Effect Of Crosslinking Time Research Articles

Robust water‐stable poly (ethersulfone)/poly (ethyleneimine) nanofibrous membranes for nitrate adsorption

AbstractNanofibrous media or electrospun webs are widely used as affinity membranes due to their extraordinary properties. In this study, the micro‐nano structure PES/PEI membrane was fabricated by electrospinning. The stability of the membrane during adsorption and washing is very important for affinity membranes. The fabricated web was insolubilized through an optimized crosslinking reaction by glutaraldehyde. Effect of crosslinking time and concentration on adsorption efficiency of adsorbent for nitrate studied using batch experiments. The morphology of the nanofibrous web before and after crosslinking was characterized by scanning electron microscopy (SEM). Fourier transform infrared spectroscopy was used for studying the change in functional groups of PES/PEI composite. Results show that 90 min of crosslinking reaction by immersion method in 0.71% glutaraldehyde in water/acetone medium could successfully insolubilize the polyethyleneimine and change the smooth surface of the nanofibrous web to a rough state with nano spherules. The kinetics studies show that nitrate adsorption by PES/PEI composite follows a pseudo‐second‐order kinetic model. The adsorption isotherm was also investigated using Langmuir and Freundlich models. Results show that the adsorption of nitrate on PES/PEI follows the Langmuir model with a maximum adsorption capacity of 53.47 mg/g which is considered a high value comparing other studies.

Controlled Release of Gentamicin from Electrospun Poly(Vinyl Alcohol)/Gelatin Nanofibers: The Effect of Crosslinking Time Using Glutaraldehyde Vapor

AbstractIn this study, polyvinyl alcohol (PVA), gelatin (GEL) and gentamicin (GEN) were used and 13PVA/0.5GEL/GEN nanofibers were fabricated with the electrospinning method. These nanofibers were crosslinked chemically with glutaraldehyde (GA) at different time intervals (2, 3, 4, 5, 5.5 and 6 h) to observe the crosslinking effect on the properties of the nanofibers. Morphological analysis reported that as the crosslinking time increased, the nanofiber diameters also increased from 369.26 nm (non‐crosslinked) to 447.72 nm (6 h/crosslinking), respectively. The thermal characterization results demonstrated that crosslinking with different times noticeably shifted the thermal points.The tensile testing results proved that application of crosslinking enhanced the mechanical strength of the nanofibers from 3.31 MPa (non‐crosslinked) to 5.8 MPa (5.5 h/crosslinking), respectively. The GEN release profiles from the nanofibers showed similar behaviors under crosslinking and indicated that the crosslinking time did not have a significant effect on the amount of the GEN released.

Effect of Cross-linking Time on Sodium Alginate Based Blend Films as a Supporter of Bordeaux Mixture

Blend films based on sodium alginate (SA) are synthesized and the use of these films as a supporter for Bordeaux mixture to adhere the crops for longer time and sustained release of active ingredient were studied. An aqueous solution of Sodium alginate was prepared and the obtained solution was added to bordeaux mixture of fixed compositions. Alginate solution is cross-linked by the multivalent cations present in bordeaux mixture and forms films. Blends based on sodium alginate with gelatin(SAGN) and sodium alginate with guar gum(SAGM) were synthesised. The thickening and cross linking action of these films were controlled by varying the cross linking time. The films were dried at 50oC in an oven and kept in different buffer solutions for swelling studies. From the swelling data, rate and kinetics of swelling were studied and swelling parameters were tabulated. The swelling parameters showed that the various bordeaux mixture cross-linked films were stable and they can absorb sufficient quantity of water and may prevent leaching out of active ingredients on rough weathers. Also the cross-linked polymer film may serve in increasing life and sustained release of active ingredients. Keywords: Blends, Bordeaux mixture, ionic cross linking, pH sensitivity, sustained release

Gelatin nanoparticles with tunable mechanical properties: effect of crosslinking time and loading.

