PU Elastomers Research Articles

Synergistic integration of dynamic acylsemicarbazide bonds and disulfide bonds into polyurethane: A facile strategy to surmount the tradeoff between mechanical strength and self‐healing capacity of elastomers

AbstractThe polymeric materials can simultaneously possess high mechanical properties and outstanding self‐healing performance under mild condition have found widespread applications in various fields. However, this type of polymers is exceedingly rare due to the trade‐off between mechanical robustness and chain flexibility for healing. In this study, we designed a facile strategy for synergistic integration of dynamic acylsemicarbazide (ASC) bonds and disulfide bonds into polyurethane elastomer by the reaction between 3,3′‐dithiobis(propionohydrazide) and isocyanate‐terminated Pre‐PU. The obtained elastomer ASC‐SS‐PU not only possesses an outstanding tensile strength (17.1 MPa), good stretchability (735%) and high toughness (57.16 MJ·m−3), but also exhibits excellent self‐healing performance under mild condition. The healing efficiency of the damaged ASC‐SS‐PU samples (breakage rate >90%) can reach over 70% healing at 60°C for 40 min, which is much lower than conventional ASC‐based PU elastomer. Considering the simple and easy‐to‐scaleup preparation process and commercially available low‐cost raw materials, outstanding mechanical strength and toughness, as well as high healing efficiency under mild condition, the ASC‐SS‐PU elastomer as self‐healing but strong materials have great potential for use in various fields.

Silicone‐containing polyurea elastomer possessing main‐chain boron–oxygen bonds with delayed stress relaxation and improved adhesive properties

AbstractPolyurea (PU) elastomers have attracted considerable attention in the field of protective polymeric coatings. In this work, a dithiol‐terminated boronic ester was synthesized and used to incorporate dynamic boron–oxygen (B–O) bonds in the PU main chain based on thiol isocyanate while amino‐terminated polydimethylsiloxane (PDMS) was introduced to retain good chain flexibility. The modified PU elastomer was found to have a microphase‐separated structure in which the hard blocks served as physical crosslinks. The glass transition temperature (Tg) slightly increases when dynamic B–O bonds exist while further introduction of PDMS soft segment can lower Tg to −55.63 °C. The introduction of dynamic B–O bonds and diminished hydrogen bonding led to a decrease in mechanical strength and elongation at break. Interestingly, the simultaneous incorporation of PDMS and dynamic B–O bonds is favorable for strain rate dependence and suppressing stress relaxation. The potential for bond‐exchange interactions between the dynamic B–O bonds and hydroxyl groups on metal surfaces substantially improved the adhesion of the PU elastomer to metal substrates. Therefore, our work can offer valuable insights for the structural design of functional PU coatings tailored for anti‐impact applications. © 2024 Society of Chemical Industry.

Gelation of PU elastomers: rheological characterization for liquid additive manufacturing

AbstractPolyurethane (PU) is a versatile polymer with many applications in a wide range of products. A novel 3D printing technology called liquid additive manufacturing (LAM) extended its possibilities by generating PU elastomers with gradient properties in continuous processing. LAM, being a relatively new technique, has not been extensively researched, particularly in terms of the curing behavior of the liquid resin. In this work, we investigated the effect of composition on gelation time tGP as measured by time-resolved mechanical spectroscopy (TRMS) and analyzed using the Winter–Chambon criterion with the assistance of the IRIS software. This method is more accurate than the previous approach, which involved time sweeps with a constant frequency. It was found that the gel time tGP first decreased and then increased with increasing polyol ratio, ranging from 231 to 378 min. Furthermore, the crosslink densities of the different PU elastomers measured from the rheological and tensile tests were calculated and compared based on the theory of rubber elasticity. The crosslink density decreased with an increasing polyol ratio in both methods. However, the crosslink density values obtained from the rheological measurements were higher than those from the tensile tests. These findings demonstrate that adjusting the polyol ratio is an effective means of achieving gradient properties. The composition effects we measured offer valuable insights for the design of LAM–PU elastomers.

