The cover image is based on the article Temperature-Dependent Energy Storage Mechanism in Polyimide Films: Optimizing High-Temperature Performance via Dihedral Angle Engineering by Xuefei Bi et al., https://doi.org/10.1002/app.57616.
The cover image is based on the article Temperature-Dependent Energy Storage Mechanism in Polyimide Films: Optimizing High-Temperature Performance via Dihedral Angle Engineering by Xuefei Bi et al., https://doi.org/10.1002/app.57616.
Porous organic polymers are a new class of polymeric materials that combine permanent porosity, high surface area, monomer diversity, and synthetic tunability, making them highly promising candidates for application in heterogeneous catalysis and pollutant removal from aqueous solution. Herein, three Tröger's base-linked POPs were prepared using 1,3,5-tris(4-aminophenyl)triazine, benzidine, or 4,4′-diamino-[1,1′-biphenyl]-2,2′-disulfonic acid, to obtain TAPT-Tr-POP, TAPT-Bd-Tr-POP, and TAPT-Bd(SO3Na)2-Tr-POP. The polymers exhibited BJH average pore diameters ranging from 1.4 to 27.0 nm, BET surface areas up to 177 ± 8 m2 g−1, and thermal stabilities up to 213°C. The POPs were tested as heterogeneous catalysts in the metal-free Henry and Knoevenagel reactions, between aromatic aldehydes and nitromethane and ethyl cyanoacetate, respectively, with moderate to virtually complete conversions. The three POPs were subsequently used as solid adsorbents for the removal of the organic pollutants methylene blue (MB), crystal violet (CV), phenol red (Phr), and phenol (PhOH), with the sulfonated material TAPT-Bd(SO3Na)2-Tr-POP exhibiting maximum adsorption capacities up to 700 ± 234 and 522 ± 72 mg g−1 toward the adsorption of MB and CV, respectively. The obtained results showcase the enormous potential of Tröger's base-linked polymers as versatile new materials for greener, more sustainable catalysis and environmental remediation.
The current global development trend increasingly prioritizes green initiatives and environmental protection. The use of epoxy resin (EP) across various fields has been limited due to its flammability and high smoke emission. In light of this, enhancing the flame retardancy of EP through clean and non-toxic methods is both crucial and urgent. Drawing inspiration from mussels' innate properties, a novel flame retardant (ADCM) was developed by coating aluminum hydroxide with polydopamine, followed by the grafting of a pre-synthesized Co-MOF (derived from 2-methylimidazole and cobalt nitrate hexahydrate) onto the surface. This flame retardant was subsequently added to EP. The study results indicate that the addition of 15 wt% ADCM significantly enhances both the flame retardancy and smoke suppression capabilities of the EP composites. The specific manifestations are as follows: the peak heat release rate (pHRR) has been reduced by 42.5%, the peak smoke production rate (pSPR) has decreased by 40%, the total smoke production (TSP) has been diminished by 34.4%, the LOI value has increased to 32.8%, and the UL-94 flame retardant classification has achieved a V-1 level. The preparation of ADCM provides new ideas and effective strategies for the application of surface modification engineering in the development of multifunctional materials.
This work aims to improve the processing window and melt strength of cellulose acetate (CA) with low acetyl content as a greener alternative to non-biodegradable plastics for rigid-packaging applications. It presents the first scientific evaluation of inorganic and organic fillers on plasticized CA (pCA) using two plasticizers, bio-based triacetin (pCTA) and petro-based triethyl citrate (pCTEC). Low-acetyl CA is used to improve biodegradability over conventional high-acetyl CA. Melt extrusion followed by injection molding is performed to make pCTA and pCTEC, and composites are formulated with organic/inorganic fillers including talc, clay, calcium carbonate (CaCO3), and microcrystalline cellulose (MCC). Talc-based composite reveals a well-balanced mechanical performance and is thus combined with luperox (LUP), which further increases the matrix's tensile strength and Young's modulus. The pCTEC/10 wt.% talc shows ~130% rise in maximum extensional viscosity, while pCTA/0.01LUP/10 wt.% talc achieves a ~70% gain. The pCTEC/0.01LUP/15 wt.% talc improves the water vapor and oxygen barrier by 55.1% and 58.1%, respectively. Talc's platy morphology enhances interfacial adhesion, and its easier delamination in LUP's presence contributes to these barrier improvements. CA's thermal degradation shifts ~10°C higher after the addition of LUP and talc. These enhancements demonstrate the potential of pCA-based composites for sustainable rigid packaging applications.
