Polyurethanes. Mark F. Sonnenschein

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СКАЧАТЬ 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.

REFERENCES

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      14 [14] J Bicerano, Prediction of Polymer Properties, 3rd Ed., Marcel Dekker, New York, NY, 2002.

      15 [15] MF Sonnenschein, Polyurethanes: Science, Technology, Markets, and Trends, Wiley, Hoboken, NJ, 2014.

      16 [16] S Thomas, A Rane, K Kanny, G Thomas, Eds., Recycling of Polyurethane Foams, William Andrew, Oxford, UK, 2018.

      17 [17] S Cooper, J Guan, Eds., Advances in Polyurethane Biomaterials, Elsevier, Amsterdam, the Netherlands, 2016.

      18 [18] B Obi, Polymeric Foams: Structure–Property–Performance. A Design Guide, William Andrew, Oxford, UK, 2017.

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