The challenge faced in the US and globally today is the shortage of both meltblown fabrics (the most critical component of the mask) and the converting capacity.
In response, NWI has developed meltblown filter media for both surgical masks and N95 and N99 masks and is working with partners who are converting these into masks. This, however, is not sufficient.
One question that comes up is: How about reusable masks or masks that do not rely on meltblown structures for filtration?
This is an interesting question and there have been many attempts in the last decade or so targeted at reusable masks or masks that can be re-sterilized.
Many of the cleaning steps result in the loss of electrostatic charge and meltblown structures are too fragile to undergo significant mechanical action. The challenge is how to recharge the mask after laundry or sterilization… And, what structures can be used to form a structure that can be decontaminated and reused without losing performance or damaging the filtration medium?
There are many “cloth” masks on the market since March 2020. Most of these are based on simple textile structures that offer little or no protection, unfortunately. A study by NIOSH scientists extends back to the last pandemic. The title of the study was: Respiratory Protection: Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particles. The study concluded that “the penetration levels obtained for fabric materials against both polydisperse and monodisperse aerosols were much higher than the value for the control N95 respirator filter media“. When measured according to the protocols used for surgical masks, the results are improved but this is more due to the test method which uses unneutralized particles at 01 micron at a face velocity of your choice. FDA recently announced guidelines for non-regulated masks.
With respect to alternatives to meltblown structures for filters, The Nonwovens Institute has spent a lot of effort in developing high-efficiency spunbond filter media. The material is a structure that is bonded by hydroentangling and can offer pressure drops below the range of what you find for most facemasks (60 to 45 Pascals/cm2). The efficiency is in the range of 80 to 92% (measured on TSI 8130 at a face velocity of 5.3 cm/s) for a single layer, and is durable, and can be reused if decontaminated by appropriate methods. For more information, contact us by email at firstname.lastname@example.org.
These structures in a properly designed mask design can reach N95 or higher levels of performance, while a single layer can easily be designed to pass the FDA surgical mask requirements in terms of particle and bacterial efficiency.
We believe that in this time of crisis, a properly-designed reusable mask may be worthwhile to consider and while it may not reach the performance levels of the N95, they still provide a significant level of protection to the public; see recent publication on the topic of re-use.
What if the current crisis continues into the next year? The strategies would include the following short term and longer-term options. And, it is important to allow new structures that may not have the FDA or NIOSH approval in hand. This is not to say that we should compromise quality but allow the use of non-certified masks that meet the pressure drop and efficiency requirements of the certified masks documented by a 3rd party certified lab. FDA recently published guidelines that must be strictly followed.
The Nonwovens Institute stands ready to help with the current crisis and will be happy to engage in a dialog. NWI has redirected ALL of its efforts to forming filter media for the current crisis.