ACS Sustainable Chemistry & Engineering
pubs.acs.org/journal/ascecg
Research Article
Figure 5. Exemplarily scanning electron micrograph of curvature of EFB/(hairy) cellulose fiber nonwoven containing 10 wt % (A) unrefined cellulose fibers and (B) hairy cellulose fibers refined for 30 min, produced through the never-dried approach. Warpage on the EFB/hairy cellulose fiber nonwoven containing (C) 20 wt % and (D) 30 wt % hairy cellulose fiber refined for 30 min. (E) Molded EFB/hairy cellulose fiber nonwoven containing 10 wt % hairy cellulose fibers refined for 30 min (left), mimicking the shape of FFP2 mask (right), through the steam-rewetted approach. (F) EFB/hairy cellulose fiber nonwoven containing 10 wt % hairy cellulose pulp fibers refined for 30 min molded into a blunted cone through the never-dried approach. Scale bar: 500 μ m.
(hairy) cellulose fibers to bind EFB fibers together produces a rigid nonwoven with a flexural modulus of up to ∼ 2.9 GPa. 29 This makes the molding of the already-formed nonwoven into complex shapes difficult. Nevertheless, we can exploit the hygroscopic nature of the (hairy) cellulose fibers. Exposing a network of cellulose fibers (i.e, a hand sheet) to a high- humidity environment significantly weakens its structure. The tensile modulus of the cellulose fiber network decreases by ∼ 40% when conditioned at a relative humidity of 90%. 54 This weakening occurs as water penetrates the cellulose structure, particularly in the less ordered regions, disrupting hydrogen bonds and replacing them with the weaker water-mediated interactions. 54,55 Here, two approaches were taken to mold EFB/(hairy) cellulose fiber nonwovens into complex shapes: (i) from their never-dried state (Figure 4A) and (ii) steam- rewetted state (Figure 4B). In the approach where we started from the never-dried state, a suspension consisting of the EFB fibers and (hairy) cellulose fibers was first prepared, followed by vacuum-driven filtration (similar to the initial fabrication process) to form a wet cake of EFB/(hairy) cellulose fiber mat. In the other approach where we started with an already-formed EFB/(hairy) cellulose fiber nonwoven, the rigid nonwoven was first steamed until the water content reached ∼ 70% to soften the overall nonwoven structure. The wet filter cake or steamed nonwoven was then
ln(1 )
=
QF
P (1) where η and Δ P refer to the aerosolized particulate filtration efficiency and the pressure drop across the filter medium, respectively. Figure 3F summarizes the QF of the various EFB/ (hairy) cellulose fiber nonwovens fabricated in this work. The highest QF is achieved when 10 wt % of hairy cellulose fibers reinforced for 30 min was used as the binder for the EFB nonwoven ( ∼ 36 kPa − 1 for PM 1 , ∼ 44 kPa − 1 for PM 2.5 , and ∼ 49 kPa − 1 for PM 4 ). This can be attributed to the combination of high filtration efficiency (Figure 3E) and a relatively low pressure drop (Figure 3C). Neat EFB fiber nonwoven without any binder possessed low QF due to its poor aerosolized particulate filtration efficiency. At higher (hairy) cellulose fiber loading of 20 and 30 wt %, the low QF is due to the increased pressure drop across the material and is particularly worse with longer refining time (see Figure 3C), which outweighed the benefits of high filtration efficiency. 29 2.5. Molding EFB/(Hairy) Cellulose Fiber Nonwoven into Complex Shapes. The previous sections demonstrated the need to incorporate (hairy) cellulose fiber into the resulting EFB fiber nonwovens to achieve a high aerosolized particulate filtration efficiency. While neat EFB nonwoven without (hairy) cellulose fiber as binder is loose, the use of
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https://doi.org/10.1021/acssuschemeng.5c00041 ACS Sustainable Chem. Eng. 2025, 13, 6209 − 6221
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