Polyester polymer and copolymer compositions containing carbon-coated iron particles

A polyester composition having improved reheat, comprising:

• a polyester polymer in which poly(ethylene terephthalate) residues comprise at least 90 wt. % of the polyester polymer;
• and
• carbon-coated metal iron particles, having a median particle size from about 1 nm to about 1,000 nm, randomly dispersed in the polyester polymer in an amount from about 1 to about 50 ppm, wherein the carbon-coated iron particles comprise an iron core in which iron is present in an amount of at least 75 wt. %, with respect to the total weight of the iron core,
• wherein the polyester composition has a reheat improvement temperature of 5° C. or more, a b* value from about minus 0.8 to about plus 7, and a preform L* value of 70 or more, and
• wherein the polyester composition is in the form of a beverage bottle preform or a beverage bottle.