Vertically Aligned Nickel 2‑Methylimidazole Metal–Organic Framework Fabricated from Graphene Oxides for Enhancing Fire Safety of Polystyrene

In this work, flowerlike nickel 2-methylimidazole metal–organic framework (Ni-MOF) was prepared by a solvothermal method. Vertically aligned Ni-MOF was fabricated from graphene oxide (GO) solution in the same way. The combination of GO and Ni-MOF (GOF) obviously suppressed the agglomeration of Ni-MOF sheets. As-synthesized, GOF has bigger pore volume and specific surface area, which are beneficial for volatile degradation products adsorption. It is noteworthy that the addition of GOF obviously reduced the fire hazard of polystyrene (PS). More than 33% decrease in the peak heat release rate for the PS/GOF composite was obtained when the content of the additives is only 1.0 wt %. Meanwhile, the reductions of total smoke and CO production were also prominent during the combustion of PS/GOF, respectively 21% and 52.3% decreases compared with that of pure PS. The synergism effects between layered GO and porous Ni-MOF realized the improved performances of PS. Thus, this work paves a feasible pathway to design efficient flame retardants for enhancing fire safety of polymers

Ultrathin Nanosheets of Organic-Modified β‑Ni(OH)₂ with Excellent Thermal Stability: Fabrication and Its Reinforcement Application in Polymers

β-Nickel hydroxide (β-Ni­(OH)₂), which combines two-dimensional (2D) structure and the catalytic property of nickel-containing compounds, has shown great potential for the application in polymer nanocomposites. However, conventional β-Ni­(OH)₂ exhibits large thickness, poor thermal stability, and irreversible aggregation in polymer matrices, which limits its application. Here, we use a novel phosphorus-containing organosilane to modify the β-Ni­(OH)₂ nanosheet, obtaining a new β-Ni­(OH)₂ ultrathin nanosheet with excellent thermal stability. When compared to pristine β-Ni­(OH)₂, the organic-modified β-Ni­(OH)₂ (M-Ni­(OH)₂) maintains nanosheet-like structure, and also presents a small thickness of around 4.6 nm and an increased maximum degradation temperature by 41 °C. Owing to surface organic-modification, the interfacial property of M-Ni­(OH)₂ nanosheets is enhanced, which results in the exfoliation and good distribution of the nanosheets in a PMMA matrix. The addition of M-Ni­(OH)₂ significantly improves the mechanical performance, thermal stability, and flame retardancy of PMMA/M-Ni­(OH)₂ nanocomposites, including increased storage modulus by 38.6%, onset thermal degradation temperature by 42 °C, half thermal degradation temperature by 65 °C, and decreased peak heat release rate (PHRR) by 25.3%. Moreover, it is found that M-Ni­(OH)₂ alone can catalyze the formation of carbon nanotubes (CNTs) during the PMMA/M-Ni­(OH)₂ nanocomposite combustion, which is a very helpful factor for the flame retardancy enhancement and has not been reported before. This work not only provides a new 2D ultrathin nanomaterial with good thermal stability for polymer nanocomposites, but also will trigger more scientific interest in the development and application of new types of 2D ultrathin nanomaterials

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

Layer-by-Layer Assembly of Hypophosphorous Acid-Modified Chitosan Based Coating for Flame-Retardant Polyester–Cotton Blends

Hypophosphorous acid-modified chitosan (PCS), as a novel phosphorus-containing chitosan derivative, was first successfully synthesized and characterized by Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. Subsequently, thin films of the ecofriendly PCS and branched polyethylenimine were deposited on polyester–cotton (PTCO) blends by the layer-by-layer assembly technique, in an effort to enhance their thermal properties and fire resistance properties. Thermogravimetric analysis, thermogravimetric analysis–Fourier transform infrared spectrometry, scanning electron microscopy, and horizontal flame test (HFT) were used to investigate the quality of the coatings as well as their fire resistance performance. The thermal and thermal oxidation stabilities at high temperature were enhanced for all coated PTCO blends. During the HFT, the afterglow phenomenon was eliminated for all coated blends, and self-extinguishing was achieved for the PCS2-20BL sample. It was found that the enhancement of the intumescent effect by the high phosphorus content in these coatings was conducive to achieving this superior performance

MoS₂ Nanolayers Grown on Carbon Nanotubes: An Advanced Reinforcement for Epoxy Composites

In the present study, carbon nanotubes (CNTs) wrapped with MoS₂ nanolayers (MoS₂–CNTs) were facilely synthesized to obtain advanced hybrids. The structure of the MoS₂–CNT hybrids was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy measurements. Subsequently, the MoS₂–CNT hybrids were incorporated into EP for reducing fire hazards. Compared with pristine CNTs, MoS₂–CNT hybrids showed good dispersion in EP matrix and no obvious aggregation of CNTs was observed. The obtained nanocomposites exhibited significant improvements in thermal properties, flame retardancy and mechanical properties, compared with those of neat EP and composites with a single CNT or MoS₂. With the incorporation of 2.0 wt % of MoS₂–CNT hybrids, the char residues and glass transition temperature (<i>T</i>_g) of the EP composite was significantly increased. Also, the addition of MoS₂–CNT hybrids awarded excellent fire resistance to the EP matrix, which was evidenced by the significantly reduced peak heat release rate and total heat release. Moreover, the amount of organic volatiles from EP decomposition was obviously decreased, and the formation of toxic CO was effectively suppressed, implying the toxicity of the volatiles was reduced and smoke production was obviously suppressed. The dramatically reduced fire hazards were generally ascribed to the synergistic effect of MoS₂ and CNTs, containing good dispersion of MoS₂–CNT hybrids, catalytic char function of MoS₂ nanolayers, and physical barrier effects of MoS₂ nanolayers and CNT network structure

