Low Degree Of Cross-linking Research Articles

Eco-friendly and novel tannin-based wood adhesive enhanced with cellulose nanofibrils grafted by hyperbranched polyamides

Tannin-based adhesives, as a natural biobased adhesive, have the potential to expand their application in wood industry as substitutes for traditional adhesives. In this study, cellulose nanofibrils and hyperbranched polyamides (HBPA) were studied to address the challenges associated with the low crosslinking degree and poor water resistance characteristics of condensed tannin-based wood adhesives. The modification strategy focuses on grafting oxidized cellulose nanofibrils with hyperbranched polyamides through the Schiff base reaction. Comprehensive analyses, including FTIR, XPS, XRD, and TG, confirm the successful binding of oxidized cellulose nanofibrils with hyperbranched polyamides, demonstrating their potential to enhance the properties of tannin adhesives. Furthermore, the investigation about bonding strength, and water resistance of tannin adhesives reveal significant improvements in the mechanical and water resistance properties through this modification strategy. In particular, the maximum wet shear strength is 0.7 MPa, meeting the requirements for Class II plywood. This study provides valuable insights into improving the performance of tannin adhesives, offering promising implications for broader applications and contributing to eco-friendly practices in the wood industry.

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.

Iron protoporphyrin IX-hyaluronan hydrogel-supported luminol chemiluminescence for the detection of nitric oxide in physiological solutions

Due to its role as a free radical signal-transducing agent with a short lifespan, precise measurement of nitric oxide (●NO) levels presents significant challenges. Various analytical techniques offer distinct advantages and disadvantages for ●NO detection. This research aims to simplify the detection process by developing a hydrogel system using iron(III)-protoporphyrin IX (hemin)-loaded hyaluronan for the detection of ●NO in solution. Various hydrogel formulations were created, and the effects of their components on hydrogel-supported luminol chemiluminescence (CL) kinetics, radical scavenging, and physicochemical properties were analysed through factorial analysis. The candidate formulations were then evaluated using two ●NO donors. An increase in the degree of crosslinking in unloaded formulations enhanced interactions with the CL reaction components, hydrogen peroxide (H2O2) and luminol, thereby affecting light generation. However, hemin loading negated these effects, resulting in more prominent luminescence kinetics in formulations with lower crosslinking degrees. Similarly, ●NO influenced the kinetics differently, interacting with both the CL reaction and hydrogel components. Hemin-loaded formulations exhibited enhanced signal propagation when exposed to ●NO, followed by H2O2 and luminol, whereas reversing the order of addition inhibited this propagation. The magnitude of these luminescence changes depended on the type and concentration of the ●NO donor, demonstrating greater sensitivity to ●NO levels compared to amperometric sensing. These findings suggest that the studied hydrogel platform has potential for the facile and accurate detection of ●NO in solution, requiring minimal sample sizes.

Correlation between synthesis parameters and hyperelasticity of hydrogels: Experimental investigation and theoretical modeling

The mechanical properties of hydrogels are significantly influenced by synthesis parameters. Although the mapping from the space of synthesis parameters to the space of properties has been investigated experimentally, a quantitative theoretical framework is still lacking. In this work, the effect of synthesis parameters on the hyperelastic behaviors of hydrogels was experimentally studied. Subsequently, we conducted theoretical analysis by combining the constitutive model and polymer physics to quantify the correlation between synthesis parameters (the initial water content, current water content, and degree of cross-linking) and hyperelasticity (the elastic modulus, degree of entanglement, and stress-stretch ratio curve) of hydrogels. The internal relation between critical polymer content for entanglement and both the initial water content and degree of cross-linking arises from the scaling laws. By analyzing the critical polymer content for entanglement and comparing it with the current polymer content, hydrogels are categorized as either cross-linking-dominated or entanglement-dominated. The current study indicates that a low degree of cross-linking, i.e., a long-chain structure, is an important prerequisite for plenty of entanglements. Hydrogels with low cross-linking are highly entangled, whether they possess high initial water content/low current water content or low initial water content/high current water content. This work paves the way for the systematic design of synthesis parameters, thereby guiding the modulation and optimization of the overall mechanical properties and the application of hydrogels.

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.

Effects of Chemical Composition and Cross-Linking Degree on the Thermo-Mechanical Properties of Bio-Based Thermosetting Resins: A Molecular Dynamics Simulation Study.

