PU Films Research Articles

NIR-light-induced plasmonic liquid metal/ionic liquid/MXene polyurethane films with excellent antifouling and self-healing capabilities

The potential of organic coatings in antifouling applications has been well-documented. Beyond their exceptional antifouling effects, these coatings should also possess good mechanical strength and self-healing capabilities. Herein, a novel vinyl-based ionic liquid [VEMIM+] [Cl–] (IL) was in situ polymerized and then assembled onto the surface of liquid metal (GLM) nanodroplets to prepare GLM-IL. Subsequently, Ti3C2Tx (MXene) was modified with GLM-IL nanodroplets to obtain GLM-IL/MXene composite, which acts as an efficient photon captor and photothermal converters and can be further composited with PU film (GLM-IL/MXene/PU). Notably, the composite film significantly increases by ∼117°C after exposure to 200 mW/cm2 light irradiation. This increase is attributed to the high photothermal conversion efficiency of MXene and the excellent plasma effect of GLM-IL. Compared with pure PU, the GLM-IL/MXene/PU film shows a 50% improvement in tensile strength and above 85.8% healing efficiency with a local temperature increase. Additionally, the as-prepared GLM-IL/MXene/PU film reveals satisfactory antifouling properties, achieving a 99.7% reduction in bacterial presence and an 80.3% reduction in microalgae. This work introduces a novel coating with antifouling and self-healing properties, offering a wide range of applications in the fields of marine antifouling and biomedicine.

Stability and photophysical study of bright day light fluorescent material and its fabrication in laser patterning and LED application

Developing aggregation-induced emission (AIE) active highly visible fluorescent dyes is of great importance because of its numerous applications. We have successfully developed and synthesized two novel napthalimide based molecules PU1 and PU2, that exhibit bright greenish yellow in day light and vivid green emission when exposed to UV light. Compounds PU1 and PU2 exhibit variable emission behavior at different solvent polarities. Upon raising the solvent polarity from ether to DMF, emission maxima of PU1 and PU2 underwent a bathochromic shift. Additionally, compounds PU1 and PU2 show signs of AIE, which cause a restriction in intramolecular mobility. A distinct self-assembled structure was generated at 30 % aqueous DMF solution following aggregation, as demonstrated by experiments using dynamic light scattering and field emission scanning electron microscopy. Compounds PU1 and PU2 have been blended with poly(urethane) to develop a polymeric film. Tensile strain studies, and TGA, DSC analyses were used to examine the thermal/mechanical stability of PU films. The photostability of PU1 and PU2 in both solution and polymeric film was examined using a 5-h UV-beam irradiation. Furthermore, in the presence of trifluoroacetic acid, the blended polymeric film and 365 nm LED light coated material exhibits distinct colorimetric and fluorimetric transformations. Finally, laser-induced periodic surface structure (LIPSS) pattern processing on PU1 coated substrates can be extended for optical applications.

Thermal-driven self-healing and recyclable thermosetting polyurethane resins for energy harvesting

Improving the mechanical properties, self-healing capabilities, and recyclability of friction layer materials is crucial for the advancement of high-performance triboelectric nanogenerators (TENG). In this study, self-healing cross-linked polyurethanes were synthesized through the prepolymer technique, employing the Diels-Alder (D-A) reaction between the furan ring and Bismaleimide (BMI). The tensile strength of PU film with 10 wt% MBI is 54 MPa, and the shape recovery rate is 96.99 %. Moreover, it exhibits excellent self-healing and recyclable characteristics. Surface cracks can be healing within 10 min under heat, reshaped through hot pressing, while retaining 93.3 % of its mechanical properties. Additionally, the 2 cm × 2 cm area PU-based TENG can generate a short-circuit current, open-circuit voltage, transferred charge, and power density of 3.6 μA, 89 V, 29 nC, and 2.5 W/m2, respectively, at a frequency of 1 Hz. Futhermore, the self-healing efficiency of mechanical properties and the triboelectric output performances were found to reach 93.3 % and 98 %, respectively, after reprocessing. This study introduces a promising method for enhancing self-healing, shape memory characteristics, and the design of wearable TENG devices.