Mechanical Behaviors of Hybrid Composites with Orthogonal Spiral Wire Mesh and Polyurethane Elastomer

This work aims to significantly improve the mechanical properties of conventional rigid lattice structures under repeatable large deformations. A novel hybrid material is proposed based on the concept of interpenetrating composite materials. The material utilizes a woven TC4 orthogonal spiral wire mesh as the skeleton and PU elastomer (OSWM‐PU) as the matrix. The uniaxial tensile tests demonstrate that OSWM‐PU possesses the excellent load‐bearing capacity, allowing for large deformations (≥60%) while maintaining partial integrity even after matrix fracture. Optical measurements and simulation analysis reveal that Poisson's ratio can be adjusted within a certain range by manipulating the microscopic parameters (p, d) of the longitudinal helical filaments. Cyclic tensile experiments further demonstrate that OSWM‐PU exhibits exceptional energy absorption performance, multiple energy dissipation modes, and a more pronounced Mullins effect. The stress relaxation experiment reveals the significant influence of the volume fraction of the skeleton on long‐term loading conditions. The orthogonal spiral wire skeleton exhibits a superior hooking effect without dividing the matrix, enabling OSWM‐PU to possess enhanced collaborative deformation capability and inherent designability in the orthogonal direction. These characteristics make it highly promising for applications in various robot joints and as flexible aircraft skin, offering excellent prospects for utilization.

Synergistic enhancement of the robustness of multifunctional polyurethane via an ionic noncovalent cross-linking network and aromatic disulfides

The preparation of functional polyurethane materials with high strength, toughness, and excellent self-healing ability is currently challenging. In this study, a multifunctional bi-dynamic supramolecular crosslinked network PU elastomer was successfully prepared by introducing ionic bonds and aromatic disulfide bonds into a PU matrix. The resulting ionic PU elastomers exhibited impressive mechanical properties, including high tensile strength (39.9 ± 4.4 MPa) and excellent elongation at break (1930 ± 345 %). They also demonstrated efficient self-healing capability (94.4 %), recyclability and processability. The distribution of hydrophilic ion bonds within the polymer networks enabled the elastomers to possess water-induced shape memory and antibacterial activity. Additionally, the hydrophilicity of the elastomers provided a self-cleaning ability when used as a coating material. The covalent bonding of the cations with the PU matrix prevented the leaching of bactericidal substances, ensuring good biocompatibility of the ionic PU. Furthermore, a double-layered self-healing composite flexible sensor was developed using the ionic PU as the substrate and carboxylated carbon nanotubes (CNTs-COOH) as the conductive medium to detect human motion. These multifunctional ionic PU elastomers offer great potential for the design and preparation of robust materials with self-healing ability for various applications across multiple fields.

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.

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.

Lignin demethylation enabled robust and reprocessable bio-polyurethane elastomer with adaptable cross-linking network

The development of sustainable bio-polyurethanes (bio-PU) from nonfood lignin has been attracting extensive attention owing to the abundant reserves, stable aromatic structures, and rich hydroxyls of lignin. However, exploiting a high-performance lignin-based PU integrating excellent mechanical properties with reprocessability is still a challenge. Herein, we proposed a dynamic phenolic-carbamates to construct robust and reprocessable bio-PU elastomers based on the reaction of phenolic lignin (PL) with isocyanate. Benefiting from the low Mw of 1692 Da and the abundant phenolic hydroxyls of 8.3 mmol/g, the adaptable cross-linking network consisting of dynamic hydrogen bonds and phenolic-carbamates were formed by PL. The synthesized phenolic lignin-based PU (PLPU) displayed tunable mechanical properties via adjusting PL substitution amount. The tensile strength, modulus and toughness of PLPU reached 58.8 MPa, 1350.3 MPa, and 57 MJ/m3 when the substitution amount of PL was 70%, respectively. Importantly, the reversible cross-linking structure endowed PLPU with excellent multi-reprocessability. After 5 reprocessing cycles, the retention ratio of strength, breaking elongation, modulus and toughness was 87.6%, 58.9%, 218.1% and 63.3%, respectively, which were 1.6, 1.1, 3.5, 2.2 times higher than those of commercial lignin-based polyurethane (CLPU). Therefore, this work not only presents a robust and multi-reprocessable lignin-based PU elastomer with high substitution amount, but also provides a promising sustainable alternative to replace petroleum-based plastic.

