Cellulose Acetate Membranes Modification by Aminosilane Grafting in Supercritical Carbon Dioxide towards Antibiofilm Properties

The study explores the grafting of cellulose acetate microfiltration membranes with an aminosilane to attain antibiofilm properties. The grafting reaction was performed in the supercritical carbon dioxide used as a transport and reaction medium. The FTIR analyses and dissolution tests confirmed the covalent bonding between the aminosilane and polymer. The membranes’ microstructure was investigated using a dual-beam SEM and ion microscopy, and no adverse effects of the processing were found. The modified membranes showed a more hydrophilic nature and larger water permeate flow rate than the neat cellulose acetate membranes. The tests in a cross-filtration unit showed that modified membranes were considerably less blocked after a week of exposure to Staphylococcus aureus and Escherichia coli than the original ones. Microbiological investigations revealed strong antibiofilm properties of the grafted membranes in experiments with Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella Enteritidis.

Additives Incorporated in Cellulose Acetate Membranes to Improve Its Performance as a Barrier in Periodontal Treatment

In this study, we prepared cellulose acetate membranes, by means of casting mold, incorporated with two additives, sodium carboxymethyl lignin and calcium glycerophosphate, in order to improve properties for periodontal applications. The membranes were characterized from the morphological, structural, thermal and mechanical point of view, as well as by physiological pH tests. The results showed that membranes with additives improve the physical-chemical and mechanical properties, especially when the two additives are present in the same membrane, which can be attributed to the important synergy between them. The most significant effects occur in increasing the thickness and decreasing the density, which reflects in the porosity of the membranes, although the added amounts do not exceed 1.4%. A 1% increase in lignin concentration does not change the thickness and density of the membrane, but that amount of lignin plus 0.4% calcium glycerophosphate increases the thickness of the membrane by 42% and decreases the density by about 6%. Although there is a decrease in mechanical properties, as observed in Young's modulus and crystallinity, the significant and intermittent increase in sample weight loss with both additives in physiological solution indicates that, in the long run, it can be used as a degradable barrier.

Synthesis and Characterization of Blended Cellulose Acetate Membranes

The casting and preparation of ultrafiltration ZnO modified cellulose acetate membrane (CA/ZnO) were investigated in this work. CA membranes were fabricated by phase inversion using dimethylformamide (DMF) as a solvent and ZnO as nanostructures materials. Ultrafiltration (UF) performance, mechanical stability, morphology, contact angle, and porosity were evaluated on both CA- and ZnO-modified CA samples. Scanning electron microscopy (SEM) was used to determine the morphology of the membranes, showing different pore sizes either on rough surfaces and cross-sections of the samples, an asymmetric structure and ultra-scale pores with an average pore radius 0.0261 to 0.045 µm. Contact angle measurements showed the highest hydrophobicity values for the samples with no ZnO addition, ranging between 48° and 82.7° on their airside. The permeability values decreased with the increasing CA concentration in the casting solution, as expected; however, ZnO-modified membranes produced lower flux than the pure CA ones. Nevertheless, ZnO modified CA membranes have higher surface pore size, pore density and porosity, and improved surface hydrophilicity compared with pure CA membranes. The results indicated that the incorporated nano-ZnO tends to limit the packing of the polymer chains onto the membrane structure while showing antifouling properties leading to better hydrophilicity and permeation with consistent UF applications.

Concentration Polarization Quantification and Minimization in Cork Process Wastewater Ultrafiltration by an Ozone Pretreatment

