In this study, waste gypsum (WGS) was used as the filler in blend of high density polyethylene (HDPE) and ethylene vinyl acetate copolymer (EVA) in order to improve the flame resistance of this composite. After modification by ethylene bis stearamide (EBS), modified gypsum (EGS) at various contents was dispersed into HDPE/EVA (95/5 wt.%) blend by meltmixing method to obtain EGS/HDPE/EVA composites. The IR analysis of the EGS showed the interaction between EBS and gypsum. | Vietnam Journal of Science and Technology 56 (3B) (2018) 87-95 MECHANICAL PROPERTIES AND FLAME RESISTANCE OF COMPOSITE BASED ON HIGH DENSITY POLYETHYLENE/ETHYLENE VINYL ACETATE BLEND AND NOVEL ORGANICALLY MODIFIED WASTE GYPSUM Tran Huu Trung, Mai Duc Huynh, Do Van Cong, Nguyen Vu Giang* Institute for Tropical Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi * Email: nvgiang@; Received: 30 July 2018; Accepted for publication: 9 September 2018 ABSTRACT In this study, waste gypsum (WGS) was used as the filler in blend of high density polyethylene (HDPE) and ethylene vinyl acetate copolymer (EVA) in order to improve the flame resistance of this composite. After modification by ethylene bis stearamide (EBS), modified gypsum (EGS) at various contents was dispersed into HDPE/EVA (95/5 wt.%) blend by meltmixing method to obtain EGS/HDPE/EVA composites. The IR analysis of the EGS showed the interaction between EBS and gypsum. The difference in morphology of HDPE/EVA/EGS and HDPE/EVA/OGS composites was also observed in SEM images. By adding EGS and amounts of flame retardant additives such as ammonia polyphosphate and zinc borate, the thermal stability and the flame resistance of HDPE/EVA/EGS composites have improved and classified at V2 grade of UL94 standard. Moreover, the second self extinguishing time (t2) of EGS composite is shorter than that of unmodified gypsum (OGS) composite because of the quality char forming after the first burning and it plays a role as thermal barriers to protect material from heat of the second ignition. About mechanical properties, both tensile strength and elongation at break of the composite decreased with increasing the gypsum content and flame retardant additives because of filler aggregation. Keywords: waste gypsum, HDPE, EVA, flame resistance, ethylene bis stearamide. 1. INTRODUCTION Waste gypsum (WGS) has been known as a by-product of phosphate fertilizer production process. Normally, WGS is .