Tuning the elastic properties of nanoparticles intended to be used in drug delivery is of great interest. To this end, different potential formulations are developed since the particle elasticity is affecting the in vitro and in vivo performance of the nanoparticles. Here we present a method to determine the elasticity of single gelatin nanoparticles (GNPs). Furthermore, we introduce the possibility of tuning the elastic properties of gelatin nanoparticles during their preparation through crosslinking time. Young’s moduli from 5.48 to 14.26 MPa have been obtained. Additionally, the possibility to measure the elasticity of single nanoparticles revealed the influence of loading a macromolecular model drug (FITC-dextran) on the mechanical properties, which decreased with raising amounts of loaded drug. Loaded particles were significantly softer, with Young’s moduli between 1.06 and 5.79 MPa for the same crosslinking time, than the blank GNPs. In contrast to this, lysozyme as a crosslinkable macromolecule did not influence the mechanical properties. A good in vitro cell compatibility was found investigating blank GNPs and FITC-dextran-loaded GNPs in viability assays with the cancer cell line A549 and the human primary cell-derived hAELVi cell line.

Solvent and thermal resistant ultrafiltration membranes from alkyne-functionalized high-performance polymers

Polymeric porous membranes with excellent thermal (Td higher than 500 °C) and solvent resistance were prepared. The membranes were based on three high-performance polymers (polyoxindolebiphenylene, polytriazole and polybenzimidazole), functionalized with alkyne side groups. The functionalization enabled the polymer crosslinking by a fast and simple wet-state thermal process in hot glycerol. The effect of crosslinking time and temperature was evaluated. The obtained membranes were characterized by spectroscopy and thermal analysis. The membrane morphology was investigated by electron microscopy. The liquid separation performance of the crosslinked membranes was evaluated in several organic solvents. The stability in filtration experiments was demonstrated in dimethylformamide at temperatures up to 140 °C. The solvent resistance in various solvents was confirmed in long-term tests (up to 21 days) at room temperature.

Development of hydrolysed protein-based plywood adhesive from slaughterhouse waste: effect of chemical modification of hydrolysed protein on moisture resistance of formulated adhesives.

Specified risk materials (SRM) constitute the proteinaceous waste of slaughterhouses and are currently being disposed off either by incineration or by land filling. Over the last few years, our efforts have focused on developing technology platforms for deployment of this renewable resource for various value-added industrial applications. This report describes a technology for utilization of SRM for the development of an environmentally friendly plywood adhesive with an improved water resistance property. The feedstock (SRM) was first thermally hydrolysed according to a standard protocol, and the hydrolysed protein fragments (peptides) were recovered from the hydrolysate. The recovered peptides were chemically modified through esterification reaction using ethanol, and then chemically crosslinked with polyamideamine-epichlorohydrin (PAE) resin to develop a wood adhesive system. Plywood specimens were then developed using the peptides–PAE resin-based adhesive. The effects of crosslinking time, solid content of the adhesive formulation, ratio of peptides and crosslinking agent in the formulation, and curing conditions of specimen preparation on lap shear strength of resulting plywood specimens were systematically evaluated. Despite the hydrophilic nature of hydrolysed protein fragments, the peptides–PAE resin formulations exhibited remarkable water resistance property after curing. Capping of polar carboxyl groups of peptides by converting them to esters further improved the water resistance property of this adhesive system. Under the optimum conditions of adhesive preparation and curing, the ethyl ester derivative of peptides and PAE resin-based formulations resulted in plywood specimens having comparable dry as well as soaked shear strengths to those of commercial phenol formaldehyde resin.

