High Degree Of Crosslinking Research Articles

Hydrogel formed in situ through Schiff base reaction between gallic acid-grafted soybean protein isolate and oxidized dextran: Interactions, physicochemical properties, and digestive characteristics.

Herein, we developed multifunctional hydrogels formed between soybean protein (SPI)-gallic acid conjugate and oxidized dextran (ODex) via a Schiff base reaction. The effects of ODex on the morphology, structure, and functional properties of the hydrogels were elucidated. The results showed that the crosslinking modes in the hydrogels include hydrogen bonding, Schiff bases, Michael addition, and π-π stacking. The synergistic crosslinking of gallic acid and ODex conferred the hydrogels with an appropriate equilibrium swelling ratio, dense morphology, excellent mechanical properties, high thermal stability, and water-holding properties. When the addition of ODex was 0.8 (w/w), the hydrogel had a higher crosslinking degree (76.31%), smaller average pore diameter (0.322μm), and higher zero shear viscosity (748.5mPa. s). In addition, in vitro digestion tests showed that hydrogel degradation was delayed upon increasing the degree of crosslinking, which improved the hydrogel's capacity to adsorb bile salts and control the release of curcumin. This study provides a theoretical basis for the design of high-quality protein hydrogels and other multifunctional materials suitable for various applications.

New Chloroprene Rubber/Styrene-Butadiene Rubber (CR/SBR) Blends Cross-Linked with Tin(II) Oxide (SnO): Curing Characteristics, Swelling Studies, Mechanical Properties, and Flame Resistance.

This study aimed to investigate the properties of tin(II) oxide (SnO) as an unconventional cross-linking agent for chloroprene (CR) and styrene-butadiene (SBR) rubbers compositions. The use of tin(II) oxide results from the need to reduce the use of zinc oxide as a cross-linking agent due to environmental regulations and its toxic impact on aquatic environments. The studied elastomeric blends can be cross-linked with tin(II) oxide, and the results demonstrate the significant potential of this oxide in such applications. The CR/SBR vulcanizates cross-linked with SnO exhibit good mechanical properties and a high degree of cross-linking. The studies clearly show that the proportions of both rubbers as well as the amount of tin(II) oxide used influence the cross-linking of the CR/SBR blends and the properties of vulcanizates. FTIR spectrum analysis allowed the identification of the cross-linking mechanism, which followed the Friedel-Crafts alkylation reaction mechanism. The AFM analysis determined the miscibility of the rubbers and interelastomeric reactions, proving that the rubbers studied are partially miscible. The results of the oxygen index measurements indicated that the obtained vulcanizates showed flame resistance and self-extinguishing properties. Multivariate regression was performed to fit the models to the experimental value and to determine the influence of the content of the cross-linking agent and the CR and SBR proportions on the properties of the blends.

Low-temperature rapid fabrication of crosslinked poly(quaterphenyl piperidine) membrane for anion exchange membrane water electrolyzers

While nonsolvent-induced phase separation (NIPS) is widely recognized as an established method for creating porous polymer membranes, this study uniquely employs a nonsolvent to produce a dense, nonporous membrane instead. Specifically, the membranes were rapidly fabricated at low temperatures using dimethyl sulfoxide (DMSO), a high-boiling-point solvent, and water as the nonsolvent. We successfully prepared a series of crosslinked poly(quaterphenyl piperidine) (PQP-BM) network membranes with high crosslinking degrees (up to 47.2 %). By combining a hydrophobic extended polyaromatic backbone with a hydrophilic piperidine-based crosslinker, we achieved distinct microphase separation, which enhanced ion transport, dimensional stability, and thermal and mechanical properties compared to the linear uncrosslinked membranes. The optimized AEM exhibited exceptional mechanical strength (tensile strength >63 MPa), high ion conductivity (151.5 mS cm⁻¹ at 80 °C), and excellent alkaline durability. In single-cell water electrolyzer tests, the PQP-BM membrane demonstrated a remarkable current density of 3.99 A cm⁻² at 2.0 V in 1 M KOH at 50 °C, outperforming the commercial FAA-3–50 membrane by 126 %. This study highlights the potential of the energy-efficient NIFF process as a scalable method for producing advanced AEMs for energy conversion applications.

