Crosslinker Concentration Research Articles

Evaluating physiochemical characteristics of tragacanth gum-gelatin network hydrogels designed through graft copolymerization technique

The present work deals with the evaluation of the physiochemical and biomedical properties of hydrogels derived from copolymerization of tragacanth gum (TG) and gelatin for use in drug delivery (DD) applications. Copolymers were characterized by field emission-scanning electron micrographs (FE-SEM), electron dispersion X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), 13C-nuclear magnetic resonance (NMR), thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. FE-SEM revealed heterogeneous morphology and XRD analysis demonstrated an amorphous nature with short range pattern of polymer chains within the copolymers. The release of the drug ofloxacin occurred through a non-Fickian diffusion mechanism and the release profile was best described by the Korsmeyer-Peppas kinetic model. The hydrogels exhibited blood compatibility and demonstrated a thrombogenicity value of 75.63 ± 1.98 % during polymer-blood interactions. Polymers revealed mucoadhesive character during polymer-mucous membrane interactions and required 119 ± 8.54 mN detachment forces to detach from the biological membrane. The copolymers illustrated the antioxidant properties as evidenced by 2, 2′-diphenylpicrylhydrazyl (DPPH) assay which demonstrated a 65.71 ± 3.68 % free radical inhibition. Swelling properties analysis demonstrated that by change in monomer and cross linker content during the reaction increased the crosslinking of the network. These results suggest that the pore size of network hydrogels could be controlled as per the requirement of DD systems. The copolymers were prepared at optimized reaction conditions using 14.54 × 10−1 molL−1 of acrylic acid monomer and 25.0 × 10−3 molL−1 of crosslinker NNMBA. The optimized hydrogels exhibited a crosslink density of 2.227 × 10−4 molcm−3 and a mesh size of 7.966 nm. Additionally, the molecular weight between two neighboring crosslinks in the hydrogels was determined to be 5332.209 gmol−1.The results indicated that the combination of protein-polysaccharide has led to the development of hydrogels suitable for potential applications in sustained drug delivery.

High performance all lignin derived supercapacitors for energy storage applications

The development of next-generation sustainable energy storage devices is attracting a lot of attention. This study explores the potential use of lignin, a biopolymer typically considered a byproduct of the paper and pulp industry, as a starting material for producing hydrogels through chemical crosslinking. The resulting hydrogels are then evaluated for their efficacy as precursors for electrolyte and electrode preparation in the development of a supercapacitor. Several concentrations of lignin and crosslinker were evaluated to determine the optimal conditions for producing hydrogel electrolytes. The optimised hydrogels exhibited excellent properties, including high swelling capacity, an interconnected macroporous morphology, and structural integrity. The carbonisation of lyophilised lignin hydrogels produced lignin-derived carbon materials with tailored nanoporous honeycomb-like structures. The integration of chemically crosslinked lignin hydrogel electrolytes with lignin-derived carbon electrodes resulted in a sustainable supercapacitor with superior electrochemical properties. The resulting all-lignin-based supercapacitors demonstrated a capacitance of 40.7 F/g at 0.5 A/g current density, with a capacity retention of 60% at higher current densities. The results of this study highlight the promise of lignin-based materials as both electrodes and electrolytes for the creation of environmentally sustainable, high-performance supercapacitors.

Multifunctional graft-IPN hydrogels of cellulose nanofibers and poly(N-isopropyl acrylamide) via silver-promoted decarboxylative radical polymerization

