Kinetics Of Crosslinking Reaction Research Articles

Improved direct current electrical properties of XLPE modified by graftable antioxidant and crosslinking coagent at a wide temperature range

AbstractTo enhance the DC electrical performance of cross‐linked polyethylene (XLPE), the graftable antioxidant methacrylic acid 2‐hydroxy‐3‐(4‐anilinoanilino) propyl ester (GA), which contains carbonyl and amino groups, and the crosslinking coagent trimethylolpropane trimethacrylate (TMPTMA), which contains carbonyl groups, are individually or co‐grafted onto XLPE. The slightly higher deep trap density introduced by higher grafting concentration of TMPTMA results in more significant suppression effect of conductance current and enhanced breakdown strength at a lower temperature, while the suppression effect for the conductance current at 90°C becomes weakened due to limited trap energy. Meanwhile, the deeper energy level introduced by GA suppresses the conductance current and improves the electrical strength of XLPE at 90°C more significantly. By co‐grafting, the conductance current of XLPE in a wide range temperature can be significantly reduced, especially for the temperature dependence of conductance current, which is beneficial to suppress the field strength reversal. The results of thermally stimulated current and molecular simulation show that the polar groups of two monomers introduce deep charge traps in XLPE. The co‐grafting system ensures the rationality of the crosslinking reaction kinetics and does not affect the cable manufacturing.

Evaluation of Storage Stability for Delayed-Curing Non-Iron Finishing Sensitized Fabrics via Characteristic Group and Cross-linking Reaction Kinetics

In delayed-curing and non-iron finishing, the sensitized fabric after low-temperature drying should have good surface planeness before curing at high temperatures, which implies that the finishing agent has not reacted with the cellulose fibers during storage; therefore, a suitable non-iron finishing agent is essential for achieving the above objectives. Meanwhile, there are currently no mature and efficient evaluation methods for the storage stability of sensitized fabrics. In this article, the content of characteristic groups of the sensitized fabrics with different storage conditions was measured. The storage time can be shortened from 30 to 6 days with high-temperature storage (40–60°C). The reaction kinetics equation was established under high-temperature storage; then using this equation to predict the cross-linking degree of sensitized fabrics during long-term storage at low temperature, the storage stability of sensitized fabrics can also be evaluated. The relative error of 2.5% between the predicted value and the measured value of the reaction degree showed the accuracy and effectiveness of the established method. This article provided a basis for the stability evaluation of the sensitized fabric and the selection of the finishing agent, finishing process, and storage conditions for the delayed-curing and non-ironing finishing process.

Mammalian-specific decellularized matrices derived bioink for bioengineering of liver tissue analogues: A review.

The absolute shortage of compatible liver donors and the growing number of potential recipients have led scientists to explore alternative approaches to providing tissue/ organ substitutes from bioengineered sources. Bioartificial regeneration of a fully functional tissue/organ replacement is highly dependent on the right combination of engineering tools, biological principles, and materiobiology horizons. Over the past two decades, remarkable achievements have been made in hepatic tissue engineering by converging various advanced interdisciplinary research approaches. Three-dimensional (3D) bioprinting has arisen as a promising state-of-the-art tool with strong potential to fabricate volumetric liver tissue/organ equivalents using viscosity- and degradation-controlled printable bioinks composed of hydrous microenvironments, and formulations containing living cells and associated supplements. Source of origin, biophysiochemical, or thermomechanical properties and crosslinking reaction kinetics are prerequisites for ideal bioink formulation and realizing the bioprinting process. In this review, we delve into the forecast of the potential future utility of bioprinting technology and the promise of tissue/organ- specific decellularized biomaterials as bioink substrates. Afterward, we outline various methods of decellularization, and the most relevant studies applying decellularized bioinks toward the bioengineering of in vitro liver models. Finally, the challenges and future prospects of decellularized material-based bioprinting in the direction of clinical regenerative medicine are presented to motivate further developments.

