Study On The Modification Of Calcium Carbonate In Reconstituted Tobacco By Papermaking And Its Retention Mechanism

As a functional filler,calcium carbonate is widely used in rubber,plastics,paper and other industries.Adding calcium carbonate in paper-making reconstituted tobacco can not only reduce the production cost,but also effectively improve the physical and chemical properties of the finished products.The main problems in the application of reconstituted tobacco filler are:calcium carbonate filler is easy to lose in the process of copying,resulting in low retention rate,white water pollution,abrasion of copying machine,uneven filling of sheet base,etc.Aiming at the practical problems of current application,the retention mechanism of chitosan and guar gum as two retention aids for tobacco pulp was studied in this paper.Chitosan was used as a modifier to modify calcium carbonate in order to improve the retention rate of calcium carbonate in paper-making reconstructed tobacco.To study the effect of guar gum and chitosan on the micromorphology of tobacco pulp and the retention mechanism of different retention aids by the MorFi Compact fiber analyzer,changes in the micromorphology of the tobacco pulp fibers and the fiber fines were studied by adding different dosages of guar gum and chitosan.The results indicated that the retention mechanisms of guar gum and chitosan on fibers and fiber fines were different.Addition chitosan,components of pulp intertwined to form a spatial reticular through the neutralization effect that consists of tobacco fiber bundles,fiber fines and fillers.The reticular size increased,fiber fines（especially those below the detection limit）and fillers bonded with chitosan to combined with fiber and fiber fines.Guar gum wrapped the fiber through"nucleation and growth"to achieve the retention effect.Multivariate linear fitting using SPSS Statistics 22,the equation for adding for chitosan was found through multiple linear fitting to be Y=48.041-0.064x_∣PCD∣+1.328x_kink;for guar gum,it was found to be Y=80.780-0.034x_∣PCD∣-0.513x_∣Zeta∣.Furthermore,at the same time,the results of the linear fitting of the retention rate and ln(x_∣PCD∣)indicate that ln(x_∣PCD∣)and slope k can be used as characteristics value to characterize the retention effect of pulp.The modified calcium carbonate coated with chitosan was prepared by alkali deposition method.The effects of crystal form of calcium carbonate,degree of deacetylation of chitosan and amount of Chitosan on the properties of modified calcium carbonate were studied.The modified calcium carbonate was characterized by XRD,SEM,FT-IR,particle size,Zeta potential and specific surface test.Scanning electron microscopy images showed that chitosan was selectively adsorbed on the crystal surface of calcium carbonate,the selective adsorption of chitosan on the crystal surface of calcite（104）was also found.Infrared spectroscopy showed that chitosan had hydrogen bonds with the surface of calcite and aragonite crystalline calcium carbonate,forming a coating.The degree of deacetylation of chitosan and the amount of chitosan added have great influence on the particle size and Zeta potential of modified calcium carbonate.The application of modified calcium carbonate in tobacco pulp and bleached hardwood pulp can obviously improve the retention rate of fillers.The optimum process combination of modified calcium carbonate is:in bleached hardwood pulp,When aragonite calcium carbonate was used,the deacetylation of chitosan was 58.16%,and the retention rate of modified calcium carbonate was 91.66%when chitosan content was 3%.When aragonite calcium carbonate was used,chitosan deacetylation was 82.25%,and the retention rate of modified calcium carbonate was 93.03%when chitosan content was 5%.Modified calcium carbonate improves the retention of fillers mainly by colloidal adsorption and mechanical interception.It can be found that broken calcium carbonate has more active sites which help to adsorb on the surface of fibers.At the same time,spindle-shaped calcium carbonate helps to form"bridging"and improve the retention rate.