SUMMARY

During production, the paper is transformed from a sheet high in water content to a sheet low in water content. As water is removed, the cohesive energy of the paper increases. In this investigation the development of the sheet cohesive strength is investigated through experimental testing, simulating the most important conditions the paper supports during its production. The cohesive strength of the sheet depends mainly on the entanglement of the individual fibers when the consistency is low, and as the consistency goes up the cohesive strength depends on the hydrogen bonding between the same fibers or bonding between the fibers and the chemical additives included in the sheet. Both the entanglement and the bonding can be manipulated during the production process. The cohesive strength of the paper was evaluated for consistencies that correspond with the paper production process, a range from 20% to 95% was considered. Additional variables were also investigated, these include basis weight, refining level, clay filler addition, and starch content. Cohesive strength was evaluated using a unique apparatus developed at IPST. Tensile strength and strain were also measured using a standard Instron device. The results show how the cohesive strength slowly increases in the range form 20 to 55% solids, and then it grows up exponentially following the same behavior of the stress-strain curve. The primary results of this work were 1. A linear relationship between tensile index and cohesive energy index was established 2. The linear relationship between tensile index and cohesive energy has a basis weight dependence which is linear and can be eliminated yielding a single tensile index – cohesive energy index 3. The splitting apparatus results can be used to calculate strain based on the work of Osterberg. The resultant strain has an offset compared to that obtained form the Instron tensile test, but is consistent with Osterberg’s results