Resorcinol‐Derived Vitrimers and Their Flax Fiber‐Reinforced Composites Based on Fast Siloxane Exchange

Abstract

Natural fiber‐reinforced composites are gaining increased interest for their significantly reduced carbon footprint compared to conventional glass or carbon fiber‐based counterparts. In this study, natural fibers are used in a resorcinol‐based epoxy resin that is thermally reshapable at higher temperatures (>180 °C) by using fast exchanging siloxane bonds, catalyzed by 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene. Stress relaxation times of only about 6 s at 220 °C can be reached. A resorcinol‐based epoxy compound is selected because it can be derived from cellulose, opening ways for more sustainable and reshapable composite materials. In a last step of the research, the low viscosity vitrimer formulation (<200 mPa s) is applied to make a flax fiber‐reinforced composite using an industrially relevant vacuum‐assisted resin infusion process. A section of this composite is successfully reshaped, which allows for envisioning a second life for natural fiber‐reinforced composites.

Catalyst-Free, Mechanically Robust, and Ion-Conductive Vitrimers for Self-Healing Ionogel Electrolytes

“…Stress relaxation tests were performed between 60 to 180 °C, as the materials maintained in the rubbery state (Figure S9). The activation energy for CP3 calculated from Figure C and Figure S13 is about 174 kJ/mol, which is significantly higher than the values observed for other catalyst-promoted Si–O-based systems. ,− Since we were not using catalysts to promote Si–O metathesis, as expected, our values (174 kJ/mol) were higher by at least a factor of 2 and revealed vitrimeric behavior at around 160–180 °C, comparable to other catalyst-free Si–O systems. , We also proved material stabilities up to 300 °C by TGA analysis (Figure S11). Because of the silyl ether bond exchange reaction, the materials could self-heal after being damaged.…”

“…34,41−46 Since we were not using catalysts to promote Si−O metathesis, as expected, our values (174 kJ/mol) were higher by at least a factor of 2 and revealed vitrimeric behavior at around 160−180 °C, comparable to other catalyst-free Si−O systems. 47,48 We also proved material stabilities up to 300 °C by TGA analysis (Figure S11). Because of the silyl ether bond exchange reaction, the materials could self-heal after being damaged.…”

Oligosiloxane-Based Epoxy Vitrimers: Adaptable Thermosetting Networks with Dual Dynamic Bonds

“…Previously reported higher T g siloxane-based vitrimers required elevated temperatures (>180 °C) to achieve similar relaxation times. 15,16 This rapid stress relaxation correlates with the low topology freezing transition temperature (T v ) determined from the Arrhenius plot of τ* (Tables 1 and S12 and S13). This, in conjunction with the low T g of these materials, leads to accelerated stress relaxation.…”

“…10,13 Du Prez and coworkers have developed siloxane-containing vitrimers with very fast dynamics (below 10 s) in the presence of basic catalysts. 15,16 Due to the flexibility of the siloxane units, the prepared resins exhibited low viscosities, which offers significant advantages for fiber-reinforced polymer composite manufacturing. Additionally, it has been shown that the incorporation of siloxane groups into reprocessable networks improves the dielectric properties and ductility.…”

“…These results align with prior reported TBD-catalyzed siloxane-based vitrimers (∼87 kJ•mol −1 ). 15,16 The slight decrease in the observed E a for Si2-PDAA may be a result of multiple relaxation modes occurring (siloxane exchanges and transesterification). We can visualize the full distribution of relaxation time scales without making assumptions about the number of modes using a continuous relaxation spectrum, based on an infinite number of Maxwell elements 24,25 (Figures S14 and S15).…”