Cross-linked Polyurethane Research Articles

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Investigation of the Gum Stock Behavior of Polyurethane Crosslinking Matrix by Adding Triol Diol Mixtures for the Application of Composite Solid Rocket Propellants

The addition of some advanced additives to improve the mechanical properties of polyurethane (PU) polymeric matrix, which acts as a binder system in composite solid rocket propellants (CSRPs), is a target for the energetic materials researchers. In this investigation, 45 compositions of different crosslinked PU matrices were produced to demonstrate the effect of adding crosslinking mixture (CM) on the mechanical capabilities of polyurethane gum stock. The crosslinking mixture (CM) is composed of a triol crosslinker, trimethylolpropane (TMP), and a chain extender, 1,4-butanediol
 (BD). For comparison, traditional PU samples without crosslinking additives were formulated. As a prepolymer, HTPB was used with a curing agent (HMDI). The research was carried out with different ratios of TMP to BD, different curing ratios (NCO/OH=0.7, 0.9, and 1.1), and crosslinking mixture contents in the range of 0-5 wt.%. The mechanical characteristics of all the cured formulations were measured. It was demonstrated that changing the ratio of TMP to BD has a significant impact on the mechanical performance causing a wide range of elongation and strength qualities. Increasing the wt.% of triol crosslinker in the sample enhanced the tensile strength, whereas the strain has been decreased. The addition of diol chain extender increased the strain rate of the samples. The mechanical parameters were adjusted simply by employing the crosslinking ingredients to get exceptional mechanical characteristics at each NCO/OH curing ratios. Also it was concluded that PU samples of curing ratio (NCO/OH= 0.7-0.9) with TMP:BD (1:1) showed a promising results and could be used according to the requirements of the rocket system designers.

NIR-induced self-healing and recyclable polyurethane composites based on thermally reversible cross-linking for efficient solar-to-thermal energy storage

Conventional chemically cross-linked phase change materials (PCMs) possess many merits, such as reliable structural stability, high mechanical strength, and excellent form stability, but they unable to be self-healed, recycled and reprocessed because of permanently covalent cross-linking structure. Furthermore, the poor solar-to-thermal performance of organic PCMs severely restricts their practical usage for solar energy utilization. Herein, novel dynamically covalent cross-linked PEG-based polyurethane (FMPCMs) with superior solar-to-thermal conversion performance, satisfactory self-healing ability and admirable recyclability were synthesized by introducing furan-decorated Ti3C2Tx MXene nanosheets (f-MXene) into polyethylene glycol-based polyurethane (PEG-PU). f-MXene, which is dynamically and covalently linked in polymeric FMPCMs, served not only as an efficient photon capturer in PEG-PU for converting solar to thermal energy but also as a dynamic cross-linked point for thermal-induced recycling and self-healing. Due to the reversible Diels-Alder (DA) covalent bond, f-MXene nanosheets endows the FMPCMs with significantly increased near-infrared-induced (NIR-induced) self-healing efficiency (90.6%) and satisfactory recyclability. Furthermore, the solar-to-thermal conversion and storage efficiency of FMPCMs were effectively increased with the incorporation of f-MXene. In conclusion, FMPCMs show tremendous potential in solar-to-thermal energy storage.

Preparation and characterization of cross-linked polyurethanes using β-CD [3]PR as slide-ring cross-linker

