Polyurethane Elastomers Research Articles

Origami Metamaterials Enable Low-Stress-Driven Giant Elastocaloric Effect.

Elastocaloric materials, capable of achieving reversible thermal changes in response to a uniaxial stress, have attracted considerable attention for applications in advanced thermal management technologies, owing to their environmental friendliness and economic benefits. However, most elastocaloric materials operating on the basis of first/second-order phase transition often exhibit a limited caloric response, field hysteresis, and restricted working temperature ranges. This study resorts to origami engineering for realizing multifunctional metamaterials with exceptional elastocaloric effects at both nano (exemplified by computational simulations for graphene) and meso (demonstrated by experimentation on thermoplastic polyurethane elastomers) scales. The findings uncover that the graphene origami exhibits low-stress-driven reversible and giant elastocaloric effects without a hysteresis loss and with a high elastocaloric strength. These effects are achieved across a wide working temperature range (100-600 K) and are tailorable by fine-tuning the topological parameters and configurational status of the origami metamaterials. We demonstrate the scalability of the origami design strategy for magnifying the elastocaloric effect by the 3D printing of a mesoscale origami-inspired thermoplastic polyurethane metastructure that showcases enhanced elastocaloric performance at room temperature. This study presents the potential for the realization of architected elastocaloric materials through surface functionalization and origami engineering. The findings impart exciting prospects of elastocaloric origami metamaterials as the next generation of multiscale and sustainable thermal management technologies.

Self-Healing and Degradable Polycaprolactone-Based Polyurethane Elastomer for Flexible Stretchable Strain Sensors

Self-Healing and Degradable Polycaprolactone-Based Polyurethane Elastomer for Flexible Stretchable Strain Sensors

Flexible Bioinspired Healable Antibacterial Electronics for Intelligent Human-Machine Interaction Sensing.

Flexible electronic sensors are receiving numerous research interests for their potential in electronic skins (e-skins), wearable human-machine interfacing, and smart diagnostic healthcare sensing. However, the preparation of multifunctional flexible electronics with high sensitivity, broad sensing range, fast response, efficient healability, and reliable antibacterial capability is still a substantial challenge. Herein, bioinspired by the highly sensitive human skin microstructure (protective epidermis/spinous sensing structure/nerve conduction network), a skin bionic multifunctional electronics is prepared by face-to-face assembly of a newly prepared healable, recyclable, and antibacterial polyurethane elastomer matrix with conductive MXene nanosheets-coated microdome array after ingenious templating method as protective epidermis layer/sensing layer, and an interdigitated electrode as signal transmission layer. The polyurethane elastomer matrix functionalized with triple dynamic bonds (reversible hydrogen bonds, oxime carbamate bonds, and copper (II) ion coordination bonds) is newly prepared, demonstrating excellent healability with highly healing efficiency, robust recyclability, and reliable antibacterial capability, as well as good biocompatibility. Benefiting from the superior mechanical performance of the polyurethane elastomer matrix and the unique skin bionic microstructure of the sensor, the as-assembled flexible electronics exhibit admirable sensing performances featuring ultrahigh sensitivity (up to 1573.05kPa-1 ), broad sensing range (up to 325kPa), good reproducibility, the fast response time (≈4ms), and low detection limit (≈0.98Pa) in diagnostic human healthcare monitoring, excellent healability, and reliable antibacterial performance.

STUDYING THE MODIFICATION OF NANOSTRUCTURED POLYURETHANE ELASTOMER/POLYVINYL CHLORIDE BLEND BY LOW-MOLECULAR PLASTICIZERS

