**Van-Huy Nguyen 1,2, Cuong Manh Vu 3,\*, Hyoung Jin Choi 4,\* and Bui Xuan Kien <sup>5</sup>**


Received: 30 July 2019; Accepted: 21 August 2019; Published: 23 August 2019

**Abstract:** Nanosilica particles are extracted from waste water containing a hexafluorosilicic acid discharged from Vietnamese fertilizer plants as an effective way not only to reduce waste water pollution but also to enhance the value of their waste water. Amorphous nanosilica particles are produced with diameters ranging from 40 to 60 nm and then adopted as a reinforcing additive for natural rubber (NR) composites. Morphological, mechanical, rheological, and thermal behaviors of the nanosilica-added NR composites are examined. Especially, mechanical behaviors of nanosilica-filled NR composites reach the optimum with 3 phr of nanosilica, at which its tensile strength, hardness, and decomposition temperature are improved by 20.6%, 7.1%, and 2.5%, respectively, compared with the pristine vulcanized NR. The improved mechanical properties can be explained by the tensile fractured surface morphology, which shows that the silica-filled NR is rougher than the pristine natural rubber sample.

**Keywords:** natural rubber; nanosilica; mechanical property; fertilizer plant; hexafluorosilicic acid; waste water
