## 3 Results and Discussion
As can be seen in the TEM photographs, CO\({}_{0\%}\)-WPU presented bimodal PSD and large particles were around 200 nm while small particles were around 50 nm. When compared with the CO\({}_{5.04\%}\)-WPU dispersion, exhibiting an average particle size of 50 nm diameter, a smaller particle size of 20 nm diameter was observed for CO\({}_{9.66\%}\)-WPU with a larger CO content. These results were consistent with the particle size results, which further confirmed that the cationic hydrophilic group (N-MDEA) was located on the main chain of the polymer and embedded easily in the process of the formation of latex particles. CO in the samples, which could be related with restrictions in chain mobility and phase mixing increase, hindered the chain packing of polycaprolactone segment. Therefore, hydrophilic group was no longer the crucial influencing factor in determining particle size. The combination of CO exhibited a positive effect on the dispersion and stability properties of WPUs. It is found that the particle size and zeta potential of the WPUs influence the storage stability of the dispersion. As shown in Table 1, these WPUs demonstrate excellent storage stability. No obvious perception or stratification was observed when the WPUs were centrifuged at 300 rpm for 30 min and stored for 6 months at room temperature. Figure 2: The particle size distribution of WPUs. As shown in Figure 5, the WPUs exhibited two diffraction peaks attributing to the (200) and (110) planes of the PCL crystalline phase. There was no shift in the positions of these peaks and the peak intensity qualitatively declined on increasing castor oil concentrations, implying that the crystallinity decreased in the CO/WPU systems without affecting the crystal structure, and the crosslinking by castor oil restricted the chain packing of PCL crystals in the castor oil/PCL-based WPUs, thus leading to a reduction in crystallinity. In addition, the XRD diffractograms showed shoulder of the peak at 2 theta = 21\({}^{\circ}\). The observed phenomenon could be attributed to the fact that the amorphous hard segment (CO) of the polymer was inductively produced to crystallize because of the formation of more hydrogen bonds. To further explore the crystallinity of WPU films, the thermal properties of the films casted from the dispersion with various TMPM content were analyzed using DSC. According to Figure 6, all samples presented melting peak temperatures ranging from 45 \({}^{\circ}\)C to 49 \({}^{\circ}\)C. This observed melting temperature could be attributed to the melting of pure PCL around 60 \({}^{\circ}\)C. Moreover, it was found that the peak melting temperatures of WPU films decreased with an increase in CO/PCL-OH molar ratio. As shown in Table 2, increasing the CO content led to a decrease in melting temperature and melting enthalpy. This result was consistent with the XRD result, which further confirmed that the crosslinking by castor oil restricted the PCL segment crystallization ability, enabling the formation of amorphous domains. Figure 4: TEM micrographs of (**a**) CO\({}_{0\%}\)–WPU, (**b**) CO\({}_{5.04\%}\)–WPU and (**c**) CO\({}_{9.66\%}\)–WPU.