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Barriers To Entry

Flexible, breathable extruded monolithic films block penetration by viruses and other blood-borne pathogens, providing comfortable, cost-effective protection in medical apparel.

Janet Bealer Rodie, Assistant Editor

P rotection from nasty viruses and other infectious microorganisms is a paramount concern within the medical sector. Antimicrobial and sterilization treatments do their part to eliminate surface contaminants, but there are times when a physical barrier is needed to prevent penetration of blood- or other fluid-borne pathogens — for example, in a surgical or emergency response environment where the practitioner or responder may come in direct contact with such pathogens, or to protect a wound from outside infection while it heals.

Waterproof, breathable membranes bonded to fabrics used for surgical gowns and masks, wound dressing and cast coverings, and other protective clothing can provide such protection. The membranes may be monolithic or microporous, or a bicomponent film that takes advantage of the particular attributes of each.

While monolithic and microporous films may provide similar protective and comfort properties, they differ in their physical structures and ways of functioning.

Microporous films have microscopic pores through which vapor such as perspiration may be transmitted via gaseous diffusion or convection. Depending on pore size, liquid molecules are too large to pass through. However, liquids under pressure may be able to penetrate these films; and contamination by substances such as body oils, pollutants, cleaning substances and others also may adversely affect the membrane’s water repellency.

Monolithic films contain no pores that might allow liquid penetration, and moisture vapor is transmitted via a solid-state diffusion process. However, the films will swell and stretch when wet, which can cause cracking and weakening over time if the film is made from a polymer that does not offer good stretch and recovery.

Monolithic films made with thermoplastic polyurethane (TPU), copolyester or ether-amide polymers are said to offer good to excellent stretch and recovery, reducing the likelihood of cracking and increasing the film’s durability and abrasion resistance, according to Paul Darby, president, Omniflex Inc. — the Greenfield, Mass.-based maker of Omniflex Transport®, a line of extruded monolithic films made with these materials.

Darby said extruded films are more supple than liquid films, which are coated onto a fabric or a nonwoven, stiffening it in the process. He also noted there are advantages to using extruded films such as Transport that are made without the use of processing aids that can reduce the fabric’s breathability and affect the strength of the bond between film and fabric.

Darby pointed out that TPU, copolyester and ether-amide films are quiet and comfortable and offer a soft hand — with TPU offering the highest degree not only of these qualities, but also of stretch and recovery and breathability. Because such films also are chemical- and temperature-resistant, they are more cost-effective to use than bicomponent films that include polytetrafluoroethylene to provide those qualities, and yield garments that are lighter-weight and more compressible than those made with bicomponent films.

November/December 2005