Polyurethane Networks Research Articles

Construction of eco-friendly multifunctional cashew nut shell oil-based waterborne polyurethane network with UV resistance, corrosion resistance, mechanical strength, and transparency

Vegetable oil-based waterborne polyurethane possesses numerous advantages, including its sustainability, environmental friendliness, and economic benefits. Nevertheless, its application is constrained by inferior mechanical properties and a low glass transition temperature. Hereon, the renewable polyols of sorbitan monooleate/cytidine were incorporated into the anionic cashew nut shell oil-based WPU network through molecular structure design. Series of CNSL-based WPU with outstanding UV resistance, mechanical properties, corrosion resistance, and transparency were successfully synthesized. The effects of Ce/SP content on the performance of CNSL-based WPU dispersions and films were investigated. The results demonstrated a remarkable enhancement in the properties of the modified WPU films. Specifically, the tensile strength and Tg were increased from 9.7 MPa to 23.9 MPa and 1.1 °C to 45.8 °C, respectively, while maintaining a toughness of 26 MJ/m−3, which attained or even surpassed the current vegetable oil-based WPU systems. It was confirmed excellent UV resistance within the UVB and UVC spectrums. Furthermore, with the increase in Ce/SP content, the water contact angle of films increased slightly, enhancing its water resistance. The IE of WPU-Ce and WPU-SP films reached 97.93 % and 98.42 % respectively, indicating outstanding corrosion resistance. This work presented novel strategies for the advancement of high-performance bio-based WPU, which held promising potential in diverse areas including coatings, corrosion protection, inks, and wearable applications.

Thermally Reversible Organocatalyst for the Accelerated Reprocessing of Dynamic Networks with Creep Resistance.

The industrial implementation of covalent adaptable networks hinges on the delicate task of achieving rapid bond exchange activation at specific temperatures while ensuring a sufficiently slow exchange at working temperatures to avoid irreversible deformation. In this pursuit, latent catalysts offer a potential solution, allowing for spatiotemporal control of dynamic exchange in vitrimer networks. However, the irreversible nature of their activation has led to undesired creep deformation after multiple cycles of reprocessing. In this work, we demonstrate that a tetraphenylborate tetramethyl guanidinium salt (TPB:TMG) undergoes a reversible thermal dissociation, releasing free TMG. This thermally reversible organocatalyst can be readily introduced as an additive in industrially relevant materials such as disulfide-containing polyurethane networks (PU) that undergo disulfide exchange in the presence of a base catalyst. In contrast with a free-base-catalyzed process, we demonstrate the dual benefit of adding the thermally reversible TPB:TMG in preventing creep at lower temperatures and also enabling reprocessability of disulfide-containing PU networks at elevated temperatures. The remarkable reversibility of this thermally activated catalyst allows for multiple reprocessing cycles while effectively maintaining a creep-free state at service temperature.

Design of Sustainable Self‐Healing Phase Change Materials by Dynamic Semi‐Interpenetrating Network Structure

AbstractThe design of sustainable self‐healing phase change materials (SHPCMs) remains challenging depending on sustainable fatty alcohols without compromising high enthalpy efficiency. Herein, the semi‐interpenetrating network (semi‐IPN)‐based SHPCMs are developed by introducing dynamic disulfide crosslinking polyurethane networks and sustainable fatty alcohols as phase change components in a semi‐IPN structure, enabling the combination of ultrahigh enthalpy efficiency of ≈100% and excellent self‐healing ability with 99% of mechanical stain healing efficiency. The latent heat (61.6–144.3 J g−1) and phase change temperature (29.2–64.2 °C) can be readily adjusted by the type and content of fatty alcohols in SHPCMs. The SHPCMs present high thermal reliability, thermal and shape stability, and solid‐like rheological properties benefiting from the advantage of the semi‐IPN structure. The SHPCMs are endowed with tunable mechanical stress (1.23–6.16 MPa) and strain (5.77–379.48%). More importantly, the SHPCMs can be nearly completely self‐healed after thermal stimulus, complying with the Arrhenius model, with a low activation energy of 33.831 kJ mol−1. This innovative strategy opens new avenues for preparing efficient and durable thermal energy storage materials with high enthalpy efficiency, self‐healing ability, and sustainable phase change components, broadening their potential applications.

