Quantifying Polymer Loading in Bentonite-Polymer Composites Using Loss on Ignition and Total Carbon Analyses

Abstract

Three methods were evaluated to measure polymer loading in bentonite-polymer composites (BPCs): component loss on ignition (LOI), composite LOI, and composite total carbon (TC). Component methods are based on a series of measurements (e.g., LOI) conducted independently on bentonite and polymer components. Composite methods are based on a series of measurements (e.g., LOI or TC) conducted on BPCs with known polymer loadings. All three methods were evaluated using three different BPCs, with polymer loading ranging from 20 to 100 g polymer/kg BPC. Polymer loading measured with the component LOI method was biased because of the effects of the bentonite on thermal degradation reactions occurring in the polymer component. Polymer loading of unhydrated BPCs measured with the composite LOI or TC methods showed no polymer-dependent bias. Measured polymer loading deviated from actual polymer loading by an average of −3.3 to 0.1 g polymer/kg BPC for the composite LOI method, and by an average of 2.5 to 3.8 g polymer/kg BPC for the composite TC method. Hydration of the BPCs influenced the accuracy of the composite LOI method, which produced consistently lower polymer loading measurements for BPCs hydrated with DI water than 50 mM CaCl2. In contrast, polymer loading measured with the composite TC method was not measurably different for hydrated and unhydrated samples. The composite LOI method is recommended for quality control testing on BPCs prior to hydration, whereas the composite TC method is recommended for testing BPCs prior to and/or following hydration.