Waterborne Polyurethane Films Research Articles

Ultra-tough, strong and transparent bio-based waterborne polyurethanes with exceptional anti-corrosion properties

Waterborne polyurethane (WPU) is increasingly favored because of its affordability, eco-friendliness, and water-based storage convenience. However, the inclusion of hydrophilic groups can diminish its mechanical strength and water resistance. Herein, a range of bio-based waterborne polyurethanes were synthesized by using economical and sustainable poly(trimethylene ether) glycol (PO3G), isophorone diisocyanate (IPDI), and poly(propylene glycol) (PPG) as raw materials. They exhibited superior mechanical properties, transparency, and corrosion resistance. We explored the effect of PO3G content on the properties of these bio-based WPU emulsions and films. The findings revealed that films with over 30 % PO3G content demonstrated a high tensile strength (above 10 MPa) and maintained a high elongation at break (above 4000 %), matching or surpassing existing bio-based WPU systems. The corrosion resistance of these films was also exceptional, with a high inhibition efficiency (above 99.97 %). This research introduces a new approach for creating high-performance bio-based WPUs with promising applications in coatings, leather, and biomedical materials.

Synthesis and Application of Dendritic Waterborne Polyurethane with Long Alkyl Chains and Silicone Chains as a Fluorine-Free Water Repellent

With environmental and health issues being raised, researchers have shifted their study from fluorinated to fluorine-free waterproof agents. However, most of the reported fluorine-free water repellents exhibit a significant drawback in their poor stability and durability of water repellency. In addition, the use of higher concentrations in these repellents results in the fabric becoming stiff, which negatively impacts the hand of the treated fabrics. To address these issues, dendrimer-like waterborne polyurethane prepolymers were initially synthesized using isophorone diisocyanate, polytetrahydrofuran, N-methyldiethanolamine, and trimethylolpropane as the primary materials. In this synthesis, sorbitan tristearate served as the dendrimer-like blocking agent, while single-ended bis-hydroxypropyl silicone oil was employed as functional monomers to enhance the hand and water repellency of the prepolymers. Then, dendrimer-like waterborne polyurethane was finished on the cotton fabric using a pad–dry–cure procedure. The test results showed that the water contact angle of dendrimer-like waterborne polyurethane film increased from 104.28° to 107.00° with the content of single-ended bis-hydroxypropyl silicone oil increasing, and the water contact angle of dendrimer-like waterborne polyurethane-finished fabrics reached 148.6° alone with a standard spray test rating of 90–95. In addition, the water contact angle of dendrimer-like waterborne polyurethane-finished fabrics was still greater than 140° even after five standard washes. The single-ended bis-hydroxypropyl silicone oil addition facilitated similar hand to the original fabric in dendrimer-like waterborne polyurethane-finished fabrics with high concentrations, surpassing market water repellents. This work is of great significance for improving the stability and durability of water repellency, and the hand of waterborne polyurethane fluorine-free water repellents in the textile industry.

Improving Water Resistance and Mechanical Properties of Crosslinked Waterborne Polyurethane Using Glycidyl Carbamate

Waterborne polyurethane (WPU) often suffers from poor water resistance and mechanical properties due to hydrophilic emulsifiers. To address these issues, this study introduces glycidyl carbamate (GC) as a crosslinker to improve WPU performance. Three types of GC were synthesized using aliphatic, cycloaliphatic, and aromatic isocyanates, respectively. The crosslinked network was established through a reaction between the epoxide group of GC and the carboxylic acid and amine groups of WPU. Among these, the WPU film utilizing aromatic isocyanate-based GC exhibited the highest crosslink density, modulus, hardness, and water resistance, due to the rigidity of the aromatic molecular structure. However, the film displayed excessive brittleness, resulting in reduced tensile strength, along with yellowing typically associated with aromatic compounds. The WPU crosslinked with cycloaliphatic GC demonstrated the next best mechanical properties and water resistance, with a 2.7-fold increase in tensile strength, a 1.5-fold increase in hardness, and a 66% reduction in the water swelling ratio compared to neat WPU. This study presents a novel and effective strategy to enhance the water resistance and mechanical properties of WPU films, making them suitable for advanced coating applications.