Interpenetrating polymer networks (IPNs) have emerged as innovative materials for a wide range of applications. Owing to the crosslinked structure of their polymer components, IPNs exhibit superior properties relative to their single component counterparts. Here, we report a new class of multifunctional graft-interpenetrating polymer network (graft-IPN) hydrogel composites of poly(N-isopropylacrylamide) (PNIPAM) grafted onto cellulose nanofibers (CNFs) via silver(I)-promoted decarboxylative polymerization. This novel approach involves the Ag-promoted graft polymerization and the crosslinking of PNIPAM in the CNF network, forming a hybrid of semi-IPN and graft-copolymer hydrogel. Different from conventional PNIPAM-CNF IPNs, the CNFs in graft-IPN hydrogels form an interconnected network as a result of crosslinking between neighboring grafted PNIPAM. Silver nanoparticles (AgNPs) are also formed in situ in the graft-IPN hydrogel matrix, demonstrating the dual functionality of silver as both a catalyst in the polymerization and an eventual antibacterial agent in the hydrogel. The network structure of graft-IPN hydrogels can be controlled by crosslinker and Ag(I) concentration, therefore modulating their thermo-responsive, mechanical, and swelling properties. The grafting of PNIPAM from CNFs shifts the volume phase transition to 36 °C and significantly improves the mechanical strength and swelling capacity of the hydrogels. Ultimately, this work demonstrates the excellent potential of these multifunctional graft-IPN hydrogels with controllable thermosensitivity, mechanical strength and anti-microbial activity as engineered biomaterials for advanced applications in biomedicine, engineering, and industry.

Development of chitosan microparticles via interfacial polymeric crosslinking method utilizing sodium trimetaphosphate

Chitosan derived from the alkaline deacetylation of chitin found in crustacean exoskeletons, is a natural biopolymer. It has been employed as a matrix for microparticles and crosslinked systems, facilitating the immobilization and controlled release of drugs, ensuring stability, safety, and efficacy. Microencapsulation, a technique involving the coating of active products in polymeric layers, allows for their release under specific conditions and controlled rates, achieved through the formation of microspheres or microcapsules. The distinctive features of chitosan, such as its non-toxicity, biodegradability, and cost-effectiveness, make it advantageous over other polysaccharides. This study aimed to produce chitosan microparticles through the interfacial polymeric crosslinking method, utilizing sodium trimetaphosphate as the crosslinking agent. A pre-formulation study, involving varying concentrations of polymer, crosslinking agent, and two stirring speeds, was conducted to assess their direct correlation with microparticle size. The interfacial polymeric crosslinking method successfully yielded spherical microparticles, maintaining a wrinkled surface aspect, with size variations according to the formulation. Parameters such as crosslinking agent concentration and stirring speed were identified as influencing factors on microparticle size. In conclusion, interfacial polymeric crosslinking using sodium trimetaphosphate proves effective in obtaining chitosan microparticles.

Optimization of Particle Size Distribution with Gaussian Analysis of Albumin Microcarriers Cross-linked by Natural Phenolic Compounds

The biodegradation of albumin into natural products and nontoxicity besides its antigenicity has many advantages in controlled drug delivery of therapeutic agents. A bifunctional covalent bonding agent, glutaraldehyde is extensively used for linking amine groups of albümin microparticles/microcarriers (AlbMC’s). But its cytotoxicity and the rapid calcification of the glutaraldehyde-treated tissue limit the use of glutaraldehyde. Phenolic compound showed non-covalent and covalent chemical interactions with proteins. The objective of this research is to prepare three different natural phenolic compound cross-linked/stabilized AlbMC’s and estimate the cross-linker concentration which is giving narrow size distributions since it is important to gain higher surface area. The influence of qallic acid (GA), tannic acid (TA) and quercetin concentrations on AlbMC’s size was investigated by Gaussian function analysis of microcarriers determined after optical micrograph measurements. Gallic acid (GA) stabilized AlbMC’s have 3.35  0.71 μm average mean size distribution while it was 3.56  0.71 μm for Quercetin and 3.71  0.69 μm for TA stabilized microcarrier formations. Average mean particle size distribution of AlbMC’s synthesized with synthetic cross-linker, glutaraldehyde was calculated as 5.12  0.50 μm. All statistical analysis were evaluated by MATLAB program. New approach for albumin microcarrier synthesis by using phenolic compounds as a cross-linker can be proposed as an alternative microcarrier preparation system with narrow size distributions.

