Incorporating Functionalized Cellulose to Increase the Toughness of Covalent Adaptable Networks

Abstract

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. File list (3) download file view on ChemRxiv 2020_03_ChemRxiv_Swartz_Manuscript.pdf (1.31 MiB) download file view on ChemRxiv 2020_03_ChemRxiv_Swartz_TOC.jpg (68.46 KiB) download file view on ChemRxiv 2020_03_ChemRxiv_Swartz_Supporting_Information.pdf (5.12 MiB)

Fully Biobased Vitrimers: Future Direction toward Sustainable Cross‐Linked Polymers

“…Only examples of partially biobased carbonate vitrimers have been found in literature. [107][108][109] With the substitution of highly toxic phosgene by organic carbonates, the use of CO 2 for carbonatation reactions, and naturally occurring hydroxyl functionalized raw materials, biobased polycarbonate vitrimers are good candidates for the development of sustainable cross-linked materials. [100,110]…”

Regioregular Polymers from Biobased (R)-1,3-Butylene Carbonate

“…Initially, transcarbonylation and depolymerization were observed from a regioregular polymer using a range of transesterification catalysts, indicating the reversible nature of these carbonate bonds under these conditions (Figures S24 and S25). , When the conversion was kept below a threshold (70–80%), the polymers were regioregular, but beyond that the process was not well understood (Table ). As shown in Figure , transcarbonylation can be observed in polymerizations at 70 °C (Figure A) and 110 °C (Figure B).…”

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

“…Alternatively, the CANs can be strengthened by incorporating some permanent cross-links or inorganic/organic fillers. [25][26][27] However, the presence of irreversible bonds in the permanent crosslinks and between the CAN matrix and fillers will limit the complete chemical recycling of the material, especially when the amounts of permanent crosslinks and/or fillers exceed a critical value where a percolating network is formed. The other issue is the performance reduction after reprocessing and/or recycling.…”