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

Conceptually Novel Few-Layer Black Phosphorus/Supramolecular Coalition: Noncovalent Functionalization Toward Fire Safety Enhancement

Black phosphorus (BP) has been widely concerned in the field of composite materials because of its special geometrical and physicochemical properties. As a red phosphorus allotrope, BP has the dual function of physical barrier and catalytic carbonization and has the potential to be a highly effective flame retardant. In this article, the aminated BP/melamine cyanurate (BP–NH–MCA) coalition with a sandwich structure was prepared by an in situ self-assembly of MCA supramolecules on the surface of aminated BP. TEM, SEM, and the surface distribution scan results showed that the hybrid nanosheets were successfully fabricated and uniformly distributed in the matrix. The analysis of the data of cone calorimetry showed that with the loading of BP–NH–MCA increasing from 0.5 to 2.0 wt %, the peak value of heat release rate of composites decreases by 21.9–47.2%, and the total heat release value decreases by 26.7–42.3%. In addition, the EP/BP–NH–MCA2.0 nanocomposite has the lowest emission intensity of typical volatile products, including toxic CO during combustion, compared to EP/BP2.0 and pure EP samples, significantly improving the fire safety of composites. This work provides a reference for the application of BP in flame-retardant fields and reveals the flame-retardant mechanism of its hybrid materials

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

Nanolayered Graphene/Black Phosphorus Films for Fire-Retardant Coatings

As one of typical bottom-up self-assembly natural materials, the abalone nacre with a special layered “brick-and-mortar” structure exhibited unique physical and chemical properties. Inspired by this structure, we developed a biomimetic material by combining linear polyvinyl alcohol (PVA) with hydroxyl-functionalized black phosphorus (BP-OH) nanosheets and graphene oxide (GO) nanosheets in an evaporation-induced self-assembly method. Owing to the strong interfacial hydrogen bond between linear PVA and two-dimensional BP-OH-GO, the PVA/BP-OH-GO 25 composite film exhibited outstanding mechanical properties, with tensile fracture strain up to 86.6% and tensile strength up to 74.3 MPa (1.63 and 2.14 times that of pure PVA, respectively). In addition, the toughness of the PVA/BP-OH-GO 25 film reached 2–3 times that of pure PVA, achieving the purpose of increasing strength and toughness simultaneously. In addition, the composite film also achieved admirable fire resistance, thermal stability, smoke suppression, and toxicity reduction performance. Therefore, a type of bionic PVA/BP/GO film was designed and prepared, which provided a direction for designing synthetic biomimetic composite materials with high fire safety and mechanical properties

Studies on Synthesis of Electrochemically Exfoliated Functionalized Graphene and Polylactic Acid/Ferric Phytate Functionalized Graphene Nanocomposites as New Fire Hazard Suppression Materials

Practical application of functionalized graphene in polymeric nanocomposites is hampered by the lack of cost-effective and eco-friendly methods for its production. Here, we reported a facile and green electrochemical approach for preparing ferric phytate functionalized graphene (f-GNS) by simultaneously utilizing biobased phytic acid as electrolyte and modifier for the first time. Due to the presence of phytic acid, electrochemical exfoliation leads to low oxidized graphene sheets (a C/O ratio of 14.8) that are tens of micrometers large. Successful functionalization of graphene was confirmed by the appearance of phosphorus and iron peaks in the X-ray photoelectron spectrum. Further, high-performance polylactic acid/f-GNS nanocomposites are readily fabricated by a convenient masterbatch strategy. Notably, inclusion of well-dispersed f-GNS resulted in dramatic suppression on fire hazards of polylactic acid in terms of reduced peak heat-release rate (decreased by 40%), low CO yield, and formation of a high graphitized protective char layer. Moreover, obviously improvements in crystallization rate and thermal conductivities of polylactic acid nanocomposites were observed, highlighting its promising potential in practical application. This novel strategy toward the simultaneous exfoliation and functionalization for graphene demonstrates a simple yet very effective approach for fabricating graphene-based flame retardants

A 3D Nanostructure Based on Transition-Metal Phosphide Decorated Heteroatom-Doped Mesoporous Nanospheres Interconnected with Graphene: Synthesis and Applications

