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Polyethylene ionomers as thermally reversible and aging resilient adhesives

Low-density Polyethylene (LDPE) is a widely used thermoplastic polymer in various industries due to its versatility and cost-effectiveness. However, its inherent limitations, including low strength, poor UV resistance, and poor adhesion properties, have spurred efforts to enhance its applicability. We recently developed a LDPE ionomer based on ion pair comonomers (IPC) that can extend the range of application where traditional LDPE are limited. In this work, we report the effect of the reaction conditions on IPC content and melt flow index (MFI) for the PE ionomer obtained by copolymerizing ethylene with the ion pair dimethyl-amino methacrylate and methacrylic acid. The resulting ionomers exhibited improved mechanical properties, including higher elongation and stress at break, making them superior to conventional LDPE. The developed ionomers display enhanced adhesion properties on aluminum substrates with respect to LDPE. Remarkably, the adhesives exhibit thermal reversibility, making them suitable for applications requiring disassembly. Accelerated aging tests demonstrate the ionomers' durability, with some even showing increased adhesion after exposure to harsh conditions. Overall, this study highlights the potential of PE-based ionomers as advanced materials that combine the benefits of thermosets and thermoplastics, while offering outstanding adhesive properties when the IPC content is higher than 1 mol %.

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Ultrafast-degradable and super-elastic PBAT/polybutylene succinate foam with stable cellular structure and enhanced thermal insulation

PBAT is considered a leading eco-friendly polymer known for its exceptional biodegradability and mechanical properties. However, the production of high-performance PBAT foam remains challenging owing to poor foaming ability and intrinsic shrinkage. Herein, this study presents a flexible approach to prepare super-elastic and ultrafast-degradable PBAT/polybutylene succinate (PBS) foams achieved by microcellular foaming with CO2 & N2 as co-blowing agents. Firstly, the SEM, FTIR, as well as XPS spectra, confirmed a uniform and miscible distribution of PBS. Further, the crystallization kinetics and rheological analysis demonstrated that PBS effectively promoted crystallization and molecular chain entanglement. Thus, the PBAT/PBS foam exhibited significantly refined cellular structure, higher expansion ratio of 20.3, and restricted shrinkage of less than 4 %. More importantly, compared with neat PBAT foam, the compression strength of PBAT/PBS foam was dramatically enhanced by 47.7 %, and the energy loss coefficient was pronouncedly reduced by 58.8 % under the expansion ratio of 15.0. Meanwhile, the PBAT/PBS foam showed a thermal conductivity as low as 35.9 mW/m·K, enhanced hydrophobicity, and an exceptionally rapid degradation ratio. Considering the eco-friendly and flexible characteristics of this process, anti-shrinkage and ultrafast-degradable PBAT/PBS foams with improved mechanical and thermal insulation performance present promising prospects to replace the nondegradable polymer foams.

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Ultra-stretchable, high conductive, fatigue resistance, and self-healing strain sensor based on mussel-inspired adhesive hydrogel for human motion monitoring

Conductive hydrogels have been widely applied in various electronics, such as artificial skin, flexible devices, and implantable bioelectronics. However, it is still a challenge to develop high-performance hydrogel with high conductivity without compromising the toughness, stretchability, self-healing, and adhesion properties. Herein, inspired by the mussel-adhesion mechanism, an adhesive hydrogel that simultaneously achieves high conductivity (27.0 S·m−1), ultra stretchability (strain ˃ 3700 %), and strong toughness (1930 kJ·m−3) was developed by incorporating polydopamine (PDA)/sodium caseinate (SC) cross-linked network into the poly(acrylamide-co-acrylic acid) (P(AM-co-AA))/Al3+ network. Due to the abundant metal coordination and hydrogen bonds in the network, the obtained hydrogel displayed rapid self-healing capability (healing efficiency, HE > 97 %) and excellent fatigue resistance. Moreover, the introduction of PDA-SC cross-linked network endowed the hydrogels with robust adhesion (36.5 kPa for pigskin) and high conductivity. The conductive hydrogel was assembled into a strain sensor, which demonstrated prominent sensing performance with a wide detection range (∼2500%), high sensitivity (gauge factor (GF) of 23.7), fast response time and reliable repeatability. The hydrogel strain sensor can be attached on human body to distinguish and monitor both large and subtle movement signals. The developed conductive hydrogel strain sensor is expected to have promising applications in wearable devices, human–machine interaction, and electrical skin, and to extend for use in other portable and wearable energy related devices with multifunction.

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Alloying synergistic flame retardant effect on PA6 by polyimide containing alkyl hypophosphate structure

A novel flame retardant − bismaleimide polyalkyl phosphinate aluminium (BPPA), containing both imide and phosphinate structures, was designed and synthesized to investigate the intramolecular synergistic flame retardant effect between imide and phosphinate structures and alloying effect of the imide structure with PA6. Based on the flame retardant and mechanical properties of BPPA/PA6 composites, the alloying flame retardant effect of BPPA on PA6 was systematically investigated. The PA6 material had almost no char after burning; however, BPPA can produce a large amount of residue and form a dense char layer during combustion of PA6 matrix, effectively reducing the heat release, while BPPA also improved the mechanical properties of PA6 composites through the alloying effect. The peak heat release rate (pk-HRR) decreased by 55.8 %, and the residue yield increased by 9.2 wt% for 20BPPA/PA6, compared with the PA6. After compounding aluminum diethylphosphinate (ADP) and BPPA, the flame retardancy of the composites can be further improved. The LOI value of the 8ADP/6BPPA/PA6 was increased to 29.8 % and passed the test of UL94 V-0 level. Its pk-HRR and residue yield were similar to that of the 14BPPA/PA6, which indicated that the compounding system of ADP and BPPA can provide excellent charring properties and gas-phase flame retardancy of PA6. Meanwhile, the alloying BPPA with PA6 not only reduced the effect on the tensile strength of ADP on PA6, but also improved the breaking elongation of the composite. In conclusion, it provides a new direction for developing high-performance halogen-free flame retardant polyamides.

