Abstract
We conducted a quantitative study, following the degree of activation (i.e. the transformation to alkali cellulose, denoted as DoA) over time for dissolving cellulose pulp treated with different [NaOH] at low NaOH/anhydroglucose unit stoichiometric ratio (denoted as (r) ≤ 2.6). Our quantitative approach was based on Raman spectroscopy data, evaluated by partial least squares regression modelling. The results show strong influence of the (r) on DoA (increasing from DoA = 45% at (r) = 0.8, to DoA = 85% at (r) = 2.6), and its complex dependence on [NaOH]. At (r) = 0.8 the highest DoA (DoA ≳ 60%) was found at 30% [NaOH], while at (r) = 1.3 it was found at 20% [NaOH] (DoA ≳ 80%). Although activation of cellulose happens in minutes at the studied temperature (30 °C), it was found that the reaction may be slow when a low (r) is used. A gradual increase of the DoA from ≈ 30 to ≈ 70% in time was seen when samples were activated with 30% [NaOH] at (r) = 0.8. At the same (r), a similar increase of DoA from ≈ 30 to ≈ 60% was also observed when 40% [NaOH] was used. Slow diffusion of NaOH through poorly swollen cellulose fibres is proposed as an explanation for this phenomenon. Lastly, solid-state CP/MAS NMR measurements suggest that at a fixed temperature, the Na-Cell allomorph mostly depends on [NaOH]. However, in the transition area between Na-Cell I and Na-Cell II, its influence might be affected by (r).Graphical abstract
Highlights
In the first step of manufacturing cellulose-based value-added products, e.g. viscose fibres and cellulose ethers, the cellulose, i.e. parallel crystalline structure cellulose I (Cell I), is treated with aqueous NaOH to alter its physical and chemical properties in a process called mercerisation
The Calibration samples consisted of a blend of dissolving cellulose pulp (Cell I, depicting degree of activation (DoA) = 0%) and fully mercerised material (Cell II, depicting DoA = 100%) with their amounts known
The main peaks in the loading line plot generated using the first component (R2 = 98%) of the calibration model agree with the Raman bands for Cell I and cellulose II (Cell II) described by Schenzel et al (2009) and Atalla (1975) (Fig. S1, Supplementary material)
Summary
In the first step of manufacturing cellulose-based value-added products, e.g. viscose fibres and cellulose ethers, the cellulose, i.e. parallel crystalline structure cellulose I (Cell I), is treated with aqueous NaOH to alter its physical and chemical properties in a process called mercerisation. Cell I transforms into a swollen crystalline structure, alkali cellulose (Na-Cell) This increases the reactivity of the cellulose and makes it more accessible for reagents to penetrate and react with the hydroxyl groups. Mercerising cellulose in excess of NaOH may be appropriate when making viscose fibres (Mozdyniewicz and Sixta 2012; Wilkes 2001), but less so in processes related to cellulose ethers. The use of such high (r) leads to the formation of unwanted by-products, which are generated by the reactions of the added chemicals with water and excess OH- ions We refer to low (r) when mercerisation is done at (r) B 5
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
