Green Antibacterial Nanocomposites from Poly(lactide)/Poly(butylene adipate-<i>co</i>-terephthalate)/Nanocrystal Cellulose–Silver Nanohybrids

Silver nanoparticles (AgNPs) with a diameter of 3–6 nm were uniformly reacted onto the surface of nanocrystal cellulose (NCC) via complexation leading to NCC–Ag nanohybrids with an AgNP content of 8 wt %. Subsequently, antibacterial green nanocomposites containing renewable and biodegradable poly­(lactide) (PLA), poly­(butylene adipate-<i>co</i>-terephthalate) (PBAT) and NCC–Ag nanohybrids were synthesized and investigated. The PBAT as flexibilizer improved the toughness of the PLA matrix while the uniformly dispersed NCC–Ag nanohybrids enhanced the compatibility, thermal stability, crystallization, and antibacterial properties of the PLA/PBAT blends. The crystallization rate and the storage modulus (<i>E</i>′) of the green nanocomposites were increased obviously with increasing content of CNC–Ag nanohybrids. Meanwhile, notably the antibacterial activity of the PLA/PBAT/NCC–Ag nanocomposites was achieved against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus cells. The antibacterial performance was mainly related to the antibacterial nature of the finely dispersed NCC–Ag nanohybrids. The study demonstrates great potential of the green nanocomposites in functional packaging and antibacterial textile applications

l‑Citrulline-Modified Ti₃C₂T_<i>x</i> MXene Nanosheets Embedded in Polyacrylamide/Sodium Alginate Hydrogels for Electromagnetic Interference Shielding

In this work, a robust and mechanically composite hydrogel with an efficient electromagnetic interference shielding performance was successfully fabricated via the incorporation of l-citrulline-modified Ti3C2Tx MXene nanosheets into the polyacrylamide/sodium alginate hydrogels by using ferrous chloride as the adhesive. A l-citrulline-modified Ti3C2Tx MXene nanosheet was the main shielding medium; ferrous chloride could not only enhance the mechanical property of the resultant hydrogels but also slightly improve the EMI shielding efficiency. The optimal tensile strength (3.42 MPa) and the EMI shielding effectiveness (26.8 dB) were achieved for the composite hydrogels with 6.5 wt % l-citrulline-modified Ti3C2Tx MXene nanosheets and 0.6 mol/L ferrous chloride, and the high ductility (780% elongation at break) of the composite hydrogel was reached with 0.5 wt % l-citrulline-modified Ti3C2Tx MXene and 0.8 mol/L ferrous chlorides. With outstanding mechanical and EMI shielding performances, the prepared composite hydrogels could apply in the electronic skin field

High-Sensitivity Flexible Sensor Based on Biomimetic Strain-Stiffening Hydrogel

Recently, flexible wearable and implantable electronic devices have attracted enormous interest in biomedical applications. However, current bioelectronic systems have not solved the problem of mechanical mismatch of tissue–electrode interfaces. Therefore, the biomimetic hydrogel with tissue-like mechanical properties is highly desirable for flexible electronic devices. Herein, we propose a strategy to fabricate a biomimetic hydrogel with strain-stiffening property via regional chain entanglements. The strain-stiffening property of the biomimetic hydrogel is realized by embedding highly swollen poly(acrylate sodium) microgels to act as the microregions of dense entanglement in the soft polyacrylamide matrix. In addition, poly(acrylate sodium) microgels can release Na+ ions, endowing hydrogel with electrical signals to serve as strain sensors for detecting different human movements. The resultant sensors own a low Young’s modulus (22.61–112.45 kPa), high nominal tensile strength (0.99 MPa), and high sensitivity with a gauge factor up to 6.77 at strain of 300%. Based on its simple manufacture process, well mechanical matching suitability, and high sensitivity, the as-prepared sensor might have great potential for a wide range of large-scale applications such as wearable and implantable electronic devices

Biobased Poly(lactide)/ethylene-<i>co</i>-vinyl Acetate Thermoplastic Vulcanizates: Morphology Evolution, Superior Properties, and Partial Degradability

