For simple face masks, a crowd production has been established. Europe’s sewing machines are running again, in living rooms, at theater workshops, sail producers and at still remaining garment productions. All kind of textile materials, nonwovens, woven and knitted fabrics are used.
Protection of people around us is in focus. Those simple masks’ barrier function against viruses is equally as effective as trying to prevent a bumblebee from passing through a wire mesh fence (Fig.). Nevertheless, these simple masks should be worn when meeting others, and all of us will enjoy if the mask is also an attractive accessory or a nice print, generating a smile on our faces – although nobody could see it.
For our own protection against Covid 19 – and this is especially important for potential risk patients, doctors and medical staff – a face mask with much higher filter efficiency is needed. Face masks of the FFP2 and FFP3 (Face Filtering Piece) types consist of a minimum of 3 layers. The outer layer is hydrophobic, preventing droplets from entering. The inner layer is hydrophilic, so that the exhaled moisture could be buffered. For the filtering, the central layer is decisive.
What are the requirements for this filter layer? A human hair has a diameter of around 100 µm, i.e. 0.1 mm. A virus is approx. 0.1 µm, i.e. 0.0001 mm. There is a need for high-density nonwovens materials, to restrain viruses, but at the same time allowing sufficient breathing volume. The performance of such nonwovens is tested by a special method. 2 parameters are tested: on one hand, whether sufficient air volume can pass the filter material and on the other hand the capability to separate viruses. Instead of real viruses, aerosols made of sodium chloride or of paraffin are generated. These aerosols are sucked through the filter media with a volume flow of 95 l/min. FFP2 masks reach a separation of 94 %, FFP3 of 99 % of viruses respectively the aerosols. This is also the base for American and Chinese mask classification N95 for 95 % or 99 %, K95 or 99 respectively. Whereas the hydrophobic and hydrophilic layers could be produced on spunbond lines, the middle of today’s filter masks needs a meltblown line. Only by drawing the filaments in a controlled hot air between the spinning nozzles and a collecting belt, “endless” finest fibers with a diameter of approx. 1 µm could be generated. By this, such a meltblown material of 25 g/m2 could consist of up to 500 single layers. Those nonwovens are preventing viruses, or at least bigger doses of them (94 %, 95 % or 99 % respectively) to find their way through the mask.
Before Covid 19, there was already a limitation of worldwide meltblown production capacities. Not only because the investment for such lines are quite high, but also due to increasing requirements and demand in hygiene, safety and ecological applications over the last years. In addition, the output of meltblown lines for finer fibers and therefore for finer filters is lower than for coarse fibers. Output and fiber gauge are anti-proportional.
The establishment of new meltblown production capacities is already running at full speed, but needs time, as there is only a hand full of manufacturers for suitable lines. Installation and commissioning – for which longtime experienced specialists are needed – take already 2 months. At a usual delivery time of 8 months a period of nearly 1 year has to be considered for establishing new meltblown capacities in the market. During the current situation, this is done quicker, but most probably this will not cover the tremendous increase in demand.
Are there alternatives?
Yes and no. There are ideas, but these are yet to be proofed considering the filter capability of meltblown material:
- Breathable garments
Breathable garments, protecting against humidity (rain), but allowing water evaporation (perspiration) to pass through, consist mostly of a robust woven material which is partially laminated by hotmelt with a breathable membrane. This membrane does not allow liquid water drops to pass, but allows gaseous water molecules to pass through. Most probably the necessary filter capability could be reached by such laminates, but the necessary airflow for sufficient breathing might be too low.
Instead of a membrane, a textile substrate (woven or nonwovens) could be coated with a foam or something alike, which has the necessary air flow permeability and the necessary separation capability. The textile substrate would be only used as a supporting structure.
- Split fibers
Very fine fibers, as they are generated in the meltblown process, could not be run on a staple fiber nonwovens line, especially not on the carding machine. It is possible to use so-called split fibers, where very fine fibers are imbedded in a matrix, which later will be “washed-out” in a spunlace process. Appropriate processes are established and could be developed further.
Today, there is is still an imaginary line between spunlaid and staple fiber nonwovens producers. But more and more staple fiber nonwovens producers are considering, whether it is the right time to step into meltblown and spunbond technology. Companies with such an idea are looking for answers to the following questions:
- Will the current boom continue or are there too many investments ongoing right now, which will lead to a worldwide over-capacity?
- Will there be – similar to the European “milk-quota” – a government established quota especially for protective material?
- Are there simplifying advantages and supports for executing such projects (financing, subsidies, simplified construction and other approvals) right now?
- How big is the technological risk to run such a line?
- Are there alternative line concepts? Instead of big high-performance lines, small and flexible installations? Is it possible to recreate similar results at a high-performance line on a small and flexible line?
- Are there sufficient local converting capacities to manufacture face masks from this produced material or is it necessary to ship roll goods to Asia and masks back?
Unlike staple fiber nonwovens lines, meltblown and spunbond lines usually have to be purchased as one unit. Buying a new carding machine and replacing the crosslapper in 3 years is not really possible with a spunbond line, as it would be possible with a staple fiber line. Therefore, a high investment has to be made in one go, which is however not that far away from an investment into a complete staple fiber nonwovens line.
Within the last decades spunlaid products have not only substituted staple fiber nonwovens, but also created new wide fields of applications. For functionalization of textiles – especially of nonwovens – there is a huge market potential. This also covers laminates consisting of staple fiber and spunlaid nonwovens. Companies having both technologies in-house could not only serve the separate markets for spunlaid and for staple fiber nonwovens but could in addition serve new markets for multi-layer, i.e. mulit-functional-products.
Not only for those who are already producing filter nonwovens right now, a look to a possible entry to meltblown and spunbond technology could be worthwhile. There was hardly ever a better time.
Michael Junge, Junge-Engineering, Aachen/Germany