RECYCLING OF WET-STRENGTH TISSUE PAPER. PART 2. BASIC PROPERTIES OF SECONDARY FIBERS
The present investigation focuses on morphological characteristics, tensile and optical properties of secondary fibers obtained in various conditions of batch low-consistency repulping process for wet-strength tissue paper with 100% of bleached softwood kraft pulp. It was found that length-weighted fiber length and fiber width values as well as fiber length and fiber width distributions remained almost unchanged regardless of the repulping time and the presence of persulfates. The shortened repulping cycle due to the use of persulfates lead to an increase in the shape factor from 83.0% to 84.1-84.4%, decrease in the number of fiber kinks from 0.84 to 0.72-0.74 and an increase in zero-span tensile strength of recycled handsheets by 10-12%. At the same time, the shortened repulping cycle resulted in increase in the coarseness of secondary fibers from 190 mg/m to 230-235 ;mg/m leading to a slight increase in the bulk of the paper and a decrease in its internal bond strength by an average of 8%. The use of persulfates during wet-strength tissue paper repulping improves the color of recycled handsheets and its brightness by up to 3%.