Aqueous Calcium Thiocyanate Solution as a Cellulose Solvent. Structure and Interactions with Cellulose

Shimaya

Saito

1998

Self Cite

ABSTRACT:Attempt was made to clarify the structural change of wood pulp during the treatment of concentrated aqueous (aq) calcium thiocyanate (aq Ca(SCN)z) solution at room temperature. For this purpose, X-ray, DSC, and CPIMAS 13 C NMR were used to measure changes of crystalline structure and formation of cellulose-solvent complex. X-Ray data indicated that 55 wt% aq Ca(SCN)2 so ln. causes intracrystalline interplanar swelling of the wood pulp, forming cellulose--calcium thiocyanate addition compound. The interplanar spacing of (ITO), (110), and (200) planes increased for the former two planes and slightly decreased for the last one for treatment time td of 90 min. From DSC thermo grams of cellulose-55 wt% aq Ca(SCN)z soln. mixture, exothermic heat !'J.H for the formation of the addition compound was estimated to be ca. II kcal mol-1 , which was far iower than that for generation of cellulose sodium salt. The cellulose recovered from the system has quite different crystalline structure depending on treatment time and the reagents used for recovery. Up to td = 90 min, water recoverd the mixture of natural cellulose crystal (Cell

Section: Structure Of Cellulose Regenerated By Various Reagents Aftermentioning

confidence: 97%

Section: Structural Changes In Wood Pulp Dipped In Aq Calciummentioning

confidence: 99%

Structural Changes in Wood Pulp Treated by 55 wt% Aqueous Calcium Thiocyanate Solution

Shimaya

Saito

1998

Self Cite

“…Figure 6 shows the 13 C-1 H COSY spectrum. Horizontal and longitudinal axes are 13 C and 1 H chemical shifts, respectively and projections on each axis are also shown. Peaks on 2D-spectrum clearly show C-H scalercoupling, indicating correlation between 13 C-1 H peaks.…”

Section: Nm R Spectra Ofcellulose/aq Ca(scn)2 Solution Systemmentioning

confidence: 99%

Solubility and Dissolved Cellulose in Aqueous Calcium- and Sodium-Thiocyanate Solution

Shimaya

Saito

1998

Self Cite

ABSTRACT:Attempt was made to investigate the solubility and the dissolved state of various cell uloses in aqueous (aq) calcium-and sodium-thiocyanate solution. Almost all cell uloses used in this study were soluble in 55 wt% aq calcium thiocyanate (Ca(SCN) 2) soln. at about 100°C, while 60wt% aq sodium thiocyanate (NaSCN) soln. dissolves only limited cellulose mainly regenerated from cellulose solution. The solubility of cellulose in 60wt% aq NaSCN was independent of the crystal form, crystallinity and the degree of polymerization of cellulose and this was explained only in terms of the degree of breakdown of intramolecular hydrogen bonds in the cellulose solid. Using 2-dimensional NMR six carbon peaks in 13 C NMR spectra of cellulose in two solvents were successfully assigned. The comparison of chemical shifts of cellulose in 55 wt% aq Ca(SCN)2 solution and 10% sodium hydroxide (NaOH) solution strongly suggested that calcium atoms as electron acceptors coordinate with oxygen atoms in glucose ring and primary alcohol at C(6) position, in the same manner of cellulose dipped in 55 wt% aq Ca(SCN)z solution at room temperature. In the 13 C NMR spectrum of cellulose-60% aq NaSCN solution system, C(3), C(2), and C(6) peaks were observed at lower magnetic field side, implying that sodium atoms interact with hydroxide groups at C(2), C(3), and C(6) positions of glucopyranose in cellulose molecules.

“…Multihydrate of LiSCN and Ca(SCN) 2 Á4H 2 O showed high solubility of 174 g and 152 g, respectively, in 100 g of ethylenediamine, however, these solutions did not dissolve cellulose at all. It is known that a concentrated Ca(SCN) 2 Á4H 2 O aqueous solution dissolves cellulose above 100 C. 5 Hattori et al 20 also showed that cellulose interacts with Ca(SCN) 2 Á4H 2 O in water at the concentration of 2 was not dissolved in ethylenediamine at 25 C, so that no dissolution of cellulose occurred in the system. Saturated solutions of NaSCN and KSCN in ethylenediamine, i.e., the systems of ethylenediamine/ NaSCN 54/46 (w/w) and ethylenediamine/KSCN 55/45 (w/w) dissolved cellulose (DP210) with high concentrations of 16 and 15 % (w/w), respectively.…”

Section: Resultsmentioning

confidence: 99%

New Solvents for Cellulose. II. Ethylenediamine/Thiocyanate Salt System

Abe

Yoshida

et al. 2004

ABSTRACT:The ethylenediamine/thiocyanate salt system was found to be a new solvent for cellulose. The solubility, dissolution behavior, solution properties, and cellulose recovered from the solutions were investigated. The dissolution took place at room temperature, and the maximum solubility achieved was 16 % (w/w) for cellulose of DP210 in the ethylenediamine/sodium thiocyanate 54/46 (w/w). The dependence of cellulose solubility on DP is also described. Tracing the dissolution behavior of the cellulose by CP/MAS 13 C NMR measurements revealed the polymorphic conversion of cellulose I to III to amorphous structure during the dissolution process. The cellulose dissolved was stable for 30 days storage at room temperature. Microscopic observations and steady-shear viscosity measurements of the solutions indicated mesophase formation of cellulose in the ethylenediamine/sodium thiocyanate system. This anisotrpoic phase appeared from ca. 10 % (w/w) cellulose with DP210 and greatly depended on the cellulose concentrations. Coagulation studies disclosed that cellulose II and amorphous cellulose were recovered from the cellulose/ethylenediamine/thiocyanate salt solutions when water and alcohol were used as a coagulant, respectively. It was suggested that this solvent system has high potential for cellulosic fiber and film formations.KEY WORDS Cellulose / Cellulose Solvent / Cellulose Solution / Amine / Thiocyanate / Dissolution Mechanism / Regenerated Cellulose / Cellulose is a linear and high molecular weight polymer as well as a natural, renewable, and biodegradable material. However, due to its considerable inter-and intramolecular hydrogen bonds, cellulose neither melts nor dissolves readily in common solvents. The complicated crystalline and amorphous morphology has also been preventing cellulose from being exploited to its fullest potential. Any process which simplifies or hastens the dissolution of cellulose represents a significant step forward in the development of cellulose as a viable, ecologically favorable polymer source. Furthermore, the ability of cellulose and cellulose derivatives to form mesophase in certain solvents has resulted in attempts to develop high-performance cellulosic fibers and membrane. At present, there are a few solvents that can directly dissolve cellulose without heavy metal complexation and any chemical derivatization, which are lithium chloride/dimethyl acetamide (LiCl/DMAc), 3 N-methylmorpholine-N-oxide/water (NMMO/H 2 O), 4 calcium thiocyanate/water (Ca(SCN) 2 /H 2 O), 5 etc. Quite recently, ionic liquids containing 1-butyl-3-methylimidazolium cations were discovered to dissolve high M w pulp (DP % 1000) with 10 % (w/w) at elevated temperatures. 6 However, almost known solvents still have some undesirable points, for example, chemical safety, environmental concern, degradation of cellulose, requirements of high temperatures and/or pretreatment of cellulose, poor mechanical properties of the cellulose recovered, and high cost for commercial use.We have been studied new solvent for ...