JP4520843B2 - Method for producing biodegradable film - Google Patents

Description

  The present invention relates to a method for producing a biodegradable film, and more particularly to a method for producing a film made of a thermoplastic resin containing polyhydroxyalkanoate (hereinafter abbreviated as “PHA”) as a main component.

  Biodegradability that is decomposed in the natural environment and reduced to carbon dioxide and water since the social problem that the huge amount of plastics discarded in the natural environment causes environmental destruction The development of plastic is underway. At present, known biodegradable plastics are classified according to production methods, such as chemical synthesis methods (for example, polylactic acid and polybutylene succinate), natural product blends (for example, starch and cellulose, and these and other degradable plastics). ), Microorganism-produced polyester (for example, poly (3-hydroxybutyrate) (hereinafter abbreviated as “PHB”), poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter, Abbreviated as “PHBV”))) and the like.

  Among these, microbial-produced polyester is a storage material in which microorganisms accumulate in the body, and is a polymer substance that is used as an energy source when microorganisms are starved. There are many microorganisms in the natural environment that decompose microorganism-producing polyester. Polyesters produced by microorganisms are found in natural environments such as soil, rivers, lake water, seawater, activated sludge, and compost. Even if it exists, it shows the decomposability | degradability which was excellent in any environment of aerobic and anaerobic. In addition, it has excellent characteristics such that it does not generate toxic gas during combustion, uses plant-derived materials, and is carbon neutral that does not increase carbon dioxide on the earth. Among PHA, PHB which is a homopolymer has the highest crystallinity and a high melting point. When PHA is a copolymer, physical properties such as melting point (heat resistance) and flexibility can be changed by controlling the composition ratio of the monomer units (components) constituting the PHA.

  In this way, PHA is manufactured from renewable plant raw materials and is excellent in biodegradability, which solves the problem of waste and is excellent in environmental compatibility.・ It is expected to be applied to civil engineering, agriculture, horticultural materials.

  On the other hand, PHA has two major problems with processability. One is poor processability resulting from a slow crystallization rate, and the other is a decrease in molecular weight due to thermal decomposition when heated to a high temperature. For example, among PHAs, PHB has a high melting point of 175 ° C. and a high processing temperature. Therefore, it is easy to be thermally decomposed during heat processing, and the molecular weight of the molded body is reduced, so that the processing width is narrow. On the other hand, in the case of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter abbreviated as “PHBH”), the proportion of the 3-hydroxyhexanoate component among the copolymer components increases. Then, melting | fusing point falls, heat processing temperature can be lowered | hung and thermal decomposition can be suppressed. Further, in order to improve the slow crystallization speed of PHAs, many studies have been made on the addition of a crystal nucleating agent, and boron nitride, talc and the like are known as the crystal nucleating agent.

  When PHA is cooled from the molten state, it crystallizes at a temperature equal to or higher than the glass transition temperature (hereinafter abbreviated as “Tg”). However, the film is brittle and difficult to stretch, and thus a high strength film is produced. I couldn't. The reason why the drawing is difficult is said to be due to large spherulites generated by crystallization of PHA, or because of the occurrence of cracks due to secondary crystallization that occurs in the amorphous part of PHA (for example, Non-Patent Document 1, (Refer nonpatent literature 2.).

  In order to solve this problem, in fiberization, a method has been proposed in which PHA melted in an extruder is rapidly cooled to Tg of a polymer immediately after extrusion, and then heated and stretched to Tg or more (for example, a patent) Reference 1). Also, in the production of films, after forming a PHA melt film, it is proposed to rapidly cool and solidify to Tg + 10 ° C or lower to produce an amorphous film, and then stretch the amorphous film, followed by tension heat treatment. (For example, see Patent Document 2).

