Optimization of polyurethane membranes

Red Seaweed (Gracilaria verrucosa Greville) Based Polyurethane as Adsorptive Membrane for Ammonia Removal in Water

Polyurethane membranes are widely developed polymers by researchers because they can be made from synthetic materials or natural materials. Red seaweed (Gracilaria verrucosa Greville) is a natural material that can be developed as a raw material for polyurethane membranes. This study used red seaweed biomass (RSB) as a raw material to manufacture polyurethane as an adsorptive membrane for removing ammonia in water. The membrane composition was determined using the Box–Behnken design from Response Surface Methodology with three factors and three levels. In the ammonia adsorption process, the adsorption isotherm was determined by varying the concentration, while the adsorption kinetics was determined by varying the contact time. Red seaweed biomass-based polyurethane membrane (PUM-RSB) can adsorb ammonia in water with an adsorption capacity of 0.233 mg/g and an adsorption efficiency of 16.2%. The adsorption efficiency followed the quadratic model in the Box–Behnken design, which resulted in the optimal composition of RSB 0.15 g, TDI 3.0 g, and glycerin 0.4 g with predicted and actual adsorption capacities of 0.224 mg/g and 0.226 mg/g. The ammonia adsorption isotherm using PUM-RSB follows the Freundlich isotherm, with a high correlation coefficient (R²) of 0.977, while the Langmuir isotherm has a low R² value of 0.926. The Freundlich isotherm indicates that ammonia is adsorbed on the surface of the adsorbent as multilayer adsorption. In addition, based on the analysis of adsorption kinetics, the adsorption phenomenon follows pseudo-order II with a chemisorption mechanism, and it is assumed that the bond that occurs is between the anion –SO₄²⁻ with the NH₄⁺ cation to form ammonium sulfate (NH₄)₂SO₄ and between isocyanates (NCO) with NH₄⁺ cations to form substituted urea.

High-Performance Polyurethane Nanocomposite Membranes Containing Cellulose Nanocrystals for Protein Separation

With the aim of exploring new materials and properties, we report the synthesis of a thermoplastic chain extended polyurethane membrane, with superior strength and toughness, obtained by incorporating two different concentrations of reactive cellulose nanocrystals (CNC) for potential use in kidney dialysis. Membrane nanocomposites were prepared by the phase inversion method and their structure and properties were determined. These materials were prepared from a polyurethane (PU) yielded from poly(1,4 butylene adipate) as a soft segment diol, isophorone diisocyanate (IPDI) and hexamethylenediamine (HMDA) as isocyanate and chain extender, respectively (hard segment), filled with 1 or 2% w/w CNC. Membrane preparation was made by the phase inversion method using N,N-dimethylformamide as solvent and water as nonsolvent, and subjected to dead-end microfiltration. Membranes were evaluated by their pure water flux, water content, hydraulic resistance and protein rejection. Polymers and nanocomposites were characterized by scanning electronic and optical microscopy, differential scanning calorimetry, infrared spectroscopy, strain stress testing and ¹³C solid state nuclear magnetic resonance. The most remarkable effects observed by the addition of CNCs are (i) a substantial increment in Young’s modulus to twenty-two times compared with the neat PU and (ii) a marked increase in pure water flux up to sixty times, for sample containing 1% (w/w) of CNC. We found that nanofiller has a strong affinity to soft segment diol, which crystallizes in the presence of CNCs, developing both superior mechanical and pure water flow properties, compared to neat PU. The presence of nanofiller also modifies PU intermolecular interactions and consequently the nature of membrane pores.

Synthesis of Polyurethane Membranes Derived from Red Seaweed Biomass for Ammonia Filtration

The development of membrane technology is rapidly increasing due to its numerous advantages, including its ease of use, chemical resistant properties, reduced energy consumption, and limited need for chemical additives. Polyurethane membranes (PUM) are a particular type of membrane filter, synthesized using natural organic materials containing hydroxy (-OH) groups, which can be used for water filtration, e.g., ammonia removal. Red seaweed (Rhodophyta) has specific molecules which could be used for PUM. This study aimed to ascertain PUM synthesis from red seaweed biomass (PUM-RSB) by using toluene diisocyanate via the phase inversion method. Red seaweed biomass with a particle size of 777.3 nm was used as starting material containing abundant hydroxy groups visible in the FTIR spectrum. The PUM-RSB produced was elastic, dry, and sturdy. Thermal analysis of the membrane showed that the initial high degradation temperature was 290.71 °C, while the residue from the thermogravimetric analysis (TGA) analysis was 4.88%. The PUM-RSB section indicates the presence of cavities on the inside. The mechanical properties of the PUM-RSB have a stress value of 53.43 MPa and a nominal strain of 2.85%. In order to optimize the PUM-RSB synthesis, a Box–Behnken design of Response Surface Methodology was conducted and showed the value of RSB 0.176 g, TDI 3.000 g, and glycerin 0.200 g, resulting from the theoretical and experimental rejection factor, i.e., 31.3% and 23.9%, respectively.

