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Incorporating Functionalized Cellulose to Increase the Toughness of Covalent Adaptable Networks

preprint
submitted on 01.04.2020 and posted on 03.04.2020 by Jeremy Swartz, William Dichtel

Covalent adaptable networks (CANs) are cross-linked polymers that have mechanical properties similar to thermosets at operating conditions, yet can be reprocessed by cross-link exchange reactions that are activated by a stimulus. Although CAN exchange dynamics have been studied for many polymer compositions, the tensile properties of these demonstration systems are often inferior compared to commercial thermosets. In this study, we explore toughening CANs capable of forming covalent bonds with a reactive filler to characterize the trade-off between improved toughness and longer reprocessing times. Polycarbonate (PC) and polyurethane (PU) CANs were toughened by incorporating cellulose modified with cyclic carbonate groups as a reactive filler with loadings from 1.3-6.6 wt%. The addition of 6.6 wt% of the cellulose derivative resulted in a 3.2-fold increase in average toughness for the PC CANs, yet only increased the characteristic relaxation time of stress relaxation (*) via disulfide exchange at 180 °C from 63 s to 365 s. The cellulose-containing samples also showed >80% recovery in crosslinking density and mechanical properties after reprocessing. The addition of 3.2 wt% of the functionalized cellulose into a PEG-based PU CAN led to a 2.3-fold increase in toughness, while increasing * at 140 °C from 106 s to 157 s. These findings demonstrate the promise of functionalized cellulose as an inexpensive, renewable, and sustainable filler that toughens CANs containing hydroxyl groups.

Funding

NSF CHE-1901635

NSF DGE-1842165

NSF DMR-1121262

NSF NNCI-1542205

History

Email Address of Submitting Author

wdichtel@northwestern.edu

Institution

Northwestern University

Country

United States

ORCID For Submitting Author

0000-0002-3635-6119

Declaration of Conflict of Interest

The authors declare no conflict of interest.

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