Layered double hydroxides (LDHs) with their highly flexible and tunable chemical composition and physical properties have attracted tremendous attention in recent years. LDHs have found widespread application as catalysts, anion exchange materials, fire retardants, and nano-fillers in polymer nanocomposites. The ability to exfoliate LDHs into ultrathin nanosheets enables a range of new opportunities for multifunctional materials. In this review we summarize the current available LDH exfoliation methods. In particular, we highlight recent developments for the direct synthesis of single-layer LDH nanosheets, as well as the emerging applications of LDH nanosheets in catalyzing oxygen evolution reactions and preparing light emitting devices, supercapacitors, and flame retardant nanocomposites.

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Preparation of two dimensional layered double hydroxide nanosheets and their applications

Supercapacitors represent a major technology to store energy for many applications including electronics, automobiles, military, and space. Despite their high power density, the energy density in supercapacitors is presently inferior to that of the state-of-the-art Li-ion batteries owing to the limited electrochemical performance exhibited by the conventional electrode materials. The advent of two-dimensional (2D) nanomaterials has spurred enormous research interest as supercapacitor electrode materials due to their fascinating electrochemical and mechanical properties. This Review discusses cutting-edge research on some of the key 2D supercapacitor electrode materials including transition metal dichalcogenides, transition metal oxides and hydroxides, MXenes, and phosphorene. Various synthetic approaches, novel electrode designs, and microstructure tuning of these 2D materials for achieving high energy and power densities are discussed.

Recent Advances in Two-Dimensional Nanomaterials for Supercapacitor Electrode Applications

Fire retardancy of polymeric materials is a subject of major preoccupation due to the need to minimize fire risk and meet fire safety requirements. Numerous efficient conventional flame retardants based on halogen, mineral, and other compounds have been developed. However, some of these compounds, particularly halogen flame retardants, are harmful to our health and the environment, and their use has been restricted. In addition, the increasing concern about the reduction of the ecological footprint of materials, has encouraged the development of new plastics and additives made from renewable resources. As a result, renewed interest is emerging for the development of sustainable solutions for flame retardants for polymeric materials. This paper focuses on the identification of biomass compounds that have a potential as flame retardants for polymers due to their high availability and inherent properties. The last section of this paper explores the recent progress in flame retardant systems, based on the use of renewable products, which constitutes a promising approach to provide materials with improved fire resistance.

Bio-based flame retardants: When nature meets fire protection

Epoxy is a crucial engineered thermosetting polymer with wide industrial applications in adhesive, electronics, aerospace and marine systems In this review, basic knowledge of epoxy resins and the challenge for the preparation of epoxy nanocomposites are summarized The state-of-art multifunctional epoxy nanocomposites with magnetic, electrically conductive, thermally conductive, and flame retardant properties of the past few years are critically reviewed with detailed examples The applications of epoxy nanocomposites in aerospace, automotives, anti-corrosive coatings, and high voltage fields are briefly summarized This knowledge will have great impact on the field and will facilitate researchers in seeking new functions and applications of epoxy resins in the future

An overview of multifunctional epoxy nanocomposites

Flame retardant polymeric nanocomposites through the combination of nanomaterials and conventional flame retardants