Microstructure Evolution of Reactive Polyurethane Films During In Situ Polyaddition and Film-Formation Processes.

Due to the advantages of low energy consumption, no air and water pollutions, the reactive polyurethane films (RPUFs) are replacing the solvated and waterborne PUFs nowadays, which significantly promotes the green and low-carbon production of PU films. However, the microstructure evolution and in situ film-formation mechanism of RPUFs in solvent-free media are still unclear. Herein, according to time-temperature equivalence principle, the in situ polyaddition and film-formation processes of RPUFs generated by the typical polyaddition of diisocyanate terminated prepolymer (component B) and polyether glycol (component A) are thoroughly investigated at 25 °C. According to the temporal change of viscosity, the RPUFs gradually transfer from liquid to gel and finally to solid state. Further characterizing the molecular weight, hydrogen bonds, crystallinity, gel content, and phase images, the polyaddition and film-formation processes can be divided into three stages as 1) chain extension and microcrystallization; 2) gelation and demicrocrystallization; 3) microphase separation and film-formation. This work promotes the understanding of the microstructure evolution and film-formation mechanism of RPUFs, which can be used as the theoretical guidance for the controllable preparation of high-performance products based on RPUFs.

Preparation of high-performance laminated glass interlayer by modifying epoxy resin composite polyurethane

Laminated glass has been widely used in glass curtain walls, windshields, and other structures due to its high safety, light weight, and aesthetics. The safety of polymer laminated glass depends on the performance of the polymer between the glasses. Polyurethane elastomer (PU) has become a universal polymer material due to its excellent mechanical strength and toughness. The aliphatic thermoplastic polyurethane has attracted people's interest about its application in the field of laminated safety glass due to its transparency and adhesion. In this work, a polyurethane-modified epoxy (EK-PU) composite film with superior bonding strength, mechanical properties, and transparency was successfully achieved. The tensile strength of the PU composite film was confirmed to be 45 MPa, while the bonding strength was 4.73 MPa. The improvement is attributed to the change of microphase separation structure and the introduction of silicone. The excellent impact resistance of the laminated glass based on polyurethane composite film have been confirmed by the falling ball impact test, which is 6.5 times of the common PU film. The laminated glass based on the EK-PU film will be applied in aerospace, defense, and automotive fields.

Polyurethane foam reinforced with Ag nanoparticle decorated ZnO nanorods: a dual-functional approach for improved antibacterial and mechanical properties

Abstract This study introduces a novel approach by incorporating pristine ZnO nanorods and Ag nanoparticles decorated ZnO nanorods into a polyurethane foam matrix. This synergistic combination aims to enhance the foam’s antibacterial properties while investigating its impact on mechanical strength. Nanoparticles and prepared nanopolymer were characterized by different methods like XRD, TEM, SEM, and EDS. The mechanical characteristics and antibacterial properties of prepared polyurethane composites were investigated in the presence of Escherichia coli and Bacillus subtilis. A much higher level than reported in the literature was found for PU films filled with ZnO nanorods. Incorporating nanoparticles into polyurethane nanocomposites has been demonstrated to significantly improve polyurethane’s antibacterial properties. The results revealed that ZnO/PU antibacterial efficiency decreased with increasing ZnO nanofiller content, while AgNPs@ZnO/PU composite antibacterial efficiency increased with increasing AgNPs@ZnO nanofiller content. Also, the weak coordinate bond between ZnO and Ag in the PU chain extender was demonstrated. Increasing the ZnO content to 1.4 wt% resulted in greater Young’s modulus and tensile strength, which increased when the ZnO content was increased further. Such a dual-functional enhancement holds promise for applications requiring both antimicrobial efficacy and mechanical integrity.