For the SiC/epoxy resin composites which are commonly used for end corona protection (ECP) in large generator stators and are prone to wear failure, this study investigates the applicability of thermoplastic alternatives poly(ether ether ketone) (PEEK), providing new material directions for future research. Conductivity and dielectric property studies were conducted on pure PEEK and samples with varying contents of nano-silicon carbide. The conductivity of the films was measured in the temperature range of 30°C–200°C and the electric field range of 1–3 kV/mm. Results showed that the film with 5% silicon carbide exhibited the highest conductivity, with a nonlinearity coefficient of approximately 0.98. An Arrhenius analysis was conducted to understand the conduction mechanism and to obtain the trap activation energy. Dielectric spectroscopy revealed the dielectric loss characteristics, and fitting with the Havriliak–Negami (HN) model indicated different relaxation mechanisms in the studied samples. Given sample test results compliance with the required conductivity and nonlinearity coefficients, along with their lower dielectric loss and field dependence on temperature and electric field, PEEK films doped with 3% silicon carbide present a promising potential replacement for epoxy resin in the ECP in generators.
This work has developed a polylactic acid/starch composite with enhanced performance and cost-effectiveness via oxidative modification of starch. Oxidized corn starch (OCS) with different oxidation degrees was prepared using a hydrogen peroxide/copper sulfate pentahydrate catalyst system, and PLA/OCS composites were prepared using melt blending. Tensile test results showed that the tensile strength of the PLA/10OCS4.0 composite (71.2 MPa) was markedly higher than that of the PLA/10CS composite (66.4 MPa) and even surpassed that of neat PLA (68.5 MPa). To probe potential interfacial reactions between the PLA matrix and oxidized starch, Soxhlet extraction followed by FTIR spectroscopy was performed. The results confirmed in situ formation of PLA-g-OCS copolymers, evidencing that the CHO groups on the OCS surface acetalization reacted with the terminal -OH groups of PLA molecular chains to form covalent linkages. Meanwhile, SEM and DSC results demonstrated that the PLA-g-OCS copolymers formed at the two-phase interface significantly enhanced the interfacial compatibility between the PLA matrix and starch granules, while also improving the crystallization ability of PLA. Furthermore, after introducing triglycidyl isocyanurate (TGIC) into the PLA/10OCS4.0 composite material, the interfacial bonding strength and crystallization ability of the PLA/10OCS4.0/0.5TGIC composite material were further enhanced, with its tensile properties surpassing those of the PLA/10OCS4.0 composite material. The PLA/OCS composite approach proposed in this work not only reduces material costs and enhances tensile properties but is also expected to improve biodegradability, offering a novel technical approach for the application of PLA in the disposable plastics field.
The development of composite polymer materials with quadratic nonlinear optical (NLO) activity is presented; long-term stability of NLO response is provided by polymer chains cross-linking. For this purpose, polymer matrices based on methyl methacrylate and glycidyl methacrylate copolymers (P1) or hydroxyethyl methacrylate (P2) containing epoxy and hydroxyl groups, respectively, intended for polymer chains cross-linking, were synthesized. Based on these copolymers, quinoxaline chromophores and cross-linking agents (succinic acid, terephthalic acid, and 4,4′-diphenylmethane diisocyanate), polymer composite materials were developed that exhibit quadratic NLO activity up to 37 pm/V for the best samples. Composites were poled to achieve chromophores' polar order in the material necessary for the quadratic NLO response; polymer matrix chains were cross-linked during poling. An extremely important role of time–temperature poling protocols for the materials' enhanced NLO response is demonstrated. The materials were shown to exhibit high relaxation stability of the NLO coefficient, d33: 92%–95% of the initial value preserved after keeping at ambient temperature for several months; after heating at 55°C for 50 h, d33 for non-crosslinked samples decreases noticeably (to 80%–86%), while cross-linked samples keep d33 unchanged.