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Different solvents accompanied by different structures: Catalyst-free one step construction of highly branched polythioureas and its properties

In this study, tris(2-aminoethyl)amine and carbon disulfide were used as raw materials for the construction of highly branched polythioureas. Firstly, a highly branched polythiourea adsorbent was synthesized through a heating condensation reaction using N, N-dimethylformamide (DMF) as solvent without any catalyst. Interestingly, this study also revealed that a highly branched polythiourea resin was successfully synthesized without any catalyst when water was used as the solvent. Through nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), gel chromatography column (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and other means to characterize the comprehensive properties of the polymer. Then, mercury ions were used as the adsorption model. The effects of adsorbent dosing, adsorption time, and different pH on the adsorption of mercury ions (Hg2+) were investigated by intermittent adsorption experiments. The adsorption kinetics, isotherm model, sensitivity test of mercury extraction, single metal ion test, and the adsorption capacity of the adsorbent for nine metal ions were studied. In addition, bond strength tests were utilized to explore the adhesive properties of the prepared aqueous phase highly branched polythioureas. The results show that in the adsorption performance test, when the dosage of highly branched polythiourea adsorbent is 10 mg, the pH is acidic or neutral, and the adsorption time is 60 min, the adsorption efficiency of P-DMF for Hg2+ is as high as 99.99 %. The adsorption follows the Langmuir isotherm model and fits well with the pseudo-second-order kinetic model. In addition, P-DMF has a certain selectivity for Hg2+, and the adsorption efficiency is positively correlated with the mercury ion concentration. When Hg2+ is 100 mg/L, the adsorption efficiency reaches 99.98 %. In the bond strength test, the dry shear strength of the plywood reached 1.6 MPa, and the strength after soaking in hot water and boiling water for 3 h was 1.5 MPa and 1.4 MPa respectively, exceeding the requirements of GB/T9846-2015 for type II plywood (≥0.7 MPa).

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Tongue-inspired gelatin/poly(acrylate-co-acrylamide)-Fe3+ organic hydrogel with tunable mechanical, electrical, and sensory properties

Conductive hydrogels have emerged as one of the most promising candidates for the next generation of wearable soft electronics. However, they face limitations during practical implementation owing to their unbalanced overall properties. In this study, we present a dynamic cross-linked gelatin/poly(acrylic acid-co-acrylamide) (GxPyFez) hydrogel with tunable mechanical strength, self-healing, freezing resistance, electrical conductivity, and high sensitivity, which was prepared by incorporating dynamic Fe3+ ions. The hydrogel was prepared based on the tongue, in which gelatin/poly(acrylic acid-co-acrylamide) and Fe3+ ions mimic the connective tissue and receptor cells of the human tongue. The synergistic effect of reversible crosslinking, along with the modulation of rigid and flexible components enabled tunable flexible structures that exhibit excellent mechanical properties such as elongation at break (569 %) and toughness (8.82 MJ m−3). Notably, the G2P3Fe0.1 hydrogel exhibited remarkable self-healing ability, even at room temperature, while maintaining a good freezing resistance. Furthermore, the G2P3Fe0.1 demonstrated fast response characteristics along with a high sensitivity (GF = 2.75). Consequently, it could be assembled into sensors capable of effectively detecting various movements of the human body; it serves as an electronic skin that responds to diverse external stimuli and monitors underwater motion signals. This study provides new insights into the design of conductive hydrogels with tunable overall properties that can be modified to suit specific application scenarios.

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In situ polymeric nanomicelle-generating dissolving microneedle patch for enhanced transdermal methotrexate delivery in rheumatoid arthritis treatment

Rheumatoid arthritis (RA) presents a chronic autoimmune pathology. Methotrexate (MTX), a primary therapeutic agent for RA, often administered orally or via injection, has shown dose-dependent systemic toxicity upon prolonged use. Consequently, a pressing need exists for a secure and facile MTX delivery system in RA management. In the current study, the methoxy poly (ethylene glycol)-poly (lactide) polymer (mPEG-PLA) and hyaluronic acid (HA) were used as materials for both nanomicelles and dissolving microneedles (MNs) to facilitate the effective transdermal delivery of MTX in RA therapy. HA, a specific ligand for the CD44 receptor, could deposit on the outer surface of nanomicelles by interacting with mPEG-PLA, which serve as a targeting ligand for macrophages activated at inflamed joints. Upon MTX-loaded polymeric nanomicelles MNs (MTX@PMs MNs) application to the skin, MNs could effectively puncture the stratum corneum and in situ generate nanomicelles with the dissolution of MNs. In vivo therapeutic efficiency evaluations suggested that the MTX@PMs MNs demonstrated enhanced efficacy in mitigating the progression of RA without inducing treatment-related toxicity. Our findings suggest that the utilization of in situ polymeric nanomicelle-generating dissolving microneedle patches holds promise as a potential strategy for the clinical treatment of RA.

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