Thermally Induced Phase Separation Research Articles

Preparation, characterization and performance evaluation of ZnO deposited polyethylene ultrafiltration membranes for dye and protein separation

In this research, polyethylene (PE) membrane was prepared by the thermal induced phase separation and its surface was modified by the growth of zinc oxide (ZnO) crystals on the surface and inside of the pores by chemical bath deposition method. Effect of different coating parameters such as immersion time in ZnO precursor, precursor concentration and KMnO4 concentration as a PE surface activator were investigated on ZnO layer growth to obtain a membrane with the least fouling against the protein and organic dye wastewater with suitable flux and rejection. The presence of grown ZnO nanoparticles on the membrane surface was confirmed by FTIR-ATR, SEM, XRD, contact angle and EDX analyses. Water flux of the membrane containing 0.5 M ZnO precursor concentration and 5 mM KMnO4 solution reached to its maximum. The more addition of the precursor concentration was blocked membrane pores and reduced the pure water flux. Also, the analysis of the water contact angle showed an increase in the membrane's water hydrophilicity by increasing the ZnO growth. The BSA fouling test was carried out, which the results showed better performance in reducing fouling of the modified membranes rather than the uncoated membranes. Blue indigo dye was selected for rejection testing, which rejection of the layered membranes was more than 99%. All the modified membranes were better performance in filtration of the colored solution than the uncoated membrane. In addition, these membranes were compared by plasma modified membrane and the results showed that the ZnO grown membranes have better performance compared to the plasma modified membranes.

Biodegradable Films: Microporous Biodegradable Films Promote Therapeutic Angiogenesis (Adv. Healthcare Mater. 17/2020)

In article number 2000806 by Richard M. Day and co-workers, highly porous biodegradable films are prepared using thermally-induced phase separation. In vivo implantation of the films into ischemic tissue stimulates increased expression of pro-angiogenic growth factor genes. This provides a favourable local environment for neovascularization, increased tissue perfusion, and therapeutic angiogenesis in ischemic tissue. The findings pave the way to establishing new materials-based strategies to achieve therapeutic angiogenesis.

Fabrication of polypropylene/lignin blend sponges via thermally induced phase separation for the removal of oil from contaminated water

Polypropylene is widely used in oil spillage cleanup due to excellent characteristics. However, polypropylene is not renewable and biodegradable, which is unacceptable to introduce new pollutants while solving environmental disasters. Therefore, there is a high demand to explore a low-cost, environmentally friendly, and renewable technique for the fabrication of porous materials. In this work, lignin was chosen as the second blend in the polymer matrix. Polypropylene and renewable lignin sponges were successfully prepared using simple, inexpensive, controllable, scalable, and an environment-friendly method named thermally induced phase separation (TIPS). The surface morphology of obtained sponges was investigated using FTIR and SEM. FTIR analysis indicated that PP and lignin were physically blended. SEM analysis observed an interconnected porous network that acts as a capture site of oil, and lignin merged into PP. The contact angle of PP, PP5L, PP10L, PP15L, and PP20L was found to be 127.4°, 118.71°, 113.89°, 109.45°, and 107°, respectively. Furthermore, polypropylene/lignin sponges have good adsorption ability toward oils compared to polypropylene itself. The research detected that the highest oil sorption tests exhibited by PP10L sponge, which could absorb 983% of soybean oil, 788% of engine oil, and 550% of lubricating oil in the oil system, with high oil retention more than 90% after 24-h dripping. Besides, the results revealed that temperature has a significant effect on oil absorption. All of these features make polypropylene/lignin blend sponges promising sorbents for the oil spills cleanup, not only for oil recovery but also helps in cleaning the environment.