Mechanical Robust, Self-Healable Polyurethane Elastomer Enabled by Hierarchical Hydrogen Bonds and Disulfide Bonds.

The fabrication of mechanically robust and self-healing polymeric materials remains a formidable challenge. To address the drawbacks, a core strategy is proposed based on the dynamic hard domains formed by hierarchical hydrogen bonds and disulfide bonds. The dynamic hard domains dissipate considerable stress energy during stretching. Meanwhile, the synergistic effect of hierarchical hydrogen bonds and disulfide bonds greatly enhances the relaxation dynamics of the PU network chains, thus accelerating network reorganization. Therefore, this designed strategy effectively solves the inherent drawback between cohesive energy and relaxation dynamics of the PU network. As a result, the PU elastomer has excellent mechanical properties (9.9 MPa and 44.87 MJ/m3) and high self-healing efficiency (96.2%). This approach provides a universal but valid strategy to fabricate high-performance self-healing polymeric materials. Meanwhile, such materials can be extended to emerging fields such as flexible robotics and wearable electronics.

Controlling the reactivity of hydrophilic bark extractives as biopolyols in urethane-formation reactions using various catalysts

The composition, functionality, and reactivity of black alder (Alnus glutinosa) bark extractives as a biopolyol with polymeric diphenyl methane diisocyanate (PMDI) have been studied using a variety of methods, including HPLC, GPC, GC, wet chemistry, and isothermal calorimetry. The Black alder (BA) bark extractives were identified as a prospective polyol consisting mainly of the oregonin-xyloside form of diarylheptanoid, which contains OH groups that are almost equally represented by phenolic and aliphatic origins. To identify catalysts that effectively increase the reactivity of low-active phenolic OH groups in urethane formation reactions, the kinetics of extractives and model compounds' interaction with PMDI catalyzed with tin organic, dibutyl tin dilaurate (DBTDL) and tertiary amine, 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyst in dimethylsulfoxide (DMSO) solution were studied. The results showed that DABCO resulted in a fourfold higher reactivity of phenolic groups with PMDI compared to DBTDL catalyzed reactions. Furthermore, the reactivity of phenolic groups with PMDI catalyzed by DABCO was almost twofold greater than that of aliphatic OH catalyzed by DBTDL. The second-order constants of 31.9 × 10−4 mol·L−1·s−1 and 53.7 × 10−4 mol·L−1·s−1 were determined for the interaction of extractives with PMDI in the presence of DBTDL and DABCO, respectively. The disappearance of the radical scavenging effect of phenolic compounds in extractives derived PU elastomers obtained with DABCO catalyst indicates complete reactions of phenolic groups with isocyanate, while these groups remain partly free in the case of DBTDL catalysis. It is assumed that a combination of DBTDL and DABCO catalysts will be necessary to achieve high crosslinking while leaving a small portion of free phenolic groups in the bio-based PU network, thus obtaining material with high mechanical properties and thermal oxidative stability.

Polyurethane/perovskite quantum dot elastomer composite with high stability and self-repairable properties

How to improve the stability and processability of organic-inorganic hybrid perovskite quantum dots (OHPQD) is an important topic in recent research. In this work, the stability and machinability of OHPQD were improved by blending with PU elastomer. The CsPbBr 3 −PU composites can be achieved easily by pouring molding process with rather excellent humidity and thermal stability. The tensile strength of 14 ​MPa and elongation of 580% at break of PU/CsPbBr 3 elastomer composites with self-repair properties were obtained, which was attributed to the introduction of disulfide bonds. It lays a foundation for the application of OHPQD. Polyurethane/perovskite quantum dot composites with high environmental stability, excellent mechanical properties and self-healing function are constructed by pouring process. The blending rule and the luminescence mechanism of which are revealed and clarified. It will promote the practical application of perovskite quantum dots in the industrial field.

