Starch-derived Cationic Inclusion Complexes And Polyelectrolyte Complexes For Papermaking Applications

Starch is oftentimes praised as an "inexhaustible" renewable resource.Starch and its derivatives are an important group of bio-based additives for papermaking applications.The efficient use of sustainable starch-derived additives fits well into the concept of green economy.In this project,the existing theories for the formation of starch inclusion complexes and starchbased polyelectrolyte complexes were used as a driver for identifying new possibilities associated with the use of starch in paper production.Key hypotheses of the current study are:Since both unmodified starch and cationic starch can form inclusion complexes upon contact with guest molecules,the combination of unmodified starch and a small amount of cationic starch would allow the fabrication of starch-fatty acid complexes with cationic characteristics.The anchoring of these complexes onto mineral filler particles would enhance filler-fiber interaction in paper production.Due to the amphiphilic nature of surfactant molecules,the interaction of unmodified starch with a cationic surfactant would allow the trapping of the hydrophobic tails inside the helical structures.In this case,the hydrophilic heads(i.e.,cationic groups)would somehow stay outside the helical structures.This unique selfassembly would lead to the fabrication of cationic inclusion complexes with favorable interaction with other components of the papermaking stock.The interaction of cationic starch with anionic starch in the presence of unmodified starch granules suspended in an aqueous medium would allow the in-situ anchoring of starch-based polyelectrolyte complexes,leading to enhanced interaction of starch granules with other components of the papermaking stock.The results relevant to starch-fatty acid complexes showed that,cationic inclusion complexes were easily formed on the basis of the combined use of unmodified starch and a small amount of cationic starch,and these complexes were then anchored onto mineral filler particles.The “starch precipitation efficiency” was found to be closely related to the dosage of cationic starch.Specifically,“starch precipitation efficiency” was above 90% at the cationic starch dosage of 3%(based on the total dry weight of unmodified starch and cationic starch),however,a high cationic starch dosage was unfavorable for efficient starch deposition.Surface engineering of mineral filler particles with the aforementioned starch-based cationic complexes resulted in significant enhancement of filler bondability factor and filler/starch retention.The results relevant to starch-surfactant complexes showed that,unmodified starch interacted with hexadecyltrimethylammonium chloride(a cationic surfactant)in an aqueous medium,leading to the decrease in the “blue value”.This change in “blue value” suggested the formation of inclusion complexes.The wet-end addition of starch-surfactant complexes resulted in pronounced enhancement of filler retention and filler bondability factor,particularly when the dosage of hexadecyltrimethylammonium chloride was 6%(based on the dry weight of unmodified starch).Interestingly,the impact of starch-surfactant complexes as regards filler bondability increment was found to be better than that of a commercial cationic tapioca starch(degree of substitution of 0.036),under otherwise identical conditions.The interaction of anionic starch with cationic starch in the presence of unmodified starch granules suspended in an aqueous medium resulted in the precipitation of starch-based polyelectrolyte complexes onto these granules,which led to the formation of surfaceengineered starch granules.Encouragingly,this surface engineering concept directed the retention of total starch in paper production towards around 100%,when the dosage of anionic starch was 10%(based on the dry weight of anionic starch and cationic starch).This surface engineering concept was also found to be quite effective in enhancing filler retention and filler bondability with cellulosic components.