Changes in the structure of flax cellulose induced by solutions of lithium, sodium, and potassium hydroxides

Abstract

In the reaction of cellulose-containing flax material with aqueous solutions of LiOH, NaOH, and KOH, the degree of swelling, sorption of water and alkali, parameters of the crystal lattice formed by alkali cellulose, degree of removal of lignin, and change in the degree of polymerization are a function of the type of cation. For the sorption characteristics and crystal lattice parameters of alkali cellulose, this dependence is determined by the change in the structure of the first and second hydrate shells of the cations. Despite the important differences in the degree of swelling, crystal lattice parameters of alkali cellulose, and degree of removal of lignin, the changes in the crystal structure of the cellulose related to the transition from crystalline modification I to modification II under the effect of the three different bases are similar and take place in approximately the same concentration region.In order to obtain cellulose from plant raw material (flax, jute, hemp) with industrially acceptable reactivity and a broad spectrum of applications, it is necessary to know the structural changes it undergoes both during modification and in chemical processing into cellulose ethers.The reaction of alkali metal hydroxides with purified cellulose (basically wood and cotton cellulose) is examined in sufficient detail in the literature, but the structural changes in cellulose in cellulose-containing plant material have been studied much less. For this reason, we investigated the specific features of structural rearrangement of flax cellulose treated with different basic solutions. We used intermediate-flax fibres undergoing mechanical separation from chaff alone and ground in a impact-pulse loading dry grinding mill.The method of determination of swelling and sorption of base and water were similar to the methods reported in [1,2]. The fibre samples were treated with solutions of bases (LiOH, NaOH, and KOH) at 20°C and ratio of 1:10 for 1 h. The degree of swelling of the fibres and sorption of water and base were determined by the method in [2] and excess base was forced out with a centrifuge.Sorption of water and base from solutions by the cellulose was measured with the following method. A weighed portion of air-dried cellulose with a known moisture content, taken with an accuracy of under 0.0002 g, was placed in a special vessel for swelling, a solution of the base was poured in, and it was thermostated for 1 h. The vessels were then placed in a previously tempered centrifuge, and the alkali cellulose was treated for 10 min at a centrifuge rotor rotation rate of 8000 min -1 . The results of the preliminary experiments showed that these conditions of swelling and wringing out were sufficient to attain the equilibrium state of the cellulosebasewater system. The samples were weighed and then the amount of absorbed NaOH was determined by titration with a 0.1 N solution of H 2 SO 4 (the sample was held in distilled water for 3 h before titration). Three parallel experiments were conducted for each solution of base....

Morphological change induced with NaOH–water solution for ramie fiber: change mechanism and effects of concentration and temperature

“…Nakano [24,25], Ishikura and Nakano [26], and Tanimoto and Nakano [27,28] reported changes in the dimensional and mechanical properties of wood that occurred after treatment with NaOH-water solution; they attributed these changes to morphological changes in the microfibrils in the wood cell walls. Their results were later confirmed by Voronova et al [29] and Ray and Sarkar [30]. Although many studies concerning treatments of wood and cellulose with NaOH-water solution have been reported, a quantitative description of the morphological changes of the microfibrils and fibers after treatment, particularly with respect to conformational changes, has not been reported to our knowledge.…”

Sorption studies on regenerated cellulosic fibers in salt–alkali mixtures

“…The initial increase in cellulose swelling with increasing alkali concentration results from the second factor being predominant at lower alkali concentrations, while the decrease in cellulose swelling at higher alkali concentrations results from a predominance of the first factor. The lower SRV in KOH treatments, as compared to NaOH treatments, is attributed to the smaller hydration radius of K + ions in comparison to that of Na + ions (Kielland 1937;Voronova et al 2004).…”