Surface modification of commercial cellulose acetate membranes using surface-initiated polymerization of 2-hydroxyethyl methacrylate to improve membrane surface biofouling resistance

Radiation‐Induced Admicellar Graft Polymerization of 2‐Hydroxyethyl Methacrylate onto Polyvinylidene Fluoride Membranes Using an Electron Beam Accelerator

The efficiency of admicellar graft polymerization in functionalizing polyvinylidene fluoride (PVDF) membranes was explored. The effect of 2‐hydroxyethyl methacrylate (HEMA) concentration and the absorbed dose was investigated using a simultaneous method of radiation‐induced graft polymerization. The degree of grafting increased with raising the absorbed dose and HEMA concentration. The Fourier transform infrared (FTIR) peak for C–O stretch and the asymmetric and symmetric stretching of the C–O–C bridge, respectively, proved the presence of poly(2‐hydroxyethyl methacrylate) (PHEMA) on the modified PVDF. As the grafting yield increased, rougher surfaces were observed. According to contact angle analysis, the grafted membrane with a higher grafting yield outperformed the low grafting yield membrane in terms of water flux and hydrophilicity.

The Application of Cellulose Acetate Membranes for Separation of Fermentation Broths by the Reverse Osmosis: A Feasibility Study

Recently, there has been a special research focus on the bioconversion of glycerol to 1,3-propanediol (1,3-PD) due to its significance in the chemical industry. However, the treatment and separation of fermentation broths is a great challenge. Currently, the reverse osmosis (RO) process is a reliable state-of-the-art technique for separation of biological solutions. This study (as the first to do so) investigated the feasibility of separation of 1,3-PD broths with the use of cellulose acetate (CA) membrane by the RO process. The experiments were carried out using the installation equipped with the plate module, under the transmembrane pressure (TMP) and temperature of 1 MPa and 298 K, respectively. It was found that the used membrane was suitable for broth separation. Indeed, it was noted that 1,3-PD, as a target product, migrated through the membrane; meanwhile, other broth components were rejected in various degrees. Moreover, it was proven that retention of carboxylic acids tended to increase with increasing molecular weight, according to the following order: succinic acid > lactic acid > acetic acid > formic acid. With regards to ions, retention degree increased with the increase of ionic radius and decrease of diffusion coefficient. Finally, it was demonstrated that the CA membrane is resistant to irreversible fouling, which has a positive effect on the economic viability of the process.

Cellulose acetate in fabrication of polymeric membranes: A review

Developing biodegradable polymers to fabricate filtration membranes is one of the main challenges of membrane science and technology. Cellulose acetate (CA) membranes, due to their excellent film-forming property, high chemical and mechanical stability, high hydrophilicity, eco-friendly, and suitable cost, are extensively used in water and wastewater treatment, gas separation, and energy generation purposes. The CA is one of the first materials used to fabricate filtration membranes. However, in the last decade, the possibility of modification of CA to improve permeability and stability has attracted the researcher's attention again. This review is focused on the properties of cellulose derivatives and especially CA membranes in the fabrication of polymeric separation membranes in various applications such as filtration, gas separation, adsorption, and ion exchange membranes. Firstly, a brief introduction of CA properties and used molecular weights in the fabrication of membranes will be presented. After that, different configurations of CA membranes will be outlined, and the performance of CA membranes in several applications and configurations as the main polymer and as an additive in the fabrication of other polymer-based membranes will be discussed.

Novel Grafted/Crosslinked Cellulose Acetate Membrane with N-isopropylacrylamide/N,N-methylenebisacrylamide for Water Desalination

This work aims to prepare new types of grafted and crosslinked cellulose acetate (CA) reverse osmosis (RO) membranes by phase inversion technique. The grafting and/or crosslinking processes of the pristine CA-RO membrane were conducted using N-isopropylacrylamide (N-IPAAm) and N,N-methylene bisacrylamide (MBAAm), respectively. The grafting/crosslinking mechanism onto the CA-RO membrane surface was proposed. Atomic force microscope (AFM) images of the pure CA-RO and 0.1 wt% N-IPAAm-grafted CA-RO membranes revealed that the surface roughness was 42.99 nm and 11.6 nm, respectively. Scanning electron microscopy (SEM) images of the 0.1 wt% grafted/crosslinked membrane indicated the finger-like macrovoids structure. It was observed that the contact angle of the pristine CA-RO membrane was 66.28° and declined to 49.7° for 0.1 wt % N-IPAAm-grafted CA-RO membrane. The salt rejection of the pristine CA-RO membrane was 93.7% and increased to 98.9% for the grafted 0.1 wt % N-IPAAm/CA-RO membrane. The optimum grafted/crosslinked composition was 0.1 wt %/ 0.013 wt % which produced the salt rejection and water flux of 94% and 3.2 L/m²h at low pressure, respectively. It was concluded that both the grafting and crosslinking processes enhanced the performance of the CA-RO membranes.

