The two isolated biorefinery lignosulfonates (LSs), Na-LS and Ca-LS, both had a molecular weight of approximately 9000 Da. Fundamental lignin properties such as chemical structure, functional groups were analyzed. The two LSs showed slightly better to equal performance in modifying CWS rheology than a commercial dispersant naphthalene sulfonate formaldehyde condensate (FDN), despite they were less sulfonated than FDN.
The practical importance of this study is that the pilot-scale pretreatments that produced the two LSs also produced excellent bioethanol yields at high titer without detoxification and washing. This suggests SPORL pretreatment is a promising technology for economic bioconversion of under-utilized woody biomass.
Viscosity-reducing capacity of dispersants
The CWS prepared in this study was very viscous and did not flow under normal rheological testing conditions without the application of a dispersant. At application dosages of 0.75 and 1.0 wt%, similar performance in terms of modifying rheological properties of CWS was achieved when applying the two biorefinery LSs compared with the performance achieved using FDN (Fig. ). The apparent viscosity of CWS decreased rapidly with increasing shear rate, i.e., shear thinning behavior.
Replicate rheological tests at shear rate 100 (1/s) indicated that the standard deviations in apparent viscosity measurements were very low of less than 1 %, i.e., η100η100 = 624 ± 5.9, 698 ± 6.7, 857 ± 6.5 (mPa.s) for the CWS applied Na-LS, Ca-LS, FDN, respectively, suggesting the differences in modifying CWS viscosity by the three dispersants shown in Fig. were significant. CWS applied with Na-LS resulted in the lowest shear stress, suggesting Na-LS performed better than FDN for CWS to disperse and flow. It is generally believed that divalent Ca-LS is not a suitable dispersant for CWS due to the destruction of the double electrostatic layer. However, the results showed that the performance of Ca-LS is equivalent to Na-LS, perhaps due to the low amount of Ca.
The stress-shear rate curves at dispersant dosage of 1.0 wt% suggested the CWSs dispersed by Na-LS and Ca-LS were Newtonian like. However, the CWS dispersed using FDN had two viscosities which was also observed in a previous study .