Effect of cross-linking agents on sodium alginate-based quercetin beads: physicochemical properties and controlled release kinetics

Alginates have a variety of biological, physical, and chemical properties that can be modified to meet a specific purpose. Ionic crosslinking is an easy method of alginate modification. This study examined the ionic crosslinking agents (Ca2+, Ba2+, Mg2+) on swelling ratio, water solubility, and % sol-gel fraction of modified alginate. The performance of the modified alginate used to encapsulate quercetin, such as % encapsulation efficiency (% EE), % release of quercetin, and quercetin release kinetics were examined. The variables used in this study were the concentration of alginate and ionic crosslinking agents. At 3% alginate concentration and 0.3 M, ionic crosslinking agent concentration positively correlated with swelling ratio and water solubility. In contrast, the ionic crosslinking agent that positively correlates to the % sol-gel fraction is Ca2+. Encapsulation of quercetin using a crosslinking agent with ion Ca2+ and 2.5 ppm of quercetin concentration showed the highest % EE of 87%. Modified alginate induced quercetin release from beads at pH 1.4 and 7. The release of quercetin from modified alginate followed the Korsmeyer-Peppas kinetic model (R2 >0.99). The results of the FTIR analysis confirmed that a new peak at 1271 cm-1 was C-O-C characteristic of quercetin, indicating quercetin loaded on encapsulated beads. The morphological analysis showed that the surface of modified alginate (Ca-Ag/Ba-Ag/Mg-Ag) was rough and porous. This study established that modified alginate using different ionic crosslinking agents can be a suitable matrix for encapsulating quercetin.

Investigation of swelling behaviour monolayer and double Layer polysaccharide based composite hydrogels

ABSTRACT In this study, monolayer and double layer (core-shell) composite hydrogel beads with and without hydroxyapatite which have potential applications in drug delivery systems were synthesized, and their swelling behaviours were investigated in different pH mediums. The composite hydrogel beads was prepared by crosslinking sodium alginate and kappa-carrageenan (by using Ca+2 and K+1). Core-shell hydrogel beads were formed by coating monolayer composite hydrogel beads with the mixture of sodium alginate and kappa-carrageenan. The structure of hydrogel beads was characterized by Fourier Transform Infrared Spectrophotometer, Scanning Electron Microscopy and Differential Scanning Calorimetry. The effects of the composite hydrogel beads combination and the concentration of crosslinker on swelling behaviours were investigated. Swelling kinetics data were tested using pseudo-second-order model, and the pseudo-second-order model is estimated as a convenient model to represent the swelling kinetic. The results indicated that swelling behaviours of hydrogel beads changed with composite hydrogel beads combination and concentration of crosslinker.

Highly-efficient sustainable ionic thermoelectric materials using lignin-derived hydrogels

The efficient and economical conversion of low-grade waste heat into electricity has promising potential to combat the greenhouse effect and expedite the shift towards sustainable development. This study presents an innovative and appealing approach through the utilization of lignin, an abundant waste product derived from the paper and pulp industry, to develop hydrogels as compelling and sustainable materials for application in ionic thermoelectricity. Various compositions were evaluated to examine the impacts of varying lignin concentrations, types of electrolytes, concentrations of crosslinkers, and electrolyte concentrations on the ionic thermoelectric performance of the hydrogels. The optimized lignin-derived hydrogel, infiltrated with a 6 M KOH electrolyte, demonstrates high ionic conductivity (226.5 mS/cm) and a superior Seebeck coefficient of 13 mV/K. This results in a remarkable power factor (3831 µW/m·K2) that leads to an impressive Figure of merit (ZTi) (3.75), surpassing most of the existing state-of-the-art materials and making it the most efficient sustainable ionic thermoelectric material reported until now. These findings underscore the exceptional performance of lignin-based hydrogels in the realm of low-grade waste energy harvesting applications. The present study contributes to address the challenges posed by waste heat through effectively harnessing low-grade waste heat through the utilization of sustainable lignin-based hydrogels while reducing the reliance on fossil fuels and minimizing greenhouse gas emissions.Graphical

Chitosan-based foam composites for hexavalent chromium remediation: Effect of microcellulose and crosslinking agent content

