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Abstract
In the present work, the silane grafting and water cross-linking of low density polyethylene (LDPE) were investigated. The grafting reaction was carried out in an internal mixer and polyethylene cross-linking was done in hot water. The effect of silane, peroxide, catalyst, carbon black, cross-linking time, and cross-linking temperature on the grafting and cross-linking processes are reported. Vinyl trimethoxy silane (VTMO) and di-cumyl peroxide (DCP) were selected as grafting agent and initiator respectively. Silane grafting on polyethylene was determined using Fourier transform infrared (FTIR) spectroscopy and torque monitoring of the mixer. Absorption peak due to –Si–OCH3 groups in FTIR and torque increasing due to silane grafting in the mixer illustrated that silane-grafting reactions occurred. The FTIR data demonstrated that the extent of silane grafting was increased as the concentration of silane and peroxide was increased. Thermogravimetry analysis (TGA) determined that the thermal stability of LDPE increased by increasing the amount of silane grafting. Gel fraction increased with silane and peroxide concentration. As the percent of of catalyst increase the time scale for specified gel content shifted to shorter times. Incorporation of carbon black into LDPE decreased the extent of silane grafting and gel fraction. Water temperature increasing in cross-linking stage reduced the time to maximum degree of cross-linking.