Effect of thermal, mechanical and photophysical properties of high emissive photoluminescence organic pigments

This research aims to synthesize highly visible, bright emission fluorescent dye molecules in daylight to produce PU films and PU resource safety materials. Here we have developed four different types of highly visible PU films in which a cyano-substituted methoxyphenylene core with an additional electron-withdrawing and-donating unit is used to produce a bright orange color with twisted rigid conformational dyes. Modifications in the mechanical behavior and thermal stability properties of PU films were tested by tensile tests, TGA and DSC. The samples of PU film exhibit exceptional elasticity, with a high elongation breaking point and good young's modulus value. Furthermore, these synthesized dyes were measured for photophysical properties and other parameters such as solvent effect, quantum yield and lifetime. The quantum yields of highly visible dyes were measured in both solution and solid phase and found to be in the range of 0.25–0.48 and 0.15 to 0.55, respectively. The HOMO-LUMO energy gap of the dyes in the solid state is significantly lower than that in the solution state. This related to the dyes which exhibiting a lifetime in THF solution of about 1.96–2.41 ns, whereas in the solid state, the lifetime is much better about 6.43–19.61 ns. This indicating that the dyes in the solid state are energetically easier and hence the solid state of dyes shows higher lifetime.

A high-efficient antibacterial and biocompatible polyurethane film with Ag@rGO nanostructures prepared by microwave-assisted method: Physicochemical and dermal wound healing evaluation

Wound infections are a significant issue that can hinder the wound healing process. One way to address this problem is by enhancing the antibacterial activity of wound dressings. Accordingly, this work focuses on developing a castor-oil-based antibacterial polyurethane nanocomposite film impregnated with silver nanoparticles (AgNPs) decorated on the surface of reduced graphene oxide (rGO) nanostructures (Ag@rGO). To this aim, rGOs act as a platform to stabilize AgNPs and improve their bioavailability and dispersion quality within the PU film. The microwave-assisted synthesis of Ag@rGO nanohybrids was proved by FTIR, XRD, TGA, FE-SEM, EDS, and TEM analyses. Compared to PU/GO, the effect of Ag@rGO nanohybrids on thermo-mechanical features, morphology, antibacterial activity, cytocompatibility, and in vivo wound healing was assessed. SEM photomicrographs revealed the enhanced dispersion of Ag@rGO nanohybrids compared to GO nanosheets. Besides, according to XRD results, PU/Ag@rGO nanocomposite film demonstrated higher microphase mixing, which could be due to the finely dispersed Ag@rGO nanostructures interrupting the hydrogen bonding interactions in the hard segments. Moreover, PU/Ag@rGO nanocomposite showed excellent antibacterial behavior with completely killing E. coli and S. aureus bacteria. In vitro and in vivo wound healing studies displayed PU/Ag@rGO film effectively stimulated fibroblast cells proliferation, migration and re-epithelialization. However, the prepared antibacterial PU/Ag@rGO nanocomposite film has the potential to be used as a biomaterial for dermal wound healing applications.

Promoting antibacterial activity of polyurethane blend films by regulating surface-enrichment of SiO2 bactericidal agent

Abstract Polyurethane (PU) blended with nano-bactericidal agents was one of the most ways to obtain PU with antimicrobial properties. However, the bactericidal agent nanoparticles cannot effectively enrich the PU surface to reduce their antimicrobial properties. In this study, nano-silica particles with a large number of polar quaternary ammonium salt (N,N-dimethyl-3-aminopropyl-12-alkyl-ammonium bromide trimethylsilyl, denoted as QAC) can easily enrich the PU surface to endow PU with excellent antibacterial properties after they were blended with PU film. The QAC on the surface of silica with different diameters (denoted as SiO2-Q-X) can endow silica with antimicrobial properties and improve the repulsion between silica and PU to enhance the enrichment on PU surface of silica. A series of SiO2-Q-X/PU blend films were prepared and applied to inhibit the growth of the bacterial colony. The SiO2-Q-X/PU films can inhibit the growth of Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis. The SiO2-Q-X with more polar QAC was easily enriched on the surface of PU and had a better bactericidal effect than those of SiO2-Q-X with a minor polar QAC. Moreover, the aging of the SiO2-Q-X/PU films did not affect their antibacterial effect.