Development of Dispersion Process to Improve Quality of Hyaluronic Acid Filler Crosslinked with 1,4-Butanediol Diglycidyl Ether.

This study proposes a new and simple process that improves the quality of a hyaluronic acid (HA) filler crosslinked with 1,4-butanediol diglycidyl ether (BDDE) using solution dispersion at a low temperature. This process involves the solvent being dispersed among the solute naturally after the mixing process. The process used in this study involved two reactions. First, the solution was dispersed among HA molecules (Mw = ~0.7 MDa) creating a well-homogenized mixture. Second, the decomposition and synthesis of HA occurred naturally in an aqueous alkaline solution (>pH 11), the weight average molar mass (Mw) was adjusted (Mw = ~143,000), and the crosslinking surface area was expanded, allowing for a high degree of crosslinking. Therefore, the viscoelasticity and cohesion of the filler increased with the new method compared to the previous process both at the lab scale (previous process:new process, viscosity (cP) = 24M:43M, storage modulus (Pa) = 306:538, loss modulus (Pa) = 33:61, and tack (N) = 0.24:0.43) and at the factory scale (previous process:new process, complex viscosity (cP) = 19M:26M, storage modulus (Pa) = 229:314, loss modulus (Pa) = 71:107, and tack (N) = 0.35:0.43).

Fluid Imbibing Super Absorbent Textiles for Comfort Wear Performance

Textile is a basic human need, it not only provides the aesthetic appeal but also imparts necessary sweat absorption and relevant functional effects. The textile material is widely used for various hygiene and comfort wear applications where the absorption as well as leak proof retention of various body fluids is an essential parameter. This effect is achieved when the textile material is treated with suitable super absorbent chemicals. Superabsorbent finishes are polymeric coatings that significantly enhance the liquid absorption capacity of textile substrates. Known as superabsorbent polymers (SAPs), these materials can be natural, synthetic, or hybrid, characterized by their high degree of cross-linking and three-dimensional network structure. Capable of absorbing up to 100,000% of their weight in water, SAPs form stable hydrogels due to their hydrophilic groups. These properties make them suitable for diverse applications, including hygiene products, water purification, horticulture, and pharmaceuticals. In the past few decades, super absorbent polymers and fibres have found a lot of applications, especially in the field of textiles. This report briefly discusses the various application fields of SAP in textiles. With applications in hygiene products, medical textiles, protective apparel, automotive textiles, and geotextiles, the study explores how SAPs are incorporated into textile fibres (SAFs) to improve moisture absorption and management. Lastly, a comprehensive outlook for the future is given, highlighting encouraging prospects in SAP-based textile research and industry.

A novel rapid fabrication method and in-situ densification mechanism for ceramic matrix composite

The extensive application of ceramic matrix composites has always been limited due to the long-period and expensive process. Hence, this research introduces a rapid manufacturing method named as ViSfP-TiCOP (High Viscosity Solvent-free Precursor Combined Elemental Titanium Controlled Pyrolysis). The solvent-free precursor possesses high viscosity (30 °C, 106 mPa S) and wide molecular weight distribution (Mz/Mw = 3.3), accomplishing stable loading of inorganic fillers. Simultaneously, the elementary titanium and ZrB2, as the active and inert filler, are dopped into the precursor to control the pyrolysis. The ViSfP-TiCOP technique offers a rapid method to manufacture CMCs under pressureless and low pyrolysis temperature conditions (1200 °C). Comparing to the addition of ZrB2, the precursor with titanium provides an exceptional ceramic yield of 87 wt%, leading a notable enhancement in the rate of densification. This high densification efficiency is attributed to an in-situ titanium gas-phase reaction, besides with the high degree of cross-linking and low volatile of precursor. After undergoing three cycles of impregnation-pyrolysis, the porosity of C/SiBCN–Ti was discovered to be below 10 vol%, whereas that of C/SiBCN-25 wt%ZrB2 still remained as high as 20.91 vol%. The ViSfP-TiCOP technology can provide guidance for low-cost and rapid preparation of CMCs.

