Boosting the elongation potential of paper by mechanical refining and additives

Abstract

The procedures used in restraining the web during drying will severely affect paper properties. In this work, the main differences between restrained drying and unrestrained drying on paper properties were identified. The mechanical properties of paper were studied as a function of low-consistency mechanical refining energy; wet-end additions of carboxymethyl cellulose (CMC) with cationic starches; as well as spray addition of alginate, chitosan, and cationic guar gum. After restrained drying, the tensile index and tensile stiffness increased with increasing refining energy, but the elongation at break was severely limited. After unrestrained drying, the elongation at break increased linearly with increasing refining energy. However, unrestrained drying also resulted in significantly lower tensile index and tensile stiffness values. After restrained drying, the largest increases in tensile index and stiffness were obtained by sequential wet-end addition of CMC and cationic starches. Certain combinations could mitigate all of the decrease in tensile index from unrestrained drying, while maintaining the distinctively high elongation potential of the paper. Wet-end addition of CMC and cationic starches could mitigate some of the decrease in tensile stiffness, but not completely. Spray addition of alginate, chitosan, or cationic guar gum increased the tensile index after both restrained and unrestrained drying. Spray addition of alginate resulted in significant increases in elongation at break and two-dimensional formability of the handsheets after unrestrained drying. After restrained drying, the tensile stiffness increased after spray addition of all of the different polysaccharides. After unrestrained drying, however, stiffness was unaffected by all of the tested polysaccharide spray additions. The same pulp treatment/additives will increase either stiffness or stretch, depending on the drying technique, but both properties could not be maximized simultaneously.