JPH06212510A - Cellulosic acetate fiber having regulated biodegradability, its production and seedling cultivating container and greening sheet formed from the same fiber - Google Patents

Abstract

PURPOSE:To obtain cellulose acetate fiber, suitable as a biodegradable material and having a desired biodegradation rate, a method for producing the fiber and a seedling culture container and a sheet for greening a slope having moderate biodegradability. CONSTITUTION:This cellulose acetate fiber has 5-57% acetyl content, 5-90 biodegradation index and regulated biodegradability. Furthermore, this seedling culture container and this sheet for greening containing the fiber as a constituent component are provided. The fiber is obtained by deacetylating fiber composed of cellulose diacetate, cellulose triacetate or cellulose acetate having the intermediate acetyl content with an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate or a mixture thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellulose acetate fiber whose biodegradation rate is adjusted to a desired value, a method for producing the same, and a seedling cultivation container and a slope greening sheet formed from the fiber. .

[0002]

2. Description of the Related Art In recent years, environmental damage has become a very serious problem, and it is a serious problem that synthetic products such as synthetic resins and synthetic fibers, which are difficult to decompose, remain as they are and pollute the environment. .

For example, herbaceous seedlings such as vegetables and flowers,
As a seedling cultivation container for growing woody seedlings such as perennials, a synthetic film-made seedling cultivation container such as PVC is often used.

These containers are inexpensive, have sufficient strength, and are lightweight, but have the following disadvantages.・ You have to take out the seedlings once and replant them in the fields.・ As a result of the roots of the seedlings being densely packed in the container, the roots are wound along the wall of the container (hereinafter, abbreviated as root winding). For this reason, it is necessary to loosen the dense roots at the time of replanting, and in some cases to cut the roots and prun the leaves in order to promote good growth later.・ Replanting may impede the growth of seedlings or even cause them to die. -Used containers have been incinerated, but materials such as vinyl chloride may damage the incinerator and cause air pollution. or,
Does not decompose even if left in the environment and pollutes the environment.

In order to solve such a problem, for example, JP-A-5-103548 discloses a container obtained by padding a semi-dried jute cloth with an alkaline organic binder, and the container is a binder. PH of alkali
It has been shown that the seedlings can be putrefaction within a desired period of time by adjustment, and seedlings can be planted as they are in a field without having to remove them from the container.

However, since the container uses a non-biodegradable urethane resin as a binder, it does not fundamentally solve the environmental problem.

Further, cellulose, which is the main component of jute, has a very short biodegradation period, and the one treated with alkali has a further shorter decomposition period. Moreover, jute has the property of being weakened by the action of sunlight, air, and moisture. Therefore, when such a jute cloth is used, the container will start to deteriorate and decompose during use, and the strength will decrease. In some cases, it could not be used.

That is, the above-mentioned seedling cultivation container has a required biodegradation period which varies depending on the type of plant organism used, and ranges from a short one such as several months to a long one such as 1 to 3 years.

However, since a cellulose product has a very high biodegradation rate, it can be applied in a short period of time such as several months, but it is difficult to set a long-term degradation period of 2-3 years or more. Therefore, it was impossible to meet all uses with cellulosic products.

Japanese Unexamined Patent Publication (Kokai) No. 5-148840 discloses a vegetation bag for greening in which a net-like body made by weaving strong rayon and then preservatively sewn is sewn in a bag shape, and is decomposed for a maximum of about two years. Although it is shown that it has a period, since the constituent material is high in strength, the mesh is formed so as not to hinder the growth when rooting of planting organisms, so the disadvantage that seeds and soil are washed away Had.

On the other hand, although cellulose acetate obtained by acetylating cellulose has a lower decomposition rate than cellulose, it is said to be biodegradable for many years.
It is considered that the above problem can be solved by using this cellulose acetate as a substitute for cellulose.

However, the actual rate of biodegradation of cellulose triacetate is extremely low, and it is difficult to put it to practical use as a biodegradable material.

On the other hand, the method of deacetylating fibers made of cellulose diacetate, cellulose triacetate or cellulose acetate having an intermediate degree of acetylation by alkali treatment has been known for a long time. However, the conventionally known method is a method in which deacetylation is completely performed to obtain cellulose, and high-strength fibers such as hollow fibers for artificial dialysis and fortisane are produced, and biodegradability is not adjusted. It was

[0014]

DISCLOSURE OF THE INVENTION An object of the present invention is to solve the above problems and to provide a cellulose acetate fiber having a desired biodegradation rate, which is suitable as a biodegradable material, a method for producing the same, and an appropriate biodegradation. To provide a seedling cultivation container having a property and a sheet for slope greening.

