Effects of surface modifying macromolecules on the structural characteristics of different structured and nanofibrous membranes

Different surface modification techniques such as coating, radiation graft polymerization and plasma polymerization are used to modify the structural characteristics and chemical properties of different types of membranes. In general, these techniques involve more steps during the fabrication line of membranes increasing their cost and changing the physical structure of their surface (e.g. change of the pore shape reducing its size or even closing it). In this study we propose the use of surface modifying macromolecules (SMMs) that can migrate to the air/membrane interface during its fabrication changing its surface chemistry while leaving its bulk properties intact. The SMMs were synthesized by a two-step solution polymerization method and characterized by different techniques analyzing their fluorine content, molecular weights, polydispersity, glass transition temperature, etc. Composite hydrophobic/hydrophilic polymeric membranes of different structures (i.e. porous, dense, flat sheet and hollow fiber membranes) and different characteristics were prepared. Attempts are made to fabricate SMMs modified electrospun nanofibrous membranes. During membrane formation, the SMMs migrate to the air/membrane interface because of their low Gibbs free energy compared to the host hydrophilic polymer. Following this method, modified membranes can be prepared in only one step instead of two (i.e. membrane fabrication and then modification) employing a polymer solution containing the host hydrophilic polymer and the SMMs. Based on different SMMs characterization techniques such as X-ray photoelectron microscopy (XPS), water contact angle measurements and scanning electron microscopy (SEM)+energy dispersion spectrometry (EDS), it was confirmed that the surface of the SMM electrospun modified nanofibrous membranes was enriched with fluorine groups

Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions

Background Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals. Results Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall. Conclusions The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions

Synthesis and characterization of hybrid organic-inorganic materials based on sulphonated polyamideimide and silica

The preparation of hybrid organic–inorganic membrane materials based on a sulphonated polyamideimide resin and silica filler has been studied. The method allows the sol–gel process to proceed in the presence of a high molecular weight polyamideimide, resulting in well dispersed silica nanoparticles (<50 nm) within the polymer matrix with chemical bonding between the organic and inorganic phases. Tetraethoxysilane (TEOS) was used as the silica precursor and the organosilicate networks were bonded to the polymer matrix via a coupling agent aminopropyltriethoxysilane (APTrEOS). The structure and properties of these hybrid materials were characterized via a range of techniques including FTIR, TGA, DSC, SEM and contact angle analysis. It was found that the compatibility between organic and inorganic phases has been greatly enhanced by the incorporation of APTrEOS. The thermal stability and hydrophilic properties of hybrid materials have also been significantly improved

Optimization of UV-photografting factors in preparation of polyacrylic-polyethersulfone forward osmosis membrane using response surface methodology

Commercial nanofiltration polyethersulfone (NF2) membrane was modified via ultraviolet (UV) photografting to prepare a high-performance forward osmosis (FO) membrane. The optimized condition of grafting parameters was obtained using central composite design (CCD) and response surface methodology (RSM). UV-photografting time and acrylic acid (AA) monomer concentration were the considered variables, while the two RSM responses were water permeate flux and reverse salt diffusion flux (RSD). Quadratic models were established between the responses and the independent parameters using analysis of variance (ANOVA). The membranes were characterized with functional group, morphology and surface roughness. The obtained optimum conditions were 2.81min grafting time and 27.85g/L AA monomer concentration. Under these conditions, a maximum water permeate flux of 1.52±0.04L/m2·h was achieved with an RSD value of 10.09±0.36g/m2·h. The optimized membrane exhibited a higher water flux compared to the unmodified NF2 membrane without any significant change of the RSD value

Cyclic olefin polymer as a novel membrane material for membrane distillation applications

A first attempt was made to prepare cyclic olefin polymer/copolymer (COP/COC) flat-sheet porous membranes by the well-known non-solvent induced phase separation method. In this study, two solvents (chloroform and 1,2,4-trichlorobenzene), different additives (polyvinylpyrrolidone, PVP, polyethylene glycol, PEG400, polyethylene oxide, PEO, and Sorbitan monooleate, Span 80) and coagulants (acetone and 70/30 wt% acetone/water mixture) were employed. The prepared membranes were characterized in terms of the thickness (70-85 mu m), porosity (-50-80%), liquid entry pressure (1.16-4.55 bar), water contact angle (similar to 86 degrees - 111 degrees), mean pore size (158-265 nm), mechanical properties (tensile strength: 0.74-5.51 MPa, elongation at break: 3.34%-7.94% and Young's modulus: 29-237 MPa), morphological and topographical characteristics. Short-term direct contact membrane distillation (DCMD) tests showed maximum permeate fluxes of 20 kg m(-2) h(-1) and 15 kg m(-2) h(-1) when using as feed distilled water and 30 g/L sodium chloride aqueous solution, respectively, with a high salt separation factor (99.99%). Long-term DCMD tests of some selected membranes carried out during 24-50 h showed that the membranes prepared with PEG additive exhibited more stable DCMD performance. In general, it was proved that COP can be successfully used as a novel polymer candidate in membrane distillation (MD) applications

Effect of methacrylic acid monomer on UV-grafted polyethersulfone forward osmosis membrane

UV irradiation is one of the procedures that has been considered for membrane surface graft polymerization. It is commonly utilized for enhancing the wettability of polyethersulfone (PES) membranes. In this research study, the monomer methacrylic acid (MAA) was used for the UV grafting process of a commercial NF2 PES membrane for the preparation of a forward osmosis (FO) membrane. Three different monomer concentrations and three different UV irradiation times were considered. The intrinsic characteristics of both the surface-modified and pristine membranes were determined via a non-pressurized test method. Compared to the NF2 PES, the surface of the modified membranes was rendered more hydrophilic, as the measured water contact angle was reduced considerably from 65° to 32–58°. The membrane surface modification was also confirmed by the data collected from other techniques, such as atomic force microscopy (AFM), field emission-scanning electron microscope (FESEM) and Fourier-transform infrared spectroscopy–attenuated total reflectance (FTIR–ATR). Additionally, the modified membranes exhibited a greater water permeate flux (Jw) compared to the NF2 PES membrane. In this study, the water permeability (A), solute permeability (B) and structural parameter (S) were determined via a two-stage FO non-pressurized test method, changing the membrane orientation. Compared to the FO pressurized test, smaller S values were obtained with significantly high A and B values for the two non-pressurized tests. The adopted method in the current study is more adequate for determining the intrinsic characteristics of FO membranes

Current progress on removal of recalcitrance coloured particles from anaerobically treated effluent using coagulation–flocculation

The palm oil industry is the most important agro industries in Malaysia and most of the mills adopt anaerobic digestion as their primary treatment for palm oil mill effluent (POME). Due to the public concern, decolourisation of anaerobically treated POME (AnPOME) is becoming a great concern. Presence of recalcitrant-coloured particles hinders biological processes and coagulation–flocculation may able to remove these coloured particles. Several types of inorganic and polymers-based coagulant/flocculant aids for coagulation–flocculation of AnPOME have been reviewed. Researchers are currently interested in using natural coagulant and flocculant aids. Modification of the properties of natural coagulant and flocculant aids enhanced coagulation–flocculation performance. Modelling and optimization of the coagulation–flocculation process have also been reviewed. Chemical sludge has the potential for plant growth that can be evaluated through pot trials and phytotoxicity test