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Author: | Rakkolainen, Minna |
Title: | Vessel picking phenomenon and its control |
Vessel picking -ilmiƶ ja sen hallinta | |
Publication type: | Master's thesis |
Publication year: | 2008 |
Pages: | 89 s. + liitt. 19 Language: eng |
Department/School: | Puunjalostustekniikan laitos |
Main subject: | Puunjalostuksen kemia (Puu-19) |
Supervisor: | Vuorinen, Tapani |
Instructor: | Isogai, Akira ; Kontturi, Eero |
OEVS: | Electronic archive copy is available via Aalto Thesis Database.
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Location: | P1 Ark TKK 451 | Archive |
Keywords: | vessel picking vessel element eucalyptus CMC modification microscopy putkisolu eukalyptus CMC-modifiointi mikroskopia |
Abstract (eng): | The effect of irreversible attachment of carboxymethyl cellulose (CMC) on vessel picking tendency and vessel element structure was studied. Comparison was done between unbeaten reference and CMC modified pulp and beaten reference and CMC modified pulp. Bleached Eucalyptus kraft pulp which has a high tendency for picking was used in the experiments. CMC modification of pulp increased the strength properties of handsheets and especially the internal strength improved notably. Laboratory printing test showed substantial decrease in the vessel picking tendency of CMC treated handsheets. However, surface strength of unbeaten pulps was low and print quality poor. It was found out that the refining level used (30 kWh/t) was not intensive enough to decrease picking tendency since several white spots were present on the surface of printed samples. The beaten CMC samples were almost pick-free and had excellent visual print quality. According to FiberLab analysis, vessel content decreased during CMC modification which can be considered as another reason for the decreased vessel picking tendency, besides improved bonding due to CMC addition. SEM (scanning electron microscope) observations revealed that the CMC treated handsheets had more film-like structures present in fibrillated areas. Electrostatic repulsion between the fibrils increases due to CMC addition causing them to disperse more easily. This may contribute to formation of the film-like structures, which may reinforce the bonding between vessels and fibers and improve strength. Similarly to fiber analysis, it was found out that both the CMC treatment and the refining decreased the percentage of unbroken vessels whereas more vessel fragments were present. Most of the unattached vessels were unbroken and breaking vessels can therefore be concluded to be an effective way to control the problem. Broken vessels are smaller and their edges are generally highly fibrillated and prone to bonding. Further structural differences were not detected. Since the breakage of vessels during CMC modification is somewhat surprising, the effect of high alkalinity and agitation was separately studied as well. Based on SEM observations, high alkalinity during modification had no effect on vessel breakage and the reason for the fragmentation of vessels through CMC modification - also reported in an earlier study - remained unsolved. However, alkalinity decreased picking tendency minutely, probably by increasing conformability of fibers. |
ED: | 2008-09-18 |
INSSI record number: 36277
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