A New Class of Biobased Paper Dry Strength Agents: Synthesis and Characterization of Soy-Based Polymers

Abstract

The goal of the current effort was to develop a new soy-based (soy flour) derivative to impart high fiber–fiber strength improvements to two-dimensional paper sheets. The success of the research hinged on successful proliferation of carboxylic and/or amine functionalities onto the polymeric backbone of the soy flour to significantly contribute to improved interfiber bonding of the paper–fiber sheets. Diethylenetriaminepentaacetic acid (DTPA) was reacted with soy flour in the presence of sodium hypophosphite and complexed with chitosan for the development of a new class of dry strength agents to improve integration into pulp fibers and thus increase interfiber bonding. The synthetic conditions including surface modifier concentration, time, temperature, pH, and material-to-liquor ratio were optimized. The paper materials incorporating the DTPA cross-linked (modified) soy flour agent demonstrated unprecedented tensile strength increases. A 1% soy protein flour–DTPA–-chitosan agent by mass of pulp-based slurry was thoroughly mixed before generating two-dimensional hand sheets whose tensile indices increased 52.6%, 53%, and 57.8% for recovered (OCC, old corrugated containerboard), NSSC (virgin) pulp, and kraft (virgin) pulp sheets, respectively. The modified soy flour agent-treated pulp sheets also provided significantly increased gloss and water repellency with diminished surface roughness.