Molecular dynamics simulations of the micro mechanism of functionalized SiO2 nanoparticles and carbon nanotubes modified epoxy resin adhesives

AbstractThe bonding interface of carbon‐fiber‐reinforced polymer (CFRP)‐reinforced steel structure is a weak part, and nanomaterial‐modified adhesives are expected to improve its comprehensive performance. This paper investigates the micro‐modification mechanisms of nanomaterials on epoxy resin adhesives using molecular dynamics simulation method. It explores how the functionalized nano SiO2 and carbon nanotubes affects the thermal and mechanical properties of the epoxy resin adhesive. The models established using Materials Studio software include the pure epoxy resin adhesive model (EP) with varying degrees of crosslinking, the functionalized nano‐SiO2‐modified epoxy resin adhesive model (EP + SiO2/OH), the single‐walled carbon nanotube‐modified epoxy resin adhesive model (EP + SWNT), and the synergistic enhancements model of the epoxy resin adhesive with nano‐SiO2 and carbon nanotubes (EP + SWNT + SiO2/OH). Based on the aforementioned models, the Forcite module is used to calculate the free volume, glass transition temperature and mechanical properties of the adhesive. The results show that the degree of crosslinking effects significantly the mechanical performance of epoxy resin adhesive. A high degree of crosslinking restricts the movement of the molecular chain, enhancing the strength of the epoxy resin adhesive. Furthermore, the trend of the mechanical and thermal properties of the four models remains constant with the rise of temperature, and the properties decrease most significantly in the range of the glass transition temperature. Moreover, the epoxy resin adhesive doped with nanomaterials exhibits varying degrees of enhancement in mechanical and thermal properties. The epoxy resin adhesive reinforced with functionalized nano‐SiO2 and carbon nanotubes exhibits better properties compared to those with a single nanomaterial.Highlights The micro‐modification mechanism is revealed for nanomaterial modified epoxy resin adhesive. The degree of crosslinking effects significantly the mechanical performance of epoxy resin adhesive. The epoxy resin adhesive doped with nanomaterials exhibits varying degrees of enhancement in mechanical and thermal properties.

Diffusion-Regulated Interfacial Polymerization of Hierarchically Microporous Polyamide Membranes for Permselective Gas Separations.

Interfacial polymerization has emerged as a robust method for fabricating task-specific polyamide (PA) membranes. However, the limited microporosity of highly cross-linked PA membranes constrains their effectiveness in gas separation applications. Herein, we introduce an ionic liquid (IL)-regulated interfacial polymerization process to fabricate polyamide nanofilms incorporating kinked tetrakis (4-aminophenyl) methane monomers. In situ ultraviolet-visible spectroscopy demonstrates that the diffusion of 1,3,5-benzenetricarbonyl trichloride (TMC) toward the interface increases with the IL/H2O ratio, leading to the formation of a more compact membrane with a higher cross-linking degree. The PA-TAM7/3-60 min membrane exhibits a CO2 permeance of 29.8 GPU and a CO2/CH4 selectivity of 109, exceeding the 2008 Robeson upper bond. Additionally, the highly cross-linked structure imparts the membranes with notable plasticization resistance. Mixed-gas tests (CO2/CH4 = 50/50, v/v) reveal that the PA-TAM7/3-60 min membrane experiences only a 2% reduction in CO2 permeance and a 10% decrease in CO2/CH4 selectivity at a CO2 partial pressure of 300 PSIG, compared to its performance at 30 PSIG. The ease of tuning membrane structure and gas separation performance, along with its excellent plasticization resistance, underscores the potential of these PA membranes for task-specific gas separations.

Pre-Coordination Induced Further Deamination to Create Inter-Chain Cross-Linking in Carbon Nitride for Enhanced Photocatalytic H2O2 Production.

