JPH10219088A - Control of degradability of polylactic acid-based resin, degradable film/sheet and formed material from the film/sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject polymer capable of effectively forming an initial degradation thereof e.g. a crack and as a result accelerating a hydrolysis by water so as to enhance the degradability of the polymer by blending a specific amount of an inorganic particles. SOLUTION: This method for controlling the degradability of a polylactic acid-based polymer is to blend (A) 100 pts.wt. polylactic acid-based polymer (e.g.; a polymer having 50,000-100,000 weight averaged molecular weight and containing >=94% lactic acid unit, with (B) 1-120 pt.wt. inorganic particles (e.g.; silica, titania, talc, alumina, a clay, calcium carbonate, magnesium carbonate and a glass powder, and having a large specific surface area) for enhancing the degradability of the component A. Further, the blending of the components A and B can be performed simultaneously with the formation, but it is more preferable to be performed by melt extruding the sufficiently dried components A and B by separate extruders for peletization before the formation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the degradability of a polylactic acid-based polymer, and to a degradable film / sheet or a molded article comprising the film / sheet.

[0002]

2. Description of the Related Art Among biodegradable resins, aliphatic polyesters have been attracting attention because alcohols and carboxylic acids produced during decomposition are extremely low in toxicity, and have become commercially available. Typically, there are polycaprolactone, polyhydroxybutyrate, polyhydroxybutyrate / valerate copolymer, polyethylene succinate, polybutylene succinate and the like. However, these resins have a problem that the glass transition point is considerably low at -60C to 10C.

[0003]

On the other hand, among the aliphatic polyesters, polylactic acid polymers have a high glass transition point, exhibit properties similar to polyethylene terephthalate, are crystalline, and are oriented by biaxial stretching. In addition, extrusion casting is possible and transparency is good, but biodegradability is very poor.

[0004]

Means for Solving the Problems As a result of a detailed study of the decomposition mechanism of polylactic acid-based polymer, the present inventors have found that polylactic acid-based polymer is firstly hydrolyzed by water and then biodegraded by microorganisms. Biodegradation by microorganisms is extremely slow at low temperatures, but is sufficiently fast at high temperatures.Hydrolysis by water causes initial disintegration of molded articles, for example, on the surface of a film or sheet. It has been found that it is promoted by the cracks that occur.
In addition, they have found that the blending of the inorganic particles is effective in causing this initial disintegration.

That is, the present invention relates to a polylactic acid-based polymer 1
A method for controlling degradability and a degradable film or sheet comprising the polylactic acid-based polymer in an amount of from 1 to 120 parts by weight to increase the degradability of the polylactic acid-based polymer. Exists in molded products.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid polymer used in the present invention is a homopolymer of lactic acid (referred to as "polylactic acid").
Alternatively, it is a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture thereof. Lactic acid is L-
Lactic acid, D-lactic acid, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, and 6-hydroxycaproic acid. Can be
Thus, in order to enhance the crystallinity of the polylactic acid-based polymer, the mixing ratio of L-lactic acid or D-lactic acid is preferably set to 94% or more.

[0007] The weight average molecular weight of these polymers is preferably in the range of 50,000 to 100,000.
Below this range, problems such as practically no practical properties are exhibited. On the other hand, if it exceeds, the melt viscosity becomes too high and the moldability is poor. Further, in order to improve the thermal stability, it is preferable that the amount of the remaining monomer or the catalyst is small. For the production of such a polymer, any known method such as a condensation polymerization method and a ring-opening polymerization method can be adopted.For the purpose of increasing the molecular weight, a small amount of a chain extender, for example, a diisocyanate compound, diepoxy Compounds, acid anhydrides, acid chlorides and the like may be used.

In the present invention, the polylactic acid-based polymer is mixed with inorganic particles. Examples of the inorganic particles used include particles of silica, titania, talc, alumina, clay, calcium carbonate, magnesium carbonate, glass powder, and the like. The size and shape of the particles are not particularly limited, but a larger specific surface area is preferable because it enhances the disintegration effect. In addition, the mixing ratio is 100% of the polylactic acid-based polymer.
1 to 120 parts by weight of inorganic particles, preferably 3 to 1 part by weight
When the amount of the inorganic particles is less than 1 part by weight, the decomposability cannot be enhanced, and when the amount is more than 120 parts by weight, the physical properties of the molded article, for example, the tensile strength are reduced and the practicality is lost.

In the above compounding, other polymer materials may be added as long as the effects of the present invention are not impaired. Also,
Additives and modifiers such as plasticizers, lubricants, reinforcing agents, UV absorbers, light stabilizers, fungicides, pigments, fluorescent agents, etc. for the purpose of adjusting moldability and other physical properties of films and sheets It is also possible. Of course, auxiliary materials such as the above-mentioned polymer materials, additives, and modifiers can be added in advance to the polylactic acid-based polymer or the inorganic particles before blending.

