Merging CO2 transformation and utilization with renewable bio-resources: a step forward to a double vision of sustainable chemistry

Valorizing waste CO2 as a cheap, inexhaustible and renewable C1 feedstock is an early stage technology with strong innovation potential that imposes itself as a strategic driver for developing future low carbon footprints materials. Beside its use as raw chemical, the “physical” valorization of CO2 in a series of industrial cost-efficient processes will also accelerate the development of a low carbon economy and support the elaboration of a global low carbon vision scheme. The synergistic and paradigm-transforming holistic project we propose perfectly illustrates these concepts by encompassing a “cradle” to “grave” vision, i.e. from the products conception from CO2 and bio-resources to their production and processing through sustainable processes compatible with existing industrial relevant infrastructures. It focuses on the elaboration of sustainable isocyanate-free polyurethane foams with promising thermal insulation properties. By its objectives, this study also proposes an ideal alternative to the conventional synthesis of PUs and a practical answer to the challenge the PU sector is facing due to changes in the REACH regulations limiting the use of isocyanates.
The success of the project relies on 3 key steps involving:
i) The synthesis of bio- and CO2-sourced cyclic carbonates monomers: Due to the low reactivity of CO2 versus epoxides, addition of catalysts is necessary. To overcome this limitation, we developed a new highly-efficient bicomponent homogeneous organocatalyst that showed unexpected activity for the fast (within a few minutes) and selective addition of CO2 onto model epoxides and epoxidized vegetable oil under solvent-free and mild experimental conditions at the multiKg scale. The use of this powerful dual organocatalyst was further extended to the first organocatalytic coupling of CO2 with less reactive oxetanes to produce hydroxyl telechelic oligocarbonate entering the synthesis of CO2-sourced conventional PUs.
- The synthesis of sustainable bio- and CO2- sourced isocyanates-free polyurethanes (NIPU): Sustainable NIPUs were produced by step-growth polymerization between the so-produced bio- and CO2-sourced cyclic carbonates and biosourced amino-telechelic comonomers derived from linseed fatty acids according to a process compatible with existing industrial infrastructures (extrusion).
- The foaming of NIPUs: Sustainable foams with thermal insulation were produced by the supercritical CO2 assisted foaming technology. Due to its solubility in polymers, CO2 can replace conventional flammable VOCs and ozone depletion physical blowing agents as hydro- or fluorocarbons exhibiting long atmospheric life-time and/or mean global warming potential 2800 higher than CO2. By finely choosing the CO2 impregnation and the foaming conditions, low density microcellular NIPU foams with a thermal conductivity as low as 0.050 Wm-1K-1 were produced.
Our study shows that CO2 is not only sequestered in the material for long-term application, but is also valorized as a blowing agent in the production of sustainable thermally insulating NIPU foams. Such low carbon footprints materials will contribute to energy conservation and savings by reducing CO2 emissions.