Colorless, transparent, and shape memory polyurethane networks with high strength and recyclability

AbstractThe traditional thermoset polyurethanes (PUs) can be recycled through the dynamic carbamate bonds under specific conditions. However, there is limited research on the structural evolution and property changes of these PUs before and after recycling. Herein, we designed and fabricated a thermoset polyurethane network (PCU) using polyhexamethylene carbonate diol (PHMC‐diol) as soft segments, and isophorone diisocyanate (IPDI) and glycerol (GLY) as hard segments. Through careful formulation design, the PCU demonstrated colorless transparency (with up to 86% transmission), shape memory properties, and reprocessing capabilities, all achieved without introducing other dynamic covalent bonds. Furthermore, the PCU exhibited excellent mechanical properties, boasting a tensile strength of 59.2 ± 3.7 MPa and the elongation at break of 674.8 ± 37.3%. Of particular interest, the PCU samples displayed solid‐state plasticity and impressive shape memory performance, with shape fixity and recovery ratios exceeding 90%. Leveraging the combination of solid‐state plasticity and shape memory, the PCU samples demonstrated the ability to achieve arbitrary shape manipulations. Upon recycling, it was observed that the cross‐linking density of the PCU samples decreased, resulting in the formation of byproducts and subsequently leading to a reduction in tensile strength. Nonetheless, the PCU samples prepared in this study exhibit potential as thermadapt shape memory and recyclable materials.

Mechanically Robust and Self‐Healing Polyurethane Elastomer Based on Hierarchical Hydrogen Bonds

AbstractIt is a formidable challenge to fabricate mechanically robust and self‐healing polymeric materials. In this work, a facile but effective approach based on constructing hierarchical hydrogen bonds (H‐bonds) is used to combine high mechanical robustness and healing efficiency into one artificial polyurethane (PU) elastomer. The infrared spectrum and molecular simulations demonstrate the formation of hierarchical H‐bonds, which are assembled by the strong and weak H‐bonds. The hierarchical H‐bonds appear to have two advantages. On the one hand, the hierarchical breaking of the strong and weak H‐bonds can effectively strengthen and toughen the PU elastomer. The strong H‐bonds maintain the integrity of the PU network, while the weak H‐bonds dissipate considerable energy during stretching; on the other hand, the rapid dissociation and organization of hierarchical H‐bonds provides the driving force for the healing process. Thus, the hierarchical H‐bonds efficiently solve the inherent contradiction between mechanical strength and healing dynamics. As a result, the PU elastomer exhibits excellent mechanical properties (32.5 MPa of tensile strength and 84.1 MJ m−3 of toughness). Meanwhile, this PU elastomer shows high healing efficiency (91.4%) and also exhibits 100% scratch recovery. This design strategy may provide a simple yet effective way to produce robust self‐healing polymeric materials.

Intrinsic Flame Retardancy and Flexible Solid-Solid Phase Change Materials with Self-Healing and Recyclability.

Conventional polymeric phase change materials (PCMs) have been widely used due to their high heat storage density, small temperature variation, and nontoxicity. However, the high flammability and unrecyclable problems restrict their applications in energy storage devices (ESDs). Although it is facile to introduce a flame retardant into phase change materials to improve fire resistance, the physical blending will deteriorate the mechanical performance and thermal stability of PCMs. Herein, flame-retardant solid-solid PCMs (FRPCMs) with intrinsic flame retardancy, phase change property, self-healing, and recyclability were synthesized by simultaneously integrating tetrabromobisphenol A (TBBPA) and poly(ethylene glycol) (PEG) into polyurethane network skeletons. PEG ingredients acted as phase change materials, and TBBPA not only worked as an efficient flame retardant but also provided dynamic covalent bonds for thermally induced self-healing and recyclability. FRPCMs possess the highest latent heat of 124.7 J/g, high self-healing ability, and high thermal reliability and recyclability. Besides, with the introduction of TBBPA, the limiting oxygen index (LOI) value and char residue significantly increased, the heat release rate (HRR) and total heat release (THR) values decreased, and most of the FRPCMs reached UL94 V-2 rating as well. Hence, the synthesized FRPCMs could expand the application scope of PCMs for thermal energy storage.

