Polyurethane Elastomers Research Articles

An antibacterial, highly stretched and self-healing polyurethane elastomer for flexible electronic devices

Broadening the range of practical applications of self-healing materials has become a research hotspot for the development of durable and smart materials. This study the development of a hydrogen bond-rich of self-healing elastomer, formed by the combination of disulfide and diazolidinyl urea (DU) cross-linked polyurethane polymers (PDD). The prepared polyurethane elastomer material possessed extremely high mechanical properties (including a stress of 25 MPa and high toughness of 306 MJ/m3). Besides, PDD exhibited an excellent self-healing performance. Even if it is subjected to long-term tensile deformation or extreme strain, it could recover almost completely to its initial state within 12 h in a 60 °C environment. In addition, the synergistic effect of diazolidinylurea and element S on the polymer film gave the material excellent antimicrobial properties. Finally, we added carbon nanotubes into the polyurethane system and assembled them into smart sensors for applications in flexible electronic devices. The versatility of this sensor has been demonstrated in human motion applications.

Moisture-driven degradation mechanisms in the viscoelastic properties of TPU-Based syntactic foams

Syntactic foams have found widespread usage in various applications including, marine, aerospace, automotive, pipe insulation, electrical cable sheathing, and shoe insoles. However, syntactic foams are often exposed to moisture when used in these applications that potentially alter their viscoelastic properties, which influences their long-term durability. Despite their significance, previous research has mainly focused on experimental studies concerning mechanical property changes resulting from filler loading and different matrix materials, overlooking the fundamental mechanisms resulting from moisture exposure. The current paper aims to bridge this gap in knowledge by elucidating the impact of long-term moisture exposure on TPU and TPU-based syntactic foam through multi-scale materials characterization approaches. Here, we choose a flexible syntactic foam manufactured using thermoplastic polyurethane elastomer (TPU) reinforced with glass microballoons (GMB) through selective laser sintering. Specifically, the research investigates the influence of moisture exposure time and the volume fraction of GMB on chemical and microphase morphological changes, along with their associated mechanisms. The study further examines how these microphase morphological changes manifest in viscoelastic properties.

Healable, degradable polyurethane elastomers with excellent mechanical properties based on multiple hydrogen bonds

AbstractDue to its comprehensive properties, polyurethane elastomer (PU) plays a vital role in ships, construction, transportation facilities, and other fields. However, it is challenging to design polyurethane elastomer materials with good mechanical properties, self‐healing ability, and degradable ability. Herein, a kind of polyurethane elastomer based on multiple hydrogen bond crosslinking was successfully synthesized by using polycaprolactone with substantial crystallization as a soft chain segment and introducing adipic dihydrazide (ADH) and U2‐diol (a ureido‐pyrimidinone with two hydroxyl groups at the end) to achieve ordered hydrogen bond assembly design and control. The elastomer has good tensile strength, healability, degradability, and solubility. The maximum tensile strength and toughness of the prepared polyurethane elastomer (PUAD) were 46.34 MPa and 687.66 MJ/m3, respectively. With the increase of U2‐diol content, the self‐repair efficiency was greatly enhanced. After seven repair cycles, the self‐repair efficiency can still reach 66.88%. In addition, the bacterial degradation test using Pseudomonas aeruginosa as a strain showed that PUAD film had excellent degradability. The dissolution test with N,N‐dimethylformamide (DMF) as solvent showed that the tensile strength was almost unchanged after three dissolutions.

Structure-Property Relationship and Multiple Processing Studies of Novel Bio-Based Thermoplastic Polyurethane Elastomers.