Creating cross-linking to establish efficient inter-chain charge-transfer channels in carbon nitride represents a promising strategy for enhancing its photocatalytic capabilities. Molten salt-assisted calcining has emerged as a method for preparing cross-linked carbon nitrides. However, the precise influence of molten salts on the molecular structure of carbon nitride remains to be fully elucidated. Herein, we develop a KCl guided cross-linking reaction to preliminarily reveal the formation mechanism of cross-linking. The cross-linking reaction is initiated by the pre-coordination of amino groups with K+. Subsequent heating at high temperature converts the amino groups into chlorines. Then, dechlorination leads to the formation of cross-linking. Thus, this cross-linking reaction can be accurately described as a pre-coordination-induced, two-step deamination reaction. The pre-coordination step plays a pivotal role in the cross-linking process. Sufficient pre-coordination results in a relatively high cross-linking degree of the as-prepared CNK-2. Consequently, CNK-2 demonstrates a significantly enhanced photocatalytic H2O2 production, with a generation rate of 682 μmol L-1 h-1, about 59 times that of traditional carbon nitride.

Lactiplantibacillus plantarum ACCC 11095 microencapsulated by lotus seeds cross-linked resistant starch: Survival under simulated gastrointestinal conditions and its structural changes

Under simulated gastrointestinal digestion, we investigated the protective and releasing effects of lotus seed cross-linked resistant starch (LSCS) with low, medium, and high cross-linking degree toward Lactiplantibacillus plantarum ACCC 11095 and associated structural changes. Probiotic microcapsules (PM) made of high crosslinking starch showed better encapsulation rates (48.81%) and released 6.26 log CFU/g of viable bacteria after digestion, which helped colonize and exert probiotic effects in the intestinal tract. Scanning electron microscopy and Fourier Transform Infrared spectroscopy confirmed better high crosslinking starch protection for probiotic bacteria. This was closely related to PM embedded materials. Correlation analysis showed that agglomeration between high crosslinking starch starch granules in PM was significantly enhanced, and amorphous zones were hydrolyzed to a lesser extent, providing better Lactiplantibacillus plantarum ACCC 11095 protection. Thus, high crosslinking starch demonstrated potential as an oral probiotic carrier in terms of cost, suitability for functional foods, and commercialization potential.

Molecular heterostructured interlayer for fabrication of high-performance thin film composite reverse osmosis membranes

To solve the scarcity of fresh water, reverse osmosis (RO) technology for seawater desalination and wastewater reuse has been developed rapidly. However, the performance of RO is limited by poor selectivity towards certain harmful small molecule constituents (e.g., boron in seawater and N-nitrosodimethylamine in wastewater) and the permeability-selectivity trade-off. Herein, a metal polyphenol network interlayer including both hydrophobic zone and monomer adsorption zone is proposed to optimize interfacial polymerization (IP) process for fabrication of RO membrane. This heterogeneous characteristic is endowed by well-chosen phenol (i.e. TTSBI) and metal (Ni). The physicochemical properties of the substrate are also optimized. An ultra-selective RO membrane with thinner separation layer, higher crosslinking degree and larger surface area is obtained. The RO membranes exhibit separation performance beyond the upper selectivity limit for NaCl and hazardous small molecules. The membrane water permeance is 3.50 L m−2h−1bar−1while the NaCl rejection is 99.5 %. Meanwhile, the mechanism of the interlayer influencing IP process is investigated by combining molecular simulation and experimental methods. Our work provides a novel design direction of substrate used for fabricating RO membrane with outstanding performance.

