mature competition can provide ballast to minimize market fluctuations and provide a stimulus to improve business performance. In contrast to rational industrial practices, the recent haphazard expansion of polyurethane elastic fiber production has witnessed rapid capacity expansion concomitantly with falling prices. Very few major manufactures from the year 2000 are still in the market, and commercial profitability and market value have probably been permanently destroyed. This is covered in detail in Chapter 9.
The trends in polyurethane manufacturing reflect global competitive pressures and global opportunities. This has resulted in expansion of manufacturing assets close to raw material feedstocks and also close to geographies with increasing economic growth. It is not immediately clear whether it is cheaper to ship commodity feedstocks to centers of economic activity or ship finished polyurethane chemicals from low-cost manufacturing sites. However, low feedstock cost manufacturing is probably less prone to geopolitical factors and will always maintain a low-cost position. On the other hand, market and commercial flexibility is enhanced by proximity to customers.
There is continuing movement toward manufacturing innovation using processes that reduce usage of solvents and reagents and involve less purification and environmental impact. There is probably little incentive for production of new families of polyurethane building blocks, particularly for new polyisocyanates. It would appear that the regulatory burden of new isocyanate production inhibits innovation, and currently available products perform adequately and at acceptable cost. In the same regard, there has been relatively weak growth of polyols derived from new DMC catalysts despite the performance advantages of the polyol product (see Chapter 2). Again, this is probably due to insufficient performance/cost incentive for manufacturers or customers resulting in slow adoption. On the other hand, improvements in established products, such as production of copolymer polyols with ever higher solid content, lower viscosity, and smaller particle size, will undoubtedly continue and find success in the market.
The trend for polyurethane applications is being driven by overriding trends in the industries in which polyurethanes find purpose. Thus, automotive trends toward lighter weight dictate a trend toward higher performance at lower foam density. Higher performance includes achieving required comfort factors with lower vibration and noise transmission. In construction markets, the trend is toward improved thermal insulation with new blowing agents that exhibit lower ozone depletion potential and now lower global warming potential as well. Restrictions on acceptable flame retardant packages for both flexible foams and rigid foams are also a driver of polyurethane industrial innovation. Thus, blowing agents and flame retardants score highly in the intensity of industrial activity associated with polyurethanes. Industrially, reactive catalyst innovation has been consistently pursued (to reduce fugitive catalyst emissions). This trend may intensify in the future due to governmental and consumer pressures, particularly in Europe. The trend toward further employment of renewable feedstocks has been slow and based on patent activity will probably remain so for the near future.
The science of polyurethanes is ongoing and will continue a high level of activity in the future. While a great deal is known about the fundamentals of polyurethane structure-property relationships, the control of these relationships is still being actively pursued. Most understanding of polyurethanes is based on equilibrium properties; however, due to kinetic limitations of reaction-induced phase separation, theory and reality are often in conflict. Exponential increases in computing power allow for finer-grained simulations of larger volumes that can be harnessed by modern self-consistent field theoretical techniques to better predict or simulate experimental results.