MOLECULAR WEIGHT DISTRIBUTION IN GEOMEMBRANE

The molecular weight distribution (MWD) is a fundamental polymer property which determines the processability and the end use properties of the polymer. Since an increase in the molecular weight of a polymer improves the physical properties, there is a strong demand for polymers having high molecular weights. However, it is the high molecular weight molecules that render the polymer more difficult to process. A broadening in the molecular weight distribution tends to improve the flow of the polymer when it is being processed at high rates of shear as the low molecular weight tail acts as a “processing aid” for the higher MW chains.

Thus due to the high viscosity of higher molecular weight resins such as low HLMI HDPE used for geomembranes, the molecular weight distribution becomes a very important consideration in the processability of these HDPE resins. Resin manufacturers can tailor the molecular weight distribution (MWD) by catalyst and process selection. Geomembrane resins benefit from a broad to very broad distribution. While narrow distribution resins are tougher than broad distribution resins (at equivalent molecular weights), processability becomes easier as the MWD broadens. Table shows the effect of molecular weight distribution on polymer geomembrane properties.