In the present invention, the blending of the polylactic acid-based polymer with the inorganic particles and the addition of the above-mentioned auxiliary materials may be carried out simultaneously with the extrusion of the film / sheet described below.
Prior to film / sheet extrusion, it is preferred that the extruder is melt-extruded into a strand shape using another extruder and pelletized. In order to prevent the hydrolysis of the polylactic acid-based polymer at the melting temperature in the extruder, it is desirable that the raw materials are sufficiently dried in advance.

Next, the pelletized polylactic acid-based polymer is usually melt-extruded from a die using an extruder and formed into a film or sheet. As a special case, if it passes through a molten state, it may be pellet press-molded or calendered.

As the extruder used for the above-mentioned pelletizing or film sheeting, any known form such as a single-screw, co-rotating twin-screw, and different-direction twin-screw extruder can be used. For pelletization, it is common to use a co-rotating twin-screw extruder having a high kneading effect. The set temperature of the extruder is appropriately determined depending on the chemical composition and molecular weight of the polylactic acid-based polymer, but is preferably in the range of 170 to 230 ° C. That is, at 170 ° C. or lower, polylactic acid having a high melting point does not melt, and at 230 ° C. or higher, thermal decomposition becomes remarkable.

In order to obtain a film, a flat or cylindrical material melt-extruded from a T-die, an I-die, a round die or the like is quenched by a cooling cast roll, water, pressurized air or the like. The film is uniaxially or biaxially stretched by a roll method, a tenter method, a tubular method, or the like.
Further, a so-called inflation method, in which melt extrusion is performed from a round die and air is blown into a cylindrical material that is still in a molten state to reduce the thickness, can also be preferably used.

Further, by using a film stretching and heat fixing technique disclosed in Japanese Patent Application Laid-Open No. 5-508819 and Japanese Patent Application Laid-Open No. 6-23836, transparency, mechanical strength, rigidity, and thermal dimensional stability can be improved. A polylactic acid-based film having excellent properties and the like can be obtained. The thickness of the film is determined in the range of 10 to 250 μm according to the application.

The most preferable method for obtaining a sheet is a method in which the sheet is extruded into a flat shape using a T-die and quenched by a metal cast roll equipped with a temperature control device. If necessary, the sheet is separated from the cast roll. By nipping with a metal roll, a polylactic acid-based sheet having extremely excellent transparency and smoothness can be obtained. The thickness of the sheet is generally determined in the range of 250 μm to 1 mm depending on the application.

The present invention is also directed to the decomposable film / sheet obtained as described above and a molded product comprising the film / sheet. Examples of a method for obtaining a molded product from a film / sheet include a thermoforming method, such as a vacuum forming method and a pressure forming method, which can be used for blister processed products, food cups, trays, and the like. Also,
It can also be used as a box-shaped package, for example, by folding a sheet with a folding ruled line. In addition, paper and metal foil,
It is also used for sheets laminated with other plastic films and molded products thereof.

[0017]

The present invention is not limited by the following examples. The measurement and evaluation shown in the examples were performed under the following conditions.

(1) Tensile strength Using Toyo Seiki Tensilon II type machine, JIS K712
7 was measured. Tensile speed during measurement is 10
0 mm / min.

(2) Degradability test Simplified compost test A commercially available domestic composter is compared with 10 kg of horticultural humus and 5 kg of commercially available dog food.
, And further mixed with 500 ml of water, and
The burial was 0 mm. The sample is 40m from the film
The sample was cut into mx 100 mm, inserted into a sample holder composed of two 60 mm x 150 mm wire meshes (3 mm mesh), and bound with a fine wire through the mesh. The sample was minimized from coming into contact with the outside and being disintegrated and scattered. The sample is one example or one
Six comparative samples were prepared and buried together with the sample holder so that the six posters were vertically parallel in the embedding of the composter. The lower bottom of each holder is 25mm from the bottom of the buried soil
And the upper base was placed at a depth of 25 mm from the surface of the embankment. One holder was removed every week after embedding, and the state of the surface of the sample was observed to confirm the presence or absence of collapse. The weight loss of the sample for the first week after embedding was examined and used as an index of the decomposition speed. From the weight loss, the reduction of the polylactic acid polymer itself was calculated by the following equation. Loss of polylactic acid polymer (mg) = Weight loss (mg)
X ratio Ratio = [number of polylactic acid polymer] / [number of polylactic acid polymer + number of inorganic particles]

Submerged Immersion Degradation Test In-water immersion method in the field test of the Biodegradable Plastics Study Group (“Field Test of Biodegradable Plastics” Technical Committee Report of the Biodegradable Plastics Study Group Report 1 (September 1992) ), And the test was performed.
That is, a film sheet was cut out into a size of 120 mm × 30 mm, and was sandwiched between the central portions of three stainless steel sample holders. A window with the same shape as the sheet sample is opened in the center of the sample holder, and two stainless steel meshes (40 mesh) are used to prevent the sheet from flowing out and have good contact with water. It was in a state. The appearance of the sample after immersion in fresh water for 2 years was observed.

