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The basics and the alternatives

Features | May 25, 2020 | By:

A multidisciplinary approach to innovations in PPE could support needed development. 

by Seshadri Ramkumar 

Personnel Protective Equipment (PPE) are important and even mandatory procurements under any circumstance. The COVID-19 pandemic has heightened the need for the development of a variety of items, including new materials to be used in medical, consumer and defense products. The current crisis has exposed vulnerabilities internationally—in both medical and nonmedical countermeasures—to emerging and unexpected outbreaks. Additionally, it has made clear that solutions to such scenarios lie in more than one field—a timely reminder of the need for multidisciplinary approaches. 

While disruptive technologies that attract consumers’ attention and cater to their needs are often successful, these technologies are few and far between. Innovations need not be disruptive to offer solutions to problems, and lead to new products, new processes and cost savings, where discoveries, inventions and new marketing approaches are important components. A case in point is the evolution of face coverings and masks, which has developed rapidly during the COVID-19 outbreak. These new ideas and products highlight the ingenuity and entrepreneurship of their innovators.     

Surface Vision’s inspection and monitoring solutions provide quality and consistency by identifying typical material defects across a range of nonwoven production processes, even at the high-speed production volumes required to support the manufacture of single-use items. Photo: AMETEK

PPE: the basics

PPE should have three critical characteristics: functionality, proper fit, and form or comfort. The priority of these attributes may vary, depending on the environment where they are used. PPE products used in hospitals, caregiving facilities and by first responders demand functionality at a higher scale. 

Based on the type of filtration needs and above criteria, face masks can be broadly classified as:

  1. Filtering Facepiece Respirators (FFRs, commonly referred to as N95 masks)
  2. Surgical Masks
  3. Face covers with enhanced filtration (FISORS)
  4. Face covers without enhanced filtration

Prior to COVID-19, medical and first responders widely used N95 and surgical masks. However, due to the incidence and ease of transmission and to support social distancing, face covers made from other fabrics have evolved. However, depending on the structure and the material makeup, their ability to filter varies. 

Face covers with enhanced filtration capability (FISORS) can have multiple types of filter substrates, depending on what is required in the given environment, but in any case, there is a need to improve the filtration capability of common face covers. 

Meltblown materials for PPE 

It is generally understood that structures providing a tortuous air flow can serve as better filters. Due to the random arrangement of fibers, nonwovens have been used as filters, but other materials, such as cotton, could be used to make a nonwoven to enhance filtration. 

Meltblown webs with fibers distributed ubiquitously with an electric charge are a common filter substrate, which also forms an important component of N95 masks. The efficiency increases with the number of layers, which may lead to higher pressure drop, affecting comfort. 

Interest in standalone meltblown webs is gaining momentum, as the meltblown machinery technology has evolved to develop submicron size webs. A study at the Nonwovens and Advanced Materials Laboratory at Texas Tech University in collaboration with The University of Tennessee, Knoxville, has shown that single-layer meltblown webs with fibers ranging from 520 nm to 2100 nm could be conveniently developed that can serve as filter medium. Increase in fiber diameter beyond one-micron size decreases the filtration efficiency. 

Single layer webs with 520 nm fibers could give filtration efficiency about 80 percent, showing that a meltblown single layer can be effective. Polypropylene is the industry standard for developing surgical masks because of its fluid repulsion capability, melt extrusion property and cost. Carded resin-bonded webs are also used to develop layers for making high-efficiency filters.

Destabilizing with cellulosics

Recently, a collaborative study involving scientists from the National Institutes of Health (NHS), Centers for Disease Control and Prevention (CDC) and academia has shown that SARS-CoV-2 was more stable on plastic and stainless steel up to 72 hours; however, the virus was stable on cellulosics such as cardboard for just 24 hours. This indicates that copper and cellulosics do a better job of destabilizing a virus, compared to plastics. 

An earlier study in the late 1960s, carried out by USDA scientists using the vaccinia virus, showed that this virus could not be detected beyond three days from exposure on cotton cloths. Interestingly, the stability of the virus depended on the humidity: the higher the humidity, the less stable the virus. This leads to an understanding that fibers with higher moisture regain, such as cotton, may do a better job in destabilizing viruses.

The COVID-19 situation has revealed that cotton could be useful in emerging applications that can help save lives. “Cotton is an industrial product, and as such, we have to always be looking for any new or additional uses that can provide opportunities for our cotton producer,” says Steve Verett, chief executive officer of Lubbock, Texas-based Plains Cotton Growers Inc.

Regarding gowns and drapes, coated hydrophobic materials such as polypropylene are commonly used. Breathable barrier, coated spunbond-meltblown-spunbond gowns are used in in hospital settings. The comfort aspect of these olefin-based materials is still a challenge. Cotton scrubs and gowns, which demand proper washing and sanitizing, are also still used. 

A discussion with an internal medicine specialist at Lakeridge Health, Oshawa, Canada, emphasized the importance of ease-of-use and comfort in PPE, which is the reason some care givers prefer cotton materials when they must wear PPE for extended periods of time. One good example is cotton head covers, which have become mandatory in many hospitals due to COVID-19. 

Sample-collecting swabs can be made using rayon, cotton and foam; these are important for testing use. In addition to PPE, sampling swabs and wipes are also essential items for decontamination. Carded resin-bonded and hydroentangled structures are common for wipes. Normally, polyester, rayon, and bleached and clean cotton are used in developing the wipes. Both dry and wet wipes with multiple formulations are common.

Single use vs. reusables

With the scarcity of PPE, interest has emerged in reusing some products, even N95 masks. Not only microbial contamination aspects in case of reusable materials is under scrutiny, the structural integrity of the products is also under investigation. 

Vapor hydrogen peroxide decontamination is normally followed using strict guidelines. The process involves several stages and takes about 5–6 hours. While materials could be decontaminated, the process may not lead to full sterilization, depending on the microbes. Care must be taken to avoid product mixing, and proper inventory control must be practiced. 

COVID-19 has provided the need to work collaboratively—beyond one’s specific field—to develop PPE products. New material combinations, exploiting different processes and involving different disciplines will lead to new products that can be used beyond the common fiber to fashion supply chain. It has shown that innovations will play an important role in waging war against diseases, as well as enhancing manufacturing activities. 

Seshadri Ramkumar, Ph.D., is a professor in the Nonwovens and Advanced Materials Laboratory, Texas Tech University, and a frequent contributor to Advanced Textiles Source.

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