Healable, luminescent, notch-insensitive waterborne polyurethane via noncovalent crosslinking with hydrogen bonds and ionic interactions

Luminescent materials display their fascinating performance in wearable electronics, optoelectronics, and information interactions. Enhancing reliability and longevity is particularly attractive for next-generation luminescent polymeric materials. Here we fabricate a supramolecular healable, luminescent waterborne polyurethane (Supra-LWPU) by incorporating reversible hydrogen bonds and ionic interactions into the noncovalent crosslinking network. The Supra-LWPU polymer exhibits excellent mechanical performance with robust tensile strength (6.8 MPa), superior stretchability (1755.4 %), high toughness (70.9 MJ m−3), and damage tolerance (44.7 KJ m−2). Owing to the sacrificial and reversible hard domains, the damaged network demonstrates a dynamic rearrangement with efficient healing efficiency (92.1 %), accompanying the restored toughness (65.3 MJ m−3) at 60 °C after 24 h. Multiple H-bonds induce aggregation domain formation of tertiary amine groups, rendering a luminous polyurethane network. An aggregate luminescence behavior can effectively assist in observing the healing process of Supra-LWPU networks. The mechanically responsive luminescent (MRL) device with well-organized microcracks exhibits strain-dependent luminescence for fluorescent patterns, demonstrating promise in next-generation stimuli responsive light-emitting materials.

Dual-strategy-encapsulated phase change materials with thermal immune functions for efficient energy storage and all-climate battery thermal management

The utilization of phase-change materials (PCMs) has garnered great interest in purposes of energy storage and thermal management due to its lightweight, high-energy efficiency, and cost-competitiveness. However, the intrinsic limitations of low thermal conductivity and leakage in PCMs impede their usage in high-power-density energy harvesting applications. Here, we designed multifunctional phase-change composites (PCCs) via a dual-encapsulation strategy to realize all-climate thermal managements for lithium-ion batteries. For PCMs, polyethylene glycol was interpenetrated into porous polyurethane network (PEG@PU) to enclose a considerable amount of PEG. Then, the PCMs were infiltrated into the highly oriented graphite frameworks (HOGF). A series of processes enabled to form multi-layered structures as well as alleviate the leakage issue of PEG, and thereby improving the thermal storage ability. The so-obtained PCCs exhibited excellent electrothermal properties (134.9 °C at 1.8 V) and high electromagnetic interference performances (larger than 90 dB). These findings presented that the thermal managements of PCCs can be utilized as active preheating or passive cooling system in a battery thermal management system for the all-climate demands.

Chemical upcycling of commodity thermoset polyurethane foams towards high-performance 3D photo-printing resins.

Polyurethane thermosets are indispensable to modern life, but their widespread use has become an increasingly pressing environmental burden. Current recycling approaches are economically unattractive and/or lead to recycled products of inferior properties, making their large-scale implementation unviable. Here we report a highly efficient chemical strategy for upcycling thermoset polyurethane foams that yields products of much higher economic values than the original material. Starting from a commodity foam, we show that the polyurethane network is chemically fragmented into a dissolvable mixture under mild conditions. We demonstrate that three-dimensional photo-printable resins with tunable material mechanical properties-which are superior to commercial high-performance counterparts-can be formulated with the addition of various network reforming additives. Our direct upcycling of commodity foams is economically attractive and can be implemented with ease, and the principle can be expanded to other commodity thermosets.

Impact of Bark-Sourced Building Blocks as Substitutes for Fossil-Derived Polyols on the Structural, Thermal, and Mechanical Properties of Polyurethane Networks.