Concentration polarization and membrane fouling have been identified as the main problems during the ultrafiltration treatment of cork processing wastewaters. These problems drastically reduce the permeate fluxes and, therefore, their potential applications. In this work, a soft ozonation pretreatment was applied to minimize these undesirable effects. A new systematic study was carried out for membranes with different molecular weight cut-offs and at different operating conditions to monitor and quantify the concentration polarization caused by the wastewater’s remaining ozonated compounds. Film theory was used to correlate the mass transfer coefficient, k, and the intrinsic rejection coefficient, f′, with the resistance introduced by concentration polarization. The ultrafiltration treatment was carried out under varying hydrodynamic operating conditions (circulating flow rates of 100–200 L/h) and transmembrane pressures (1–3 bar) for a set of four cellulose acetate membranes covering a wide range of molecular weight cut-offs (5000–100,000 Da) and hydraulic permeabilities (25–110 kg/h/m2/bar). The ozone pretreatment (at wastewater pH) reduced the phenolic content selectively (direct oxidation) by more than 50%, reducing membrane fouling and concentration polarization and increasing permeate fluxes (by 22–45%) and mass transfer coefficients (up to six times).

DEVELOPMENT OF ACID MODIFIED CELLULOSE ACETATE MEMBRANES FOR SALT WATER TREATMENT

The main objective of this work has been to study the performance of membranes developed for water treatment. Polymeric membranes (CTP and CTP-Acid) were developed from solutions containing cellulose acetate (CA), cellulose triacetate (CTA) and polysulfone (PSF), using maleic acid (MA) and acetic acid (AA) as additives and chloroform/dioxane as solvent. The NIPS-type phase inversion method was chosen as the membrane film manufacturing technique. The incorporation of 2.5% and 5% by weight of acids in the membrane mixture allowed us to study the additive effect on the morphological structure, and to predict the performance of the membranes formed. The characterization of the membranes was performed by SEM and FTIR analyses. Examining the flux, permeability and selectivity of the membranes also permitted to study the efficiency and performance of each membrane. The addition of AA and MA additives within the mixture increased the hydrophilic character and improved the flux rate by increasing it from 75 Lm-2h-1 to 142.74 Lm-2h-1 for 5% maleic acid addition. The 5% CTP AA membrane gave very satisfactory results in terms of selectivity, with a maximum removal of 84% of NaCl salt. Therefore, this membrane has been considered to be the most efficient one, with a flux of 120 Lm-2h-1 to 15 bar and a NaCl salt retention that meets the standards required by the World Health Organization (WHO).

Crown Ether-Immobilized Cellulose Acetate Membranes for the Retention of Gd (III)

This study presents a new, revolutionary, and easy method of separating Gd (III). For this purpose, a cellulose acetate membrane surface was modified in three steps, as follows: firstly, with aminopropyl triethoxysylene; then with glutaraldehyde; and at the end, by immobilization of crown ethers. The obtained membranes were characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), through which the synthesis of membranes with Gd (III) separation properties is demonstrated. In addition, for the Gd (III) separating process, a gadolinium nitrate solution, with applications of moderator poison in nuclear reactors, was used. The membranes retention performance has been demonstrated by inductively coupled plasma mass spectrometry (ICP-MS), showing a separation efficiency of up to 91%, compared with the initial feed solution.

Cellulose acetate obtained from Schizolobium parahyba (vell.) blake wood

Currently, non-biodegradable polymers are produced on a large scale and cause several environmental problems, especially due to their low degradation. Cellulose acetate is a non-toxic, low-flammable and low-cost polymer, playing an important environmental role. The objective of this study was to synthesize cellulose acetate membranes from Schizolobium parahyba wood (“guapuruvu”) with particles sizes of 20 and 60 mesh. The materials were submitted to acetosolv pulping, bleaching and acetylation to produce the acetates. The yields and the degree of substitution were found. The fibers were chemically characterized and the samples obtained at each processing step were analyzed by FTIR. It was possible to prepare acetates from both granulometries wood. The FTIR analysis showed changes on the samples’ bands, indicating that the chemical processes were efficient. Cellulose acetate obtained from the 60 mesh material presented a higher degree of substitution (2.74 ± 0.12) when compared to the 20 mesh acetate (2.59 ± 0.13), showing that the particle size of the material influenced on the efficiency of the acetylation reaction. DMA tests have demonstrated that the 60 mesh membrane has higher flexibility and transparency when compared to the 20 mesh membrane.