Effects Of Crosslinker Concentration Research Articles

Effects of crosslinker concentration on curing process and performances of needled fiber preform reinforced phenolic aerogel composite using process simulation and comprehensive experiments

A kind of needled quartz/carbon fiber preform reinforced phenolic aerogel composite (NQCF/PR) was fabricated through impregnating needled fiber preform with phenolic resin precursor solution, followed by sol–gel polymerization and solvent drying. The needled fiber preform serves as lightweight quasi-three-dimensional reinforcement, while phenolic aerogel matrix provides high porosity and low thermal conductivity. During fabrication of aerogel composite part using vacuum-assisted resin infusion process, distribution of crosslinker hexamethylenetetramine (HMTA) in precursor solution can be problematic, as precipitated crosslinker particles may be filtered by fibrous preform. In this study, the impact of HMTA filtration induced heterogeneous structure on subsequent curing process was investigated using process simulation. Temperature effects of sol–gel polymerization and solvent evaporation were considered through establishment of corresponding kinetic models. Impacts of heterogenous structure on distribution of temperature, resin curing degree and solvent conversion degree in large hemispherical aerogel composite structure were investigated. This leads to variations in gel network and pore structure of aerogel, thereby affecting final material performance. Based on experimental results, as HMTA concentration increases, compressive performance of NQCF/PR obviously increases. Among these, NQCF/PR with 4.7 wt% HMTA provides a balance of lightweight nature (0.25 g/cm3), excellent thermal insulation property (0.052 W·m−1·K−1) and compressive performance (strength of 0.35 MPa).

Highly interconnected porous monolithic and beaded polymers using high internal phase emulsion polymerization: tuning porous architecture through synthesis variables

AbstractOpen porous polymeric materials have gained popularity due to their exceptional properties and applications in tissue engineering scaffolds, drug delivery, enzyme immobilization and catalysis support. This study developed a novel two‐stage approach to create networked, crosslinked poly(2‐hydroxyethyl methacrylate‐co‐N,N′‐methylenebisacrylamide) HEMA‐MBA beads. The first part involves producing an oil‐in‐water‐in‐oil high internal phase emulsion (HIPE). This is followed by suspension polymerization using a redox initiator pair. In this study, a mixed surfactant combination with low and high hydrophilicity–lipophilicity balance surfactants was identified and successfully utilized to prepare a stable oil‐in‐water‐in‐oil HIPE. The effect of crosslinker concentration (i.e. crosslink density), surfactant concentration and monomer‐to‐porogen ratio on pore architecture and surface area were successfully evaluated. In addition, a new protocol was developed to synthesize HEMA‐MBA monoliths using an oil‐in‐water HIPE method at ambient temperature using a redox initiator pair. The effect of crosslink density and oil phase on pore architecture and surface area was evaluated. Key variables affecting the morphology of porous HEMA‐MBA beads and monoliths were identified and quantified, allowing future development of porous HEMA‐based polymer beads and monoliths with tunable morphologies which are suitable for numerous applications, especially in the biomedical field. © 2022 Society of Industrial Chemistry.

The effect of crosslinking concentration, time, temperature and pH on the characteristic of genipin-crosslinked small intestinal submucosa