Currently, the growing demand for polymeric materials has led to an increased need to develop effective recycling methods. This study focuses on the multiple processing of bio-based thermoplastic polyurethane elastomers (bio-TPUs) as a sustainable approach for polymeric waste management through mechanical recycling. The main objective is to investigate the influence of two reprocessing cycles on selected properties of bio-TPUs. Two series of bio-based TPUs were synthesized via a solvent-free two-step method with the use of hexamethylene diisocyanate or hexamethylene diisocyanate/partially bio-based diisocyanate mixtures, bio-based poly(triamethylene ether) glycol, and bio-based 1,3 propanediol. Both the raw bio-TPUs and those subjected to two reprocessing cycles were examined with respect to their chemical, physical, thermal, thermomechanical, and mechanical properties. The conducted research revealed that reprocessing led to changes in the phase separation between the hard and soft segments, thereby affecting the bio-TPUs' properties. Both series of materials showed similar chemical structures regardless of reprocessing (slight changes were observed in the range of carbonyl peak). The thermal properties of TPUs exhibited slight differences after each reprocessing cycle, but generally, the non-processed and reprocessed bio-TPUs were thermally stable up to about 300 °C. However, significant differences were observed in their mechanical properties. The tensile strength increased to 34% for the twice-reprocessed bio-TPUs, while the elongation at break increased by ca. 200%. On the other hand, the processing cycles resulted in a decrease in the hardness of both bio-TPU series (ca. 3-4 °ShA). As a result, the prepared bio-TPUs exhibited characteristics that were closer to those of the sustainable materials model, promoting the circular economy of plastics, with environmental benefits arising from their recyclability and their high content of bio-based monomers (78.4-78.8 wt.%).

Towards Three-Dimensional Printed Thermal Conductive Polymeric Composites using a Binary-Composite Hybrid based on Boron Nitride Nanoparticles and Micro-Diamonds.

Thermally conductive polymeric composites are promising for heat management in microelectronic devices. This work presents a binary-hybrid composite of boron nitride (BN) nanoparticles and micro-diamond (D) fillers in an elastomeric polyurethane (PU) matrix which can be three-dimensionally printed to produce a highly flexible and self-supporting structure. The research shows that a combination of 16.7wt.% BN and 16.7wt.% D results in a robust network within the polymer matrix to improve the tensile modulus more than 9 times with respect to neat PU. Significantly, the hybrid matrix enhances the thermal conductivity by more than 2 times when compared to neat PU. The enhancement in mechanical, and thermal features make this three-dimensional printable multiscale hybrid composite suitable for flexible and stretchable microelectronic applications. This article is protected by copyright. All rights reserved.

Mechanically strong, soft yet tough, tear-resistant and room-temperature healable elastomers via dynamic biphasic hard segment strategy for flame retardant application

Due to the inherent weak molecular chain migration ability of hard polymer materials, leads to their inability to recover after damage. Hence, a novel approach as the “dynamic biphasic hard segment” strategy is proposed. This strategy involves introducing hard segments with both hard and soft phase structures into the molecular chain to balance high mechanical strength with self-healing properties. The essential features of dynamic biphasic hard segments include: (Ⅰ) asymmetric continuous loose structure, (Ⅱ) controllable binding energy strength, (III) sequential dissociation and recombination of multiple hydrogen bonds. To synthesize supramolecular polyurethane elastomers (PUMI-A3D7) based on this dynamic biphasic hard segment strategy. PUMI-A3D7 exhibits high mechanical strength, toughness, notch insensitivity and room temperature self-healing ability. Specifically, the mechanical tensile strength of PUMI-A3D7 is 26.59 MPa, and 96.54% of its original mechanical properties can be restored within 24 h after a fracture. Using the superior properties of PUMI-A3D7 as the matrix, a flexible room temperature repairable flame-retardant composite (PUMI-A3D7/Al(OH)3/GP) is developed. PUMI-A3D7/Al(OH)3/GP possesses both room temperature self-healing function and flame-retardant properties. Notably, few studies have been conducted on repairable flexible flame-retardant materials. The combination of self-healing and flame-retardant properties provides valuable guidance for the development of multi-functional materials in the future.

Strategy for Constructing Phosphorus-Based Flame-Retarded Polyurethane Elastomers for Advanced Performance in Long-Term.

Polyurethane elastomer (PUE), which is widely used in coatings for construction, transportation, electronics, aerospace, and other fields, has excellent physical properties. However, polyurethane elastomers are flammable, which limits their daily use, so the flame retardancy of polyurethane elastomers is very important. Reactive flame retardants have the advantages of little influence on the physical properties of polymers and low tendency to migrate out. Due to the remarkable needs of non-halogenated flame retardants, phosphorus flame retardant has gradually stood out as the main alternative. In this review, we focus on the fire safety of PUE and provide a detailed overview of the current molecular design and mechanisms of reactive phosphorus-containing, as well as P-N synergistic, flame retardants in PUE. From the structural characteristics, several basic aspects of PUE are overviewed, including thermal performance, combustion performance, and mechanical properties. In addition, the perspectives on the future advancement of phosphorus-containing flame-retarded polyurethane elastomers (PUE) are also discussed. Based on the past research, this study provides prospects for the application of flame-retarded PUE in the fields of self-healing materials, bio-based materials, wearable electronic devices, and solid-state electrolytes.