Liquefaction of banana peel as the source of renewable and sustainable polyols for preparation of waterborne polyurethane

A set of waterborne polyurethane (WPU) were prepared with the bio-polyol synthesized from the liquefaction of banana peel. The effect of the bio-polyol amount on water adsorption ability, tensile strength and elongation at break of WPU films was evaluated. The WPU prepared using 12 g bio-polyol exhibited a low water adsorption ability of 5.37 %, high tensile strength of 32.5 MPa, and appropriate elongation at break of 259.5 %.

Performance and Morphology of Waterborne Polyurethane Asphalt in the Vicinity of Phase Inversion.

Waterborne polyurethane asphalt emulsion (WPUA) is an environmentally friendly bituminous material, whose performance is highly dependent on the phase structure of the continuous phase. In this paper, WPUAs in the vicinity of phase inversion were prepared using waterborne polyurethane (WPU) and asphalt emulsion. The chemical structures, thermal stability, dynamic mechanical properties, phase-separated morphology and mechanical performance of WPUAs were studied. Fourier-transform infrared (FTIR) spectra revealed that there are no -NCO bonds in either the pure WPU or WPUAs. Moreover, the preparation of WPUA is a physical process. The addition of WPU weakens the thermal stability of asphalt emulsion. WPU improves the storage modulus of asphalt emulsion at lower and higher temperatures. The glass transition temperatures of the WPUA films are higher than that of the pure WPU film. When the WPU concentration increases from 30 wt% to 40 wt%, phase inversion occurs; that is, the continuous phase shifts from asphalt to WPU. The WPUA films have lower tensile strength and toughness than the pure WPU film. However, the elongations at break of the WPUA films are higher than that of the pure WPU film. Both the tensile strength and toughness of the WPUA films increase with the WPU concentration. Due to the occurrence of phase inversion, the elongation at break, tensile strength and toughness of the WPUA film containing 30 wt% WPU are increased by 29%, 250% and 369%, respectively, compared to the film with 40 wt% WPU.

Enhanced mechanical strength and water resistance in waterborne polyurethanes through hydroxyl-functionalized MQ silicone resin modification

As an alternative to solvent-based polyurethane, waterborne polyurethane (WPU) uses water as dispersants and can significantly reduce VOC. However, dispersing polyurethanes with hydrophobic backbones in water requires hydrophilic groups, which undermine the water resistance. It remains a challenge to simultaneously improve water resistance and mechanical properties. Here we report a polyurethane with superior mechanical properties and water resistance through the introduction of an organic-inorganic hybrid material, MQ silicone resin. Hydroxyl functionalized MQ silicone resin increases chemical crosslinking and improves the microphase separation and hydrogen bonding strength of polyurethanes. When the MQ-OH content was 10.1 wt%, the tensile strength increased from 27 MPa to 37.3 MPa, and the toughness increased from 74.8 MJ/m3 to 97.4 MJ/m3. Si-O-Si backbones with low surface energy can migrate to the film surface, increasing the surface hydrophobicity. WPU films with MQ silicone resin exhibited remarkable tensile strength retention, with 84.7 % after 40 h hydrolysis in 80 °C water, while WPU retained only 24.6 %. MQ silicone resin offers a novel approach to enhance the hydrophobic properties of WPU without compromising the mechanical properties.