These methods are characterized in that the melted polymer is rapidly cooled to Tg or less and solidified once in an amorphous state. In general, the Tg of PHA is room temperature or less, and it is industrially necessary to rapidly cool to Tg or less. It is not economical. Further, in the case of a film, there is a problem that large spherulites are likely to be generated because the degree of stretching is smaller than that of fibers and no large tension is applied.
JP 2002-371431 A JP 2003-31824 A “Biopolymers” Volume 4, Polyesters III Applications and Commercial Products, WILEY-VCH, p64 Supervised by Yoshio Inoue, latest green plastic technology, CM Publishing, p147

  An object of the present invention is to find a practical method that enables stretching with a film using PHAs, and to provide a production method capable of obtaining a high-strength biodegradable film. A further object of the present invention is to provide a biodegradable film that is excellent not only in strength but also in flexibility and elongation.

  As a result of intensive studies to achieve the above object, the present inventors once crystallized the molten film, and then applying pressure at a temperature below the softening temperature of the resin and above the glass transition temperature. By stretching (rolling), it has become possible to stretch to a higher degree and a film having high strength can be obtained, and the present invention has been completed.

  That is, in the first aspect of the present invention, when producing a film made of a thermoplastic resin mainly composed of polyhydroxyalkanoate, the resin is melted to form a film, and the melted film is once crystallized. Thereafter, the biodegradable film is produced by rolling at a temperature not higher than the melting point of the resin and not lower than the glass transition temperature, followed by primary stretching, and further secondary stretching at a temperature higher than the rolling temperature.

  A second aspect of the present invention is a method for rolling the primary stretching using a roll in the method for producing the biodegradable film.

  A third aspect of the present invention is a method of performing roll rolling at a temperature in the range of 20 to 90 ° C. in the method for producing the biodegradable film.

4th of this invention is a manufacturing method of the said biodegradable film, The said polyhydroxyalkanoate is produced from microorganisms, following formula (1)
[—CHR—CH ₂ —CO—O—] (1)
(However, in the formula (1), R is an alkyl group represented by C _n H _{2n + 1, n} is an integer of 1 to 15.)
It is the method which is an aliphatic polyester copolymer which consists of 2 or more types of repeating units shown by these.

  According to a fifth aspect of the present invention, in the method for producing a biodegradable film, the polyhydroxyalkanoate is a poly (3-hydroxybutyrate-co-3- wherein n = 1 and 3 in the formula (1). Hydroxyhexanoate) (PHBH).

  Furthermore, a sixth aspect of the present invention is the method for producing a biodegradable film, wherein the composition ratio of the copolymer component in the poly (3-hydroxybutyrate-co-3-hydroxyhexanoate, PHBH) is (3 -Hydroxybutyrate) / (3-hydroxycyhexanoate) = 99/1 to 70/30 (mol / mol).

  According to the method for producing a biodegradable film according to the present invention, a PHA that has conventionally been difficult to obtain a high-strength film has sufficient strength as a film, and is flexible and stretchable as necessary. A good film can be obtained. This makes it possible to produce films that can be used for applications such as garbage bags, compost bags, agricultural films, etc., taking advantage of the excellent biodegradability characteristic of PHA. PHA is a plant-derived polymer that is gentle to the global environment without increasing carbon dioxide and can contribute to the prevention of global warming.

As PHA used for this invention, PHB and following formula (1)
[—CHR—CH ₂ —CO—O—] (1)
(However, in the formula (1), R is an alkyl group represented by C _n H _{2n + 1, n} is an integer of 1 to 15.)
And an aliphatic polyester copolymer (polyhydroxyalkanoic acid copolymer (polyhydroxyalkanoate copolymer) such as PHBV and PHBH). Among these PHAs, it is possible to obtain a high-strength film even if PHB is used, but this polymer is close to the melting temperature and processing temperature and the processing temperature range is narrow, and the resulting film is hard and flexible. Tend to be poor. In addition, although physical properties of PHBV change depending on the content of 3-hydroxyvalerate, the difference in structure between 3-hydroxybutyrate and 3-hydroxyvalerate is a difference in one methylene group in the side chain. The degree of conversion does not change greatly and the flexibility is still limited. On the other hand, in PHBH, when the content of 3-hydroxyhexanoate is increased, the crystallinity is drastically decreased, and it is possible to obtain a flexible polymer having high tensile elongation. Accordingly, PHBH is more preferable as the PHA used in the present invention. In this case, it is more preferable that the composition ratio of the copolymerization component in the PHBH is (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 99/1 to 70/30 (mol / mol). When the composition ratio is higher than 99/1, that is, when 3-hydroxybutyrate is too much, it is close to PHB, the processing temperature width is narrowed, and the film tends to be hard. When the composition ratio is lower than 70/30, that is, when 3-hydroxyhexanoate is too much, the melting point of the resin becomes too low and the heat resistance of the film tends to be lowered.