Large-scale dispersion of the hierarchical (1D, 2D and 3D) carbonaceous nanofillers in thermoplastic polyurethane through supramolecular self-assembly and extrusion

ABSTRACT The hierarchical carbonaceous nanofillers viz. carboxylated multiwalled carbon nanotube (MWCNT-COOH as 1D), hydroxylated few-layer graphene (FLG-OH as 2D), and hybrid 3D i.e., MWCNT-COOH immobilized into FLG-OH were dispersed into segmented thermoplastic polyurethane (TPU) by twin-screw extrusion (TSE). The concentration of nanofillers was varied as 0.25, 0.5, 1.0, 2.0 and 5 wt%. To increase the level of dispersion, hybrid 3D nanofillers were also incorporated into TPU by producing cellular structures through supramolecular self-assembly route (SSAR). The cellular structure in which the nanofillers were found to be uniformly dispersed was then compounded by TSE technique. The large-scale uniform dispersion was observed at higher loading (2 wt%) by SSAR followed by TSE when compared with direct TSE. Uniform dispersion was found at 1 wt% loading by direct TSE. PU nanocomposite film reinforced with 2 wt% hybrid 3D nanofillers showed good gas barrier property with ~63% reduction of helium gas permeability to 472 cm3/m2/day from 1287 cm3/m2/day of neat PU film.

Flexible strain sensor based on PU film with three-dimensional porous network

Flexible strain sensors are widely used in wearable applications such as human motion and health detection, but it is challenging to prepare sensors with excellent performance, such as a wide sensing range and high sensitivity with a simple process and low cost. By taking the advantages of the electrostatic spinning technique that can prepare micro-structured films with fibrous porous networks, and this paper investigated the effect of the distance between the electrostatic spinning needle and the collection drum on the mechanical properties of the PU films produced. Then, the most mechanically excellent three-dimensional porous PU fiber film was selected as the substrate, and Carbon Black (CB) particles were selected as the conductive filler to prepare the CB/PU/Ecoflex strain sensor (CPESS) with a three-dimensional porous fiber network structure by spraying CB on the PU fiber film for the sensitive layer and applying a layer of biocompatible Ecoflex on the surface as the encapsulation layer. Owing to the substrates of this three-dimensional network microstructure with excellent mechanical properties such as high Young's modulus and elongation at break, the CPESS has an excellent sensing performance, with a detection range of 200 %, a sensitivity of up to 1443.95, rapid dynamic response of 50 ms, a low detection limit of (0.3 % strain), favorable repeatability, and excellent dynamic response at a large-scale tensile strain of 150 % − 200 %. The CPESS can be used to detect human joint movements and fine motion changes, and it exhibits great potential for smart wearable applications.

Study on the preparation and performance of SiC nanoparticle reinforced polyurethane coatings

AbstractPolyurethane (PU) coatings display several advantages such as easy construction, adjustability, and excellent mechanical properties, and therefore have potential applications in the coating of rocket engines and warheads. However, mechanical strength, high ductility and thermal stability are often difficult properties to combine, which has become a key limitation in efforts toward developing PU coatings for these applications. In this paper, a fast‐curing PU film was developed by reacting between polytetrahydrofuran and diphenylmethane 4,4'‐diisocyanate. The mechanical strengthening effect of SiC nanoparticles on the film was studied and compared with other common fillers, including TiO2, XFM13. The results revealed that SiC nanoparticles substantially increased the mechanical properties in PU coating, increasing the material's tensile strength and elongation at break to 34.14 MPa and 434% respectively. In addition, the inclusion of SiC nanoparticles generally improved the thermal stability and low temperature resistance of PU film. The results generated in this research has established a foundation for the application of PU materials in fields requiring high performance properties, such as rocket engines coatings and warhead manufacture.