To explore the toughening and damping potential of slide-ring (SR) structure as an energy dissipation unit, a β-cyclodextrin (CD) [3]polyrotaxane (β-CD [3]PR) was prepared via the self-assembly of β-CDs with polyethylene glycol (PEG) diamine 1,1′-disubstituted ferrocene as a site-complementary polymer axle followed by end-capping with N-(triphe-nylmethyl)glycine. Subsequently, it served as a SR cross-linker to cross-link PEG and poly- (1,6-hexanediol)carbonate (PC) diols in the presence of 4,4′-diisocyanato dicyclohexyl-methane (HMDI) to give polyurethanes (PUs). Similar to β-CD as a cross-linker, the β-CD [3]PR cross-linked PUs also held a low, but relatively higher sol fraction range of 0.50 w%-3.20 w%. As a semi-crystalline prepolymer, the β-CD and β-CD [3]PR cross-linked PEG PUs presented a typical crystalline polymer tensile stress-strain behavior, while the cross-linked PUs using PC as an amorphous polymer showcased a pseudo-J-shaped stress-strain curve. Compared to the β-CD cross-linked PUs, the β-CD [3]PR cross-linked ones exhibited remarkably higher swelling ratio, fracture energy and loss tangent values, indicating β-CD [3]PR as an energy dissipation unit enabling to toughen and damp a variety of polymer materials. Compared to the β-CD cross-linked PEG and PC PUs, the β-CD [3]PR cross-linked ones showed remarkably higher swelling ratio, fracture energy and loss tangent values, indicating β-CD [3]PR as an effective energy dissipation unit enabling to toughen and damp a variety of polymer materials. • β-CD [3]PR as a sliding-ring cross-linker. • β-CD [3]PR cross-linked PEG and PC PUs showing remarkably higher swelling ratio, fracture energy and loss tangent values. • β-CD [3]PR cross-linked PC PUs showing pseudo-J-shaped stress-strain curves.

Synthesis, Characterization and Thermal Properties of Intrinsic Self‐Healing Polyurethane Nanocomposites

AbstractA hybrid thermo‐reversible crosslinking polyurethane nanocomposite containing 0.5, 1, and 2 wt.% of nano‐silica was prepared with three intrinsic self‐healing bonds (reversible covalent bonds supported by intrinsic hydrogen bonds and dangling chains). Owing to the introduction of pseudo‐tannin and polyester diol that could form phenol‐urethane networks and using nano‐silica that causes dangling chains and hydrogen bonds, the prepared polyurethanes are capable of being reversed at 110 °C and rejoin at low temperatures. Thermoset self‐healing polyurethane nanocomposites are prepared from pseudo‐tannin, nano‐silica, and a urethane‐based prepolymer. The investigations of chemical structure, self‐healing behavior, and cross‐link network are carried out by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) technique, and swelling test. dissociation of phenolic urethane at 110 °C was confirmed by temperature variable FTIR. By swelling test, it was found that the self‐healing polyurethane nanocomposites with 0.5 wt.% of nano‐silica have the most hard‐domain, gel content, and crosslink density in the samples. DSC technique shows that polyurethane samples have two heat transfer transitions (dangling chains and self‐healing). Thermogravimetric analysis (TGA) findings show that nanocomposites decompose at elevated temperatures than neat PU, and the rate of degradation diminishes as silica content increases.

Synthesis and Characterization of Cross-Linked Waterborne Polyurethane Dispersion

Due to high-performance property, many industries interested recently for production of waterborne polyurethane dispersions (WPUDs). In the present study first WPUDs were prepared by polyaddition reaction of hydroxy terminated unsaturated polyesters (HTUPEs) and isophorone diisocyanate (IDPI) in presence of dibutyl dilaurate (DBTL) as a catalyst. Cross-linking bridge were created between WPUD chains to enhance the thermal and mechanical properties by addition of ethylene diacrylate, hydroxy ethyl acrylate as end capped and methyl ethyl ketone peroxide cobalt naphthenate as a catalyst. All the resultant cross-linked WPUDs (designated as CWPUDs) were studied by thermal and mechanical properties.

Photosensitive titanium-containing interpenetrating polymer networks for photonics

Kinetic investigations of titanium-containing interpenetrating polymer networks (Ti-IPNs) formation based on cross-linked polyurethane and Ti-containing copolymer (Ti-CP) were carried out using differential calorimetry method. Analysis by the SAXS method revealed that the systems possessed nanosized regions of heterogeneity. The increase of (–TiO2–) fragments content led to increase of both overall level of heterogeneity and of Tg of Ti-СP component. Ti-IPNs are optically transparent with optical transparency coefficient value up to 90–91% at 650 nm. The reverse visible darkening at UV-irradiation was observed for Ti-IPNs, thereby allowing their application in optical data recording on exposure to laser radiation.