Comparison of Antibacterial Adhesion When Salivary Pellicle Is Coated on Both Poly(2-hydroxyethyl-methacrylate)- and Polyethylene-glycol-methacrylate-grafted Poly(methyl methacrylate)

Although poly(2-hydroxyethyl methacrylate) (pHEMA) and polyethylene glycol methacrylate (PEGMA) have been demonstrated to inhibit bacterial adhesion, no study has compared antibacterial adhesion when salivary pellicle is coated on polymethyl methacrylate (PMMA) grafted with pHEMA and on PMMA grafted with PEGMA. In this study, PMMA discs were fabricated from a commercial orthodontic acrylic resin system (Ortho-Jet). Attenuated total reflection-Fourier transform infrared spectra taken before and after grafting confirmed that pHEMA and PEGMA were successfully grafted on PMMA. Contact angle measurements revealed PMMA-pHEMA to be the most hydrophilic, followed by PMMA-PEGMA, and then by PMMA. Zeta potential analysis revealed the most negative surface charges on PMMA-PEGMA, followed by PMMA-pHEMA, and then by PMMA. Confocal laser scanning microscopy showed green fluorescence in the background, indicating images that influenced the accuracy of the quantification of live bacteria. Both the optical density value measured at 600 nm and single plate-serial dilution spotting showed that pHEMA was more effective than PEGMA against Escherichia coli and Streptococcus mutans, although the difference was not significant. Therefore, the grafting of pHEMA and PEGMA separately on PMMA is effective against bacterial adhesion, even after the grafted PMMA were coated with salivary pellicle. Surface hydrophilicity, bactericidality, and Coulomb repulsion between the negatively charged bacteria and the grafted surface contributed to the effectiveness.

Surface Modification of Wood Flour via ARGET ATRP and Its Application as Filler in Thermoplastics

Wood flour is particularly suitable as a filler in thermoplastics because it is environmentally friendly, readily available, and offers a high strength-to-density ratio. To overcome the insufficient interfacial adhesion between hydrophilic wood and a hydrophobic matrix, a thermoplastic polymer was grafted from wood flour via surface-initiated activators regenerated by electron transfer-atom transfer radical polymerization (SI-ARGET ATRP). Wood particles were modified with an ATRP initiator and subsequently grafted with methyl acrylate for different polymerization times in the absence of a sacrificial initiator. The successful grafting of poly(methyl acrylate) (PMA) was demonstrated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and water contact angle (WCA) measurements. To confirm the control over the polymerization, a cleavable ATRP initiator was immobilized on the particles, allowing the detachment of the grafted polymer under mild conditions. The grafted particles were incorporated into a PMA matrix using solvent casting and their influence on the mechanical properties (Young's modulus, yield strength, and toughness) of the composite was investigated. Tensile testing showed that the mechanical properties improved with increasing polymerization time and increasing ratio of incorporated grafted particles.

“Click-chemical” modification of cellulose acetate nanofibers: a versatile platform for biofunctionalization

We demonstrated a platform for the biofunctionalization of cellulose acetate nanofibers using a new type of click chemistry, namely “sulfur(vi)–fluoride exchange reaction”.