Carbon-family materials for flame retardant polymeric materials

Functionalized layered double hydroxides (LDHs) based on a multi-modifier system composed of hydroxypropyl-sulfobutyl-beta-cyclodextrin sodium (sCD), dodecylbenzenesulfonate (DBS) and taurine (T) have been designed and fabricated in this paper, aiming at developing high performance fire retardant epoxy nanocomposites. In this multi-modifier system, sCD was utilized to improve the char yield, DBS was used to enlarge the inter-layer distance of LDH and T was used to enhance the interaction between the epoxy matrix and LDH layers. Based on these functionalized LDHs, bisphenol A epoxy resin and diamino diphenyl sulfone (DDS), a series of functionalized LDH/epoxy nanocomposites have been developed. The structural morphologies of the LDH/epoxy nanocomposites were investigated by transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS), revealing that sCD-DBS-T-LDH/EP shows a much better dispersion state than the epoxy composites containing unmodified LDHs or single modifier modified LDHs. Importantly, with only 6 wt% functionalized LDH, the sCD-DBS-T-LDH/EP nanocomposite reached V0 rating in the UL-94 vertical burning test. Furthermore, the incorporation of sCD-DBS-T-LDH into epoxy resins led to a significant reduction in peak heat release rate, total heat release and total smoke production, which exhibited superior fire resistance over its counterparts at the equivalent filler loading. The notably improved fire resistance could be attributed to the formation of the consolidated and compact char layers during combustion which significantly suppressed heat and mass transfer between the polymer matrix and flame zone. Additionally, sCD-DBS-T-LDH/EP showed the best impact and tensile strength compared to those of other LDH/epoxy composites. This work offers a new approach to develop high performance fire retardant polymer/LDH nanocomposites.

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Functionalized layered double hydroxide-based epoxy nanocomposites with improved flame retardancy and mechanical properties

A sustainable, eugenol-derived epoxy resin with high biobased content, modulus, hardness and low flammability: Synthesis, curing kinetics and structure–property relationship

A biobased modifier (cardanol-BS) was successfully synthesized from renewable resource cardanol via the ring-opening of 1, 4-butane sultone (BS). Cardanol-BS modified layered double hydroxide (m-LDH) was developed through a one-step coprecipitation method and subsequently incorporated into epoxy resins (EPs) with different loadings using a combined technique of three-roll mill and ultrasonication. As a comparison, a pristine LDH/EP composite was also prepared using the same procedure. The XRD result indicated that the interlayer spacing of m-LDH was about 5-fold enlarged compared with that of pristine LDH. As a result, the enlarged interlayer spacing of m-LDH facilitated the homogeneous dispersion of the nanoadditive in the epoxy matrix, as evidenced by TEM and XRD results. The flame retardant properties were improved with the increase of the m-LDH loading. With only 6 wt % m-LDH, the EP composite reached a limiting oxygen index (LOI) of 29.2% and UL-94 V0 rating. The peak heat release rate (PHRR), total ...

Renewable Cardanol-Based Surfactant Modified Layered Double Hydroxide as a Flame Retardant for Epoxy Resin

Multifunctional intercalation in layered double hydroxide (LDH) has been developed via designed multi-modifiers with varied functions in order to transfer these functions to epoxy materials by using nanocarriers. The functions of the multi-modifier system include: (i) functionalized hydroxypropyl-sulfobutyl-beta-cyclodextrin (sCD) and phytic acid (Ph) aiming at enhancing flame retardancy; (ii) sodium dodecylbenzenesulfonate (SDBS) enlarges the interlayer space of LDHs for facilitating LDH's dispersion in the epoxy matrix; (iii) chalcone imparts the anti-UV property to the epoxy matrix. In contrast to conventional LDH-based epoxy composites, the functionalized LDH-(fLDH) based epoxy nanocomposites show a significant improvement in both flame retardancy, such as passing the UL94 V0 rating and reduction of the peak heat release rate over 70%, and anti-UV properties in terms of well maintenance on the impact, flexural and micro-mechanical properties after 100, 200, 300, and 400 h of UV irradiation, respectively. Such multifunctional nanohybrids may be used to develop varied functional and sustainable epoxy-based materials for some advanced applications.

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Ehsan Naderi Kalali

Papers

Carbon-family materials for flame retardant polymeric materials

Functionalized layered double hydroxide-based epoxy nanocomposites with improved flame retardancy and mechanical properties

A sustainable, eugenol-derived epoxy resin with high biobased content, modulus, hardness and low flammability: Synthesis, curing kinetics and structure–property relationship

Renewable Cardanol-Based Surfactant Modified Layered Double Hydroxide as a Flame Retardant for Epoxy Resin

Multifunctional intercalation in layered double hydroxide: toward multifunctional nanohybrids for epoxy resin