Potentially toxic metal ions, such as hexavalent chromium (Cr6+), present in water concern the population's health due to their persistence, bioaccumulation potential, and high toxicity. Highly porous materials based on polysaccharides are promising technologies for metal removal due to their high surface area, biodegradability, and low toxicity. This study evaluated the effect of concentrations of microcellulose (0.5, 1, and 1.5 %) and glutaraldehyde (1, 2, and 3 %) in the adsorption capacity and mechanical properties of chitosan foams. The developed foams exhibited a three-dimensional structure with interconnected pores. Compared to foams without microcellulose, adding 1.5 % microcellulose increased up to 180 % in maximum stress supported by the foams and up to 135 % in Young's modulus. However, Cr6+ sorption capacity decreased with increasing microcellulose and crosslinking agent content due to the occupation of amino groups. Still, the foams exhibited a highly favorable sorption behavior, and the Sips isotherm model provided the best fit to the experimental data. The maximum sorption capacity reached approximately 1.4 mmol·g−1 at pH 4.0 and 25 °C. The foam structural integrity, enhanced mechanical properties, and efficient sorption capacity make them viable alternatives for environmentally friendly and cost-effective treatment of water contaminated with Cr6+ ions.

Influence of Ionic Liquid and Light Intensity on a Polymer Nanostructure Formed in Lyotropic Liquid Crystalline Templates.

Utilizing self-assembled lyotropic liquid crystal (LLC) templates with radical photopolymerization shows promise in controlling polymer structure on the nanometer scale This control of nanostructure allows tailoring and enhancement of material properties not attainable in traditional polymerization in applications including hydrogels and stimuli-responsive systems. However, thermodynamically driven phase separation between the polymer and LLC templates often hinders the control of local polymer order and resultant polymer properties. This study investigates an alternative method to control the hydrogel nanostructure and avoid phase separation using imidazolium ionic liquids (ILs) in the LLC template while modulating the light intensity used in photopolymerization. The addition of the IL improves the thermodynamic stability and enhances the polymerization rate in the LLC system. The degree of LLC nanostructure retention is increased by increasing light intensities during polymerization. In addition, intermediate concentrations of cross-linker allow a balance between phase stability and cross-linking to lock in LLC morphology. With enhanced retention, the maximum water uptake is significantly higher compared with isotropic controls. These results demonstrate a method to increase the structure on the nanometer scale of a polymer by combining the addition of ILs with the proper selection of light intensity and cross-link density that allows access to unique hydrogel properties. These templated polymers demonstrate enhanced swelling and a stimuli response that show promise in applications ranging from drug delivery to water remediation.

Removal of dyes from aqueous media using environmentally friendly aerogels based on chitosan

According to the World Health Organization, between 17% and 20% of water pollution is caused by dye treatments in the textile industry, which makes the development of efficient technologies for its removal essential. Environmentally friendly adsorbent materials, such as aerogels, can be effectively used in adsorption processes involving water remediation because of their high specific surface area and the possibility of an easy separation from the contaminated solutions. In this work, aerogels were obtained by a simple procedure that includes the cross-linking of chitosan with glutaraldehyde, followed by a freeze-drying step to eliminate water by water sublimation. The obtained aerogels presented low density (0.049–0.083 g/cm3), a three-dimensional skeletal structure that provides them with high porosity, acceptable swelling capacity and good dimensional stability. FTIR and X-Ray analysis were used to identify aerogels’ chemical structure and dynamic-mechanical analysis to complement the characterization of these materials. Selected formulations were also tested as adsorbents of Congo Red in aqueous media. The adsorption results demonstrated that the aerogels adsorption capacity strongly depended not only on the crosslinking agent content but also on the amount of chitosan in the initial solution used in their synthesis. Moreover, preliminary thermodynamic studies of the adsorption process indicate that both adsorption rate and aerogel sorption capacity increase with increasing temperature.

Effect of carbonyl-amino condensation, non-covalent cross-linking and conformational changes induced by ultrasound-assisted Maillard reaction on lysinoalanine formation in silkworm pupa protein

The inhibition of cross-linked lysinoalanine (LAL) formation in silkworm pupa protein isolates (SPPI) by Maillard reaction (using varying xylose concentration) and ultrasound treatment was studied. Results showed that sonicated SPPI was effectively grafted with high concentration of xylose (5 %), resulting in the lowest LAL content, which was 48.75 % and 30.64 % lower than the control and ultrasound-treated samples, respectively. Chemical bond analysis showed that the combined treatment destroyed the ionic bonds, intrachain (g-g-t), and interchain (g-g-g) disulfide bonds, but stimulated the polymerization of hydrogen and hydrophobic bonds between SPPI and xylose, and as well enhanced the net negative charge between SPPI/Xylose complexes. The particles of the complexes were more loose, dispersed and rough, and had a stronger hydrophilic microenvironment, accompanied by alterations in microscopic, secondary and tertiary structures. Ultrasound treatment induced the breakdown of the oxidative cross-linking in SPPI, and promoted the sulfhydryl group-dehydroalanine binding and the carbonyl-amino condensation of the protein and xylose, and thus inhibited the formation of cross-linked LAL. Furthermore, the physicochemical and structural parameters were highly interrelated with cross-linked LAL content (|r| > 0.9). The outcomes provided a novel avenue and theoretical basis for minimizing LAL formation in SPPI and improving the nutrition and safety of SPPI.

