Dupont Safety & Construction, Inc.

E.i. Dupont De Nemours and Company

Orest Skoplyak

Serge Rebouillat

Corneille Schmitz

Jan Van Meerveld

Noel Stephen Brabbs

Joseph Mathieu

Christine Lemoine

A process for the preparation of plexifilamentary film-fibril strands of polymer. The process includes the steps of generating a spin fluid containing (a) 5 to 30 wt. % containing one or more polymer types, (b) a primary spin agent selected from the group consisting of dichloromethane, cis-1,2-dichloroethylene and trans-1,2-dichloroethylene, and (c) a co-spin agent comprising 1H,6H-perfluorohexane or 1H-perfluorohexane or 1H-perfluoroheptane. The spin fluid is flash-spun at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure to form plexifilamentary film-fibril strands of the polymer. The co-spin agent is present in the spin fluid in an amount sufficient to form an azeotrope-like composition with the primary spin agent in the presence of the one or more polymer types. The polymer may be selected from the group consisting of high density polyethylene, polypropylene, polybutene-1, polymethylpentene, polyvinylidene fluoride, poly (ethylene tetrafluoroethylene), and blends of the foregoing.

Flash spinning process

A sheet comprising a plexifilamentary film-fibril network consisting essentially of high density polyethylene in an overlapping multi-directional configuration, the sheet, as-produced from a spin cell, having a normalized Frazier air permeability of between 0.002 and 0.2 m/m·minute at 50 gsm, a BET surface area of between 9 and 20 m/gm, and a normalized hydrohead of between 150 and 250 cm at 50 gsm, wherein the plexifilamentary film-fibril network in an overlapping multi-directional configuration is flash-spun from a spin fluid comprising polymer and spin agent, the spin fluid temperature being 190° C. or greater, the spin agent comprising dichloromethane, the spin fluid having a polymer concentration of 12 to 14 weight percent.

Plexifilamentary sheets

A sheet having a plexifilamentary structure with a normalized Frazier air permeability of between 0.002 and 0.2 (m/m&#xb7;minute)@50 gsm, and a normalized hydrohead of between 150 and 250 centimeters@50 gsm.

A flash-spun plexifilamentary fiber strand having a BET surface area of less than 12 m/g, a crush value of at least 0.9 mm/g wherein said fiber strand comprises predominantly fibers formed from polyethylene, said fibers having a total crystallinity index of less than 55%, said fiber strand having an elongation at break greater than 55% and sheets made thereof.

Flash spun plexifilamentary strands and sheets

A flash-spun plexifilamentary fiber strand having a BET surface area of less than 12 m/g, a crush value of at least 0.9 mm/g wherein said fiber strand comprises predominantly fibers formed from polyethylene, said fibers having a total crystallinity index of less than 55%, and sheets made thereof.

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Newark, DE, United States of America

Orest Skoplyak