Polyurethane Foam System
Publication No. 12408
Try this amazing demonstration! Simply mix two liquids together and watch as the mixture expands to about 30 times its original volume. The result is a hardened, lightweight polyurethane foam.
Food coloring (optional)
Polyurethane Foam System (Part A and Part B)*
Disposable cups (clear plastic, if available), 2
Disposable glove, clear (optional)
Paper towels or newspaper
Tongue depressor or stirring rod
*Materials included in kit.
This activity should only be performed in a fume hood or well ventilated area. Avoid breathing any vapors produced and avoid skin contact, as both Part A and Part B may contain skin and tissue irritants. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The disposable cups may be thrown in the trash. Any leftover liquids should be mixed together, allowed to react, and then the solidified polymer may be disposed of in the trash according to Flinn Suggested Disposal Method #26a.
There are many forms of polyurethane such as fibers, coatings, elastomers, flexible foams and rigid foams. The foam in this system is a rigid foam that is used in furniture, packaging, insulation, flotation devices and many other items. Here, a rigid polyurethane foam is produced by mixing equal parts of two liquids, called Part A and Part B. This lightweight foam expands to about thirty times its original liquid volume and will become rigid in about five minutes.
Part A is a viscous cream-colored liquid containing a polyether polyol, a silicone surfactant, and a catalyst. The polyether polyol may be a substance such as polypropylene glycol [HO(C3H6O)nH]. The hydroxyl (–OH) end of the polymer is the reactive site. The silicone surfactant reduces the surface tension between the liquids. The catalyst is a tertiary amine which aids in speeding up the reaction without being chemically changed itself. Part B is a dark brown viscous liquid containing diphenylmethane diisocyanate [(C6H5)2C(NCO)2] and higher oligomers (dimers, trimers or tetramers) of diisocyanate. When the polyether polyol (Part A) is mixed with the diisocyanate (Part B), an exothermic polymerization reaction occurs, producing polyurethane (see Equation 1).
During the course of the polymerization reaction, a small amount of water reacts with some of the diisocyanate. A decomposition reaction occurs and produces carbon dioxide gas, thus causing the solution to foam and expand in volume. Pores in the mixture are created from the gas; these pores are visible when looking at the rigid substance. The multifunctionality of both reactants leads to a high degree of crosslinking in the polymer, causing it to become rigid within minutes (see Equation 2).
Rosato, D. V. Rosato’s Plastics Encyclopedia and Dictionary; Hanser: New York, 1993; pp 318–320, 572.