Anchoring Starch Inclusion Complexes Onto Precipitated Calcium Filler Particles For Improving Their Use In Papermaking

Calcium carbonate is one of the commonly used mineral fillers in the paper industry. The use of calcium carbonate as a filler material can contribute to cost/energy savings and improvements in optical properties, printability, and writability of cellulosic paper products. However, the increase in the amount of filler particles has a negative impact on paper strength. Thus, the improvement of bondability of filler particles with cellulosic fibers is critical for maximizing the potential associated with filler addition.According to the existing basics related to the formation of starch inclusion complexes, certain small guest molecules can enter into the helical structure of starch, leading to the formation of inclusion complexes. In an aqueous medium, the increase in the water solubility of cooked starch upon the introduction of small guest molecules with high hydrophobicity provides the possibility of starch precipitation/deposition. In this context, the hypothesis of calcium-ions-induced deposition of starch/fatty acid complexes and starch/rosin complexes on filler particles was proposed, and the impact of filler modification was determined based on various parameters including "filler bondability factor".In the presence of calcium ions, starch/fatty acid complexes and starch/rosin complexes were deposited onto filler particles. Due to the fact that either strong acids or weak acids were not used as precipitation agents, the proposed concept of filler modification can be applicable to acid-unstable calcium carbonate filler particles. Both sodium oleate and rosin soap were found to have significant interactions with starch, leading to the formation of inclusion complexes. In-situ deposition/encapsulation of these complexes on filler particles was induced by the action of extra calcium ions. As a result of filler modification, the interactions of filler particles with pulp fibers were improved, and "filler bondability factor" was significantly increased (> 100% at certain conditions). Thus, the negative impact of filler addition on paper strength was mitigated by employing the proposed concept of filler modification. A noticeable improvement in filler retention in the paper-sheets was also identified. Simultaneously, the anchoring of starch inclusion complexes to filler particles resulted in improved acid-tolerance. Furthermore, filler modification led to pronounced improvement of the efficiency of alkyl ketene dimer (AKD) sizing agent.