ACS Sustainable Chemistry & Engineering
pubs.acs.org/journal/ascecg
Research Article
Figure 1. (A) Fabrication of porous nonwoven EFB fiber-derived rigid panels as air filters using (hairy) cellulose pulp fibers as the binder. Morphology of (B) unrefined (neat) cellulose pulp fibers, (C) recirculating colloid mill, as well as hairy cellulose pulp fibers refined for (D) 10 min, (E) 20 min, and (F) 30 min. In the row showing the morphology, the top row presents optical microscopy images, and the bottom row presents SEM images. Scale bar is 50 μ m. The symbol “a” shows the presence of fines. The illustrations in (A) were designed using BioRender.com.
grow to 142 million metric tons by 2050. 24 Currently, the end- of-life option for EFB is incineration or open disposal, and this leads to significant greenhouse gas emissions. 25 While the mulching of EFB within oil palm plantations is highly encouraged, 26 logistical and economic challenges limited its widespread application, particularly for smallholder farmers who prefer to discard EFB in large piles on open area. 27 Therefore, exploring innovative ways to upcycle EFB for use in air filtration applications offers dual benefit: mitigating waste while addressing the growing demand for ecofriendly filtration solutions. In this study, we report the upcycling of EFB fibers into nonwovens for use as air filters using “hairy” cellulose pulp fibers (i.e., micrometer-sized primary pulp fibers with micro- fibrils partially attached its surface) as the binder, producing a fully biobased nonwoven air filter. In addition to air filtration performance, the moldability of flat and rigid EFB/hairy cellulose fiber nonwoven panels was investigated to demon- strate its ability to form complex shapes for use in different air filtration applications. 2. RESULTS AND DISCUSSION 2.1. Fabrication of EFB/(Hairy) Cellulose Fiber Non- woven. Even though EFB fibers can be needle-punched to produce a nonwoven, 28 we opted to produce EFB fiber nonwovens using a process mimicking papermaking. This allows us to introduce (hairy) cellulose fibers, which act as the binder to increase the mechanical rigidity of the resulting nonwoven, as well as to reduce porosity and to increase tortuosity to remove PM from air. The production of EFB/ (hairy) cellulose fiber nonwovens (Figure 1A) has been reported in our prior work. 29 Briefly, the EFB fibers were cut into a length of ca. 10 mm and suspended in water containing (hairy) cellulose pulp fibers. The suspension was then vacuum filtered, followed by pressing drying at 120 ° C for 1 h under a weight of 0.5 ton. Hairy cellulose fibers were prepared by refining neat cellulose pulp (Figure 1B) using a recirculating colloid mill (Figure 1C) consisting of two toothed surfaces. 30 In this work, refining times of 10, 20, and 30 min were used
methods can be employed to produce nonwoven air filters from natural fibers. 15 Needle-punching, a technique that mechanically entangles natural fibers into durable mats, has been applied to flax fibers and hemp fibers. 16,17 The resulting needle-punched nonwoven flax fiber mat was found to be suitable for coarse particle (50 μ m in effective diameter) filtration applications, achieving a particulate filtration efficiency of up to 93%. 16 Nevertheless, for finer PM, a needle-punched flax fiber mat and a hemp fiber mat showed a lower PM 1 filtration efficiency of ∼ 45% and ∼ 21%, respectively. 17 Another approach to manufacture natural fiber-derived air filters is to first chemically and/or mechanically pulp them, followed by wet-laying (i.e., paper making). 18,19 Suriaman et al. 18 processed ramie fibers into alkali-treated pulp, containing ∼ 80% cellulose, ∼ 12% hemi- cellulose, and ∼ 2% lignin, and refined to a fineness of 350 mL CSF prior to wet laying to produce the nonwoven air filters. However, a PM 2.5 filtration efficiency of only 46% and a high pressure drop of 167 Pa were obtained. To increase the particulate filtration efficiency of natural fiber-derived air filter media, a composite approach can also be taken. Kim et al. 19 produced a composite air filter consisting of bamboo-derived organosolv pulp, bamboo-derived cellulose nanofiber and low melting point polyethylene terephthalate. The resulting composite air filter achieved a PM 2.5 filtration efficiency of ∼ 90% but possessed a low air permeability of 31 cm 3 cm − 2 s − 1 . These studies demonstrated the potential of natural fibers for use in future filtration applications. Considering that air filters are typically single use, using agricultural residue as feedstock as opposed to virgin natural fibers is expected to produce greener air filters. 20,21 Empty fruit bunch (EFB), a fibrous byproduct of the palm oil milling process, represents a particularly promising agricultural residue due to their abundance and the environ- mental challenges they pose. 22 Each ton of crude palm oil production generates ca. 1.1 tons of EFB. 23 The global EFB production reached an estimated 87 million tons in 2023 and is projected to rise as the demand for palm oil is expected to
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https://doi.org/10.1021/acssuschemeng.5c00041 ACS Sustainable Chem. Eng. 2025, 13, 6209 − 6221
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