Determination of gel content of silane cross-linked polyethylene copolymers using FTIR technique

Silane cross-linking of metallocene-based polyethylene-octene elastomer (POE)/linear low density polyethylene (LLDPE) blend was carried out using two-step Sioplas process in an industrial scale twin-screw extruder. In the study, grafting and cross-linking reactions of vinyl trimethoxy silane (VTMS) were analyzed using FTIR technique. It was found that the cured compound showed absorption peaks at 1078 cm-1 and 955 cm-1 related to Si-O-Si bonds. A peak was also observed at 3405 cm-1 of hydroxyl group produced from hydrolysis of methoxyethylene group during of curing process, reflecting that curing reaction was not completed. The samples were cured at different time intervals (15 min-16 hours). The gel content values determined by solvent extraction and FTIR were in good agreement at curing times more than 4 hours. The efficiency of the silane grafting reaction was determined using the ratio of the absorption peak at 1092 cm-1 characteristic of methoxy to the transmittance peak at 1378 cm-1 characteristic of methyl group, which  is considered as the internal standard. The results showed the highest efficiency of silane grafting reaction at 5 w% of VTMS with the least amount of internal standard ratio (0.029), at which the lowest MFI value, and the highest values for gel content, tear strength, compression set and hot set 200 °C were obtained.