Tough and Healable Elastomers via Dynamic Integrated Moiety Comprising Covalent and Noncovalent Interactions

Elastomers that combined excellent mechanical performance and healability are essential to the advancement of stretchable electronics. However, the strength and toughness of healable elastomers tend to be mutually exclusive. Herein, a new strategy of the dynamic integrated moiety is developed to construct covalent and noncovalent cross-linked polyurethane (CNPU) elastomers. The covalent and noncovalent interactions synergistically enhance the overall mechanical properties of polyurethane elastomers such as tensile strength (48.8 MPa), toughness (282.9 MJ·m–3), stretchability (1740%), and healing efficiency (116%). Finally, elastic conductive wires are fabricated with high load capacity, stable electrical conductivity under static/dynamic stretching, and robust healability to demonstrate the potential use of CNPU elastomers in stretchable electronics.

Achieving simultaneously toughening and flame-retardant modification of poly(lactic acid) by in-situ formed cross-linked polyurethane and reactive blending with ammonium polyphosphate

Achieving simultaneously toughening and flame-retardant modification of poly(lactic acid) by in-situ formed cross-linked polyurethane and reactive blending with ammonium polyphosphate

A composite of cross-linked polyurethane as solid–solid phase change material and plaster for building application

This paper presents the thermal and mechanical characterizations of a composite material made of plaster and home-made solid–solid Phase Change Material (s-s PCM) to be considered as a building material in order to: increase thermal inertia of buildings, improve comfort of the inhabitants, and reduce the primary energy needs of buildings.The use of those s-s PCM allows to avoid the problems of liquid–solid PCM that were considered into building materials. The s-s PCM involves a transition from polymeric amorphous to crystalline phase. They remain in a solid state under 100 °C and are water resistant. Physical properties of the s-s PCM are such that the grain size can be controlled for incorporation and mixing with plaster before water addition.The thermal properties of the composite were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Further composite is instrumented with K type thermocouple during exposition to thermal cycling around ambient temperature in a stove with fixed humidity. The microstructure of the PCM-bearing composite was observed by scanning electron microscopy (SEM). The incorporation of the PCM into the plaster matrix does not change the thermal properties of PCM. The thermal monitoring of the composite shows a modification of the maximum and the minimum peaks of temperature as well as a time offset of temperature variations. Some mechanical properties of the composite, such as compressive strength were investigated. Those preliminary results suggest that our s-s PCM can be considered further for incorporation into plasterboard that will passively contribute to a better thermal comfort in building application.

Ionic Cross-Linkable Alendronate-Conjugated Biodegradable Polyurethane Films for Potential Guided Bone Regeneration

Ionic Cross-Linkable Alendronate-Conjugated Biodegradable Polyurethane Films for Potential Guided Bone Regeneration

Ice-Shedding Polymer Coatings with High Hardness but Low Ice Adhesion

Ice readily sheds from weak oil-swollen polymer gels but tends to adhere to mechanically robust coatings. This paper reports bilayer coatings that simultaneously possess high bulk hardness but low ice adhesion. These coatings are prepared by cocuring a triisocyanate, P#'-g-PDMS [a methacrylate polyol bearing poly(dimethylsiloxane) (PDMS) side chains with # being 1, 2, or 3 and g denoting graft], and optionally a methacrylate polyol P#. The self-assembly of the system during coating formation yields a PDMS brush layer on the surface of the cross-linked polyurethane matrix. After the surface PDMS layer is lubricated with a silicone oil, this coating exhibits an ice adhesion τ that is 10 000-fold lower than that of a triisocyanate/P# coating. Ice slides under its own weight on such a coating at a tilt angle of 3°. Yet, the coating matrix is harder than poly(ethylene terephthalate), a widely used plastic. Additionally, such a coating maintains its low τ values for more than 10 consecutive icing/deicing cycles. Subsequent increases in τ are reversed by allowing time for the replenishment of the depleted surface lubricant with that released from the coating matrix. This design opens the door for effective yet hard ice-shedding polymer coatings.

Ultrahigh Elastic Polymer Electrolytes for Solid-State Lithium Batteries with Robust Interfaces.

