Ehsan Naderi Kalali

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

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.

Multifunctional intercalation in layered double hydroxide: toward multifunctional nanohybrids 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 LDHs 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.

Synthesis and characterization of functional eugenol derivative based layered double hydroxide and its use as a nanoflame-retardant in epoxy resin

Aiming to develop a multi-functional flame retardant for epoxy resins, a novel bio-based eugenol derivative containing silicon and phosphorus [((1,1,3,3-tetramethyldisiloxane-1,3-diyl)bis(propane-3,1-diyl))bis(2-methoxy-4,1-phenylene)bis(phenylphosphonochloridate), SIEPDP] was synthesized, and was further used to modify Mg–Al layered double hydroxide (SIEPDP-LDH). This modified SIEPDP-LDH was used as a novel nanoflame-retardant for bisphenol epoxy resins and compared with unmodified pristine LDH. X-ray diffraction (XRD) analysis justified that intercalation of SIEPDP into LDH increased the interlayer distance to 2.95 nm. Morphological analysis (XRD and TEM) revealed that the SIEPDP-LDH was dispersed well in the epoxy matrix in a partially exfoliated manner. Results from the cone calorimeter tests showed that even a low loading of SIEPDP-LDH into epoxy resin led to a significant decrease in heat release rate and total heat release compared to unmodified LDH/epoxy composites. More interestingly, SIEPDP-LDH/epoxys UL-94 classification passed V-0 with only 8 wt% loading. Moreover, the addition of SIEPDP-LDH enabled the increase in the impact strength and modulus of the cured epoxy. These data indicated that SIEPDP-LDH could serve as not only a nanoflame retardant but a good reinforcing agent as well.

An in situ polymerization approach for functionalized MoS2/nylon-6 nanocomposites with enhanced mechanical properties and thermal stability

The enhancement in the thermal and mechanical properties of polymer/inorganic nanosheet composites depends strongly on their interfacial interaction. Herein, we exfoliated bulk MoS2 into nanosheets which was subsequently functionalized using lipoic acid. Nylon-6 (PA6) nanocomposites were prepared through in situ ring-opening polymerization of e-caprolactam initiated by lipoic acid functionalized MoS2 (f-MoS2). MoS2/PA6 composites were prepared by melt blending of pristine MoS2 powder with PA6 in parallel with f-MoS2/PA6 composites. The morphology of MoS2/PA6 and f-MoS2/PA6 composites observed using scanning electron microscopy and transmission electron microscopy demonstrated that f-MoS2 exhibited a better dispersion state than pristine MoS2 within a PA6 matrix. The incorporation of f-MoS2 induced significant thermal stabilization in the PA6 matrix: with 1 wt% loading of f-MoS2, the T−5% and T−50% of the resultant PA6 nanocomposite were increased by 36 and 23 °C, respectively, relative to those of neat PA6. As demonstrated by the increase in the storage modulus and the glass transition temperature determined from dynamic mechanical analysis, f-MoS2 was more effective than MoS2 in terms of reinforcing mechanical properties of PA6. At very low fractions of f-MoS2 nanosheets (≤1% by weight), PA6 nanocomposites exhibited up to 80% improvement in tensile properties compared to neat PA6 because of strong covalent polymer–filler interfacial interactions. These findings corresponded well with the nanoconfinement effect including a nanoscale interfacial layer that can support the superior reinforcements of f-MoS2 over pristine MoS2. The in situ polymerization approach proposed herein will open a new and exciting avenue for the development of transition metal dichalcogenide reinforced polymer nanocomposites.