Sustainable Soil Additives for Water and Micronutrient Supply: Swelling and Chelating Properties of Polyaspartic Acid Hydrogels Utilizing Newly Developed Crosslinkers.

Drought and water shortage are serious problems in many arid and semi-arid regions. This problem is getting worse and even continues in temperate climatic regions due to climate change. To address this problem, the use of biodegradable hydrogels is increasingly important for the application as water-retaining additives in soil. Furthermore, efficient (micro-)nutrient supply can be provided by the use of tailored hydrogels. Biodegradable polyaspartic acid (PASP) hydrogels with different available (1,6-hexamethylene diamine (HMD) and L-lysine (LYS)) and newly developed crosslinkers based on diesters of glycine (GLY) and (di-)ethylene glycol (DEG and EG, respectively) were synthesized and characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) and regarding their swelling properties (kinetic, absorbency under load (AUL)) as well as biodegradability of PASP hydrogel. Copper (II) and zinc (II), respectively, were loaded as micronutrients in two different approaches: in situ with crosslinking and subsequent loading of prepared hydrogels. The results showed successful syntheses of di-glycine-ester-based crosslinkers. Hydrogels with good water-absorbing properties were formed. Moreover, the developed crosslinking agents in combination with the specific reaction conditions resulted in higher water absorbency with increased crosslinker content used in synthesis (10% vs. 20%). The prepared hydrogels are candidates for water-storing soil additives due to the biodegradability of PASP, which is shown in an exemple. The incorporation of Cu(II) and Zn(II) ions can provide these micronutrients for plant growth.

Up- and Down-Regulation of Enzyme Activity in Aggregates with Gold-Covered Magnetic Nanoparticles Triggered by Low-Frequency Magnetic Field.

The modern global trend toward sustainable processes that meet the requirements of "green chemistry" provides new opportunities for the broad application of highly active, selective, and specific enzymatic reactions. However, the effective application of enzymes in industrial processes requires the development of systems for the remote regulation of their activity triggered by external physical stimuli, one of which is a low-frequency magnetic field (LFMF). Magnetic nanoparticles (MNPs) transform the energy of an LFMF into mechanical forces and deformations applied to enzyme molecules on the surfaces of MNPs. Here, we demonstrate the up- and down-regulation of two biotechnologically important enzymes, yeast alcohol dehydrogenase (YADH) and soybean formate dehydrogenase (FDH), in aggregates with gold-covered magnetic nanoparticles (GCMNPs) triggered by an LFMF. Two types of aggregates, "dimeric" (with the enzyme attached to several GCMNPs simultaneously), with YADH or FDH, and "monomeric" (the enzyme attached to only one GCMNP), with FDH, were synthesized. Depending on the aggregate type ("dimeric" or "monomeric"), LFMF treatment led to a decrease (down-regulation) or an increase (up-regulation) in enzyme activity. For "dimeric" aggregates, we observed 67 ± 9% and 47 ± 7% decreases in enzyme activity under LFMF exposure for YADH and FDH, respectively. Moreover, in the case of YADH, varying the enzyme or the cross-linking agent concentration led to different magnitudes of the LFMF effect, which was more significant at lower enzyme and higher cross-linking agent concentrations. Different responses to LFMF exposure depending on cofactor presence were also demonstrated. This effect might result from a varying cofactor binding efficiency to enzymes. For the "monomeric" aggregates with FDH, the LFMF treatment caused a significant increase in enzyme activity; the magnitude of this effect depended on the cofactor type: we observed up to 40% enzyme up-regulation in the case of NADP+, while almost no effect was observed in the case of NAD+.