Growing global energy shortages necessitate advanced flexible energy storage devices. Although poly(vinylidene fluoride) (PVDF) is widely used in flexible energy storage materials, its inherently low energy density and high dielectric loss limit its practical applications. To address these issues, we developed a novel ternary composite film by incorporating hydroxyapatite (HAP, ε r ~ 48) to enhance dielectric polarization and poly(methyl methacrylate) (PMMA) to improve breakdown strength and suppress dielectric loss. Innovatively, HAP nanoparticles serve as nucleating agents that optimize crystalline domains, while PMMA restricts charge carrier mobility in amorphous regions through molecular chain entanglement and hydrogen bonding. Through this synergistic dual-phase modulation, the composite achieves a high energy density of 9.96 J/cm3 at 440 kV/mm, representing a 44.56% enhancement over pure PVDF, along with significantly reduced dielectric loss. Furthermore, this composite film exhibits excellent flexibility, offering a novel and effective strategy for preparing flexible energy storage films with superior energy density.
EXPRESSION OF CONCERN: Y.-H. Xue, S.-C. Yan, and Y. Chen, “ Thermomechanical and Tribological Properties of Polyimide and Polyethersulfone Blends Reinforced with Expanded Graphite Particles at Various Elevated Temperatures,” Journal of Applied Polymer Science 139, no. 28 (2022): e52512, https://doi.org/10.1002/app.52512.
This Expression of Concern is for the above article, published online on 30 April 2022 in Wiley Online Library (wileyonlinelibrary.com), and has been issued by agreement between journal Editor-in-Chief, Stefan Spiegel; and Wiley Periodicals, LLC. A third party shared a report from the National Natural Science Foundation of China which indicated that authors of this article had included images from other publications, manipulated image scale, included co-authors in the publication without their consent, and included reference to other researcher's funding without consent [1].
An investigation by the publisher found that all images in Figure 4 in this article had been re-used from Figure 7 in an earlier publication by some of the same authors [Yan et al. 2016 (https://doi.org/10.1002/pc.24211)]. Both sets of images are intended to show different experimental conditions. The investigation also found that many of the magnified panels in Figure 12 did not correspond to their matching images and that the inset magnified panel in Figure 4A was a copy of the panel at the same scale. The other concerns included in the report by the National Natural Science Foundation of China could not be confirmed.
The authors did not respond to an inquiry and request for original data by the publisher, and therefore the data and conclusions in this article could not be validated. The journal has decided to issue an Expression of Concern to inform and alert readers. The authors did not respond to our notice regarding the Expression of Concern.
The growing demand for self-powered electronics, such as touch sensors and wearable devices, highlights the need for reliable and efficient triboelectric systems. However, performance inconsistencies frequently originate from uncontrolled material morphology and processing conditions. This study explores the processing–structure–performance relationships in polymer-based triboelectric systems, focusing on poly(vinylidene fluoride) (PVDF). Through controlled experiments incorporating auxiliary materials, poly(3-hydroxybutyrate) (PHB) and carbon nanotubes (CNTs), and characterization via Differential Scanning Calorimetry (DSC), polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), we demonstrate that triboelectric performance is primarily driven by crystal size reduction rather than increased crystallinity. Additionally, optimized surface morphology, achieved through electrospinning, significantly enhances output by balancing fiber diameter and defect density. This work establishes a systematic framework for interpreting triboelectric behavior, emphasizes the need for standardization and morphological transparency, and provides guidelines for designing high-performance devices via scalable fabrication methods.
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