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Tissue - mekaniska egenskaper på ark med låga ytvikter
KTH, School of Chemical Science and Engineering (CHE).
2016 (Swedish)Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesisAlternative title
Tissue - Mechanical properties of low grammage sheets (English)
Abstract [sv]

Tissue-pappersmarknaden växer fort och är konkurrenskraftig, det finns i dagsläget intresse att producera ett papper med hög mjukhet till ett lägre pris. Vid tissue-papper produktionen står fibrerna för en stor andel av den totala kostnaden, därför finns det en efterfrågan att kunna minska materialkostnaderna. Barrveden ger främst styrka till tissue-pappret och lövveden bidrar med mjukhet till pappret. Tissue-papper tillverkas vid låga ytvikter, därför fokuserade studien på de mekaniska egenskaperna vid lägre ytvikter.

Tidigare forskning har påvisat att mekaniska egenskaperna minskar kraftig vid lägre ytvikter [5]. Att jämföra löv-och barrvedsmassor för att erhålla information om fiberegenskaper och mekaniska egenskaper är därför intressant, speciellt vid lägre ytvikter. I denna studie har de mekaniska egenskaperna testats på ark som tillverkats i Innventias massaprovningslabb, för att se hur egenskaperna ändras med ändrad ytvikt och hur olika massatyper skiljer sig. Relationer mellan barr-och lövvedsmassorna kommer uppmärksammas och trender åskådliggöras.

Studien delades upp i tre tester. Första testet var utvärdering av finmaterialretentionen med slutet bakvatten vid arkning, vilket utfördes för att veta när finmaterialhalten i bakvattnet nått jämvikt. Andra testet var utvärdering av massor och mekaniska egenskaper. Ark tillverkades av 3 barrvedsmassor och 3 lövvedsmassor med olika ursprung och fiberegenskaper. De mekaniska egenskaperna testades i dragprovare, Ball Burst Strength och fibrerna karaktäriserades i fibertester. Tester för att erhålla avvattningsegenskaper och fibersvällningsgrad utfördes även i massaprovningslabbet. Det tredje testet var utvärdering av björkmassa vid olika malningsnivåer. Testet utfördes på en björkmassa som malts vid 3 olika malningsnivåer (50, 100, 150 kWh/ton), för att undersöka malningens inverkan och om malningen kunde optimeras. Testerna på massorna var precis som i det andra testet.

Finmaterialretentionen i första testet nådde en jämvikt vid ungefär 4 – 6 tillverkade ark och då visade de mekaniska egenskaperna stabila värden. Finmaterialuppbyggnaden fortsattes därför med 10 labark i resterande försök för att säkerställa att finmaterialjämvikt nås. De mekaniska egenskaperna i test 2 var högst för barrvedsarken och de relativa skillnaderna mellan olika råvaror var tydliga för barrvedsarken, även vid lägre ytvikter. Lövvedarkens relativa skillnader var svåra att tyda vid lägre ytvikter, över 30 g/m2 kunde skillnader ses. Lövvedarkens mekaniska egenskaper nådde ett maximum vid 30 g/m2 därefter nådde alla mekaniska egenskaper en platå, medan ingen platå kunde identifieras hos barrveden. Barrvedsarken når förmodligen ett maximum efter 60 g/m2. De massor som erhöll högst mekaniska egenskaper var de med långa och flexibla fibrer, medan de med korta och styva fibrer fick lägre mekaniska egenskaper. Ball Burst-styrkorna var generellt sett högre hos barrvedsarken, vilket berodde på barrvedens längre fibrer.

De malda björkmassorna erhöll högre mekaniska egenskaper än både barr-och lövvedsarken, vilket berodde på den ökade bindningsgraden som uppstått. Malda massornas egenskaper ökade kraftigt vid den första malningsgraden (50 kWh/ton) för att sedan avta. Ju längre malningen fortgår desto sämre blir bulken och mjukheten hos pappret [1]. En högre malning än 100 kWh/ton ansågs därför onödig eftersom avvattningsegenskaperna försämrades och ingen markant skillnad i mekaniska egenskaper erhölls. Ett optimum för malningen verkade finnas mellan 0 – 100 kWh/ton.

Abstract [en]

The tissue paper market is growing fast and is very competitive. The interest right now is to produce a paper with high softness at a lower cost. During the production of tissue paper the fibers stands for a large portion of the total cost, therefore there is a demand to reduce the material costs. Softwood mainly provides with strength to the tissue paper whilst hardwood contributes with softness to the paper. Tissue paper is manufactured at a low grammage, therefore the study is focusing on the mechanical properties at lower grammages.

Previous research has shown that the mechanical properties decrease rapidly at lower basis weight. To compare hardwood and softwood pulps to obtain information on the fiber properties and mechanical properties is therefore interesting, especially at lower basis weights. In this study the mechanical properties has been tested on sheets that was manufactured at Innventias pulp testing lab, to see how the properties change with modified basis weight and when pulp types differs. Relations between hardwood and softwood pulps were recognized and trends were illustrated.

The study was divided into three tests. The first test was to evaluate the fines retention in a closed white water system with recirculation, whilst making sheets. The evaluation was performed in order to know when the fines reached equilibrium in the system. The second test was the evaluation of different pulps and mechanical properties. The sheets were made with 3 softwood pulps and 3 hardwood pulps, all the pulps had different origin and fiber properties. The mechanical properties were tested in a tensile tester, Ball Burst Strength and the fiber characterization was performed in a fibertester. There were also tests to obtain the dewatering and fiber swelling properties. The third test was the evaluation of birch pulp at different refining levels. The test was conducted on a birch pulp which had 3 different refining levels (50, 100, 150 kWh/ton), to investigate the effect of the refining and if the refining process could be optimized. The paper testing and characterization was exactly as the second test.

The fines retention in the first test reached equilibrium at 4 – 6 sheets and the mechanical properties showed stable values after the equilibrium was reached. The fines retention process was therefore decided to be made with 10 laboratory sheets to ensure that the fines reached equilibrium. The mechanical properties in test 2 were highest for the softwood sheets and the relative changes between various pulps were clear, even at lower basis weight. The hardwoods relative changes were hard to decipher at lower basis weights, differences could be seen at grammages higher than 30 g/m2. The hardwood sheets mechanical properties reached a maximum at 30 g/m2, followed by a plateau, whilst no plateau was identified for the softwood sheets. The softwood sheets probably reach a maximum after 60 g/m2. The pulps that obtained highest mechanical properties were those with long and flexible fibers, whilst those with shorter and stiffer fibers had lower mechanical properties. Ball Burst Strength was generally higher for the softwood sheets, due to the long fibers that the softwood had.

The refined birch pulps received higher mechanical properties than the unrefined hardwood and softwood pulps, due to the increased degree of bonding that has occurred in the sheets. The refined pulps properties increased vigorously at the first refining degree (50 kWh/ton) and then decreased. The longer the refining proceeds, the worse the paper bulk and softness become [2]. A higher refining than 100 kWh/ton was considered unnecessary as the dewatering properties became worse and no significant difference was received in mechanical properties. An optimum for the refining process seemed to be in the interval 0 – 100 kWh/ton.

Place, publisher, year, edition, pages
2016.
Keyword [sv]
Tissue, ytvikt, fibrer, mjukpapper, sheets
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-189297OAI: oai:DiVA.org:kth-189297DiVA: diva2:945317
Educational program
Bachelor of Science in Engineering - Chemical Engineering
Available from: 2016-07-01 Created: 2016-07-01 Last updated: 2016-07-01Bibliographically approved

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