How the Crosslinker Amount Influences the Final Properties of Hydroxyethyl Methacrylate Cryogels.

The investigation of the mechanical, thermal, and adsorption properties of hydroxyethyl methacrylate (HEMA) cryogels as a function of a reactant ratio is herein reported to better address materials for specific applications. To this aim, cryogels have been synthesized using different monomer/crosslinker (N,N'-methylene-bisacrylamide-MBAA) ratios. The study of SEM images made it possible to identify the trend in the material's macroporosity. As would be expected, the average measured pore width decreased as the amount of MBAA increased while the number of pores grew. Swelling capacity ranges from 8.7 gW/ggel (grams of water per gram of gel) to 9.3 gW/ggel. These values are strictly connected with the pore's size and distribution, revealing that the water uptake for the most crosslinked sample is inferior to other samples. The equilibrium-adsorption capacity (Qe) towards the methylene violet (MV) was also assessed, revealing no remarkable differences after 24 h of a batch test. As expected, thermogravimetric analysis (TGA) also showed no significant changes in stability that ranged from a maximum weight loss temperature (T Max) of 420 °C to 425 °C, which increased as a function of crosslinker content. Conversely, compression strength measurements showed a notable difference of about 50% in modulus (Ec), moving from the higher to the lower HEMA/MBAA ratio. These new comparative results indicate how slight variations in the reactant's ratio can steadily improve the mechanical properties of the HEMA cryogel without affecting its adsorption efficiency. This can be helpful in the design of materials for water and energy purposes. Since swelling properties are needed in the case of biomedical applications, the HEMA/MBAA ratio should be tuned versus high values.

A reactive electrochemomechanical theory for growth and remodeling of polyelectrolyte hydrogels and application to dynamic polymerization of DNA hydrogels

This study develops a framework for growth and remodeling of active polyelectrolyte hydrogels that accounts for effects of compositional changes on the mechanical response. By developing a reactive electrochemomechanical theory, thermodynamical constraints upon reactive and remodeling processes are elucidated within a general framework that allows any number of chemical reactions to evolve the response of the gel and transfer mass and charge between constituents. Fully coupled, nonlinear constitutive relations are adopted for molar fluxes, allowing exploration of effects including cross-diffusion, electrophoresis, and electro-osmosis. A robust finite element implementation is developed in the open source FEBio software (febio.org) by exploiting an equivalence between electrochemomechanics and mixture theory. The implementation is verified against analytical solutions for free swelling, and a proper reduction to a prior chemomechanical theory is demonstrated for neutral gels swollen only by a solvent with no solutes. The theory and implementation are then applied to model the tunable large swelling achieved through dynamic polymerization of DNA crosslinkers seen in our recently developed experimental hydrogel system (Cangialosi et al., 2017). A novel constitutive model for reaction-driven evolution of the locking stretch λL in a non-Gaussian mechanical free energy was developed, where the increasing concentration of DNA crosslinkers makes further swelling energetically favorable. With a single free parameter, excellent agreement was found between measured and predicted equilibrium swelling ratios. This study demonstrated the ability to extend the electrochemomechanical framework to include chemical reactions and composition-aware constitutive models, and showed that development of reactive models allows simulation of complex dynamic polymerization phenomena not treated before. The theoretical frame here can be further expanded in scope to incorporate additional non-ideal and nonlinear phenomena.

Preparation of Low-Molecular-Weight Polyacrylamide as the Delayed Crosslinking Plugging Agent for Drilling Fluid.