The effect of chemical structure of low molecular weight plasticizers (LMWP) on intermolecular interactions and mechanical properties of nanostructured polyurethane elastomer (PU)/polyvinyl chloride (PVC) was investigated. Polymer composite films were prepared by solution casting technique using dimethylformamide (DMF) or by rolling the melt. FTIR data showed a maximum level of intermolecular hydrogen bond degradation for PU or the polymer blend modified with trichloroethyl phosphate (TCEP) due to the formation of H-bonds between NH of rigid urethane/urea fragments of PU elastomer and chlorine of TCEP. The low compatibility of di-(2-ethylhexyl)-о-phthalate (DOP), compared with di-n-butyl-о-phthalate (DBP), and PU elastomer provided a minor effect of plasticizer on intramolecular and interfaсial interactions in PU or polymer blend. The resulting composites are characterized by increased tensile strength in the whole composition range. The results of DSC analysis of melt-rolled blends of PU/PVC modified by DOP had one wide glass relaxation transition range and their thermal and mechanical properties could be controlled by changing the ratio of initial components. The aforementioned results provide new possibilities of manufacturing the novel nanostructured thermoplastic elastomers with improved mechanical properties.

Synthesis of Diels–Alder bond and hydrogen bond synergistic shape memory self‐healing polyurethane elastomers

AbstractSelf‐healing materials exhibit the ability to repair damage and restore their function. Shape memory assisted self‐healing (SMASH) materials are smart materials that automatically close localized microscopic cracks and repair these cracks by bonding damaged surfaces. A novel temperature‐responsive SMASH polymer composite was established by introducing Diels–Alder bonds (D–A) in polyurethane. In this article, dynamic D–A produced by the polymerization of furfurylamine and 4,4’‐bismaleimidodiphenylmethane was introduced into the molecular chain to enable the polyurethane elastomers containing D–A bonds to acquire self‐repairing capability. The self‐healing properties of the synthesized material were examined using polarized light microscopy, which revealed excellent fracture healing. The mechanical properties before and after healing were tested, in which the initial maximum tensile strength of the material could reach 7.9 MPa, and the maximum tensile strength after self‐healing was 7.3 MPa, with a repair rate of 91.8%; the maximum elongation was 585.9%, and the maximum elongation after self‐healing was 469.5%, with a repair rate of 80.1%. In addition, this material has excellent repair performance for microcracks of different scales, and the micromolten part of the surface after heating can fill the micrometer cracks, play the role of antiaging, and extend the service life of the material.

The strengthening mechanism of mechanical performance for polyurethanes with micro-content crosslinkers

Chemical crosslinking is one widely used method to endow polyurethane (PU) with desirable properties. However, the introduction of crosslinkers in PU elastomers can often lead to the destruction of phase separation, resulting in weakened mechanical properties. Herein, a series of PUs with micro-content crosslinker were synthesized from poly(oxytetramethylene) glycol (PTMG), diphenylmethane-4,4′-diisocyanate (MDI), and chain extender of butane-1,4-diol (BDO) containing varied amounts of glycerol. The phase separation of PUs decreases with increased glycerol content, while the tensile strength increases. To elucidate this enhancement in mechanical properties, morphology investigation with capability of direct observation of components distribution is employed. An increased thickness of interphase between the domain of hard segment (HS) and soft segment (SS) is observed, which indicates that more HS is moved to the interphase upon the introduction of glycerol. The results of electron energy loss spectroscopy (EELS) further disclosed that glycerol formed aggregations located at the interphase. These aggregations increase the crosslinking density of the interphase, which strengthens HS domains and prevents them from being destroyed under tension, thereby increasing the tensile strength. It is the first time of disclosing distribution feature of micro-content crosslinker of PU as well its strengthening mechanism in tensile strength, which could assist in developing PU with desirable mechanical properties.

Construction and mechanism of phase-locked structured PU elastomers with tunable mechanical and self-healing properties

Self-healing elastomers with great mechanical properties have attracted much attention, however how to balance the mechanical property and self-healing performance is still challenging. In this work, we prepared polyurethane elastomers (PU-n) with different phase-locked structures in which dynamic disulfide bonds and hydrogen bonds are locked at low temperature to provide great mechanical strength and activated by heating to promote self-healing. PU-n exhibit tensile strength from 0.83 MPa to 11.98 MPa because of different microphase separation structures, which is attributed to different thermodynamic compatibility and hydrogen bonds between hard segment with different lengths and soft segment. PU-n can repair surface scratches within 10 min and the well-designed elastomer (PU-50) can achieve a full-cut self-healing efficiency above 90 % at 60 ℃ for 2 h. The self-healing process is dependent on the dynamic recombination of hydrogen bonds and disulfide bonds, which can be accelerated by heating because of the faster molecular motion. The dynamics characteristics of hydrogen bonds and disulfide bonds also endows PU-n with the recyclability, the recycled elastomer exhibits similar mechanical and self-healing properties with original elastomer. This work provides an effective strategy to achieve self-healing polyurethanes with the high mechanical strength.