[0015]

Means for Solving the Problems The present inventors have conducted various studies in order to achieve the above-mentioned object, and as a result, can control the biodegradation rate by changing the acetylation degree of cellulose acetate fiber, and The inventors have found that it is possible to improve the drawbacks of conventional seedling cultivation containers or slope-vegetation mats by using cellulose acetate fibers having an optimized decomposition rate, and completed the present invention.

That is, according to the present invention, the degree of acetylation is 5 to 53.
%, And a biodegradation index of 5 to 90, the biodegradable modified cellulose acetate fiber, and cellulose diacetate, cellulose triacetate, or cellulose acetate having an acetylation degree intermediate between these. There is provided a method for producing the above cellulose acetate fiber, which comprises deacetylating the resulting fiber with an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate or a mixture thereof.

Further in accordance with the present invention, 50 of the constituents
A seedling cultivation container formed from a cloth having a weight percentage of cellulose acetate fibers of at least 5% to 53% and a biodegradation index of 5 to 90. And a biodegradable controlled seedling cultivation container, and a greening sheet formed from a woven or knitted fabric in which 50% by weight or more of the constituents are cellulose acetate fibers, and the degree of acetylation of the cellulose acetate fibers is 5 There is provided a biodegradable regulated greening sheet, characterized in that it has a biodegradation index of 5 to 90 and a biodegradation index of 5 to 90%.

The cellulose acetate fiber of the present invention must have an acetylation degree of 5 to 57%. The biodegradation rate of cellulose acetate fiber is easily affected by environmental conditions such as soil type, season, humidity, etc., but depending on these environmental conditions and purpose of use, the cellulose acetate fiber has a degree of acetylation of 5 to 57%. Can be used to obtain the desired biodegradation rate.

When the degree of acetylation is less than 5%, the biodegradation rate becomes substantially equal to that of cellulose, and the biodegradation rate is too fast to cause the above-mentioned problems. On the other hand, when the degree of acetylation exceeds 57%, the rate of biodegradation rapidly decreases, and it cannot be put to practical use as a biodegradable material.

Further, the cellulose acetate fiber of the present invention is required to have a biodegradation index of 5 to 90.

When the biodegradation index is less than 5, the biodegradation rate is rapidly reduced and it is difficult to put it into practical use as a biodegradable material. On the other hand, when the biodegradability index exceeds 90, the biodegradability is substantially the same as that of cellulose, and the seedling cultivation container or the vegetation sheet for greening intended by the present invention cannot be obtained.

Here, the biodegradation index is defined as follows. That is, a cellulose acetate fiber having a single yarn denier of 3.0 was used as a commercially available cellulase (manufactured by Wako Pure Chemical Industries, Trichode
(derived from rmaviride), it is treated by shaking in 50 mmol / l acetate buffer (pH 4.0) at 40 ° C. for 4 days. In this case, the enzyme concentration is 1 mg / ml and the sample concentration is 0.5%.

Tensile strength was measured 5 times on the treated fiber,
The ratio of the strength of the fiber before treatment to the strength of the fiber is calculated by the following formula and used as a biodegradation index.

[0024]

[Equation 1]

The cellulose acetate fiber of the present invention is required to have an appropriate strength and elongation in accordance with the purpose of use, and usually has a strength of 1.3 g / de or more and an elongation of 15%. The above is preferable.

In order to produce the cellulose acetate fiber of the present invention, a fiber made of cellulose diacetate, cellulose triacetate or cellulose acetate having an intermediate degree of acetylation is used to form sodium hydroxide, potassium hydroxide, sodium carbonate or a mixture thereof. It may be deacetylated with an aqueous solution of the mixture.

Examples of the alkaline compound used in the deacetylation treatment include sodium hydroxide, potassium hydroxide, sodium carbonate and mixtures thereof. Sodium hydroxide and sodium carbonate are preferable in view of cost and the like. is there.

Weak alkaline compounds such as disodium hydrogen phosphate, sodium hydrogen carbonate, calcium carbonate and the like are not suitable because they cannot perform rapid and sufficient deacetylation in a usual treatment method.

Fibers made of cellulose diacetate, cellulose triacetate or cellulose acetate having an intermediate degree of acetylation may be subjected to deacetylation treatment in the form of yarn or cloth, or seedling cultivation containers or slope greening. It may be processed after being formed into a sheet for use.