In an attempt to prepare genipin-crosslinked collagen scaffolds with different crosslinking characteristics for experimental and clinical applications, the porcine small intestinal submucosa (SIS) was crosslinked with genipin under different conditions (concentrations, duration times, temperatures, pHs), and their crosslinking degree, macroscopic morphology, microstructure, swelling ratio, shrinkage temperature, degradation degree, maximum stress and cytotoxicity were determined respectively. SIS was efficiently crosslinked with all genipin concentrations, yielding genipin-crosslinked small intestinal submucosa (GP-SIS) with a high crosslinking degree (≥60%) and shrinkage temperature (≥80 °C), as well as a low swelling ratio (≤85%) and degradation degree (≤5%). However, only the concentration greater than or equal to 0.12% did significantly increase the maximum stress. Additionally, the fixation of different concentrations of genipin did not introduce cytotoxicity in SIS. As for the effect of duration times, enough crosslinking time was required for high crosslinking efficiency. When the crosslinking time was less than 24 h, GP-SIS had a crosslinking degree of less than 60%, and there was no significant decrease in swelling ratio in comparison to native SIS. When the crosslinking time was less than 24 h, the maximum stress did not reach 7 MPa. Only 3 h-fixed GP-SIS had a shrinkage temperature of less than 75 °C and a degradation degree of more than 6%. GP-SIS prepared at all temperatures and pHs, except for 4 °C, 25 °C and pH 4.0, had a crosslinking degree greater than 80%, a swelling ratio less than 50%, a shrinkage temperature greater than 80 °C, a degradation degree less than 4%, and a maximum stress greater than 8 MPa. Notably, only the fixation at alkaline conditions can increase crosslinking degree and maximum stress of SIS to 90% and 11 MPa respectively.

Breaking and Connecting: Highly Hazy and Transparent Regenerated Networked-Nanofibrous Cellulose Films via Combination of Hydrolysis and Crosslinking

High optical transparency combined with high optical haze are essential requirements for optoelectronic substrates. Light scattering caused by haze is responsible for increasing light harvesting in photon-absorbing active materials, hence increasing efficiencies. A trade-off between transparency and haze is common in solar substrates with high transparency (~90%) and low optical haze (~20%), or vice versa. In this study, we report a novel, highly transparent film fabricated from regenerated cellulose after controlled acid-hydrolysis of microcrystalline cellulose (MCC). The developed networked-nanofibrous cellulose was chemically crosslinked with glutaraldehyde (GA) and vacuum-cured to facilitate the fabrication of mechanically stable films. The effects of crosslinker concentration, crosslinking time, and curing temperature were investigated. Optimum conditions for fabrication unveils high optical transparency (~94%) and high haze (~60%), using 25% GA for 24 hr with a curing temperature of 25 °C; therefore, conveying an optimal substrate for optoelectronics applications. The high haze arises primarily from the crystalline, networked crystals of cellulose II structure formed within the regenerated cellulose upon hydrolysis. Moreover, the developed crosslinked film presents high thermal stability, water resistance, and good mechanical resilience. This high-performance crosslinked cellulose film can be considered a potential material for new environmentally-friendly optical substrates.

Crosslinker concentration effect on the poroviscoelastic relaxation of polyacrylamide hydrogels using depth-sensing indentation

The effect of crosslinker concentration on the mechanical behaviour of polyacrylamide based hydrogels is established by using depth sensing indentation. In this work, hydrogels are considered as poroviscoelastic solids, being viscoelasticity and poroelasticity taken into account at intermediate length scales such as those here explored. A constrained fitting method is derived to implement a multiplicative rule that accommodates the contribution of each deformation mechanism on the global material response. The proposed method is robust enough to properly separate poroelastic and viscoelastic contributions from relaxation curves measured at different indentation depths and strain rates. At the length scales here tested viscoelasticity appears as dominant, but the poroelastic contribution becomes increasingly important as the crosslinker concentration is reduced.

Liquid crystal polymer networks directed by scanning wave photopolymerization of oxetane monomer and crosslinker

In this study, we fabricated liquid crystal polymer networks (LCNs) containing a large amount of crosslinker by scanning wave photopolymerization, and examined the effect of crosslinker concentration on molecular alignment behavior. Samples with different crosslinker concentrations were photopolymerized by unidirectionally scanning ultraviolet light, resulting in LCN films with uniaxial molecular alignment. The LCN films obtained from the compositions of only monomer or monomer and crosslinker had mesogens aligned in parallel to the light scanning direction. Moreover, the LCN films with high crosslinker concentrations were able to maintain their initial molecular alignment after repeated heating cycles.

