Recyclable and elastic highly thermally conductive epoxy-based composites with covalent-noncovalent interpenetrating networks.

High-power electronic architectures and devices require elastic thermally conductive materials. The use of epoxy resin in thermal management is limited due to its rigidity. Here, based on epoxy vitrimer, flexible polyethylene glycol (PEG) chains are introduced into covalent adaptable networks to construct covalent-noncovalent interpenetrating networks, enabling the elasticity of epoxy resins. Compared to traditional silicone-based thermal interface materials, the newly developed elastic epoxy resin shows the advantages of reprocessability, self-healing, and no small molecule release. Results show that, even after being filled with boron nitride and liquid metal, the material maintains its resilience, reprocessability and self-healing properties. Leveraging these characteristics, the composite can be further processed into thin films through a repeated pressing-rolling technique that facilitates the forced orientation of the fillers. Subsequently, the bulk composites are reconstructed using a film-stacking method. The results indicate that the thermal conductivity of the reconstructed bulk composite reaches 3.66 W m-1 K-1, achieving a 68% increase compared to the composite prepared through blending. Due to the existence of covalent adaptable networks, the inorganic and inorganic components of the composite prepared in this work can be completely separated under mild conditions, realizing closed-loop recycling.

Carbon emissions in China's urban agglomerations: spatio-temporal patterns, regional inequalities, and driving forces.

Urban agglomerations are the centers of carbon emissions. However, research on sector-specific carbon emissions in different urban agglomerations is still limited. Drawing on the data of China's six urban agglomerations in 2005, 2010, and 2015, this study investigates the spatio-temporal patterns, regional inequalities, and driving forces of total, industrial, transportation, and residential carbon emissions. The study found that Beijing-Tianjin-Hebei was the total and sectoral emission center among the studied urban agglomerations. Additionally, regional carbon inequalities gradually decreased, implying a growing regional synergistic carbon pattern. The driving forces of carbon emissions, including population, GDP, energy intensity, secondary industry, tertiary industry, foreign investment, urbanization, and green coverage, varied across sectors and regions. Notably, foreign investment could lead to lower carbon emissions in less developed agglomerations like Beijing-Tianjin-Hebei, the Central Plains, and the middle reaches of the Yangtze River, whereas more developed agglomerations like the Yangtze River Delta and the Pearl River Delta benefited less from foreign investment. Besides, ChengYu has good ecological conditions and sustainable development modes, which linked urbanization and green space to reduced carbon emissions in the industrial sector. The findings can help formulate differentiated carbon policy and support sustainable development.

In Situ-Generated Heat-Resistant Hydrogen-Bonded Organic Framework for Remarkably Improving Both Flame Retardancy and Mechanical Properties of Epoxy Composites.

In this study, the heat-resistant hydrogen-bonded organic framework (HOF) material HOF-FJU-1 was synthesized via in situ generation and then used as flame retardants (FRs) to improve the flame retardancy of epoxy resin (EP). HOF-FJU-1 can maintain high crystallinity at 450 °C and thus function as a flame retardant in EP. The study found that HOF-FJU-1 facilitates the improvement of char formation in EP, thus inhibiting heat transfer and smoke release during combustion. For EP/HOF-FJU-1 composites, the in situ-generated HOF-FJU-1 can remarkably improve both the mechanical properties and the flame retardancy of EP. Furthermore, the in situ-generated HOF-FJU-1 has better fire safety than the ex situ-generated HOF-FJU-1 at the same filling content. Thermal degradation products and flame retardation mechanisms in the gas and condensed phases were further investigated. This work demonstrates that the in situ-generated HOF-FJU-1 is promising to be an excellent flame-retardant candidate.

Exploration of the Fire-Retardant Potential of Microencapsulated Ammonium Polyphosphate in Epoxy Vitrimer Containing Dynamic Disulfide Bonds.

Epoxy vitrimers appear as a promising alternative to common epoxy thermoset composites. Nevertheless, the possibilities of applying these materials are limited due to their high flammability which may cause high fire risks. To date, the flame-retardant epoxy vitrimer systems reported in the literature almost all rely on intrinsic flame retardancy to achieve high fire safety; however, the complex and expensive synthesis process hinders their large-scale application. In this work, disulfide-based epoxy vitrimer (EPV) was fabricated with 4, 4'-dithiodianiline as the curing agent, and microencapsulated ammonium polyphosphate (MFAPP) was employed as a potential additive flame retardant to improve their fire retardancy. As a comparative study, common epoxy (EP) composites were also prepared using 4,4'-diaminodiphenylmethane as the curing agent. The results showed that the introduction of dynamic disulfide bonds led to a reduction in the initial thermal decomposition temperature of EPV by around 70 °C compared to EP. Moreover, the addition of 7.5 wt.% of MFAPP endowed EP with excellent fire performance: the LOI value was as high as 29.9% and the V-0 rating was achieved in the UL-94 test (3.2 mm). However, under the same loading, although EPV/MFAPP7.5% showed obvious anti-dripping performance, it did not reach any rating in the UL-94 test. The flame-retardant mechanisms in the condensed phase were evaluated using SEM-EDS, XPS, and Raman spectroscopy. The results showed that the residue of EPV/MFAPP7.5% presented numerous holes during burning, which failed to form a continuous and dense char layer as a physical barrier resulting in relatively poor flame retardancy compared to EP/MFAPP7.5%.