The deacetylation treatment may be a batch treatment or a continuous treatment as long as the treatment conditions are appropriately selected. In any of the treatments, it is necessary to select an appropriate alkali concentration, treatment temperature and treatment time, and if they are mistaken, it is impossible to obtain a cellulose acetate fiber having a desired acetylation degree and biodegradation index.

In the case of batch processing, the processing time is usually 20.
Minutes to 2 hours, preferably 30 minutes to 1.5 hours, and in the case of continuous treatment, within 20 minutes, preferably within 10 minutes,
More preferably, it is 1 to 7 minutes.

In any case, the treatment temperature and alkali concentration should be adjusted to the treatment time in consideration of the thickness of thread, the structure, the structure of the cloth when the cloth is processed, the characteristics of the processing apparatus, and the like. I have to decide.

From a practical point of view, a suitable treatment temperature is 30 to 120 ° C. If the treatment temperature is lower than this, a rapid and sufficient deacetylation reaction does not occur, and if the treatment temperature is higher than this, deacetylation is performed. Becomes too rapid, making it difficult to freely adjust the acetylation degree.

The cellulose acetate fiber of the present invention is required to have an appropriate strength and elongation depending on the purpose of use, and usually has a strength of 1.3 g / de or more and an elongation of 15 or less.
% Is preferable, but when the deacetylation treatment is carried out for a long time in a high temperature alkaline solution, a decrease in fiber strength may be observed.

Therefore, it is desirable to avoid long-time treatment at a high temperature, but deacetylation treatment should be performed while tension is applied to the fiber, or tension or elongation should be applied to the fiber after the deacetylation treatment. As a result, a decrease in fiber strength can be prevented.

In this case, if the elongation of the fiber becomes too low, the toughness of the fiber is lost and it becomes difficult to put it into practical use. Therefore, it is important to take care not to reduce the elongation too much.

In the present invention, various additives may be added to the alkaline solution used for the deacetylation treatment for the purpose of promoting or delaying the deacetylation treatment and improving the structure and physical properties of the fiber after the treatment. it can.

In the seedling cultivation container of the present invention, the cloth made of the above-mentioned cellulose acetate fiber and, if necessary, the binder and the like are directly put into a mold and subjected to pressure / heat molding, or the cloth is cut and attached. It can be obtained using a known method such as a method of obtaining.

Here, the cloth means a woven fabric, a knitted fabric or a non-woven fabric made of cellulose acetate fibers, and a paper made of powder, pulp or capsules obtained by crushing the fibers,
Also includes sheet-like materials.

The fabric weight, thickness, woven structure, etc. of the cloth may be appropriately set according to the desired biodegradation index, and the preferable range of biodegradation index is 10 to 5 for herbaceous seedlings.
0, 10-80 for woody seedlings.

Further, the cloth for forming the seedling cultivation container of the present invention must contain 50% by weight or more of the above-mentioned cellulose acetate fiber. If this value is less than 50%, it becomes difficult to control the biodegradation rate.

Other constituent materials contained in a proportion of less than 50% by weight may be used as long as they do not impair the ability to adjust the biodegradation period from the short term to the long term, which is the object of the present invention, and the physical properties and air permeability of the container. , Materials that can improve water permeability, and more preferably, materials that biodegrade. In addition to this, agents such as pesticides and fertilizers may be added to the seedling cultivation container for the purpose of promoting growth of seedlings and improving soil.

The slope greening sheet of the present invention can be obtained by weaving and weaving the above-mentioned cellulose acetate fibers.

There is no particular limitation on the design of the knitting and weaving, and a plain weave, a twill weave, a leno weave, a dummy weave or the like, and a warp knit, a flat knit or a circular knit can be used.

Here, when the sheet is made of a non-woven fabric, the object of the present invention cannot be achieved because it is caught by stones or trees when it is laid and is torn.

The basis weight and thickness of the sheet may be appropriately set according to the desired biodegradation rate.

The slope greening sheet of the present invention must contain the above-mentioned cellulose acetate fiber in an amount of 50% by weight or more. If this value is less than 50%, it becomes difficult to control the biodegradation rate.

Other constituent materials contained in a proportion of less than 50% by weight may be used as long as they do not impair the ability to adjust the biodegradation period from the short term to the long term, which is the object of the present application, and the physical properties and breathability of the sheet. , Materials that can improve water permeability, and more preferably, materials that biodegrade. In addition, agents such as agricultural chemicals and fertilizers may be added to the slope greening sheet for the purpose of promoting growth of plant life and improving soil.

