Polyurethane Foam Formation

Overview

Polyurethane foam is made by mixing equal amounts of a two component foam system. When these two liquids mix, the resultant foam produced has a volume 20-30 times the original.

Materials

  • 40 ml Part A and

    40 ml Part B of two component polyurethane foam system

    Two 50 ml paper cups

    Paper Towels

    1 large disposable cup

    2 stirring rods

    •

    • Procedure

      1. Measure equal amounts of Part A and Part B liquids into the two 50 ml paper cups.
      2. Cover an area of about 2 square feet with paper towels.
      3. Place the large cup in the center of the covered area and pour the A and B liquids into the cup.
      4. Mix the liquids with a stirring rod and stop stirring when foam begins to form.
      5. Do not handle the fresh foam until it has cured because it may contain unreacted iso-cyanate.

    Discussion

    The polyurethane system used consists of Part A which is an amber colored viscous liquid that contains a polyether polyol, a blowing agent, silicone surfactant, and a catalyst. Part B is a dark colored viscous liquid containing a polyfunctional isocyanate.

    When the liquids are mixed, they make a thick amber mixture. Once foam starts to form, it takes a matter of seconds to greatly increase in size. After the foam is cured, it makes a light amber colored hard mass.

    The foam is made by producing polyurethane polymer in the presence of a freon propellant fluorocarbon blowing agent which causes the void volume to increase within the polymer. The polymer is formed by the following reaction:

     Due to the functionality of the reactants, a high degree of crosslinking occurs and a rigid foam results. Bubbles of gas are trapped in the polymer matrix as it is formed, and a cellular product results. In order for the foam to form well, the gas evolution process and polymer formation must occur at a matched rate. This is why a catalyst is used. The silicone polyalkylene oxide block copolymer acts as a foam stabilizer during the early stages of foam formation when the polymer is still weak.

    Rigid foams, such as the one formed by this experiment are used for thermal insulation. The gas trapped inside the closed cells makes them useful for this purpose. Flexible foam s which are not as highly cross-linked are used in cushioning applications such as upholstery and garment shoulder pads. Intermediate products know as semi-rigid foams are used in the manufacture of car crash-pads and packaging.

    References

    1. Direen, G.E., Shakhashiri, B.Z., Journal of Chemical Education, 1977, 54, 431.

    2. Saunders, K.J. Organic Polymer Chemistry. London: Chapman and Hall, 1973.