  As the PHAs used in the present invention, those produced by microorganisms, that is, those obtained by a fermentation synthesis method are preferably used. The microorganism that can be used in the fermentation synthesis method is not particularly limited as long as it is a microorganism having the ability to produce PHAs. Examples of PHB-producing bacteria include natural microorganisms such as Alkigenes eutrophus (Alcaligenes eutrophus, Ralstonia eutropha), Alkigenes latus, Alcaligenes faecalis, and other natural microorganisms. In these microorganisms, PHB accumulates in the microbial cells. Examples of the copolymer-producing bacteria of hydroxybutyrate and other hydroxyalkanoates include PHBV and PHBH-producing bacteria such as Aeromonas caviae and poly (3-hydroxybutyrate-co-4-hydroxybutyrate). Alcaligenes eutrophus, which is a rate producing bacterium, is known. In particular, with regard to PHBH, in order to increase the productivity of PHBH, Alcaligenes eutrophus AC32 strain (FERM BP-6038) into which genes of PHA synthase group have been introduced (J. Bateriol., 179, 4821-4830) (1997)) is more preferable, and microbial cells obtained by culturing these microorganisms under appropriate conditions and accumulating PHBH in the cells are used.

  Carbon sources and culture conditions used for culturing microorganisms having the ability to produce PHAs as described above are described in JP-A-5-93049, JP-A-2001-340078, and the like. For example, fats and oils such as vegetable oil and fish oil are used as the carbon source, and culture is performed to produce PHA as a storage substance inside the microbial cell under the restriction of nutrients such as nitrogen, phosphorus and minerals other than the carbon source. In addition, pH, temperature, aeration volume, culture time and the like as culture conditions are appropriately adjusted.

  The PHA used in the present invention has a weight average molecular weight (hereinafter abbreviated as “Mw”) in the range of 50,000 to 3,000,000. If the Mw is too low, the melt viscosity becomes too low and difficult to process, and if it is too high, the melt viscosity becomes too high and the fluidity becomes poor, and the shear heat generation becomes large and the process becomes difficult. The range of Mw of PHA suitable for processing is about 100,000 to 1,500,000.

  The PHA film of the present invention usually contains compounding agents used in the production of resin films, for example, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, colorants such as dyes or pigments, plasticizers, thickening agents. Agents, lubricants, crystal nucleating agents, antistatic agents, inorganic fillers such as talc or calcium carbonate, and the like can be used depending on the purpose.

  Moreover, you may blend another polymer in the range which does not impair the characteristic of PHA. The polymer to be blended is preferably a polymer that does not impair the biodegradability of PHA, and includes natural products such as polylactic acid and polybutylene succinate, such as starch and cellulose, which are produced by a chemical synthesis method.

  The method for producing a biodegradable film according to the present invention uses a thermoplastic resin mainly composed of PHA as a raw material, melts the resin with a hot press, an extruder, a roll, a calender, or the like to form a film. Once crystallized, the resin is stretched (rolled) by applying pressure at a temperature lower than the softening point temperature of the resin and higher than the glass transition temperature (Tg) (primary stretching), and further stretched at a temperature higher than the rolling temperature. (Secondary stretching).

  In the above method, the temperature at which the melted film is crystallized is not particularly limited, but the melted film is rapidly cooled to a temperature near Tg, and then the temperature is raised to crystallize, or the melted film is left in a room temperature atmosphere. It may be cooled and crystallized. In the examples described later, for the purpose of experimentation, the former method was used for crystallization.

