Silica–Epoxy Vitrimer Nanocomposites

Abstract

Reinforced silica–epoxy vitrimer nanocomposites have been made in a solvent-free, easily processable, and economical way with filler contents up to 40 wt %. Increasing silica content leads to higher modulus materials in both glassy and rubbery regions. These nanocomposites are insoluble like permanent cross-linked networks but can completely relax stresses by thermoactivated exchange reactions that rearrange the network topology. Furthermore, the surface functionalization of particles improves the dispersion of fillers and accelerates the relaxation process. Similar results were obtained with industrial precipitated silica, which would allow vitrimer nanocomposites to be produced on an industrial scale.

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin–Silica Nanoparticles Interface

“…As Figure 7A shows, the composite that does not contain any exchangeable bonds exhibits the highest degree of shrinkage stress, 0.7 MPa, while the formulation containing exchangeable bonds both throughout the network and at the particle interface (AN–AI) exhibits the lowest degree of shrinkage stress, only 0.2 MPa. While this substantial difference is to be expected, [34] a truly surprising result is observed when comparing samples that limit AFT capabilities to either the resin (AN) or the interface (AI). Figure 7B shows that the PN–AI composite where AFT is limited to the interface exhibits similar values of toughness and tensile strength to AN–PI composite where AFT occurs only in the resin despite having an order of magnitude fewer dynamic bonds.…”

“…Organic nanoparticles with aggregation induced emission properties based on dynamic bonds have previously been developed. [29–31] Fiber-reinforced composites, [32] carbon nanotube composites, [33] and silica nanocomposites [34] made of a dynamic epoxy resin have been investigated. Also, transesterification-based shape memory composites based on graphene-filled vitrimers were prepared.…”

Vitrimerization: A Novel Concept to Reprocess and Recycle Thermoset Waste via Dynamic Chemistry

“…Vitrimers belong to the second category of CANs in which the crosslinking bonds have an associative nature resulting in the ability of the material to change its topology via exchange reactions. These reactions normally are triggered by heat, which causes the gradual decrease in system viscosity with increasing temperature and provides malleability to the network.…”

“…Since vitrimerization also allows for the processing of a thermoset just like a thermoplastic, it affords the unique advantage of incorporating fillers into the thermoset network during recycling to compensate for the drop in mechanical properties due to the catalyst. The addition of fillers to enhance the properties of vitrimers has already been studied extensively . Just as an example, 10 wt% of highly branched carbon nanotubes with a diameter of 7–9 nm known as carbon nanostructures (CNS) were extruded along with the vitrimerized PU samples with the same parameters mentioned above and tested for mechanical properties as can be seen in Figure c.…”

Ultra‐Fast Microwave Assisted Self‐Healing of Covalent Adaptive Polyurethane Networks with Carbon Nanotubes

“…[6] Dynamic networks based on Diels-Alder exchange reactions [12,13] form an example of dissociative covalent adaptive networks.On the other hand, in the case of associative CANs, a crosslinking bond does not break until a new bond forms, which makes the network permanent and dynamic. Vitrimers [14][15][16][17][18][19][20][21][22] are polymeric associative covalent adaptive networks that exhibit a gradual viscosity decrease upon heating, which is a distinctive character of vitreous silica. The cross-linking bonds of such networks have an associative nature which results in the ability of the material to change its topology via exchange reactions.…”