Cross-Linked Gelatine by Modified Dextran as a Potential Bioink Prepared by a Simple and Non-Toxic Process.

Essential features of well-designed materials intended for 3D bioprinting via microextrusion are the appropriate rheological behavior and cell-friendly environment. Despite the rapid development, few materials are utilizable as bioinks. The aim of our work was to design a novel cytocompatible material facilitating extrusion-based 3D printing while maintaining a relatively simple and straightforward preparation process without the need for harsh chemicals or radiation. Specifically, hydrogels were prepared from gelatines coming from three sources—bovine, rabbit, and chicken—cross-linked by dextran polyaldehyde. The influence of dextran concentration on the properties of hydrogels was studied. Rheological measurements not only confirmed the strong shear-thinning behavior of prepared inks but were also used for capturing cross-linking reaction kinetics and demonstrated quick achievement of gelation point (in most cases < 3 min). Their viscoelastic properties allowed satisfactory extrusion, forming a self-supported multi-layered uniformly porous structure. All gelatin-based hydrogels were non-cytototoxic. Homogeneous cells distribution within the printed scaffold was confirmed by fluorescence confocal microscopy. In addition, no disruption of cells structure was observed. The results demonstrate the great potential of the presented hydrogels for applications related to 3D bioprinting.

Globule and fiber formation with elastin-like polypeptides: a balance of coacervation and crosslinking.

Elastic fiber assembly is a complex process that requires the coacervation and cross-linking of the protein building block tropoelastin. To date, the order, timing, and interplay of coacervation and crosslinking is not completely understood, despite a great number of advances into understanding the molecular structure and functions of the many proteins involved in elastic fiber assembly. With a simple in vitro model using elastin-like polypeptides and the natural chemical crosslinker genipin, we demonstrate the strong influence of the timing and kinetics of crosslinking reaction on the coacervation, crosslinking extent, and resulting morphology of elastin. We also outline a method for analyzing elastin droplet network formation as a heuristic for measuring the propensity for elastic fiber formation. From this we show that adding crosslinker during peak coacervation dramatically increases the propensity for droplet network formation.

Chemo-mechanical modelling of swelling and crosslinking reaction kinetics in alginate hydrogels: A novel theory and its numerical implementation

Hydrogels are mechanically stabilized through the action of external agents which induce the formation of crosslinks in the polymer network as a consequence of transport and reactive mechanisms. Crosslinking increases the stiffness of the construct, produces inelastic deformations in the polymer network and interacts with the swelling capacity of hydrogels. The control of this process is hence crucial for fulfilling functional criteria in several technological fields, like drug-delivery or bioprinting. Nevertheless, experimental approaches for monitoring the crosslinking kinetics with the required resolution are currently missing. The development of new computational models in the field might open the way to novel investigation tools. This paper presents a thermodynamically consistent chemo-mechanical model in large deformation for reactive–diffusive mechanisms occurring during crosslinking in alginate hydrogels. The system accounts for shrinking and swelling effects, fluid movements, as well as the reaction kinetics of calcium-induced crosslinking. Crosslinks alter mechanical and diffusive properties in the hydrogel. Moreover, on the basis of thermodynamic arguments, internal stresses directly affect the crosslinking kinetics, revealing a two-way coupling between mechanics and chemistry. The model is implemented in a finite element framework, considering a monolithic coupling between chemical transport and mechanics. The computational framework allows characterizing the (experimentally inaccessible) heterogeneous distribution of mechano-chemical quantities and properties in the hydrogel. Parametric campaigns of simulations are presented to investigate hydrogels’ behaviour and compare numerical outcomes with available experimental evidence.

Freeze-Thawing-Induced Macroporous Catechol Hydrogels with Shape Recovery and Sponge-like Properties.

