| MadSci Network: Engineering |
Cameron, First, we need to clear up some confusion over what Styrofoam is and isn't. Styrofoam is the trademark that Dow Chemical uses for it's line of rigid, foamed polystyrene products used for home and industrial insulation, flotation and as a base for floral displays. It is sold in two to twelve inch thick blocks and sheets. Styrofoam is NOT the familiar foam coffee or drink container, nor what McDonald's used to use for burger packaging and it is not what packing peanuts are made of. In the commercial manufacture of Styrofoam a volatile blowing agent such as HCFC 142b is dissolved under pressure into molten polystyrene and extruded through a slot die and allowed to expand under the reduced atmospheric pressure into a rigid foam board. Upon cooling, the board is cut and sliced to the desired dimensions. Packaging pellets based on polystyrene are made once again from polystyrene containing pentane and/or hexane diissolved in the polymer. The peanuts are usually made in a two stage process using steam to volatilize the blowing agent and a second steaming to fuse the beads together into the desired shape. But you specifically asked about "dissolving packing peanuts" These are made very much like the ones I just described but use polyvinylalcohol instead of polystyrene. Polystyrene is not water soluble and takes a relatively long time to biodegrade in the environment or a landfill. Polyvinylalcohol, on the other hand, dissolves in water and biodegrades rapidly, making it a choice in certain environmentally sensitive uses. This is a difficult topic for one without a lot of polymer chemistry education. Perhaps an analogy will help: shaving cream [aerosol type] and products like Reddi-Whip both contain a large molecule [soap or cream] which has a gas dissolved in it under pressure. When you press the valve, the product is released to atmospheric pressure and the gas expands to create a foam. With the polystyrene based products heat must also be applied to keep everything fluid. The foam solidifies when it cools down. Hope this helps... Ken
Try the links in the MadSci Library for more information on Engineering.