The evolution of the tangent of the loss angle as a function of temperature for NR and UHMWPE fibers/NR composites is presented in Fig. 9. The dynamic glass transition temperature was for all the materials close to 55 C. An insignificant decrease of the maximum tan d values was observed when adding the UHMWPE fibers. The tan d peak height is 2.47, 1.35 and 1.22 respectively for NR, as-received and treated UHMWPE fibers/NR composites. The decrease of tan d peak reflects that UHMWPE fibers have effectively immobilized NR chains near the polymer-fiber interface due to favorable interfacial interactions with the NR matrix [26]. Meanwhile,the maximum tan d value of the composites with treated UHMWPE fibers are lower than that of as-received UHMWPE fibers/NR composites. This result indicates that there is a stronger interaction between treated UHMWPE fibers and NR matrix [27].