Robust Self-Healable and Three-Dimensional Printable Thermoplastic Elastomeric Waterborne Polyurethane for Artificial Muscle and Biomedical Scaffold Applications

Robust Self-Healable and Three-Dimensional Printable Thermoplastic Elastomeric Waterborne Polyurethane for Artificial Muscle and Biomedical Scaffold Applications

Study of stress wave attenuation characteristics of particle ceramic embedded polyurethane composites

In this paper, particle ceramic embedded polyurethane composites were prepared, and the dynamic and static mechanical properties of polyurethane elastomers were tested. Experiment and simulations were used to investigate the effects of different design parameters of polyurethane elastomers and particle ceramic on the stress wave attenuation of the composites. The microscopic morphology, energy absorption, and attenuation capabilities of the composites were analyzed and discussed. The results show that the polyurethane elastomers adheres well to the particle ceramic after impact and exhibits sufficient bonding with stable interfacial strength; As the volume fraction of particle ceramic increases, the energy absorption ratio also increases; The “harder” the polyurethane elastomer, the weaker the composite attenuation ability of stress waves. The function relationship between the composite attenuation ability of stress waves and the particle ceramic area occupy ratio and the number of stacked layers is obtained by fitting, which shows that the composite attenuation ability of stress waves is inversely proportional to the area occupy ratio and positively proportional to the number of stacked layers of particle ceramic.

Catalyst-Free Synthesis of Betulin-Based Polyurethane Elastomers with Outstanding Mechanical Properties and Solvent Resistance

Catalyst-Free Synthesis of Betulin-Based Polyurethane Elastomers with Outstanding Mechanical Properties and Solvent Resistance

Polyurethane Elastomers Based on Epoxy-Terminated Oligomers

Polyurethane Elastomers Based on Epoxy-Terminated Oligomers

Shape-Programmable Liquid-Crystalline Polyurethane-Based Multimode Actuators Triggered by Light-Driven Molecular Motors.

In recent years, light-driven soft actuators have been rapidly developed as enablers in the fabrication of artificial robots and biomimetic devices. However, it remains challenging to amplify molecular isomerization to multiple modes of macroscopic actuation with large amplitude and complex motions. Here, a strategy is reported to build a light-responsive liquid-crystalline polyurethane elastomer by phototriggered overcrowded alkene-based molecular motors. A trifunctional molecular motor modified with an ethylene glycol spacer on the rotor and stator functions as a crosslinker and unidirectional stirrer that amplifies molecular motion into macroscopic movement. The shape-programmable polymeric film presents superior mechanical properties and characteristic shape-memory effect. Furthermore, diverse modes of motions including bending, unwinding, and contracting with tunable actuation speed over a wide range are achieved. Such research is hoped to pave a new way for the design of advanced light-responsive soft actuators and robots.

Graphene stripping, a convenient and environmentally friendly technology for the preparation of polyurethane/graphene nanocomposites as a new type of highly wear‐resistant materials

AbstractThermoplastic polyurethane elastomer (TPU) has excellent wear resistance properties. Graphene can further improve the friction and wear performance of TPU. However, the agglomeration of graphene in the matrix is still a serious problem. In this study, the solid‐state shear milling technology (S3M) was used to prepare the composite material with graphene stripped and dispersed in TPU. It was found that the graphene sheets were uniformly distributed in the polyurethane matrix, and the thickness of the graphene sheets was reduced from 40 to 2 nm. The mechanical strength increased from 18.4 to 23.3 MPa, an increase of 30%, and under the same conditions, the friction coefficient is reduced from 0.7 to 0.5, and the wear rate is reduced from 10.73% to 0.62%. From these results, the additive dispersion effect of silicone oil and liquid paraffin in the composite material was also investigated. The results showed that the friction coefficient was reduced from 2.0 to 1.0 because of the good lubricating effect of liquid paraffin, whereas silicone oil aggravated the agglomeration phenomenon of graphene and worsened the friction and wear properties.