Catechol-containing hydrogels have been exploited in biomedical fields due to their adhesive and cohesive properties, hemostatic abilities, and biocompatibility. Catechol moieties can be oxidized to o-catecholquinone, a chemically active intermediate, in the presence of oxygen to act as an electrophile to form catechol-catechol or catechol-amine/thiol adducts. To date, catechol cross-linking chemistry to fabricate hydrogels has been mostly performed at room temperature. Herein, we report large increases in catechol cross-linking reaction kinetics by the freeze-thawing process. The formation of ice crystals during freezing steps spatially condenses catechol-containing polymers into nearly frozen (yet unfrozen) regions, resulting in decreases in the polymeric chain distances. This environment allows great increases in catechol cross-linking kinetics, a phenomenon that can also occur during thawing steps. The increased cross-linking rate and spatial condensation in the cryogels provide unique wall and pore structures, which result in elastic, spongelike hydrogels. The moduli of the cryogels prepared by glycol-chitosan-catechol (g-chitosan-c) were improved by 3-6-fold compared to room temperature-cured conventional hydrogels, and the degree of improvement increased depending on the freezing time and the number of freeze-thawing cycles. Unlike typical cell encapsulations before cross-linking, which have often been a source of cytotoxicity, the macroporosity of cryogels allows nontoxic cell seeding with ease. This research offers a new way to utilize catechol cross-linking chemistry by freeze-thawing processes to simultaneously regulate mechanical strength and porous structures in catechol-containing hydrogels.

Reactivity of Polycyclic Aromatic Hydrocarbon Soot Precursors: Kinetics and Equilibria.

The thermodynamics and kinetics of cross-linking reactions between PAHs of various reactive edge types that are observed in soot precursors are explored using density functional theory. The forward rate constants confirm that reactions involving aryl σ-radicals are faster than others, but rate constants for reactions between aryl σ-radicals and localized π-radicals can be as large or even larger than for two aryl σ-radicals. However, rates for all cross-linking reactions between small PAHs are likely too slow to explain soot formation. The equilibrium constants show that reactions involving σ and π-radical PAHs are the most favorable at flame temperatures. Equilibrium constants for larger PAHs show that the ability to form bonded-and-stacked structures results in enhanced equilibrium constants for the reaction of two large localized π-radicals compared to those for other edge types. This suggests that combined physical and chemical interactions between larger π-radical PAHs could be important in flame environments.

Electrosprayed PMMA microcapsules containing green soybean oil-based acrylated epoxy and a thiol: a novel resin for smart self-healing coatings

For the first time, the binary components of a self-healing epoxy system was developed comprising of a green acrylated epoxy resin and its thiol-based curing agent encapsulated in a poly (methyl methacrylate) (PMMA) shell by electrospraying technique. The field emission scanning electron microscopy images revealed that the two microcapsules formed were almost spherical with rough and irregular surfaces. The average diameter of microcapsules ranged from 1.165 to 1.418 μm for the two microcapsules. FTIR spectra and thermal analysis were used to investigate the encapsulation of acrylated epoxy resin and thiol curing agent in PMMA as well as the kinetics of crosslinking reaction between the two components. Based on FTIR spectra, the thiol curing agent was involved in the crosslinking reaction with the epoxy group (810 cm−1) and the C = C segment (1634 and 1613 cm−1) of acrylated epoxy resin. The DSC results indicated an exothermic peak (at 65 °C) proving that this system is efficient in self-healing epoxy resins for coating applications. Furthermore, the ability of epoxy coatings to protect the scratched coating substrate from corrosion media (the healing performance) without microcapsule, with dual microcapsules, single healing agent-containing microcapsule and single curing agent-containing microcapsule were also evaluated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The results were in line with the potentiodynamic polarization and the EIS. The highest self-healing efficiency (78%) was obtained for binary capsule concentration of 1%, indicating presence of sufficient amount of material to heal the cracks.

Kinetics of Cross-Linking Reaction of Epoxy Resin with Hydroxyapatite-Functionalized Layered Double Hydroxides.