Encapsulation films: Investigation into the degradation mechanism of multicomponent bio-based waterborne polyurethane in natural environments

In this study, the impact of different ratios of castor oil (CO) and polycarbonate diol (PCDL) mixed soft segments, as well as the introduction of sodium 2-[(2-aminoethyl)amino]ethanesulphonate (AAS-Na) salt, on the biodegradable waterborne polyurethane (WPU) was investigated. Firstly, various waterborne polyurethanes with different mixed soft segments were prepared by adjusting the ratios of castor oil and polycarbonate diol. Subsequently, varying amounts of AAS-Na salt were introduced to assess their influence on the polymer properties. The results indicated that the ratio of CO to PCDL significantly affected the mechanical properties and biodegradability of WPU. As the ratio decreased from 10:0 to 6:4, the tensile strength of WPU films decreased from 18 MPa to 11 MPa, while the elongation at break increased from 56 % to 258 %. Furthermore, the addition of AAS salt improved the water absorption and biodegradation rate of the material. When the ratio of CO to PCDL within the system is 10:0 and the molar content of AAS-Na is 20 mol%, the sample exhibits optimal water absorption of 132.12 % after 48 h and biodegradability of 30.58 % after 28 days. The degradation mechanism was preliminarily explored using Fourier-transform infrared spectroscopy. In conclusion, by adjusting the ratios of castor oil, polycarbonate diol, and AAS salt, a series of biodegradable waterborne polyurethanes with excellent performance were obtained. This study demonstrates the feasibility of developing biodegradable packaging materials using bio-based waterborne polyurethanes as the main component.

Migration of polydimethylsiloxane chain segments toward the surface of UV-cured waterborne poly(urethane-acrylate) films

Waterborne polyurethane (WPU) has poor water resistance and low surface hydrophobicity due to the incorporation of hydrophilic chain-extender. The water resistance and the surface hydrophobicity can be improved by incorporation of polydimethylsiloxane (PDMS), which is attributed to the migration of PDMS chain segments toward the surface of WPU film. However, whether the PDMS chain segments can migrate toward the surface of WPU film after UV-curing, resulting in higher hydrophobicity, needs further investigation? We prepared the different WPUA films by changing the molar ratio of aminopropyl-terminated polydimethylsiloxane (APT-PDMS) to hydroxyethyl acrylate (HEA), to deeply understand the migrating phenomenon of PDMS chain segments toward the surface of WPUA films. The migration cause of PDMS chain segments and the influence of chemical cross-linking on the migration were investigated by thermal annealing and solvent immersion of WPUA films. In addition, the migration activation energy and the relaxation time were studied by the migration rate of PDMS chain segments in the thermal annealing and the rheological behavior of WPUA film, aiming to elucidate the migration of PDMS chain segments depending on the chain motion and the fractional free volume. This investigation provides a simple and feasible strategy for improving the hydrophobicity of waterborne polyurethane.

Porous Waterborne Polyurethane Films Templated from Pickering Foams for Fabrication of Synthetic Leather.

Waterborne polyurethane (WPU) latex nanoparticles with proven interfacial activity were utilized to stabilize air-water interfaces of Pickering foams through interfacial interaction with hydrophobic fumed silica particles (SPs). The rheological properties of the Pickering foam were tailored through adjustment of their SP content, which influenced their formability and stability. A Pickering foam stabilized with WPU and SPs was used as a template to prepare a WPU-SP composite porous film. The as-prepared film had intact open-cell porous structures, which increased its water absorption and water-vapor permeability. The porous film was used as a middle layer in the preparation of synthetic leather via a four-step "drying method". Compared with commercial synthetic leather, the lab-made synthetic leather with a middle layer made of the WPU-SP composite porous film exhibited a richer porous structure, acceptable wetting on a fabric substrate, a thicker porous layer, and higher water-vapor permeability. This work provides a novel and facile approach for preparing WPU-SP Pickering foams. Furthermore, the foams have the potential to function as a sustainable material for creating a porous-structured synthetic leather made from WPU, which may be utilized as an alternative to solvent-based synthetic leather.

