Date of Award
Bachelor of Science
Paper Science and Engineering
Sizing is the process by which a chemical additive provides paper with resistance to liquid wetting, penetration, and absorption. A common problem in the paper industry is size reversion, where the paper loses its ability to withstand liquid penetration. This problem has been significantly evident with the use of AKD, and becomes more of a concern as the paper industry shifts towards alkaline papermaking. Many variables have been studies however a direct correlation between the cause and effect of reversion has not been determined. One variable that has not been studies is the effect of light exposure. The objective of this experiment is to determine if light exposure has an effect on sizing by causing reversion.
Handsheets were made and sized with AKD at various addition levels. Samples were then exposed to indoor light conditions. Samples were also exposed to direct UV light using a fade-ometer. Sizing response and brightness were recorded over a fifteen week period. The results indicated that size reversion was evident in all samples exposed to the indoor light and the UV light. The lower sizing levels were most effected, losing more than 95% of the initial sizing level within the first week of exposure. Higher sizing levels were effected to a lesser degree but still indicated the same results. Brightness results indicated that the lower sizing levels showed a slight decrease in value while the higher addition levels gave a net increase in brightness. The decrease is attributed to deterioration of the cellulose while the increase can be due to bleaching of the cellulose.
It is believed that exposure causes reversion by forming a hydrolysis product of the unbound AKD. The light acts as a energy source to form this hydrolysis product which is a known desizing agent. Reversion is also a function of the deterioration of cellulose, where upon irradiation the chain length of cellulose is decreased and the ester bond between AKD and cellulose is cleaved. Finally, light speeds up the rate of the reverse reaction which is the breaking of the size to cellulose bond.
Aulbach, Ron W., "The Effect of Light Exposure on Sizing Response" (1995). Paper Engineering Senior Theses. 17.