posted on 2022-01-02, 14:43authored byKai Hong, Qingmei Sun, Xinyue Zhang, Liujie Fan, Tong Wu, Jianzhong Du, Yunqing Zhu
Thermosets
are important commodity polymeric materials, but they
are rarely biorenewable and recyclable. Although some previously reported
bio-based aromatic thermosets with a high aromatic content have good
thermal/mechanical properties, the mechanical properties of fully
bio-based vitrimers are relatively poor owing to low aromatic contents.
To address this important issue, vanillin-based dialdehyde and trialdehyde
containing high aromatic content were synthesized, and renewable diamines
containing short aliphatic chains were carefully screened. Then, fully
bio-based thermosets were prepared via the Schiff
base reaction between vanillin-based aldehydes and diamines. Attributed
to the high aromatic content (59.2–61.3 wt %), the mechanical
performances of these fully bio-based thermosets were significantly
improved, demonstrating comparable properties to traditional thermosets
and higher than any previously reported fully bio-based thermosets
[high mechanical properties (σ = 58.0 MPa; E′ = 3.07 GPa)]. In addition, it could be completely degraded
under mild acidic conditions. This significantly expands the end-of-life
options such as recovery of monomers. More importantly, the fully
bio-based thermosets demonstrated excellent closed-loop recyclability
without changing their chemical structures and mechanical properties
after repolymerization via commonly used approaches,
such as thermomechanical recycling and chemical recycling. Even after
three hot-pressing cycles, the recovery ratio of the tensile strength
was higher than 84%, which was even better than the results of many
reprocessable commodity thermoplastics. Therefore, these fully bio-based
thermosets are expected to be excellent alternatives to traditional
thermosets in the future.