JP2603829B2 - Drying method for bacterial cellulose membrane - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for drying a cellulose membrane produced by microorganisms, and more particularly to an improved method for drying effectively without destroying the whole membrane.

[Conventional technology and its problems]

Cellulose is the most naturally occurring organic high molecular substance, and is used as it is as cellulose and as a raw material for cellulose derivatives.

Cellulose raw materials obtained from plants are generally in the form of fibers, and can be obtained as a complex containing lignin, hemicellulose, and the like in addition to cellulose and strongly binding to them. Therefore, in order to obtain cellulose fibers, chemical treatment must be performed to remove lignin and a part of hemicellulose. The refined pulp fiber thus obtained (width: 3
(0 to 50 μm; length: 3 to 5 mm) to obtain a cellulose sheet.

On the other hand, Acetobacter xylinum (Acetobacter x
ylinum; hereinafter abbreviated as “AX”) or Acetobacter
Acetogenum (Acetobacter acetigenum; hereinafter, "AA")
Bacteria that convert glucose to cellulose are commonly known as cellulose-producing bacteria, but the cellulose produced by these cellulose-producing bacteria is high in purity and contains almost no lignin and hemicellulose. Absent.

Several proposals have been made regarding the production of cellulose by a cellulosic bacterium. Japanese Patent Application Laid-Open No. 59-120159 discloses that a cellulose thin film formed on the surface of a culture solution is peeled off from a culture medium, and a liquid containing 3% caustic soda is extracted. A method is described in which cells are treated with an aqueous solution to destroy cells, neutralized with acid, and washed with water to recover a thin film. The cellulose thin film thus obtained has a denser and thinner structure than the above-described cellulose sheet made from the purified pulp fiber, has high functionality, and is highly useful as a semipermeable membrane. Furthermore, it is excellent in terms of water retention and is used as artificial skin for treating wounds and burns.

Compared to conventional refined pulp fibers, these characteristics are largely due to the difference in the form of each cellulose fiber. That is, the pulp fiber has a width of 30 to 50 μm and a length of 3 to 5
While bacterial cells are produced as filament bundles of 46 microfibrils with a cross section of about 1.6 nm x 5.8 nm, the size per unit is about 1/1000 of bacterial cellulose. It seems that the structure is dense and functional. Bacterial cellulose also has a larger amount of free hydroxyl groups on the surface of cellulose microfibrils, and the water retention is extremely high.

However, when the bacterial cellulose membrane is dried, these characteristics are disadvantageous, and the higher the water retention rate, the greater the shrinkage due to drying. Therefore, it has been difficult to dry the bacterial cellulose membrane without wrinkles and tears.

[Means for solving the problem]

The essential point after drying according to the present invention is that the cellulose membrane produced by the cellulose-producing bacterium is dried by suspending the membrane with an elastic material, such as rubber, which expands and contracts in response to the internal stress in the membrane caused by drying. It is in.

AX and AA are a kind of aerobic Gram-negative bacteria, about 3
It is a rod-shaped bacterium having a size of μm × 0.6 μm. AX and AA
Among them, those that occur naturally during fermentation of sweet vegetable juice or decay of fruits and vegetables containing saccharose have been found, but in particular, Acetobacter xylinum, a purified strain of AX having high cellulose productivity.・ Strain ATCC
23769 is available from certain suppliers.

AX produces cellulose as a filament bundle of 46 microfibrils with a cross section of about 1.6 nm x 5.8 nm. The fiber length direction is theoretically obtained as continuous as long as the life of AX is continued. That is, it is possible to obtain cellulose having a higher molecular weight than cellulose of plant origin. Since AX is an aerobic bacterium, it is produced as a continuous thin film of aggregates of microfibrils on the surface of a culture solution based on glucose or other hydrocarbons.

Hereinafter, the method for drying a microorganism-produced cellulose membrane of the present invention will be specifically described for AX having a high cellulose production efficiency, but the same can be applied to AA and other cellulose-producing bacteria.

A medium suitable for AX culture is a complex medium containing a sugar and a protein, and for example, those having the following constitutions are known.

