Date of Award
Bachelor of Science
Paper Science and Engineering
Dr. John Cameron
Retention of fines and fillers has always been a concern in the paper industry. There has been many different types of retention aids in the past, but they lack performance under the vigorous conditions in today's paper mills. High shear forces associated with high speed paper of recycled materials into the mill brought along with it high fines content and a lot of anionic trash which readily reacts with cationic polymers. Consequently, the dosage must be increased which can lead to poor formation and increased chemical cost. A new retention aid was needed to combat these problems. Microparticle retention systems were developed by a group of papermakers, scientist, and process control experts in the late 1970's. A dramatic improvement in retention and drainage was achieved, which allowed higher filler loading, increased machine speeds, and better formation. To this date, continuing research is being done on the improvement of microparticle retention aids as well as developing new retention aids.
This paper deals with microparticle retention systems in a different way. Normally, the dosage of microparticle, anionic silica in this research, to the system is on a weight basis, i.e., pounds of microparticle per ton of paper. In this study, silica dosage will be done on a surface area basis. Silica particles have a very high specific surface area, which can range anywhere from around 500m2/g to 1200m2/g. Using this information and the typical dosage rate on a weight basis, a surface area dosage can be calculated. For example, 600m2/g X 1.0 lb./ton = 272,155m2/ton and 1200m2/g X 0.5lb./ton X 272,155m2/ton . Both give the same surface area dosage, but different only half of the weight basis dosage is needed for the high surface area silica. Therefore, the objective of this thesis is to test the hypothesis that equivalent retention will be obtained when equal surface area dosage is applied to the system.
A two level, three variable factorial design was used to test the effects of surface area of microparticle, surface area dosage, and polymer dosage. Two different furnishes were used, a fine paper grade and a wood containing grade. Both grades are similar to those found in industry. All retention studies were carried out using a Britt Dynamic Drainage Jar. Percent fines and ash retention was measured.
The results for the fine paper furnish showed no conclusive trends other than an effect of polymer dosage on fines retention. The variability in the system was extremely high. The wood containing furnish, however showed several promising results. Again, the polymer dosage was found to have a large effect on the system. There was an interaction between surface area dosage and polymer dosage. At low polymer dosages, the surface area dosage had an effect on retention, but at high polymer dosage, there was not an improved retention response as the surface area dosage increased. Finally, the wood containing furnish followed the hypothesis that equivalent retention will be obtained at equal surface area dosage.
Many chemical suppliers pride themselves on the high surface area of their microparticle and the improved performance it offers. The results of this thesis show that this may not be exactly true. The dosage needed to get the same retention with a high surface area microparticle may be less, but not necessarily improved performance. If retention could be measured as a function of surface area added to the system per ton of paper, a mill could determine what is the most economical microparticle to use. For example, a supplier could supply a low surface area microparticle at a very low price, while the another supplier is offering a high surface area microparticle at an extremely high price. The mill would have to use a lot more of the low surface area microparticle to get the retention they want, but it sill may be more economical.
Hoffmann, Jason P., "The Effect of Silica Surface Area on Microparticle Retention Systems" (1997). Paper Engineering Senior Theses. 172.