Then, the slope greening sheet is formed into a sandbag or the like in the sheet state or sewn in a bag shape,
Used for greening roads and hillside slopes.

[0050]

The present invention takes advantage of the fact that the degree of acetylation of cellulose acetate fibers and the rate of their biodegradation are closely related to each other. Cellulose diacetate, cellulose triacetate or an intermediate degree of acetylation thereof is used. By controlling the deacetylation reaction of the fiber made of cellulose acetate having, to make a cellulose acetate fiber having a desired degree of acetylation and biodegradation index, thereby, the desired biodegradation rate required depending on the application It was made possible.

Further, since the seedling cultivation container of the present invention has a biodegradability-controlled cellulose acetate fiber as a main constituent, it is less susceptible to deterioration by sunlight, air, and moisture during use, and the decomposition period can be adjusted. When it is buried in soil or the like, it can be biodegraded to a desired degree within a desired period even for a short period or a long period of time. Therefore, it is suitable for cultivating a wide variety of seedlings from herbaceous seedlings to woody seedlings.

Further, since the slope greening sheet of the present invention mainly comprises the cellulose acetate fiber whose biodegradability is adjusted, it is not easily deteriorated by sunlight, air or moisture during use, and the decomposition period is long. Can be easily adjusted, and when it is buried in soil or the like, it can be biodegraded to a desired degree within a desired period for a short period or a long period.

Further, since the fibers constituting the sheet have low strength, the growth of planting organisms is not hindered at the time of rooting, and the slope is planted with various kinds of plants having different growth periods. Suitable to do.

The present invention is described below with reference to examples, but the present invention is not limited to these examples.

[0055]

Examples 1-12, Comparative Examples 1-4 53 denier, 28
After making the cellulose diacetate multifilament yarn of the filament into a cylindrical knit, an anionic surfactant (2 g /
Using l), it was scoured at 60 ° C. for 10 minutes. The denier of the scoured multifilament yarn was 50 denier, the strength was 1.50 g / de, and the elongation was 20%. 8 This refined cylindrical knitted multifilament yarn was deacetylated at the alkali compound, alkali concentration, bath ratio, treatment temperature and treatment time shown in Table 1.

[0056]

[Table 1]

The degree of acetylation, biodegradation index, strength and elongation of each multifilament yarn after deacetylation treatment are as shown in Table 2.

[0058]

[Table 2]

These deacetylated tubular multifilament yarns were embedded in the soil collected at the Osaka Research Center of Teijin Limited in Omihara, Ibaraki City, Osaka Prefecture, and the temperature was adjusted to 3
It was kept at 0 ° C. and kept for 1 month and 3 months under sufficient humidity to measure the weight, the strength and the elongation, and the weight retention rate, the strength retention rate and the elongation retention rate were calculated. The results are as shown in Table 3.

[0060]

[Table 3]

As is clear from these results, the cellulose acetate fibers of the present invention (Examples 1 to 12) have a moderate biodegradation rate, but the degree of acetylation is less than 5%, and the biodegradation index. When it exceeds 90 (Comparative Examples 2 and 4), the rate of biodegradation is too fast, and it is almost decomposed only by burying it in the soil for only one month. When the degree of acetylation exceeds 57% and the biodegradation index is less than 5 (Comparative Examples 1 and 3)
Does not function as a biodegradable material as it hardly decomposes even after being buried in soil for 3 months.

[0062]

Example 13 Since the cellulose acetate fiber of Example 3 had a low strength of 1.17 g / de, it was left in boiling water for 30 minutes while applying the tensile load shown in Table 4. As a result, as shown in Table 4, the strength could be improved.

[0063]

[Table 4]

[0064]

Examples 14 to 17 and Comparative Examples 5 and 6 75 denier, 2
Scoured taffeta consisting of 0 filament cellulose diacetate multifilament yarn (Basis weight 60 g / m
² ) was used and the deacetylation treatment was carried out under the same conditions as in Example 1 except that the treatment temperature was changed as shown in Table 5. The acetylation degree, biodegradation index, strength and elongation of each multifilament yarn after deacetylation treatment are as shown in Table 5.