Comparative Example 1 and Example 1 The ratio of the structural unit composed of L-lactic acid to the structural unit composed of D-lactic acid was about 98: 2, the glass transition point was 58 ° C., and the melting point was 175.
C., 100 parts by weight of polylactic acid pellets having a weight average molecular weight of 180,000 were anatase type crystalline titanium dioxide A-170 (average particle size 0.15 μm) manufactured by Sakai Chemical Industry Co., Ltd.
0.5 parts by weight (Comparative Example 1) and 5 parts by weight (Example 1) were blended, respectively, and extruded in a strand shape at 220 ° C. with a 26 mmΦ biaxial kneading extruder to prepare two types of pellets. Each of the two types of titanium dioxide-containing pellets was extruded from a T-die at 210 ° C. with a 30 mmφ single-screw extruder, and rapidly cooled with a casting roll to obtain a white unstretched sheet having a thickness of about 0.4 mm. Table 1 shows the results of the measurement of the tensile strength and the results of the decomposability test (simple compost test).

Comparative Example 2 A transparent unstretched sheet having a thickness of about 0.4 mm was obtained in the same manner as in Example 1 except that titanium dioxide was not added. Table 1 shows the measured values and evaluation results.

[Examples 2 to 3 and Comparative Example 3]
In place of titanium dioxide, 10 parts by weight of fine powder silicon dioxide thyricia 310 (average particle size: 1.4 μm) manufactured by Fuji Silysia Chemical Ltd. (Example 2), 100 parts by weight
Except for using parts by weight (Example 3) and 150 parts by weight (Comparative Example 3), a thickness of about 0.4
mm transparent unstretched sheet was obtained. Table 1 shows the measured values and evaluation results.

Example 4 and Comparative Example 4 The unstretched sheets obtained in Example 1 and Comparative Example 2 were immediately roll-stretched 2.3 times at 70 ° C. in the longitudinal direction, and then 75 ° C. in the width direction. Then, the sheet was stretched to 2.6 times with a, and the sheet was guided to a heat treatment zone, and heat set at 130 ° C for 20 seconds. The thickness of the obtained stretched sheet is 0.2 mm. Table 1 shows the measured values and evaluation results.

[0025]

[Table 1]

From the results shown in Table 1, the following facts were confirmed. In the unstretched film, Example 1 was compared with Comparative Examples 1 and 2, and in Examples 2 and 3, Comparative Example 2 was used.
The weight loss in the initial stage is larger than that of, and the disintegration tends to start earlier. In Comparative Example 3, the decomposition was remarkable, but the tensile strength was significantly reduced as compared with Examples 2 and 3, and the practicality was inferior. Also, in the stretched heat-set film, the decomposition is faster in Example 4 in which the inorganic particles are blended than in Comparative Example 4 in which the inorganic particles are not blended.

Example 5 and Comparative Example 5 The unstretched sheets obtained in Example 1 and Comparative Example 2 were subjected to a water immersion decomposition test. Table 2 shows the results.

[0028]

[Table 2]

Table 2 shows that the decomposition was accelerated by the blending of the inorganic particles even in the natural environment.

[0030]

According to the present invention, the decomposability of the polylactic acid-based polymer can be increased while maintaining a practical strength by blending a specific amount of inorganic particles. Accordingly, the decomposable film / sheet of the present invention or a molded article comprising the film / sheet is used in applications where it is desired to decompose quickly in a natural environment, for example, a seedling pot or a cutting wood tape used in a one-year cycle, or It is suitable for a fishing tackle, a packaging material such as a bait or the like which is easily scattered in the environment by mistake.

Claims (2)

[Claims] 1. A method for controlling degradability, comprising adding 1 to 120 parts by weight of inorganic particles to 100 parts by weight of a polylactic acid-based polymer to enhance the decomposability of the polylactic acid-based polymer. 2. A decomposable film or sheet comprising 100 parts by weight of a polylactic acid-based polymer and 1 to 120 parts by weight of inorganic particles to enhance the decomposability of the polylactic acid-based polymer.・ Molded product consisting of sheet.