In-process rheometry studies of LDPE compounds - Part II: Magnesium hydroxide filled

The second part of a comprehensive study into the investigation and validat ion of in-process measurements on a low. density polyethylene compound duri ng extrusion is reported. A commercial grade of branched low a density poly ethylene was used in the study, compounded with various levels of magnesium hydroxide flame retardant filler, up to 50 %; by weight. In-line and on-li ne rheometry were used to monitor melt flow behaviour during single screw a nd twin screw extrusion; off-line capillary rheometry was performed on the compound before and after extrusion, to examine any change in rheology. Mor phological observations were made using scanning electron microscopy, and m olecular characterisations carried out using gel permeation chromatography. in-process rheometry, was found to be able to detect the presence of fille r at low and high loadings, brit was unable to discriminate between interme diate levels. Offline rheometry indicated that twin screw extrusion altered the rheology of the compound. and capillary wall slip was found to increas e after extrusion. Morphological observation indicated that filler in the c ompound was better dispersed after extrusion, especially at high volume fra ctions. Molecular weight and polydispersity of the LDPE were shown to incre ase after extrusion, more so in the case of low filler loadings. Overall, i n-process measurements provided useful rheological data, and the compound w as found to exhibit complex, process-dependent rheology.