Hybrid Organic–Inorganic Composites Based on Glycolyzed Polyurethane

Abstract

We present a simple approach to upcycle glycolyzed polyurethane foam products by fabricating robust, highly filled organic/inorganic composites (46–60 wt % solid loading). These composites, consisting of recycled polyols, naturally occurring or synthetic aluminosilicate minerals, and isocyanate linkers, are shown to possess superior mechanical (flexural) properties compared to ordinary Portland cement (OPC). Optimization of chemical composition (isocyanate and inorganic content) and curing temperatures (25–50 °C) results in low-density composites (up to 3× less dense than OPC) with flexural strengths comparable to OPC while exhibiting strain capacities up to 5× as compared to OPC-based systems. In contrast, parallel fabrication approaches using low OH-value virgin polyols resulted in flexible composites and much lower flexural strengths, highlighting the advantage of employing high −OH density recycled polyols. Variations in the flexural strength of the composites were correlated with differences in their morphologyuniformity in the distribution of inorganic particles contributed to improved flexural properties. The generality of this fabrication approach is demonstrated using quartz sand as the inorganic particle and recycled polyols with different hydroxyl values.

High-Strength Organic–Inorganic Composites with Superior Thermal Insulation and Acoustic Attenuation

“…The reactive isocyanate groups on TDI initiate urethane linkages with OH groups from the polyol, as well as clinoptilolite particles, thus introducing compatibility between the organic (polyol) and inorganic (clinoptilolite) components and forming a PU network (Figure B) . We note that while the high reactivity of TDI enhances the rate of covalent network formation, it is still susceptible to side reactions (with moisture or carboxylic acid groups), likely producing CO 2 and leading to increased porosity in the cured composites. ,, To aid the release of CO 2 and minimize porosity, the mixture was heated at 50 °C for 1 min to accelerate the release of gas bubbles prior to curing at room temperature (Figure A). The higher reaction rate of TDI (compared with IPDI), coupled with the modified fabrication strategy, led to fewer entrapped gas bubbles and allowed room-temperature curing of the composites.…”

“…The inorganic particles appeared to be uniformly distributed, indicating adequate binding between the inorganic and organic phases by TDI. This is a visible improvement to our prior work wherein agglomerates were noted at low (10 wt %) IPDI content …”

“…Replacing the aromatic TDI with aliphatic IPDI in the IG300 composites led to a decrease in flexural strengths, with the optimal composition shifting to 17 wt % excess isocyanate, 53 wt % clinoptilolite, and 30 wt % PU content. 17 Using TDI also enabled room temperature curing compared to IPDI composites that required curing at 50 °C. 17 The lower curing temperature and high strength of TDI-based PUC composites at a lower excess isocyanate content (10 wt %; Figure 2A) than the IPDI-based PUC composites can be attributed to the aromatic nature and resonance structures of TDI.…”

“…17 Using TDI also enabled room temperature curing compared to IPDI composites that required curing at 50 °C. 17 The lower curing temperature and high strength of TDI-based PUC composites at a lower excess isocyanate content (10 wt %; Figure 2A) than the IPDI-based PUC composites can be attributed to the aromatic nature and resonance structures of TDI. These aspects contribute to its high reactivity and benefit the formation of covalent isocyanate linkages in the TDI-based composites to a greater extent than the aliphatic IPDI-based composites.…”

“…14,15 Recently, we demonstrated a facile method to overcome particle aggregation to fabricate highly filled (up to 60 wt %) lightweight PU-clinoptilolite composites by covalently linking micron-sized inorganic clinoptilolite particles (aluminosilicates) to organic polyols by aliphatic diisocyanate linkers (isophorone diisocyanate; IPDI). 17 Our approach was inspired by strategies where grafting polymers to inorganic surfaces (e.g., polymer-calcium silicate hydrate 18 and polymer-grafted silica nanoparticles 19,20 ) led to enhanced compatibility between the organic and inorganic components, and significant improvements in mechanical properties. When compared to OPC, our composites exhibit lower density (up to 3×), comparable flexural strengths, and higher strain capacities (up to 5× OPC).…”