Hollow fiber membranes with hierarchical spherulite surface structure developed by thermally induced phase separation using triple-orifice spinneret for membrane distillation

Polyvinylidene fluoride (PVDF) hollow fiber membranes were developed by the thermally induced phase separation (TIPS) process using a triple-orifice spinneret with solvent co-extrusion at the outermost channel for applications in membrane distillation (MD). The polymer surface concentration during membrane preparation was controlled by exploiting the interfacial interactions of the diluent and polymer at the extruded solvent surface. The membrane surface was controlled from a dense to a porous structure with a large pore size and a high porosity, which considerably enhanced the membrane water vapor permeability to 13.5 L m−2 h−1. Furthermore, the solvent co-extrusion was responsible for the formation of surface spherulites with different shapes, such as contacted spherulites, isolated spherulites, and isolated spherulites with humps. The spherulites with humps constructed a novel hierarchical structure, which created a superhydrophobic surface that conferred upon the PVDF membrane a remarkable wetting resistance in the MD process toward low-surface-tension saline water. More significantly, all the unique structures were achieved using the one-step membrane fabrication process of solvent co-extrusion without additional processes and materials. Thus, this work provides a new, simple, and useful alternative for the preparation of hollow fiber membranes with high performances for MD desalination.

A Novel Anion Exchange Membrane for Bisulfite Anion Separation by Grafting a Quaternized Moiety through BPPO via Thermal-Induced Phase Separation.

Ion-exchange membranes are the core elements for an electrodialysis (ED) separation process. Phase inversion is an effective method, particularly for commercial membrane production. It introduces two different mechanisms, i.e., thermal induced phase separation (TIPS) and diffusion induced phase separation (DIPS). In this study, anion exchange membranes (AEMs) were prepared by grafting a quaternized moiety (QM,2-[dimethylaminomethyl]naphthalen-1-ol) through brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) via the TIPS method. Those membranes were applied for selective bisulfite (HSO3−) anion separation using ED. The membrane surface morphology was characterized by SEM, and the compositions were magnified using a high-resolution transmission electron microscope (HRTEM). Notably, the membranes showed excellent substance stability in an alkali medium and in grafting tests performed in a QM-soluble solvent. The ED experiment indicated that the as-prepared membrane exhibited better HSO3− separation performance than the state-of-the-art commercial Neosepta AMX (ASTOM, Japan) membrane.

A tailored polylactic acid/polycaprolactone biodegradable and bioactive 3D porous scaffold containing gelatin nanofibers and Taurine for bone regeneration

The focus of the current study was to develop a functional and bioactive scaffold through the combination of 3D polylactic acid (PLA)/polycaprolactone (PCL) with gelatin nanofibers (GNFs) and Taurine (Tau) for bone defect regeneration. GNFs were fabricated via electrospinning dispersed in PLA/PCL polymer solution, Tau with different concentrations was added, and the polymer solution converted into a 3D and porous scaffold via the thermally-induced phase separation technique. The characterization results showed that the scaffolds have interconnected pores with the porosity of up to 90%. Moreover, Tau increased the wettability and weight loss rate, while compromised the compressive strengths. The scaffolds were hemo- and cytocompatible and supported cell viability and proliferation. The in vivo studies showed that the defects treated with scaffolds filled with new bone. The computed tomography (CT) imaging and histopathological observation revealed that the PLA/PCL/Gel/Tau 10% provided the highest new bone formation, angiogenesis, and woven bone among the treatment groups. Our finding illustrated that the fabricated scaffold was able to regenerate bone within the defect and can be considered as the effective scaffold for bone tissue engineering application.

Membranes made from nonsolvent-thermally induced phase separation (N-TIPS) for decellularization of blood in dry plasma spot (DPS) applications

The dried blood spot (DBS) is widely used for collecting microvolume blood for examining free amino acid concentrations in the blood for patients with defects in amino acid metabolism. However, comparing to many clinical tests which are based on cell-free plasma, the DBS system collects whole blood, where the presence of red blood cells (RBCs) may influence the qualitative and quantitative data analyses. Thus, we report novel membranes for decellularization of blood in the dried plasma spot (DPS) system. The membrane was held tightly with an absorbent paper underneath for collecting the permeated cell-free plasma. By combining the thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS), i.e., N-TIPS, we have developed flat-sheet PAN membranes not only able to remove almost 100% RBCs but also allow most plasma to permeate through them effectively. The optimized membrane also has almost no retention to a few targeted amino acids.