Partially biobased thermoplastic vulcanizates (TPV) with novel morphology, superior properties and partial degradability were prepared by dynamic cross-link of saturated poly­(lactide) and ethylene-<i>co</i>-vinyl acetate (PLA/EVA) blends using 2,5-dimethyl-2,5-di­(<i>tert</i>-butylperoxy)­hexane (AD) as a free radical initiator. EVA showed higher reactivity with free radicals in comparison with PLA, leading to much higher gel content of the EVA phase (<i>G</i>_f‑EVA) than that of the PLA phase (<i>G</i>_f‑PLA). However, the <i>G</i>_f‑PLA increased more steeply at AD content larger than 1 wt % where the reaction of EVA approached to a saturation point. The competing reaction changed the viscosity ratio of the two components (η_PLA/η_EVA) that resulted in a novel morphology evolution of the TPV, i.e., from sea–island-type morphology to phase inversion via a dual-continuous network-like transition and finally cocontinuity again with increasing the AD content. The cross-link and phase inversion considerably enhanced the melt viscosity (η*), elasticity (<i>G</i>′) and the solid-like behavior of the PLA/EVA-based TPV. Meanwhile, superior tensile strength (σ_t = 21 MPa), low tensile set (<i>T</i>_s = 30%), moderate elongation (ε_b = 200%) and suitable stiffness (<i>E</i>′ = 350 MPa, 25 °C) were successfully achieved by tailoring the cross-link structure and phase morphology. In addition, the TPV are partially degradable in aqueous alkali. A degradation rate of approximately 5 wt % was achieved within 10 weeks at 25 °C and the degradation mechanism was investigated from both molecular and macroscopic levels. Therefore, this work provides a new type of partially biobased and degradable materials for substitution of traditional TPV

Rapid Stereocomplexation between Enantiomeric Comb-Shaped Cellulose‑<i>g</i>‑poly(l‑lactide) Nanohybrids and Poly(d‑lactide) from the Melt

In this work we report the in situ preparation of fully biobased stereocomplex poly­(lactide) (SC-PLA) nanocomposites grafted onto nanocrystalline cellulose (NCC). The stereocomplexation rate by compounding high-molar-mass poly­(d-lactide) (PDLA) with comb-like NCC grafted poly­(l-lactide) is rather high in comparison with mixtures of PDLA and PLLA. The rapid stereocomplexation was evidenced by a high stereocomplexation temperature (<i>T</i>_c‑sc = 145 °C) and a high SC crystallinity (<i>X</i>_c‑sc = 38%) upon fast cooling (50 °C/min) from the melt (250 °C for 2 min), which are higher than currently reported values. Moreover, the half-life crystallization time (175–190 °C) of the SC-PLA was shortened by 84–92% in comparison with the PDLA/PLLA blends. The high­(er) stereocomplexation rate and the melt stability of the SC in the nanocomposites were ascribed to the nucleation effect of the chemically bonded NCC and the “memory effect” of molecular pairs in the stereocomplex melt because of the confined freedom of the grafted PLLA chains

Research of Ferric Ion Regulation on a Polyimide/C-MXene Microcellular Composite Film

This paper established a new kind of polyimide/C-MXene composite films with a microcellular structure for electromagnetic interference shielding through solution mixing and liquid phase separation methods. Polyimide was used as the resin material, Ti3C2Tx MXene was used as the electromagnetic wave-shielding medium, l-citrulline was used as the surface modification agent, ferric trichloride (especially the ferric ion) was used as the cross-linking agent between the polyimide and modified C-MXene, and a microcell was used as the shielding structure. By adjusting the content of ferric ions, the foam structure, mechanical properties, thermal conductivity, and electromagnetic interference shielding efficiency of the polyimide/C-MXene microcellular composite film could be controlled. The higher the ferric ion content, the smaller the foam size and the higher the electromagnetic interference shielding efficiency. With increasing ferric ion content, the tensile strength and Young’s modulus appeared to first increase and then decrease; when the ferric ion content was 0.8 wt %, the tensile strength and Young’s modulus reached their maximum values, which were 10.06 and 325.29 MPa, respectively. In addition, with increasing ferric ion content, the thermal insulation showed first decreasing and then increasing tendency; the lowest thermal conductivity was 0.17 W/(m·K) when the ferric ion content was 0.8 wt %

Enhanced Thermal Stability and UV-Shielding Properties of Poly(vinyl alcohol) Based on Esculetin