Stratification of polyisocyanate in two-component waterborne polyurethane films

The coatings industry continually seeks advancements in waterborne two-component polyurethane (2 K WBPU) systems, given their potential for environmentally friendly applications and superior film properties. This study explores the mechanistic aspects of film formation in 2 K WBPU coatings formulated with an acrylic polyol and a polyisocyanate (PIC) derived from a trimer of hexamethylene diisocyanate (HDI-trimer). To enhance water dispersibility—a key parameter in industrial applications—the HDI-trimer is modified with a short polyethylene glycol, producing a hydrophilically modified PIC (hmPIC). While prior studies identified hmPIC as an effective reactive plasticizer for the polyol, the common practice of adding unmodified HDI-trimer (uPIC) to hmPIC for moisture sensitivity reduction necessitates a deeper understanding of film properties. Using fluorescence resonance energy transfer (FRET) and confocal fluorescence microscopy, we investigated the effects of blending uPIC with hmPIC on coalescence, phase separation, and film stratification in 2 K WBPU systems. Notably, environmental factors like relative humidity were found to influence film stratification significantly. This finding has critical implications for coating performance, such as durability and water resistance. A novel method was also introduced to monitor water permeation within stratified films, offering a valuable tool for optimizing film properties in real-world applications. This study underscores the importance of strategic component interactions in polymer coatings, suggesting that controlled film stratification can significantly enhance film performance in industrial settings.

Double crosslinked networks waterborne polyurethane with self-healing, recyclable and antibacterial functions based on dynamic bonds and used for temperature/light sensor

Waterborne polyurethanes with excellent mechanical properties, self-healing under mild controlled conditions and multiple functions are a potential alternative for preparing sensor materials with a wide application prospect. Herein, we introduced dynamic ditelluride bonds and trimethylolpropane into waterborne polyurethane main chains to achieve dynamic polymer chains while maintaining the stability of crosslink networks; subsequently, zinc ions were added to form ionic bonds with carboxyl groups between molecular chains to prepare self-healing waterborne polyurethanes (DTe-WPU-Zn-x) with double crosslinked networks containing double dynamic bonds. The prepared waterborne polyurethane film exhibited excellent mechanical properties (36.08 MPa), satisfactory elongation (665.83 %), and rapid self-healing efficiency (self-healing efficiency with 84.42 % after 90 min of visible-light irradiation). Benefiting from the excellent self-healing efficiency of DTe-WPU-Zn-3, the film fragments can be recycled under ethanol and pressure with lighting for 2 h, and its tensile stress can recover more than 80 % of its original properties after three recycling processes, which is rarely reported for double crosslinked polymers. Furthermore, owing to the combination of telluric radicals and metal ions, the film also has excellent antibacterial properties, with 99.6 % and 96.2 % against E. coli and S. aureus, respectively. Importantly, depending on the stable double crosslinked networks, the prepared sensor has long-term stability and can sensitively monitor changes in human body temperature, and the sensor also has a sensitive light response due to the photodynamic response of ditelluride bonds on polymer chains. In addition, the sensor still has better strain, temperature, and light response after recycling treatment. This research provides a facile method to fabricate environmentally friendly water-dispersible polymers with excellent properties and multiple functions, which have potential applications in the field of smart devices and human–computer interaction.

Pickering emulsion approach: A novel strategy to fabricate waterborne polyurethane with enhanced abradability and water-resistance comparable to that of solvent-based coating

The urgent requirement of replacement for solvent polyurethane (PU) makes waterborne polyurethane (WPU) coating more attractive and popular in many industrial areas. However, the simultaneous realization of good dispersion stability and high performance of the cured films especially water resistance remains challenging. Herein, we propose a novel and facile Pickering emulsion approach to fabricate WPU with enhanced abradability and water-resistance comparable to that of solvent-based PU coating. In this approach, the hydrophobic polyurethane synthesized by poly-addition reaction in ethyl acetate is directly dispersed into water with SiO2 nanoparticles as Pickering stabilizer followed by subsequent evaporation of the remaining solvent to obtain Pickering waterborne polyurethane dispersion (PWPU dispersion). The ability of SiO2 to stabilize emulsion can be modulated by hydrophobic modification with propyltriethoxysilane (PTS). SiO2 nanoparticles with an optimal PTS-grafting rate of 2.8 wt% enables the PWPU dispersion with excellent long-term, chemical, thermal, and freeze-thaw stability. The highly-transparent composite films with honeycomb structures are readily formed by casting PWPU dispersion at room temperature. The thermal and mechanical properties of PWPU films are comparable to or superior to solvent-borne polyurethane (SPU) and self-emulsifying waterborne polyurethane (SWPU) films. Moreover, the water absorption of the PWPU-5 film is approximately 20 times lower than that of SWPU, demonstrating the excellent water-resistance. We further validated the coating performance of PWPU for leather finishing. The hydrophobicity, abrasion resistance and water vapor permeability of PWPU-coated leather are superior to those of SPU and SWPU-coated leather.

