Self-healing properties of water filtration membranes containing amphiphilic comb polymer

Abstract

(cont.) and filtration experiments, as well as other characterization techniques. Surface analysis is accomplished via x-ray photoelectron spectroscopy (XPS). Membrane samples are cleaned (in hydrogen peroxide or chromic-sulfuric acid (Chromerge)) and/or annealed (in 90⁰C deionized water), and their elemental surface composition and specific carbon binding environments are determined by XPS. Filtration experiments are done by alternating feed solutions of deionized water and a foulant (either bovine serum albumin or an oil/water emulsion). The flux of the feed solution is measured before fouling, during fouling, and after fouling, to determine the extent of fouling recovery. Also, the compositions of the permeates are analyzed via ultraviolet-visible spectroscopy to determine the rejection coefficient of the membrane. The data presented in this thesis show that PVDF blend membranes containing P(MMA-r-POEM) are capable of generating a fresh surface layer of PEO multiple times, even after extended cleaning sessions using concentrated acid. Membranes of varying thickness are shown to exhibit PEO-regenerative abilities, but it appears that thick membranes have better fouling recovery than thinner, filtration-series membranes. Also, it is found that a blend membrane stripped of all of its surface PEO (by a 24-hour-long exposure to Chromerge) is able to restore PEO to its surface with roughly 24 hours of annealing ...

Freshwater shortages are a tremendous problem for certain areas of the world, and given projected world population increases, they will pose a problem for a rising number of people in the future. A variety of technologies are currently used to extract usable water from wastewater, including water filtration membranes. Membrane technologies are promising because they require little energy and are scalable. However, many membrane materials tend to foul quickly when exposed to the organic species in wastewater feed streams. Approaches to preventing membrane fouling include surface grafting of hydrophilic polymers onto membranes and the use of hydrophilic polymers as the bulk material. The former approach works moderately well, but it requires an increased number of fabrication steps, and the surface treatments tend to lose their effectiveness over time. The use of hydrophilic bulk materials leads to loss of membrane strength and resistance to wastewater elements such as chlorine. Neither option provides membranes that can maintain fouling resistance for extended periods of time. This thesis investigates an alternative method of fouling prevention, first described by Hester et al. This approach involves the fabrication of blend membranes containing poly(vinylidene fluoride) (PVDF) and roughly 10 wt% of a comb polymer additive, poly(methyl methacrylate-r-poly(oxyethylene methacrylate)) (P(MMA-r-POEM)). The additive self-segregates to the membrane surface during fabrication and imparts long-term fouling resistance to the membrane. Even after harsh cleaning, which degrades the PEO chains present at the surface, membrane performance can be partially restored with a simple 18-hour anneal in a 90⁰C water bath. Membranes are subjected to both surface