Bio-based epoxy resins have received significant attention in terms of concerns regarding carbon emission. Epoxidized soybean oil (ESO) derived from sustainable feedstock has been widely used to blend with traditional diglycidyl ether of bisphenol-A (DGEBA) to replace some of the petroleum-based components. In this work, molecular dynamics (MD) simulations were applied to track the network formation and predict the performance of methyl hexahydrophthalic anhydride (MHHPA)-cured ESO/DGEBA blend systems. The effects of ESO content and cross-linking degree on the mass density, volumetric shrinkage, glass transition temperature (Tg), coefficient of thermal expansion (CTE), Young's modulus, yield strength, and Poisson's ratio of the epoxy resin were systematically investigated. The results show that systems with high ESO content achieve gelation at low cross-linking degree. The Tg value, Young's modulus, and yield strength increase with the increase in cross-linking degree, but the CTE at the glassy state and Poisson's ratio decrease. The comparison results between the simulated and experimental data demonstrated that the MD simulations can accurately predict the thermal and mechanical properties of ESO-based thermosets. This study gains insight into the variation in thermo-mechanical properties of anhydride-cured ESO/DGEBA-based epoxy resins during the cross-linking process and provides a rational strategy for optimizing bio-based epoxy resins.

The Amount of Cross-Linker Influences Affinity and Selectivity of NanoMIPs Prepared by Solid-Phase Polymerization Synthesis.

The cross-linker methylene-bis-acrylamide is usually present in nanoMIPs obtained by solid-phase polymerization synthesis at 2 mol% concentration, with very few exceptions. Here, we studied the influence of variable amounts of methylene-bis-acrylamide in the range between 0 (no cross-linker) and 50 mol% concentration on the binding properties of rabbit IgG nanoMIPs. The binding parameters were determined by equilibrium binding experiments and the results show that the degree of cross-linking defines three distinct types of nanoMIPs: (i) those with a low degree of cross-linking, including nanoMIPs without cross-linker (0-05 mol%), showing a low binding affinity, high density of binding sites, and low selectivity; (ii) nanoMIPs with a medium degree of cross-linking (1-18 mol%), showing higher binding affinity, low density of binding sites, and high selectivity; (iii) nanoMIPs with a high degree of cross-linking (32-50 mol%), characterized by non-specific nanopolymer-ligand interactions, with low binding affinity, high density of binding sites, and no selectivity. In conclusion, the results are particularly relevant in the synthesis of high-affinity, high-selectivity nanoMIPs as they demonstrate that a significant gain in affinity and selectivity could be achieved with pre-polymerization mixtures containing quantities of cross-linker up to 10-20 mol%, well higher than those normally used in this technique.

Synthesis of yolk–shell COF with corrole and electrocatalytic property of Co-doped COF for oxygen reduction reaction

Abstract Covalent organic polymers (COP) were synthesized by polymerizing 5,10,15-tris(4-aminophenyl)corrole (TAPC) and terephthalaldehyde in the presence of acetic acid. Yolk–shells and filled structures were obtained after ripening of COP synthesized with low and high acetic acid/TAPC, respectively. The low cross-linking degree of COP synthesized by low acetic acid/TAPC resulted in a yolk–shell structure due to the easy dissolution of the interior. The Co-doped yolk–shell showed higher electrocatalytic activity for the oxygen reduction reaction than the filled structure.

ToF-SIMS analysis of ultrathin films and their fragmentation patterns.

Organic thin films are of great interest due to their intriguing interfacial and functional properties, especially for device applications such as thin-film transistors and sensors. As their thickness approaches single nanometer thickness, characterization and interpretation of the extracted data become increasingly complex. In this study, plasma polymerization is used to construct ultrathin films that range in thickness from 1 to 20 nm, and time-of-flight secondary ion mass spectrometry coupled with principal component analysis is used to investigate the effects of film thickness on the resulting spectra. We demonstrate that for these cross-linked plasma polymers, at these thicknesses, the observed trends are different from those obtained from thicker films with lower degrees of cross-linking: contributions from ambient carbon contamination start to dominate the mass spectrum; cluster-induced nonlinear enhancement in secondary ion yield is no longer observed; extent of fragmentation is higher due to confinement of the primary ion energy; and the size of the primary ion source also affects fragmentation (e.g., Bi1 versus Bi5). These differences illustrate that care must be taken in choosing the correct primary ion source as well as in interpreting the data.