In this article, PVA composites with outstanding thermal stability, UV shielding, and high transparency were fabricated on the basis of traditional Chinese medicine (esculetin). Characterization data have suggested in which the resulting PVA/esculetin (ESC) composites display excellent thermal stability compared to pure PVA and most of the PVA nanocomposites. The pyrolysis mechanism of PVA before and after modification with esculetin varies from chain unzipping degradation followed by chain random scission. The DPPH scavenging activity and FTIR measurements have illustrated that esculetin can scavenge reactive radicals, which leads to improvements in thermal stability and a change in the pyrolysis mechanism of PVA. More importantly, the resulting composites can almost completely block the whole UV region (200–400 nm) without any deterioration of the high transparency of the composites. Therefore, the composites can convert harmful UV light into blue light effectively, which is beneficial for their application as optical materials and devices

One-Pot Preparation of Autonomously Self-Healable Elastomeric Hydrogel from Boric Acid and Random Copolymer Bearing Hydroxyl Groups

Self-healable hydrogels based on the dynamically reversible boronate ester or borate ester bonds are usually prepared by reacting boronic acid or boric acid with diol compounds or polymer-like poly­(vinyl alcohol) bearing a hydroxyl group in each monomer unit. Herein, we report a finding that not only facilitates the preparation but also extends the range of self-healable hydrogels of this kind. By simply copolymerizing commercially available <i>N</i>,<i>N</i>-dimethylacrylamide and 2-hydroxyethyl acrylate (8:2 weight ratio) in the presence of boric acid in a one-pot fashion, the resulting random copolymer can gel in aqueous solution at pH = 9, giving rise to a solid hydrogel (tensile strength >0.5 MPa at water content of 30%) that, on the one hand, can autonomously self-heal (near 100% fracture stress recovery within 48 h in air at room temperature) and, on the other hand, shows the characteristics of elastomer (little stress relaxation under loading and small residual deformation after unloading upon repeated 300% elongation cycles). The results reveal that it can be sufficient to have a random copolymer with comonomer units bearing hydroxyl groups for reacting with boric acid to generate dynamically reversible borate ester bonds. This finding thus points out a general, facile, and cost-effective method to obtain and explore new borate ester bond-based self-healable hydrogels

Artificial Nacre from Supramolecular Assembly of Graphene Oxide

Inspired by the “brick-and-mortar” structure and remarkable mechanical performance of nacre, many efforts have been devoted to fabricating nacre-mimicking materials. Herein, a class of graphene oxide (GO) based artificial nacre material with quadruple hydrogen-bonding interactions was fabricated by functionalization of polydopamine-capped graphene oxide (PDG) with 2-ureido-4­[1<i>H</i>]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units followed by supramolecular assembly process. The artificial nacre displays a strict “brick-and-mortar” structure, with PDG nanosheets as the brick and UPy units as the mortar. The resultant nanocomposite shows an excellent balance of strength and toughness. Because of the strong strengthening via quadruple hydrogen bonding, the tensile strength and toughness can reach 325.6 ± 17.8 MPa and 11.1 ± 1.3 MJ m^–3, respectively, thus exceeding natural nacre, and reaching 3.6 and 10 times that of a pure GO artificial nacre. Furthermore, after further H₂O treatment, the resulting H₂O-treated PDG-UPy actuator displays significant bending actuations when driven by heat. This work provides a pathway for the development of artificial nacre for their potential applications in energy conversion, temperature sensor, and thermo-driven actuator

Artificial Nacre from Supramolecular Assembly of Graphene Oxide

Inspired by the “brick-and-mortar” structure and remarkable mechanical performance of nacre, many efforts have been devoted to fabricating nacre-mimicking materials. Herein, a class of graphene oxide (GO) based artificial nacre material with quadruple hydrogen-bonding interactions was fabricated by functionalization of polydopamine-capped graphene oxide (PDG) with 2-ureido-4­[1<i>H</i>]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units followed by supramolecular assembly process. The artificial nacre displays a strict “brick-and-mortar” structure, with PDG nanosheets as the brick and UPy units as the mortar. The resultant nanocomposite shows an excellent balance of strength and toughness. Because of the strong strengthening via quadruple hydrogen bonding, the tensile strength and toughness can reach 325.6 ± 17.8 MPa and 11.1 ± 1.3 MJ m^–3, respectively, thus exceeding natural nacre, and reaching 3.6 and 10 times that of a pure GO artificial nacre. Furthermore, after further H₂O treatment, the resulting H₂O-treated PDG-UPy actuator displays significant bending actuations when driven by heat. This work provides a pathway for the development of artificial nacre for their potential applications in energy conversion, temperature sensor, and thermo-driven actuator