The cure kinetics analysis of thermoset polymer composites gives useful information about their properties. In this work, two types of layered double hydroxide (LDH) consisting of Mg2+ and Zn2+ as divalent metal ions and CO32− as an anion intercalating agent were synthesized and functionalized with hydroxyapatite (HA) to make a potential thermal resistant nanocomposite. The curing potential of the synthesized nanoplatelets in the epoxy resin was then studied, both qualitatively and quantitatively, in terms of the Cure Index as well as using isoconversional methods, working on the basis of nonisothermal differential scanning calorimetry (DSC) data. Fourier transform infrared spectroscopy (FTIR) was used along with X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to characterize the obtained LDH structures. The FTIR band at 3542 cm−1 corresponded to the O–H stretching vibration of the interlayer water molecules, while the weak band observed at 1640 cm−1 was attributed to the bending vibration of the H–O of the interlayer water. The characteristic band of carbonated hydroxyapatite was observed at 1456 cm−1. In the XRD patterns, the well-defined (00l) reflections, i.e., (003), (006), and (110), supported LDH basal reflections. Nanocomposites prepared at 0.1 wt % were examined for curing potential by the Cure Index as a qualitative criterion that elucidated a Poor cure state for epoxy/LDH nanocomposites. Moreover, the curing kinetics parameters including the activation energy (Eα), reaction order, and the frequency factor were computed using the Friedman and Kissinger–Akahira–Sunose (KAS) isoconversional methods. The evolution of Eα confirmed the inhibitory role of the LDH in the crosslinking reactions. The average value of Eα for the neat epoxy was 54.37 kJ/mol based on the KAS method, whereas the average values were 59.94 and 59.05 kJ/mol for the epoxy containing Zn-Al-CO3-HA and Mg Zn-Al-CO3-HA, respectively. Overall, it was concluded that the developed LDH structures hindered the epoxy curing reactions.

Thermoreversible cross-linking of ethylene/propylene copolymers based on Diels–Alder chemistry: the cross-linking reaction kinetics

The kinetics of the cross-linking reaction of ethylene/propylene rubbers based on Diels–Alder chemistry was detected by the rheological method.

Post Self-Crosslinking of Phthalonitrile-Terminated Polyarylene Ether Nitrile Crystals.

A novel phthalonitrile-terminated polyaryl ether nitrile (PEN-Ph) was synthesized and characterized. The crystallization behavior coexisting with the crosslinking behavior in the PEN-Ph system was confirmed by rheological measurements. DSC was applied to study the crystallization kinetics and crosslinking reaction kinetics. Through the Avrami equation modified by Jeziorny, the nonisothermal crystallization kinetics were analyzed, and the Avrami exponent of about 2.2 was obtained. The analysis results of more intuitive polaring optical microscopy (POM) and SEM indicated that the shape of the crystals is similar to spherical. Moreover, the activation energy of the crystallization behavior and crosslinking behavior were obtained by the Kissinger method, and the values were about 152.7 kJ·mol−1 and 174.8 kJ·mol−1, respectively. This suggests that the activation energy of the crystallization behavior is lower than that of the crosslinking behavior, indicating that the crystallization behavior is more likely to occur than the crosslinking behavior and the crystals of PEN-Ph can be self-crosslinked to form single-polymer composites.

Improving Kinetics of "Click-Crosslinking" for Self-Healing Nanocomposites by Graphene-Supported Cu-Nanoparticles.

Investigation of the curing kinetics of crosslinking reactions and the development of optimized catalyst systems is of importance for the preparation of self-healing nanocomposites, able to significantly extend their service lifetimes. Here we study different modified low molecular weight multivalent azides for a capsule-based self-healing approach, where self-healing is mediated by graphene-supported copper-nanoparticles, able to trigger “click”-based crosslinking of trivalent azides and alkynes. When monitoring the reaction kinetics of the curing reaction via reactive dynamic scanning calorimetry (DSC), it was found that the “click-crosslinking” reactivity decreased with increasing chain length of the according azide. Additionally, we could show a remarkable “click” reactivity already at 0 °C, highlighting the potential of click-based self-healing approaches. Furthermore, we varied the reaction temperature during the preparation of our tailor-made graphene-based copper(I) catalyst to further optimize its catalytic activity. With the most active catalyst prepared at 700 °C and the optimized set-up of reactants on hand, we prepared capsule-based self-healing epoxy nanocomposites.

