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Despite great efforts have been made on epoxy resins modification, development of additives that can be used to efficiently and universally modify epoxy composites remains a challenging task. Herein, graphene oxide (GO) sheets were covalently linked with hyperbranched epoxy resin (HBPEE-epoxy) to form HBPEE-epoxy functionalized GO (HPE-GO), which was then incorporated into epoxy resin (EP) matrix to achieve efficient and all-purpose enhancement of the properties of EPs. Compared with unmodified GO sheets, the functionalized HPE-GO sheets were better dispersed and exhibited better interfacial compatibility with the epoxy matrix, and consequently, the mechanical and thermal properties of HPE-GO/EP composites improved significantly compared to unmodified GO/EP composites. The tensile strength, flexural strength, impact strength, and fracture toughness (K IC ) of EP composites containing 0.5 wt% HPE-GO increased by 65.0%, 36.2%, 259.1%, and 178.9%, respectively, compared with those for the neat EP. The storage modulus (E'), glass transition temperature (T g ), and thermal stability (T 5% ) also showed modest improvements. Furthermore, the HPE-GO/EP composites exhibited optimal thermal conductivities and thermal expansion properties, while maintaining higher volume resistivities compared with GO/EP composites. The results of this study support that HPE-GO is a promising, all-purpose modifier for EPs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

[Display omitted] • A phosphorus/nitrogen-containing hyperbranched epoxy resin (HPITT) was simply synthesized. • Both flame retardancy and toughness of epoxy thermosets were enhanced by HPITT. • EP/HPITT thermosets maintained excellent T g and T 5%. • HPITT was a prospective and versatile modifier for epoxy thermosets. Concurrently enhancing the flame retardancy and toughness without sacrificing strength, thermal decomposition temperature, and glass transition temperature (T g) of epoxy thermosets is still challenging. Herein, a new phosphorus/nitrogen-containing hyperbranched epoxy resin (HPITT) was synthesized from itaconic anhydride, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, piperazine, and triglycidyl isocyanurate by a facile method. The HPITT was then utilized for synergistic flame retarding and toughening modification of epoxy thermosets. Upon the introduction of 10 wt% HPITT, the epoxy thermosets reached a limiting oxygen index (LOI) of 31.5 % and UL-94 V-0 rating. Meanwhile, the peak heat release rate (PHRR) and total smoke production (TSP) decreased by 32.3 % and 27.7 % when compared to neat epoxy thermosets, respectively. Moreover, the synergistic flame retarding functions of phosphaphenanthrene, piperazine and isocyanurate segments in HPITT were demonstrated by combined gas and char phase residue analyses. Compared to neat epoxy, features such as the impact strength, tension strength, and flexural strength of the modified epoxy thermosets increased by respectively 53.9 %, 29.2 %, and 58 % owing to intramolecular cavities, rigid segments, and high crosslinking density supplied by HPITT. Moreover, the modified epoxy thermosets still maintained excellent T g and thermal decomposition temperature. In sum, an attractive strategy for concurrently enhancing flame retardancy and toughness of epoxy thermosets was proposed, useful for future advanced applications in adhesives, coatings, and composite materials. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) have been widely applied in luminescent sources due to their strong optical characteristics. However, a moisture environment causes their quenching, leading to an inferior optical performance in commercial applications. In this study, based on the high moisture resistance of epoxy resin, a novel epoxy/QDs composite particle structure was proposed to solve this issue. Flexible luminescent films could be obtained by packaging composite particles in silicone resin, combining the hydrophobicity of epoxy resin and the flexibility of PDMS simultaneously. The photoluminescence and light extraction were improved due to the scattering properties of the structure of composite particles, which was caused by the refractive index mismatch between the epoxy and silicone resin. Compared to the QD/silicone film under similar lighting conditions, the proposed flexible film demonstrated increased light efficiency as well as high moisture stability. The results revealed that a light-emitting diode (LED) device using the composite particle flexible (CPF) structure obtained a 34.2% performance enhancement in luminous efficiency as well as a 32% improvement in color conversion efficiency compared to those of devices with QD/silicone film (QSF) structure. Furthermore, the CPF structure exhibited strong thermal and moisture stability against extreme ambient conditions of 85 °C and 85% relative humidity simultaneously. The normalized luminous flux degradation of devices embedded in CPF and QSF structures after aging for 118 h were ~20.2% and ~43.8%, respectively. The satisfactory performance of the CPF structure in terms of optical and moisture stability shows its great potential value in flexible commercial QD-based LED displays and lighting applications. [ABSTRACT FROM AUTHOR]

Hyperbranched epoxy resins are efficient modifiers for epoxy resins but still require simultaneous improvements in terms of thermomechanical/mechanical properties and thermal stability. Herein, a novel resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was designed for all-purpose epoxy resin modification. To this end, hyperbranched polyether with terminal phenolic hydroxyl groups was first synthesized from commercially available 1,6-dibromohexane (A 2 -type monomer) and resveratrol (B'B 2 -type monomer). Surface modification with epichlorohydrin was afterward implemented to produce hyperbranched polyether with terminal epoxy groups (HBPEER). Next, various HBPEER-modified epoxy thermosets were prepared and characterized. The results suggested that compared to the neat diglycidyl ether of bisphenol A (DGEBA) thermoset, the 6 wt% HBPEER-modified epoxy thermoset showed an increase in impact strength, elongation at break, critical stress intensity factor (K IC), critical crack propagation energy release rate (G IC), flexural strength, tensile strength, storage modulus, glass transition temperature (T g), and initial thermal decomposition temperature (T d5%) by 69.6 %, 87.0 %, 32.0 %, 68.2 %, 29.3 %, 37.0 %, 8.1 %, 3.5 %, and 1.6 % respectively. Moreover, the dielectric constant and loss of 6 wt% HBPEER-modified epoxy thermoset decreased by 16.2 % and 16.5 %, respectively. Such comprehensive performance modifications were caused by the combined effects of crosslink density improvement, efficient intramolecular cavity, rigid stilbene units, and flexible aliphatic backbone of HBPEER. [Display omitted] • A resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was synthesized. • HBPEER was synthesized via A 2 + B'B 2 polycondensation strategy. • The toughness and strength of HBPEER-modified epoxy thermosets were significantly improved. • HBPEER is an efficient and all-purpose modifier for epoxy thermosets. [ABSTRACT FROM AUTHOR]