Date of Award
Bachelor of Science
Recycling is an area of interest for much of the industry because of all the environmental concerns with the cutting down of trees, and the pulping operations to make paper. However, virgin fibers are still desired because they make stronger paper. Virgin fibers have a higher swelling capability than recycled fibers, that accounts for better bonding. Paper's physical properties also decrease rapidly as filler is substituted for fiber. Filler impairs interfiber bonding by preventing close contact with fibers. Filler is added to paper to increase opacity and brightness. However, there is a poor retention of filler in the sheet during papermaking, which is only partially solved with retention aids.
Never been dried softwood pulp was kneaded with a swelling agent and refined. Ten calcium carbonate runs and ten conventional runs were conducted. Pulp was kneaded with calcium chloride, refined, and then washed over a screen. Sodium carbonate and PEI were mixed together and then washed over a screen.
The ash content decreased with each recycle run for the calcium carbonate runs. The scattering coefficient also went down with each recycle. However, scattering coefficient goes up in the conventional recycle run, because less bonding ocurs with each recycle. The amount of calcium carbonate in the sheet has a bigger effect on scattering coefficient than the degree of recycling.
Recycled fibers are less conformable than virgin fibers, which accounts for the big decrease between the 1st and the 2nd nun in tensile index and bumst index of both the conventional and the calcium carbonate paper. This happens because repeated drying of fibers produce a progressive deterioration of paper tensile strength. If the fiber lumens crack and the calcium carbonate is exposed, the fibers may not attach to the other fibers as well because the calcium carbonate particles are in the way.
With recycling, the tear index increases, passes through a maximum and then declines. The conventional run seems to continually increase, with the greatest increase between the 1st and 2nd run. At first, between the 1st and 2nd run, calcium carbonate has higher tear. A lumen loaded sheet has a lesser collapsed fiber, which offers more tearing resistance than a fully collapsed fiber.
Strength properties are not higher after four runs, but many interesting observations can be made from the recycling of lumen loaded pulp.
Spruit, Anne, "The Effect of Internally-Filled Pulp on Recycling" (1995). Paper Engineering Senior Theses. 511.