Uncooked,Unmodified Starch Granules And Starch- Derived Polyelectrolyte Complexes For Improving Filler Bondability And Paper Strength

Besides mineral fillers and pigments, commercially available papermaking chemical additives can mainly be divided into two groups:(1) bio-based additives and (2) synthetic chemical additives. Starch and its derivatives are essentially the dominant bio-based chemical additives used in the pulp and paper industry. On the other hand, the widely-used synthetic chemical additives include styrene-butadiene latexes, polyacrylamide, polyamidoamine-epichlorihydrin, etc. In the context that the global pulp and paper industry are moving towards a green economy, the more efficient, widespread use of bio-based chemical additive would be of strategic significance.The main motivation associated with this project was to enable the efficient use of unmodified, uncooked starch and starch-based polyelectrolyte complexes in cellulosic paper, so that new, easily-scalable processes capable of delivering significant enhancements in both filler bondability and paper strength would be developed. The key concepts and hypotheses are: (1) on the basis of existing fundamentals pertaining to microparticulate retention and drainage aid systems, pretreatment of unmodified starch granules with a high-molecular-weight, low-charge-density cationic polymer prior to their addition to filler-containing cellulosic fiber slurry followed by the incorporation of an anionic microparticulate material can result in efficient entrapment of unmodified starch granules in cellulosic fiber networks, and the gelatinization of unmodified starch granules upon subsequent drying and the formation of starch-based macro molecular films in all directions of the cellulosic networks would lead to significant paper strength enhancement; (2) coaggregation of unmodified starch granules and mineral filler particles induced by sequential application of a high-molecular-weight, low-charge-density cationic polymer and an anionic microparticulate material can result in the formation of cellulose-bondable starch-mineral composites; (3) on the basis of intermolecular interaction between a cationic polymer and an anionic polymer in an aqueous medium, the sequential addition of an anionic polymer and a cationic polymer to mineral filler slurry can initiate the in-situ formation of polyelectrolyte complexes, which can be deposited, anchored onto the filler surfaces, thus enhancing filler-fiber interaction in cellulosic networks.On the basis of the above-mentioned concepts and hypotheses, the key process parameters including dosages of various polymers were investigated, and the effectiveness of these concepts/hypotheses were identified. In terms of the use of unmodified starch granules, the starch pretreatment with cationic polyacrylamide or the starch/filler coaggregation induced by the combined use of cationic polyacrylamide and bentonite played a dominant role in retaining starch granules in cellulosic networks, and hence delivering significant paper strength increment. Such an increment was highly dependent upon key process parameters, such as the dosage of cationic polyacrylamide. The interaction between cationic starch and anionic starch in the presence of filler particles resulted in pronounced improvement in both filler bondability and paper strength. Interestingly, a synergy between cationic starch and anionic starch as regards filler bondability was identified, and cationic-to-anionic weight ratio was the key parameter determining the efficiency of the resulting starch-derived polyelectrolyte complexes. These research findings and implications would provide a useful basis for enabling the efficient use of starch-based chemical additives cellulosic paper-based products and enhancing the value of mineral fillers for papermaking wet-end applications.