Hydrogels of Polysaccharide Carboxymethyl Hydroxypropyl Guar Crosslinked by Multivalent Metal Ions

Hydrogels of polysaccharide carboxymethyl hydroxypropyl guar crosslinked by chromium(III) ions are synthesized. The effect of crosslinker concentration on the mechanical behavior of the gels is studied, and the amount of chromium compounds able to interact with polymer chains and the amount of carboxyl groups of the polymer involved in crosslinking are compared. It is shown that the elastic modulus of the gels attains a constant value when not all but only about 10% functional groups interact with chromium compounds. At high concentrations, crosslinker molecules basically bind to one functional group; as a result, the gel recharges. This binding proceeds until all carboxyl groups are filled.

Epoxy Functionalized Carboxymethyl Dextran Magnetic Nanoparticles for Immobilization of Alcohol Dehydrogenase

Microbial inhibition of carboxymethyl dextran (CMD) magnetic nanoparticles (MNPs) was investigated on two different bacterial cultures, Escherichia coli and Staphylococcus aureus, where inhibition properties of CMD-MNPs were confirmed, while uncoated MNPs exhibited no inhibition properties. To such CMD-MNPs, enzyme alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae was immobilized. Later on, CMD-MNPs were functionalized, using an epoxide cross-linker epichlorohydrin (EClH) for another option of ADH immobilization. Residual activities of immobilized ADH onto epoxy functionalized and non-functionalized CMD-MNPs were determined. Effect of cross-linker concentration, temperature of immobilization and enzyme concentration on residual activities of immobilized ADH were determined, as well. With optimal process conditions (4% (v/v) EClH, 4 °C and 0.02 mg/mL of ADH), residual activity of immobilized ADH was 90%. Such immobilized ADH was characterized using FT-IR, SEM and DLS analysis.

Cover Feature: Effects of Crosslinker Concentration in Poly(Acrylic Acid)‐KOH Gel Electrolyte on Performance of Zinc‐Air Batteries (Batteries & Supercaps 5/2020)

Cover Feature: Effects of Crosslinker Concentration in Poly(Acrylic Acid)‐KOH Gel Electrolyte on Performance of Zinc‐Air Batteries (Batteries & Supercaps 5/2020)

Preparation, Optimization, and Evaluation of Epichlorohydrin Cross-Linked Enset (Ensete ventricosum (Welw.) Cheeseman) Starch as Drug Release Sustaining Excipient in Microsphere Formulation.

Ensete ventricosum (Welw.) cheeseman which belongs to the family of Musaceae is one of the main sources of starch in Ethiopia. This study aimed at evaluating epichlorohydrin cross-linked enset starch as a drug release sustaining excipient in microsphere formulations of theophylline. Extracted enset starch was cross-linked using epichlorohydrin as a cross-linking agent. The effect of cross-linker concentration, cross-linking duration, and cross-linking temperature on the degree of cross-linking and release rate of microspheres prepared by emulsion solvent evaporation method was investigated using the two-level full factorial design. Accordingly, the concentration of epichlorohydrin and duration of cross-linking were the most significant factors affecting both the degree of cross-linking and drug release rate. Thus, the effects of these two factors were further studied and optimized using the central composite design. As per the numerical method of central composite design, the optimal points were obtained at epichlorohydrin concentration of 13.70% and cross-linking time of 3.82 h. Under these optimal conditions, the model predicts the degree of cross-linking of 74.70% and drug release rate of 28.00 h1/2. The validity of these optimal points was confirmed experimentally. The microspheres of the optimum formulation also exhibited minimum burst release with sustained release for 12 h. Besides, the optimized formulation followed the Higuchi square root kinetic model with non-Fickian diffusion release mechanism. The finding of this study suggested that cross-linked enset starch can be used as an alternative drug-release-sustaining pharmaceutical excipient in microsphere formulation.