Deep wells and ultra-deep wells often encounter cracks, karst caves, and other developed strata, which can lead to leakage during drilling. Conventional bridge slurry plugging technology is prone to leaking due to the poor plugging effect of the plugging agent. The gel plugging agent possesses characteristics of flexible plugging and adaptive matching of formation leakage channels. It can fill cracks or caves and enhance the pressure-bearing capacity of the formation. A controllable crosslinking plugging agent based on low-molecular-weight polyacrylamide was studied. Polyacrylamide with different molecular weights is synthesized from acrylamide and an initiator. A crosslinking time-controllable polymer is synthesized from low-molecular-weight polyacrylamide by adding crosslinking agent and retarder. The low-molecular-weight polyacrylamide plugging agent has low viscosity before gelation and good fluidity in the wellbore. After being configured on the ground, it is transported by pipeline and sent underground to reach the thickening condition. The gel solution rapidly solidifies, and its strength improves after high-temperature crosslinking. The synthesis conditions of the polymer were as follows: a monomer concentration of 9%, initiator 3.5%, synthesis temperature of 65 °C, and hydrogen peroxide initiator. The optimal formula of the gel plugging agent is as follows: a polymer concentration of 6%, a crosslinking agent concentration of 1%, and a retarder concentration of 8%. The generated polymer molecular structure contains amide groups. This crosslinking time-controllable plugging agent based on low-molecular-weight polyacrylamide has stable rheology, and its temperature resistance can reach 150 °C. At 150 °C, the gelation time can be controlled by adjusting the concentration of retarder, and the longest can reach 4 h. The plugging efficiency of the gel plugging agent is more than 95%. With the increase in seam width, the pressure of the gel plugging agent gradually decreases.

The Effects of a Crosslinking Agent on the Microrheological Properties and Cellular Structure of Silicone Rubber Foam Prepared via a Green Process.

Chemical foaming technology is widely used in the preparation of silicone rubber foam and is attributable to its one-step molding capability and eco-friendly production processes. The microrheological properties of silicone rubber play a pivotal role during the foaming process. In this study, Rheolaser Lab (Formulaction, Toulouse, France) was used to conduct in situ examinations for the influence of a crosslinking agent on the microrheological properties of silicone rubber foam for the first time. This study monitors the entire reaction process of silicone rubber foam from liquid to solid, as well as the matching of crosslinking and foaming reactions. Various parameters, including solid-liquid balance, elasticity index, and macroscopic viscosity index, are measured to analyze the microrheological properties of silicone rubber foam. The results show that the silicone rubber foam exhibits good microrheological properties, thereby demonstrating excellent performance at a crosslinking agent content of 2%. Through adjusting the experimental conditions, a sustainable and efficient approach was proposed for better cellular structure control in the industrial preparation of silicone rubber foam.

Thermomechanical response of liquid crystal elastomers: role of crosslinker density

In this work thermomechanical properties of main-chain liquid crystal elastomers (MC-LCEs) with different degrees of crosslinking were investigated, and gradual loss of thermomechanical response was observed on repetitive measurements. Specifically, six samples of MC-LCEs were prepared, with crosslinker-to-mesogen relative concentration ranging from 5% to 10% in steps of 1%. The obtained results were then compared to thermomechanical response of side-chain liquid crystal elastomers (SC-LCEs). Additionally, thermomechanical response of polymer dispersed main-chain liquid crystal elastomers (MC-PDLCEs) was investigated. Results indicate that in MC-LCEs the concentration of crosslinker defines thermomechanical response and affects stability of the system. The loss of thermomechanical response is negligible in the case of crosslinker to mesogen ratio being the smallest, namely in 5% sample, and it is unaffected by glasslike to nematic phase transition. SC-LCEs do not show any sign of such behaviour and remain stable after several cycles of thermomechanical measurements.

Suspension electrospinning of SBR latex combined with photo-induced crosslinking: control of nanofiber composition, morphology, and properties

Suspension electrospinning of a styrene-butadiene rubber (SBR) latex coupled with photo-induced crosslinking in ambient conditions is proposed as a rapid method to prepare ultrafine shape-stable rubber fibrous membranes. Polyethylene oxide (PEO) is used as template polymer and can eventually be removed from the nanostructured membrane by a simple water treatment. A multifunctional thiol crosslinker and an appropriate photo-initiating system are added to the latex to allow the fast and efficient photo-induced crosslinking of the nanofibers, based on thiol addition to the SBR double bonds, as demonstrated by real-time Infrared spectroscopy analyses. It is proved that by varying the PEO template polymer and the thiol crosslinker content, a fine control of the chemical composition, morphology, water solubility, and thermal properties of the nanofibrous membranes is ensured. Moreover, comparable mechanical properties to those of fibrous membranes produced by conventional electrospinning of organic solvent-based solutions are obtained, clearly showing the attractiveness of the present method, especially in terms of process sustainability.Graphical abstract