The hydrophilic extractives isolated from black alder (Alnus glutinosa) bark through hot water extraction were characterized as novel renewable macromonomers capable of forming polyurethane (PU) networks based on a commercial polyisocyanate, with partial or complete replacement of petroleum-derived polyol polyether. The bark-sourced bio-polyol mainly consists of the xyloside form of the diarylheptanoid oregonin, along with oligomeric flavonoids and carbohydrates, resulting in a total OH group content of 15.1 mmol·g-1 and a molecular weight (Mn) of approximately 750 g∙mol-1. The 31P NMR data confirmed a similar proportion of aliphatic OH and phenolic groups. Three-component PU compositions were prepared using polyethylene glycol (Mn = 400 g∙mol-1), bio-polyol (up to 50%), and polymeric diphenylmethane diisocyanate, which were pre-polymerized in tetrahydrofuran (THF) solution with tin organic and tertiary amine catalysts. The resulting mixture was cast and subjected to thermal post-curing. Calculation and experimental data confirmed the crosslinking activity of the bark-sourced bio-polyol in PU, leading to an increase in glass transition temperature (Tg), a decrease in sol fraction yield upon leaching of cured PU networks in THF, a significant increase in Young's modulus and tensile strength. The macromonomers derived from bark promoted char formation under high temperature and oxidative stress conditions, limiting heat release during macromolecular network degradation compared to bio-polyol-free PU. It was observed that amine catalysts, which are active in urethane formation with phenolic groups, promoted the formation of PU with higher Tg and modulus at tensile but with less limitation of heat liberation during PU macromolecular structure degradation. The high functionality of the bark-derived bio-polyol, along with the equal proportion of phenolic and aliphatic OH groups, allows for further optimization of PU characteristics using three variables: increasing the substitution extent of commercial polyethers, decreasing the NCO/OH ratio, and selecting the type of catalyst used.

Coupling between hydrolysis and mechanical relaxation in an ester‐based polyurethane network

AbstractIn this study, we first investigate the impact of a chain scission process due to hydrolysis on the relaxation behavior of an elastomer. We then explore the possible influence of a deformed state on the chemical reactions associated with hydrolysis. To perform the experiments coupling mechanical relaxation and hydrolysis, we select not only specific conditions such as the type of elastomer but also severe conditions such as immersions at high temperatures. Here, an ester‐based polyurethane network is chosen to easily hydrolyze the ester function, thus leading to a chain scission process. In addition, relaxation tests are performed in water at several temperatures (i.e., 40, 60, and 80 °C) to accelerate the hydrolysis rate. Results show that a deformed state does not accelerate the hydrolysis rate. However, a chain scission process clearly modifies the relaxation behavior. Finally, this behavior is modeled by coupling the chain scission kinetics with the relaxation time based on the Kohlrausch–Williams–Watts approach.

Multifunctional Polyurethane Networks Combining Strength, Toughness, and Fast Autonomous Self-Healing via the Synergy of Multiple Dynamic Bonds

Multifunctional Polyurethane Networks Combining Strength, Toughness, and Fast Autonomous Self-Healing via the Synergy of Multiple Dynamic Bonds

Chemically Recyclable Biobased Non-Isocyanate Polyurethane Networks from CO2 -Derived Six-membered Cyclic Carbonates.

Non-isocyanate polyurethanes (NIPUs) are widely studied as sustainability potential, because they can be prepared without using toxic isocyanates in the synthesis process. The aminolysis of cyclic carbonate to form NIPUs is a promising route. In this work, a series of NIPUs is prepared from renewable bis(6-membered cyclic carbonates) (iEbcc) and amines. The resulting NIPUs possess excellent mechanical properties and thermal stability. The NIPUs can be remolded via transcarbamoylation reactions, and iEbcc-TAEA-10 (the molar ratio of tris(2-aminoethyl)amine in amines is 10%) still get a recovery ratio of 90% in tensile stress after three cycles of remolding. In addition, the obtained materials can be chemically degraded into bi(1,3-diol) precursors with high purity (>99%) and yield (>90%) through alcoholysis. Meanwhile, the degraded products can be used to regenerate NIPUs with similar structures and properties as the original samples. The synthetic strategy, isocyanate-free and employing isoeugenol and carbon dioxide (CO2 ) as building blocks, makes this approach an attractive pathway to NIPU networks taking a step toward a circular economy.

