What is Polyurethane?

Polyurethanes play a key role in society, yet most people are unaware of what they are or where they are used.

Polyurethanes are all around us. We sit on them, walk on them, and even sleep on them. They contribute to improving our living standards at home, work, throughout industry and in the leisure sector.
The most versatile of any group of plastics, polyurethanes are capable of an almost infinite number of variations in chemistry, structure and application.

Rigid polyurethane foam is a good insulant because it consists of 92-98% of closed cells. Only 2-8% of the foam depending on the density is solid polyurethane polymer. The closed cells are filled with insulating gases that are released by blowing agents during the manufacture of foam. The cell gas composition can be influenced by different blowing agents. Blowing agents that have a lower vapour thermal conductivity will lower the foam thermal conductivity. The insulating gas accounts for 60-65% of the final foam thermal conductivity.

Polyurethane foam’s popularity is based on these outstanding insulation properties, which prevent heat loss, or alternatively maintain temperatures in cold environments to prevent freezing or cracking. These energy conservation qualities improve the overall cost efficiency of customers’ networks and pipeline systems.

In the table below, the thermal conductivity at 50°C is given for a number of pipe insulation materials, along with the relative insulation thickness at an equal heat loss. Polyurethane foam is clearly the most effective material. Further advantages are that the polyurethane foam adheres well to both the service pipe and the casing pipe. As a result of the closed cell structure of the foam, penetration of water in the foam and along the length of the pipe is inhibited should the casing pipe be damaged.

Starting in the early 1980s, water-blown microcellular flexible foam was used to mold gaskets for panel and radial seal air filters in the automotive industry. Since then, increasing energy prices and the desire to eliminate PVC plastisol from automotive applications have greatly increased market share. Costlier raw materials are offset by a significant decrease in part weight and in some cases, the elimination of metal end caps and filter housings. Highly filled polyurethane elastomers, and more recently unfilled polyurethane foams are now used in high-temperature oil filter applications.

Polyurethane foam (including foam rubber) is often made by adding small amounts of volatile materials, so-called blowing agents, to the reaction mixture. These simple volatile chemicals yield important performance characteristics, primarily thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol led to the greatly reduced use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). Other haloalkanes, such as the hydrochlorofluorocarbon 1,1-dichloro-1-fluoroethane (HCFC-141b), were used as interim replacements until their phase out under the IPPC directive on greenhouse gases in 1994 and by the Volatile Organic Compounds (VOC) directive of the EU in 1997 (See: Haloalkanes). By the late 1990s, the use of blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) became more widespread in North America and the EU, although chlorinated blowing agents remained in use in many developing countries.

Building on existing polyurethane spray coating technology and polyetheramine chemistry, extensive development of two-component polyurea spray elastomers took place in the 1990s. Their fast reactivity and relative insensitivity to moisture make them useful coatings for large surface area projects, such as secondary containment, manhole and tunnel coatings, and tank liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. During the same period, new two-component polyurethane and hybrid polyurethane-polyurea elastomer technology was used to enter the marketplace of spray-in-place load bed liners. This technique for coating pickup truck beds and other cargo bays creates a durable, abrasion resistant composite with the metal substrate, and eliminates corrosion and brittleness associated with drop-in thermoplastic bed liners.

The use of polyols derived from vegetable oils to make polyurethane products began garnering attention beginning around 2004, partly due to the rising costs of petrochemical feedstocks and partially due to an enhanced public desire for environmentally friendly green products. One of the most vocal supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company.