Synthesis, Characterization, and Applications of Polymer-grafted Lignin Surfactants

Surfactants are among the broadest class of compounds utilized in industrial applications. However, many industrially used surfactants have detrimental environmental effects and are primarily derived from petroleum-based feedstocks. A
green surfactant based on lignin, a biopolymer found in plant cell walls, could potentially serve as a renewably sourced surfactant for dispersant and emulsion applications. As a
major waste by-product of paper production generating a use for lignin surfactants could lead to a commercially viable renewable feedstock and create another avenue for utilizing
this waste material. Lignin derivatives, primarily lignosulfonates, have seen extensive application as dispersants in cement formulations but have been slowly replaced in recent decades by more active petroleum-based synthetic polymers. In this work we sought to develop lignin surfactants by augmenting lignin’s natural surfactant activity through the grafting hydrophilic of polymers onto a lignin core. Primarily focusing on utilizing kraft lignin and lignosulfonate cores, this thesis looks at the interplay between lignin core and polymer graft length to determine design principles for cementitious and agricultural
formulations. Chapter 2 in this thesis outlines a synthetic strategy for grafting lignin cores with hydrophilic polymers under basic, aqueous conditions and examining their ability to function as emulsifiers. This strategy was developed with poly (ethylene glycol) methyl ether (mPEG) grafts utilizing a classic SN2 grafting strategy. These polymer grafted
lignins (PLGN) were then examined for their activity at air-water and oil-water interfaces and exhibited significantly greater activity than the unmodified lignin cores. It was found that higher levels of interfacial activity were exhibited by PEGylated lignins containing hydrophobic kraft lignin cores and shorter PEG graft lengths. Building upon the now
known activity of these polymer grafted lignins we sought to utilize them as dispersants in cement and as emulsifiers in agricultural formulations. In Chapter 3 we showed that polymer grafting lignins via the strategies discussed
in Chapter 2 improves the dispersing capability of the lignins in cement formulation systems. The grafting strategy was shown to work well with varying PEG graft lengths as
well as with hydrophilic acrylic polymers, poly (methacrylic acid) (PMAA) and poly (sulfopropyl methacrylate) (PSPMA). Slump, a measure of cement dispersing capability, was increased by lignins grafted with PEG, PMAA, or SPMA polymer grafts with PMAA grafts having the largest effects. The polymer grafted lignins with the charged, hydrophilic lignosulfonate cores also exhibited better dispersing abilities likely due to the electrostatic interactions the of the lignosulfonate core with the highly charged cement
mixture. While the polymer grafted lignins do not perform as well as commercially standard poly (carboxylate ether)s (PCE), the significant increase in dispersing ability
gained by grafting charged polymers to the lignin core indicates potential for lignins to be viable in future cement applications. Chapter 4 covers the steps utilized for market research on the viability of the PEGylated lignin surfactants synthesized in Chapter 2. This study was utilized to
determine the value propositions of the PGLNs and future directions for the project. It was found that the value proposition of being a multi-functional. green dispersant was of interest in agricultural applications leading to these applications being explored further in Chapters 5 and 6. Chapter 5 of this thesis takes a closer look at tank-mix agricultural applications, in which polymer grafted lignins with high oil-water interfacial activity were desired. The
highly active PEGylated lignins synthesized in Chapter 1 were then formulated with the herbicide formulation, clethodim 2EC, and sprayed on v2 stage corn plants to examine whether they increased the effectiveness of the herbicide. Results imply that an increase in clethodim 2EC effectiveness was found in formulations containing the PEGylated kraft lignin with the short PEG chain. The increase in effectiveness was comparable to commercially available industrial standards, Superb HC and Prime Oil, thus indicating a potential application for these polymer grafted lignins. Chapter 6 builds upon the agricultural applications in Chapter 5 to further explore agricultural formulations using least absolute shrinkage and selection operator (LASSO) regression analysis techniques to quantitatively identify the physiochemical properties
important to formulation biological activity with the aim of designing an optimal formulation containing polymer-grafted lignins. Emulsion concentrate (EC) agricultural
formulations dependent on oil-water interactions were examined using the oily herbicide clethodim while water dispersible granule (WDG) formulations will be examined using the solid herbicide cloransulam-methyl. Examining both EC and WDG formulations aided in creating a stronger understanding of polymer grafted lignins’ emulsifying and
dispersing capabilities.