A novel three-dimensional nanostructure based on cobalt phosphide nanoparticles (Co2P NPs) and heteroatom-doped mesoporous carbon spheres interconnected with graphene (3D PZM@Co2P@RGO) was facilely synthesized for the first time, and it was used for enhancing the flame retardancy and toxicity suppression of epoxy resins (EP) via a synergistic effect. Herein, the cross-linked polyphosphazene hollow spheres (PZM) were used as templates for the fabrication of 3D architecture. The 3D architecture based on Co2P-decorated heteroatom-doped carbon sphere and reduced graphene oxide was prepared via a carbonization procedure followed by a hydrothermal self-assembly strategy. The as-prepared material exhibits excellent catalytic activity with regard to the combustion process. Notably, inclusion of incorporating PZM@Co2P@RGO resulted in a dramatic reduction of the fire hazards of EP, such as a 47.9% maximum decrease in peak heat release rate and a 29.2% maximum decrease in total heat release, lower toxic CO yield, and formation of high-graphitized protective char layer. In addition, the mechanism for flame retardancy and toxicity suppression was proposed. It is reasonable to know that the improved flame-retardant performance for EP nanocomposites is attributed to tripartite cooperative effect from respective components (Co2P NPs and RGO) plus the heteroatom-doped carbon spheres

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

Phosphorus/Nitrogen-Codoped Molybdenum Disulfide/Cobalt Borate Nanostructures for Flame-Retardant and Tribological Applications

Polymers used in almost any situation face the threat of sudden fire, and application scenarios with high requirements on friction performances of polymers are no exception. Herein, P- and N-codoped molybdenum disulfide (PNMoS2) nanosheets were fabricated via the original process of ball milling, followed by annealing, which subsequently served as the template to grow the two-dimensional (2D) cobalt borate (Co–Bi) ultrathin nanosheets for the generation of PNMoS2@Co–Bi dual sheets. With the introduction of 2 wt % PNMoS2@Co–Bi dual nanosheets into epoxy resin (EP), defined as EP/PNMoS2@Co-Bi, an obvious reduced peak heat release rate of 28.0% and a total heat release of 27.9%, respectively, were obtained. It is noted that the total smoke release, which is vital for evacuation and life safety, has been reduced by 41.8%. In addition, EP/PNMoS2@Co–Bi achieved a significantly improved LOI, UL-94, and thermal performance, along with the high char yield (22.9 wt %) and remarkably decreased mass loss rate. Interestingly, the loading of 2 wt % PNMoS2 has the lowest friction coefficient value (decrease by 18.7%) and volume wear rate (46.1% reduction than pure EP), which is attributed to the PNMoS2 nanosheets that can generate the uniform lubricating transfer layer. The outstanding properties of EP nanocomposites are attributed to the coupled effects between PNMoS2 and Co–Bi ultrathin sheets with an enhanced interface interaction in the EP matrix. This study manifests the extensive application of well-designed PNMoS2@Co–Bi nanohybrids in the fire safety and wear resistance of polymers

Effect of Functionalized Graphene Oxide with Organophosphorus Oligomer on the Thermal and Mechanical Properties and Fire Safety of Polystyrene

A novel organophosphorus oligomer was synthesized to functionalize graphene oxide. Subsequently, the functionalized graphene oxide (FGO) was incorporated into polystyrene (PS) to enhance the integration properties of the matrix. The effect of FGO on the thermal properties, fire safety, and mechanical properties of PS nanocomposites was investigated. The results showed that the introduction of FGO significantly increased the maximum decomposition temperature (<i>T</i>_max) (25 °C increase), reduced the total heat release (20.8% reduction), and peak heat release rate (38.2% reduction) of PS. In addition, the thermogravimetric analysis/infrared spectrometry analysis results indicated that the amount of organic volatiles and toxic carbon monoxide of PS was remarkably reduced. The physical barrier effect of FGO and the synergistic effects between the organophosphorus oligomer and FGO were the main causations for these properties improvements. Homogeneous dispersion of FGO into the polymer matrix improved the mechanical properties of FGO/PS nanocomposites, as demonstrated by tensile tests results