Date of Award
Bachelor of Science
Paper Science and Engineering
The recycle movement is now bigger than ever, with more reasons than ever. Recycling has the potential to save the world's landfills millions of cubic feet per year of precious space, as well as preserve our natural supply of virgin timbers. The recycling effort has sparked many questions over the years for papermakers. One big question is "how will repeated beating of fibers affect recycling potential?, and how will the effects differ between chemical and mechanical pulps"?
Chemical pulps have been found to lose strength from recycling. By becoming stiffer, chemically pulped fibers lose critical bonding area and flexibility, whereas, mechanical pulps have been recycled with little or no constant trend on fiber strength as recycling increases. It is thought that mechanical pulps actually soften and become more pliable with increased recycling, therefore increasing bond area and strength.
The purpose of the experiment was to investigate the recycled fiber potential of mechanical pulps. The experiment was carried out using a softwood, pine TMP pulp supplied by a mill located in the state of Washington. Initially, handsheets were formed before any beating took place, to serve as a control group. The initial batch of handsheets were tested for strength properties and then beaten to a target freeness of 122CSF, this cycle of testing, repulping and beating was carried out four times.
The results of the experiment revealed and interesting trend. It was found that strength in the form of tensile wet and dry, breaking length, burst index, and scott bond all reached a strength maxima after the second recycle. After the maxima was reached strength declined through the third and fourth recycles.
Zero span tensile indicates no appreciable fiber strength loss was found throughout the recycling process. This would suggest strength gains were derived from increased bonding. Increased bonding was thought to be achieved by fiber softening and fiber unravelling, which produced greater available bond area. The production of short fibers also aided in producing increased bond area. It is believed that after two recycles, the fiber stabilized. The decrease in strength is believed to be a function of fiber shortening.
It should be mentioned that some fines were lost in handsheet making process. White water was not recycled back into the forming machine, and so some of the fines produced in the PFI mill were lost. It would also have been beneficial to utilize a fiber flexibility tester to quantify fiber flexibility.
Draze, Bill D., "The Effects of Recycling of Mechanical Pulps" (1997). Paper Engineering Senior Theses. 105.