The polydopamine-enhanced superadhesion and fracture strength of honeycomb polyurethane porous membranes

The superhydrophobic properties of biological surfaces in nature have attracted extensive attention in scientific and industrial circles. Relative to the rolling superhydrophobic state of lotus leaves, the adhesive superhydrophobic state of geckos and Parthenocissus tricuspidata is also significant in many fields. In this work, polydopamine (PDA) with its excellent biological compatibility and strong adhesion was selected as a substance to simulate the secretion of the suckers of P. tricuspidata and it was precipitated at the surface of honeycomb polyurethane porous membranes (PUPM). The results demonstrated that the honeycomb PUPM, as prepared, displayed special super-adhesion properties similar to those of geckos and P. tricuspidata. PDA formed via self-polymerization in aqueous solution was equivalent to a double-sided adhesive, acquiring a micro-nano structure of PDA and PUPM and displaying increased surface hydrophobicity and improved adhesion properties. Even when the surface precipitation of PDA and modification with n-dodecyl mercaptan made the contact angle increase to more than 160°, the surface adhesion to water was rather strong and remained stable. The addition of the PDA adhesive can effectively change the microporous structure of PUPM, enhancing the viscosity, and facilitating an enhancement in the fracture strength.

Thermal behavior, surface energy analysis, and hemocompatibility of some polycarbonate urethanes for cardiac engineering

The understanding of basic surface properties and the relationships between temperature and the configuration of the polymer surface are the key to further understand the first interaction mechanism of the polymer with the body. To this end, some poly(carbonate tetramethylene ether)urethane (PCEU), poly(carbonate siloxane tetramethylene ether)urethane (PCSiEU), and their 1:1 gravimetric mixture (PCEU/PCSiEU) membranes were prepared. In order to establish the relationships between temperature and the chemical structure of polymer surface, the polyurethane (PU) membranes were analyzed by attenuated total reflectance–Fourier transform infrared spectroscopy. The temperature has a significant influence on these PU surface structures. Surface characteristics such as wettability and surface free energy were also analyzed since the interaction between biomaterials and blood occurs at their interface. The preliminary cytotoxicity screening showed no cytotoxicity of these PU membranes. The PU samples do not accelerate the clot formation mechanisms under the tested conditions. The results suggest that these PU membranes are promising materials for the preparation of cardiovascular scaffolds.

Nanotechnological characterization of human serum albumin adsorption on wet synthetic polymer dialysis membrane surfaces

The objective of the present study was to evaluate the characteristics of protein adsorption on the inner surface of various dialysis membranes, to develop protein adsorption-resistant biocompatible dialysis membranes. The adsorption force of human serum albumin (HSA) on the inner surface of a dialysis membrane and the smoothness of the membrane were evaluated from a nanoscale perspective by atomic force microscopy. The content ratio of the hydrophilic polymer, polyvinylpyrrolidone (PVP), was determined by attenuated total reflection Fourier transform infrared spectroscopy. Nine synthetic-polymer dialysis membranes on the market made of polysulfone (PSF), polyethersulfone (PES), polyester polymer-alloy (PEPA), and ethylene vinylalcohol (EVAL) were used in the present study. The HSA adsorption force on the surface of the hydrophobic polymer PEPA membrane was higher than that on the hydrophilic polymer EVAL membrane surface. It has been considered beneficial, for decreasing the HSA adsorption force, to cover a hydrophobic polymer membrane surface with PVP. However, there were some areas on PVP-containing membrane surfaces at which much higher HSA adsorption forces were observed. The HSA adsorption force gave a nearly linear correlation with the surface roughness on the PSF membrane surface. However, the HSA adsorption force was uncorrelated with the PVP content ratio for any of the PSF membrane surfaces tested. In conclusion, protein adsorption can be minimized by the use of dialysis membranes made of hydrophobic polymers containing PVP with a smooth surface.

ATR—FTIR Studies of the Temperature Effects on Polyurethane Doped with Silver Nanoparticles

We investigated by attenuated total reflection Fourier infrared spectroscopy the chemical behavior of macromolecules on the surface of polyurethane microporous film doped with silver nanoparticles at temperatures between 25 and 200°C. Silver nanoparticles interact with the urethane group and form a urethane-silver-urethane structure with a specific surface configuration and a higher resistance to temperature. Chemical transformations of the macromolecules on the surface of polyurethane film depend on both the silver nanoparticles concentration and temperature.