Preparation of Metal–Organic Frameworks and Their Application as Flame Retardants for Polystyrene

In this work, iron-based and cobalt-based metal–organic frameworks (MOFs) were successfully synthesized by a facile solvothermal method. The obtained MOFs were added into polystyrene (PS) as flame retardants for the first time. The results of thermal gravimetric analysis and cone calorimetry indicated the addition of MOFs significantly enhanced the thermostability and flame retardancy of the PS composites. Compared with that of neat PS, greater than 14% and 28% decreases in the peak heat release rate were observed for PS/Fe-MOF and PS/Co-MOF, respectively, suggesting a flame retardant effect of MOFs. Based on thermogravimetric analysis–​infrared spectrometry results and the analysis of combustion residues, the possible mechanism of the enhanced thermostability and flame retardancy of the PS composites was proposed as the combination of thermal barrier effect and catalytic effect of MOFs, which would allow promising application in the development of fire safety polymer materials

Surface Modification of Hetero-phase Nanoparticles for Low-Cost Solution-Processable High‑k Dielectric Polymer Nanocomposites

The surface modification of nanoparticles (NPs) is crucial for fabricating polymer nanocomposites (NCs) with high dielectric permittivity. Here, we systematically studied the effect of surface functionalization of TiO2 and BaTiO3 NPs to enhance the dielectric permittivity of polyvinylidene fluoride (PVDF) NCs by 23 and 74%, respectively, measured at a frequency of 1 kHz. To further increase the dielectric permittivity of PVDF/NPs-based NCs, we developed a new hetero-phase filler-based approach that is cost-effective and easy to implement. At a 1:3 mixing ratio of TiO2:BaTiO3 NPs, the dielectric constant of the ensuing NC is found to be 50.2, which is comparable with the functionalized BaTiO3-based NC. The highest dielectric constant value of 76.1 measured at 1 kHz was achieved using the (3-aminopropyl)­triethoxysilane (APTES)-modified hetero-phase-based PVDF composite at a volume concentration of 5%. This work is an important step toward inexpensive and easy-to-process high-k nanocomposite dielectrics

DOPO-Modified Two-Dimensional Co-Based Metal–Organic Framework: Preparation and Application for Enhancing Fire Safety of Poly(lactic acid)

Co-based metal–organic framework (Co-MOF) nanosheets were successfully synthesized by the organic ligands with Schiff base structure. The laminated structure gives Co-MOF nanosheets a great advantage in the application in the flame retardant field. Meanwhile, −CN– from Schiff base potentially provides active sites for further modification. In this work, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was used to modify Co-MOF (DOPO@Co-MOF) to further enhance its flame retardant efficiency. It is attractive that DOPO has a synergistic effect with Co-MOF on improving fire safety of poly­(lactic acid) (PLA). The obvious decrease in the values of peak heat release (27%), peak smoke production (56%), and total CO yield (20%) confirmed the enhanced fire safety of PLA composites. The possible flame retardant mechanism was proposed based on characterization results. Moreover, the addition of DOPO@Co-MOF had a positive influence on the mechanical performance, including tensile properties and impact resistance. This work designed and synthesized two-dimensional MOFs with active groups. As-prepared Co-MOF with expected structure shows a novel direction of preparing MOFs for flame retardant application

Construction of Bimetallic ZIF-Derived Co–Ni LDHs on the Surfaces of GO or CNTs with a Recyclable Method: Toward Reduced Toxicity of Gaseous Thermal Decomposition Products of Unsaturated Polyester Resin

This work proposed an idea of recycling in preparing Co–Ni layered double hydroxide (LDH)-derived flame retardants. A novel and feasible method was developed to synthesize CO–Ni LDH-decorated graphene oxide (GO) and carbon nanotubes (CNTs), by sacrificing bimetal zeolitic imidazolate frameworks (ZIFs). Organic ligands that departed from ZIFs were recyclable and can be reused to synthesize ZIFs. ZIFs, as transitional objects, in situ synthesized on the surfaces of GO or CNTs directly suppressed the re-stacking of the carbides and facilitated the preparation of GO@LDHs and CNTs@LDHs. As-prepared hybrids catalytically reduced toxic CO yield during the thermal decomposition of unsaturated polyester resin (UPR). What is more, the release behaviors of aromatic compounds were also suppressed during the pyrolysis process of UPR composites. The addition of GO@LDHs and CNTs@LDHs obviously inhibited the heat release and smoke emission behaviors of the UPR matrix during combustion. Mechanical properties of the UPR matrix also improved by inclusion of the carbides derivatives. This work paved a feasible method to prepare well-dispersed carbides@Co–Ni LDH nanocomposites with a more environmentally friendly method

Magnetic Fe₃O₄ Nanoparticle/ZIF‑8 Composites for Contaminant Removal from Water and Enhanced Flame Retardancy of Flexible Polyurethane Foams