Mechanical properties and microstructure of waterborne polyurethane-modified cement composites as concrete repair mortar

With the increase in service life, the durability of a large number of concrete structures deteriorates year by year under the influence of the external environment, requiring urgent repair and reinforcement. Ordinary cement concrete materials have disadvantages such as high brittleness, low tensile strength, poor bonding ability, and insufficient durability, making it difficult to meet the repair needs of high-quality building structures. Therefore, self-synthesized anion WPU was used to study its effect on the mechanical properties of cement-based repair mortar. The research found that waterborne polyurethane (WPU)-modified cementitious composite repair materials exhibit better bonding strength with old concrete substrates compared to traditional cement-based materials. Additionally, the incorporation of WPU significantly reduces the brittleness of the repair material, ensuring enhanced efficiency in the repair process. However, according to the hydration heat test results, the addition of WPU delays the hydration process of the composite repair materials. In addition, the addition of WPU enhances the flexibility and bonding ability of the materials, with flexural strength and tensile strength at the age of 28 days reaching 13 MPa and 6 MPa, respectively. Through stress‒strain curve analysis, it was found that the maximum strain amplification of WPU cement mortar can reach 134 %. Combined with SEM testing, it was observed that cured WPU films were present in specimens aged 28 days with P/C ratios of 10 % and 15 %. WPU and cement hydration products permeate each other, forming a three-dimensional polymer network structure, improving the pore structure, and fully exerting the flexibility of WPU. This also validates the experimental results of increased ultimate tensile strain. WPU cement-based composite repair materials have higher bonding strength at a high P/C ratio (15 %), and WPU alone, used as an interface agent for pretreating the interface of old concrete, can improve the interface bonding strength, up to twice that of the group without the surface agent.

Waterborne polyurethanes with novel chain extenders bearing multiple sulfonate groups

The anionic chain extenders used in waterborne polyurethane (WPU) generally contain one anionic ion per extender. Increasing its content in WPU makes the WPU emulsion more stable, however also makes the WPU film more water sensitive, which is a dilemma needed to be solved. Herein, a novel class of anionic chain extenders bearing two or foursulfonate groups is rationally designed. The ion strength of chain extender is thus enhanced and the distribution of ionic charges on the resulting WPU is also altered. The relationship between the structure of the chain extenders and the properties of WPU is studied systematically. The results show that the critical percentage of the anionic extender needed to for stable WPU emulsion is reduced in a nonproportional way with the increase of the number of anionic groups per extender. For example, while the critical percentage of the chain extender for stable emulsion formation for aliphatic-type chain extender containing two sulfonates is 6 mol%, that for chain extender containing four sulfonates is only 2 mol%. Hence the overall hydrophilic segments on the WPU backbone is greatly decreased, which make the WPU more water resistant without sacrificing the emulsification capability of WPU. Among them, the threshold to form stable emulsion for WPU made from the ether-type chain extender containing four sulfonates is as low as 1.2 mol%, and the water absorption of the resultant film is only 3.5 %. The resulting WPU films show strong adhesion to various surfances and excellent resistance toward abrasion. This provides a new strategy to balance the emulsification capability and water-resistence property of WPU.

