Biopolymer-Based Filtration Materials

Abstract

Biobased materials such as cellulose, chitin, silk, soy, and keratin are attractive alternatives to conventional synthetic materials for filtration applications. They are cheap, naturally abundant, and easily fabricated with tunable surface chemistry and functionality. With the planet's increasing crisis due to pollution, the need for proper filtration of air and water is undeniably urgent. Additionally, fibers that are antibacterial and antiviral are critical for public health and in medical environments. The current COVID-19 pandemic has highlighted the necessity for cheap, easily mass-produced antiviral fiber materials. Biopolymers can fill these roles very well by utilizing their intrinsic material properties, surface chemistry, and hierarchical fiber morphologies for efficient and eco-friendly filtration of physical, chemical, and biological pollutants. Further, they are biodegradable, making them attractive as sustainable, biocompatible green filters. This review presents various biopolymeric materials generated from proteins and polysaccharides, their synthesis and fabrication methods, and notable uses in filtration applications.

Figure 1

Biopolymer-based filtration materials fabricated from a variety of protein and polysaccharide sources (inserted cellulose, keratin, silk, chitin, and starch photo credits: pixabay.com). These unique surface chemistries and diverse molecular interactions aid filtration of various contaminants, including particulate matter (PM), bacteria, viruses, and smoke pollutants (O–H, HCHO, and C≡O).

Figure 2

Typical mechanisms behind biopolymer (orange lines) filtration include impaction, interception, diffusion, and electrostatic interaction. Black lines indicate movement path of pollutant (VOC, bacteria, virus, etc.), shown as a blue sphere; red dotted lines indicate electrostatic interactions between biopolymer and pollutant.

Figure 3

(a) Relative size of common air contaminants and (b) fractional collection efficiency for different mechanical filters with respect to the diameter of the contaminant.

Figure 4

SEM images of nanofibers fabricated from various biopolymers that can be employed for filtering applications. (a–c) Proteins and (d–f) polysaccharides, specifically, (a) silk, (b) corn zein, (outer scale bar = 5 μm), (c) soy (scale bar = 1 μm), (d) starch, (e) chitosan, and (f) cellulose. (a) Reproduced with permission from ref (12). Copyright 2015 Elsevier. (b) Reproduced with permission from ref (13). Copyright 2005 Wiley. (c) Reproduced from ref (3). Copyright 2016 American Chemical Society. (d) Reproduced with permission from ref (14). Copyright 2018 Wiley. (e) Reproduced from ref (15). Copyright 2007 American Chemical Society. (f) Reproduced with permission from ref (16). Copyright 2002 Wiley.

Figure 5

Schematics of (a) electrospinning and (b) air-spraying of biopolymer solutions to form fibers for filtration devices, including SEM images of (c) electrospun silk-based nanofibers and (d) air-spun silk-based nanofibers. Filter paper made from (e) soy proteins is included as examples to show how biopolymer-based nanofibers interact with pollutants. (c) Reproduced with permission from ref (19). Copyright 2017 Elsevier. (d) Reproduced from ref (18). Copyright 2018 American Chemical Society. (e) Reproduced from ref (3). Copyright 2016 American Chemical Society.

Figure 6

(a) Zein nanofiber cotton fibers (Z-CoF) with a thin layer of zein nanofibers (ZNF) before (ZNF/Z-CoF) or after (Z-CoF/ZNF) the layer of Z-CoF. (b) Z-CoF formed from soaking in ethanol showed the highest removal efficiency and lowest pressure drop of all three solvents tested. (c) Normalized pressure drop and PM_2.5 removal. (d) Removal efficiency of regular cotton fibers and functionalized fibers for a range of PM sizes. (e) Efficiency of functionalized fibers against HCO and CO. (f) Normalized pressure drop and PM_2.5 removal efficiency for CoF and Z-CoF prepared from 1-butanol (Ter-), acetone (Ace-), or ethanol (Eth-). Particle size distribution of zein nanoparticles on the CoF surface is also shown for (g) acetone and (h) ethanol. Reproduced with permission from ref (2). Copyright 2019 Elsevier.

Figure 7

(a) Antibacterial property of 1.33 wt % HMW, 90% chitosan, 10% poly(ethylene oxide) (PEO) blended fibers is shown, as well as how the degree of deacetylation (DDA) plays an effect. Increasing the DDA% increases the amount of available protonated amine sites for antibacterial activity, but 80% DDA fibers here had a larger diameter, which leads to a smaller number of available sites. (b) Log reduction values of several common human coronaviruses by substituted chitosan derivatives (57–77% substituted). Error bars represent the standard error, and asterisks signify statistically significant differences (P < 0.05); hpi = hours post-infection. (a) Reproduced from ref (7). Copyright 2009 Elsevier. (b) Reproduced from ref (21) with open access CC-BY-4.0 license, 2016 PLoS.