In-situ visualization of the kinetics of low temperature thiol-epoxy crosslinking reactions by using a pH-responsive epoxy resin

The kinetics of the crosslinking reactions of model thiol-epoxy polymer networks (TEPNs) was visualized by tracking their pH variations. The color transitions of the TEPNs were monitored in real-time and the results were correlated with those of Fourier transform infrared (FT-IR) spectroscopy, isothermal differential scanning calorimetry (DSC), and oscillational rheology. The influence of the glass transition temperatures (Tg) of the TEPNs on the kinetics of the low temperature crosslinking reactions was investigated by employing various TEPNs with different crosslinker functionalities. The mechanical and chemical properties of the TEPNs were also determined and the trends in the data were related to the crosslinking densities (vcvc) calculated from dynamic mechanical analysis (DMA) measurements.

Influence of microstructure in nitrile polymer on curing characteristics and mechanical properties of carbon black-filled rubber composite for seal applications

Acrylonitrile butadiene rubber (NBR) is widely used in seal applications due to its excellent oil resistance. In this article, carbon black-filled NBR composites, which differed in their acrylonitrile (ACN) and butadiene content ratios, were prepared and their curing characteristics and mechanical properties were investigated. Curing characteristics were investigated by measuring chemical kinetics and onset temperature of cross-linking reaction. Cross-linking density was measured by the volume swelling test. Mechanical properties, oil resistance, and compression set (CS) tests were also conducted. From these results, it was found that the microstructure in NBR polymer is closely connected to the curing characteristics and mechanical properties of the composite. On increasing the ACN content, Shore A hardness, tensile strength at break, elongation at break, oil resistance, and CS were raised, while, on the other hand cross-linking density, kinetics of cross-linking reaction, and bound rubber content were decreased.

Synthesis of a novel UV crosslinking waterborne siloxane–polyurethane

Abstract A novel UV crosslinking waterborne siloxane–polyurethane (UV-WPU) was synthesized using isophorone diisocyanate (IPDI), glycidyl azide polymer (GAP), polytetramethylene glycol (PTMG), dihydroxybutyl terminated polydimethylsiloxane (DHPDMS), dimethylol propionic acid (DMPA) as main materials. The structure of UV-WPU was verified using Fourier transform infrared spectroscopy (FTIR). Attenuated total reflectance (ATR) was used to study the UV crosslinking reaction kinetics of UV-WPU under UV irradiation. The properties of UV-WPU coatings by UV and thermal curing was comparatively analyzed by thermal gravimetric analysis (TGA), as well as gel fraction, water resistance and water contact measurements. The gel fraction and TGA analyses also confirmed the formation of crosslinking structure in the UV-WPU structure after UV curing process. UV-WPU cured by UV showed good thermal stability, surface properties and water resistance.

Comparison of Isothermal with Nonisothermal Kinetics for Ethylene-Vinyl Acetate Cross-Linking Reaction in the Solid State

Cross-linking reaction kinetics of ethylene-vinyl acetate (EVA) copolymer initiated with dicumyl peroxide is studied by differential scanning calorimetry (DSC) and a cross-linking rheometer. As the degree of cross-linking (α) is less than 0.30, EVA can flow relatively freely because of insufficient cross-linking. As α ranges from 0.31 to 1, there is more of the cross-linking reaction, and the polymer becomes fully cross-linked in the later stage of the reaction so that three-dimensional cross-linked nets have been constructed. New kinetics approaches are proposed on the basis of the cross-linking parameters measured with the cross-linking rheometer incorporated into Hill and Avrami mathematical equations. As the cross-linking rheometer is popular in manufacturing the cross-linked EVA, the approaches are simpler and more convenient than the DSC method for fast studying kinetics of the cross-linking reaction of polymer in solid or melting state. The total cross-linking reaction rate changes with α, and the apparent activation energy is 91.2–175.0 kJ/mol.

