## 1 Introduction  
In the late decades, plastic products have been commonly used in different regions because of abundant sources, low cost, ease of processability, and great diversity [1; 2]. Worldwide, the annual production of plastics is approaching more than 300 million tons, and it is predicted that the global growth of plastic products can be up to 400 million tons in 2020 [3; 4; 5]. The enormous amount of plastic derivatives and their disposal have become a global and important issue as this causes problems for the ocean and the environment [2; 4; 6; 7]. Based on their inherent characteristics, they can be divided into thermoset plastic and thermoplastic, of which the latter has a noticeable feature of reversibility and is thus suitable for reclamation [1; 8; 9]. Despite the amazing reversibility, thermoplastic may demonstrate compromised performances and lose its original advantages as a result of insufficient processing conditions or mistakes. In general, the use of a single polymer cannot satisfy all demands at the same time, which makes compound polymers a remedy for modification. Subsequently, different polymers can be blended to attain a synergistic effect through the modification [10; 11]. However, not all of the polymers have good miscibility and compatibility with others due to their original chemical groups and polarity, so a compatible agent is added as a bridging element [1]. It is well known that thermoplastic polyurethane consists of rigid segments and soft segments, which are individually composed of diisocyanate groups and chain extenders and polyether or polyester chains [12; 13; 14]. Moreover, thermoplastic polyurethane has good toughness and high mechanical properties, yet, simultaneously, its expensive cost and low thermal stability also restrict the applications by end customers [15; 16; 17; 18; 19; 20]. In 2009, [PERSON] et al. concluded that the processing conditions of hot-pressing/melt mixing methods strikingly influenced the various aspects of thermoplastic polyurethane and pointed out that the thermoplastic materials could not be retreated over two or three recycling times due to its poor thermal stability. Therefore, a strategy for thermoplastic polyurethane is to find a suitable polymer that can supplement the required properties [21]. Polypropylene possesses good rigidity, good thermal stability, and a low cost [22], which qualify it to compensate for the disadvantages of thermoplastic polyurethane and, concurrently, bestow reinforcement. Thermoplastic polyurethane and polypropylene are separately a polar polymer and a nonpolar polymer; therefore, phase separation and poor phase adhesion commonly inflict thermoplastic polyurethane/polypropylene blends. With the assistance of a suitable compatibilizer, the compounds can be rid of phase separation [23]. [PERSON] et al. indicated that maleic anhydride grafted polypropylene is a useful compatibilizer to improve the interphase problem between polypropylene and wasted rubber powder [24]. Additionally, there is an imperative issue of how the blended polymer compounds can be recycled [10]. There are several recycling methods, including mechanical recycling, thermal treatment, and chemical recycling [11; 25; 26]. [PERSON] et al. mentioned that plastic waste can be reused by introducing functional fillers to obtain value-added polymer composites [27]. The motivation of this study is not only to effectively use thermoplastic materials but also to increase the use-efficiency after the first use. However, the current recycling strategy is to recycle and reuse single-composition thermoplastic wastes. It is hard to recycle multiple-composition ones at the same time; therefore, the multiple-composition ones are commonly dealt with using combustion or landfill treatment [1; 28]. Hence, how to simultaneously recycle and reuse thermoplastic materials with multiple compositions has become a prominent issue.