Evaluation of physicochemical and mechanical properties with the in vitro degradation of PCL/nHA/MWCNT composite scaffolds

The fabrication of biodegradable magnetic poly(caprolactone)(PCL)/nanohydroxyapatite (nHA)/multiwalled carbon nanotube (MWCNT) composite scaffolds by thermally induced phase separation (TIPS) for bone regeneration is reported in this study. The magnetism tests completed on the porous matrices pointed to their ferromagnetic behavior. Both in-vitro degradation and mechanical properties are studied over eight weeks in a phosphate buffered solution (PBS) at 37°C. The addition of MWCNTs at quantities of up to 5% modified the structural morphology of the composite, producing regular structures with repetitive patterns. As from that quantity, the electrostatic charge of the nanotubes within an aqueous solution was insufficient for acceptable distribution of the nanoparticles, by means of ultrasonic dispersion. It resulted in an acceleration of the degradation behavior that was clear from the mechanical properties that weakened by up to 20%. The thermal properties were also influenced in that they formed shorter chains, which could be ordered with greater ease, as a consequence of the ester hydrolysis process.

The Effect of Additional Zinc Oxide to Antibacterial Property of Chitosan/Collagen-Based Scaffold

The bone scaffold is susceptible to infection in its application due to the bacteria that often appear on the surface. To prevent this phenomenon, the scaffolds need to be modified in order to provide antibacterial properties. In this study, the bone scaffold was fabricated from chitosan-collagen with the addition of zinc oxide as an antibacterial agent. There were four variables of the amount of zinc oxide added to the scaffold: 0%, 1%, 3%, and 5%. The method used was Thermally Induced Phase Separation (TIPS). From this study, a porous scaffold with a rough surface was obtained. SEM image of the scaffold showed that more zinc oxide caused smaller pore and lower porosity. Characterization with FTIR proved that the scaffold obtained from this process has the same functional group as chitosan and collagen. The DSC-TGA curve confirmed that the heating process performed on dehydrothermal treatment (DHT) did not cause degradation of the scaffold because chitosan and collagen have higher degradation temperatures than DHT temperatures. In addition, this study also proved that the addition of zinc oxide had successfully provided the scaffold with antibacterial properties in which the protection against bacteria was related to the amount of zinc oxide in direct proportion.

The investigation of hydrophilic modification of membrane surface based on the mono-esterification between maleic anhydride and polyethylene glycol: Response surface methodology, reaction kinetics and performance analysis

In this work, the hydrophilic modified membrane of polyvinylidene fluoride (PVDF) matrix with better anti-fouling capacity was prepared via thermally induced phase separation (TIPS) method and the surface grafting of polyethylene glycol 2000 (PEG2000). Response surface methodology (RSM) was used to optimally design the best reaction conditions based on the objective of the grafting degree (GD). The results revealed that the most significant term to influence GD is reaction temperature. The rounded optimum conditions of reaction time, catalyst dosage and reaction temperature were 4 h, 0.6% and 73 °C, respectively. The investigation of kinetics indicated that the mono-esterification between styrene-co-maleic anhydride (SMA) and PEG2000 conforms to the second reaction kinetics and the activation energy (Ea) is 47.125 KJ/mol. This implied the feasibility for this solid–liquid (S-L) phase reaction, which can be attributed to the higher reactivity of MA functional group and the effectiveness of base-catalysis. Finally, the reason to improve anti-fouling capacity for the grafting membrane was explained by analyzing the filtration resistance. In a word, this work demonstrated the feasibility and significance for preparing hydrophilic modification membrane via the “physical blending-base catalysis grafting” method and provided a theoretical support for improving anti-fouling capacity of membrane.