High efficiency photothermal cyclic self-healing antibacterial coating based on in-situ dual-functional BiOI@Bi2S3

Although extremely challenging, it is highly desirable to develop self-healing materials that exhibit high efficiency under environmental conditions for marine protection applications. In this work, polyurethane elastomers with hydrogen bond and dimethylglyoxime–urethane (DOU) coordination complex were combined with in-situ dual-functional BiOI@Bi2S3 to synthesize high-efficiency photothermal cyclic self-healing antibacterial coating. The photothermal efficiency of BiOI@Bi2S3 is improved by 38% through interfacial regulation. BiOI@Bi2S3/PU rapidly rises by 50.2 °C within 300 s under near-infrared (NIR) light, which can trigger the hydrogen bond of polyurethane coating and recover the barrier properties of the coating through self-healing. Density functional theory was used to simulate and analyze the generation of multiple electron transfer paths after the vulcanization of BiOI, which improves the interfacial mobility of photogenerated carriers and generates more heat. Importantly, molecular dynamics verified the self-healing mechanism of hydrogen bond and the photothermal lifting mechanism of the coating. After 5th scratches and self-healing cycle tests, the coating has a self-healing efficiency of more than 80%, which can ensure the self-healing and anticorrosion protection performance of the coating for multiple cycles. The photocatalytic and photothermal properties of BiOI@Bi2S3 enhance the antibacterial rate of the coating up to 99%. This work provides heuristic perspectives for the design of coatings with anti-corrosion, antibacterial and self-healing properties.

Synthesis and properties of polymer electrolytes based on polyurethane elastomer and lithium salts

Polymer solid electrolytes were obtained by swelling the polyurethane elastomer with solutions of lithium salts LiBF4 and LiClO4 in DMSO at different concentration of lithium salt. The swelling effect was found to decrease with the increase in the salt concentration, whereas, the ionic conductivity has a maximum of 6–8·10–4 S/cm at 5 wt.% lithium salt. The salt solutions incorporated into the polymer pores have melting points ranging from –10 to 2 °C and de-swelling takes place at low temperatures. The obtained polyurethane elastomer materials have a high conductivity and may be promising for use in flexible lithium polymer batteries.

Self-Healing of Electrical Damage in Microphase-Separated Polyurethane Elastomers with Robust Dielectric Strength Utilizing Dynamic Hydrogen Bonding Networks

Self-Healing of Electrical Damage in Microphase-Separated Polyurethane Elastomers with Robust Dielectric Strength Utilizing Dynamic Hydrogen Bonding Networks

Synthesis and Comparative Study of Polyether-b-polybutadiene-b-polyether Triblock Copolymers for Use as Polyurethanes.

In this paper, the effects of HTPBs with different main-chain microstructures on their triblock copolymers and polyurethane properties were investigated. Three polyether-modified HTPB triblock copolymers were successfully synthesized via a cationic ring-opening copolymerization reaction using three HTPBs with different microstructures prepared via three different polymerization methods as the macromolecular chain transfer agents and tetrahydrofuran (THF) and propylene oxide (PO) as the copolymerization monomers. Finally, the corresponding polyurethane elastomers were prepared using the three triblock copolymers as soft segments and toluene diisocyanate (TDI) as hard segments. The results of an analysis of the triblock copolymers showed that the triblock copolymers had lower viscosity and glass transition temperature (Tg) values as the HTPB 1,2 structure content decreased, although the effect on the thermal decomposition temperature was not significant. An analysis of the polyurethane elastomers revealed that as the content of the 1,2 structure in HTPB increased, its corresponding polyurethane elastomers showed a gradual increase in breaking strength and a gradual decrease in elongation at break. In addition, PU-1 had stronger crystallization properties compared to PU-2 and PU-3. However, the differences in the microstructures of the HTPBs did not seem to have much effect on the surface properties of the polyurethane elastomers.

The Synergistic Effects Between Liquid Crystal and Crystalline Phase on Photo-Responsive Elastomers Toward Quick Photo-Responsive Performance.

