Date of Award
Bachelor of Science
Paper Science and Engineering
The recycled paper industry has seemingly grown faster than the technology to go along with it. It has become accepted that along with paper recycles comes a certain amount of strength loss, limiting the uses of secondary fiber. If the recycling industry is continued to grow an effective counter to this strength loss needs to be found. In order to counteract this strength loss the mechanism must first be better understood. The three mechanisms that will be focused on for this paper will be 1) The loss of fiber length, 2) Hornification, and 3) The decrease in surface bonding activity. The experimental portion of this project is designed to let two of these mechanisms be eliminated, allowing the third to be more closely examined.
Never-dried softwood fiber was recycled three times; with samples taken at 0, 1, and 3 recycles. Each of these three samples are then screened twice: first using a 150 mesh sieve to extract fines, and secondly using a 32 mesh screen to increase the homogeneity of the long fibers. Handsheets were then made with each of the long fiber/fine combinations and tested for burst, tensile, and Scott Bond.
The results show the extreme importance of fines to paper strength. It was found that by adding never-dried fines to thrice recycled long fibers, the tensile strength could be raised almost 20%. As a matter of fact, even the addition thrice recycled fines increased all of the strength properties tested. The most dramatic change was seen with Scott Bond, which almost doubled with the addition of fines. This data as a whole shows hornification to be the largest contributor to strength loss because of the fact that even the thrice dried fines bond well.
This experiment could have been more valuable had the recycles been taken to a point where the fines began having a negative effect on bonding. No sources could be found that suggested fines would have a positive effect for even three recycles.
Pschigoda, Lon E. II, "A Study of the Effect of Recycling on the Bonding Ability and Characteristics of Fines" (1996). Paper Engineering Senior Theses. 444.