Preparation of ECTFE porous membrane with a green diluent TOTM and performance in VMD process

In order to mitigate the harm of solvent volatilization during thermally induced phase separation (TIPS), more and more green solvents/diluents were developed, produced and applied in the membrane field. In this paper, trioctyl trimellitate (TOTM), an environmentally friendly diluent with high boiling point and low vapor pressure, was firstly introduced to prepare porous membranes, especially hydrophobic poly(ethylene-chlorotrifluoroethylene) (ECTFE) membranes by TIPS. Effects of ECTFE content on the membrane properties, including morphology, pore size distribution, porosity, liquid entry pressure of water (LEPw), water contact angle (WCA) and mechanical properties were characterized. Then the prepared ECTFE membranes were tested in vacuum membrane distillation (VMD). Phase diagram of this new ECTFE/TOTM binary system presented the existence of liquid-liquid (L-L) phase separation region when the ECTFE content was below 40%. The characterization results showed that the 15 wt% ECTFE membranes presented the continuous structure without the production of dense layer, but as the further increasing of polymer content, the spherulite structure began to be observed and surface became denser. Significantly, all the prepared ECTFE membranes exhibited excellent hydrophobicity. The liquid entry pressure of water (LEPw) and water contact angle (WCA) of 20 wt% ECTFE membranes reached 0.42 MPa and 139.9°, respectively. Moreover, in VMD, the prepared membranes exhibited high permeability (permeation flux was 23.09 kg/(m2.h)) and separation (salt rejection was 99.9%) performance. The above results show that the prepared ECTFE membrane showed promising stability performance in long-term operation of VMD for concentration of salt solution.

The morphology of polyethylene (PE) separator for lithium-ion battery tuned by the extracting process

Abstract Thermally induced phase separation (TIPS) is used to prepare polyethylene (PE) micro-porous membrane, consisting of melt blending, fast cooling, stretching and extracting process, which determine the pore-structure of the PE membrane. In this study, we tried to extract PE/liquid paraffin (LP) oil membrane to obtain PE porous membrane by n-hexane (n-PE) and dichloromethane (d-PE). The n-PE membrane would shrink by 10% for extractant volatilizing, less than 15% of the d-PE membrane after the extraction. These PE membranes were applied into symmetrical cells and LiCoO2/Li cells. As a result, the LiCoO2/Li cell based on n-PE separator exhibited better capacity retention (98%) than d-PE separator (91%) after 80 cycles at a current density of 1C rate for higher ionic conductivity. And the LiCoO2/Li cell with d-PE separator had higher capacity at 2C and 3C, it could be attributed to stronger interaction between solvent and wall of d-PE separator with the smaller and curved pore. In addition, the method that electrochemical impedance spectroscopy (EIS) technique carried out with cyclic voltammetry (CV) and charge-discharge curves is successfully applied to monitor the variety of impedance during the cycles, which is helpful to explore the mechanism of capacity attenuation.

Superhydrophobic and superelastic thermoplastic polyurethane/multiwalled carbon nanotubes porous monolith for durable oil/water separation

Absorbing materials with high hydrophobicity, porosity and mechanical resilience are urgently needed for oil/water separation. In this work, three dimensional (3D) porous thermoplastic polyurethane-based (TPU) composite monoliths with hierarchical porous structure were prepared by a feasible thermally induced phase separation (TIPS) method. The morphology analysis revealed the hierarchical porous structure was effectively perfected by adding 2 wt% carboxyl multiwalled carbon nanotubes (cMWNTs), which showed a uniform dispersion and compatibility in TPU skeleton. As a result, the hydrophobicity (151°), saturated adsorption capacity (6.9–42.3 g g−1) and mechanical compression and resilience property of TPU/cMWNTs monolith were improved significantly when comparing to pure monolith. Moreover, the composite monolith could maintain stable hydrophobicity and absorption capacity in corrosive environment. Besides, arising from the excellent mechanical elasticity, the monolith can be easily reused by absorbing-squeezing cycles. The recycled monolith can maintain high separation efficiency of 98.4% even reusing 40 cycles. As a kind of highly efficient absorbent, porous TPU/cMWNTs monolith shows great prospect in the application of large-scale oil/water separation.

