The hardness and tension set are also shown in this table. The results show that incorporation of blend compatibilizers increased the tensile strength and hardness and there was a tendency to recover from prolonged extension (i.e., a lower tension set). Therefore, the compatibilizers contributed to enhancing strength, toughness and set properties of the MNR/HDPE TPVs. Among the three types of compatibilizers used, the mechanical, hardness, and tension set properties of the TPVs with the phenolic modified polyethylene (i.e., PhSP-PE and PhHRJ-PE) were superior to those of the TPV with PE-g-MA. This is attributed to the compatibilizer molecules being capable of linking the polyethylene and MNR molecules. The possible reaction mechanism and final molecular structures are shown in Scheme 1, Scheme 2 and Scheme 3.