Effect of polymer structure and additives on silane grafting of polyethylene

Silane method is a preferred method in crosslinking polyethylene to modify its properties. Here, the silane grafting reactions of low density (LDPE), linear low density (LLDPE) and high density polyethylene (HDPE) were compared, all with a fixed amount of silane (vinyltrimethoxysilane) and peroxide (dicumylperoxide). Processing for silane grafting was carried out in an internal mixer, and FTIR spectra were used for comparing the silane grafting efficiencies. The effect of polymer physical form and pre-mixing the components was also determined. Molecular structure parameters were analyzed to investigate their effect on silane grafting efficiency. In case of LDPE and LLDPE, the probable interfering effect of two types of antioxidants on silane grafting reactions was studied. Ethylene propylene diene monomer (EPDM) was added to LDPE to evaluate its effect on silane grafting efficiency. Amongst different grades of polyethylene, LLDPE had a better efficiency in silane grafting. Branchings, PDI, Mw, and MFI are all determining factors and should be considered in comparing the silane grafting efficiency between different grades of polyethylene. In case of incorporating antioxidant, different results were observed when the polymer under study was different. EPDM as an additive would enhance silane grafting efficiency.