[0065]

[Table 5]

With respect to these deacetylated taffetas, the soil decomposition test described above was conducted, and the weight retention rate, strength retention rate and elongation retention rate were calculated. Also, for comparison, 7
The same soil decomposition test was carried out on a scoured rayon taffeta (weight per unit area: 70 g / m ² ) composed of rayon yarn of 5 denier and 30 filaments. The results are shown in Table 6.

[0067]

[Table 6]

From these results, taffeta (Examples 14 to 17) made of the cellulose acetate fiber of the present invention was
It has a moderate biodegradation rate, but the degree of acetylation is less than 5%,
When the biodegradation index exceeds 90 (Comparative Example 6) and the rayon taffeta has an unsuitable biodegradation rate, the degree of acetylation exceeds 57% and the biodegradation index is less than 5 (comparison). It is clear that Example 5) hardly decomposes even after being buried in soil for 3 months and does not function as a biodegradable material.

[0069]

Example 18 Using a cellulose acetate fiber having a degree of acetylation of 54.7% and a biodegradation index of 7, an acetate nonwoven fabric was produced by a known method. The single yarn fineness of the cellulose acetate fiber constituting the nonwoven fabric was 5.0 denier, and the basis weight of the nonwoven fabric was 300 g / m ² .

This nonwoven fabric was heated and pressure-molded at a temperature of 220 ° C. and a gauge pressure of 200 kg / cm ² using a mold for molding a container to obtain a desired seedling cultivation container.

Culture soil, fertilizer and the like were put in this container, seedlings of woody seedlings were grown and grown to an appropriate size. At this time,
No deterioration and decomposition of the container was observed. As a result of planting the seedlings grown to an appropriate size together with the container in the soil of the field, the container was biodegraded and composted in about 3 years.

[0072]

[Embodiment 19] As in Embodiment 18, the basis weight is 450 g /
After producing a non-woven fabric of m ^2, the non-woven fabric is treated with alkali according to a known method to obtain a degree of acetylation of 15% and a biodegradation index of 80.
A non-woven fabric composed of cellulose acetate fibers was obtained. The basis weight of this nonwoven fabric was 310 g / m ² .

This non-woven fabric was dipped in an aqueous solution of polyvinyl alcohol (hereinafter abbreviated as PVA) having a concentration of 5%, squeezed to a pickup of 100% and dried until the water content became 20%.

Thereafter, as in Example 1, the temperature was 120 ° C.,
Heat and pressure molding were carried out at a gauge pressure of 200 kg / cm ² to obtain a desired seedling cultivation container.

Culture soil, fertilizer and the like were put in this container to grow herbaceous seedlings. At this time, some deterioration and decomposition of the container was observed, but there was no problem in use. Then, as a result of planting the seedlings together with the container in the soil of the field as in Example 1, the container was biodegraded and composted in about 3 months.

[0076]

Comparative Example 7 A non-woven fabric made of rayon fiber having a single yarn fineness of 4.0 denier and having a basis weight of 300 g / m ² was used.
In the same manner as in No. 9, PVA treatment, heat and pressure molding,
A seedling cultivation container was obtained.

Culture soil, fertilizer and the like were put in this container, and seedlings were grown in the same manner as in Example 18. At this time, the deterioration and decomposition of the container was so large that it was difficult to continue to use it as a seedling cultivation container.

[0078]

[Comparative Example 8] Similar to Example 19, a basis weight of 2 consisting of cellulose acetate fibers having a degree of acetylation of 3% and a biodegradation index of 95.
A nonwoven fabric of 90 g / m ² was obtained and molded into a seedling cultivation container.

Culture soil, fertilizer, etc. were put into this container, and seedlings were grown in the same manner as in Example 18. As a result, deterioration and decomposition were large, and it was difficult to continue to use it as a seedling cultivation container.

[0080]

[Comparative Example 9] Single yarn fineness of 3.0 denier, acetylation degree of 58%,
Using cellulose triacetate fiber with a biodegradation index of 0,
A container was prepared in the same manner as in Example 18 except that the molding temperature was 290 ° C.

Culture soil, fertilizer and the like were put in this container, and seedlings were grown in the same manner as in Example 18. As a result, deterioration and decomposition of the container did not occur. Then, as a result of planting the seedlings together with the container in the soil of the field in the same manner as in Example 18, a decrease in the container strength was observed after 3 years. However, no remarkable loss of morphology was observed, and the growth of trees was inhibited.

[0082]

Example 20 A taffeta having a basis weight of 700 g / m ² made of cellulose acetate fibers having an acetylation degree of 54.7%, a biodegradation index of 7, and a single yarn fineness of 3.7 denier was sewn in a bag shape.