Debonding Detection in Aluminum/Rigid Polyurethane Foam Composite Plates Using A0 Mode LAMB Wave EMATs

Aluminum/rigid polyurethane foam composite plates (ARCPs) are widely used for thermal insulation. The interface debonding generated during manufacturing degrades the thermal insulation performance of an ARCP. In this study, the debonding of an ARCP, a composite plate with a porous and damped layer of rigid polyurethane foam (RPUF), was detected using A0 mode Lamb wave electromagnetic acoustic transducers (EMATs). The low energy transmission coefficient at the interface caused by the large acoustic impedance difference between aluminum and RPUF made the detection difficult. Based on these structural characteristics, an A0 mode Lamb wave with large out-of-plane displacement was used to detect the debonding. EMATs are preferred for generating A0 mode Lamb waves due to their advantages of being noncontact, not requiring a coupling agent, and providing convenient detection. A finite element simulation model considering the damping of the RPUF layer, the damping of the PU film at the interface, and the bonding stiffness of the interface was established. The simulation results indicated that the Lamb wave energy in the aluminum plate transmits into the RPUF layer in small amounts. However, the transmitted energy rapidly attenuated and was not reflected into the aluminum plate, as the RPUF layer was thick and highly damped. Therefore, energy attenuation was evident and could be used to characterize the debonding. An approximately linear relationship between the amplitude of the received signals and the debonding length was obtained. Experiments were performed on an ARCP using EMATs, and the experimental results were in good agreement with the simulation results.

Preparation and properties of multifunctional polyurethane synthetic leather nanocomposites

Although leather can be functionally modified well, its origin will cause concern about the destruction of the ecological environment. Here, a novel multifunctional synthetic leather (denoted as FRTL) that integrates high tensile strength, flame retardancy, Joule heating, electromagnetic shielding, and strain sensing is reported. Benefiting from the excellent mechanical properties of the PU film, the leather exhibits a high tensile strength of 100.8 MPa. Based on the high conductivity of MXene, the leather possesses an electromagnetic shielding efficiency of 30.1 dB. FRTL also exhibits excellent flame retardancy, confirmed by the reduction of more than 32% in peak heat release rate. In addition, the controlled Joule heating properties enable the leather to cope with extreme cold weather. The obtained fabric can also detect various human movements. This work provides a facile method to fabricate the next-generation multifunctional protective leather, showing promising application in the field of smart firefighting.

Effects of NCO/OH Ratios on Bio-Based Polyurethane Film Properties Made from Acacia mangium Liquefied Wood.

The compatibility between isocyanate and polyol plays an important role in determining a polyurethane product's performance. This study aims to evaluate the effect of varying the ratios between polymeric methylene diphenyl diisocyanate (pMDI) and Acacia mangium liquefied wood polyol on the polyurethane film properties. A. mangium wood sawdust was liquefied in polyethylene glycol/glycerol co-solvent with H2SO4 as a catalyst at 150 °C for 150 min. The A. mangium liquefied wood was mixed with pMDI with difference NCO/OH ratios to produce film through the casting method. The effects of the NCO/OH ratios on the molecular structure of the PU film were examined. The formation of urethane, which was located at 1730 cm-1, was confirmed via FTIR spectroscopy. The TGA and DMA results indicated that high NCO/OH ratios increased the degradation temperature and glass transition from 275 °C to 286 °C and 50 °C to 84 °C, respectively. The prolonged heat appeared to boost the crosslinking density of the A. mangium polyurethane films, which finally resulted in a low sol fraction. From the 2D-COS analysis, the hydrogen-bonded carbonyl (1710 cm-1) had the most significant intensity changes with the increasing NCO/OH ratios. The occurrence of the peak after 1730 cm-1 revealed that there was substantial formation of urethane hydrogen bonding between the hard (PMDI) and soft (polyol) segments as the NCO/OH ratios increased, which gave higher rigidity to the film.