Carbon nanotube/castor oil‐based waterborne polyurethane films with gradient structure for absorption‐dominated electromagnetic interference shielding and Joule heating

AbstractConductive polymer composites are highly demanded for practical application in electromagnetic interference shielding and Joule heating owing to their excellent flexibility and adjustable conductivity. Herein, a thin film with a gradient structure, comprising carbon nanotube/castor oil‐based waterborne polyurethane (CNT/WPU), has been fabricated through solution mixing utilizing casting technology. Scanning electron microscopy images confirm that CNTs are enriched at the top of the obtained CNT/WPU film, leading to a low resistance value. Consequently, the resultant gradient CNT/WPU films exhibit shielding effectiveness, specific shielding effectiveness, and an absorption coefficient of 22.8 dB, 1091 dB/cm, and 0.697, respectively, indicating a predominance of absorption in the shielding capacity. The temperature at the surface of the resultant gradient CNT/WPU film reaches ~77°C at a voltage of 20 V. The film with a CNT content of 14.1 wt% exhibits a good stress of 11.7 MPa and a high module of 39.9 MPa. Therefore, the obtained CNT/WPU films can be applied as thin shielding materials or coating.Highlights Fabricating a gradient CNT/castor oil–based waterborne polyurethane films. Exhibiting shielding effectiveness of 22.8 dB and A‐value of 0.697. Steady‐state temperature of CNT/WPU reaches 77°C at 20 V. Possessing green EMI shielding capability.

Synthesis and characterization of waterborne polyurethane-based ink binder modified via a silane coupling agent

The development of high-performance waterborne polyurethane ink binder presents challenges due to the lack of outstanding water resistance, adhesion, and heat resistance in traditional waterborne polyurethane. Herein, series of waterborne polyurethane emulsions were synthesized using the pre-polymerization chain expansion and self-emulsification method, with varying contents of 3-aminopropyl triethoxysilane as the modified post-chain extender. The effect of varying the concentration of 3-aminopropyl triethoxysilane on the characteristics of waterborne polyurethane dispersions and films was investigated. The results indicated that there was a significant improvement in adhesion, thermal stability, and water resistance with an increase in the concentration of 3-aminopropyl triethoxysilane. Specifically, When the introduction amount was 3 wt%, the resulting film exhibited the best overall properties, including a tensile strength of 48.4 MPa, water absorption of 4.3 wt%, shear strength and adhesion of 3.9 MPa and 3.86 MPa respectively, as well as a T-peel strength of 14.9 N/mm. This work provided meaningful guidance for developing a novel waterborne polyurethane-based ink binder with strong adhesion, high mechanical properties, and excellent water resistance.

Piezoelectric nanocomposite films based on anionic waterborne polyurethane and barium titanate nanoparticle: Fabrication, microstructure, and property characterization

AbstractWe report the fabrication, microstructure, thermal property, and piezoelectric performance of flexible waterborne polyurethane (WPU) nanocomposite films reinforced with barium titanate (BT) nanoparticles with ~50 nm diameter. An anionic segmented WPU was synthesized via bulk polymerization, and its nanocomposite films containing 10–40 wt% BT were fabricated via aqueous dispersion casting and hot pressing. Although the BT nanoparticles interacted with the urethane groups of the WPU hard segment by inducing the separation of the semicrystalline soft segment, they were aggregated in the WPU matrix. Accordingly, the glass transition temperature of the WPU matrix decreased with BT content, but the melting temperature increased. As the BT content increased in the nanocomposite films, the thermal decomposition temperature of the WPU soft segment showed a slight decrease, while the decomposition temperature of the hard segment increased. Additionally, the residue at 600°C increased significantly from 2.0% for neat WPU film to 36.3% for the nanocomposite film containing 40 wt% BT. The piezoelectric outputs attained by the nanocomposite films increased with BT content. Under compressive stress of 23 kPa, the nanocomposite film containing 40 wt% BT was able to achieve the highest piezoelectric voltage of ~0.51 V, a current of ~43.0 nA, and an electric power of ~21.9 nW. For the nanocomposite film, a linear relationship between the piezoelectric out voltage and the applied compressive stress with a slope of ~0.0253 was also observed.Highlights Anionic waterborne polyurethane (WPU) with hard/soft segments is synthesized. Barium titanate (BT) nanoparticles are adopted as a piezoelectric nanofiller. WPU/BT nanocomposites are manufactured by dispersion casting and hot pressing. Specific interactions between BT nanoparticles and WPU hard segments exist. Piezoelectric outputs of nanocomposites increase with BT content and stress.