Preparation and wear resistance of water-based UV curable ink

ABSTRACT UV water-based inks have disadvantages such as slow curing speed and low degree of crosslinking. In this paper, the copolymer P(MMA-r-HEMA) was prepared by traditional free radical polymerization using methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) as monomers, and the copolymer P(MMA-r-HEMA) was modified by acrylic acid (AA) to synthesis completely water-soluble acrylic prepolymer P(MMA-r-HEMA)-g-AA. Triethylenetetramine reacted with glycidyl methacrylate (GMA) to yield a multifunctional reactive diluent TGMA. Secondly, acrylic prepolymer P(MMA-r-HEMA)-g-AA, multifunctional reactive diluent TGMA and photoinitiator were used to prepare water-based UV curable ink. The influence of the type and quality of photoinitiator, the relative molecular weight and mass fraction of P(MMA-r-HEMA)-g-AA, the number of functional groups and mass fraction of TGMA on the UV ink curing speed and the wear resistance of the ink film were discussed. When the mass fraction of the photoinitiator TPO was 1%, the number-average relative molecular mass of the prepolymer was 1.67 × 104 g/mol and the mass fraction was 60%, the number of functional groups of the reactive diluent was 6 and the mass fraction was 40%, the light curing of UV water-based ink was completed in 0.1 s, and the mass loss after 50 times abrasion was 0.2–0.4%.

Surface-Cross-linked Protein-like Single-Chain Nanoparticle Globules Unexpectedly Stabilized with a Low Cross-linking Degree

Surface-Cross-linked Protein-like Single-Chain Nanoparticle Globules Unexpectedly Stabilized with a Low Cross-linking Degree

In situ grown cyclodextrin metal-organic framework nanoparticles templated stripe nano-wrinkled polyamide nanofiltration membranes for efficient desalination and antibiotic removal

Nanofiltration membranes composed of polyamide (PA) and characterized by a refined, periodic stripe pattern morphology are identified as promising solutions to address the permeability-selectivity trade-off in membrane technology. Modifying the morphology of PA membranes by utilizing pre-deposited soluble nanoparticles as templates has been investigated, yet the attainment of a periodic stripe pattern using this method is still a considerable challenge. This study successfully employed cyclodextrin-based metal-organic framework (CD-MOF) nanoparticles, grown in-situ, to create periodic stripe patterns on PA membranes. Morphological characterization revealed that in-situ grown CD-MOF nanoparticles, unlike those pre-deposited through vacuum filtration which formed noticeable aggregations and large flake-like PA structures, displayed a more evenly distributed pattern with reduced aggregation, aiding in the development of a striped PA morphology. The resulting membrane, with enhanced surface area, reduced thickness, increased hydrophilicity, and lower cross-linking degree, demonstrated an impressive 617 % augmentation in pure water permeance relative to the control PA membrane, achieving 29.4 L m-2 h-1 bar-1. Furthermore, this membrane displays a 99.0 % Na2SO4 rejection and maintained over 95 % efficacy in rejecting antibiotics. This research sheds light on the mechanisms by which nanoparticle templates influence polyamide morphology and introduces an innovative approach for precisely tailoring high-performance PA membranes.

High-efficiency water-transport channels using the synergistic effect of superhydrophilic PA layer and robust BU cross-linked GO laminates

Graphene oxide (GO) membranes show immense promise in nanofiltration separation for water purification and recycling of water resources. However, pristine GO membranes often suffer from insufficient membrane stability due to swelling and low water permeance under high operation pressure, which severely limits the real-world utilization of GO membranes. Herein, a strategy involving surface modification of GO membrane with superhydrophilic polyamide (PA) layer combined with cross-linking with biurea (BU) amine, is proposed to fabricate highly permeable and robust GO membranes for dye removal from aqueous solution. The PA layer is prepared onto BU cross-linked GO membrane by in-situ interfacial polymerization, which results in superhydrophilic and negative-charged membrane surface. Moreover, the low reactivity of 2,5-diaminobenzenesulfonic acid (DBS) monomer contributes to low cross-linking degree and loose network of PA layer. The BU cross-linked GO laminates possess multi-level interlayer spacings and sufficient covalent interaction between GO interlayer due to crosslinking with BU, which offer large and robust transport channels for water molecules. PA@BU/GO hybrid membrane shows the optimum pure water permeability of 140.2 L·m−2·h−1·bar−1, with water permeance and TB rejection rate of 67.4 L·m−2·h−1·bar−1 and 99.9 %, respectively. Moreover, the membrane exhibits impressive dye/salt selectivity (the dye/NaCl separation factor is up to 873), long-term operation stability and good anti-fouling property, which makes it a potential candidate for the fractionation of dye/salts in textile wastewater. This work provides a promising idea for the development of high-performance 2D membranes with high-efficiency water transport channels using the synergistic effect of superhydrophilic PA Layer and robust BU cross-linked GO laminates.

