## 1 Introduction  
Polyurethane (PU) has received great attention in a variety of applications (e.g., adhesive materials, textile, glove, paints, wood finishing, etc. ), owing to its excellent mechanical and physical properties [1, 2]. Because of the worldwide restriction on volatile organic chemicals (VCCs), there is a tendency to replace conventional, organic, solvent-based polyurethanes by waterborne polyurethanes (WPUs) [3, 4, 5, 6]. The utilization of water, rather than organic solvent, as a dispersion medium may avoid unnecessary environmental pollution as it is pollutant-free and odorless, which is in compliance with the requirements of environmental protection regulations. To be dispersible in water, WPUs should contain ionic or nonionic hydrophilic segments in their structure. According to the types of ionic groups incorporated, the dispersion can be categorized as cationic, anionic, or zwitterionic. As an important category of WPUs, cationic WPUs have an extremely high adhesion capacity to different ionic substrates, particularly for anionic substrates (e.g., glass, leather, etc.) [7, 8, 9, 10]. Thus, cationic WPUs can be utilized as an important adhesive or coagulation [11, 12, 13]. N-Methyl diethanolamine has been widely employed as a cationic hydrophilic group in WPU dispersions [8, 12]. Incorporation of strong polar cationic groups into hard segments of linear PUs considerably improves polarity, resulting in cationic WPUs with improved adhesion strength on anionic substrate [7; 11]. However, most of the WPUs molecules have linear structure and some properties of WPU still need to be improved further, such as thermal stability, water resistance, brittleness, etc. [14; 15]. To improve these properties, great effort has been made to accelerate the development of WPUs [16; 17; 18; 19]. Polymers from renewable resources have been widely studied over the past decades ref. [20; 21; 22; 23], mainly due to their environmental impacts and finite petroleum resources. Biobased polyurethane (BPU) has received considerable attention as an eco-friendly material for reducing fossil oil depletion, environmental pollution, carbon dioxide emission, and global warming [24; 25; 26]. Plant oils derived from castor, sunflower, palm, canola, and soybean have a great potential to replace petroleum for the production of polyols (a raw material used to synthesize PUs) [27; 28]. Among them, castor oil (CO) has been widely applied due to its environmental friendliness, large availability, biodegradability, cost-effectiveness, and easily extractable from castor seeds. CO consists of 88% ricinoleic acid and has an average hydroxyl functionality of 2.7. Therefore, CO can be directly employed as polyols to synthesize PUs [29; 30]. However, CO does not have the rigidity and strength properties required for structural applications because of its low functionality and relatively lower reactivity of secondary hydroxyl groups. Low hydroxyl number of CO also leads to a poor performance of the resulting polymer materials [31], which hindered their use in many applications. In addition, the soft-segment diols, hard-segment diisocyanates, and chain extenders lead to environmental pollution owing to their low biodegradability. With the rising awareness about the environmental challenges associated with the difficult-to-decompose plastics, the application of degradable materials has received a widespread attention. PCL is a hydrophobic aliphatic polyester that can be generated from petroleum or renewable resources (e.g., polysaccharides) via chemical synthesis [32]. It is often considered as a green polymer on account of its biocompatibility and biodegradability by microorganisms [33; 34]. Besides, PCL is an easily processable and completely biodegradable synthetic material that can be used with conventional melt processing equipment [35]. Indeed, PCL has been applied in a wide range of fields such as food packaging and biomedical devices [33; 36; 37].