Effect of active carbonyl-carboxyl ratio on dynamic Schiff base crosslinking and its modulation of high-performance oxidized starch-chitosan hydrogel by hot extrusion 3D printing

The quest to develop 3D starch-based printing hydrogels for the controlled release of active substances with excellent mechanical and printing properties has gained significant attention. This work introduced a facile method based on crosslinking via Schiff base reaction for preparing bicomponent hydrogels. The method involved the utilization of customizable oxidized starch (OS) and chitosan (CS), enabling superior printing performance through the precise control of various active carbonyl-carboxyl ratios (ACR, 2:1, 1:1, and 2:3, respectively) of OS. OS-CS hydrogel (OSC) with an ACR level of 2:1 (OS-2-y%CS) underwent rearrangement during printing environment, fostering increased Schiff base reaction with a higher crosslinking degree and robust high structural recovery (>95 %). However, with decreasing ACR levels (from 2:1 to 2:3), the printing performance and mechanical strength of printed OSC (POSC) declined due to lower Schiff base bonds and increased phase separation. Compared with printed OS, POS-2-2%CS exhibited a remarkable 1250.52 % increase in tensile strength and a substantial 2424.71 % boost in compressive strength, enhanced shape fidelity and notable self-healing properties. Moreover, POS-2-2%CS exhibited stable diffusive drug release, showing potential application in the pH-responsive release of active substances. Overall, controlling the active carbonyl-carboxyl ratios provided an efficient and manageable approach for preparing high-performance 3D-printed hydrogels.

Biodegradable Cassava Starch/Phosphorite/Citric Acid Based Hydrogel for Slow Release of Phosphorus: In Vitro Study.

Phosphorous (P) is one the most important elements in several biological cycles, and is a fundamental component of soil, plants and living organisms. P has a low mobility and is quickly adsorbed on clayey soils, limiting its availability and absorption by plants. Here, biodegradable hydrogels based on Cassava starch crosslinked with citric acid (CA) were made and loaded with KH2PO4 and phosphorite to promote the slow release of phosphorus, the storing of water, and the reduction in P requirements during fertilization operations. Crosslinking as a function of CA concentrations was investigated by ATR-FTIR and TGA. The water absorption capacity (WAC) and P release, under different humic acid concentration regimens, were studied by in vitro tests. It is concluded that hydrogel formed from 10% w/w of CA showed the lowest WAC because of a high crosslinking degree. Hydrogel containing 10% w/w of phosphorite was shown to be useful to encouraging the slow release of P, its release behavior being fitted to the Higuchi kinetics model. In addition, P release increased as humic acid contents were increased. These findings suggest that these hydrogels could be used for encouraging P slow release during crop production.

Preparation and properties of walnut cake-based wood adhesive with oxidation modification

Walnut cake has the potential for use in preparing wood adhesives because of its richness in protein and carbohydrate. In this work, walnut cakes were treated with sodium periodate or potassium permanganate and then were directly used as wood adhesives. Their bonding properties, curing performances, thermal properties, and chemical structures were compared. The results showed that: (1) The oxidation by KMnO4was non-selective. The reaction was very intense, accompanied by the great variability of oxidation degree and degradation degree, enormous viscosity of oxidation products, high coating difficulty, and low content of active aldehyde groups. (2) The oxidation by NaIO4 was selective; the reaction was mild and easy to control. More active aldehydes could be produced and the treatment was beneficial for constructing a spatial net structure of the adhesive. (3) Compared with oxidation of KMnO4, the walnut cake adhesive prepared by NaIO4 oxidation exhibited a more compact structure, a higher crosslinking degree, low curing temperature, and high thermal stability after curing; its bonding performances met the requirements for Class II plywood specified in GB/T 17657(2013).

In vitro degradation, swelling, and bioactivity performances of in situ forming injectable chitosan-matrixed hydrogels for bone regeneration and drug delivery.