From ultrafiltration to nanofiltration: Hydrazine cross-linked polyacrylonitrile hollow fiber membranes for organic solvent nanofiltration

Ultrafiltration-level polyacrylonitrile (PAN) hollow fiber membranes were molecularly engineered via chemical cross-linking to obtain membranes suitable for use in organic solvent nanofiltration (OSN). By adjusting the dope composition and spinning conditions, hollow fibers possessing a desirable sponge-like cross-section with minimal macrovoids were obtained. Hydrazine monohydrate was used as the cross-linker and the effects of cross-linking time on the membrane's separation performance were investigated. X-ray photoelectron spectroscopy was used to elucidate the possible reactions and indicated the successful cross-linking of the PAN hollow fiber membranes. The cross-linked nanofiltration-level hollow fibers were subjected to OSN tests using ethanol and dyes as model feed solutions. With this simple and effective modification, the PAN hollow fiber membranes were able to achieve a pure ethanol permeance of 2.32Lm−2 h−1bar−1 and an impressive Remazol Brilliant Blue R (Mw 626.54gmol−1) rejection of more than 99.9%. Given the ease of fabrication and modification, these PAN hollow fibers represent a significant step forward in the use of hollow fiber membranes for OSN, particularly in larger-scale operations.

Enhancing the Adhesive Strength of a Plywood Adhesive Developed from Hydrolyzed Specified Risk Materials.

The current production of wood composites relies mostly on formaldehyde-based adhesives such as urea formaldehyde (UF) and phenol formaldehyde (PF) resins. As these resins are produced from non-renewable resources, and there are some ongoing issues with possible health hazard due to formaldehyde emission from such products, the purpose of this research was to develop a formaldehyde-free plywood adhesive utilizing waste protein as a renewable feedstock. The feedstock for this work was specified risk material (SRM), which is currently being disposed of either by incineration or by landfilling. In this report, we describe a technology for utilization of SRM for the development of an environmentally friendly plywood adhesive. SRM was thermally hydrolyzed using a Canadian government-approved protocol, and the peptides were recovered from the hydrolyzate. The recovered peptides were chemically crosslinked with polyamidoamine-epichlorohydrin (PAE) resin to develop an adhesive system for bonding of plywood specimens. The effects of crosslinking time, peptides/crosslinking agent ratio, and temperature of hot pressing of plywood specimens on the strength of formulated adhesives were investigated. Formulations containing as much as 78% (wt/wt) peptides met the ASTM (American Society for Testing and Materials) specifications of minimum dry and soaked shear strength requirement for UF resin type adhesives. Under the optimum conditions tested, the peptides–PAE resin-based formulations resulted in plywood specimens having comparable dry as well as soaked shear strength to that of commercial PF resin.

Preparation and characterization of poly(vinyl alcohol)/sodium alginate blended membrane for alkaline solid polymer electrolytes membrane

Novel poly(vinyl alcohol)/sodium alginate membranes (PVASA) are prepared in this study. The PVASA membranes are further treated by chemical crosslinking with glutaraldehyde as a crosslinking agent to get the crosslinked PVASA (PVASA-GA). The thermal property, KOH uptakes, ionic conductivity, and methanol permeability of the PVASA and PVASA-GA membranes are measured. Differential scanning calorimetry, X-ray diffraction, and thermogravimetry analysis are used for the characterization of membranes. It is found that with increasing the content of sodium alginate in the PVASA membrane, the crystallinity and melting point of PVASA decrease. The polymer electrolyte membranes are formed by immersing the various PVASA membranes in KOH solution. The effects of crosslinking time and membrane composition of PVA/SA on ionic conductivity through the polymer electrolyte membrane are studied using AC impedance technique. The ionic conductivity (σ) through the PVASA64 membrane at 25°C, (0.091Scm−1), is higher than the other studies for the different modified PVA membranes. The effect of crosslinking time on methanol permeability is very significant. The methanol permeability (P) of the PVASA-GA membranes is on the order of 10−7cm2s−1. The value of selectivity, (σ/P), for the PVASA82-GA60 membrane is at about 21.50×103Scm−3s1. Alkaline direct methanol fuel cells comprises of PVASA82-GA membrane is assembled and examined. It shows excellent electrochemical performance. The maximum power density of 20.7mWcm−2 is achieved at Ep,max=0.232V with a peak current density (ip,max) of 89.20mAcm−2 at 30°C for the direct methanol fuel cell consisting of PVASA82-GA60 membrane.

