Method for permanently and uniformly incorporating an additive into an undrawn fiber

A method for permanently incorporating between 0.1 and 25% by weight of a liquid additive into an undrawn or partially drawn fiber formed from a molten polymer selected from the group consisting of polyesters, polyamides, polyesteramides, polypropylene and high density polyethylene, the method comprising cold drawing said fiber at a draw ratio of between 1.5:1 and the breaking elongation of the fiber to achieve a localized reduction in fiber diameter concurrently with formation of a network of interconnecting microvoids that occurs while the fiber is immersed in said liquid additive, wherein

• 1. the wetting angle defined by the additive and the surface of said fiber is less than 90.degree.;
• 2. the temperature of the additive is below the glass transition temperature of said fiber containing said additive;
• and
• 3. the additive is a non-solvent for the polymer, and penetrates into said network of interconnecting microvoids.

A method for permanently incorporating between 0.1 and 25% by weight of an additive into an undrawn or partially drawn fiber formed from a molten polymer selected from the group consisting of polyesters, polyamides, polyester-amides, polypropylene and high density polyethylene, the method consisting essentially of first cold drawing said fibers at a draw ratio of between 1.5:1 and the breaking elongation of the fiber to achieve a localized reduction in fiber diameter concurrently with formation of an interconnecting network of microvoids that occurs while the fiber is immersed in a liquid or vapor medium such that

• 1. the medium is a non-solvent for the polymer that constitutes said fiber and penetrates into said network of interconnecting microvoids;
• 2. the wetting angle defined by the liquid or liquified vapor medium and the surface of said fiber is less than 90.degree.;
• 3. the temperature of the medium is below the effective glass transition temperature of said fiber when in contact with the medium, and, then immersing the drawn fiber, while the fiber contains said medium, in a solution, dispersion or emulsion of said liquid or solid additive in a liquid diluent wherein the concentration of the additive is between 0.1 and 99%, based on the weight of combined additive and diluent, the maximum particle size of the additive does not exceed two microns, the diluent is a non-solvent for the fiber, the wetting angle defined by the diluent and the surface of said fiber is less than 90.degree., the duration of the immersion being sufficient to incorporate the desired amount of said additive into said fiber.

A method for permanently incorporating between 0.1 and 25% by weight of a liquid additive into an undrawn or partially drawn fiber formed from a molten polymer selected from the group consisting of polyesters, polyamides, polypropylene and high density polyethylene, the method consisting essentially of first cold drawing said fiber using a draw ratio of between 1.5:1 and the break elongation of said fiber to achieve a localized reduction in fiber diameter concurrently with formation of a network of interconnecting microvoids that occurs while the fiber is immersed in a liquid or vaporized liquid medium wherein

• 1. the medium is a non-solvent for the polymer that constitutes said fiber and penetrates into said network of interconnecting microvoids;
• 2. the wetting angle defined by the liquid medium or vapor medium when liquified and the surface of said fiber is less than 90.degree.;
• 3. said fiber when cold drawn in said medium exhibits a lower density relative to an undrawn fiber, and
• 4. the temperature of the medium is below the glass transition temperature of said fiber containing the medium;
• and then immersing the drawn fiber while the fiber contains said medium, as evidenced by a lower density relative to said fiber in an undrawn state, in said liquid additive wherein
• 1. said additive is a non-solvent for the undrawn fiber and penetrates said network of interconnecting microvoids, thereby displacing at least a portion of said liquid or vaporized liquid medium;
• 2. the wetting angle defined by the additive and the surface of said fiber is less than 90.degree., for a period of time sufficient to incorporate the desired amount of additive into said fiber.