Solid polymer electrolytes (SPEs) are promising for solid-state lithium batteries, but their practical application is significantly impeded by their low ionic conductivity and poor compatibility. Here, we report an ultrahigh elastic SPE based on cross-linked polyurethane (PU), succinonitrile (SN), and lithium bistrifluoromethanesulfonimide (LiTFSI). The resulting electrolyte (PU-SN-LiTFSI) exhibits an ionic conductivity of 2.86 × 10-4 S cm-1, a tensile strength of 3.8 MPa, and a breaking elongation exceeding 3000% at room temperature. A solid-state lithium battery using the electrolyte exhibits a high specific capacity of 150 mAh g-1 at 0.2C and a long cycling life of up to 700 cycles at 0.5C at room temperature, showing one of the best performances among its counterparts. The excellent performances are attributed to the fact that its ultrahigh elasticity, good ionic conductivity, tensile strength, and electrochemical stability contribute to robust electrode/electrolyte interfaces, thus greatly decreasing the charge-transfer resistance in charge/discharge processes. Our investigations provide a novel strategy to address the intrinsic interfacial issue of solid-state batteries.

Insertion of Supramolecular Segments into Covalently Crosslinked Polyurethane Networks towards the Fabrication of Recyclable Elastomers

Insertion of Supramolecular Segments into Covalently Crosslinked Polyurethane Networks towards the Fabrication of Recyclable Elastomers

Flexible crosslinking of polyurethane using grafted poly(dimethylsiloxane) with Epichlorohydrin and Bisphenol A end groups and its impact on the mechanical properties and low-temperature flexibility

Poly(dimethylsiloxane) (PDMS) was grafted onto polyurethane (PU), and Epichlorohydrin and Bisphenol A were attached to the free ends of PDMS groups and used to link the grafted PDMS to thereby introduce flexible crosslinks between the PU chains. The flexible crosslinks enhanced the crosslink density and solution viscosity of PU but did not change the melting and crystallization behaviors of the soft segments of PU. In particular, the flexible PDMS crosslinks increased the maximum tensile stress by up to 300% and the maximum tensile strain up to 180%. The shape recovery capability at 10°C and the shape retention capability at −25°C were maintained above 90% with the flexible crosslinking. Grafted PDMS moderately improved the low-temperature flexibility of PU due to its flexibility at low temperature. The flexible crosslinks of grafted PDMS successfully improved the tensile strength, shape recovery, and low-temperature flexibility of the PU.

Biomimetic integration of tough polymer elastomer with conductive hydrogel for highly stretchable, flexible electronic

Flexible electronics is booming and attracts considerable interest in monitoring physiological activities and health conditions. The development of human-friend flexible electronics with both excellent human movement monitoring and flexible electrode functions at a wide working range remains highly challenging. Herein, we report a biomimetic double-layered multifunctional flexible electronic device composed of a stretchable, tough elastomer covalently coupled with a conductive, double-network hydrogel for monitoring physiological motions. The introduction of optimal physical crosslinking including hydrogen bond and metal coordination in the covalently cross-linked polyurethane elastomer effectively provides favorable flexibility and stretchability. The elastomer-hydrogel integration (EHI) shows ultra-fast responsiveness (10 ms) and resilience (246 ms) as a skin sensor and could effectively detect diverse muscle and joint movements in a highly sensitive and signal waveform-interpreting manner. Further, such a polymer integration with skin shape-adaptive hydrogel and low contact impedance enables real-time high-quality detection of electrocardiogram (ECG) by serving as flexible electrode compared to commercial Ag/AgCl electrodes, and was successfully applied to measure electrooculogram (EOG) and electromyogram (EMG). EHI-based electrodes were feasible and effective for electroencephalogram (EEG) signal detection in brain-computer interfaces (BCI) system. Altogether, this biomimetic EHI electronic device provides an advanced platform for the design of next-generation flexible healthcare diagnostic monitors and soft robots.

