Vanillin-Based Degradable Polyurethane Thermosets Demonstrating High Bio-Content and Mechanical Properties

Abstract

Polyurethanes are widely used polymeric materials, but they are rarely biorenewable and degradable. Although some previously reported bio-based polyurethanes exhibit good thermal and mechanical properties, their bio-content is usually low, resulting from the only replacement of the diol monomer instead of the whole diol/diisocyanate pairs. In addition, traditional polyurethanes are often difficult to degrade, leading to environmental issues. To address these issues, we propose a solution by sourcing both the diols and isocyanates from biorenewable resources and introducing degradability into diols via the Tishchenko reaction, which is the disproportionation of two aldehydes to afford an ester bond with an atom economy of 100%. Commercially available bio-based vanillin was selected as the precursor for a vanillin-based diol (VBD) containing ester bonds. By reacting VBD with L-lysine diisocyanate (LDI) and trimethylolpropane (TMP) as a crosslinker, a series of bio-based thermosetting polyurethanes, VBD-TMP x , with high bio-based carbon content (>70.0%) were synthesized. The chemical structures and properties of monomers as well as polymers were characterized using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile tests. The obtained VBD-TMP x polyurethanes exhibit comparable mechanical properties (σ = 32.0 MPa; E′ = 2.7 GPa) to commercial thermosetting polyurethanes and demonstrate higher toughness (34 MJ/m 3 ) than previously reported bio-based analogues. Additionally, the inherent ester bond in the VBD monomer enables the complete degradation of VBD-TMP x in a 0.1 M NaOH solution (THF/H 2 O = 1:1, v/v) within 3.5 h. This greatly broadens the available end-of-life choices, including the recovery of the monomers. This study presents a facile approach for creating degradable polyurethane materials with high bio-content and mechanical properties.

Simultaneously Enhancing Mechanical Strength, Toughness, and Fire Retardancy of Biobased Polyurethane by Regulating Soft/Hard Segments and Crystallization Behavior

“…The Fourier transform infrared (FT-IR) spectra of vanillin, DOPO, and VDP are shown in Figure a: the absorption peaks at 3100–3500 and 1662 cm –1 belong to the characteristic peaks of −OH and the CO stretching vibration, respectively, while the peak at 2437 cm –1 is associated with the P–H bond on DOPO. , In the VDP spectrum, it can be observed that both the CO stretching vibration and P–H characteristic peaks disappeared, while characteristic peaks at 1604 cm –1 (P–C bond), 1270 cm –1 (C–N bond), 1231 cm –1 (PO bond), and 916 cm –1 (P–O bond) appeared. , The FT-IR spectra of the synthesized polyurethanes are shown in Figure b. The peaks at 3360 and 1725 cm –1 correspond to the N–H and CO stretching vibrations of the polyurethanes, respectively, and the peaks at 2941 and 2854 cm –1 are attributed to the C–H stretching vibrations of −CH 3 and −CH 2 , respectively . The peaks at 1529 and 1153 cm –1 correspond to the C–N and C–O–C stretching vibrations, and the disappearance of the NCO stretching vibration peak at 2261 cm –1 proves that all NCO groups on HDI were consumed. , After the addition of VDP, a urethane stretching vibration peak appeared at 1681 cm –1 , and the peak was significantly enhanced, which proved that the synthesized VDP successfully reacted with the −NCO groups of HDI.…”

Highly transparent polyurethane thermosets with tunable properties and enzymatic degradability derived from polyols originating from hemicellulosic sugars

“…11, the PU networks produced in this work exhibited comparable or higher tensile strength and elongation at break than most biobased PU thermosets reported in the literature or non-renewable commercially available crosslinked polyurethanes. 3,6,48–59 The attractive features of the developed PU thermosets such as good and easily tunable mechanical performance, including a very broad range of elongation at break (15–188%), Young's moduli (6.1–648.8 MPa) and tensile strength (3.3–31.1 MPa), together with their high heat resistance and good optical transparency could cement these PUs as a promising class of high-performance amorphous polyurethane materials.…”

“…3 Additionally, conventional PU thermosets that account for 31% of the thermoset market 4 are not easily biodegraded or recycled due to their permanent crosslinked structures, which can escalate their adverse environmental impact. 3 With increasing reliance on PUs and in response to the growing awareness of global challenges related to dwindling fossil resources, greenhouse gas emissions, environmental pollution and surging energy demand, 5 much work has been devoted to the development of more environmentally friendly PUs with reduced carbon footprint. 3,6–17…”

“…3 With increasing reliance on PUs and in response to the growing awareness of global challenges related to dwindling fossil resources, greenhouse gas emissions, environmental pollution and surging energy demand, 5 much work has been devoted to the development of more environmentally friendly PUs with reduced carbon footprint. 3,6–17…”

Polyurethane Detachable Lamination Adhesives Containing Alkaline Degradable Aromatic Chain Extender

“…Many stimulus conditions contributing to adhesive debonding have been studied, including optical, − thermal, − magnetic, electrical, chemical, − etc. Light can induce polymer degradation, isomerization, , or overcuring, heat can induce decomposition, , expansion, rearrangement, , and phase separation to achieve debonding.…”