Polymeric strands with enhanced tensile strength, nonwoven webs including such strands, and methods for making same

A polymeric strand having an enhanced tensile strength made according to a method comprising the steps of:

• a. extruding a molten melt-extrudable polymer through a die assembly at a substantially continuous pressure of at least 100 psig, the die assembly comprising:
• i. a die housing including:
• a chamber adapted to receive the melt-extrudable polymer;
• an inlet adapted to supply the chamber with the melt-extrudable polymer;
• and
• an exit orifice defined by the walls of a die tip, the exit orifice being adapted to receive the melt-extrudable polymer from the chamber and pass the melt-extrudable polymer out of the die housing;
• and
• ii. means for applying ultrasonic energy to a portion of the melt-extrudable polymer within the housing, which means for applying ultrasonic energy is located within the chamber surrounded by the melt-extrudable polymer, and is adapted to apply the ultrasonic energy as the melt-extrudable polymer is passed out of the die housing through the exit orifice;
• b. exciting the means for applying ultrasonic energy to apply ultrasonic energy to a portion of the melt-extrudable polymer within the chamber and without applying ultrasonic energy to the die tip, while the exit orifice receives melt-extrudable polymer from the chamber;
• and
• c. attenuating the extruded polymer to form a strand, the extrusion of the melt-extrudable polymer and the excitation of the means for applying ultrasonic energy being controlled such that the tenacity of the strand is about 1.5 to about 3 times the tenacity of an otherwise identical strand not made by applying ultrasonic energy to a portion of the melt-extrudable polymer while the melt-extrudable polymer is extruded.

A polymeric strand having an enhanced tensile strength made according to a method comprising the steps of:

• a. extruding a molten melt-extrudable polymer through an extrusion orifice in a die assembly at a substantially continuous pressure of at least 100 psig, the die assembly comprising:
• i. a die housing defining:
• a chamber adapted to receive the melt-extrudable polymer, the chamber having a first end and a second end;
• an inlet orifice adapted to supply the chamber with the melt-extrudable polymer;
• and
• an extrusion orifice located in the first end of the chamber and adapted to receive the melt-extrudable polymer from the chamber and extrude the polymer along a first axis;
• and
• ii. an ultrasonic horn having a first end and a second end and adapted, upon excitation by ultrasonic energy, to have a node and a longitudinal mechanical excitation axis, the horn being located in the second end of the chamber in a manner such that the first end of the horn is located outside of the chamber and the second end of the horn is located within the chamber and is in close proximity to the extrusion orifice;
• b. exciting the ultrasonic horn with ultrasonic energy while extruding the melt-extrudable polymer;
• and
• c. attenuating the extruded polymer to form a strand, the extrusion of the melt-extrudable polymer and the excitation of the ultrasonic horn being controlled such that the tenacity of the strand is about 1.5 to about 3 times the tenacity of an otherwise identical strand not made by applying ultrasonic energy to a portion of the melt-extrudable polymer while the melt-extrudable polymer is extruded.