In situ tailoring the hierarchical microstructures in polyethylene films fabricated by thermally induced phase separation via temperature gradient fields

In this study, a series of polyethylene thin films were prepared by thermally induced phase separation (TIPS) method with di(2-ethylhexyl)phthalate as the diluent. Morphological observations showed that the microstructures at different locations were fairly distinct and could generally be divided into three layers. When the polymer concentration was lower than the monotectic point (Φm), both pore size and porosity in TIPS films were heavily determined by growth time and growth rate of the diluent droplets. At relatively higher polymer concentration, cooling rate heavily affected the pore size in the films primarily through its influence on polymers’ crystallization process. The relationship between the film microstructure and cooling rate was quantitatively investigated (especially the effect of quenching conditions on the evolution of film morphology) with the aid of an enthalpy transformation method, which established the three-dimensional temperature profiles and supplied an insight into the competition between phase separation kinetics and polymer crystallization. In addition, our findings showed that the pore size, porosity and thermal stability of films all increased with an increasing quenching temperature, which was significantly different from the trends of variation in water vapor transmission rate as well as the $$ E^{\prime}_{ \hbox{max} } $$ and $$ E^{\prime\prime}_{ \hbox{max} } $$ values of dynamic mechanical analysis as the quenching temperature increased. The present work presents a facile way of in situ tailoring hierarchical microstructures in TIPS films of crystalline polymers, which will be very useful to the design of polymer porous films with specific properties.

Development of organically modified montmorillonite/polypropylene composite powders for selective laser sintering

Organically modified montmorillonite/polypropylene (OMMT/PP) composite powders for selective laser sintering (SLS) were developed using four powder preparation methods including melt extrusion combined with cryogenic grinding, thermally induced phase separation (TIPS), surface coating, and mechanical mixing. Evaluations were conducted on the shape and size, powder-bed surface roughness, and thermal behavior of the developed composite powders as well as the mechanical properties of their injection-moulded tensile specimens. Melt extrusion proved to be the most favorable as the powders exhibited the highest thermo-oxidative stability (Td,max = 378 °C) and enhanced mechanical strength and ductility. TIPS could produce powders with reduced crystallization temperatures and increased melt enthalpies that were beneficial for SLS, and with powder morphology ideal for SLS without post-processing. It was found that at low loadings, nanofillers with sheet-like structures such as OMMT could limit the increase in crystallization temperatures of the composite powder, thus ensuring their wide sintering windows for SLS.

High‐Performance Polymer Foams by Thermally Induced Phase Separation

Macroporous, low-density polyetheretherketone, polyetherketoneketone, and polyetherimide foams are produced using a high-temperature, thermally induced phase separation method. A high-boiling-point solvent, which is suitable to dissolve at least 20 wt% of these high-performance polymers at temperatures above 250 °C, is identified. The foam morphology is controlled by the cooling procedure. The resulting polymer foams have porosities close to 80% with surface areas up to 140 m2 g-1 and elastic moduli up to 97 MPa.

Controlling spherulitic structures at surface and sub-layer of hollow fiber membranes prepared using nucleation agents via triple-orifice spinneret in TIPS process

In this study, the growth of a spherulitic structure at the surface and sub-layer of the polyvinylidene fluoride (PVDF) hollow fiber membrane was controlled by co-extruding nucleation agent (NA) solutions as the outermost layer of a triple-orifice spinneret in the thermally induced phase separation (TIPS) process. Using this method, the spherulites were tailored to be a variety of morphologies having different combinations with the bi-continuous network at the membrane surface and sub-layer, while the bulk membrane structure remained almost unchanged. These typically tailored spherulitic structures dramatically enhanced the surface roughness, hydrophobicity, liquid entry pressure, and permeation stability of the TIPS-prepared PVDF hollow fiber membranes. The experimental results from the pressure-driven filtration and the direct contact membrane distillation demonstrated great potential of the tailored membranes to achieve water treatment and seawater desalination. The electrostatic interaction between NA and PVDF played a key role in tailoring the special membrane spherulite structures, providing new possibilities for engineering TIPS-prepared hollow fiber membranes with desirable structures and performances to address current and future water shortages.

