JP2010106051A - Biodegradable starch composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable starch composition that can be used in place of a plastic material to be useful in various applications such as vessels for eating and drinking, various packaging materials such as a sheet, a film and the like, cushioning materials, daily commodities, agrochemical supplies, and the like, and exhibits molding processability and excellent properties which neither inhibit the use in various applications nor damage its value. <P>SOLUTION: A natural rubber latex as an essential ingredient in an amount of 3-10 pts.wt., in terms of solid content, is incorporated with 100 pts.wt. of starch to obtain the starch composition that is excellent in molding processability and gives a molded article exhibiting excellent properties. Thus, the starch composition has biodegradability, exhibits excellent molding processability and has excellent properties such as impact strengths, and resistance to flexing crack and an elongation ratio of a sheet. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a starch composition mainly composed of starch that biodegrades or disintegrates in a short period of time when it is disposed of, and in particular, various packaging materials such as food and drink containers, sheets and films, cushioning materials, life The present invention relates to a starch composition that can be suitably used in various applications such as articles and agricultural products, and has biodegradability with improved impact strength and bending cracking of sheets.

  Conventional plastic molded products are difficult to decompose in the natural environment when discarded, and are a factor that pollutes the environment. Therefore, in recent years, it has been studied to use a molded product made of a material that can be decomposed in a natural environment, and is actually used. Various types of biodegradable resins such as polylactic acid and modified starch are known as resin materials that can be decomposed in such a natural environment. Since these biodegradable resins are finally decomposed by microorganisms in the natural environment even if discarded, they do not have an adverse effect on the environment, and are therefore environmentally friendly resin materials.

  Starch, one of these biodegradable resins, is a plant-derived natural polymer material that is absorbed by the original plant (starch) during the growth process, based on the amount of carbon dioxide emitted during combustion. It is a so-called carbon neutral material that has the same amount of carbon dioxide. However, starch itself is a high molecular weight material, and if it remains as starch, it lacks fluidity during molding and has difficulties in molding processability. Starch that has been plasticized by treatment such as chemical modification such as etherification is used.

On the other hand, it is also handled by additives, and considering that it is biodegradable and environmentally friendly, the additive added to the starch composition is preferably as natural as possible.
Since petroleum-based plastic additives are often used to improve physical properties and moldability (Patent Documents 1 and 2), when manufacturing a molded product using a starch composition as an environmentally friendly material, The amount added should be considered to be minimal.

  Conventional starch compositions include starch, plasticizers such as glycerin, ethylene glycol, propylene glycol and sorbitol, hydrophilic polymer materials such as polyvinyl alcohol and carboxymethylcellulose, lubricants such as glycerin esters and fatty acids, polypropylene and polyethylene. It is used with the addition of fillers such as petroleum-based plastics, talc and clay, and coloring materials such as dyes and pigments.

  In addition, such starch compositions are produced by various molding methods such as extrusion molding, T-die extrusion molding, injection molding, vacuum pressure forming, etc., and various packaging materials and disposable products such as shopping bags and garbage collection bags. , Disposable lunch boxes, cups, food trays, knives, forks, spoons, toothbrushes, combs and agricultural products such as agricultural bags, seedling pots, cultivation sets, compost bags and cushions, food and beverage containers, etc. In recent years, such starch molded products have begun to be partially used as environmentally friendly molded products in place of petroleum-based plastic molded products.

  However, the starch composition is fragile, for example, there is a problem of bending cracking of the sheet that breaks when the sheet obtained from the T-die extruder is bent at 180 ° θ, and the injection made of the starch composition There is also a problem that when a thick container, which is a molded product, is dropped on a concrete floor, it is easily broken, so that it cannot be used practically.

In petroleum-based plastics, a rubber-based impact resin is added to improve impact resistance (Patent Document 3). However, the present condition is that the starch composition which does not produce impact resistance and bending cracking while maintaining the biodegradability corresponding to the environment is still undergoing trial and error.
JP 2001-64458 A JP 2004-155842 A JP-A-8-259800

  The present invention, when using a starch composition in various fields of application, emphasizes the above-mentioned environmental friendliness, and forms moldings for food and beverage containers, various packaging materials, cushioning materials, agricultural products, daily necessities, etc. Provided is a starch composition useful as a material and having biodegradability excellent in impact strength and bending cracking of a sheet.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors, in the present invention, as follows, by adding a predetermined amount of natural rubber latex as a starch composition, it is gentle to the natural environment after disposal, And it can be set as the starch composition which has the biodegradability which is excellent in impact strength and the bending crack of a sheet | seat, and came to solve the said subject.

In order to solve the problems of the present invention, the first of the present invention is that the natural rubber latex, which is an essential component, is added in an amount of 3.0 to 10.0 parts by weight with respect to 100 parts by weight of starch. It is the starch composition which has the biodegradability characterized.
The second of the present invention is a starch composition having biodegradability, characterized in that a natural rubber latex is added with a storage stabilizer.

The third of the present invention is a starch composition having biodegradability, characterized in that natural rubber latex is a storage stabilizer added with ammonia.
The fourth aspect of the present invention is a starch composition having biodegradability, characterized in that natural rubber latex has neutralized ammonia.

