Batch Light Scattering Study of Microgel Formation in Film Resins, 1998 Polymers, Laminations & Coatings Conference Proceedings

Microgels can cause processing problems in polyethylene because the microgel fractions of the melt possess extremely high melt viscosities compared to those of linear polyethylene. Comparing zero shear viscosity measurements with high shear viscosity measurements using rheology techniques can preliminarily indicate the presence of microgels. Further indication of the presence of microgel content can be shown by Temperature Rising Elution Fractionation (TREF) experiments, which can detect the presence of high melting fractions. However, when confirming gel presence by Gel Permeation Chromatography (GPC) methods, microgels (due to their high size) tend to be filtered by the columns and not detected. Furthermore, since microgels are formed in the high molecular weight region (as high molecular weight species combine to form microgels), traditional GPC methods may even show a contradictory decrease in high molecular weight content (as the even higher molecular weight content is undetectable by this method). This contradictory data in terms of gel presence vs. standard GPC techniques can be resolved through the batch light scattering technique which can measure the total molecular weight content of the sample (including both the separated polymer molecules and the gelled molecular weight species). Comparison between on-line chromatographic light scattering detection and batch light scattering detection can be used effectively to discern whether a change in molecular weight is due to changes in the molecular weight of the base polymer distribution or if it is caused by changes in the microgel content.