Effects of Crosslinker Concentration in Poly(Acrylic Acid)‐KOH Gel Electrolyte on Performance of Zinc‐Air Batteries

AbstractZinc‐air batteries (ZABs) using gel polymer electrolytes suffer from low energy efficiency and poor cyclability. This issue is not only associated with the air electrode, as early failure of the battery is often due to the Zn electrode. Here, the cycle life of ZABs using alkaline poly(acrylic acid) (PAA‐KOH) as the electrolyte is shown to vary by changing its crosslinking density. For ZABs using hydrogel electrolytes, understanding the failure mechanism and optimization of the hydrogel composition are key to achieving better utilization of the Zn electrode and battery rechargeability. In addition, the effects of crosslinker concentration on rheological properties, sol‐gel fraction, ionic conductivity, and water retention ability of the hydrogel are discussed. PAA‐KOH gels with lower crosslinking concentrations are weaker, but they have higher conductivity and better water retention, whereas gels with higher crosslinking concentrations affect the diffusion of zincate ions and facilitate passivation of the Zn electrode, resulting in early failure of the battery.

Preparation and salt-insensitive behavior study of swellable, Cr3+-embedded microgels for water management

The microgels have been used in the oilfield for water management and enhanced oil recovery (EOR). Fully swollen size of the microgels is very sensitive to salt, which brings uncertainties on the performance of microgel treatments. Herein, a Cr3+-embedded polyacrylamide based microgel, synthesized via a free-radical suspension polymerization, is described which could significantly weaken the salt-sensitivity of the microgels. Embedment of Cr3+ in the polymeric networks of microgels crosslinked through covalent bonds has been studied using the scanning electron microscopy (SEM), FT-IR, and dialysis analysis. The effects of crosslinker concentration, initiator concentration, and the stirring rate during polymerization on the size of the microgels have been characterized. In addition, contrary to the commercial microgels, the fully swollen size of the Cr3+-embedded microgels performed insensitivity to the salts, such as sodium chloride (NaCl), calcium chloride (CaCl2), and aluminum chloride (AlCl3). Moreover, the pore occlusion experiments demonstrated the Cr3+-embedded microgels also have the same viscoelasticity at different salt concentrations, resulting in the similar plugging performance. The Cr3+-embedded microgel shows a great potential for improving the microgel plugging for water management and enhanced oil recovery.

Cellulose nanocrystal/amino-aldehyde biocomposite films

From the suspensions of cellulose nanocrystals (CNCs) derived from cotton and flax by acidic hydrolysis, transparent and smooth films were produced with different plasticizers and an amino-aldehyde based cross-linking agent in a wide composition range by a simultaneous casting and wet cross-linking process. The effect of cross-linker concentration on the optical and tensile properties and on the morphology of CNC films was investigated by various measurements. The interaction of films with liquid water and water vapour was also characterized by water sorption and water contact angle as well as performing a sinking test. Cross-linking improved the transparency, reduced the porosity and surface free energy, and prevented the delamination of CNC films in water at a concentration of 10% or higher. The surface of CNC films is basic in character and has an electron donor property. The CNC/amino-aldehyde films had a high tensile strength (45 MPa) and modulus (11 GPa).

Ion Transport in Dynamic Polymer Networks Based on Metal–Ligand Coordination: Effect of Cross-Linker Concentration

The development of high-performance ion conducting polymers requires a comprehensive multiscale understanding of the connection between ion–polymer associations, ionic conductivity, and polymer mechanics. We present polymer networks based on dynamic metal–ligand coordination as model systems to illustrate this relationship. The molecular design of these materials allows for precise and independent control over the nature and concentration of ligand and metal, which are molecular properties critical for bulk ion conduction and polymer mechanics. The model system investigated, inspired by polymerized ionic liquids, is composed of poly(ethylene oxide) with tethered imidazole moieties that facilitate dissociation upon incorporation of nickel(II) bis(trifluoromethylsulfonyl)imide. Nickel–imidazole interactions physically cross-link the polymer, increase the number of elastically active strands, and dramatically enhance the modulus. In addition, a maximum in ionic conductivity is observed due to the competing e...