Intrinsically flame-retardant vanillin-based PU networks with self-healing and reprocessing performances

Conventional polyurethane (PU) networks fabricated from nonrenewable fossil resources are difficult to be recycled, reprocessed, and reshaped because of the permanent covalent cross-linked networks, and the flammability of PU networks limits their wide application. Herein, the novel polyols were synthesized from renewable vanillin and then reacted with hexamethylene diisocyanate (HDI) trimer to obtain versatile bio-based PU networks with dynamic disulfide and imine bonds for the first time. Obtain malleable PU networks that possess excellent reprocessability and self-healing performance, as well as superior fire resistance. The vanillin-based PU networks show a high T5d of ∼180 °C, high char yield of 23% at 800 °C, fast stress relaxation of ∼38 s at 80 °C, excellent scratch self-healing performance with approximately 100% healing efficiency at 120 °C for 90 min, outstanding flame retardancy with high LOI of ∼30% and UL-94 V0 rating. Additionally, the vanillin-based PU networks display excellent malleability with the activation energy (Ea) of 30.2–54.8 kJ•mol−1 due to dual dynamic bonds in the networks, which can be recycled in 60 min at 120 °C by hot pressing. Moreover, the vanillin-based PU networks with Schiff base can be degraded rapidly in the mixture of HCl and THF. Briefly, produced PU networks from abundant and renewable resources are significant examples to foster the development of versatile PU network materials.

Biobased, Reprocessable Non-isocyanate Polythiourethane Networks with Thionourethane and Disulfide Cross-Links: Comparison with Polyhydroxyurethane Network Analogues

Here, we report the first study of the reprocessability and properties of non-isocyanate polythiourethane (NIPTU) networks in which the cross-links are of two types, thionourethane and disulfide, the latter obtained by auto-oxidation of pendant thiol groups. Our two NIPTU networks are biowaste based because starting materials can be derived from cashew nutshells or rice husks. We use dynamic mechanical analysis, tensile testing, and water sorption studies to compare our NIPTU networks with structurally analogous polyhydroxyurethane (PHU) networks, which are non-isocyanate polyurethanes (PUs). With significant advantages in reactivity, mechanical properties, and cross-link density, NIPTU networks can be favorable alternatives to PHU networks. Our biobased NIPTU networks also exhibit better water resistance, with a factor of ∼3 reductions in water sorption relative to their PHU analogues. Due to their dynamic covalent cross-links, our NIPTUs show excellent reprocessability with complete recovery of cross-link density after multiple reprocessing steps as well as potential as self-healing polymers. Although their creep viscosity activation energies differ by a factor of 2, both NIPTU networks exhibit excellent creep resistance up to 80–100 °C. Thus, with elevated-temperature creep resistance and significant advantages in reactivity, mechanical properties, and water resistance, in many applications, e.g., water-resistant coatings, biobased NIPTU networks are favored as non-isocyanate substitutes for PU networks.

Synthesis and Properties of Dynamic Crosslinking Polyurethane/PEG Shape-Stable Phase Change Materials Based on the Diels–Alder Reaction

Phase change materials (PCMs) can absorb and release energy while keeping the temperature constant; hence, they play a crucial role in the thermal management field. Shape-stable phase change materials (SSPCMs) were synthesized by chemical crosslinking to address the liquid leakage problem of solid–liquid phase change materials (SLPCMs) during the phase change process. However, the abandoned SSPCMs cannot be reused and recycled, which seriously restricts their practical application. Herein, a polyurethane network containing Diels–Alder bonds was used as the enclosure compound to obtain the encapsulation of polyethylene glycol (PEG), and then, the chemical structure, crystallization behavior, and phase transition ability of SSPCMs were systematically investigated. The results showed that the SSPCMs-3 sample (300 wt % PEG) had the best comprehensive performance, an enthalpy value of 171.7 J/g, and no leakage at 80 °C for 1 h. Moreover, the structure, crystallization behavior, and phase transition ability of SSPCMs could also basically remain unchanged after multiple thermal cycling and reprocessing.

Highly Stretchable and Flexible Electrospinning‐Based Biofuel Cell for Implantable Electronic

AbstractWith the emerging demand of implantable microelectronics, it essentially requires the fully integrated and reliable power supplies. The study reports a stretchable and flexible electrospinning‐based glucose/O2 biofuel cell with glucose oxidase bioanode, Pt/C cathode and thermoplastic polyurethane substrate, which is capable for adapting to the various stresses and strains caused by individual movement. The rigid benzene rings and elastic chain segments of thermoplastic polyurethane ensure its superior tensile property. Furthermore, the stable covalent connections between the activated carbon nanotubes (CNTs‐COOH) and glucose oxidase inside 3D thermoplastic polyurethane network are established by amide reaction to ensure the rapid direct electron transfer of bioanode and stable power output of device in flexible environments. The biofuel cell exhibits an open circuit voltage of 0.575 V, and high‐power density of 57 µW cm−2 in 5 mM glucose. Moreover, the power‐generation properties of implantable biofuel cell keep steady, and its power density exhibits limited fluctuations on the dorsum of rat when bending, stretching, and twisting in 28 days. There is no obvious local inflammation or systemic abnormalities in rats. It satisfies the impressive biocompatible requirement, demonstrating the promising potential of electrospinning‐based biofuel cell as a robust self‐sustained power source for implantable electronics.