Experimental investigation on low-velocity impact behavior of glass, Kevlar, and hybrid composites with an elastomeric polyurethane matrix

Low-velocity impacts represent a critical dynamic condition for engineering structures. Combining two reinforcing fibers in a single matrix, i.e., hybridization, is considered a feasible way to improve composite performance. In this context, this paper presents an experimental work on composites with Kevlar and glass fabrics and a novel thermoset polyurethane matrix. The coupons are manufactured by vacuum infusion technique and low-velocity impact tests are carried out. First, the impact behavior of Kevlar and glass laminates of different thicknesses is assessed, and then impact tests are performed on different configurations of hybrid laminates, both symmetric and non-symmetric. For the non-symmetric specimens, impact tests were conducted on both sides of the stack. Load vs displacement curves are reported along with absorbed energy. To investigate the damage mechanism, the front, back, and cross-section views of the specimens are analyzed, and features related to the stacking sequences are discussed. Thermographic analyses are carried out on the impacted specimens to further analyze damage. The failure mechanisms are different from traditional epoxy composites and a hybridization effect is reported. The results evidence that the hybrid coupons are viable for structural applications, being capable of absorbing high-impact energies, in particular, non-symmetric hybrid laminates outperformed the Kevlar, glass, and symmetric ones, absorbing roughly 15% less energy for the highest energy impact.

Deformation-Induced Photoprogrammable Pattern of Polyurethane Elastomers Based on Poisson Effect.

Elastomers with high aspect ratio surface patterns are a promising class of materials for designing soft machines in the future. Here, a facile method for fabricating surface patterns on polyurethane elastomer by subtly utilizing the Poisson effect and gradient photocrosslinking is demonstrated. By applying uniaxial tensile strains, the aspect ratio of the surface patterns can be optionally manipulated. At prestretched state, the pattern on the polyurethane elastomer can be readily constructed through compressive stress, resulting from the gradient photocrosslinking via selective photodimerization of an anthracene-functionalized polyurethane elastomer (referred to as ANPU). The macromolecular aggregation structures during stretching deformation significantly contribute to the fabrication of high aspect ratio surface patterns. The insightful finite element analysis well demonstrates that the magnitude and distribution of internal stress in the ANPU elastomer can be regulated by selectively gradient crosslinking, leading to polymer chains migrate from the exposed region to the unexposed region, thereby generating a diverse array of surface patterns. Additionally, the periodic surface patterns exhibit tunable structural color according to the different stretching states and are fully reversible over multiple cycles, opening up avenues for diverse applications such as smart displays, stretchable strain sensors, and anticounterfeiting devices.

Preparation and properties of block copolymerization thermoset polyurethane elastomers prepared in situ

Polyurethane elastomers are commonly employed as binder in propellant propellants and explosives due to their excellent mechanical properties. In-situ block copolymer synthesis of polyurethane for several advantages, including the elimination of the need for solvents in the reaction process, avoidance of excessive reaction steps, and minimizing the generation of byproducts. On the other hand, the in-situ method utilizes a low-cost prepolymer, making it highly suitable for large-scale production. Polyethylene glycol is currently one of the most widely used prepolymer in polymerization. PCL possesses favorable solubility and exhibits hydrophobicity with a low melting point, remarkably noteworthy are its thermoplastic properties, including a high decomposition temperature and a low glass transition temperature. This work employed an in-situ block copolymerization method to synthesize polyurethane elastomers and subsequently investigated their mechanical properties, surface structure, evolution over time, and thermal decomposition process. Polyurethane elastomers exhibited favorable mechanical properties, the elongation properties of these polyurethane systems herein are influenced by the proportion of hydrogen-bonded carbonyl groups within the urethane. The thermal decomposition of polyurethane elastomers can be divided into two distinct processes. Random scission of the polyurethane yielding PCL occurs under low-temperature conditions, while specific cleavage events take place at higher temperatures.

