An investigation of water crosslinking reactions of silane-grafted LDPE

Factors-including time, temperature, morphology, and thickness of sample, t he extent of silane grafting, and water concentration-that affect the fate and degree of water crosslinking reactions of the silane-grafted LDPE are i nvestigated. The gel content of the water-crosslinked sample increases with increasing time, temperature, and water concentration, but with decreasing content of the crystalline component in the sample and thickness of the sa mple. The relationship between the gel content and the crosslinking time is dependent on thickness and morphology of the sample, and the extent of sil ane grafting in the sample. The crosslinking rates and the resultant gel co ntent are inversely proportional to the content of crystalline component of tile sample, suggesting that the crosslinking reactions occur mainly in th e amorphous domain of the sample. For those samples with high resultant gel contents, the crystallizations of the samples are significantly enhanced b y crosslinking when the gel contents are higher than about 40%, leading to a dual relationship between the gel contents of the samples and the crossli nking times. For low temperatures, the rate-determining step of the crossli nking reactions is the diffusion of water, rather than the hydrolysis and t he subsequent condensation reactions of the silyl trimethoxy groups, For hi gh temperatures and high extents of silane grafting in the samples, however , the chemical reactions dominate the crosslinking process. The overall act ivation energy of the crosslinking reactions is dependent on thickness of t he sample. (C) 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 166-196, 2 001.