Abstract: The present invention concerns a reactive carrier that forms no by-products during melt injection of polymer into articles such as sheets, films, fibers and containers. The reactive carrier is used to mix additives into the polymer resin. More particularly, the invention relates to the use of one or more cyclic anhydrides or substituted cyclic anhydrides as the reactive carrier. The polymer can be polyester or polyamide. Suitable cyclic anhydrides are those with a melt point of less than the polyester or polyamide, preferably less than about 160° C., and more preferably less than about 125° C. Most preferable are cyclic anhydrides with a melt point less than about 100° C. and especially suitable are those that are liquid at room temperature (25° C.).

Abstract: A spun polyester fiber, a drawn polyester yarn, and methods for making them. Polyethylene terephthalate yarn is prepared by extruding a molten melt-spinnable polyethylene terephthalate having an intrinsic viscosity of at least about 0.8 through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn; solidifying gradually said molten spun yarn by passing said molten spun yarn through a solidification zone which comprises (i) a retarded cooling zone and (ii) a cooling zone adjacent said retarded cooling zone where, in said cooling zone, said yarn is rapidly cooled and solidified in a gaseous atmosphere; withdrawing at sufficient speed said solidified yarn from said solidification zone to form a crystalline partially oriented yarn; and hot drawing said crystalline partially oriented yarn at a total draw ratio between about 1.5/1 and about 2.5/1 to produce a drawn yarn having an effective crosslink density (N) between about 10×1021 and about 20×1021 crosslinks per cubic centimeter.