Self-healing polyurethane elastomer with ultra-high mechanical strength and enhanced thermal mechanical properties

Polyurethane (PU) materials are widely used due to their excellent comprehensive properties including high strength, good wear resistance and weather resistance. To further improve the service life and safety of polyurethane materials, self-healing polyurethane materials have been developed. However, self-healing polyurethane generally suffers from low mechanical strength and poor thermal mechanical properties. Here, we have constructed a strong dual network by introducing benzene-1,4-diboronic acid (PDBA) into poly(urethane-urea) (PUU). On one hand, PDBA can form coordination bonds with nitrogen atoms in PUU, leading to the formation of a dual network consisting of boron-nitrogen coordination and hydrogen bonding. This dual network imparts PUU with a maximum tensile strength of 84.2 MPa. On the other hand, boron-nitrogen coordination is more stable than hydrogen bonding at high temperature, thereby significantly enhancing the thermal mechanical properties of PUU (the mechanical strength of PUU-PDBA-50 % and PUU-PDBA-100 % increased by 1.8 times and 2.4 times, respectively, compared to PUU at 100 °C). Meanwhile, the dynamic nature of the dual network endows the material with self-healing ability.

Mechanically Robust yet Body-Temperature Self-Healable Polyurethane Elastomer via the Cross-Linking of Dynamic Boroxines

Mechanically Robust yet Body-Temperature Self-Healable Polyurethane Elastomer via the Cross-Linking of Dynamic Boroxines

Novel Single Emissive Component Tridurylboron-TPU Solid Polymer Ratiometric Fluorescence Thermometers.

Temperature measurements with high spatial resolution and accuracy can provide crucial data for understanding the changing process of microregion. Non-contact ratiometric fluorescence thermometers have received widespread attention for their sensitivity and interference resistibility. However, polymer and organic dye thermometers with such ratiometric fluorescence are very rare, and their applicability and processability are limited. In this study, novel tridurylboron compounds PPB1, PPB2, and PPB3 are designed and synthesized. They exhibit significant temperature responsive ratiometric fluorescence when dispersed in thermoplastic polyurethane elastomers (TPU). With a self-referencing feature and protection of TPU solid polymer, such fluorescence thermometers possess strong interference resistibility. From -10° to 60°C, the fluorescence peak of PPB1-TPU system redshifted by 41nm, the fluorescence color changes from blue to green. For the fluorescence ratiometric temperature measurement procedure, the absolute sensitivity is 14.5%°C-1 (40°C) and relative sensitivity is 6.3%°C-1 (35°C), which is much higher than reported solid polymer fluorescence thermometers. The temperature-responsive ranges can be adjusted by altering the types of polymer substrate and the number of the substituents. Such tridurylboron-TPU polymer fluorescence thermometers can be applied in aqueous environment and processed into devices of various shapes and sizes, demonstrating great potential for application.

High Toughness, Multi-dynamic Self-Healing Polyurethane for Outstanding Energy Harvesting and Sensing.

Triboelectric nanogenerators (TENGs) are an emerging class of energy harvesting devices with considerable potential across diverse applications, including wearable electronic devices and self-powered sensors. However, sustained contact, friction, and incidental scratches during operation can lead to a deterioration in the electrical output performance of the TENG, thereby reducing its overall service life. To address this issue, we developed a self-healing elastomer by incorporating disulfide bonds and metal coordination bonds into the polyurethane (PU) chain. The resulting elastomer demonstrated exceptional toughness, with a high value of 85 kJ m-3 and an impressive self-healing efficiency of 85.5%. Specifically, the TENG based on that self-healing PU elastomer generated a short circuit current of 12 μA, an open circuit voltage of 120 V, and a transfer charge of 38.5 nC within a 2 cm × 2 cm area, operating in contact-separation mode. With an external resistance of 20 MΩ, the TENG achieved a power density of 2.1 W m-2. Notably, even after self-healing, the electrical output performance of the TENG was maintained at 95% of the undamaged device. Finally, the self-healing TENG was employed to construct a self-powered noncontact sensing system that can be applied to monitor human motion accurately. This research may expand the application prospects of PU materials in future human-computer interaction and self-powered sensing fields.