Dipentaerythritol‐Derived Hyperbranched Polyurethane Elastomers and Their Applications in Flexible Strain Sensors

AbstractPolyurethane (PU) elastomers have great potential to work as flexible substrates in electronic materials. In this work, hyperbranched PU elastomers are designed and prepared utilizing dipentaerythritol, isophorone diisocyanate, and polytetrahydrofuran as the monomers. The mechanical properties and transparency of the PU elastomers are regulated by the molar ratio of hydroxyl group to isocyanate group (OH/NCO). High tensile strength (26 MPa) and elongation at break (>600%) are achieved. Furthermore, PU elastomer composites are developed by introducing graphene into the surface of PU elastomers. PU elastomer composites are further utilized in assembling flexible strain sensors, which achieve a gauge factor (GF) of 170 in the strain range of 0–75% and a GF of 549 in the strain range of 75–225%. The response time is as low as 140 ms and at least 1000 reversible sensing cycles are successfully conducted. Utilizing such flexible sensors, monitoring of various human motions, including biceps motion, finger bending, knee joint bending, elbow bending, and vocal cord vibration, are demonstrated. Overall, this work not only develops a new kind of PU elastomer with hyperbranched structure but also provides candidate materials for flexible sensors and other flexible electronic devices.

Hydrophilic and hydrophobic films based on polyurethane cationomers containing TiO2 nanofiller

Polyurethane cationomers thin films containing (0–2 wt%) surface functionalized TiO2 as ecological water dispersions were obtained, and the structure of the cationomers have been confirmed using FTIR and NMR methods. Incorporation of the surface modified TiO2 nanoparticles caused considerable changes in the thermal, mechanical, and surface properties of the PU films. Importantly, films made with MDI isocyanate surface-modified TiO2 were hydrophobic and their free surface energy (FSE) was below 35 mJ/m2, while films containing unmodified TiO2 were hydrophilic with FSE above 48 mJ/m2. SEM observations exhibited uniform dispersion of nanoparticles in PU matrix. The activation energy of the glass transition process was calculated based on multifrequency TOPEM DSC data and the higher activation energy was found for composites with higher content of PU/TiO2 or PU/f-TiO2 due to the stronger hydrogen bonding between soft segment microdomains and hard segments after incorporation of PU/TiO2 or PU/f-TiO2. Good thermal and mechanical properties, which correspond to those of PU elastomers, are promising features for the application of the obtained cationomers as modern coating materials.

Transparent, flame‐retarded, self‐healable, mechanically strong polyurethane elastomers: Enabled by the synthesis of phosphorus/nitrogen‐containing oxime chain‐extender

AbstractPolyurethane (PU) elastomer has been widely used due to its excellent mechanics, acid and alkali resistance, abrasion resistance, and other properties. However, obtaining simultaneous mechanically strong, flame‐retarded, transparent, and efficient self‐heal ability of PU elastomer is of great challenge due to the structural design. Here, a phosphorus/nitrogen‐containing Oxime chain extender (PSK‐2) was introduced into the synthesis of PU elastomers to obtain a transparent, flame‐retarded, self‐healable, mechanically strong PU elastomers. The PU elastomers exhibited high tensile strength of ~23.3 MPa, breaking strain of ~1693%, good flame retardancy with high LOI of ~29.2%, and UL‐94 V1 rating with the addition of 4.67 mmol (mass fraction 1.37 wt%) PSK2. Furthermore, the PUPSK2 elastomer material also had good healing ability up to 60% at room temperature and good transparency of 83.7% at 350–800 nm visible.

Development of Dash insulation with PU elastomer based sound insulation materials for increasing the sound insulation performances of electric vehicle noise derived from motor

At present, fuel efficiency improvement technologies for example weight, engine efficiency improvement, design modification, and eco-friendly car are being proceed due to the tightened international regulations. Therefore, production of eco-friendly cars specially electric car has increased. Due to that, the main noise source has changed from engine to motor noise and road noise as it has been changed from engine cars that have led engine technology to eco-friendly cars. As the noise source has changed, it is necessary to manufacture sound absorption/insulation structure for the noise characteristics generated by electric vehicles. In this work, the elastomer sheet was applied to the Dash outer as automotive terior parts for reducing engine noise. We applied the elastomer sheets for generation Dash outer layers (nonwooven/PU foam/nonwooven) to improve sound insulation properties. The elastomer sheet showed surface wetting between PU foam and elastomer sheets by optical microscopy. The acoustic properties were measured by APAMAT-II and BUCK tests.

