June 28, 2008 - ...plastics is squeezing companies that supply finished goods to retailers or parts to manufacturers because they are often locked into contracts that don't allow price changes, said Michael Greenberg, chief executive of The Plastics Exchange, a Chicago based marketplace for plastics and resins. Thanks to record oil prices, the cost of polypropylene, the plastic frequently used in autos, has jumped 54 percent in the past year, to 91 cents a pound, Greenberg said.