JPH0735401B2 - Method for producing type I cellulose triacetate - Google Patents

Description

[Industrial Application Field] The present invention relates to improving the properties of cellulose triacetate in adsorbents, fibers, and other applications, and more particularly to a method for obtaining type I cellulose triacetate (hereinafter abbreviated as CTAI) from cellulose triacetate.

[Prior art and problems]

It is known that cellulose triacetate (hereafter abbreviated as CTA) has crystal polymorphs, just like cellulose. One of them is called CTAI, which is usually obtained by heterogeneous acetylation of natural cellulose (acetylation method that does not go through a dissolved state during the reaction process), but this is considered to be a thermodynamically unstable polymorph. In other words, what is obtained by precipitation or drying from a CTA solution is, in principle, type II cellulose triacetate (hereafter abbreviated as CTAI).
CTAI is a polymorph that is considered to be stable and is called CTA II. Therefore, CTAI cannot be prepared from a solution system, with one exception, which means that it is difficult to prepare CTAI that is fundamentally different from the morphology of the natural cellulose used as a raw material. CTAI has been studied for example in terms of its adsorption properties [T. Shibata, I. Okamoto, K. Ishii, J. Liq. Chroma
It is known that CTAI shows different properties from CTA II in the field of nanotubes, such as in the field of nanotubes, ...
A method has been reported in which a concentrated solution of trifluoroacetic acid is solidified with water or methanol, but this method has limitations, such as the need to use a strongly acidic solvent.

[Means for solving the problem]

As a result of extensive investigations, the present inventors have found that CTAI can be produced by preparing a solution of CTA in a phenolic liquid as a solvent and then drying or solidifying this solution.

That is, the present invention relates to a method for producing CTAI, which comprises drying or solidifying a solution of CTA in a phenolic liquid as a solvent.

The CTAI in the present invention is defined by the powder X-ray diffraction spectrum.
The X-ray diffraction spectrum of A II is shown in FIGS.
The difference between the two is clear. CTA II has a diffraction angle 2θ of 8
The CTAI is characterized by three peaks at 17°, 10°, and 13°, and a clustered peak at 17° to 19°.
The peaks of CTAI and CTA II are characterized by peaks at 7-8° and 16-17°, respectively, so that they can be easily distinguished from each other. In some cases, the peaks of CTAI and CTA II may appear together, but in such a case, for convenience, the diffraction intensities of the peaks at 7-8°, which is characteristic of CTAI, and the peaks at 10-11°, which is characteristic of CTA II, are compared, and if the former is stronger, it is deemed to belong to the category of CTAI as referred to in the present invention.

The cellulose triacetate (CTA) referred to in the present invention refers to a cellulose having a weight average degree of polymerization of 10 or more, in which 90% or more of the hydroxyl groups of the corresponding cellulose are acetylated.

Phenol-based liquids are phenol, cresol (o,m,p), 2,3-dimethylphenol, chlorophenol (o,m,p), bromophenol (o,m), iodophenol (o,m), and fluorophenol (o,m,p).
This refers to liquids with a melting point of 60°C or less.

In carrying out the present invention, it is not always necessary to use only a phenol-based liquid as the solvent, and other solvents having lower boiling points may be mixed therewith.

In the present invention, to prepare CTAI from a phenolic liquid solution of CTA, the phenolic liquid solvent or the phenolic liquid together with other solvents may be distilled off under moderate reduced pressure to dry or solidify the solution. In this case, it is difficult to completely distill off the phenolic liquid, but when the phenolic liquid content is usually reduced to 20% or less, the characteristic X-ray diffraction peak of CTAI appears, and the target product can be obtained.

On the other hand, it is also possible to precipitate CTA using a non-solvent for CTA, which is particularly effective for removing phenolic liquids from CTA obtained by the above solvent distillation, which has a sufficiently high CTA content and already shows a CTAI diffraction pattern. In this case, a non-solvent with low swelling properties for CTA (e.g., hexane) or a mixture mainly containing this non-solvent (e.g., hexane-2-propanol mixture) is used.

The CTAI produced by the method of the present invention may be in any form, such as particles, fibers, or films, depending on the intended use, and may also be a composition with a carrier or other substance that is incompatible with the CTA.

[Action]

The reason why phenolic liquids form CTAI in the method of the present invention is unclear, but it is thought that strong solvation interactions probably change the molecular conformation, or that high compatibility creates a highly concentrated solution state that takes on a special state such as liquid crystal, resulting in a crystal lattice different from that of a normal solution.

[Effects of the Invention]

The method of the present invention makes it possible to easily produce CTAI of various shapes.
This will make it possible to produce cellulose, which will contribute to the effective use of cellulose.

[Example]

The present invention will be described in detail below with reference to examples. However, it goes without saying that the present invention is not limited to these examples.

In the present embodiment, a Geigerflex manufactured by Rigaku Denki was used to measure the X-ray diffraction spectrum. The slit widths were DS 1/2° and RS
0.15, SS 1/2° was used.

Example 1 Relatively low molecular weight (weight average molecular weight in terms of polystyrene determined by GPC using chloroform as the mobile phase is 9960,
2 g of cellulose triacetate (number average 6500) and 660 mg of phenol were dissolved in 10 ml of dichloromethane, and the dichloromethane was then evaporated to dryness under reduced pressure (0.1 mmHg).
The mixture was heated to 0°C and some of the phenol was distilled off. The cellulose triacetate produced by this treatment contained 19% residual phenol as determined by NMR spectroscopy. The X-ray diffraction spectrum is shown in Figure 3, and clearly shows a diffraction pattern characteristic of CTAI.

Example 2 The cellulose triacetate obtained in Example 1 was dissolved in hexane and 2-
When the mixture was washed with a 9:1 mixture of propanol, the phenol was removed down to trace amounts, but the X-ray diffraction spectrum of the resulting cellulose triacetate was almost the same as that of Example 1.

Example 3: The weight average molecular weight calculated using polystyrene standards by GPC (chloroform solvent) was 166,000, and the number average molecular weight was 58,000.
3g of cellulose triacetate, 2g of phenol, dichloromethane
The mixture was dissolved in 30 ml of water and treated in the same manner as in Examples 1 and 2, after which the X-ray diffraction spectrum was measured. The spectrum obtained was characteristic of CTAI.

[Brief description of the drawings]

1 and 2 show the X-ray diffraction spectra of CTAI and CTA II, respectively, and FIG. 3 shows the X-ray diffraction spectrum of CTAI obtained in Example 1.
FIG. 2 is a diagram showing the X-ray diffraction spectrum of

Claims (1)

[Claims] 1. A method for producing type I cellulose triacetate, comprising drying or solidifying a solution of cellulose triacetate in a phenolic liquid as a solvent.