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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 polytetrafluoroethylene (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, in the fibers of your clothing, insulation of your walls and roof, in your refrigerator, dishwasher, water heater, automotive seating, automotive structural foam, automotive paints and coatings, furniture coatings, your bed mattress, 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 if polyurethanes are not the most versatile class of materials, then they are 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 of 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 industrial concerns. While BASF continues to engage with and maintain a significant presence within the polyurethane industry, Bayer spun off its polyurethane business and the rest of its industrial chemicals concerns into a new company called Covestro.

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. du Pont de Nemours and Company (now known as DuPont) and The Dow Chemical Company. While Dow Chemical remains one of the world’s largest manufacturers of polyurethane chemicals, DuPont has exited its polyurethanes businesses, which were primarily textile and coatings 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 global consumption of plastics by volume (Figure 1.1).

FIGURE 1.1 Percentage global consumption of plastics in 2018. Polyethylene encompasses all densities; styrenics includes all copolymers along with atactic polystyrene. These relative values are similar to those in the first edition using 2012 data. The consumption of many plastics grows at a rate relative to economic activity plus a small accelerator or decelerator for each given plastic’s role in the market. PET = polyethyene terephthate.

The structures of the listed commodity polymers are relatively simple repeating units (Figure 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, for instance, introducing branches, but these complexities do not fundamentally alter the basic polymer structure.

FIGURE 1.2 Illustrative structures of high‐volume commodity polymers.

Polyurethane is the largest volume commodity polymer that cannot be characterized by a simple structure such as that 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 (Figure 1.3).

FIGURE 1.3 The urethane unit within a polyurethane polymer chain.

Specific polyurethane structures used for making mattress foam, 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‐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 it is testament to the versatility and performance of polyurethanes that they 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, for example, the following categories: polyisocyanates, polyethers, polyesters, water, and amines (Figure 1.4). As building block categories they also cannot be represented by unique structures and are denoted by “R” to allow designers to insert any conceivable chemically allowable unit.

FIGURE 1.4 Chemical structures of isocyanate, polyester, and polyether. To make a polyurethane the Rʹ of the isocyanate structure must also have an isocyanate function [1].

The polyurethane unit is easily mistaken for the related polyester, polyurea, or polyamide (nylon) structures (Figure 1.5). In fact, polyureas, polyesters, and polyurethanes are often joined into polyurethane materials and still broadly classified as polyurethane. (Polyamides were not previously a part of polyurethane chemistry because of their vastly different processing characteristics. However, recent literature indicates nascent explorations of urethane–amide hybrids; see Chapter 13.)

FIGURE 1.5 Structures of urea, ester, amide, and urethane functionalities.

As commodity products, polyurethanes have achieved a certain establishment status in academic science. However, activity in polyurethane science shows no sign of abating owing to its high potential for design and innovation [1–18]. Figure 1.6 shows total global publication activity, including patents, journal articles, reviews, meeting abstracts, governmental documents, etc., for the years 1954–2019 and for the period 2013–2019 for all of the commodity plastics named in Figure 1.1. While many plastics exhibit publication activity approximately in proportion to their production, polyurethane publication activity is more than double its production. Figure 1.7 shows polyurethane publishing activity by language for the same periods, demonstrating the explosive growth in materials research in China. 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 patent publications predominate but open literature activity is nearly as prevalent. In the first edition of this book it was found that open literature and patent literature were produced at very similar levels.

FIGURE 1.6 Publication activity focused on commodity plastics for (a) 1954–2019 and (b) 2013–2019. The total includes all public literature, patent filings, conference proceedings, and books where the subject focus is the plastic. The total number of publications for all listed plastics is 2.5 million.

FIGURE 1.7 Publication activity in polyurethane science by language from (a) 1954–2013 and (b) 2014–2019. Data demonstrate the recent explosive growth in materials research in China.

FIGURE 1.8 Types of publication (all languages) where the focus of the work is polyurethane polymer properties for 2013–2019. 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.