Study on the surface properties of the regenerated polyurethane foam micropowder via cryogenic pulverization and its application

The micropowder obtained by cryogenic pulverizing flexible polyurethane foam (FPUF) as a filler is a waste recycling approach which is highly efficient and eco-friendly. Currently, the micropowder has merely been applied roughly and simply in various fields, so it makes sense to study its surface activity in depth to achieve quantitative and efficient reuse. This paper is focused on studying the surface physicochemical properties of the micropowder and its reactivity and compatibility as a filler in polyurethane elastomers. The FPUF was pulverized into a particle of 0–900 μm. The hydroxyl and amine values of the micropowder surface increased from 48.82, 5.99 mg KOH/g to 73.78, 9.12 mg KOH/g, respectively, with the decrease of particle size range from 500-900 μm to 0–100 μm. However, the amount of substance of effective active hydrogens that could react with NCO groups in the polyurethane prepolymer was uncertain due to the viscosity and temperature. Thus, a preliminary attempt was to quantify the effective active hydrogens by FTIR coupled with titration of the NCO content. The mixture with 5% FPUF-1 micropowder had the maximum effective active hydrogens of 3.30 mmol, which could react with NCO groups to form new chemical crosslinking sites. Compared with the pure PU film, microcrosslinking and strong hydrogen bonding are contributors to the good mechanical properties of the composite. Thus, the FPUF micropowder as an organic filler exhibits considerable potential for converting thermoset FPUF into value-added performance materials.

Preparation of recyclable fluorescent electrospinning films and their application in distinguishing and quantitatively analyzing acid gases

AbstractAcid gas, as a kind of polluting gas, poses a great threat to human health. Therefore, there is a need for a material that can detect it, and it is of great significance to find and deal with acid gas leakage in time. In this paper, the fluorescent micromolecule NAP‐OH, a naphthalimide derivative modified by morpholine, was introduced into polyurethane as an end‐capping agent, and the prepared nanometer fluorescent sensing material E‐NAP0.5/PU by electrospinning technology exhibited a sensitive ratiometric fluorescence response behavior to acid gas. The E‐NAP0.5/PU's specific surface area was 9.142 m2/g and its diameter was 200–400 nm. In 6 ppm HCl gas, TFA and FA gases, the response time of E‐NAP0.5/PU (deep orange red) films were 2, 20, and 40 s, and the colors were green, light green and light orange‐red, respectively. This showed that the membrane has great potential application in distinguishing acid gases. In addition, the E‐NAP0.5/PU changed from orange‐red to colorless within 30 s in SO2 gas with a concentration of 360 ppm. The detection limits of E‐NAP0.5/PU for HCl, TFA, FA and SO2 gases were 996 ppb (0–10 ppm), 660 ppb (0–8 ppm), 724 ppb (0–10 ppm) and 39 ppm (0–360 ppm), respectively. More importantly, E‐NAP0.5/PU could be reused multiple times. After five times of recovery, the E‐NAP0.5/PU film still recovered to its original fluorescence intensity, and kept a good response to acid. The 1H NMR and fluorescence spectra results indicated that the possible mechanism for acid gas detection of NAP‐OH was attributed to the protonation of morpholine group. To sum up, E‐NAP0.5/PU had a broad application prospect in acid gas detection.