Enhanced permeability and antifouling performance of cellulose acetate ultrafiltration membrane assisted by l-DOPA functionalized halloysite nanotubes

l-Dopa functionalized halloysite nanotubes (HNTs) were prepared by the self-polymerization of l-dopa in the weak alkaline condition. Then different contents of l-dopa coated HNTs (LPDHNTs) were blended into cellulose acetate to prepare enhanced performance ultrafiltration membranes via the phase inversion method. The HNTs and LPDHNTs were characterized by FTIR, XPS, and TEM anysis. And the membranes morphologies, separation performance, antifouling performance, mechanical properties and hydrophilicity were also investigated. It was found that the composite membranes exhibited excellent antifouling performance. The pure water flux of 3.0wt% LPDHNTs/CA membrane increased from 11.4Lm^-2h^-1 to 92.9Lm^-2h^-1, while the EA rejection ratio of the membrane was about 91.2%. In addition, the mechanical properties of the resultant membranes were strengthened compared with the CA ultrafiltration membrane.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Fine-Tuning the Surface of Forward Osmosis Membranes via Grafting Graphene Oxide: Performance Patterns and Biofouling Propensity

Graphene oxide (GO) nanosheets were attached to the polyamide selective layer of thin film composite (TFC) forward osmosis (FO) membranes through a poly L-Lysine (PLL) intermediary using either layer-by-layer or hybrid (H) grafting strategies. Fourier transform infrared spectroscopy, zeta potential, and thermogravimetric analysis confirmed the successful attachment of GO/PLL, the surface modification enhancing both the hydrophilicity and smoothness of the membrane's surface demonstrated by water contact angle, atomic force microscopy, and transmission electron microscopy. The biofouling resistance of the FO membranes determined using an adenosine triphosphate bioluminescence test showed a 99% reduction in surviving bacteria for GO/PLL-H modified membranes compared to pristine membrane. This antibiofouling property of the GO/PLL-H modified membrane was reflected in reduced flux decline compared to all other samples when filtering brackish water under biofouling conditions. Further, the high density and tightly bound GO nanosheets using the hybrid modification reduced the reverse solute flux compared to the pristine, which reflects improved membrane selectivity. These results illustrate that the GO/PLL-H modification is a valuable addition to improve the performance of FO TFC membranes.

Polymeric membranes: surface modification for minimizing (bio)colloidal fouling

This paper presents an overview on recent developments in surface modification of polymer membranes for reduction of their fouling with biocolloids and organic colloids in pressure driven membrane processes. First, colloidal interactions such as London-van der Waals, electrical, hydration, hydrophobic, steric forces and membrane surface properties such as hydrophilicity, charge and surface roughness, which affect membrane fouling, have been discussed and the main goals of the membrane surface modification for fouling reduction have been outlined. Thereafter the recent studies on reduction of (bio)colloidal of polymer membranes using ultraviolet/redox initiated surface grafting, physical coating/adsorption of a protective layer on the membrane surface, chemical reactions or surface modification of polymer membranes with nanoparticles as well as using of advanced atomic force microscopy to characterize (bio)colloidal fouling have been critically summarized.

Preparation of Polymer Brushes by Surface-Initiated ARGET ATRP

This paper firstly summarized the latest research progress on the polymer brushes preparation by surface-initiated ARGET ATRP polymerization. It mainly includes the surface modifications of inorganic substrate (silicon dioxide and carbon nanotubes), and the organic substrate (cellulose and polymer microspheres). This method needs less catalyst and operates more easily, compared to the classical ATRP. Besides, it also has good polymerization controllability, and the polymer brushes have higher grafting density and molecular weight. Therefore, surface-initiated ARGET ATRP polymerization has become an effective method for modifying the surface of materials. Then, we prepared the polymer brush supported TEMPO by the surface-initiated ARGET ATRP and characterized.

pH-Responsive Brush-Modified Silica Hybrids Synthesized by Surface-Initiated ARGET ATRP

Brush-modified silica hybrids have been synthesized by growing poly(2-(diethylamino)ethyl methacrylate) (poly(DEA)) brushes on 120 nm diameter silica particles by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). This is the first report of using SI-ARGET ATRP to synthesize poly(DEA) brushes. The kinetics of poly(DEA) brush growth in 4:1 v/v ethanol/water was monitored. The hydrodynamic diameter of the resulting brush-modified particles was dependent on the solution pH due to the weak polybasic nature of the brushes. Below the pK_a of poly(DEA), the hydrodynamic diameter of the brush-modified particles increased with decreasing pH as a consequence of brush protonation, rearrangement and solvent uptake. This pH-response of the brushes was reversible and the hybrid particles exhibited significant hydrodynamic volume changes of up to 200% when the solution pH was cycled from pH 7 to pH 4.