Synthesis and characterization of PAA microgels using multifunctional epoxy cross-linkers with a new cross-linking mechanism via a precipitation polymerization method

Polyacrylic acid (PAA) microgels were prepared by a free radical precipitation polymerization method. Initially, epoxy type cross-linkers were used to prepare PAA microgels by the precipitation polymerization method. Different types of multifunctional cross-linkers such as ethylene glycol diglycidyl ether (EGDGE), Triphenylol methane triglycidyl ether (TMTGE) and 4,4′- Methylenebis(N,N-diglycidyl aniline) (MBDGA) were used as bi-, tri- and tetra-functional cross-linkers, respectively. Epoxy type cross-linkers are able to cross-link PAA by reaction between the –COOH groups of PAA and the epoxide groups of the cross-linkers. Some of the epoxy rings do not react with acid groups of PAA chains during the polymerization stage; unreacted epoxy rings can be reacted during the sample drying time, a stage we designated as the ‟post-curing stage”. The effect of cross-linker concentration and its functionality on the behaviors of samples (i.e., swelling capacity, gel content, glass transition temperature and rheological properties) were investigated. A new relationship between average molecular weight of two successive cross-links ( Mc) and epoxy concentration ([epoxy]) was defined. The microgel properties, such as rotational viscosity and rheological properties, were compared with those of microgels prepared by divinyl type cross-linkers. Our results show that microgels synthesized by this novel mechanism have higher rheological properties (at low shear rate, strain and frequency) than those synthesized by conventional methods. These behaviors can be due to the increase in polymer side chains of the polymer network generated by this new cross-linking method.

Effect of Cross-Linker Concentration on the Synthesis and Swelling Behaviour of Superabsorbent Polymers (SAP) Using Graft Polymerization Techniques

The graft polymerization of acrylic acid by varying the amount of cross-linker in ranging of 0.001 g to 0.05 g was investigated. The effect of cross-linker in synthesized superabsorbent polymers (SAP) was identified in terms of water absorbency responses by keeping the values of monomer and initiator. The implementation of SAP in agriculture could develop plant growth, enhancing water retention capacity in soils which can reducing dewatering system and improved the efficiency of soil condition so higher yield of product can be obtained particularly in arid regions. The SAPs were synthesized by graft polymerization using acrylic acid (AA) as monomer, N,N’-methylene bisacrylamide (MBA) as cross-linker and ammonium persulfate (APS) as initiator. The optimum water absorbency of synthesize SAP was defined using tea-bag method in deionize water. The structures of synthesize SAP was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and morphologies of synthesize SAP was examined by Scanning Electron Microscope (SEM) testing. From the result, it was obvious showed that water absorbency will decreased as the increased of concentration of cross-linker which is MBA in synthesize SAP. The best value content of MBA was 0.01 g which achieved the highest water absorbency response which is 170 g water/g sample. In conclusion, SAP has hydrophilic structure of which renders them capable for holding a large amount of water which can help to retain nutrients and absorb water in soil with various applications for plant growth and soil condition which will be useful especially in agriculture field.

Study on the inverse emulsion copolymerization of microgels based on acrylamide/2-acrylamido-2-methylpropane sulfonic acid

Inverse emulsion copolymerization of acrylamide and AMPS was conducted, and the effects of cross-linker concentration, initiator type, and reaction temperature on particle size distribution, equilibrium swelling and thermal properties were studied. Fourier transform infrared spectrophotometry (FTIR) and differential scanning calorimetry (DSC) results were used to confirm the copolymerization of the monomers. In this study, relatively high amounts of AMPS comonomer were used successfully to synthesize AAm/AMPS based microgels. Thermal properties were determined using thermogravimetric analysis (TGA) and it was found that degradation threshold shifted to higher temperatures with increasing cross-linking. There was a good agreement between the DSC and TGA thermograms depicting the different stages of microgel degradation including the departure of amide and sulphonic acid groups. Dynamic light scattering (DLS) demonstrated that higher cross-link densities resulted in the formation of smaller particles with narrower distribution and lower swelling capacity. The results of scanning electron microscopy (SEM) showed that the more hydrophobicity of the initiator led to the decrease in particle size and swelling capability. Swelling ratio reached its maximum value at about 50 °C. Interestingly, mean particle size had a close relation with equilibrium swelling as samples with lower mean particle diameters exhibited lower swelling capacities.