Adopting only a small amount of azobenzene molecular to design liquid crystal photo-responsive materials capable of quick response and flexible adjustability is in high demand but is challenging. Herein, we introduced azobenzene molecules into polyurethane elastomer containing crystalline structure for preparing azobenzene liquid-crystal elastomers (ALCEs) and discovered this phenomenon of the synergistic effects between liquid crystal and crystalline phase. The key point of the work is that the synthetic ALCEs can utilize the reversible isomerism capability of azobenzene molecules under light irradiation, which can pry the motion of the macromolecular crystalline region in system to realize the large macroscopic deformation of the photo-responsive behavior. Obviously, the ALCEs sample containing azobenzene molecule and polyethylene glycol (PEG) crystallization can quickly bend illuminated by UV light and rapidly straighten under green light. Under the same UV irradiation, the bending speed, final bending angle, recovery rate and recovery ratio of ALCEs are larger than that of ALCEs without any crystalline structure. This devised ALCEs based on the synergistic effects between liquid crystal and crystalline phase can break through the current dilemma that the application of traditional azobenzene photo-responsive materials is limited by their concentration, greatly expanding the design thought and their scope of application. This article is protected by copyright. All rights reserved.

Optimization of Selective Laser Sintering Three-Dimensional Printing of Thermoplastic Polyurethane Elastomer: A Statistical Approach

This research addresses the challenge of determining the optimal parameters for the selective laser sintering (SLS) process using thermoplastic polyurethane elastomer (TPU) flexa black powder to achieve high-quality SLS parts. This study focuses on two key printing process parameters, namely layer thickness and the laser power ratio, and evaluates their impact on four output responses: density, hardness, modulus of elasticity, and time required to produce the parts. The primary impacts and correlations of the input factors on the output responses are evaluated using response surface methodology (RSM). A particular response optimizer is used to find the optimal settings of input variables. Additionally, the rationality of the model is verified through an analysis of variance (ANOVA). The research identifies the optimal combination of process parameters as follows: a 0.11 mm layer thickness and a 1.00 laser power ratio. The corresponding predicted values of the four responses are 152.63 min, 96.96 Shore-A, 2.09 MPa, and 1.12 g/cm3 for printing time, hardness, modulus of elasticity, and density, respectively. These responses demonstrate a compatibility of 66.70% with the objective function. An experimental validation of the predicted values was conducted and the actual values obtained for printing time, hardness, modulus of elasticity, and density at the predicted input process parameters are 159.837 min, 100 Shore-A, 2.17 MPa, and 1.153 g/cm3, respectively. The errors between the predicted and experimental values for each response (time, hardness, modulus of elasticity, and density) were found to be 4.51%, 3.04%, 3.69%, and 2.69%, respectively. These errors are all below 5%, indicating the adequacy of the model. This study also comprehensively describes the influence of process parameters on the responses, which can be helpful for researchers and industry practitioners in setting process parameters of similar SLS operations.

Effects of structural symmetry of introduced polyether diol on low temperature tolerance of laminated polyurethane bearings in bridges

Laminated seismic isolators are installed on highway bridges worldwide to minimize the risk of seismic collapse. In recent years, Laminated Polyurethane Bearing (LPB) has gained immense popularity in the field of large-span bridge construction due to its advantages such as ultra-high bearing capacity, low cost, and simplicity of production. However, Polyurethane (PU) elastomers of LPB undergo cold hardening, which reduces the ability of LPB to protect bridges from seismic damage in freezing regions. In this study, four kinds of polyether diols with varied chemical symmetry were added to PU consisting of PTHF, TDI, and MOCA, respectively. The introduced polyether diols include polytrimethylene ether diol (POTG) and polytetrahydrofuran (PTHF) with symmetric linear structures, and poly(oxypropylene) (PPG) and 3-methyl-tetrahydrofuran/tetrahydrofuran co-polyether diol (3MTHF) with asymmetric structures. The microscopic characterization performance tests and low-temperature mechanical experiments were conducted to investigate the effect of structural symmetry of added polyether diol on the low-temperature tolerance of LPB. Results prove that due to the significant structural irregularity of the chains, the 3MTHF-based PU exhibits the least amount of microphase separation and the lowest elastic modulus among all specimens, yielding the best low-temperature tolerance of corresponding LPB. It was further discovered that the Bouc-Wen model with proper parameters can accurately simulate the lateral response of the 3MTHF based LPB at different temperatures. Finally, the seismic responses of bridges isolated by 3MTHF based LPB were investigated and compared with those of the bridges with the conventional PTHF based LPB under near-fault earthquake loadings at low temperatures. The results shows that 3MTHF significantly enhances the horizontal flexibility of the LPB, thus improving the effectiveness of the isolation system in low-temperature environments.