Study On The Structure And Properties Of HDPE/EVA Nanocomposites Irradiated By Electron Beam

Irradiation technology is widely applied to industrial, agricultural, biomedical sectors due to its overwhelming advantages such as no resistance to temperature, strong penetration power and easy control. Currently, irradiation tenchnology has become industrial development in electrical wire and cable, rubber vulcanization, foamed plastics, surface curing, medical sterilization and food irradiation. Ionized by high energy irradiation in polyolefins, macro-radiacals can combine with each other to form a crosslinking network structure which can increase the mechanical properties effectively.The present dissertation focuses on the structure and properies of HDPE/EVA nanocomposites irradiated by high energy electron beam. Effect of the irradiation on thermal and mechanical properties, combustion and rheological behaviours of irradiated HDPE/EVA nanocomposites are compared with un-irradiated ones. Four kinds of nano-fillers, C6o, MWCNTs, Clay and Mg(OH)2, are employed into the HDPE/EVA blend, and various measurements and characterization are used to confirm the structural change of the irradiated nanocomposites.Firstly, the structure and properies of irradiated HDPE/EVA/C60 nanocomposites are studied. The results show that at very low loading (≤2 wt%), C6o could remarkably improve the thermal stability, especially postpone the temperature of the maximum mass loss rate (Tmax) in air atmosphere. Meanwhile, C60 could prolong the time to ignition (tign) and dramatically reduce the peak heat release rate (PHRR), which implies that at very low loading, C60 could reduce the flammability greatly. After irradiation, it was proved that the "bridge" structure, between C60 and HDPE/EVA blend, increases the thermal oxidation degradation, storage modulus, glass transition temperature and mechanical properties. However, the flame retardancy of irradiated HDPE/EVA/C60 nanocomposites decreased.Secondly, the structure and properies of irradiated HDPE/EVA/MWCNTs nanocomposites are studied. The results show that at very low loading (≤2 wt%), MWCNTs could remarkably improve the thermal stability, especially postpone the Tmax in air atmosphere. Meanwhile, MWCNTs could dramatically reduce the values of PHRR but shorten the tign. After irradiation, the structure of MWCNTs was slightly destroyed but the contour structure kept intact. The network structure in the irradiated HDPE/EVA/MWCNTs nanocomposites increases the thermal oxidation degradation, storage modulus, glass transition temperature and mechanical properties. The flame retardancy decreased, which is similar to the results of the irradiated HDPE/EVA/C60 nanocomposites.Thirdly, the structure and properies of irradiated HDPE/EVA/Clay nanocomposites are studied. The intercalated structure was formed in HDPE/EVA/Clay nanocomposites, which could remarkably improve the thermal stability and postpone the Tmax. Meanwhile, at very low loading (1 wt%), clay could prolong the tign and dramatically reduce the values of PHRR, but when the content of clay is higher than 3 wt%, the values of PHRR increase. After irradiation, the flammability property of irradiated HDPE/EVA/Clay nanocomposites is reduced due to the increased layer space, which is different from the results of the irradiated HDPE/EVA/C60 nanocomposites and irradiated HDPE/EVA/MWCNTs nanocomposites.Finally, the properies of irradiated HDPE/EVA/Mg(OH)2 composites are studied. The degree of crosslinking network is enhanced with increasing the irradiation dose. The network structure improves the thermal stability, the temperature of melting, the heat of melting and the glass transition temperature of irradiated HDPE/EVA/Mg(OH)2 composites and does favor to the smoke suppression.