Preparation and characterization of high solid content cationic waterborne polyurethane with core‐shell structures

AbstractIn this study, core‐shell structured cationic waterborne polyurethane (WPU) dispersions with high solid content were prepared. To this end, prepolymer A was synthesized from polytetramethylene ether glycol (PTMG), isophorone diisocyanate (IPDI), castor oil (CO) and 1,4‐butanediol (BDO) without integration of the hydrophilic groups. Prepolymer B with hydrophilic groups was prepared from PTMG, IPDI, CO, BDO and N‐methyldiethanol amine (MDEA). WPU dispersion with a core‐shell structure could be generated by mixing, neutralizing, and emulsifying of the prepolymer A and the prepolymer B. The results indicated that the generation of WPU dispersions through this technique exhibited a milky appearance while the pH values range from 5.30 to 5.60. The optimal combination of prepolymer A and prepolymer B (at a ratio of 5:5) resulted in a dispersion with the highest solid content (50.4%), lowest viscosity (69 mPa·s), and narrowest particle size distribution. As the proportion of prepolymer A to prepolymer B decreases, the tensile strength of WPU film reduces while the elongation at break and glass transition temperature increases. Moreover, initially the contact angle with water was decreased instead of increase. However, modifications in a ratio of prepolymer A and B was not showed any significant impact on the thermal stability performance of the WPU films.

High strength, high stiffness and toughness, defect‐tolerant waterborne polyurethane with healing and antibacterial abilities

AbstractThe nature creates many biomaterials such as spider silk which exhibits a combination of stiffness, strength and toughness. However, most of synthetic unfilled materials suffer from a trade‐off between toughness and stiffness. Inspired by the structure of spider silk but beyond it, we proposed a novel molecular design to achieve transparent unfilled waterborne polyurethane (WPU) with simultaneously enhanced stiffness (280.9 MPa), tensile strength (25.1 MPa) and toughness (140.0 MJ/m3) as well as good elasticity (710%). The designed WPU comprised homogeneous continuous phase (soft segments) and diverse H‐bonds (hard segments) dispersed in it. The increase of rigid molecular chain content and H‐bonds contributed to the high stiffness of WPU. Furthermore, the mismatch of stiffness between hard domains and soft segments might promote crack deflection and branching, which endowed the robust WPU with fracture energy of 81.16 kJ/m2. The robust WPU film could be healed to recover most of its original mechanical properties (strength for 24.4 MPa and elongation for 610%) under heating. In addition, the WPU films demonstrated good antibacterial performance against Staphylococcus aureus and Escherichia coli after chlorination.

Construction of ultrathin self-healing films with highly efficient electromagnetic interference shielding and Joule heating capability by MXene decorating liquid metal

Improving the compatibility of liquid metal (LM) in polymers to develop self-healing LM-based flexible films with electromagnetic interference (EMI) shielding and Joule heating capability remains a considerable challenge. In this work, LM nanoparticles encapsulated by MXene are introduced into waterborne polyurethane (WPU) matrix to construct LM@MXene/WPU (LMW) films by the electrostatic attraction interaction and the casting method. MXene can form strong interactions with both LM and WPU to enhance the dispersion stability of LM, thus avoiding phase separation. The ultrathin LMW films exhibit a high electrical conductivity of 374 S/cm, resulting in an extremely high SE/t value (77640 dB/cm). Moreover, the LMW composite films with outstanding Joule heat capability can raise their surface temperature to above 135 ℃ under a constant voltage of 5 V within 10 s, which can activate the hydrogen bonds between LM@MXene and WPU chain to achieve a gratifying self-healing performance. In addition, the excellent EMI shielding stability of the LMW films is verified, providing a guarantee for their practical application. Therefore, this work provides a feasible strategy for developing ultrathin self-healing films with EMI shielding and Joule heating capability for next-generation electronics.