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

Abstract

Growing environmental concerns and the goal of a circular economy for polymers necessitate the development of biowaste-based materials and efficient recycling of polymer materials. Here, we developed a series of self-blowing network polyhydroxyurethane (PHU) foams by leveraging 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-based content. By systematically varying the blowing agent concentrations, we demonstrated the tunability of the morphologies and mechanical properties of CNSL-based PHU foams. Using dynamic mechanical analysis (DMA), compression testing, and hysteresis testing, we showed that these foams fall into the category of flexible foams with potential as memory foams or resiliency foams. To address the recyclability challenges of thermoset foams, we repurposed these CNSL-based PHU foams into bulk materials and reprocessed them by exploiting the dynamic chemistries of the hydroxyurethane linkages. Notably, the reprocessed bulk networks exhibited full property retention. Moreover, the systematic inclusion of permanent linkages to substitute dynamic cross-links presents an avenue to study the interplay of permanent linkages and cross-link density toward the dynamic characteristics. We showed that average relaxation times and activation energies increase with increasing levels of permanent linkages in the system, demonstrating highly tunable dynamic behaviors in PHU network materials.

Cascade Exotherms for Rapidly Producing Hybrid Nonisocyanate Polyurethane Foams from Room Temperature Formulations

“…Importantly, the pendant hydroxyl groups of this hybrid flexible biobased foam F21 were exploited to repurpose/upcycle it into film by a combination of transcarbamoylation and dissociative hydroxyurethane reactions. Such strategy was exploited for recycling PHU foams ,− and also commercial PU foams. , By pressing the cross-linked hybrid biobased foam F21 under the same conditions as those previously reported for other self-blown PHU foams (160 °C, 2 T, 2 h), , a thin homogeneous polymer film (width = 0.19 mm, Figure E) with a modulus of 1.66 MPa and a strain at break of 14% was obtained (Figure E1). Neither the T g of the obtained film (−3 °C for the film vs −7 °C for the foam) nor the comparative infrared analysis (Figure E1) indicated a significant change in the chemical structure during this first foam reprocessing.…”

Non-isocyanate polyurethanes synthesized from terpenes using thiourea organocatalysis and thiol-ene-chemistry

“…However, other works also include thioether linkages, e.g. for self-blowing NIPU foams 69 , 70 , showing the potential of such new structures. Further, this work brings forward the use of thiourea catalysis for NIPU production 71 , as potential strategy to activate more hindered cyclic carbonates.…”

Foam-to-Elastomer Recycling of Polyurethane Materials through Incorporation of Dynamic Covalent TAD–Indole Linkages

“…Already around 70 years ago, Offenbach and Tobolsky reported a stress-relaxation character under specific temperature and pressure. , Besides incorporation of intrinsically reactive dynamic groups, ,,, numerous attempts to increase the internal dynamicity of PU-elastomers are reported. ,,– Another chemorheological study , toward PU materials containing free hydroxyl groups (polyhydroxyurethanes) contributed to the idea of recyclable PU materials. For example, Dichtel and Fortman studied a reprocessable PU-like material without the aid of an external chemical entry. , Since the materials were obtained starting from cyclic carbonates, the pioneering work contributed to nonisocyanate polyurethane (NIPU) foam literature. ,,,– …”