Among the characteristics of dissolving pulps that are frequently cited as of great interest, two can be significantly enhanced by the CSI process. The first is the activity of the pulp or its accessibility to modifying chemical reagents. The second is the hemicellulose content, which must be reduced as much as possible to achieve cellulose of the highest purity possible.
The enhancement of activity in CSI treated pulps is illustrated by the response of fibers to the iodine based Graf C stain. While untreated fibers show the yellowish grey color typical of a high purity dissolving pulp, the CSI treated fibers show a dark blue color indicating that the large polyiodide ions responsible for the color have penetrated deeply into the fiber.
Yet another indication of greater accessibility is the observation, that CSI treated celluloses are much more accessible to cellulase enzymes. Indeed the rate of conversion of CSI treated celluloses to glucose is increased by an order of magnitude. The blue color response to Graf C stain and the enhanced response to hydrolytic enzymes suggest that CSI treated pulps will be more accessible to reagents used to produce cellulose derivatives or to produce solutions for regeneration into fibers or films.
The other key characteristic is the content of hemicelluloses. The CSI process opens up the structure of cellulose so that hemicelluloses are not as tightly bound. Furthermore the inclusion of ethanol in the solvent system enhances the solubilization of hemicelluloses in an alkaline environment as they are, in many respects, poly-alcoholates that associate more favorably with ethanol than with water.
Application of the CSI process to typical kraft pulps of both softwoods and hardwoods has resulted in significant increases in the alpha cellulose content and reduction of hemicellulose content.
The benefit of the CSI process in production of dissolving pulps is that it could result in significant increase in the yield from wood. At present most dissolving pulps are produced at a yield level of 33% to 35% because of the severe pulping conditions necessary to attain desired alpha cellulose content and corresponding reduction of hemicelluloses. We believe use of the CSI process to complement currently practiced technologies will allow reduction in the severity of pulping conditions. Operation of the CSI process at ambient conditions requires less capital investment and lower operating costs than most operations in a pulp mill.
When pulp fibers are treated by the CSI process they become both nanoporous and elastic. These properties can be very valuable when CSI treated fibers are incorporated in pulp furnishes to be used for the production of sanitary paper products.
Handsheets made from these pulps are much softer in feeling to the touch and they have significantly higher bulk. It is not anticipated they could be used alone in most applications because their elasticity limits interfiber bonding. But their nonbonding character can be valuable in many contexts if they are included as part of the pulp furnish at a level of 10% to 20%.
Their elasticity enables removal of more of the water by pressing during manufacture thus reducing the amount of energy required for drying. It is anticipated that inclusion at the levels indicated above could reduce the cost of energy for drying on a tissue or towel machine by approximately 30%. Inclusion in the pulp furnish of any papermaking operation can be expected to enhance bulk without adding to basis weight. This benefit however may be diminished by any pressing operations that include bonding agents.
The porosity of pulp fibers treated by the CSI process will enhance absorbency and it is anticipated that such pulps can be included in the manufacture of diapers and similar personal hygiene products. The softness and absorbency will significantly improve their performance and value.