Fully biomass-derived polyurethane based on dynamic imine with self-healing, rapid degradability, and editable shape memory capabilities

In this study, a novel bio-based diol containing imine dynamic bonds (Vanp2) were synthesized using vanillin and bio-based 1,5-pentanediamine. Vanp2 was then introduced into the cross-linking network of betulin-based polyurethanes to obtain betulin-based polyurethanes containing covalent adaptive networks (CANs). Imine dynamic bonds within CAN endowed these betulin-based polyurethanes with self-healing, re-processability, degradability, and editable shape memory functionalities. Meanwhile, the mechanical and thermal properties of these fully bio-based polyurethane materials were characterized. The maximum tensile strength reached 9.5 MPa, while the maximum strain at break was 248 % and the maximum toughness was 13.2 MJ/m3. Thermal decomposition temperature was greater than 300 °C. Since the imine structure could be dissociated under acidic conditions, these polyurethanes could be rapidly degraded in a mixed acid solution at 50 °C in 4 h. This study demonstrated a strategy for synthesizing betulin-based polyurethane elastomers containing CAN using only bio-based feedstock.

Microporous Polyurethane Elastomer’s Comprehensive Properties Affected by Flame Retardant EG/APP

The mechanical characteristics, creep resistance, fatigue resistance, and other comprehensive properties of flame retardants/microporous polyurethane elastomers (FRs/MPUE) have not been systematically researched. Because of this, we used expandable graphite (EG) and ammonium polyphosphate (APP) to conduct this study on FRs/MPUE composites. The thermal degradation and flame retardant characteristics, tensile strength, compressive creep, and dynamic and static stiffness ratio of FRs/MPUE were studied. The findings demonstrated that the optimum synergistic flame retardant effect occurred when the ratio of EG to APP was 2:1. The LOI of MPUE reached 30.5%. The vertical combustion grade achieved V-0. The stage of thermal decomposition was the most stable. However, compared with pure MPUE, the tensile strength was slightly decreased, and the compressive creep and dynamic and static stiffness ratio were slightly increased. The MPUE’s LOI value was more than or equal to 26% when the EG to APP ratio was 2:1 to 1:2. The tensile strength was basically the same as that of pure MPUE. The compression creep was less than 5%, which met the B1 flame retardant requirements and creep resistance performance indicators of floating floor vibration-damping pads.

Production of Polyurethane Elastomers from Ximenia americana L (Wild Olive) Seed Oil and Diisocyanates

Seed oils readily undergo derivatization by alcoholysis to yield biodegradable polyols and Ximenia americana plant from the family of Olacaeae has oily seeds. Hence, the objective of this paper is to assess the production of polyurethane elastomers from Ximenia americana L (Wild Olive) Seed Oil with diisocyanates, namely, hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI) and 4,4’-methylene diphenyl diisocyanate (MDI) respectively using standard procedure and characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Instron Tensile Testing Machine and Thermogravimetric Analyzer (TGA). The tensile strength and tensile modulus for HDI-based polyurethane elastomers, 5.83±0.15 and 3.95±0.07 MPa respectively are higher than the corresponding ones for TDI- and MDI-based polymers. This is consistent with the highest crosslink density (γ) of 5.05×10-3 for HDI-based polymer with corresponding average molecular weight between crosslinks (Mc) of 197.87 gmol-1 The polyurethane elastomers are stable up to 250-265oC with order of stability: HDPU-1.50>MDPU-1.50>TDPU-1.50. The results showed that diol from Ximenia americana seed oil is effective for production of polyurethane elastomers with properties which are comparable to ones of the non-oil-based polymers.