In Situ Growth of Ca2+-Based Metal-Organic Framework on CaSiO3/ABS/TPU 3D Skeleton for Methylene Blue Removal.

The work reports a novel strategy for combining polymers and metal-organic frameworks (MOFs) into composites for adsorption applications. Calcium silicate (CaSiO3) was introduced into acrylonitrile butadiene styrene/thermoplastic polyurethane (ABS/TPU) alloy, and the CaSiO3/ABS/TPU skeleton was fabricated by 3D printing technology. The Ca-MOF was directly loaded on the surface of acetone-etched 3D skeleton by in-situ growth method. The obtained 3D skeleton was characterized and the performance of methylene blue (MB) adsorption was determined. It is clear that Ca-MOF is successfully loaded on the surface of 3D skeleton due to the presence of CaSiO3. The MB adsorption ratios of the solutions with initial concentrations of 50, 100 and 200 mg/L at the equilibrium time (5 h) are 88%, 88% and 80%, respectively, revealing good MB adsorption performance of the 3D skeleton. The MB adsorption ratio remains 70% at six runs of adsorption-desorption experiment, indicating the excellent recovering property of the skeleton. The results show that the prepared CaSiO3/ABS/TPU 3D skeleton is a candidate adsorbent for printing and dyeing effluent treatment.

Preparation of Layered Polyethylene Oxide/rGO Composite: Flexible Lateral Heat Spreaders.

In this paper, high thermal conductive polyethylene oxide (PEO)/reduced graphene oxide (rGO) composite is prepared via large-scale green reduction. Flexible layered PEO/GO composites are pre-prepared in aqueous solution. It is demonstrated that PEO chains can form hydrogen bonds with GO. Being driven by hydrogen bonds, GO/PEO composites show homogeneous and lateral highly oriented structures, resulting in excellent mechanical properties. The pre-prepared composite films are large scale soaked into ascorbic acid solution. GO nanosheets in the matrix of the composites can be reduced by ascorbic acid. The results indicate that PEO chains can repair the damage of the films caused by the reduction process. Therefore, the films can maintain their original configuration and still keep excellent flexibility. By comparison, pristine GO films are totally destroyed when the same reduction is experienced. Due to the presence of PEO, the lateral highly oriented structure of the composite will not be damaged. After reduction, the thermal conductivity of the composite reaches to 12.03 W m-1 K-1 along the rGO nanosheet oriented direction.

Simultaneously enhanced mechanical properties and flame retardancy of UHMWPE with polydopamine-coated expandable graphite.

The potential prospect of expandable graphite (EG) in the development of polymer composites is severely limited by required large additions and poor interface compatibility with the polymer. Inspired by mussels, polydopamine (PDA) can be used as an effective interface modifier for EG to prepare ultra high molecular weight polyethylene (UHMWPE) composites with superior mechanical properties and high flame retardancy. The surface of expandable graphite (EG) was coated with a thin adhesive PDA film through self-polymerization of dopamine. The modified expandable graphite (EG@PDA) was combined with APP to prepare UHMWPE flame retardant composites. Compared with UHMWPE/APP/EG (with 20 wt% APP/EG), UHMWPE/APP/EG@PDA (with 20 wt% APP/EG@PDA) gives a decrement by 16.7% in limiting oxygen index, 29.7% in the peak of the heat release rate, 20.4% in total heat release and 49.3% in total smoke release, with an increment by 37% in tensile strength and 67.9% in elongation at break, respectively. It is suggested that the presence of PDA as an interface modifier can greatly improve the interfacial compatibility between EG and UHMWPE. Moreover, it can lead to forming more char residue and reducing the release of smoke particulates during combustion of the composites.

Largely enhanced thermal conductivity and thermal stability of ultra high molecular weight polyethylene composites via BN/CNT synergy.

In recent years, thermally conductive polymer-based composites have garnered significant attention due to their light weight and easy formation process. In this work, the thermal conductivity of ultra high molecular weight polyethylene (UPE) composites was improved through construction of a hybrid filler network of boron nitride sheets (BNs) and carbon nanotubes (CNTs) in the matrix via hot compression. The morphology, UPE aggregate structure, thermal conductivity, heat dissipation capacity and thermal stability of the UPE composites were investigated. The thermal conduction mechanism of the UPE composites was explored through simulations with Agari's semi-empirical formula. The results showed that the thermal conductivity of the UPE composite with 40 wt% BNs and 7 wt% CNTs was 2.38 W m-1 K-1, which was 495% higher than that of pure UPE, showing a synergistic effect between BNs and CNTs. The simulations with Agari's semi-empirical simulation suggested that increasing the CNT content contributed to synergistically assist BNs to form a better continuous and effective hybrid filler thermal network, thereby reducing phonon scattering and thermal resistance between BNs. In addition, UPE composites doped with BNs and CNTs presented better heat dissipation capacity and higher thermal stability as compared to that of pure UPE.