Further exploration of these trends shows (Figure 1.9) that patent activity is broad across technologies and focused on specific applications in the areas of coatings and fibers, and is related to performance in construction applications and fire resistance. Exploration of the coatings applications shows broad use of polyurethanes for fiber sizings, hair colorants, wound dressings, traffic paints, golf ball coatings, and numerous other unrelated fields. In contrast, categorization of topics studied in the open literature related to polyurethane properties tends more toward fundamental physical materials science issues.

FIGURE 1.9 Analysis of (a) patented polyurethane topics during 2013–2019 and (b) open literature topics during 2013–2019 by prevalence. The patents analysis is for patents in English, whereas the open literature analysis reflects activity in all languages.

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 unacceptable to another. They take into consideration regional preferences and 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 that are important to specific customers or groups of customers, such as the advantages or value a product may have versus a competitive material or a competitive company in specific cases. 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 are common commercial failures, and the ability to shrewdly navigate price movements is the hallmark of well‐run companies.

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 globally and especially in China. In particular, this capacity growth has injected chemical production during a period of global economic growth but uncertain economics in the future. Figure 1.10 shows the extent of isocyanate overproduction. The 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. In the past manufacturers with a strong financial base have decided to wait out the failure of financially weaker producers. The closure of these weak assets will reduce production volumes, called “tightening the market.” It is also the case that in the past 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 to 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 because of 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. In that same spirit, 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. Lastly, it has recently been dramatically demonstrated that temporary occurrences, such as plant disruptions, can have significant effects on supply. From the middle of 2016 until the middle of 2018 commodity isocyanates nearly doubled in price as a confluence of planned and unplanned plant shutdowns during a time of vigorous economic growth put significant constraint on supply, allowing unaffected producers to greatly increase market share and profitability during this period. Upon resolution of these temporary issues, prices fell to historical trend levels.

FIGURE 1.10 Percentage isocyanate plant capacity utilization. The triangle denotes a published expectation for 2017 from the first edition while the circles show the actual. Predictions of future economic activity should always be viewed skeptically. MDI is methylene bisphenyl diisocyanates and its oligomers.

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. For example, during 2017–2019 there were polyurethane feedstock expansions in Saudi Arabia and the US Gulf Coast (areas of high petrochemical resources) as well as in China and Europe (areas with lower petrochemical resources). 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 political 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 towards 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. Innovation has rather focused on the development of gas‐phase phosgenation processes that reduce solvent and energy consumption. While the large majority of polyols are produced by conventional KOH catalysis there has been moderately increasing production of polyols derived from new double‐metal cyanide (DMC) catalysts. While DMC catalysis offers significantly improved production economics, it has been limited to primary utility making slab foam polyols and has been excluded from molded foaming operations because of performance issues (see Chapter 2). On the other hand, improvements in established products, such as production of copolymer polyols with ever higher solids content, lower viscosity, smaller particle size, and improved production operations, will undoubtedly continue and find success in the market. There has been increasing attention paid toward circular economy issues related to polyurethanes, particularly as components of large visible items such as mattresses. There has been progress in processing these materials back to useable feedstocks (see Chapter 14); however, the economics of polyurethane recycle collection and conversion of finished product back to useable polyols is still questionable. Meaningful progress in the circular economy of polyurethanes may await organized municipal collection and rational recovery processes to handle the waste. Lastly, there is a growing initiative in the development of polyurethane structures hybridized with backbones that would normally be thermodynamically immiscible. The goal in this development is to obtain desirable properties of polymer backbones while minimizing any negative attributes that may evolve from thermodynamic incompatibility (see Chapter 13).

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 as a result of governmental and consumer pressures, particularly in Europe. The trend toward the use 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, because of kinetic limitations of reaction‐induced phase separation, theory and reality are often in conflict. The exponential increase in computing power allows for finer grained simulations of larger volumes that can be harnessed by modern molecular dynamics, self‐consistent field, and coarse‐grained theoretical techniques. Additionally, advances in predictive intelligence from massive dataset analysis now allows researchers to better predict or simulate experimental results. Such advances have resulted in commercial software such as Materials Studio® and GeoDict® achieving wide use for prediction of polyurethane properties industrially.