The Fundamental Characteristics Of Alkali Recovery White Lime And Its Influence On AKD Sizing

White lime is a kind of by-product in alkali recovery process. The conventional approachwas not only a waste of resources, but also likely to cause environmental pollution. The usageof white lime, especially which from non-wood pulp alkali recovery, as filler in papermakingwas a good way to solve both of the problems above. However, many problems still existedwhen white lime was filled, low efficiency of AKD sizing was one among them. Thus, whitelime, even refined, was probably unable to completely replace commercial precipitatedcalcium carbonate. In order to clarify the difference between white lime and commercialcalcium carbonate and improve AKD sizing efficiency, differences of basic characteristics andfilling performance were investigated between commercial calcium carbonate and refinedwhite lime from reed pulp alkali recovery in Yueyang paper mill. Then the white lime wasmodified by coating with starch-sodium stearate complex, and the effects of some wet endadditives on AKD sizing optimization were investigated.The basic characteristics of the white lime and commercial calcium carbonate werecompared firstly, and then the drainage&retention performance, AKD sizing effect andphysical properties of the filled paper sheet. The results showed that the white lime was lowerin brightness and15.6%higher in the specific surface area. The white lime particles whichwere amorphous in microstructure had a wider size distribution. When filled, the white lime’sdrainage rate and retention rate is slightly higher, while the sizing degree of the paper sheetwas much lower, especially under heavy filler load. Besides, some of the physical propertyindexes of the filled paper increased while others decreased.Subsequently, the white lime particles were coated with starch-sodium stearate complexand variation of the basic characteristics as well as its filling effects were investigated. Theresults showed modified white lime had a wider size distribution and an increased ratio oflarge particles. Zeta potential and specific surface area decreased by28.3%and35.1%separately and hydrophobicity was obtained. Loading application revealed that the sizingdegree could reach100.5%of that commercial calcium carbonate filled paper under22%filler loading. The sizing degree of the paper sheet increased by119%and sizing loss ratioafter a month declined by24.9%when the filling load was42%. Improved retention, overallenhanced paper strength and slightly decreased optical properties were also observed.In addition, the influence of PAE, PEI and chitosan, which were used as sizing promoters,on AKD sizing efficiency and the mechanism thereof was investigated. The study found that the sizing degree of26%white lime filled paper could be respectively increased by63.3%,50.2%and38.4%as long as the three sizing promoters, PAE, PEI and chitosan were added atthe optimal dosage and sequence. Curing time and temperature could have significant impacton the effect of the three sizing promoters above. Mechanism analysis revealed that all thethree sizing promoters were able to eliminate anionic trash, while only PAE could promote theesterification reaction between AKD and fibers.