## 2 Materials and Methods
### Characterization  
The free-standing WPU films were prepared according to the following method: The WPU dispersions were poured in the Teflon molds for drying at room temperature for 7 days followed by drying for 24 h in a vacuum oven at 40 \({}^{\circ}\)C. Subsequently, the films were stored in a desicator to avoid moisture uptake. The FT-IR analysis was carried out on Bruker TENSOR-27 spectrometer at a resolution of 4 cm\({}^{-1}\) in the wavenumber range of 4000-400 cm\({}^{-1}\), For this purpose, the acetone solutions of the specimens were cast on the KBr pellets. The average particle size and particle size distribution (PSD) of the WPUs were measured using an ALV CGS-3 light scattering spectrometer equipped with an ALV-5000 multi-tau digital time correlator and a He-Ne laser (\(\lambda\) = 632 nm). The WPU dispersions were first diluted in deionized water to a concentration of 0.3 wt%, followed by ultrasonic wave treatment to homogenize the dispersion. For the stress-strain test, the WPU free-standing films were cut into dumb-bell shaped samples with 20 mm length and 4 mm width. The tensile stress-strain test was performed on an Instron-1121 at an extension rate of 100 mm min\({}^{-1}\) at 25 \({}^{\circ}\)C.  
The stability of the CO2-WPU emulsion was evaluated by centrifugation of the sample at 3000 rpm for 30 min on an ANKE TGL-10C system. The zeta potential of the dispersions was measured on a Malvern-ZS90 system. A FEI XL30 ESEM field emission scanning electron microscope (SEM) with an operating voltage of 15 kV with chromium coating was used to observe the particle of WPU and the tensile fracture surfaces of the various WPU samples. The 0.1 wt% emulsion was dyed with 2 wt% phosphotungsttic acid and then subjected to JEOL JEM-2010 Transmission Electron Microscope (TEM) at an acceleration voltage of 200 kV. X-ray diffraction (XRD) was carried out on Brucker D 8 Advance diffractometer with Cu K\(\alpha\) radiation (\(\lambda\) = 1.542 A). The specimens were scanned from 10\({}^{\circ}\) to 40\({}^{\circ}\), with a step size of 0.02 and a scan speed of 6\({}^{\circ}\)/min. The tensile stress-strain test was performed on an Instron-1121 at an extension rate of 100 mm min\({}^{-1}\) at 25 \({}^{\circ}\)C and 50% relative humidity. The average of three tests was reported for each specimen. Adhesive strength (under peeling stresses) of the WPU dispersions was determined using the T-peel tests on the solvent-wiped, plasticized, ABS/polyurethane adhesive/solvent-wiped, plasticized, PVC joints. The ABS test samples had the dimensions of 25 mm \(\times\) 150 mm \(\times\) 5 mm. Prior to applying the PU dispersion, the ABS surface was wiped with methyl ethyl ketone, followed by solvent evaporation for 30 min in air. Subsequently, 0.45-0.92 g PU dispersions were applied by brush to the ABS strips for the joining. After water evaporation (90 min), the adhesive film was rapidly heated at 80 \({}^{\circ}\)C for 10 s under infrared radiation (reactivation process). The PVC strips were immediately placed in contact with the ABS test samples, and a pressure of 0.8 MPa was applied for 10 s to achieve optimal bonding. The T-peel strength was measured 72 h after joint formation using Instron-1121 universal testing machine at a crosshead speed of 100 mm/min. The average of three tests was reported for each specimen. Differential scanning calorimetry analysis was carried out using Perkin Elmer Thermal Analysis DSC-7. In total, 10 mg samples were enclosed in the aluminum pans and were subsequently heated from 0 to 150 \({}^{\circ}\)C at a scanning rate of 10 \({}^{\circ}\)C min\({}^{-1}\) under a constant nitrogen flow. The rectangular test bars were immersed into water for durations (72 h). The water absorption (A%) of the samples was calculated according to Equation (1):  
\[\mathrm{A\%=(W_{1}-W_{0})/W_{0}\times 100\%} \tag{1}\]  
where W\({}_{0}\) is the weight of the dry sample, and W\({}_{1}\) is the weight of the wet sample, measured immediately after the residual water was removed from the sample surface using filter paper.