Rotaxane-Based Dual Function Mechanophores Exhibiting Reversible and Irreversible Responses.

Mechanochromic mechanophores permit the design of polymers that indicate mechanical events through optical signals. Here we report rotaxane-based supramolecular mechanophores that display both reversible and irreversible fluorescence changes. These responses are triggered by different forces and are achieved by exploiting the molecular shuttling function and force-induced dethreading of rotaxanes. The new rotaxane mechanophores are composed of a ring featuring a luminophore, which is threaded onto an axle with a matching quencher and two stoppers. In the stress-free state, the luminophore is preferentially located in the proximity of the quencher, and the emission is quenched. The luminophore slides away from the quencher when a force is applied and the fluorescence is switched on. This effect is reversible, unless the force is so high that the luminophore-carrying ring slips past the stopper and dethreading occurs. We show that the combination of judiciously selected ring and stopper moieties is crucial to attain interlocked structures that display such a dual response. PU elastomers that contain such doubly responsive rotaxanes exhibit reversible fluorescence changes over multiple loading-unloading cycles due to the shuttling function, whereas permanent changes are observed upon repeated deformations to high strains due to breakage of the mechanical bond upon dethreading of the ring from the axle. This response allows one, at least conceptually, to monitor the actual deformation of polymer materials and examine mechanical damage that was inflicted in the past on the basis of an optical signal.

Application of polyurethane in the production of shoe soles

Good footwear should be comfortable, long-lasting and fit for purpose, polyurethanes allow designers to meet all of these objectives. Polyurethanes are used in the footwear industry to make insoles and shoe soles.There are two types of PU soles a polyether and polyester based PU sole. Polyether based PU soles have a high resistance against hydrolysis and low oil resistance while polyester based PU soles have a low resistance against hydrolysis and high oil resistance. In this work thermal and mechanical properties of PU elastomers with polyether and polyester polols with different hard segment content were investigated. Differential scanning calorimetry (DSC) indicated partial crystalinity structure of the PU elastomers. PU elastomers based on polyether type polyol show the higher degree of crystalization. Based on DMAresults , Tgvalues of the PU increases and broadened with increasing hard segment content in the PU elastomers based on polyester polyol, due to the interaction between the urethane groups and the ester carbonyl groups. Mechanical studies indicated that the tensile strength of PU elastomers increased with hard segment.

Fabrication and properties for novel graphene oxide powder with extra large interlayer spacing and high reactivity

Exfoliation and preparation of large interlayer spacing and reactive graphene oxide (GO) powder are of crucial importance and neck technologies for their applications in polymer composites. Herein, we reported an innovative approach to prepare a large interlayer spacing reactive NCO-GO powder by covalent functionalization of GO with 4,4’-diphenylmethane diisocyanate (MDI). The morphology, microstructure, interlayer spacing, dispersion, and thermal stability of the NCO-GO powder were seriously investigated by FT-IR, XPS, XRD, TEM, TG, and Raman. Interlayer spacing of NCO-GO nanosheets was successfully expanded from 0.83 nm to 2.43 nm after modification, the NCO-GO powder showed better dispersion stability than GO in polar solvents and higher decomposition temperature. The fabricated novel NCO-GO powder showed a great prospect in the future to prepare graphene-based PU composites with significantly enhanced electrical conductivity and mechanical properties of PU elastomer.

A colorless, transparent and self-healing polyurethane elastomer modulated by dynamic disulfide and hydrogen bonds

A self-healing PU elastomer modulated by disulfide and hydrogen bonding with high transparency of 97% was reported.

Designing a Highly Energetic PCL-GAP-PCL-based PU Elastomer; Investigation of the Effect of Plasticizers on Its Properties

Designing a Highly Energetic PCL-GAP-PCL-based PU Elastomer; Investigation of the Effect of Plasticizers on Its Properties