Ionic Cross-linked Network Research Articles

Effect of in situ synthesis reaction of methacrylic acid (MAA)/zinc oxide (ZnO) on frictional wear of metals during compounding

During prolonged operation, the end face of the internal mixer, a crucial component in rubber processing, experiences wear, resulting in an increased gap between the mixing chamber and the end face. This gap can lead to material leakage and reduced mixing efficiency, negatively impacting rubber properties. To address this issue, researchers have introduced dynamic covalent bonds into the molecular rubber chains, giving the material self-healing properties. This advancement is essential for extending rubber lifespan and reducing production costs. One common approach involves adding methacrylic acid (MAA) and excess zinc oxide (ZnO) to create ionic crosslinking networks, limiting covalent crosslinking and enabling in-situ polymerization of MAA/ZnO, resulting in self-healing capabilities. However, the strong acidity and corrosive nature of MAA can cause metal wear. In our study, we mechanically blend MAA with ZnO to produce zinc methacrylate (ZDMA)/rubber composites. We investigate the in-situ synthesis mechanism of MAA and ZnO and assess the impact of MAA on the friction and wear of the internal mixer's end face. Our findings reveal that ZDMA ion pairs form an “ion cross-linked network” within the rubber chain, hindering SiO2 particle dispersion and increasing aggregation within the rubber matrix. This compromises dispersion and leads to abrasive wear from SiO2 particles, corrosive wear from high-temperature water vapor, and corrosive wear from MAA. Additionally, excessive ZDMA self-polymerization alters SiO2 particle agglomerates. The strong acidity of MAA and the “ion cross-linked network” within the rubber matrix significantly affect SiO2 particle dispersion, friction coefficients, metal surface roughness, and metal wear. Our comprehensive analysis, including SEM, dispersion, RPA, metal surface morphology, and CSM friction wear tests, identifies the optimal cross-linking effect with the addition of 15 phr of MAA, resulting in a well-defined “ion cross-linked network” within the rubber matrix, enhancing rubber performance. However, SiO2 particle dispersion is compromised, leading to increased agglomeration and heightened metal wear.

Recyclable and super-stretchable conductive elastomeric composites with a carbon nanostructure interconnected network structure for effective thermal management and excellent electromagnetic wave suppressor

ABSTRACT The increasing demand for flexible electronics and portable gadgets has resulted in an increase in the amount of emitted EM radiation in recent years. Conductive carbon black (VCB XC 72) is a quasi-graphitic structure of clustered carbon particles that was deemed an ideal material for the development of extremely flexible electromagnetic interference (EMI) shielding materials. The sequential solution and melt mixing process has been used to generate a flexible and recyclable zinc oxide cross-linked, and VCB XC 72 nanofiller reinforced EMI shielding material. The ionic cross-linked network, created by other self-clustering ion duplets of Zn2+ ions, gave rise to the amazing recycling and reprocessing abilities of carboxylated acrylonitrile butadiene rubber (XNBR). The cross-linked XNBR and conductive black combination formed a tunable inferential framework that provided absorption, reflection, and multiple reflection shielding mechanisms. Based on the findings of the morphological study, it has been determined that the scattered and distributed carbon black clusters included inside XNBR rubber are creating the pathway for electrical hopping. As a result, the electrical percolation threshold has been lowered, and EMI shielding has significantly improved. The rubber composites had improved thermal characteristics in addition to having outstanding mechanical performances. Hopefully, these findings will pave the way forward for the development of smart electronic devices and environmentally friendly EMI shielding materials.

Facile and eco-friendly functionalization of basalt fiber with polyelectrolyte complex toward excellent interfacial adhesion of epoxy composites

In an attempt to increase the interfacial adhesion of basalt fiber/epoxy composites, a surface modification strategy by constructing ternary polyelectrolyte complex consisted of silane coupling agent-phytic acid-polyethyleneimine via dip-coating is proposed for the first time in the present work. The as-prepared functionalized basalt fiber composite exhibits markedly improved interfacial shear strength, with an average value of 81.9 ± 4.5 MPa, 75% augmentation over that of untreated basalt fiber composite. The reinforcing mechanisms are attributed to the multiple interactions of ionic cross-linked network, covalent and hydrogen bonding at interphase, also including the improved wettability and relatively rough fiber surface. Together with facile preparation approach, nature and low-cost material, the ternary polyelectrolyte complex system developed in this paper offers great potential in practical functionalization of basalt fiber, which could be hopefully extended to other high-performance fibers.

Facile Fabrication of Eucommia Rubber Composites with High Shape Memory Performance.

We processed a series of shape memory Eucommia rubber (ER) composites with both carbon–carbon and ionic cross-linking networks via a chemical cross-linking method. The influence of the carbon–carbon cross-linking and ion cross-linking degree of ER composites on curing, mechanical, thermal, and shape memory properties were studied by DSC, DMA, and other analytical techniques. Dicumyl peroxide (DCP) and zinc dimethacrylate (ZDMA) played a key role in preparing ER composites with a double cross-linking structure, where DCP initiated polymerization of ZDMA, and grafted ZDMA onto polymer molecular chains and cross-linked rubber molecular chains. Meanwhile, ZDMA combined with rubber macromolecules to build ionic cross-linking bonds in composites under the action of DCP and reinforced the ER composites. The result showed that the coexistence of these two cross-linking networks provide a sufficient restoring force for deformation of shape memory composites. The addition of ZDMA not only improved the mechanical properties of materials, but also significantly enhanced shape memory performance of composites. In particular, Eucommia rubber composites exhibited outstanding mechanical properties and shape memory performance when DCP content was 0.2 phr.

Bio‐based Eucommia ulmoides gum/low density polyethylene shape memory composites reinforced by zinc methacrylate

AbstractIn this paper, we present an efficient and green extraction process for Eucommia ulmoides gum (EUG) to solve the tricky problems in separation and precipitation, providing a new idea for the industrialization of EUG extraction. Subsequently, the obtained EUG was blended with low density polyethylene (LDPE) and zinc methacrylate (ZDMA) to fabricate novel shape memory composites with both covalent and ionic crosslinking networks. It was found that the improvement in mechanical performance and enhancement in shape recovery ability of the EUG/LDPE/ZDMA composites was attributable to the Zn2+‐based ionic crosslinks. The EUG/LDPE/ZDMA shape memory composites could be candidates in the production of medical fixing materials, hot‐shrinkable tubes and packaging products. © 2021 Society of Chemical Industry

Development of 3D bioprinted GelMA-alginate hydrogels with tunable mechanical properties

3D bioprinting is gaining attention as a biofabrication technique due to its potential to recreate the complex structure of native human tissue, combining high precision additive manufacturing, biocompatible inks, cells and biochemical factors. In this work, we evaluated the combination of covalent and ionic crosslinking networks as a strategy to modulate the properties of hydrogel inks and stripe-pattern printed structures to induce anisotropic mechanical properties. We found that for optimum printing, gelMA-alginate concentrations should be between 11 and 15% w/v and the polymer ratio and concentration modulate the rheological and compressive moduli of hydrogels. Furthermore, degradation and swelling rates are also adjustable, with some blends showing less than 20% degradation and negligible swelling over a 14 days period. Sheep adipose derived stem cells were included in three formulations and cell viability was >75% after bioprinting in all hydrogels. Stripe-patterned hydrogels were successfully printed using a dual printhead allowing us to modify the mechanical properties of 3D printed hydrogel scaffolds in each axis. The printed structure with gelatin (10% w/v) and gelMA-alginate (8% w/v - 7%w/v) hydrogel stripes showed a noticeable anisotropic mechanical behaviour. Thus, we demonstrated that chemical and structural factors could modulate the properties of printed biocompatible hydrogels, including anisotropic mechanical behaviour, with potential application in tissue engineering.

Synthesis, characterization and properties of self-healable ionomeric carboxylated styrene–butadiene polymer

The paper describes synthesis and properties of carboxylated styrene–butadiene rubber (XSBR) and its ionomer using the reaction between carboxyl groups of XSBR and zinc stearate. The self-aggregation of Zn2+ ion pairs resulted in the formation of an ionic cross-linked network, which gave excellent properties to XSBR. The transitions due to the self-association of the ionic cross-links in the ionomers in addition to the glass transition were observed in the dynamic mechanical analysis. The cross-linked XSBR with 1 and 3 wt% of zinc stearate showed a tensile strength value of 4.2 and 5.2 MPa, which were much higher than that (2.5 MPa) of pristine XSBR. Self-healing test was done for the ionomer, where a tensile strength value of 5.2 MPa (before healing) and a value of 3.5 MPa (after healing) were observed, which indicated that the ionic cross-links could heal the interphase. The ionic network polymers also displayed excellent self-healing ability, triggered by heating at 100 °C for 3 h via atomic force microscopy. The healing efficiency of the XSBR/Zn stearate compound was calculated as 68%. Thermoreversible behaviour of the polymer via ionic cross-links showed regular reversal of storage modulus (E’) with varying temperature at constant frequency and strain. This study thus opens up a route for developing the self-healable ionic cross-linked XSBR with considerable mechanical properties for various engineering applications.

Self-healing Behavior of Ethylene Propylene Diene Rubbers Based on Ionic Association

To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer rubber (EPDM) is reported, which was designed by graft-polymerization of zinc dimethacrylate (ZDMA) onto rubber chains to form a reversible ionic cross-linked network. Single ionic cross-linked network and dual network, combining covalent and ionic cross-links, could be tuned by controlling vulcanization process to achieve tailorable mechanical and self-healing properties. It was found that ionic cross-linked EPDM showed a recovery of more than 95% of the original mechanical strength through a healing process of 1 h at 100 °C. The covalent cross-links could improve mechanical properties but block self-healing. Adding 50 wt% liquid rubber to “dry” EPDM could effectively enhance self-healing capability of the dual cross-linked network and the healed tensile strength could reach 0.9 MPa. A compromise between mechanical performance and healing capability could be potentially tailored by controlling vulcanization process and liquid rubber content.

Ultrastiff, Tough, and Healable Ionic-Hydrogen Bond Cross-Linked Hydrogels and Their Uses as Building Blocks To Construct Complex Hydrogel Structures.

We report the ultrastiff and tough poly(acrylamide- co-acrylic acid)/Na-alginate/Fe3+ (P(AM- co-AA)/Na-alginate/Fe3+) hydrogel via the formation of hybrid ionic-hydrogen bond cross-linking networks. The optimal P(AM- co-AA)/Na-alginate/Fe3+ hydrogel possessed super high elastic modulus (∼24.6 MPa), tensile strength (∼10.4 MPa), compression strength (∼44 MPa), and toughness (∼4800 J/m2). The P(AM- co-AA)/Na-alginate/Fe3+ hydrogel was highly stable and maintained its superior mechanical properties in 0.5-2 M NaCl solution, aqueous solution with pH ranging from 4 to 10. The ionic cross-linking networks of the P(AM- co-AA)/Na-alginate/Fe3+ hydrogels can be locally and selectively dissociated by treating with aqueous NaOH solution with pH of 13 for 1 min and reformed by locally adding the additional Fe3+ solutions, making the hydrogels healable and cohesive. The healed hydrogels from the cutting surfaces can bear a tensile strength of up to 7.1 MPa. Various complex hydrogel structures can be constructed by using the P(AM- co-AA)/Na-alginate/Fe3+ hydrogels as building blocks via the adhesion of as-prepared hydrogels.

Catalytic and ionic cross-linking actions of l-glutamate salt for the modification of cellulose by 1,2,3,4-butanetetracarboxylic acid

The sodium l-glutamate is reported as an efficient catalyst for the cross-linking between 1,2,3,4-butanetetracarboxylic acid (BTCA) and cellulose. Results presented ester absorbance of the treated fabrics strongly increased in the presence of the homemade l-glutamate salt, a mixture of l-glutamic acid (LGA) and NaOH at a specific ratio. Importantly, anti-wrinkle properties of the treated fabrics were significantly improved. Based on the relative concentration calculation, l-glutamate promoted the reaction of BTCA with cellulose by accelerating the formation of BTCA anhydrides and the esterification of anhydrides with cellulose. Besides, the improved anti-wrinkle property was partially attributed to the fact that the generated LGA reacted with cellulose and formed ionic cross-linking networks through amino groups with carboxyl groups in BTCA, which was confirmed by the Fourier transform infrared spectra and the computational calculations. Through detailed comparisons, l-glutamate catalyzed fabrics showed as good durability as sodium hypophosphite, indicating a possible alternative for phosphorus-containing catalysts.

Construction of bioinspired organic-inorganic hybrid composite by cellulose-induced interfacial gelation assisted with Pickering emulsion template

The construction of organic-inorganic hybrid materials has shown great potential for the development of multifunctional superior protein-based composites. However, it is still a challenge to effectively disperse and dominate the mineralization of inorganic minerals in a hybrid system. In this study, we presented a simple and green strategy to construct a biomineralized soy protein (SP)-based hybrid resin with a controllable mineralized skeleton. It was found that the Pickering emulsion served as a mineralized template efficiently inducing the uniform dispersion of inorganic particles while the incorporated cellulose nanocrystals (CNC) were able to regulate the mineralization process, thus forming an optimized mineralized skeleton structure. Acting as a reactive reinforcer, the regulated mineralized skeleton formed in situ interactions with SP matrix, giving rise to the multiple covalent and ionic crosslinking networks. As a result, the introduction of mineralized skeleton increased the wet shear strength of composites from 0.46 MPa to 1.21 MPa, exhibiting a 163% increment compared to the pristine SP composite. Moreover, the formation of rigid inorganic mineralized skeleton in hybrid SP-based resin facilitated an obvious improvement of thermal stability compared with the control samples. Overall, we envisage that this strategy could provide a creative strategy for the design and fabrication of superior sustainable biocomposites for engineered wood products.

Bioinspired graphene-based nanocomposites via ionic interfacial interactions

Abstract In nature, small amount of metal ions play a critical role in improving mechanical properties, such as the jaws of marine polychaete Nereis and Glycera. Recently, the multivalent cations metals have been successfully introduced to enhance the interfacial strength of graphene based-nanocomposites through forming ionic crosslinking networks with graphene oxide (GO) nanosheets by coordination. Combination with other interfacial interactions, the synergistic effect was constructed in the resultant bioinspired nanocomposites, leading to outstanding integrated performance, including thermal, electrical, fatigue resistant and mechanical properties. These excellent properties make this bioinspired graphene-based nanocomposites to be great candidates for applications in many fields, for example, flexible electronics devices, artificial muscles, supercapacitors , and aerospace.

Design of “Zn2+ Salt-Bondings” Cross-Linked Carboxylated Styrene Butadiene Rubber with Reprocessing and Recycling Ability via Rearrangements of Ionic Cross-Linkings

Constructing a reversible supramolecular network cross-linked by noncovalent bonds is an effective approach to realize self-healing as well as reprocessing and recycling for rubbers. Unfortunately, in most case the resultant noncovalent cross-linked rubbers cannot hold enough forces to meet the routine applications. In this paper, our strategy was based on a simple reaction between carboxy groups in carboxylated styrene butadiene rubber (XSBR) and zinc oxide (ZnO), where the formed Zn2+ salt bondings connect separate XSBR molecules. The further self-aggregation of ion pairs of Zn2+ salts resulted in an ionic cross-linked network, whose rearrangements brought XSBR excellent reprocessing/recycling ability. Additionally, the reclaimed XSBR exhibited valuable mechanical properties due to the compensation of additional formed new Zn2+ salt bondings during recycling. The fresh XSBR with 5 wt % zinc oxide showed a tensile strength of 6.7 MPa, and it was further increased to 10.3 MPa after 3 recycles, which was f...

Quaternized graphene oxide modified ionic cross-linked sulfonated polymer electrolyte composite proton exchange membranes with enhanced properties

A series of novel ionic cross-linked sulfonated poly(ether sulfone) (SPES)-based proton exchange membranes (PEMs) were successfully constructed by using quaternized graphene oxide (QGO) as the inorganic fillers and cross-linking agents. The ionic cross-linking networks were implemented by the interactions between the sulfonic acid groups of SPES and the quaternary ammonium groups of QGO. The influences of different loading contents of QGO on the properties of the ionic cross-linked composite membranes were studied. The composite membranes showed the enhanced mechanical properties and improved oxidative stabilities. Meanwhile, the swelling ratio, water uptake and methanol permeability of the ionic cross-linked SPES/QGO composite membranes were much lower than that of the pristine SPES membrane. The swelling ratio and water uptake of SPES-10-QGO composite membrane had the minimum values among all the composite membranes. In addition, although the proton conductivity of ionic cross-linked SPES membranes by QGO decreased, SPES-10-QGO still exhibited high proton conductivity of about 0.08Scm−1 at 80°C. All the results indicated that the ionic cross-linked composite membranes with balanced properties were the potential candidate materials for PEMs.

Switching the Adhesive State of Catecholic Hydrogels using Phototitration

A polyacrylamide hydrogel system that can be liquefied by remote activation using UV irradiation is investigated as a degradable adhesive. The linear polyacrylamide copolymer, formed by conventional free-radical polymerization, contains biomimetic catechol–iron-mediated cross-linkers that are sensitive to pH changes. Hydrogel films and bulk gels are prepared by basic titration of a polymer solution doped with a photoacid generator, diphenyliodonium chloride, generating an ionic cross-linked network via the catechol pendant groups. Irradiation of these hydrogels with UV light affords a viscous liquid solution, demonstrating a gel–sol transition with a subsequent decrease in the adhesive strength of the material. These gels may be prepared in high throughput and require few synthetic steps with commercially available precursors.

Synthesis and properties of novel benzimidazole‐containing sulfonated polyethersulfones for fuel cell applications

AbstractA novel series of benzimidazole‐containing sulfonated poly(arylene sulfones)s with controllable amount of basic 2,6‐bis(benzimidazol‐2‐yl)pyridine (BIP) and sulfonic acid groups have been prepared by the copolycondensation of a new BIP‐containing arylene difluoride monomer (DFSBIP) with a sulfonated arylene difluoride (DSDFS) and 4,4′‐biphenol (BP). All the resulting polymers have high molecular weights, good thermal stability, and can form uniform and tough membranes by simple solution casting. Because of the strong acid–base interaction between BIP and sulfonic acid groups, ionic crosslinking networks forms that resulted in polymer membranes with good dimensional stability in water even at high temperature (e.g., 100 °C). The ion exchange capacity (IEC) of the polymer membranes was investigated through a new simple pH‐determination method. A comparison between the experimental IEC values with the calculated ones based on the polymer structures indicated that each BIP unit interacted with one sulfonic acid group. Thus, by controlling the relative content of BIP units and sulfonate groups in the polymers, the intra‐ and intermolecular acid–base interactions could be readily optimized so as to achieve polymers with high IEC values, high proton conductivities as well as low swelling ratios, demonstrating good potential for proton exchange membrane applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1920–1929, 2009