The molecular weight (Mw) of the lignin-based superplasticizer GCL1-JB was determined by static light scattering (SLS) and gel permeation chromatography (GPC).Results showed that the Mw value determined by SLS (Mw

SLS) was much larger than that determined by GPC (Mw

GPC) because of the polyelectrolyte effect and aggregation behaviors.To determine the real Mw 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

Mw

SLS was determined to be 121300

which was considered to be the real Mw of GCL1-JB single molecules. Mw 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 Mw

GPC was smaller than the true Mw of the GCL1-JB.This work provides a method to determine the true Mw of GCL1-JB

which is significant for determining the absolute Mw of lignin and its derivatives that having polyelectrolyte effect and aggregation behaviors.