Glucose 2.0 w / v% Peptone 0.5 w / v% Yeast extract 0.5 w / v% Disodium phosphate 0.27 w / v% Citric acid 0.11 w / v% Water balance pH using dilute HCl and / or dilute NaOH Adjusted to 6.

Cellulose production by AX desirably has a high space-time yield. The culture temperature is preferably around 28 ° C. since the production rate of cellulose is the highest. When AX is statically cultured, most of the cellulose is obtained as a thin film on the surface of the culture solution.
A gel is obtained in some liquids. In this case, the obtained thin film can be used as an artificial skin as described in JP-A-59-120159.

The AX-producing cellulose in the medium is in a state swollen with water. In the separation and recovery of cellulose, first, an operation of purging remaining water and nutrients contained therein is performed. In the laboratory, all the thin film cellulose is collected on gauze, squeezed and washed with water. In this way, a product containing substantially only cellulose and cells is obtained.

If it is necessary to separate the cells from the above product to obtain only cellulose, alkali treatment, ultrasonic treatment, centrifugation and the like are performed as necessary.

The bacterial cellulose membrane thus obtained is suspended by an elastic material extending in response to shrinkage due to drying as shown in the figure, such as rubber or a spring, and is dried while being held with an appropriate tension. A bacterial cellulose membrane free of germs can be obtained.

The elastic material used in the present invention is weaker than the tensile strength of the membrane, and any material may be used as long as it has a strength that makes the cellulose membrane have an appropriate tension. For example, there are rubber and spring.

The drying temperature may be in the range of 0 to 100 ° C, preferably 20 ° C to 60 ° C. Also, it is better to avoid sudden drying in a short time. It can be air-dried with an appropriate air volume to promote drying.

〔The invention's effect〕

According to the cellulose membrane drying method of the present invention, the membrane can be effectively dried without destroying the whole membrane.

This cellulose membrane has a denser structure than pulp sheets and filter papers obtained from conventional wood fibers and is used not only as a semi-permeable membrane, but also obtained after removal of bacterial cells has high cellulose purity and is used for medical materials and the like. It is also useful.

〔Example〕

Hereinafter, the method of the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1 Acetobacter xylinum strain ATCC23769
Was used and cultured at 30 ° C. for 7 to 14 days in a composite medium having the following composition to form a cellulose membrane.

Glucose 2.0 w / v% Peptone 0.5 w / v% Yeast extract 0.5 w / v% Disodium phosphate 0.27 w / v% Citric acid 0.11 w / v% Water Remaining pH = 6 Adjustment of cellulose separation from culture solution The unit operation performed for this is as follows.

Squeezing: The solid content in the culture solution is taken out on a gauze, wrapped, lightly pressed, and squeezed.

Rinse A: Wash with tap water while wrapping the solid content in the culture solution in gauze.

Alkali treatment: The solid content after squeezing and washing is 100%
Immerse in twice the volume of 1% NaOH and keep at room temperature for 24 hours.

Ultrasonic treatment: The solid content is suspended in water about 100 times the absolute dry volume, and treated at 28 kHz (SONO CLEANER 100, manufactured by KAIZO DENKI) for 1 hour.

Centrifugation: The sonicated suspension is used as is (KUBOTA
(KR / 20000) at 10,000 rpm for 1 hr. Cellulose solids collect below, some of the cells float, and some settle further below the cellulose mass. Except for the cellulose mass, water is added to the original amount, and centrifugation is repeated again to remove cells.

Rinse B: The solid content in the culture solution is rinsed on a filter.

An acrylic case (21.5 mm long, 25.5 mm wide, 28 cm high) was used to dry the bacterial cellulose membrane thus obtained.
5mm), and the ends of the cellulose membrane are fixed in several places with double clips with rubber that can be contracted freely, and one end of the rubber is fixed to an acrylic case so that the cellulose membrane is suspended. The length of the rubber was adjusted to adjust the tension, and the cellulose membrane was uniformly and well stretched.Leave it overnight and air-dry to obtain a flat dried cellulose membrane.Remove the double clip. However, the film did not tear.

Claims (1)

(57) [Claims] 1. A method for drying a bacterial cellulose membrane, wherein a cellulose membrane biosynthesized by a cellulose-producing bacterium is suspended by an elastic body and dried.