Degradable Plasma-Polymerized Poly(Ethylene Glycol)-Like Coating as a Matrix for Food-Packaging Applications.

Currently, there is considerable interest in seeking an environmentally friendly technique that is neither thermally nor organic solvent-dependent for producing advanced polymer films for food-packaging applications. Among different approaches, plasma polymerization is a promising method that can deposit biodegradable coatings on top of polymer films. In this study, an atmospheric-pressure aerosol-assisted plasma deposition method was employed to develop a poly(ethylene glycol) (PEG)-like coating, which can act as a potential matrix for antimicrobial agents, by envisioning controlled-release food-packaging applications. Different plasma operating parameters, including the input power, monomer flow rate, and gap between the edge of the plasma head and substrate, were optimized to produce a PEG-like coating with a desirable water stability level and that can be biodegradable. The findings revealed that increased distance between the plasma head and substrate intensified gas-phase nucleation and diluted the active plasma species, which in turn led to the formation of a non-conformal rough coating. Conversely, at short plasma-substrate distances, smooth conformal coatings were obtained. Furthermore, at low input powers (<250 W), the chemical structure of the precursor was mostly preserved with a high retention of C-O functional groups due to limited monomer fragmentation. At the same time, these coatings exhibit low stability in water, which could be attributed to their low cross-linking degree. Increasing the power to 350 W resulted in the loss of the PEG-like chemical structure, which is due to the enhanced monomer fragmentation at high power. Nevertheless, owing to the enhanced cross-linking degree, these coatings were more stable in water. Finally, it could be concluded that a moderate input power (250-300 W) should be applied to obtain an acceptable tradeoff between the coating stability and PEG resemblance.

Preparation of crosslinked starches with enhanced and tunable gel properties by the cooperative crosslinking-extrusion combined modification

Due to its safety and palatability, the citric acid crosslinking modification is an excellent way to modify the properties of starch gels. However, the application of this method is restricted by the low degree of crosslinking of gels produced by this method in the hydrogel system. To produce citric acid-crosslinked starch with improved strength and tunable gel characteristics, a novel ion-esterification cooperative crosslinking-extrusion combined (CCEC) modification approach is presented in this study. The linear and nonlinear rheological characteristics of the samples were measured to evaluate the effectiveness of CCEC modification. Findings disclosed that at 0.1 % strain, the elastic modulus of the CCEC-modified starch (SC-0.5Zn2+, G' = 1522.29 ± 36.31) exhibited a significant rise of 387.27 % as compared to the elastic modulus of citric acid-crosslinked starch (SC, G' = 318.29 ± 11.62). Furthermore, changing the cation concentration allowed for efficient control of the gel's rheological characteristics. The samples were characterized by SEM, FTIR, XRD, and XPS. The CCEC-modified gels had a smaller pore size distribution and a denser honeycomb porous structure. The CCEC modification reaction involves ester bonds and electrostatic attraction. This research is essential to elucidate how coupled physicochemical modification techniques affect the manipulation of starch gel characteristics.

Ultra-permeable polyamide nanofiltration membrane modified by hydrophilic-hydrophobic alternated lignocellulosic nanofibrils for efficient water reuse

Polyamide nanofiltration (NF) membranes are instrumental in water reuse due to their capability to efficiently remove trace organic contaminants (TrOCs), which pose potential health risks. However, while the current NF membranes offer acceptable TrOC rejection, their water permeance, which is highly related to the process energy consumption in water reuse, is relatively low. To address this limitation, we introduced a novel NF membrane by incorporating a lignocellulosic nanofibril interlayer—specifically, nanowires with alternating hydrophilic-hydrophobic regions (denoted as HONW). The resultant NF membrane achieved remarkable water permeance (52.4 L m−2 h−1 bar−1) while still ensuring high TrOC retention (including endocrine-disrupting compounds, pharmaceuticals, and antibiotics). A detailed mechanistic investigation revealed that the eliminated funnel effect or introduced gutter effect induced by the HONW interlayer, improved polyamide layer structure characterized by lower cross-linking degree and higher surface wettability, and reduced interlayer resistance (due to a unique water transport pattern: hydrophilic regions absorbed water molecules while hydrophobic regions strengthened water penetration) were significantly responsible for the enhanced membrane permeance. Moreover, the membrane also demonstrated low specific energy consumption as well as outstanding stability. This investigation unveils an appealing approach for constructing the ultra-permeable NF membrane for efficient water reuse.