The Effect of Crosslinking Time and Nanoparticle Content on Electroactive, Multi-Component Scaffolds

The Effect of Crosslinking Time and Nanoparticle Content on Electroactive, Multi-Component Scaffolds

High durable poly(vinyl alcohol)/Quaterized hydroxyethylcellulose ethoxylate anion exchange membranes for direct methanol alkaline fuel cells

Novel alkaline anion-exchange membranes composed of chemically cross-linked poly(vinyl alcohol) modified quaternized hydroxyethylcellulose ethoxylate (PVA/QHECE) are prepared. The hydroxide conductivity (σOH−), water and methanol uptakes, ion exchange capacity (IEC), mechanical property, dimensional and alkaline stabilities of PVA/QHECE membranes are measured to evaluate their applicability in direct methanol alkaline fuel cells (DMAFC). The effects of cross-linking time, membrane composition and catalyst dosage (H+) on membrane OH− conductivity are studied using AC impedance technique. FTIR, SEM and TG analysis are used for structural characterization of these membranes. It is found that the OH− conductivity of the membranes increases with temperature and reaches up to 7.5 × 10−3 S cm−1 at 90 °C but no apparent changes on both water uptake and methanol uptake with temperature. The methanol permeability coefficients of the membranes are in the range of 1.26–1.72 × 10−7 cm2 s−1 at 25 °C. In addition, the PVA/QHECE membranes show the high alkaline stability in hot 6.0 M KOH at 80 °C without losing their integrity and OH− conductivity during a week of evaluation. The membrane electrode assembly (MEA) fabricated with PVA/QHECE (= 1:0.25 by mass) gives an initial power density of 4.6 mW cm−2 using 2.0 M methanol and 2.0 M KOH as the fuel and O2 as oxidant at room temperature.

Preparation and in vitro Characterization of Gelatin Microspheres Containing 5-fluorouracil

Gelatin microspheres containing 5-fluorouracil (5-FU) were prepared by water/oil (W/O) emulsion and chemical cross-linking with glutaraldehyde. In order to obtain microspheres with an appropriate drug release profile, the effects of cross-linking time and amount of cross-linking agent on the swelling properties of microspheres and their release profile were investigated. Gelatin microspheres prepared with a larger amount of cross-linking agent, or after longer cross-linking time, showed a reduced swelling ratio in aqueous media. The in vitro release pattern of 5-FU from gelatin microspheres showed a biphasic profile and the release rates were reduced upon increasing the amount of cross-liking agent and prolonging the cross-linking time.

Effect of Crosslinking Time on Ion Exchange Capacity of Polystyrene Nanofiber Ion Exchangers

In this study, polystyrene nanofiber ion exchangers (PSNIE) were successfully prepared by a new method comprising of electrospinning and the subsequent crosslinking with formaldehyde and sulfonation in sulfuric acid to create the cation exchange functionality on the fibers surfaces. The PS solution at 15% w/v in dimethylacetamide (DMAc) produced the smallest PS nanofibers (399±38 nm) with good performance. The degree of crosslink and ion exchange capacity (IEC) of PSNIE depended upon the crosslinking time. The longer crosslinking time caused the greater crosslinked PS fibers. At the longest crosslinking time of 75 min, the remaining crosslinked PS fibers in dichloromethane were 94.12%; whereas, the starting fibers completely dissolved. This crosslinking agent (e.g. formaldehyde) might introduce methylene bridges in addition to sulfone bridges into the fibers. However, IEC decreased as crosslinking time increased, probably due to the difficulty of sulfonic functional groups to react with crosslinked PS fibers. The PSNIE crosslinked for 10 min showed the maximum IEC of 2.86 meq/g-dry-PSNIE, and the diameter of the PSNIE after sulfonation increased to 450-460 nm. Since cationic drug could be loaded onto this novel PSNIE, this nanofiber ion exchanger may be applied for controlled release delivery.