Bioinspired Conductive Enhanced Polyurethane Ionic Skin as Reliable Multifunctional Sensors.

Ionogels prepared from ionic liquid (IL) have the characteristics of nonevaporation and stable performance relative to traditional hydrogels. However, the conductivities of commonly used ionogels are at very low relative to traditional hydrogels because the large sizes of the cation and anion in an IL impedes ion migration in polymer networks. In this study, ultradurable ionogels with suitable mechanical properties and high conductivities are prepared by impregnating IL into a safe, environmentally friendly water-based polyurethane (WPU) network by mimicking the ion transport channels in the phospholipid bilayer of the cell membrane. The increase in electrical conductivity is attributed to the introduction of carboxylic acid in the hard segment of WPU; this phenomenon regularly arranges hard segment structural domains by hydrogen bonding, forming ionic conduction channels. The conductivities of their ionogels are >28-39 mS cm-1 . These ionogels have adjustable mechanical properties that make the Young's modulus value (0.1-0.6MPa) similar to that of natural skin. The strain sensor has an ultrahigh sensitivity that ranges from 0.99 to 1.35, with a wide sensing range of 0.1%-200%. The findings are promising for various ionotronics requiring environmental stability and high conductivity characteristics.

ZnO Nanorods Grown on Flexible Polyurethane Foam Surfaces for Photocatalytic Azo Dye Treatment

A flexible photocatalyst hybrid structure made up of aligned ZnO nanorods and three-dimensional networks of polyurethane (PU) foam struts was fabricated. The surfaces of the PU struts were first functionalized by the two-step chemical solution treatment method. The functional groups of the PU foam and the nanohybrid structure were characterized using Fourier transmission infrared spectroscopy (FTIR). Their crystal structures and morphologies were examined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The adequacy of the chemical surface modification process was examined by analyzing the differences in the −N ═ C ═ O and O–H regions of the FTIR spectrum. The hybrid photocatalyst samples were also tested in terms of their structural integrities under ultrasonic irradiation. It was observed that the ZnO layers remained intact and adherent on the surfaces even after 1 h of sonication. The optical properties of the samples were also characterized by ultraviolet–visible (UV–vis) and photoluminescence (PL) spectroscopies. Aqueous Acid Red 88 (AR88) azo dye solutions were prepared and used to assess both the color and the total organic carbon (TOC) removal efficiencies of the samples utilizing the laboratory-scale photoreactor. The maximum color removal of 97% was reached in 180 min under UVA light irradiation as a consequence of simultaneous adsorption and photocatalysis mechanisms.

Design and fabrication of shape memory polyurethane network with rapid recoverable plastic deformation

The flexible polymer substrate brings the possibility of recycling and reusing to the disposable electronics. Thus, it is necessary to explore a strategy to realize the structural reconfigurability and then improve the service life of polymers. Plastic deformation is one of key issues in failure of materials. Shape memory polymers (SMPs) with specific block structures are capable of remembering permanent shapes responding to various external stimuli. This excellent property is expected to contribute to the research of recoverable plastic deformation. In this work, a kind of plastic deformation-recovery shape memory polyurethane (PR-SMPU) was synthesized through bulk polymerization, where the semi-crystalline polycaprolactone (PCL) serves as soft segment and stimuli-responsive phase to achieve the recoverable character. By characterizing the mechanical properties and thermal stability, material with 40 wt% hard segment was selected, of which the breakage elongation ratio is 1126% at 20 °C and 1070% at 60 °C, the thermal stability can be guaranteed below 250 °C, and the plastic deformation can be recovered at 60 °C within 3 s. By analyzing the in-situ microstructural evolution in the constrained recovery after both elastic and plastic deformation, the mechanism of the recoverable plastic deformation of the proposed PR-SMPU were explored.