Type of Polymer Polymer Ambassadors（类型的高分子聚合物大使）.pdf

Polymer Activity from the: Teachers may reproduce this activity for their use. Polyethylene Grades: 6-8 and 9-12 Science Standards: Content Standard A: Science as Inquiry; Content Standard B: Physical Science; Content Standard E: Science and Technology Background The ethylene (properly but infrequently called “ethene”) monomer is CH =CH and so 2 2 polyethylene is [-CH —CH -] where the monomer double bond has been “opened”, enabling 2 2 n the carbons to join together in a long chain. Polyethylene is the most important synthetic organic (carbon based) chemical in terms of volume, sales, value and number of derivatives in the United States. The United States plastics industry produces 15 billion pounds annually. This unsaturated hydrocarbon, ethylene, is produced by “thermal cracking” petroleum. “Thermal cracking” corresponds to breaking the molecules down with heat, and then allowing the atoms to recombine into smaller units, often with double bonds. Petroleum refining to produce polyethylene has four basic steps: separation or fractionation, conversion using heat, reorganization using chemical reactions, and finishing or purifying the product. Crude oil is contaminated with 4-5% salt and so desalting and settling occurs first. Then an emulsion- breaker is added to eliminate water which is suspended in the oil. The distillation tower separates the lower molecular weight fractions from the higher ones. Steam at about 1600° C and 30 lbs/in2 is necessary to produce low molecular weight gases. Ethane (C H ) and