Controlled release fertilizer with temperature-responsive behavior coated using polyether polyol (PPG) / polycaprolactone (PCL) blend-based polyurethane performs smart nutrient release

The development of the temperature-responsive controlled release fertilizers (CRFs) can tune the nutrient release matching plant demands even when temperature fluctuates. Herein, polycaprolactone (PCL) with different molecular weights (PCL500, PCL1000, PCL2000 and PCL3000) were used as raw materials and six types of PU films as coating materials for CRFs were synthesized by reacting the polyether polyol (PPG)/PCL blends and methylene diphenyl diisocyanate (MDI). Furthermore, the CRFs coated using PU films (PUCFs) were prepared in a fluidized bed device by in-situ reaction method, and the nitrogen (N) release rate of PUCFs was measured by water immersion experiment. The temperature sensitivity and compositions of PU films were evaluated with differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Results showed that PUCFs based on PCL500 satisfied the CRF ISO standard, but the corresponding PU film had no temperature-responsive property. However, PUCFs based on PCL2000 and the corresponding PU film showed the opposite results. FTIR and XRD results showed that the PPG/PCL2000 blends could copolymerize with MDI to format the block copolymer with the two-phase structure of crystalline phase/amorphous phase. The block copolymer comprising of PPG and PCL2000 at a molar ratio of 8 to 2 was indicated to have shape memory characteristics and the CRFs coated by this copolymer had excellent N release characteristics with a controlled release period of more than 30 days. Moreover, these CRFs showed significant temperature-switch at 33 °C. In conclusion, the production of temperature-responsive PUCF which is suitable for the application into agriculture will improve nutrient availability, indicating that the stimuli-responsive system has potential application in sustainable and green development of agriculture.

Fabrication of azobenzene non-covalent bonding grafting graphene composite and its application in weathering and corrosion resistant polyurethane coating

The azobenzene non-covalent bonding grafting graphene composite (GN-Py-AZO) is fabricated by π-π interaction between Py-AZO (with a pyrene ring, a hydrophilic group and azobenzene structure) and graphene, which is confirmed by FT-IR, 1HNMR, XRD, UV–vis and XPS. The impact resistance, hardness and hydrophobic properties of the composite polyurethane coating (PU) are significantly increased after adding GN-Py-AZO in PU. Electrochemical impedance spectroscopy and Tafel polarization curves show that GN-Py-AZO improves effectively the anti-corrosion performance of the composite polyurethane coating and 0.5% GN-Py-AZO/PU composite coatings have best anti-corrosion performance. FT-IR and SEM are applied to investigate the weather-resistance of PU films which showed that 0.5% GN-Py-AZO/PU films had the weakest changes and can maintain the basic planar morphology without defects such as wrinkles, big cracks and protrusions after UV aging for 650 h with the best UV-aging resistance. In conclusion, 0.5% GN-Py-AZO/PU showed excellent overall performances in weathering resistance and anti-corrosion. The weathering-resistance and anti-corrosion mechanism of GN-Py-AZO/PU composite coating is also discussed.

Stretching induced alignment of graphene nanoplatelets in polyurethane films for superior in-plane thermal conductivity and electromagnetic interference shielding

The rapid innovation of flexible smart electronics has increased the demand for flexible thermally conductive films with the high performance of electromagnetic interference shielding (EMI). This study focuses on graphene nanoplatelets/polyurethane (GnP/PU) films that were fabricated utilizing the solution casting approach. The stretching-induced alignment method was then used to align the GnP sheets horizontally in the PU matrix by uniaxially stretching to a particular degree. The resultant stretched GnP/PU films with 10 wt% GnP loading at a stretching degree of 130% show an excellent in-plane thermal conductivity (λ∥) and EMI shielding effectiveness values of 10.68 W m−1 K−1 and 41 dB in the frequency range of 8–12 GHz which are 679% and 60%, respectively, higher than that of corresponding unstretched ones. The outstanding λ∥ and EMI shielding effectiveness can be ascribed to the horizontal alignment of GnP sheets in the PU matrix. That, in turn, may decrease the interfacial thermal resistance, and facilitate the establishment of effective phonon and electron transfer in the stretched GnP/PU films. The obtained films demonstrated superior heat dissipation and mechanical properties compared to neat PU film. Therefore, the prepared GnP/PU films have great potential as heat spreaders and EMI shielding material in flexible smart electronics.