Evaluation of the crosslinking reaction kinetics of cationic polyol dispersions with differential scanning calorimetry and dielectric analysis

The crosslinking reaction kinetics of two-component waterborne polyurethanes (2K-WPUs) composed of cationic polyol dispersions and hydrophilically modified hexamethylene diisocyanate (HDI) tripolymer were investigated by differential scanning calorimetry (DSC) and dielectric analysis (DEA) techniques. DSC data fit for the 2K-WPUs was carried out with Málek's mechanism function method. The kinetic parameters and kinetic models of crosslinking reaction were determined by the kinetic analysis with Málek's method. The result showed that the crosslinking process of the reaction followed an autocatalytic reaction. Sestak–Berggren model (S–B model) could favorably describe the crosslinking reaction process of the studied 2K-WPUs. The reaction rate curves derived from the experimental data showed a good agreement with the theoretical calculation under 5–20°Cmin−1 heating rate. Isothermal DSC and DEA of the crosslinking process of the 2K-WPUs were used to confirm the obtained kinetics equations. The conversion–time curves from isothermal DSC matched favorably with the calculated curves from the obtained kinetic equations, and the log ion viscosity–time curves from isothermal DEA matched roughly with the conversion–time curves from DSC.

Crosslinking reaction and properties of two‐component waterborne polyurethane from terpene‐maleic ester type epoxy resin

AbstractA two‐component waterborne polyurethane (2K‐WPU) is prepared with the terpene‐maleic ester type epoxy resin‐based polyol dispersion and a hydrophilically modified hexamethylene diisocyanate tripolymer. Laser particle size analyzer and transmission electron microscopy are used to characterize the particle size distribution and the micromorphology of the 2K‐WPU. Crosslinking reaction kinetics of the 2K‐WPU is examined by fourier transform infrared spectrometry (FTIR) spectra. In the preliminary stage of the crosslinking reaction, it shows a very good fit with a second order reaction kinetics, and the apparent activation energy is 94.61 kJ mol−1. It is also shown from the FTIR spectra that the complete crosslinking reaction of the 2K‐WPU needs 7 h at 70°C. The crosslinked products of the 2K‐WPU have good thermal resistant properties, with glass‐transition temperatures (Tg) in the range of 35–40°C and 10% weight loss temperatures (Td) in the range of 275–287°C. The films obtained from the crosslinked products have good water‐resistance, antifouling, blocking resistance properties and impact strength of &gt;50 cm, flexibility of 0.5 mm, adhesion of 1 grade, pencil hardness of HB‐2H. The pencil hardness and thermal‐resistant properties of the crosslinked products increase with the molar ratio of isocyanate (NCO) group to hydroxyl (OH) group. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Kinetics of the crosslinking reaction of nonionic polyol dispersion from terpene-maleic ester-type epoxy resin

The bulk crosslinking reaction kinetics of a novel two-component waterborne polyurethanes (2K-WPUs) composed of a bio-resin-based polyol dispersion and a hydrophilically modified hexamethylene diisocyanate tripolymer are investigated by freeze–drying and differential scanning calorimetry (DSC) technique at different heating rates. The data fit for the above two components is implemented with the nth-order kinetics equation and Malek’s mechanism function method, respectively. The kinetic parameters of crosslinking reaction are determined by the kinetic analysis of the data obtained from the thermal treatment, and then the kinetic model is built. The results indicate that the nth-order model deduced from Kissinger and Crane equation has great distinction with the experimental data, while the Malek analytic mechanism shows that the crosslinking process of the crosslinking reaction follows an autocatalytic reaction. The two-parameter (m and n) autocatalytic model (S–B model) can well describe the crosslinking reaction process of the studied 2K-WPU. The DSC curves derived from the experimental data show a good agreement with the theoretical calculation under 5–20 °C min−1 heating rate. The results provide theoretical basis for the choice of the manufacturing process and the optimization of processing window.