How Polyurethane Foam Is Made and Tested

Polyurethane foam is a versatile material used in a wide range of applications. It is highly flexible with a high load-bearing capacity and is known for its durability. It can be combined with other materials such as a nonwoven substrate, netting, and fabric. Foam is commonly bonded to these materials using a heat process such as flame bonding, hot film adhesion, and powder laminating. The result is a padded product such as headliners for automobiles, or mattresses and seat cushions. The most important properties of polyurethane foam are its density, tensile strength, and elongation at break.

Polyurethane is made by reacting a polyol with a diisocyanate and blowing agents to form a polymer. The polyols are typically derived from either polyether or polyester. Polyethers are resistant to hydrolysis and oxidation, while polyesters are more stable to oxidation but less resistant to hydrolysis. Polyurethane is produced in a variety of ways, depending on the intended application. These include slabstock, continuous slab production, and foam lamination.

Slabstock production of polyurethane is a continuous process that forms slabs of foam directly on a conveyor belt. The polymer system is poured onto the conveyor where it is mixed with blasts of water or carbon dioxide coming from a nozzle. The bubbles cause the polyurethane to rise and spread over the conveyor, forming a sheet of foam. The sheets are cut to size and then bonded to a backing or other material using one of the above heat processes.

The foam is tested in several different ways to determine its performance. Load-bearing capacity is measured by pressing an indenter into the foam at 25%, 50%, and 65% of its thickness. The test results are recorded in newtons (N) and kilodeks (kN). The higher the value, the greater the load it can support.

In addition to measuring the load-bearing capacity of the foam, other tests are performed to measure its tensile and tear strengths, elongation at break, and air permeability. These are based on the same testing methods as those used to determine its load-bearing capacity.

The flammability of polyurethane foam has come under scrutiny following the dramatic increase in fire deaths in the UK between the late 1950s and early 1980s, with many of these deaths attributable to low-cost upholstered furniture products containing polyurethane foam. The fire toxicity of polyurethane is a result of the rapid decomposition and release of toxic chemicals such as polymerized toluene, hydrogen chloride, and methyl chloride. These chemicals are emitted into the atmosphere during the polyurethane synthesis process and can be absorbed through the skin of workers involved in the manufacture of the foam. To improve worker safety, research is underway to develop a substitute for CFC-11 blowing agent which is currently used. Research has indicated that substituting this chemical with a lower boiling point, less toxic, and a water-based blowing agent will provide a safer working environment.