Simultaneous Enhancement of the Mechanical Properties, Performance and Insensitivity of an Energetic Elastomeric Polyurethane Binder by Kinetically Grafting Reactive Spiranes.

A series of robust energetic polyurethane binders was developed by in situ grafting reactive spiranes to achieve the migration-resistant processing aid and compensate for the energy output. The reactive grafting spiranes (RGSs), bearing two highly ring-strained spiranes, were synthesized sequentially to provide a promising ring strain energy up to a maximum value of 290 kJ mol-1. The thermodynamic compatibility of the RGS with uncured glycidyl azido polymer (GAP) was studied quantitatively by analyzing the glass transition temperature of their blendings. The reactivity study of the catalyst-free click reaction with respect to spacer-dependent species was amplified by tracing the extent of the reaction and measuring the activation energy. The faster reactivity of propargyl species was evident from two experimental approaches, which were verified further by theoretical predictions. Interestingly, the energy gap difference in the frontier molecular orbitals agreed well with the difference in activation energy between the two types of spacer-dependent species. The mechanical and thermochemical enhancements of GAP-based polyurethane with RGS were basically gained from those highly ring-strained moieties.

Experimental studies and molecular dynamics simulation of the compatibility between thermoplastic polyurethane elastomer (TPU) and asphalt

Compatibility between polymer and asphalt is an important issue to be considered when the polymer is added to base asphalt as a modifier. It determines the stability of the modified asphalt system. The purpose of this paper is to investigate the effect of shearing temperature and the content of thermoplastic polyurethane elastomer (TPU) on the compatibility between TPU and asphalt by means of experiments and molecular dynamics simulations. Firstly, the molecular models of base asphalt, TPU chain and TPU/asphalt blends were constructed by using Materials Studio 8.0. Based on the rational construction of the model, the effect of shearing temperature on the storage stability of TPU modified asphalt was evaluated by the calculation of solubility parameter (δ) and mean square displacement (MSD). In addition, the effect of different TPU admixtures on the compatibility of TPU with asphalt was characterized by interaction energy and radial distribution function (RDF). The results of molecular dynamics calculation were compared with the results of fluorescence microscopy test (FM) and segregation test. It showed that the minimum difference in solubility parameters between TPU and asphalt occurs when the shearing temperature was 170 °C, at which the diffusion movement of TPU in asphalt was the most active. The interaction energy between TPU and asphalt reached the peak when the content of TPU in asphalt was 17 wt%. Furthermore, the RDF results also indicated that the optimum dispersion effect of TPU in asphalt is achieved at this TPU content. The molecular dynamics simulation results are in agreement with the experimental results.

Room-temperature self-healing polyurethane elastomers with high strength and superior self-healing efficiency based on aromatic disulfide-induced

Polymers are inevitably subject to mechanical damages during molding, processing, and application. Self-healing of internal and surface damage in polymers can be achieved by endowing the materials with room-temperature self-healing functions. This improvement significantly eliminates safety risks caused by material damage, enhances the safety, stability, and service life of polymer materials, facilitates the realization of sustainable resource development, and aligns with the concept of "low carbon". Room-temperature self-healing materials mainly rely on motility of molecular chain segments and dynamical equilibration of forces acting within the system. However, there have been few reports of polyurethane elastomers with high strength and high self-healing efficiency. In this paper, PUIPBD polyurethane elastomers were prepared by the chemical reacting of polytetrahydrofurandiol PTMEG-2000, isophorone diisocyanate IPDI, 1,4-butanediol (BDO) with 4,4′-dihydroxydiphenyl disulfide (DHDDS) as monomers. It was found that the self-healing efficiency of the synthesized polyurethane elastomer series was very high after 48 h of self-healing at 25 °C, all of which exceeded 79 %, and the tensile strength, elongation and fracture toughness of best performing elastomer PU90/10 could reach 89.8 %, 99.9 %, and 95.6 %, respectively after 48 h of self-heal at room temperature, showing good simultaneous room temperature self-healing efficiency.