عنوان مقاله [English]
Background and objectives: Many additives are usually used in wet end papermaking in different sections for specific goals. When using several additives, the sequence of adding materials often influences differently on final paper properties. In this research, the sequence of adding cellulose nanofibers, cationic starch and polyacrylamide to pulp and their impact on drainage time, handsheet density and tensile strength were investigated.
Materials and methods: In this research, bagasse bleached pulp from Pars paper mill, supper grinded cellulose nanofibers, cationic starch with 0.035 mol/mol substitution degree, and high molecular weight and low electrical charge cationic polyacrylamide were used. Prior to make papers, 3% cellulose nanofibers (with 0.3 % concentration), 1% cationic starch (with 0.5 % concentration), and 0.3% cationic polyacrylamide (with 0.05 % concentration) were added in different orders to bagasse pulp to make handsheets.
Results: The results showed that adding materials in every sequence increased density, tensile strength, and drainage. The best sequence of two adding materials was for adding cationic polymer firstly and cellulose nanofibers secondly to dilute pulp suspension through which it is assumed that fibers and cationic polymers make large agglomerates which break to smaller fractions afterwards with shear force. In the following, adding cellulose nanofibers and being absorbed to cellulose fiber networks resulted in paper higher tensile strength and a limited increase in drainage. Between the sequences of adding three materials, tensile index and density of papers showed no significant differences. Nevertheless, adding three materials in every sequence increased tensile strength significantly compared with two materials and control specimen. In addition, when cationic starch is added firstly the least drainage time and when cellulose nanofibers added firstly the highest drainage time were observed. Furthermore, in specimen with three adding materials, the highest thickness was measured when cellulose nanofibers had been added firstly.
Conclusion: using cellulose nanofibers together with cationic starch and polyacrylamide, while implementing shear forces, retains micro and nano fines and can increase paper density and pulp drainage time. To sum up the influences of additive sequences on tensile, density and drainage, it can be concluded that the sequence of adding two materials of cationic starch at first and cellulose nanofibers at second, and the sequence of adding three materials in the order of cationic starch, polyacrylamide, and cellulose nanofibers respectively were introduced as the best orders for papermaking from bagasse pulp to be able to gain the highest tensile strength and the least drainage time.