  Moreover, the rolling in the primary stretching is preferable because roll rolling performed using a roll is simple and can be applied industrially. Roll rolling can be performed by heating the roll in a temperature range of about 20 to 90 ° C., and adjusting the draw ratio by adjusting the clearance of the roll. Roll rolling ratio can be performed in the range of about 1.2 to 5 times.

  Furthermore, the secondary stretching is also carried out at a temperature range below the melting point and above the glass transition temperature, preferably at 30 to 90 ° C. If the temperature is too low, the secondary stretching ratio cannot be increased. If the temperature is too high, the resin is softened and fractured, and the secondary stretching ratio cannot be increased. The secondary stretching can be suitably performed in warm air or warm water.

  Hereinafter, although the manufacturing method of the biodegradable film which concerns on this invention is demonstrated in detail based on an Example, this invention is not restrict | limited only to these Examples.

(Examples 1-6, comparative example)
In Example 1 of JP 2001-340078 A, using Alcaligenes eutrophus AC32 strain (accession number FERM BP-6038) into which a PHA synthase group gene derived from Aeromonas caviae was introduced. Culture was performed by the method described to produce PHBH. Specifically, Alcaligenes eutrophus AC32 strain (Alcaligenes eutrophus C32, accession number FERM BP-6038) (hereinafter abbreviated as “AC32 strain”) was cultured as follows. The composition of the pre-medium was 1 w / v% Meat-extract, 1 w / v% Bacto-Trypton, 0.2 w / v% Yeast-extract, 0.9 w / v% Na ₂ HPO ₄ · 12H ₂ O, 0.15 w / It was set as v% KH ₂ PO ₄ (pH 6.7). The composition of the polyester production medium is 1.1 w / v% Na ₂ HPO ₄ · 12H ₂ O, 0.19 w / v% KH ₂ PO ₄ , 0.6 w / v% (NH ₄ ) ₂ SO ₄ , 0.1 w / v% MgSO ₄ .7H ₂ O, 0.5 v / v% trace metal salt solution (1.6 W / v% FeCl ₃ .6H ₂ O in 0.1 N hydrochloric acid, 1 w / v% CaCl ₂ .2H ₂ O, 0 0.02 w / v% CoCl ₂ .6H ₂ O, 0.016 w / v% CuSO ₄ .5H ₂ O, 0.012 w / v% NiCl ₃ .6H ₂ O, 0.01 w / v% CrCl ₃ .6H ₂ O 2 w / v% Proextract AP-12 (Banshu seasoning), 5 × 10 ⁻⁶ w / v% kanamycin. The carbon source was oil and fat alone, and palm oil, palm kernel oil or palm oil 4 w / v% was added in three portions. The glycerol stock of the AC32 strain was inoculated into the pre-culture medium and cultured for 20 hours, and then inoculated at 1.5 v / v% into a 10 L jar fermenter (Maruhishi Bio-Engineered MD-500 type) containing 6 L of production medium. The operating conditions were a culture temperature of 30 ° C., a stirring speed of 400 rpm, an aeration rate of 1.8 L / min, and a pH controlled between 6.6 and 6.8. For control, 5N sulfuric acid and sodium hydroxide were used. The culture was performed for up to 72 hours. The cells were collected by centrifugation, washed with methanol, and lyophilized. After the polyester (PHBH) was extracted from the dried cells using chloroform, the cell components were removed from the chloroform solution containing PHBH by filtration, and methanol was added to the filtrate to precipitate PHBH. Thereafter, the supernatant was removed by centrifugation and dried to recover PHBH. The average Mw of PHBH after completion of the culture was 1.38 million. This was pelletized with a 35 mm single screw extruder at an extrusion temperature of 190 ° C., and the content of 3-hydroxyhexanoic acid was 7 mol%, Mw = 400,000, melting point (hereinafter abbreviated as “Tm”) = 144 to 147. A PHBH resin pellet having a Tg of about 4 ° C. was obtained. The PHBH resin pellet sample was placed in a vacuum press machine, and the sample was melted at a vacuum press machine internal temperature of about 150 ° C. to remove air. Thereafter, the press machine was put into ice water and rapidly cooled to Tg or less to produce a film having a thickness of about 1 mm. The produced film was crystallized at 40 ° C. for 12 hours. The crystallized film is cut into 5 mm × 25 mm square, and using a heat stretching machine manufactured by Imoto Seisakusho, at a roll rolling temperature of 40 ° C., the roll rotation speed is changed so that the stretching ratio is about twice. Roll rolling was performed in the gap between the two rolls. The roll-rolled film was cut into a width of 1 mm and secondarily stretched at various magnifications with a hand-drawing stretcher in a warm bath at 40 ° C., 60 ° C., 80 ° C., and 90 ° C. Immediately after stretching, it was cooled in ice water.