Self-healable organic light-emitting devices based on electronic textiles

Wearable displays that can be applied to smart clothing systems are attracting attention as a core technology in terms of the communication between machines and humans. However, currently available displays still lack durability under random deformations of clothes. Here, we report a self-healable organic light-emitting devices (OLEDs) for smart clothing system, which can recover from the various physical deformations of clothing. The reduced luminance of damaged OLEDs can be recovered again, and the structure variation caused by repetitive motions of the OLEDs can be restored to the original shape. In addition, the operating voltage of the self-healable OLEDs is 2.9 V, which is the lowest among those reported for light-emitting devices with self-healing materials. The electroluminescence intensity at 514 nm of a damaged OLEDs is only about 14.2% of its initial value due to the formations of leakage currents around internal and external cracks. However, the electroluminescence intensity at 514 nm of a damaged device recovers to 95.3% of its initial value due to the self-healing property of the polyvinyl alcohol:Agar nanocomposite and the shape-memory property of the cross-linked polyurethane. Furthermore, we demonstrate that our newly developed self-healable OLEDs represents a new core technology for future smart clothing systems because it can self-recover from damage.

Suppressing shuttle effect by large oxygen-containing crosslinked hyperbranched polyurethane as cathode encapsulated layer for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have attracted a lot of attention because of their high energy density, low cost, and environmental friendliness. However, shuttle effect is one of the most obstacles to make the poor cycling performance and inhibit the development of Li-S batteries. Herein, a kind of large oxygen-containing polymer coated cathode, named polyurethane coated carbon-nanotube/sulfur composites (PU@S-CNT), is prepared from sulfur capsulated by the reaction of hyperbranched polyether and diisocyanate via a simple “one-pot” strategy to impede the shuttle effect. This PU@S-CNT cathode can not only inhibit the dissolution of lithium polysulfides by physical barrier, but also can absorb the lithium polysulfides by the chemical effect. Especially, the cell with PU@S-CNT electrode shows an excellent initial cycling capacity of 892 mAh g−1 at 2C and remarkable capacity retention (a low decay rate of 0.051% per cycle at 2C after 450 cycles). More importantly, this coated cathode (PU@S-CNT) demonstrates a good inhibition of shuttle effect, high transmission speed of lithium ion and good cycle reversibility. This work exhibits the cross-linked hyperbranched polyurethane is used as coatings of the sulfur cathode for the first time, which can reveal a potential prospect of high-level heteroatom doped coated cathodes for high-performance lithium-sulfur batteries.

Concise and Efficient Self-Healing Cross-Linked Polyurethanes via the Blocking/Deblocking Reaction of Oxime Urethanes

The development of self-healing polymers can extend the service life of polymer materials. However, it is still a challenge to prepare a polyurethane with high healing efficiency and maximum retention of the properties of polyurethane itself. In this research, we proposed a new scheme for the industrial production of self-healing polyurethane and successfully synthesized a self-healing polyurethane using diacetyl oxime as the chain extender and triethanolamine as the cross-linking agent. Oxime-blocked isocyanates deblock at a higher temperature and regenerate oxime urethanes at a lower temperature, thereby achieving thermal reversibility and self-healing due to the concise and efficient thermal reversible reaction of oxime urethanes. Fourier transform infrared and differential scanning calorimetry experiments confirmed that the oxime urethanes in the polyurethane deblock efficiently at around 90 degrees C and re-block after the temperature is lowered. The process can be cycled at least three times. Microscopic observation confirmed that the cracks disappeared within 60-90 min at 90 degrees C. The tensile test shows that the synthetic DiO-c-PU has a self-healing efficiency of over 94% at 90 degrees C for 1.5 h, which is more efficient. From the results, it appears that DiO-c-PU has good self-healing properties.

(3-Mercaptopropyl)triethoxysilane-Modified Reduced Graphene Oxide-Modified Polyurethane Yarn Enhanced by Epoxy/Thiol Reactions for Strain Sensors.

In the current work, a method was proposed to fabricate strain-sensing yarns via epoxy/thiol reactions by a dip-coating method. Reduced graphene oxide (rGO) was modified with (3-mercaptopropyl)triethoxysilane, and polyurethane yarn was cross-linked with 3-glycidoxypropyltrimethoxysilane. The existence of thiol in modified rGO and epoxy in the cross-linked polyurethane yarn contributed to the formation of the covalent bond between the elastic substrate and the conductive layer, resulting in good adhesion between the substrate and the conductive layer, as well as excellent electromechanical performance. The outstanding strain-sensing performance make the prepared yarn show excellent potential in practical applications when monitoring human motions, which makes it a promising candidate for wearable sensing devices.