Morphology and size control of gelatin/hyaluronic acid composite microsphere for drug delivery

Composite microspheres based on gelatin (Gel) and hyaluronic acid (HA) were prepared by an emulsion–coagulation method with glutaraldehyde as a crosslinker. The influences of stirring speed, crosslinker concentration, HA content and water/oil ratio on the particle size and surface morphology were investigated. The Fourier transform infrared spectra characterisation indicated that Gel and HA were crosslinked successfully by the glutaraldehyde. The in vitro release behaviours of 5-fluorouracil (5-FU) from Gel/HA microspheres were also studied. The results showed that the adhesion and agglomeration phenomena were apparent when the HA content reached 10.0 wt-%. The particle diameter of the microspheres decreased greatly with increasing stirring speed; however, the adhesion of smaller microspheres could be observed when the stirring speed reached 800 rev min− 1. The effect of crosslinker concentration on the particle size was not significant, but the dispersion degree of the Gel/HA microspheres decreased with decreasing crosslinker content. The particle size of the microspheres gradually became uniform with the increase of the water/oil ratios. The dispersion and surface smoothness level could be improved by optimising the experimental conditions. The cumulative drug release of 5-FU from the microspheres decreased with increasing glutaraldehyde content. The results of 5-FU release kinetics from Gel/HA microspheres indicated Fickian diffusion.

Modelling Gelation Time of Organically Cross-linked Water-shutoff Systems for Oil Wells

Water production is one of the major challenges in the petroleum industry, especially brown fields and water drive reservoirs. Water production can weaken the cementation of sand grains, thereby rendering formations partially or completely unconsolidated. This in turn initiates fines migration and aggravates safety concerns. The gelation time is an important characteristic of water-shutoff systems and it is influenced by different parameters. The gelation time gives an indication of the time required for a gel to transit from free flowing fluid to solid or semi-solid gel making it difficult to pump. Organically cross-linked gels have numerous applications in the industry such as shutoff systems. They are used to control water and gas production in oil wells. The effect of cross-linker concentration, temperature and brine concentration on the gelation time of an organically crosslinked system was studied. Based on the experimental results a mathematical model was developed for predicting the gelation time of the water-shutoff system. The results showed that temperature had the highest impact on the gelation time of the water-shutoff system with an effect estimate of (-2.292). The brine concentration of the mix water recorded the lowest impact with an effect estimate of 0.2083 and the interaction between cross-linker concentration and brine concentration of mix water had neutral impact. A predictable and effective water-shutoff system has been developed with an excellent initial viscosity which can easily be pumped and applied to solve water production and its associated problems. The gelation time of organically crosslinked water-shutoff system can be optimised in water control operations using this model and the effect estimates of these parameters.

The effect of cross-linker concentration on the physical properties of poly(dimethyl acrylamide-co-stearyl acrylate)-based shape memory hydrogels

Chemically cross-linked shape memory hydrogels were synthesized, and their physical properties were studied. The gels were made from a hydrophilic monomer, i.e., N,N-dimethyl acrylamide (DMAA), and a hydrophobic monomer, i.e., stearyl acrylate (SA). The properties were characterized by varying the concentration of the cross-linker methylene bisacrylamide (MBAA), whereas the concentrations of other chemical components were held constant. It was observed that the mechanical properties strongly depended on the cross-linker concentration. The cross-linked hydrogels showed improved toughness compared to the hydrogel counterparts without cross-linking. Thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC spectra of dried samples exhibited a complex crystalline nature, while swollen samples showed homogeneous crystallinity. The experimental results of DSC and TGA suggested that there was no significant influence of MBAA concentration on the crystallinity and thermal properties of swollen SMG hydrogels.