Into this bag, predetermined soil, fertilizer and plant seeds were mixed, charged, and the mouth was tied to make a sandbag.

As a result of laying this sandbag on the slope, there was no problem in handling the sandbag during installation (ease of handling, damage to the cloth, etc.) and there was no damage due to stones, trees, roots, etc. on the slope.

Three years after the laying, the strength of the exposed portion of the bag is about half that of the original strength, and the growth of the plant that broke the bag was completely inhibited. There wasn't.

After a further two years had passed, corrosion had progressed to a tattered surface, and the slope was vegetated and plants were growing.

[0087]

[Embodiment 21] Similar to Embodiment 20, the basis weight is 300 g /
The taffeta m ² alkali and reduced by known methods, the degree of acetylation 15%, biodegradation index 80, basis weight 205g / m to give a ² taffeta, which was sewn into a bag shape given soil, fertilizers and plant Seeds were mixed, thrown in, tied at the mouth, and sandbags were created.

When laid on the slope as in Example 20,
There was no problem in handling the sandbags during installation (ease of handling, damage to the cloth, etc.).

After the lapse of half a year after laying, the shape of the bag exposed on the surface remained firmly, but the strength was considerably lowered. However, no soil or plant seed runoff was observed, and good plant growth was observed.

One year after the laying, the corrosion was severe and the plants were broken down, but the plants were well grown and the slope was green.

[0091]

Example 22 The same cellulose acetate fiber as in Example 20 was used as a warp knit and was laid in a sheet shape on the slope.

At this time, a predetermined fertilizer, a water retaining material and plant seeds were laid on the slope at the same time. There was no problem in handling the knitted fabric when it was laid, and there was no damage caused by stones, trees, roots, etc.

After 5 years from the laying, corrosion had progressed to a tattered surface, and the slope was vegetated and plants were planted.

[0094]

[Comparative Example 10] A commercially available hemp bag (with a fabric weight of about 300 g / m2)
² ), a bag made of a cotton cloth (plain weave) having a basis weight of 300 g / m ² , and a bag made of cellulose acetate taffeta having a basis weight of 193 g / m ^2, an acetylation degree of 3% and a biodegradation index of 95 are the same as in Example 20. It was laid on the slope.

At the time half a year passed after the installation, all the bags were broken, and some of them were damaged, and soil was washed away. In addition, part of the greening of the slope was done, but it was not enough due to soil loss.

[0096]

The cellulose acetate fiber of the present invention is
Biodegradability is controlled by controlling the degree of acetylation,
Depending on the purpose of use, a suitable biodegradation rate can be obtained, and after achieving the intended purpose, it does not decompose and pollute the environment, so agricultural materials, marine products, packaging materials It can be widely used as a building material and the like.

Further, the seedling cultivation container and the slope greening sheet containing the above-mentioned cellulose acetate fiber as a main component are not easily deteriorated and decomposed by sunlight, air and moisture during use, and when they are buried in the soil or the like. Causes a desired degree of biodegradation within a desired period regardless of a short period or a long period, and does not inhibit the growth of plant organisms.

Further, since the required seedling cultivation container is completely biodegraded, it is extremely useful without any special disposal treatment or fear of environmental pollution.

Claims (6)

[Claims] 1. A biodegradable cellulose acetate fiber having a degree of acetylation of 5 to 57% and a biodegradation index of 5 to 90. 2. The strength is 1.3 g / de or more and the elongation is 15.
% Of the biodegradable cellulose acetate fiber according to claim 1. 3. Deacetylation of fibers made of cellulose diacetate, cellulose triacetate or cellulose acetate having an intermediate degree of acetylation with an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate or a mixture thereof. A method for producing a cellulose acetate fiber according to claim 1. 4. The method according to claim 3, wherein tension is applied or stretching is performed after deacetylation. 5. A seedling cultivating container formed from a cloth in which 50% by weight or more of the constituents are cellulose acetate fibers, and the acetylation degree of the cellulose acetate fibers is 5 to 5.
A biodegradable controlled seedling cultivation container, which is 7% and has a biodegradation index of 5 to 90. 6. A greening sheet formed from a woven or knitted fabric in which 50% by weight or more of the constituent components are cellulose acetate fibers, wherein the cellulose acetate fibers have a degree of acetylation of 5 or less.
A biodegradable regulated greening sheet, which has a biodegradation index of 5 to 90%.