In order to separate heavy-metal ions from contaminated wastewater and further realize the reutilization of waste adsorbent, magnetic composites with flowerlike structure were successfully synthesized. After the absorption of Cu2+ ions, hybrids can be used as effective coatings to enhance the fire safety of flexible polyurethane foam (FPUF) through a dip-coating method. As-fabricated metal–organic framework (MOF)-based composites exhibited a core–shell and flowerlike structure with high thermal stability. The maximum adsorption capacity for Cu2+ could reach 292.13 mg·g–1, calculated from the Langmuir isotherm model. In order to reutilize the adsorbed Cu2+ ions, the CuO-loaded MOF-derived Fe3O4@ZnO@CuO (MO) was obtained with a simple heat treatment. The effectivity of MO as a fire-safety coating for inhibiting the release of heat and toxic gases of FPUF was satisfactory. The application of this MOF-based composite will provide useful insights into the design of bifunctional materials for efficient wastewater remediation and fire-safety coatings

Hierarchical Structure: An effective Strategy to Enhance the Mechanical Performance and Fire Safety of Unsaturated Polyester Resin

It is still a big challenge to prepare polymer/layered double hydroxide (LDH) composites with high performance, due to the strong agglomeration tendency of LDHs in the polymeric matrix. In this study, to avoid the agglomerated situation, the orientated LDH nanosheets were vertically grown on a ramie fabric surface, which was then embedded in unsaturated polyester resin (UPR) through the combination method of hand lay-up and vacuum bag. Due to the increased contact area and the restricted interfacial slip in the in-plane direction, the hierarchically LDH-functionalized ramie fabrics (denoted as Textile@LDH) significantly enhanced the mechanical performance of UPR composites. Then, the phosphorus- and silicon-containing coating (PSi) was used for the further improvement of the interfacial adhesion. The tensile strength of UPR/Textile@LDH@PSi composites increased by 121.67%, compared to that of neat UPR. The reinforcement mechanism was studied through analyzing the surface nano/microstructure and wetting properties of the raw and modified textiles, as well as the interfacial interaction between the ramie fabrics and UPR. Meanwhile, the thermal stability, thermal conductivity, and flame-retardant performance of ramie-reinforced UPR composites were improved. Particularly, as-prepared hierarchical Textile@LDH@PSi inhibited the heat release during the combustion process of fabric-reinforced UPR composites, and the peak heat release rate and total heat release values decreased by 36.56 and 47.57%, respectively, compared with the neat UPR/Textile composites. The suppression mechanism was further explored by analyzing the microstructure and chemical compositions of char residues. This research paved a feasible solution to improve the poor dispersion of LDHs in polymers and prepared the high-performance UPR composites with multifunctional applications

Novel Flame-Actuated Soft Actuator Based on a Multilayer Liquid Crystal Elastomer/Hydrogel Composite

A novel flame-actuated soft actuator based on a multilayer liquid crystal elastomer/hydrogel composite was fabricated in this work. Flame is a preferable external stimulus over light, heat, and electricity in terms of its abundant accessibility in a fire scenario. Nevertheless, employing flame as the external stimulus introduces novel challenges for soft actuator materials as they must possess incombustible properties. Here, hydrogel layers are grafted on both surfaces of the liquid crystal elastomer (LCE), resulting in the fabrication of a trilayered LCE-hydrogel composite. The LCE-hydrogel composite demonstrates remarkable flame retardancy, shape memory performance, and tailorable surface adhesion. The hydrogel’s remarkable water absorption and heat insulation properties confer excellent flame retardancy to the composite, preventing ignition for at least 10 s during the open flame test. The shape memory performance is attributed to the orientation of the internal LCE layer and the flexibility of the external hydrogel layers. The surface adhesion of the hydrogel layers is tailored by adjusting their water content. As the water content decreases from 100 to 60%, the surface adhesion energy increases from 6.2 to 70.3 J/m2. A flame-actuated, clip-like soft robot capable of cyclically grasping and releasing objects was constructed, showcasing its promising application potential. This work presents an unprecedented flame-actuated LCE-based composite for the first time, which offers a fresh perspective for researchers to investigate alternative actuation approaches in the field of soft robotics

Investigation of the mechanical properties of polyimide fiber/polyamide 12 composites printed by Multi Jet Fusion

Multi Jet Fusion (MJF) has attracted extensive attention because of its ability to print support-free complex structures. However, the mechanical properties of MJF-printed polymer parts are still unsatisfactory for certain industrial requirements. Herein, by leveraging the fibre reinforcement effect and high specific strength of polyimide (PI) fibres, this work developed PI/polyamide 12 (PA12) composites with largely enhanced mechanical performance via MJF. Specifically, the tensile strength and modulus were increased by 43% and 42%, and the flexural strength and modulus were improved by 39% and 46%, respectively, compared to those of the neat PA12 parts. Furthermore, the incorporation of lightweight PI fibres endowed the composites with high specific tensile strength (67.60 kN·m/kg) and specific flexural strength (93.70 kN·m/kg), which are superior to those of MJF-printed PA12 composites reinforced with other fibres. This work provides new insights into enhancing the mechanical performance of lightweight parts printed by MJF and other powder-based techniques.</p