1981 Volume 1

Interest in the application of press-drying to paper-making has arisen primarily because of the possible improvements to the physical properties of paper using high yield pulp furnishes and increasing amounts of hardwood fibres. A major proportion of the development work on press-drying has centred around the production of heavy paper grades, specifically liner-board.

The need for the increased use of hardwood in the pulp and paper industry has been recognised for a long time. At the present time, only 42% of the forested land in the United States is occupied by softwood timber which in turn supplies wood for 75% of the forest products. On the other hand, the lesser used hardwood species occupy 55% of the forested land area, but supply wood for only 25% of the forest products⁽⁴¹⁾. Satellite photography land surveys have shown that when softwood forests are cut, the tendency is for the land to grow back with hardwood species rather than the original softwood species. As a result, the amount of forested land being occupied by hardwood species trees has been increasing each year. The lesser demand for hardwood has resulted in a price differential where hardwoods are now $10-20 U.S. per cord cheaper than softwoods.

The effects of different drying strategies on the development of the strain to failure of paper and its relationship with drying shrinkage is studied. It is postulated that the linear superposition principle can be applied to drying strategies. The general mathematical expressions to describe the strain to failure due to drying strategies are given.

The linear relationship between the strain to failure and sheet shrinkage is not found. The relationship is entirely dependent upon the drying strategies.

Using the linear superposition principle, a graph which can predict the strain to failure by different drying strategies is constructed.