New approaches for the development of cellulose acetate/tetraethyl orthosilicate composite membranes: Rheological and microstructural analysis

A critical review with emphasis on the rheological behavior and properties of polymer solutions and their role in membrane formation, morphology, and performance

Considering the importance of asymmetric membrane morphology in controlling the performance of various membrane systems as well as the rapid development of membrane technologies in different industries, the control of membrane manufacturing processes and effective parameters is considered an outstanding subject. Therefore, it seems that investigating the rheological properties of polymer solutions, including gelation behavior, viscoelasticity, and their effect on membrane formation, as well as the morphological structure of membranes, such as hollow fiber and flat sheet membranes, is a requirement for the production of asymmetric membranes with desirable properties. One of the most widely used techniques for the preparation of asymmetric membranes is phase separation. Its two main mechanisms are liquid-liquid demixing and solid-liquid demixing, which can affect the morphology of the membranes in the membrane formation process. Therefore, the membrane morphology can be greatly influenced by controlling the phase separation in the early stages. In this study, an attempt has been made to investigate the rheological behavior of polymer solutions and other factors during the membrane fabrication process, affecting the morphological structure of membranes. The principles governing the rheology of polymer solutions, such as shear, elongation, viscosity, and viscoelasticity have a vital role in determining the membrane morphology and separation performance. Due to the interaction of the rheology of polymer solutions and phase separation, the effects of changes in the rheological properties of the phase separation and the formation of membranes with different structures and morphologies are studied. Furthermore, in addition to the analysis of the effect of the relaxation time and gelation mechanisms, discussions are provided for the determination of the final membrane morphology considering the competition between the domain growth and gelation rates. Finally, the effect of controlling the rheological behavior and phase separation on the membrane structure and performance was investigated in several membrane applications.

Cellulose acetate/silica composites: Physicochemical and biological characterization

Cellulose acetate is of remarkable scientific interest, becoming more useful when is used in obtaining of the composite materials containing nanoparticles, as result of its improved properties. Thus, cellulose acetate/silica composite films obtained by casting the solutions of cellulose acetate (CA)/tetraethyl orthosilicate (TEOS) in different mixing ratios were analyzed in this paper. The impact of TEOS addition, and implicitly of the silica nanoparticles on the mechanical strength, water vapor sorption properties and antimicrobial activity of the cellulose acetate/silica films were mainly monitored. The results of the tensile strength tests were discussed in correlation with data obtained from Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. It was found that samples with low TEOS content show improved mechanical strength compared to samples with high amounts of TEOS. The microstructural characteristics of the studied films affect their moisture sorption capacity so that the weight of the adsorbed water increases with the addition of TEOS. These features are complemented with the antimicrobial activity against Staphylococcus aureus and Escherichia coli bacterial species. The obtained data show that the cellulose acetate/silica films, and especially those with low silica content have improved properties that can recommend them for applications in the biomedical field.

Matching the Cellulose/Silica Films Surface Properties for Design of Biomaterials That Modulate Extracellular Matrix

The surface properties of composite films are important to know for many applications from the industrial domain to the medical domain. The physical and chemical characteristics of film/membrane surfaces are totally different from those of the bulk due to the surface segregation of the low surface energy components. Thus, the surfaces of cellulose acetate/silica composite films are analyzed in order to obtain information on the morphology, topography and wettability through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle investigations. The studied composite films present different surface properties depending on the tetraethyl orthosilicate (TEOS) content from the casting solutions. Up to a content of 1.5 wt.% TEOS, the surface roughness and hydrophobicity increase, after which there is a decrease in these parameters. This behavior suggests that up to a critical amount of TEOS, the results are influenced by the morphology and topographical features, after which a major role seems to be played by surface chemistry-increasing the oxygenation surfaces. The morphological and chemical details and also the hydrophobicity/hydrophilicity characteristics are discussed in the attempt to design biological surfaces with optimal wettability properties and possibility of application in tissue engineering.

Recent Advances in Applications of Cellulose Derivatives-Based Composite Membranes with Hydroxyapatite

The development of novel polymeric composites based on cellulose derivatives and hydroxyapatite represents a fascinating and challenging research topic in membranes science and technology. Cellulose-based materials are a viable alternative to synthetic polymers due to their favorable physico-chemical and biological characteristics. They are also an appropriate organic matrix for the incorporation of hydroxyapatite particles, inter and intramolecular hydrogen bonds, as well as electrostatic interactions being formed between the functional groups on the polymeric chains surface and the inorganic filler. The current review presents an overview on the main application fields of cellulose derivatives/hydroxyapatite composite membranes. Considering the versatility of hydroxyapatite particles, the hybrid materials offer favorable prospects for applications in water purification, tissue engineering, drug delivery, and hemodialysis. The preparation technique and the chemical composition have a big influence on the final membrane properties. The well-established membrane fabrication methods such as phase inversion, electrospinning, or gradual electrostatic assembly are discussed, together with the various strategies employed to obtain a homogenous dispersion of the inorganic particles in the polymeric matrix. Finally, the main conclusions and the future directions regarding the preparation and applications of cellulose derivatives/hydroxyapatite composite membranes are presented.