About the film obtained as mentioned above, the mechanical property measurement was performed with the following method.
Tensile test: A tensile tester CATY500BH manufactured by Yonekura Seisakusho was used (test length: 20 mm, tensile speed: 200 mm / min).

  Table 1 shows the maximum total stretch ratio (stretch ratio after secondary stretching) of the film when the primary stretching ratio was changed at a crystallization temperature of 40 ° C. and a roll rolling (primary stretching) temperature of 40 ° C.

  As is apparent from Table 1, unless primary stretching by roll rolling is performed as in the comparative example, stretching is almost impossible (the film breaks), and the maximum total stretching ratio is not twice or more. On the other hand, when roll rolling (primary stretching) is performed, secondary stretching is possible, and the maximum total stretching ratio is 20 times. When the roll rolling ratio was doubled, the maximum draw ratio was the highest.

  Further, the tensile property of the film when the roll stretching ratio of the primary stretching is fixed to 2.0 and the secondary stretching temperature is changed to 60 ° C. (Example 4-1) and 80 ° C. (Example 4-2). It shows in Table 2.

  As is clear from Table 2, the higher the total draw ratio, the higher the tensile strength and the tensile modulus, and the highest value was obtained for the film stretched 20 times. Further, stretching at 80 ° C. showed higher tensile physical properties.

  Furthermore, the tensile physical properties of the film when the secondary stretching speed is 50 mm and 500 mm / min are shown in FIGS. As is clear from FIGS. 1 and 2, the tensile property was higher when the secondary stretching speed was 500 mm / min. Further, even when the crystallization temperature was changed to 30 ° C., 40 ° C., 60 ° C., and 80 ° C., the draw ratio did not change so much, and the tensile properties were equivalent.

It is a graph which shows the relationship between the draw ratio (times) and tensile strength in case secondary stretch speed is 50 mm / min and 500 mm / min. It is a graph which shows the relationship between a draw ratio (times) and a tensile elasticity modulus in case secondary stretch speed is 50 mm / min and 500 mm / min.

Claims (6)

  In manufacturing a film made of a thermoplastic resin mainly composed of polyhydroxyalkanoate, the resin is melted to form a film, and after the molten film is crystallized, the melting point of the resin is below the melting point. And the manufacturing method of the biodegradable film characterized by rolling at the temperature more than a glass transition temperature, carrying out primary extending | stretching, and also extending | stretching secondary at temperature higher than the said rolling temperature.   The method for producing a biodegradable film according to claim 1, wherein the primary stretching is performed using a roll.   The method for producing a biodegradable film according to claim 2, wherein the roll rolling temperature is in the range of 20 to 90 ° C. The polyhydroxyalkanoate is produced from a microorganism and has the following formula (1)
[—CHR—CH ₂ —CO—O—] (1)
(However, in the formula (1), R is an alkyl group represented by C _n H _{2n + 1, n} is an integer of 1 to 15.)
The manufacturing method of the biodegradable film in any one of Claims 1-3 which is an aliphatic polyester copolymer which consists of 2 or more types of repeating units shown by these.   The biodegradable film according to claim 4, wherein the polyhydroxyalkanoate is poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) consisting of n = 1 and 3 in the formula (1). Production method. The composition ratio of the copolymerization component in the poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) is (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 99/1 to 70 / The method for producing a biodegradable film according to claim 5, which is 30 (mol / mol).

Images