Injectable, tissue mimetic, bioactive, and biodegradable hydrogels offer less invasive regeneration and repair of tissues. The monitoring swelling and in vitro degradation capacities of hydrogels are highly important for drug delivery and tissue regeneration processes. Bioactivity of bone tissue engineered constructs in terms of mineralized apatite formation capacity is also pivotal. We have previously reported in situ forming chitosan-based injectable hydrogels integrated with hydroxyapatite and heparin for bone regeneration, promoting angiogenesis. These hydrogels were functionalized by glycerol and pH to improve their mechano-structural properties. In the present study, functionalized hybrid hydrogels were investigated for their swelling, in vitro degradation, and bioactivity performances. Hydrogels have degraded gradually in phosphate-buffered saline (PBS) with and without lysozyme enzyme. The percentage weight loss of hydrogels and their morphological and chemical properties, and pH of media were analyzed. The swelling ratio of hydrogels (55%-68%(wt), 6 h of equilibrium) indicated a high degree of cross-linking, can be suitable for controlled drug release. Hydrogels have gradually degraded reaching to 60%-70% (wt%) in 42 days in the presence and absence of lysozyme, respectively. Simulated body fluid (SBF)-treated hydrogels containing hydroxyapatite-induced needle-like carbonated-apatite mineralization was further enhanced by heparin content significantly.

Effects of two types of corn starches on physicochemical and structural properties of red bean protein isolate acid-induced cold gels

A mixture of red bean protein isolate (RBPI) with common starch (CS) or waxy starch (WS) from corn was heated, and induced by glucono-δ-lactone (GDL) to form a RBPI-starch complex cold gel. The physicochemical and structural properties of these gels were also investigated. Compared with the RBPI gels, the complex gels with CS had higher gel strength, water retention, viscoelasticity, and deformation resistance, forming a denser and more continuous microstructure with a high degree of crosslinking and small pores. Compared with the RBPI-CS complex gels, the RBPI-WS complex gels exhibited higher water retention and stronger transformation ability of free water to immobilized water; however, they exhibited poor mechanical properties and microstructures. The difference in the physicochemical properties of the gels was mainly related to the change in the hydrophobic interactions between the two gel systems. In addition, protein structure modification affected the gelation properties of the RBPI-CS and RBPI-WS complexes. The RBPI-CS complex gel exhibited strong X-ray peaks and fluorescence quenching ability. The addition of CS promoted the flexibility of the secondary structure and tightness of the tertiary conformation of the protein in the complex gel, forming a stronger and more compact non-covalent gel structure. However, the protein in the RBPI-WS complex gel showed an ordered secondary structure and a loose tertiary conformation, which weakened the gel network.

Evaluation of cell‐laden three‐dimensional bioprinted polymer composite scaffolds based on synthesized photocrosslinkable poly(ethylene glycol) dimethacrylate with different molecular weights

AbstractThis manuscript aims to three‐dimensional bioprint and evaluate new polymer composite scaffolds based on synthesized poly(ethylene glycol) dimethacrylate (PEGDMA) as well as methyl cellulose and gelatin. The PEGDMA was synthesized by a simple microwave‐assisted method using three distinct molecular weights (MWs) of poly(ethylene glycol) (PEG), 3, 6, and 12 kDa, and methacrylic anhydride. The percent functionalization of the PEGDMA was analyzed using the nuclear magnetic resonance spectrum, and the theoretical calculations indicated that over 50% of methacrylation was achieved in all samples, with the PEGDMA synthesized from 6 kDa PEG surpassing 66% methacrylation. These three PEGDMA‐based bioinks were investigated for their suitability for bioprinting scaffolds. It was observed that lower MW PEGDMA resulted in a higher degree of crosslinking, leading to more stable composite scaffolds. However, higher crosslinking degree did not support long‐term cell viability when encapsulated with cells. Higher MW PEGDMA showed higher cell viability over time though overall stability was lower. Synthesized PEGDMA with 6 kDa PEG showed both stability and long‐term cell viability after postprinting. Over 80% of cell viability was maintained for a 7‐day study period, showing potential use in tissue engineering applications as a cell delivery vehicle.