Preparation and modification of poly (vinyl) alcohol membrane: Effect of crosslinking time towards its morphology

This paper is concerned with the crosslinking of poly (vinyl) alcohol (PVA) using glutaraldehyde as the crosslinking agent. PVA is highly hydrophilic and has excellent film-forming and chemical resistance properties. Chemical crosslinking is the most common approach for stabilizing PVA membranes, which makes it less swollen in the water. Asymmetric PVA membranes were prepared by the immersion–precipitation technique and were further crosslinked with glutaraldehyde. Then, the effects of the crosslinking time on the pore size distribution were examined by porometer. Also, the porosity of the crosslinked PVA membranes was observed via the SEM images and the functional groups that exist in the membrane were determined using Fourier-transform infrared spectroscopy (FTIR). Ultimately, the pure water permeate flux of the crosslinked membrane is done to observe the permeability of produced membrane.

A facile technique to prepare cross-linked enzyme aggregates using p-benzoquinone as cross-linking agent

To obtain robust and thermo-stable enzyme aggregates, p-benzoquinone was used as cross-linker and bovine serum albumin (BSA) as crowding macromolecules to prepare cross-linked enzyme aggregates (CLEAs) of lipase. Effects of cross-linking time and cross-linker content on the activity, thermal stability and characteristics of enzyme aggregates were examined carefully. It was observed that when the content of p-benzoquinone was 5 mM and amount of BSA was 125% of that of lipase (w/w), the specific activity of cross-linked co-aggregates of lipase and BSA was 79.8 U mg−1, 2.44-fold of that of cross-linked enzyme aggregates of lipase without BSA. Moreover, after heat treatment for 96 h at 50 °C, the CLEAs prepared with this facile routine kept 75.18% of their initial activity, 5.01-fold more than that of the just CLEAs using glutaraldehyde. Furthermore, BSA macromolecules in lipase CLEAs enhanced the catalytic efficiency of free and just lipase CLEAs without BSA by 1.45 and 2.83 times, respectively. The proposed crosslinking technique would rank among the potential strategies for efficiently preparing robust and thermo-stable enzyme aggregates.

Effects of different cross-linking conditions on the properties of genipin-cross-linked chitosan/collagen scaffolds for cartilage tissue engineering

A cross-linking reagent is required to improve mechanical strength and degradation properties of biopolymers for tissue engineering. To find the optimal preparative method, we prepared diverse genipin-cross-linked chitosan/collagen scaffolds using different genipin concentrations and various cross-linking temperatures and cross-linking times. The compressive strength increased with the increasing of genipin concentration from 0.1 to 1.0%, but when concentration exceeded 1.0%, the compressive strength decreased. Similarly, the compressive strength increased with the increasing of temperature from 4 to 20°C, but when temperature reached 37°C, the compressive strength decreased. Showing a different trend from the above two factors, the effect of cross-linking time on the compressive strength had a single increasing tendency. The other results also demonstrated that the pore size, degradation rate and swelling ratio changed significantly with different cross-linking conditions. Based on our study, 1.0% genipin concentration, 20°C cross-linking temperature and longer cross-linking time are recommended.

Influence of cross-linking density on swelling and estradiol permeation of chitosan membranes

Chitosan membranes were obtained by a casting/solvent evaporation method and cross-linking with sodium tripolyphosphate. The effect of cross-linking time was studied and the cross-linked membranes were characterized with respect to equilibrium water content, sodium content, IR spectroscopy and permeability to a model drug (Estradiol). Sodium content increased with increasing cross-linking time. Equilibrium water content was higher in the membrane with the lowest cross-linking time. This membrane also showed a higher flux of Estradiol compared with the other which exhibited an increment in equilibrium water content and flux of Estradiol with the increase in cross-linking duration. These dissimilar results could be explained by a significant correlation between the hydrophilicity of the membrane and the hydrophobicity of Estradiol.

