NEWEPOXY · New Generation High-performance Fire Retardant Epoxy Nanocomposites: Structure-Property Relationship

New Generation High-performance Fire Retardant Epoxy Nanocomposites: Structure-Property Relationship

Epoxy resins have many attractive properties, and find a myriad of important applications in coating, adhesives, electrical insulting and electronic encapsulating materials, structural composites and so on. The most important and wildly used epoxy resins are made out of epichlorohydrin and bisphenol A, namely bisphenol A based epoxy resins; however, they are intrinsically lack of flame retardancy. To this end, the NEPOXY project aims to develop a new generation of high-performance epoxy nanocomposites with good flame retardancy while retaining and further improving other desired properties to meet some important and demanding applications as insulation and encapsulation materials for electronics and light-weight composites for aircrafts. The ultimate goals of the NEWEPOXY project are to seek the new opportunities to develop halogen-free high-performance epoxy materials and epoxy nanocomposites loaded with a functional filler. To achieve NEWEPOXY’s goal, two approaches were proposed: (1) Synthesizing new and sustainable epoxy monomers with improved flame retardancy and other properties; (2) Developing a sustainable, scalable approach to preparing multifunctional graphene oxide (GO) and/or layered double hydroxide (LDH) hybrids suitable for modification of standard bisphenol A epoxy resins. Accordingly, two aspects of the relevant work were conducted under support of NEWEPOXY. (1) We designed and synthesized a number of new epoxy monomers allowing for the influence of the molecular structure on the flammability, thermal, mechanical and other properties of the cured resultant epoxy materials. Traditionally, the cured epoxy and other thermosetting polymeric materials are hard to recycle after use, so that we attempted to use a renewable biobased feedstock as the starting material to synthesize new sustainable epoxy monomers to achieve the improved flame retardancy and other properties. A number of new biobased epoxy monomers bearing two or three curable epoxy groups have been developed. We have systematically characterized these monomers using Fourier Transform Infrared Spectroscopy (FTIR), nuclear magnetic resonance (NMR), mass spectra (MS), etc. and confirmed their molecular structures. Subsequently, we systematically studied curing characteristics and ultimate properties of these epoxy monomers. With suitable aromatic diamine curing agents, we systematically studied the curing characteristics of these biobased epoxy monomer/curing agent systems, and found that they could be sufficiently cured under ambient conditions. Their curing kinetics and reaction mechanisms were investigated systematically, and the cured epoxy systems were prepared. The structure-property studies showed that all these newly developed biobased epoxy monomers endowed the cured epoxy materials with the improved flame retardancy and other properties. In particular, some of them were self-distinguishing in burning tests. Moreover, the cone calorimeter results ascertained that one of these biobased epoxy resins was characterized by not only good flame retardancy but also significantly suppressed smoke production during burning. Also, all these biobased epoxy resin systems showed the improved mechanical properties as the high Young’s modulus, hardness and storage modulus. Interestingly, by altering their molecular structure, the glass temperature of these cured epoxy monomers could be tuned in a broad range. Furthermore, another one of these biobased epoxy resins exhibited the good dielectric properties (lowered permittivity and dielectric dissipation over a broad bandwidth), ultrahigh elastic modulus, hardness, rather high glass temperature (>200 oC) and decrease cure rate, compared with a standard bisphenol A epoxy resin. Overall, these developed biobased epoxy resins could not only find high promising applications in flame retardant epoxy-based materials, but also could meet requirement from some more demanding and even cutting-edge applications. Also, they could fulfill the requirement of green and sustainable development of epoxy-based materials. (2) We attempted to prepare the novel multifunctional organic-inorganic hybrids as nanofillers to modify epoxy resins. These hybrids were designed and prepared based on the further functionalization of graphite oxide (GO) and layered double hydroxide (LDH). To illustrate, an updated new method was develop to functionalize GO to yield a novel functional GO hybrid with multiple advantages, such as high effectiveness, mild reaction condition and potential scalability. The obtained GO hybrid was well characterized using FTIR, thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), etc. The obtained functionalized GO hybrid could be used to functionalize bisphenol A epoxy resin to yield novel epoxy nanocomposites. On the other hand, a novel multifunctional compound was designed, synthesized, and used to modify LDH. XRD results approved that this molecule could be intercalated into the gallery of the layered double hydroxide via an anion exchange method to yield a novel functionalized LDH hybrid. This hybrid could be used as a multifunctional filler for the epoxy systems to improve the flame retardancy as well as other properties. In summary, the research outcomes of the NEWEPOXY project will impact the current epoxy chemistry and technology and shed new light on developing high-performance biobased epoxy monomers and high-performance epoxy nanocomposites. In particular, the research outcomes related to the new biobased epoxy monomer and innovative approach to highly functionalize GO hybrids for high-performance flame retardant epoxy nanocomposites could likely capture interest from the scientific community and industry cycles. Moreover, beyond the epoxy-based materials, our developed approached to the multifunctional GO and LDH hybrids could be transformative to fabricate other kinds of high-performance flame retardant polymer nanocomposites.

Data: CORDIS, © European Union