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Aiming at developing highly efficient nano fire retardants and fire retarding epoxy resins, a series of functionalized layered double hydroxides (LDHs) based on a multi-modifier system have been developed. These functionalized LDHs were used as novel nano flame-retardants for bisphenol epoxy resins and compared with unmodified LDHs.

Abstract:To develop functional sustainable epoxy resins, we report a novel epoxy resin (DEU-EP) with high net biobased content (70.2 wt%) derived from renewable eugenol. We comparatively study DEU-EP with a commercial bisphenol A epoxy resin (DGEBA) in the presence of a most representative aromatic diamine curing agent, 4,4'-diaminodiphenyl methane (DDM).Differential scanning calorimetry reveals that DEU-EP can be sufficiently cured by DDM at a slower rate than DGEBA. By applying an autocatalytic reaction model, we adequately simulate the curing rate of DEU-EP/DDM, and reveal its detailed kinetic mechanisms from model-free isoconversional analysis. Dynamic mechanical analysis shows that DEU-EP/DDM takes higher storage modulus up to ~97 o C than DGEBA/DDM with the glass temperature of 114 o C. Nanoindentation and thermogravimetric analysis demonstrate that compared with DGEBA/DDM, DEU-EP/DDM exhibits a 20%, 6.7% and 111% increase in Young's modulus, hardness and char yield, respectively. Microscale combustion calorimetry data show that DEU-EP/DDM expresses 55% and 38% lower heat release rate and total heat release than DGEBA/DDM, respectively.Macroscopically, the horizontal burning test approves DEU-EP/DDM can self-extinguish in a short time. Our results demonstrate that the eugenol building blocks and their arrangement greatly affect the cure behaviors of DEU-EP/DDM, and contribute significantly to its enhanced mechanical properties, high-temperature charring ability and chain motions at glass state, as well as the reduced flammability. To summarize, DEU-EP exhibits a high promise as a new sustainable epoxy monomer for fabricating high biobased content, high rigid and low flammable epoxy materials.

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 heat release (THR), and total smoke production (TSP) values of EP/m-LDH-6% were decreased by 62%, 19%, and 45%, respectively, compared to those of pure EP. In contrast, pristine LDH did not show so high an efficiency as m-LDH in terms of the reduced PHRR, THR, and TSP, and also the EP/LDH-6% composite exhibited no rating in the UL-94 vertical burning test. These findings supported that the flame retardant behavior increased with improved dispersion of nanofiller in the polymer matrix. The well-dispersed m-LDH nanofillers were beneficial to improving the quality of char residue, which effectively inhibited flammable volatiles escaping from the interiors and served as an effective thermal insulation layer to shield the underlying matrix from the exterior heat irradiation.

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 via nanocarriers.

Aiming to develop a multi-functional flame retardant for epoxy resins, a novel bio-based eugenol derivative (SIEPDP) was synthesized, and was 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.

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