Graphic shows how SMS medical-grade protective fabric is manufactured.
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HEALTH

Elusive face mask protective fabric

By Ninian Carter

April 24, 2020 - Higher than usual demand for a niche sythetic fibre is contributing to a global shortfall in protective masks and gowns for healthcare workers.

European countries are struggling to acquire enough Personal Protective Equipment (PPE) for healthcare professionals treating Covid-19 patients. Much of it utilises a synthetic fabric, able to filter out coronavirus-filled droplets, and is used for making protective gowns, aprons and face masks.

The fabric is known as Spunbond Meltblown Spunbond (SMS) and is a tri-laminated material formed from differently treated layers of polypropylene – a thermoplastic polymer (pliable molecular mass), offering bacterial filtration efficiency of 95%-99%.

The structure is composed of a non-woven layer of meltblown polypropylene (an excellent, but weak, fluid and particulate barrier) sandwiched between two layers of spunbonded polypropylene (providing good tensile strength). The triple layered fabric is then ultra-sonically welded to provide additional strength, and further treated with additional repellents to withstand alcohol, oil and blood – making it an ideal fabric for the medical industry.

For added protection, the fabric can come in thicker configurations such as SMMS (four layers comprising spunbond, meltblown, meltblown, spunbond), SSMMS (spunbond, spunbond, meltblown, meltblown, spunbond) and even SMMMS (spunbond, meltblown, meltblown, meltblown, spunbond).

Meltblown polypropylene production is highly specialised and involves molten thermoplastic chips being melted, extruded, filtered and finally blown with high velocity air into a fine-diameter filament.

Europe has so far relied heavily on Asian suppliers for SMS, which is now in short supply due to overwhelming demand. Building industrial-scale meltblowing machines is a highly specialised process that ordinarily takes over a year, although lead times are now being reduced to a few months.

European production in 2019 of non-woven materials was 2.8 million tonnes, with meltblown only a fraction of that. China on the other hand is the number one manufacturer, producing 25,000 tonnes of meltblown material a year.

PUBLISHED: 24/04/2020; STORY: Graphic News; PICTURES: Getty Images
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