Epoxy Matrices Modified by Green Additives for Recyclable Materials

Abstract

Epoxy-based thermosets are one of the most popular matrix materials in many industries, and significant environmental benefits can be obtained by developing a recyclable variant of this widely utilized material. Incorporation of a bio-based disulfide additive within a commercial epoxy system leads to a cross-linked material that can be fractionated under mild and environmentally benign conditions. The material has been analyzed by FTIR and solid-state NMR. Furthermore, modified epoxy matrices with low additive concentrations are demonstrated to have similar mechanical and thermal properties compared to commercially available benchmarks. Thus, additive formulation and fractionation based on green chemistry principles have been demonstrated, and a recyclable epoxy matrix has been developed.

A Review on the Potential and Limitations of Recyclable Thermosets for Structural Applications

“…118 To increase the circularity of these thermosets bio-based monomers can be used. Partial 126 and full 100,[127][128][129][130][131] bio-based vitrimers are already reported in recent literature.…”

Recyclable carbon fibre composites enabled by cystine containing epoxy matrices

“…Hardener substitution is based on molar equivalent active sites and CYS 20 denotes a 20 mol% L-cystine hardener substitution as described by ESI eqn (S1). † 14 766H is added, mixed, degassed and cured at 50 C for 1 h and subsequently 80 C for 3 h. 14 Optimized dismantle time of epoxy matrices with respect to acetic acid concentration 2.0-2.2 g (4 mm  10 mm  50 mm) CYS 5 samples are placed in an empty snap cap glass (25 mL, Thomas Scientic), which is lled to the rim with an aqueous (demineralized water) acetic acid at a mole fraction (x AA ) of 0.07, 0.17, 0.24, 0.32, 0.42, 0.56, 0.64, 0.74, or 1.00 and sealed with a cap. A needle (B 1.2 mm by 40 mm, Sterican, B. Braun, DK) is pierced into the lid for pressure equalization and the vial is placed in a preheated oven at 70 C (Steva, Elgiganten, DK), which is thermostatic controlled by a PID regulator (Sestos, D1S-VR-220, HK, CN).…”

“…SEM images are post processed in ImageJ (v. 1.51r) to measure the thickness of the carbon bres. Measurements (14) are performed on the virgin carbon bres giving the average bre diameter and its standard deviation.…”

“…The calculated volume fractions from both burning and pyrolysis are given in Table 3 together with the composites' density and exural modulus. The density and exural modulus ( 14 as the number of recycling increase. Further, the individual ply thickness and the total composite thickness increased as the number of recycling increase and a decrease in FVF when composites are thermal converted with and without oxygen present.…”

“…Potential trigger solutions have not been industrialized either due to expensive and/or hazardous triggers or due to the degradation products. A recent study has demonstrated that the addition of 0.97 wt% of L-cystine to a commercial epoxy system rendered a matrix that could be fractionated in glacial acetic acid at 70 C. 14 Although promising results, the fractionation time is long and bre recyclability is yet to be demonstrated.…”