On Heat and Paper : From Hot Pressing to Impulse Technology

作者：Marco F. C. Lucisano · 发表于：KTH Publication Database DiVA (KTH Royal Institute of Technology) · 年份：2002 · 被引用次数：10 · 研究领域：Lignin and Wood Chemistry、Advanced Cellulose Research Studies

Impulse technology is a process in which water is removedfrom a wet paper web by the combined action of mechanicalpressure and intense heat. This results in increased dewateringrates, increased smoothness on the roll side of the sheet, andincreased density. Although the potential benefits of impulsepressing have been debated over the past thirty years, itsindustrial acceptance has been prevented by web delamination,which is defined as a reduction in the z-directional strengthof paper. This thesis deals with the mechanism of heat transfer withphase change during impulse pressing of wet paper. The resultsof four complementary experimental studies suggest that littleor no steam is formed in an impulse nip prior to the point ofmaximum applied load. As the nip is unloaded and the hydraulicpressure decreases, hot liquid water flashes to steam. Weadvance the argument that the force expressed upon flashing canbe used to displace liquid water, in a mechanism similar tothat originally proposed by Wahren. Additionally, modelexperiments performed in a novel experimental facility suggestthat the strength of flashing-assisted displacement dewateringcan be maximized by controlling the direction of steam venting.If this solution could be exploited in a commercially viableimpulse press, delamination would cease to be an issue ofconcern. The thesis includes a study of the web structure ofdelaminated paper. Here, we characterized delaminated paper bythe changes in transverse permeability and cr...