Dissolution Process and Dissolved State of Cellulose in Dimethylformamide–Chloral–Pyridine System

Abstract

The dissolution process and dissolved state of cellulose into a dimethylformamide-chloral-pyridine (D-C-P) system were studied by optical microscopy, nuclear magnetic resonance (NMR), polarimetry, infrared (IR) spectroscopy, and X-ray diffraction method. Natural cellulose with crystal form I dissolves rapidly at room temperature, via hemiacetaltype reaction with chloral, in which pyridine acts as a reaction accelerator. Cellulose exists as cellulose trichlorate in the mixture. When the pretreatment period of cellulose with dimethylformamide (DMF) is short, the cellulose dissolves into the system without swelling. But when the pretreatment period is relatively long, the cellulose swells considerably and then dissolves. Cellulose monochlorate was recovered by casting from the solution but cellulose trichlorate could not be isolated, probably because of the considerable tendency of the polymer to hydrolyze, especially when the solution is acidic. Cellulose having the crystal form II was regenerated by addition of water to the solution. KEY WORDS Cellulose Chlorate I Dissolution Process I Dissolved State I Dimethylformamide-Chloral-Pyridine System I

New class of cellulose fiber spun from the novel solution of cellulose by wet spinning method

“…3 ) . Table I1 (column [11][12][13][14] shows that (1) the crystallinity x, of the new fibers is relatively high ranging 0.65-0.67, compared with those (ca. 0.6) of the commercial regenerated Table 11.…”

Determination of the Distribution of the Substituent Group in Cellulose Acetate by Full Assignment of Au Carbonyl Carbon Peaks of 13C{1H} NMR Spectra

“…Applying the low-power selective spin decoupling method to almost completely substituted CA ({F)>=2.92), Kowsaka et al 12 assigned, from the lower magnetic field, the carbonyl carbon peaks to the acetyl groups at C6 , C 3 , and C2 positions and simultaneously demonstrated that there are not only 3 but also many peaks in the carbonyl carbon region of 13 C NMR spectra of partially substituted CA ( {F)> = 2.46 and 0.68), insisting that these peaks correspond to 12 carbonyl carbon peaks, originating from magnetically different all ( = 12) -OR groups existing in 8 pyranose rings as shown in Figure 3. In order to evaluate {fk)> for not-fully substituted CA with good accuracy, the reliable assignment of the abovementioned 12 peaks is very prerequisite because rough classification of these peaks into three parts (carbonyl at C 2 , C 3 , and C 6 ) made by Kamide 13 and Kamide and his collaborators 5 came to the same conclusion that CA samples with the same {F)>, prepared under different conditions, had different degrees of water solubility, and discussed the relations between {fk)> by NMR method and the water solubility for CA: CA having {f 2 )> {f 3 )> {f 6 )> (i.e., CA with uniformly distributed acetyl groups) dissolves almost completely in water at room temperature in the range of {F)> from 0.6 to 1.0. In contrast to this, CA having {f 6 )> {f 2 )> + {f 3 )> (i.e., CA with acetyl groups highly selectively located at C 6 position) is little better than insoluble in water over the entire {F)> range.…”

“…1 -5 Thus, the total degree of substitution was also expressed by iF)). In addition, Kamide et al 6 showed by thin-layer chromatography (TLC) that CA sample consists of molecules with different average total degrees of substitution <F) [here, F is the degree of substitution of a given glucopyranose unit and <F) is obtained by averaging F over all glucopyranose units constituting a single molecule] and evaluated the distribution of <F), denoted as g( <F)) (see Figure 2). However, when we see the possible substituted glucopyranose units of cellulose derivative, there are 8 kinds of unsubstituted and partially or fully substituted glucopyranose units as shown in Figure 3: single trisubstituted, three disubstituted, three monosubstituted and one unsubstituted glucopyranose units.…”

“…In contrast to this, CA having {f 6 )> {f 2 )> + {f 3 )> (i.e., CA with acetyl groups highly selectively located at C 6 position) is little better than insoluble in water over the entire {F)> range. In addition, Kamide et al 5 demonstrated that CA having {f2 )> {f 3 )> {f 6 )> easily dissolves completely in dimethylacetamide (DMAC) at room temperature irrespective of {F)>, if {F)> is at least larger than 0.6, and CA having {f6 )> {f2 )> + {f 3 )> dissolves only partly in DMAC even at 80°C in the same {F)> range. Now, we conclude that neither {F)>, {f 2 )>, {f 3 )> nor {f 6 )> control individually the solubility.…”

“…Note that in this study, all not-fully substituted CA samples were prepared by acid hydrolysis, which is expected to occur randomly (or homogeneously), and the above conclusion is consistent with what is expected in the case of random acid hydrolysis of CA. Kamide et al 6 pointed out from TLC analysis on CTA that "CTA" with {F:» of2.92 is a mixture ofCTA with {F:» = 3 (i.e., trisubstituted unit) and notfully substituted CA. This finding was repeatedly and more firmly ascertained in this NMR study.…”