Electrical treeing phenomena in two‐layer silicone gel with different crosslinking degrees and its dielectric strength

AbstractSilicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel—crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength.

A new PERVAPTM membrane to enhance the dehydration of isopropanol by pervaporation

The performance of a new commercial polyvinyl alcohol (PVA) membrane (PERVAPTM 4100HF) was investigated and compared with a standard membrane (PERVAPTM 4100) for the dehydration of isopropanol (isopropyl alcohol) with an azeotropic point using pervaporation process. Both membranes were also characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and contact angle (CA) goniometer. The results showed that the PERVAP™ 4100HF was thinner (1–1.5 μm) and had a lower degree of cross-linking than the PERVAP™ 4100HF (2–3 μm). The effect of the feed water concentration and operating temperature on the membranes separation performance in terms of the permeation flux, separation factor, selectivity, and permeance was investigated. The water permeates in the PERVAP™ 4100HF (∼3350 GPU) was seven times higher than that in PERVAP™ 4100 (∼463 GPU) at 70 °C and for 7 wt.% of water concentration in the feed. The water/isopropanol selectivity of the new membrane under these operating conditions was very high (∼17,000). The total permeation flux of water and isopropyl alcohol (IPA) was increased with the feedwater concentration (0.0690–1.0275 and 0.0079–0.6384 kg/m2.hr) for PERVAP™ 4100HF and PERVAP™ 4100, respectively with feed water concentration increased from 7 to 18 wt.%. The temperature dependence of the pervaporation behaviors was investigated in detail in terms of the Arrhenius activation energy. The effect of the feedwater concentration on the Arrhenius activation energy was also studied to evaluate the mass transfer across the membrane under other operating conditions, such as high temperatures and low feedwater concentrations. The new membrane PERVAP™ 4100HF exhibited the best dehydration properties at water concentrations in the azeotropic region and below, making it possible to pervaporate even at low feedwater concentrations.

Effect of genipin crosslinking on the property of chitosan‐soy protein isolate film

AbstractGenipin (GP) as a natural crosslinker has gained much attention in the food industry on account of its high biocompatibility and safety. In this paper, chitosan (CS)‐soy protein isolate (SPI) crosslinked films were prepared using GP as a crosslinking agent. Crosslinking reaction with high contents of GP (0.03%, 0.05%) changed the rheological property of the film matrixes. The crosslinking degree was positively correlated with the content of GP, which was from 21.08 ± 3.95% of CS‐SPI‐1 to 39.66 ± 1.62% of CS‐SPI‐5. Fourier transform infrared spectroscopy spectra confirmed the crosslinking reaction. The X‐ray diffraction and scanning electron microscopy analyses indicated that the crosslinking reaction decreased the crystallinity degree and enhanced the surface roughness of CS‐SPI film, respectively. The crosslinking reaction did not significantly affect the thickness, moisture content and water solubility of CS‐SPI film. Crosslinked films presented better light barrier capacity. The tensile strength (TS) of CS‐SPI‐1 was increased by 50%, however, further increasing the contents of GP (0.03%, 0.05%) reduced the TS of the crosslinked films. With the increasing incorporation with GP, the EAB was significantly decreased, while the modulus increased from 95.76 ± 25.78 to 508.78 ± 77.95 MPa. The crosslinking reaction improved the rigidity of CS‐SPI film. Low crosslinking degree could improve thermal stability of CS‐SPI, while higher GP addition (0.03%, 0.05%) decreased the thermal stability and prolonged the degradation time of the film in soil. The results indicated that low crosslinking reaction could improve the property of CS‐SPI film, enhancing its potential application in food packaging.

Electrical Treeing Phenomena in Two-Layer Silicone Gel with Different Crosslinking Degrees and its Dielectric Strength

Silicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel - crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength.