Cross-linked Elastomers Research Articles

Highly efficient self-healing materials with excellent shape memory and unprecedented mechanical properties

Novel dual-physical cross-linked elastomers with unprecedented mechanical, highly efficient self-healing, and excellent shape memory properties are designed, which will offer new guild for future body-sensors, stimulating reactive and wound healing.

Cross-Linked Polyacrylonitrile-Based Elastomer Used as Gel Polymer Electrolyte in Li-Ion Battery

Gel polymer electrolytes (GPEs) based on polyacrylonitrile elastomer (HNBR) are investigated for lithium-ion batteries application. This study examines the acrylonitrile content, as well as the sol...

Facile Strategy for the Biomimetic Heterogeneous Design of Elastomers with Mechanical Robustness, Malleability, and Functionality.

It remains challenging to simultaneously realize mechanical robustness, malleability, and functionality in elastomers via facile yet efficient methods. Herein, a simple strategy for the biomimetic heterogeneous design is proposed to achieve mechanically strong, malleable, and functionalized elastomers. We demonstrate the strategy by straightforward mechanical mixing of a highly cross-linked vitrimeric elastomer with a homogeneous gum and subsequent curing, resulting in heterogeneous vitrimeric elastomers (hetero-VEs). The hetero-VEs comprise two phases: a hard phase with dense cross-links and a soft matrix with few cross-links, with excellent interface between the two phases. The hard phases can be deformed upon loading, dissipating energy, which significantly improves the overall mechanical performance of the hetero-VEs. When conductive fillers are incorporated into the soft matrix, due to the volume exclusion effect of the hard phases, the resultant hetero-VEs exhibit high conductivity with a small fraction of fillers. In view of the facile and generic preparation process, this strategy should be a promising way to reinforce and functionalize many vitrimeric elastomer systems.

Unique molecular networks: Formation and role of elastin cross-links.

Elastic fibers are essential assemblies of vertebrates and confer elasticity and resilience to various organs including blood vessels, lungs, skin, and ligaments. Mature fibers, which comprise a dense and insoluble elastin core and a microfibrillar mantle, are extremely resistant toward intrinsic and extrinsic influences and maintain elastic function over the human lifespan in healthy conditions. The oxidative deamination of peptidyl lysine to peptidyl allysine in elastin's precursor tropoelastin is a crucial posttranslational step in their formation. The modification is catalyzed by members of the family of lysyl oxidases and the starting point for subsequent manifold condensation reactions that eventually lead to the highly cross-linked elastomer. This review summarizes the current understanding of the formation of cross-links within and between the monomer molecules, the molecular sites, and cross-link types involved and the pathological consequences of abnormalities in the cross-linking process.

Uniaxial Stretching-Induced Alignment of Carbon Nanotubes in Cross-Linked Elastomer Enabled by Dynamic Cross-Link Reshuffling.

The fascinating properties of carbon nanotubes (CNTs) make them highly promising in fabricating polymer composites. Yet, the property enhancements of polymer/CNTs composites remain far behind the theoretical predictions. A critical issue to resolve this dilemma is to align CNTs in polymer matrices. Thus far, the state of art approaches to create CNT alignment either require complicated preparation processes and specific apparatuses, or is limited to thermoplastic polymers. Here, inspired by the network rearrangement ability of vitrimer in the solid state, we bring forth a facile methodology to align CNT in covalently cross-linked polymers by uniaxially stretching dynamic. Specifically, dynamic boronic ester bond-cross-linked epoxidized natural rubber/CNTs vitrimer composites with randomly dispersed CNTs are prepared, which are able to rearrange the network topologies and release stress at elevated temperatures through boronic ester transesterifications. The alignment of CNTs is performed by the uniaxial stretching of the composites and subsequent cross-link reshuffling at elevated temperatures, which results in anisotropic composites with remarkably enhanced mechanical properties and reduced electrical conductivity along the stretching direction. Furthermore, the mechanical properties of the composites can be readily adjusted by changing the applied strain, relaxation time and temperature due to the modulated CNT alignment degree. With this example, we envisage that this work offers a conceptual and facile approach to align anisotropic fillers in covalently cross-linked polymers.

THERMAL TRANSPORT IN CROSS-LINKED ELASTOMERS SUBJECTED TO ELONGATIONAL DEFORMATIONS

ABSTRACT Investigations on thermal transport in cross-linked elastomers subjected to elongational deformations are reviewed and discussed. The focus is on experimental research, in which the deformation-induced anisotropy of the thermal conductivity tensor in several common elastomeric materials is measured using novel optical techniques developed in our laboratory. These sensitive and noninvasive techniques allow for the reliable measurement of thermal conductivity (diffusivity) tensor components on samples in a deformed state. When combined with measurements of the stress in deformed samples, we are able to examine the validity of the stress–thermal rule, which predicts a linear relationship between the thermal conductivity and stress tensor in deformed polymeric materials. These results are used to shed light on possible underlying mechanisms for anisotropic thermal transport in elastomers. We also present results from a novel experimental technique that show evidence of a deformation dependence of the heat capacity, which implies that, in addition to the usual entropic contribution, there is an energetic contribution to the stress in deformed elastomers.

Influence of stearic acid in zinc based Maleated-EPM ionomer: A novel approach towards recyclability

In recent decades, the relevance of recyclability and reprocessability of cross-linked elastomers has increased rapidly, especially taking into account that cross-linked elastomers constitute a great mass of non-recyclable and non-biodegradable waste. This research article highlights some key impacts of using stearic acid at different dosage levels in zinc-based maleated ethylene propylene (M-EPM) ionomers. As inferred from several experimental analysis, a relatively small amount of stearic acid (7.5–10 phr) is sufficient to yield similar properties as one would obtain from the high dosage of conventional ionic plasticizer (10–30 phr) in zinc-based M-EPM ionomer system. All samples were easily prepared by a general rubber processing equipments like internal mixer, two-roll mill, electrically heated hydraulic press, etc. Additionally, 7.5–10 phr of stearic acid can make Zn based M-EPM ionomer reprocessable at high temperature (≥150 °C), exhibiting a typical thermoplastic behavior. Samples were studied using general characterization techniques such as, ODR, DMTA, FTIR, AFM, and TEM analysis. A phenomenal ten-fold rise in the tensile strength, and a significant improvement in the hardness (Shore A) values were observed after the addition of 7.5–10 phr of stearic acid in zinc-based M-EPM ionomer system.

Photoplastic Self-Healing Polyurethane Springs and Actuators

Typical cross-linked polymer networks have rubbery elasticity and do not exhibit thermoplasticity such as linear polymers. However, thermodynamically cross-linked polymer networks exhibit certain thermoplasticity that allows for thermal processing. Here, we introduce a new concept of photoplasticity, that is, under light illumination, the covalently cross-linked polymer elastomers become flexible and plastic-like linear polymers. A novel class of photoplastic polyurethane elastomers based on dynamically covalent cross-linker hexaarylbiimidazole (HABI) and permanent cross-linker glycerol is designed and synthesized. Under the dual actions of light and stretching, the photoplastic elastomer exhibits reversible elongation and contraction-like springs. Because of the photoinduced reversible dissociation/recombination of HABI, two cut samples of solvent-free elastomers can be healed under irradiation at room temperature. Under asymmetric illumination, the photoplastic elastomer exhibits the appreciative phototropism, which demonstrates that artificial crucifer actuators are selectively driven by light. Photoplastic elastomers integrate photodriven healing, reversible stretching, and bending deformation, which offers the potential for new applications as optical actuators through optimized design of molecular structure, composition, and geometry.

Ground tire rubber thermo-mechanically devulcanized in the presence of waste engine oil as asphalt modifier

Cross-linked elastomers network is main limitation for industrial usage of ground tire rubber (GTR) as asphalts’ and road pavements modifier. GTR was thermo-mechanically devulcanized via extrusion in the presence of waste engine oil (WEO) at temperature ranges from 150 to 280 °C. Combined impact of WEO content and extruder barrel temperature on the change of cross-linked structure of degraded GTR (DTGR) was investigated through sol fraction measurements and thermogravimetric analysis. Fourier-transform infrared spectroscopic analysis, storage stability, viscosity, temperature susceptibility and rheological properties of asphalt modified with DGTR were studied via infrared spectrometer, conventional tests, viscosity, dynamic shear rheology, dynamic mechanical analysis. Fluorescence microscopy was also applied to observe microstructure and the interfacial interaction between DGTR and asphalt. The results shown that the sol fraction of DGTR increases with the increase of WEO content, which results in low dynamic viscosity and storage modulus of the modified asphalts. Barrel temperature strongly affects the form of DGTR and final properties of modified asphalt. Modified asphalts with DGTR at barrel temperature in 180 °C and 210 °C show better rheological properties and broader operating temperature than that of at 280 °C, which is related to degradation of polymer main chain. In addition, 30 %wt. of DGTR content resulted in significant improvement rheological properties and storage stability of modified asphalt. Moreover, it was observed that higher content (above 40 %wt.) of DGTR causes the deterioration of performance properties of modified asphalts, due to the excessive quantities of undissolved rubber particles in asphalt.

Moisture curable non-isocynated polyacrylate triblock copolymer elastomers: synthesis and properties

In this study, novel polyacrylate triblock copolymer elastomers containing methoxysilane groups, poly(methyl methacrylate-co - 3-methacryloxypropyl-methyldimethoxysilane)-b - poly(ethyl acrylate)-b - poly(methyl methacrylate-co - 3-methacryloxypropylmethyldimethoxy-silane) [(PMMA-co - PDMMSPMA)-b - PEA-b - (PMMA-co - PDMMSPMA)], are synthesized and investigated. The triblock copolymers are synthesized via ARGET ATRP using copper wire as the reducing agent and the copolymers can be crosslinked under moisture conditions due to the hydrolyzation of methoxysilane groups. Results show that the triblock copolymers are successfully synthesized in a good controlled way. Copper wire is a better reducing agent in the ARGET ATRP of the methoxysilane monomers than stannous octoate and ascorbic acid. The melt viscosity of the triblock copolymers can be obviously reduced after introducing the methoxysilane groups into the copolymers, which is beneficial for the processing. The triblock copolymers can be crosslinked under moisture and the tension strength and elongation at break of the cross-linked elastomers are greatly enhanced simultaneously.

Chain Structure in a Cross-Linked Polyurethane Magnetic Elastomer Under a Magnetic Field.

The morphology of magnetic particles with a size of 7.0 μm was observed for magnetic elastomers with a concentration of magnetic particles of 70 wt% using an X-ray microscope remolded into high resolution. Computed tomography images revealed that magnetic particles were distributed isotopically in the absence of a magnetic field, but they formed a chain structure in the polyurethane network under a magnetic field of 270 mT. It was also established, by image analysis, that magnetic elastomers had an anisotropic structure under the magnetic field.

Facile Preparation and Properties of Crosslinked Copolyether Elastomers with 1,2,3-Triazole and Urethane Subunit via Click Polymerization.

An azide terminated ethylene oxide‐tetrahydrofuran copolymer with urethane segments (ATUPET) as a novel binder pre‐polymer, has been prepared through ethylene oxide‐tetrahydrofuran random copolymer (PET) end‐capping modification via one‐pot method. The structure characterization of the modifier has been analyzed by FTIR, 1H NMR, 13C NMR and GPC. In comparison with PET, ATUPET has a slightly higher viscosity because it has additional hydrogen bonding interaction generated by the urethane in ATUPET. Triazole cross‐linked elastomers based on ATUPET with various functional molar ratios were prepared using tripropargylamine as a curing agent and cross‐linker. Mechanical properties indicate that the modulus E and tensile strength σ b exhibit a parabolic dependence with the increase in R. At around the stoichiometric ratio, the modulus E and tensile strength σ b reach a maximum and the elongation at break exhibit an acceptable value at the same time. Swelling tests demonstrate that the apparent cross‐linking densities (N0) have a maximum value at the stoichiometric ratio. Thermal analysis shows that the ATUPET prepolymer and its polytriazoles elastomers exhibit a satisfactory stability. The results demonstrated that ATUPET might be a promising polymeric binder for future propellant formulations especially in the field of isocyanate‐free curing technology.

Mechanical and Fracture Properties of Dynamically Cross-Linked Polymer Gels and Elastomers with Molecular Necklaces

Mechanical and Fracture Properties of Dynamically Cross-Linked Polymer Gels and Elastomers with Molecular Necklaces

Stretchable and Low-Haze Ag-Nanowire-Network 2-D Films Embedded into a Cross-linked Polydimethylsiloxane Elastomer.

We report the fabrication of stretchable transparent electrode films (STEF) using 15-nm-diameter Ag nanowires networks embedded into a cross-linked polydimethylsiloxane elastomer. 15-nm-diameter Ag NWs with a high aspect ratio (˃1000) were synthesized through pressure-induced polyol synthesis in the presence of AgCl particles with KBr. These Ag NW network-based STEF exhibited considerably low haze values (<1.5%) with a transparency of 90% despite the low sheet resistance of 20 Ω/sq. The STEF exhibited an outstanding mechanical elasticity of up to 20% and no visible change occurred in the sheet resistance after 100 cycles at a stretching-release test of 20%.

Self-Healing Alkyl Acrylate-Based Supramolecular Elastomers Cross-Linked via Host–Guest Interactions

We prepared acrylamide monomers with permethylated cyclodextrins (PM-CDAAmMe) or peracetylated cyclodextrins (PAc-CDAAmMe). PM-CDAAmMe and PAc-CDAAmMe are soluble in various hydrophobic liquid acrylate monomers, and they can form inclusion complexes with guest monomers such as adamantane or fluoroalkyl groups tethered to a vinyl residue. The bulk polymerization of the liquid acrylate monomers with the PM-CDAAmMe or PAc-CDAAmMe monomers and the guest monomers gave highly flexible and tough elastomers. Tensile tests on the obtained supramolecular elastomers showed fracture strains of over 800% and fracture energies that were 12 times larger than those of covalently cross-linked conventional elastomers, indicating that the host–guest cross-linking made the supramolecular elastomers quite tough. During the deformation process, the applied stress is dispersed into the supramolecular elastomers by dissociation and recombination of the reversible host–guest complex. Moreover, these host–guest complexes also allo...

Experimental Verification of the Theory of Structural-Mechanical Behavior of a Filled 3D Cross-Linked Elastomer

With the example of a silicon dioxide-filled 3D cross-linked plasticized elastomer based on a SCID-L highmolecular copolymer, the theory of structural-mechanical behavior of the polymer composite material has been tested experimentally. Theoretically calculated values of mechanical fracture energy are compared with experimental data, including the construction of their locus in uniaxial tension at temperatures of 223-323 K. The difference between theoretical and experimental data does not exceed 5%, which is acceptable for the engineering practice.

A Facile Synthesis and Characterisation of Novel Mesoporous Bioactive Glass Nanoparticles/ Xylitol Based Biodegradable Polyester Composites For In Vitro Degradation Studies And Anti-Inflammatory Activity

Abstract Xylitol is a biocompatible polyol that has been used to make highly cross-linked polyester elastomers and dendrimers for medical applications such as wound healing, tissue engineering, bioimaging, orthopedic devices, implant coatings and drug delivery. The incorporation of mesoporous bioactive glass (MBG) nanoparticles in polymeric structure enhances the biocompatibility of the polymers. In the present study, poly (xylitol maleate suberate) and poly (xylitol citrate sebacate) copolyesters were synthesised by catalyst free melt polycondensation method. The MBG nanoparticles (SiO2–CaO–P2O5) was prepared through a novel sacrificial liquid template method by sol–gel process using ethyl acetate added in the cetyltrimethylammonium bromide (CTAB) aqueous solution to form micro-emulsion droplets as liquid template in which aqueous ammonia was added as template corrodent catalyst for hydrolysis. The polyester/ n-MBG composite was prepared by solution mixing method. The synthesized pre-polymers were characterized by solubility studies, FTIR, 1H NMR and 13C NMR spectral methods. The molecular weight (Mw) and polydispersity index were determined by Gel Permeation Chromatography (GPC). The glass transition (Tg) and melting temperature (Tm) of polymer and its nanocomposites were studied by Differential Scanning Calometry (DSC). The viscosity of the polyesters and tensile strength (Mpa), young’s modulus (Mpa), elongation at break % of polymers and its nanocomposite were characterized by Rheometry and universal testing machine (UTM). In vitro degradation and swelling studies of the polyester were examined. The polymer nanocomposite thin film was characterised by XRD, HRSEM and EDX. The polymer and its nanocomposites were studied by anti-inflammatory activity. Thus, the prepared polymer and its nanocomposites may be a good candidate as therapeutic molecules carriers for bone and dental tissue regeneration.

Mechanical and self-recovery properties of supramolecular ionic liquid elastomers based on host-guest interactions and correlation with ionic liquid content.

Supramolecular materials have received considerable attention due to their higher fracture energy and self-recovery capability compared to conventional chemically cross-linked materials. Herein, we focus on the mechanical properties and self-recovery behaviours of supramolecular polymeric elastomers swollen with ionic liquid. We also gained insight into the correlation between ionic liquid content and mechanical properties. These supramolecular polymers with ionic liquid can be easily prepared from bulk copolymerization of the host–guest complex (peracetylated cyclodextrin and adamantane derivatives) and alkyl acrylates and subsequent immersion in ionic liquid such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The supramolecular polymeric elastomers showed a self-recovery ability, which the conventional chemically cross-linked elastomers with ionic liquid cannot achieve.

A new hypothesis on the mechanism of nano-filled elastomers reinforcement

Incorporation of active fillers to rubber markedly improves the strength properties and deformation characteristics of such materials. One possible explanation of this phenomenon is suggested in this work. It is based on the fact that for large deformations the binder (high-elastic, cross-linked elastomer) in the gaps between the filler particles (carbon black) is in a state close to the uniaxial extension. The greater part of polymer molecular chains are oriented along the loading axis in this situation. Therefore it can be assumed that the material in this state has a higher strength compared to other ones at the same intensity of deformation. In this paper, a new strength criterion is proposed, and a few examples are given to illustrate its possible use. It is shown that microscopic ruptures that occur during materials deformation happen not in the space between filler particles but at some distance around from it without breaking particle “interactions” through these gaps. The verification of this approach in modeling the stretching of a sample from an unfilled elastomer showed that in this case it works in full accordance with the classical strength criteria, where the presence in the material of a small defect (microscopic incision) leads to the appearance and catastrophic growth of the macrocrack.

Multiscale analysis of large-strain deformation behaviour of random cross-linked elastomers

ABSTRACTThe hyperelastic behaviour of elastomers is characterised by a complex and strongly non-linear response at large deformations, which leads to several modelling challenges. While the existing macroscopic-strain-invariants based models can qualitatively capture the trend of elastomer’s deformation behaviour, incorporating network scale dynamics of polymeric chains becomes important in order to account for lower length-scale phenomena like chemical cross-linking and Langevin chain dynamics. In this work, the mechanical behaviour of SBR-1502 (unfilled) cross-linked elastomer has been simulated using a multiscale modelling approach. All atomistic MD simulations were performed to compute the equilibrium density, glass transition temperature and two lower length scale parameters – volumetric segment density of polymeric chains () and the average number of Kuhn segments between two cross-linking points (). These parameters are fed into a constitutive modelling framework based on the 8-chain network concept of Arruda and Boyce to obtain the bulk equilibrium stress-strain response up to large values of strain. Hyperelastic stress-strain plots are obtained for uniaxial, biaxial and shear modes of deformation (up to ∼750% strain) and limiting chain extensibility is investigated for the random network structure. Coupled model predictions are compared with available experimental data for SBR-1502 and the results are encouraging.