Waste Reutilization in Polymeric Membrane Fabrication: A New Direction in Membranes for Separation

Abstract

In parallel to the rapid growth in economic and social activities, there has been an undesirable increase in environmental degradation due to the massively produced and disposed waste. The need to manage waste in a more innovative manner has become an urgent matter. In response to the call for circular economy, some solid wastes can offer plenty of opportunities to be reutilized as raw materials for the fabrication of functional, high-value products. In the context of solid waste-derived polymeric membrane development, this strategy can pave a way to reduce the consumption of conventional feedstock for the production of synthetic polymers and simultaneously to dampen the negative environmental impacts resulting from the improper management of these solid wastes. The review aims to offer a platform for overviewing the potentials of reutilizing solid waste in liquid separation membrane fabrication by covering the important aspects, including waste pretreatment and raw material extraction, membrane fabrication and characterizations, as well as the separation performance evaluation of the resultant membranes. Three major types of waste-derived polymeric raw materials, namely keratin, cellulose, and plastics, are discussed based on the waste origins, limitations in the waste processing, and their conversion into polymeric membranes. With the promising material properties and viability of processing facilities, recycling and reutilization of waste resources for membrane fabrication are deemed to be a promising strategy that can bring about huge benefits in multiple ways, especially to make a step closer to sustainable and green membrane production.

Keywords: cellulose; keratin; liquid separation; plastic; polymeric membrane; solid waste.

Figure 1

The illustration of the concept of (a) circular economy and (b) waste hierarchy. Source: Europa.eu (official website of European Union).

Figure 2

Chemical structure of (a) beta-keratin, (b) cellulose, (c) polyethylene terephthalate, (d) polystyrene, and (e) polyvinyl chloride.

Figure 3

(a) SEM images of (i) keratin and (ii) keratin/PEO nanofibre membrane [134]. (b) Schematic diagram of the preparation of antibacterial nanofibre recyclable ((Bmim)Cl) IL as solvent. (c) Antibacterial test of PAN and PAN/keratin using S. aureus and E. coli colony, (d) weight loss ratio curve, and the elements distribution after dialysis of PAN/keratin for IL solvent recycling [136].

Figure 4

(a) Permeability and the retention values of cellulose membranes prepared from waste cotton textile, commercial CA membrane (RC70pp), and cellulose membrane from commercial source (Durmaz) (Sample n/m, n: cellulose wt% m: polymer thickness in µm) [141]. (b) Schematic illustration of hydrogen bonding between recycled cellulose and TiO₂ nanorods, (c) optical properties of TiO₂ nanorods incorporated cellulose photocatalytic membranes, and (d) kinetic profile of cellulose photocatalytic membranes incorporated with difference concentration of TiO₂ nanorods under visible light irradiation [143].

Figure 5

(a) Surface morphology of electrospun cigarette filters-derived CA membrane, (b) static oil and water droplets showing the superwettability of underwater and underoil, (c) separation efficiency and dispersoid content, and (d) filtrate flux of various oil/water emulsions (K, kerosene; D, diesel; H, hexane; P, petroleum ether; T, trichloromethane; W, water). [148] (e) Oil-in-water emulsion permeability of waste cigarette filter-derived CA membrane, PSF membrane, and PVDF membrane as a function of time for five cycles [149].

Figure 6

(a) Ternary phase diagram constructed based on cloud point measurements with commercial HIPS and recycled HIPS as base polymer and DMF as a solvent. (b) Cross-sectional images of membranes formed from (i) commercial HIPS and (ii) recycled HIPS [127].

Figure 7

(a) (i) Steady permeate flux and (ii) diltiazem rejection of recycled PET NF membrane prepared from different concentration of XA and types of coagulants [158]. (b) Water flux and salt rejection of PET nanofibrous NF membrane as a function of (i) hot-pressing temperatures with duration of 10 s and (ii) hot-pressing duration at 130 °C (c) anti-wetting ability of (i) pristine and (ii) fluorinated membranes to water and oil; (d) water flux of (i) pristine and (ii) fluorinated membranes as function of surfactant concentration [160].

Figure 8

Flux and separation efficiency of PDMS-coated recycled PET nanofibrous membrane as a function of (a) PDMS concentration, (b) cycle number, and (c) types of hydrocarbon substances in oil–water separation [161].

Figure 9

(a) Schematic illustration of hydration layer formation on rubber selective layer supported on ceramic substrate, (b) pure-water and permeate permeability of recycled rubber-derived NF membrane as a function of time, (c) permeate permeability of the membrane as a function of filtration cycles [163], (d) schematic illustration of the exfoliation of Kevlar fibre, (e) scanning electron microscope images of aramid nanofibre aerogel membrane, and (f) illustration of water-in-oil emulsion separation phenomena using aramid nanofibre aerogel membrane [164].