GO and surfactant assisted regulation of polyamide nanofiltration membranes for improved separation performance

Fabricating nanofiltration membranes with high water permeance and selectivity by tailoring the structure and morphology is crucial to efficient water purification. In this work, the fabrication of thin film nanocomposite (TFN) nanofiltration membranes by combining two methods, the surfactant-assembly interfacial polymerization (SARIP) and the addition of graphene oxide (GO) or ionic liquid functionalized graphene oxide (GO-IL) for the preparation of the selective PA layer on a novel porous substrate is reported. For the preparation of the porous substrate, mechanically robust, aromatic polyethers containing polar pyridine units (PDSPP) were chosen targeting to improved hydrophilicity and thus enhanced water permeability. The anionic sodium dodecyl sulfate (SDS) surfactant was used to regulate the interfacial polymerization thereby enabling the formation of dense PA layers with high cross-linking degree and consequently high salt rejections. On the other hand, the addition of GO/GO-IL nanosheets could impart hydrophilicity and antifouling properties. The novel porous PDSPP substrate was selected for the fabrication of TFN membranes due to its improved water permeability and superior salt rejection and increased hydrophilicity compared to commercial PSf substrate. The detailed study of the fabricated TFN membranes by ATR-FT-IR, SEM, AFM, XPS, contact angle measurements revealed the formation of polyamide selective layers with rougher surfaces, increased hydrophilicity and high cross-linking degrees (from 44 % to 94 %), resulted from the synergistic effect of SDS and GO incorporation. Moreover, the prepared TFN membranes exhibited high salt rejections while maintaining a moderate water permeability. In particular, the membrane containing the neat GO (TFNGO50) displayed excellent Na2SO4 and MgSO4 rejections (98.8 % and 99.5 %, respectively) while the NaCl rejection was 47.0 % and a water permeability value of 4.2 L m-2h−1 bar−1. The divalent salt rejections were among the highest values reported in the literature in comparison with commercial NF membranes and TFN membranes containing GO/functionalized GO. When GO-IL nanosheets were embedded in the PA layer, the water permeability was slightly improved while the salt rejections were significantly reduced compared to TFNGO50. Lastly, the incorporation of GO enhanced the anti-fouling properties of the prepared membranes due to increased hydrophilicity of the PA surface.

Structurally tuned polyamide membranes via the polyvinylpyrrolidone-modulated interfacial polymerization reaction for enhanced forward osmosis performance

Controllable interfacial polymerization (IP) reaction is an important strategy to fabricate high-performance polyamide (PA) thin-film composite (TFC) membranes. In this work, a new TFC membrane was successfully fabricated by incorporating polyvinylpyrrolidone (PVP) with different molecular weights (K15, K30 and K60) at different concentrations into the aqueous phase of IP process. Due to an increased solution viscosity and interaction between PVP and amine monomers, the lower diffusion rate of amine monomers resulted into a thin (the thinnest basal PA layer of approximately 30 nm) and smooth PA layer with a high crosslinking degree. Among, the optimum PVP K60–0.25 TFC membranes with the highest molecular weights and lower incorporating concentrations had a more positive effect on forward osmosis performance, which presented a pure water flux of 11.2 L m−2 h−1, 25 % higher, and a specific salt flux of 0.04 g L−1, 43 % lower than the original membrane. Our work provides a low-cost and simple approach to obtain high-performance TFC membrane with an improved trade-off effect, and helps to deeply understand the role played by additives in PA layer modulation.

Polyamide reverse osmosis membrane compaction and relaxation: Mechanisms and implications for desalination performance

This work investigates the compaction and relaxation behavior of composite reverse osmosis (RO) polyamide (PA) selective layers, utilizing non-equilibrium molecular dynamic (NEMD) simulations and well-controlled permeation experiments. Composite PA-RO membranes are prepared by interfacial polymerization of para and meta diamine monomer blends to achieve different PA film crosslinking degrees (CD). Wet-testing results suggest that “tighter” (higher CD) composite RO membranes undergo 65 % less compaction and recover 17 % more of their initial permeability (termed “relaxation”) when the pressure is relieved compared to lower CD PA layers. NEMD simulations provide a visual and quantitative characterization of PA layer's free volume changes in operando. NEMD simulations also corroborate experimental findings and elucidate the viscoelastic properties of the PA layer that govern compaction and relaxation behavior. The mechanisms of compaction under water permeation derived from NEMD simulations further support the notion of viscous flow of water through interconnected free volume elements (i.e., “pores”) within crosslinked PA films.