End-Group Cross-Linked Poly(arylene ether) for Proton Exchange Membranes

End-group cross-linkable sulfonated poly(arylene ether) polymer (E-SFQK) was synthesized via direct polymerization of potassium 2,5-dihydroxybenzenesulfonate (SHQ) and decafluorobiphenyl (DFBP), followed by a reaction with ethynylphenol (EP). The cross-linking reaction of the ethynyl end group of E-SFQK was performed at 250 °C. After cross-linking, proton conductivity, water uptake, and swelling ratio of cross-linked membrane decreased from 0.16 (noncross-linked membrane) to 0.13 S/cm, from 86% to 42%, and from 31% to 13%, respectively. The effect of cross-linking time on proton conductivity, water uptake, and swelling ratio were also investigated. Methanol permeability of cross-linked membrane was compared with Nafion 117 due to solubility of noncross-linked membranes in methanol. The cross-linked membrane performed better, with a methanol permeability of 88 × 10−8 cm2/s, as compared with 154 × 10−8 cm2/s for Nafion 117. The cross-linked membrane also exhibited improved chemical resistance and oxidative ...

Development of crosslinked poly(ether-block-amide) membrane for CO 2/CH 4 separation

Thin film composite membranes of poly(ether-block-amide) (PEBAX-1657) were prepared on PVDF ultra-porous substrate by solution casting and solvent evaporation method. The membrane was crosslinked by a novel method using 2% (v/v) 2,4-toluylene diisocyanate (TDI) in hexane medium. Sorption studies were carried out in pure water to confirm crosslinking. Both the unmodified and modified membranes were characterized by scanning electron microscopy (SEM) to study the morphologies of the surface and cross-section. X-ray diffraction (XRD) experiments were carried out to understand the intermolecular interactions and separation mechanisms. Thermal stability of the membrane was assessed by differential scanning calorimetry (DSC). Single gas permeabilities of CO 2 and CH 4 and the resultant ideal selectivities were determined for unmodified PEBAX-1657 membrane using an indigenously built high-pressure gas separation manifold. A comparison was made with PEBAX-2533 membrane, also prepared in this study, to evaluate the effect of rigid block content in the polymers. As the pressure was varied from 10 to 40 kg/cm 2, the permeance and ideal selectivity for the unmodified PEBAX-1657 were found to range from 3.0 to 4.8 GPU and 18 to 25, respectively. On the other hand PEBAX-1657 membrane crosslinked for 5 min exhibited only one-fifth the permeance (0.6–0.9 GPU) but almost twice the selectivity (38–47). The effect of crosslinking time (0–60 min) and binary feed mixture composition (5–20% CO 2) on performance of membrane was studied at a constant pressure. PEBAX-1657 was found to be promising for the separation of CO 2 from CH 4.

Effects of crosslinking time and amount of sulfophthalic acid on properties of the sulfonated poly(vinyl alcohol) membrane

AbstractA proton‐exchange membrane for a direct methanol fuel cell was prepared by modifying the chemical structure of poly(vinyl alcohol) (PVA) via a sulfonation. The sulfonation was carried out by using sulfophthalic acid (sPTA) as a sulfonating agent. The sulfonated PVA membranes, with a variety of degrees of substitutions, were obtained by varying the crosslinking time and the amount of sulfonating agents. The chemical structure and thermal stability of the sulfonated PVA were characterized by using FTIR and thermogravimetric analysis techniques, respectively. The ion‐exchange capacity (IEC) and water uptake of the sulfonated membranes was evaluated by titration and gravimetry techniques, respectively. It was found that the IEC of the membrane increased with the amount of sPTA. Water uptakes of the membranes could either decrease or remain unchanged with the crosslinking time, depending on the amount of the sulfonating agent used. Methanol permeability values of the membranes treated with 10% sPTA were relatively low, comparing with that of the Nafion 115 membrane. Proton conductivity values of the sulfonated PVA membranes ranged between 0.024 and 0.035 S/cm and they did not remarkably change with the crosslinking time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1931–1936, 2006