Molecular Weight Determination of Lignin-based Superplasticizer GCL1-JB

The molecular weight (M-w) of the lignin-based superplasticizer GCL1-JB was determined by static light scattering (SLS) and gel permeation chromatography (GPC). Results showed that the M value determined by SLS (M-w,M-SLS) was much larger than that determined by GPC (M-w,M-GPC) because of the, polyelectrolyte effect and aggregation behaviors. To determine the real M-w of GCL1-JB by SLS,NaCl was added into the GCL1-JB solutions to restrain the polyelectrolyte effect, and the GCL1-JB dissolved in NaCl solution was further filtered by micro-filtration membrane with suitable pore size to remove the GCL1-JB aggregates. During DLS measurement of GCL1-JB,there existed two diffusion peaks :a fast mode and a slow mode. The fast mode is related to the GCL1-JB single molecules, and the slow mode is related to the polyelectrolyte effect and the GCL1-JB aggregates. The slow mode was inhibited gradually by adding NaCl followed by filtering, and finally disappeared when NaCl concentration reached 0.1 mol/L. With disappearance of the slow mode M-w,M-SLS was determined to be 121300, which was considered to be the real Mw of GCL1-JB. single molecules. M-w of GCL1-JB determined by SLS at this stage was still larger than that determined by GPC because of the difference in conformations between GCL1-JB and GPC standards (NaPSS). The conformations of GCL1-JB was more curling than that of NaPSS; therefore, when NaPSS was used as the GPC standard, the M-w,M-GPC was smaller than the true M-w of the GCL1-JB. This work provides a method to determine the true M-w of GCL1-JB, which is significant for determining the absolute M-w of lignin and its derivatives that having polyelectrolyte effect and aggregation behaviors.