## 3 Results and Discussion
### Tensile Properties  
Figure 4 shows the stress-strain curves and stereomicroscopic images of T/P and T/P/MA blends after tensile test and the corresponding denotations are listed in Table 1. Figure 4A-C shows the tensile properties of T90, T70, and T50, as related to whether MA is added, namely, T90/MA, T70/MA, and T50/MA. Figure 4D shows the stereomicroscopic image of the expanded T/P blends. In Figure 4A-C, the black curve means samples are treated with one-off hot-pressing, while the red and blue curves, separately, mean samples are treated with post-2 nd- and post-3 rd-recycling and the resulting samples are compared, thereby examining the reclamation efficacy of T/P blends. Meanwhile, the solid lines represent the MA-free groups, while the dotted lines represent the 5 wt % MA-containing groups. Figure 4A and Table 2 show that T90 has decreasing tensile strength and strain as a result of the number of melting-recycling cycles, which is opposite to the 5 wt % MA-containing group that shows higher tensile performances. Compared to the post-2 nd-recycling group, the tensile strength of T90 in the post-3 rd-recycling group decreased by 78.6%, while T90/MA increased by 80.5%. Figure 4B,C shows that T70 and T50 have a marginal increase in tensile stress and strain when processed with post-2 nd-recycling when comparing to first use. The results also show an obvious decrease in tensile stress and strain when processed with post-3 rd-recycling. It is surmised that post-2 nd-recycling makes thermoplastic polyurethane and polypropylene more evenly blended, but the 3 rd time may cause unrecoverable breakage to T/P blends. The insets of Figure 4A-C show the tensile stress and strain of MA-free groups, which exhibit a drastic decrease as a result of the post-3 rd-recycling. Moreover, increasing polypropylene content renders MA-free groups with a more significant differentiation effect that results from higher interfacial tension and poor adhesive performance. In particular, T50 displays the lowest tensile stress and strain, which is attributed to a rather low tensile strain of polypropylene, as well as the most remarkable differentiation effect between thermoplastic polyurethane and polypropylene. In sum, the presence of MA has a positive influence on the tensile properties of T/P/MA blends. From Figure 4B,  
Figure 4: Tensile performance of T/P and T/P/MA groups as related to the melting–recycling cycles: (**A**)–(**C**) stress–strain curves; (**D**) practical samples after tensile property tests. 1: one-off hot-pressing, 2: the post-2 nd-recycling, and 3: the post-3 rd-recycling. the tensile strength of T70/MA-3 increased up to 9.2 MPa, and that of T70/MA-2 also reached 9.0 MPa. Figure 4C shows a slight decrease in tensile strength from T50/MA-2 to T50/MA-3, where maleic anhydride may have a lighter effect when the thermoplastic polyurethane and polypropylene are both half the content of the blends. Applying a maleic anhydride grafted copolymer as a compatibilizer is an efficient strategy in reactive compatibilization for incompatible polymer systems, where the diisocyanate group on the rigid segment of thermoplastic polyurethane reacts with the maleic anhydride group and forms a copolymer layer at the interphase of T/P during the melting and reheating process, as revealed in Figure 5[4; 35]. It can be found that the mechanical properties of blended thermoplastic materials are improved, even enhanced, with the introduction of an appropriate compatibilizer of proper content [1]. Table 2 summarizes the tensile stress at break, tensile strain at break, tensile stress at yield point, and tensile strain at yield point of the T/P blends. T100 and P100 both show a decreasing trend in tensile properties due to the conduct of post-3 rd-recycling. P100 and T100 dropped by 19.4% and 21.2% in the post-3 rd-recycling and post-2 nd-recycling groups, respectively. Moreover, post-2 nd-recycling T/P and T/P/MA blends have higher tensile properties than the post-3 rd-recycling T/P and T/P/MA blends.