Reprocessable, Bio-Based, Self-Blowing Non-Isocyanate Polyurethane Network Foams from Cashew Nutshell Liquid

Growing environmental concerns and the goal of a circulareconomyfor polymers necessitate the development of biowaste-based materialsand efficient recycling of polymer materials. Here, we developed aseries of self-blowing network polyhydroxyurethane (PHU) foams byleveraging the aminolysis and decarboxylation of cashew nutshell liquid(CNSL)-based cyclic carbonate with thiols to release CO2 as a blowing agent; these foams contain up to 80 wt % bio-basedcontent. By systematically varying the blowing agent concentrations,we demonstrated the tunability of the morphologies and mechanicalproperties of CNSL-based PHU foams. Using dynamic mechanical analysis(DMA), compression testing, and hysteresis testing, we showed thatthese foams fall into the category of flexible foams with potentialas memory foams or resiliency foams. To address the recyclabilitychallenges of thermoset foams, we repurposed these CNSL-based PHUfoams into bulk materials and reprocessed them by exploiting the dynamicchemistries of the hydroxyurethane linkages. Notably, the reprocessedbulk networks exhibited full property retention. Moreover, the systematicinclusion of permanent linkages to substitute dynamic cross-linkspresents an avenue to study the interplay of permanent linkages andcross-link density toward the dynamic characteristics. We showed thataverage relaxation times and activation energies increase with increasinglevels of permanent linkages in the system, demonstrating highly tunabledynamic behaviors in PHU network materials.

Automated summary

In order to address environmental concerns and achieve a circular economy for polymers, we have developed a series of bio-waste-based polyhydroxyurethane (PHU) foams. These foams, containing up to 80 wt% bio-based content, were created by utilizing the aminolysis and decarboxylation reaction of cashew nutshell liquid (CNSL)-based cyclic carbonate with thiols to release CO2 as a blowing agent. By adjusting the blowing agent concentrations, we demonstrated the tunability of the morphologies and mechanical properties of CNSL-based PHU foams. Furthermore, we repurposed these foams into bulk materials and successfully reprocessed them by exploiting the dynamic chemistries of the hydroxyurethane linkages.