Development of a novel rheology-based method to estimate pulp reactivity

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Kemian tekniikan korkeakoulu | Master's thesis
Ask about the availability of the thesis by sending email to the Aalto University Learning Centre oppimiskeskus@aalto.fi

Authors

Date

2016-08-23

Department

Major/Subject

Fibre Products Technology

Mcode

KM3003

Degree programme

Master's Programme in Bioproduct Technology

Language

en

Pages

83+13

Series

Abstract

The recent expansion and diversification of cellulose-based products market has created the need for a more accurate pulp characterization, and new parameters have been developed, including cellulose and pulp reactivity. Cellulose reactivity has been often described as the ability degree of the reactive hydroxyl groups within the polysaccharide to react with chemicals, and it has been estimated by means of complex, time-consuming methods. Many studies have utilized these estimations as representative values of pulp reactivity. However, this approach is questionable, because the latter depends not only upon cellulose reactivity, but also on other parameters. Thus, the aim of this work was to develop an alternative fast user-friendly procedure to estimate pulp reactivity as such. This novel evaluation method was based on the monitoring of pulp dissolution in a bis (ethylenediamine) copper (II) hydroxide solution (CED) at constant measurement conditions using a rheometer equipped with a bob-and-vane geometry. Torque values were first measured throughout the reaction and then plotted as function of time. The resulting torque profile was found to consist of four phases: torque decrement, linear increment, non-linear increment, and the plateau. The dissolution began with the linear phase and ended with the plateau value. Based on the analysis of the profile, three parameters were identified as best representing pulp reactivity: pre-dissolution time (PDT), initial dissolution rate (IDR), and optimal dissolution time (ODT). The first estimated the accessibility of CED to the pulp, while the second and the third evaluated pulp reactivity as such. In particular, high IDRs and low ODTs were found to correspond to high pulp reactivities, though these two parameters were not directly proportional. In order to optimize the method, the experiments were organized in two parts. The first evaluated the measurement conditions affecting the results and allowed the standardization of the procedure. Differently, the second part verified the applicability of the procedure on a wide range of pulps, evaluating the reactivity of dissolving, kraft and mechanical pulps exposed to different physical and chemical treatments. Although the IDRs showed higher repeatability than the ODTs, all the measurements resulted consistent. Moreover, the optimal dissolution times allowed the comparison among pulps obtained by different manufacturing processes. Finally, the rheological estimations were accompanied by further analyses in order to better understand the factors influencing pulp reactivity. The here proposed rheology-based pulp reactivity estimation method was proved to be sensitive, reliable, fast, and relatively simple. Thus, the procedure was confirmed as an efficient alternative to the other methods based on cellulose reactivity. Nevertheless, the results reported also the necessity of further studies, especially to better interpret the dynamics regulating torque plateau.

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Supervisor

Maloney, Thaddeus

Thesis advisor

Kuusisto, Jonna

Keywords

cellulose, reactivity, accessibility, rheology

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Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-201609224148

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[dipl] Kemian tekniikan korkeakoulu / CHEM