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

Synthesis of a Novel Phosphorus- and Nitrogen-Containing Acrylate and Its Performance as an Intumescent Flame Retardant for Epoxy Acrylate

A novel acrylate monomer containing phosphorus and nitrogen<i> N</i>,<i>N</i>-bis­(2-hydroxyethyl acrylate) aminomethyl phosphonic acid diethylester (BHAAPE)was first synthesized by the combination of the Kabachnik–Fields reaction and esterification, and then incorporated into epoxy acrylate (EA) resins through an ultraviolet (UV) curing process. The structure of BHAAPE was confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The functionalized epoxy acrylate (FEA) resins exhibit significantly enhanced flame retardancy, which were evidenced by LOI, microscale combustion calorimetry (MCC) and cone calorimetry testing (CCT). Thermogravimetric analysis (TGA) results show that the introduction of BHAAPE promotes degradation of the EA matrix and catalyzes its char formation. The thermal degradation mechanism of FEA was further investigated by RTIR and direct pyrolysis/mass spectroscopy (DP-MS). The char structure of FEA, as characterized by scanning electron microscopy (SEM), reveals that the BHAAPE acts as a good intumescent fire retardant in the enhanced flame retardancy. Based on the analysis for thermal degradation and char structure, a detailed flame-retardant mechanism was proposed

Processable Dispersions of Graphitic Carbon Nitride Based Nanohybrids and Application in Polymer Nanocomposites

Graphitic carbon nitride (g-C₃N₄) nanosheets are endowed with extraordinary chemical and thermal stability and good optical and photoelectrochemical properties and are expected to be used in a wide range of fields. The direct dispersion of hydrophobic g-C₃N₄ nanosheets in water or organic solvents without the assistance of dispersing agents is considered to be a great challenge. Here we report novel g-C₃N₄/organic-modified montmorillonite (OMMT) nanohybrids, which were synthesized through electrostatic interaction and then introduced into polystyrene (PS) matrix to fabricate nanocomposites by a simple solvent blending–precipitation method. Hybridizing g-C₃N₄ with OMMT could easily form stable aqueous colloids through electrostatic stabilization. These nanohybrids were evenly dispersed in PS and showed strong interfacial interactions with the polymer matrix. It is noted that the generation of total gaseous products was dramatically inhibited by combining g-C₃N₄ with OMMT. Moreover, flame retardancy was improved upon incorporation of the nanohybrids into PS host. These improvements were due to the strong interactions at interface of ternary systems, synergism between g-C₃N₄ and OMMT, and physical barrier effect of the two components. This work provides a new pathway to manufacture well-dispersed polymeric materials with enhanced fire safety

A Novel Transparent Cross-Linked Poly(methyl methacrylate)-Based Copolymer with Enhanced Mechanical, Thermal, and Flame-Retardant Properties

A novel cross-linked poly­(methyl methacrylate) (PMMA)-based copolymer was first synthesized by bulk copolymerization of methyl methacrylate (MMA) and 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]­octane-4-acrylate (PEPAA) at low temperature (80 °C), which is a facile and green method. The structure of PEPAA was confirmed by FTIR, ¹H NMR, and ³¹P NMR. The morphology and structure of copolymers were characterized using FTIR and SEM. Due to the chain transfer during copolymerization, a cross-linked network is successfully introduced into the copolymers and the gel fraction increases as the PEPAA content increases, as evinced by the results from Soxhlet extraction and DMA. The copolymers exhibit relatively high transparency and significant improvements to the mechanical properties, thermal properties, and fire retardancy when compared to PMMA. From the mechanism analysis, the cross-linked network plays a key role in the improvements to the mechanical properties and thermal properties. For enhanced fire retardancy, char formation during degradation caused by PEPAA is the main factor

Influence of g‑C₃N₄ Nanosheets on Thermal Stability and Mechanical Properties of Biopolymer Electrolyte Nanocomposite Films: A Novel Investigation

A series of sodium alginate (SA) nanocomposite films with different loading levels of graphitic-like carbon nitride (g-C₃N₄) were fabricated via the casting technique. The structure and morphology of nanocomposite films were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis results suggested that thermal stability of all the nanocomposite films was enhanced significantly, including initial thermal degradation temperature increased by 29.1 °C and half thermal degradation temperature improved by 118.2 °C. Mechanical properties characterized by tensile testing and dynamic mechanical analysis measurements were also reinforced remarkably. With addition of 6.0 wt % g-C₃N₄, the tensile strength of SA nanocomposite films was dramatically enhanced by 103%, while the Young’s modulus remarkably increased from 60 to 3540 MPa. Moreover, the storage modulus significantly improved by 34.5% was observed at loadings as low as 2.0 wt %. These enhancements were further investigated by means of differential scanning calorimetry and real time Fourier transform infrared spectra. A new perspective of balance was proposed to explain the improvement of those properties for the first time. At lower than 1.0 wt % loading, most of the g-C₃N₄ nanosheets were discrete in the SA matrix, resulting in improved thermal stability and mechanical properties; above 1.0 wt % and below 6.0 wt % content, the aggregation was present in SA host coupled with insufficient hydrogen bondings limiting the barrier for heat and leading to the earlier degradation and poor dispersion; at 6.0 wt % addition, the favorable balance was established with enhanced thermal and mechanical performances. However, the balance point of 2.0 wt % from dynamic mechanical analysis was due to combination of temperature and agglomeration. The work may contribute to a potential research approach for other nanocomposites