Preparation and characterization of graphene oxide aerogel/gelatin as a hybrid scaffold for application in nerve tissue engineering

There is currently no appropriate therapy for the treatment of injuries that affect the central nervous system. Therefore, scientists have attempted to explore novel methods to improve the neural tissue regeneration, while preventing inhibitory fibro glial scars. In these methods, hollow graphene oxide aerogel was initially made. Then, a porous gelatin structure was formed through the Thermal-Induced Phase Separation (TIPS) process, which was then filled the aerogel. Scanning Electron Microscope (SEM) was then employed to examine the effect of different parameters of GO solution concentration on the morphology of the aerogel. Next, mechanical-thermal characteristics of scaffolds were measured using Dynamic Mechanical Thermal Analysis (DMTA). At −70 °C, the mechanical strength of the gelatin scaffold sample and the hybrid scaffold is approximately 1.3 MPa and 22.6 MPa, respectively. There was a significant increase in the elastic modulus of the hybrid scaffold, indicating the effect of the aerogel reinforcement on the hybrid scaffold. For in vitro evaluation, P19 mouse cells were cultured and differentiated into nerve cells on hybrid scaffolds, followed by administrating immunofluorescence test. Cell differentiation was approximately 20 and 87% on the control surface and the scaffold surface, respectively, and the P19 cells were effectively differentiated into neural cells. Experimental results indicate that this model is suitable as a platform for neural tissue engineering.

The Effect of Stretching on UHWMPE Microporous Film by Thermally Induced Phase Separation Method

UHMWPE microporous membranes were prepared via thermally induced phase separation(TIPS) combining with stretching. TIPS method was adopted to resolve processing difficulties of UHMEPE, and the subsequent stretching was used to optimize pore structure. The preparation process utilized liquid paraffin (LP) as the diluent. The effect of different stretching ratios on pore structure was investigated through SEM, XRD and mercury intrusion test. The results indicated that stretching process not only greatly improved the pore size uniformity and pore distribution uniformity, but also had a great influence on pore size controlling. When the stretching ratio was lower than 80%, the pore size was concentrated in nano-region which pore size distribution was around 0.02-0.03 μm. While the stretching ratio was larger than 80%, due to bridging breakage and liquid paraffin movement, pore size was concentrated in the micron area where pore size mainly distributed around 1μm, which had a practical significance for controlling the pore size of membranes in industrial production. And it’s obtained that at the same concentration of UHMWPE, the microporous membranes prepared in this study have more uniform pore structures than those reported previously.

Facile Preparation of a Superhydrophobic iPP Microporous Membrane with Micron-Submicron Hierarchical Structures for Membrane Distillation.

A facile method combining micro-molding with thermally-induced phase separation (TIPS) to prepare superhydrophobic isotacticpolypropylene (iPP) microporous membranes with micron-submicron hierarchical structures is proposed in this paper. In this study, the hydrophobicity of the membrane was controlled by changing the size of micro-structures on the micro-structured mold and the temperature of the cooling bath. The best superhydrophobicity was achieved with a high water contact angle (WCA) of 161° and roll-off angle of 2°, which was similar to the lotus effect. The permeability of the membrane was greatly improved and the mechanical properties were maintained. The membrane prepared by the new method and subjected to 60h vacuum membrane distillation (VMD) was compared with a conventional iPP membrane prepared via the TIPS process. The flux of the former membrane was 31.2 kg/m2·h, and salt rejection was always higher than 99.95%, which was obviously higher than that of the latter membrane. The deposition of surface fouling on the former membrane was less and loose, and that of the latter membrane was greater and steady, which was attributed to the micron-submicron hierarchical structure of the former and the single submicron-structure of the latter. Additionally, the new method is expected to become a feasible and economical method for producing an ideal membrane for membrane distillation (MD) on a large scale.