Date of Award


Degree Name

Bachelor of Science


A study of Southern Pine pulp separation into its springwood and summerwood fiber components was undertaken. Separation was accomplished through the use of two Bird Triclean centrifugal cleaner devices. Separation occurred mainly because of different apparent pulp densities in the two fiber fractions. Springwood collapsed during pulping, creating a flattened fiber, forty-five to sixty-five microns in length and ten to twelve microns in width. The thicker walled summerwood fibers, on the other hand, maintained their twenty-five to thirty-five micron diameter tubular shape. The greater surface area present in springwood fibers allowed a greater hydraulic force to be exerted to this surface, and thus they were pushed towards the center and out the top of the cleaner. A greater centrifugal force to hydraulic drag ratio acting on the lower surfaced area summerwood fibers caused them to move to the walls and out the reject nozzle at the bottom of the cleaner. The major factor governing separation (consistency) was .07% in the final run. Separation efficiencies of 73% springwood in the accepts line and 64% summerwood in the rejects line were obtained.

The main thrust of the thesis dealt with separate refining of the two fractions after separation. The pulp was then recombined in various configurations. Refining, which was done in a PFI mill, seemed to lower freeness in a similar fashion for both pulps. This is contrary to the literature on the subject. Handsheets were then made using the Noble & Wood procedure, and various tests were then run on these sheets. Springwood formed a more dense sheet with higher tensile, burst, and density, and lower porosity and tear. The two most important results were: springwood reached very high tensile and burst properties at very low refining levels and then dropped off as the individual fibers weakened, summerwood maintained high tear, tensile, and porosity simultaneously at medium to high refining levels. These results seem to indicate that the two fractions might be used to create paper with special properties. They also indicate that springwood is overrefined in almost all conventional refining processes. A simple cost analysis indicated energy savings alone to be insufficient to warrant cleaner installation, but added benefits may render the separation process viable in certain specialized cases.