A Brief Introduction to the Polyurethanes According to the Principles of Green Chemistry

Polyurethane technology started in 1937 but developed rapidly during World War II, when polyurethane coatings were used to impregnate paper and make mustard gas-resistant clothing. They have also been used in high-gloss aircraft finishes and chemical and corrosion-resistant coatings to protect metal, wood, and masonry .

 “Polyurethanes” stands for a huge group of various polymers, which only have the same urethane moiety and the remaining parts of their chemical structure are completely different, the form, structure, and, above all, the properties of polyurethanes are various. Polyurethanes cover a wide group of polymers that differ in chemical structure, morphology, and even physical state, and the method of obtaining them is also completely different. Typical cast polyurethanes, elastomers, thermoplastics, etc. are obtained as a result of the reaction of the addition of isocyanate and hydroxyl groups , during which no by-products are formed. On the other hand, polyurethane foams are obtained in a polycondensation reaction, where the foaming agent is often water (or some low-boiling, inert solvent) that reacts with isocyanate groups to form CO₂ .

Because the form of polyurethanes and their properties are so diverse, the area of application is huge. 

In 2006, Matsumura, Soeda, and Toshima published an interesting review on the synthesis of polyurethanes in accordance with a sustainable economy. They indicated the synthesis of non-isocyanate-free, biodegradable, and lipase-synthesized polyurethanes. Where did the development of green polyurethanes go over the next 15 years?

In the 1990s, it was finally recognized that preventing the generation of waste at source is better for the environment than its disposal. This changed the way of thinking of decision-makers and resulted in the term “green chemistry”, which became established with the formulation of the 12 principles of green chemistry in 1998 .

These are: 1. Prevent waste, 2. Maximize atom economy, 3. Design less hazardous chemical syntheses, 4. Design safer chemicals and products, 5. Use safer solvents and reaction conditions (avoid auxiliaries), 6. Increase energy efficiency, 7. Use renewable feedstocks, 8. Avoid chemical derivatives, 9. Use catalysts, not stoichiometric reagents, 10. Design chemicals and products to degrade after use, 11. Analyze in real time to prevent pollution, and 12. Minimize the potential for accidents.

Future Perspectives and Conclusions.

What can be done to make polyurethanes greener?

The development of the polyurethane industry goes in one direction with the polymer industry in general, the basic directions of changes, taking place during the synthesis of polyurethanes, are: (1) the use of non-toxic substrates and auxiliary compounds (solvents and catalysts); (2) obtaining products with appropriate strength during use but which degrade after their lifetime; and (3) the use of less energy-intensive processes. The modification of polyurethanes with compounds of natural origin is of significant importance. Their presence in the polyurethane network or in its chemical structure increases the non-toxicity and susceptibility to degradation in the environmental conditions of this material.

The presented results of the works of many authors show that much has already been done to make polyurethanes more environmentally friendly materials. Polyurethanes are already obtained very often in accordance with the principles of green chemistry. Perhaps, however, to obtain them, one should reach for such natural resources, which are currently useless agricultural or food post-production or post-consumer waste.