The fifth aspect of the present invention is a biodegradable starch composition characterized in that the natural rubber latex is a field (sap) latex.
The sixth aspect of the present invention is a starch composition having biodegradability, characterized in that natural rubber latex is chemically modified.

A seventh aspect of the present invention is a biodegradable starch composition characterized in that natural rubber latex is physically concentrated by centrifugation.
The eighth aspect of the present invention is a starch composition having biodegradability, wherein the starch is raw starch.

The ninth one of the present invention is a starch composition having biodegradability, wherein the starch is a physically modified starch.
A tenth aspect of the present invention is a starch composition having biodegradability, wherein the starch is a chemically modified starch.
By using the starch composition having each biodegradability, the present invention has been completed.

The starch composition obtained by adding a predetermined amount of natural rubber latex to the starch of the present invention has excellent impact strength and bending cracking of the sheet, and is also suitable for extrusion molding, injection molding, vacuum pressure molding,
Molding such as inflation molding and press molding is possible.
Therefore, the biodegradable starch composition of the present invention can be applied to food and drink containers, various packaging materials, cushioning materials, etc. as a more suitable environment-friendly composition as an alternative to petroleum-based plastics. is there.

  In the present invention, by adding a storage stabilizer and ammonia, degradation such as degradation of natural rubber latex by proteins and microorganisms contained in natural rubber latex is suppressed, and natural rubber latex is stabilized and has appropriate biodegradability. The starch composition which has is obtained. In addition, although natural rubber latex that has been adjusted to prevent pH degradation by adding ammonia is stabilized, the ammonia odor remains, so neutralization treatment removes the ammonia odor and eliminates unpleasant odor starch A molded body made of the composition can be obtained.

In addition, the natural rubber latex can be separated by protein concentration by centrifuging the natural rubber latex, so the natural rubber latex itself is stabilized and contains natural rubber latex. As a starch composition, a stable quality biodegradable product is obtained.
Furthermore, by using a field latex that is easily coagulated as a natural rubber latex, and by using a modified product obtained by reacting a vinyl monomer with a natural rubber latex and maintaining the biodegradability of the natural rubber latex, A molded article having excellent characteristics and physical properties can be molded.

The present invention will be described in more detail below.
First, regarding the composition of the starch composition of the present invention, raw starch is used as the starch composition used in the starch composition having biodegradability excellent in impact strength and bending cracking of the sheet according to the present invention. Examples thereof include starch, bean starch, tapioca starch, potato starch, wheat starch, rice starch, black mackerel starch, castor starch, lotus starch, sago starch, bracken starch, and waste starch.

  Physically modified starch can also be used, and examples include alpha starch and wet heat starch.

  Furthermore, starch chemically modified to such an extent that it does not affect biodegradability can also be used, for example, acetoacetate esterified starch, acetate esterified starch, hydroxymethyl etherified starch, hydroxypropyl ether starch, carboxymethyl etherified starch, Allyl etherified starch, methyl etherified starch, succinate esterified starch, xanthogen acetate esterified starch, nitrate esterified starch, urea phosphate esterified starch, phosphate esterified starch, phosphate crosslinked starch, formaldehyde crosslinked starch, acrolein Crosslinked starch, epichlorohydrin crosslinked starch, etc. can be mentioned.

  In the present invention, the starch can be used alone or in combination of two or more from raw starch, physically modified starch or chemically modified starch.

  In the present invention, an essential component of the biodegradable starch composition is natural rubber latex. Natural rubber latex is extracted from Hevea brazilian trees and produced mainly in tropical countries such as Thailand, Malaysia, Indonesia, etc., and it is widely used in the rubber and tire industries by taking advantage of its excellent physical properties.

A field latex is preferably used as the natural rubber latex.
Field latex contains cis-1,4-polyisoprene as the main component, and non-rubber components include proteins, lipids, sugars, and microorganisms.
If the H region is left in the range of 5 to 9 for a long time, it solidifies. The main reason for this is that microorganisms contained in the natural rubber latex decompose proteins and sugars in the natural rubber latex and release carbon dioxide.

  In the present invention, due to the instability of the field latex described above, the field latex can be a latex added with an additive, that is, the latex added with ammonia or an antiseptic that functions as a storage stabilizer as an additive. . Further, a physically treated latex obtained by concentrating field latex by centrifugation, or a latex chemically modified with vinyl monomer or the like can also be used.

  Therefore, in order to remove or stabilize proteins and lipids contained in the natural rubber latex, the present invention decomposes them by adopting an enzyme treatment as a method for removing proteins and lipids, ammonia or carbamic acid. By adding a preservative such as salt, coagulation is prevented and stabilized. In addition, since the ammonia-added latex generates odor due to ammonia, it is difficult to handle because the application field is limited. Therefore, in the present invention, it is necessary to eliminate the ammonia odor by neutralizing the ammonia. You can also. In addition, by centrifuging natural rubber latex, the components such as protein and lipid are physically separated to concentrate natural rubber latex and remove protein to stabilize natural rubber latex. The deterioration of the quality of the starch composition containing natural rubber latex is suppressed.

  Furthermore, in the present invention, by using a natural rubber latex particle that has been chemically modified with a modifying monomer, the physical properties of the rubber possessed by the starch composition containing the natural rubber latex are adjusted. As the modifying monomer, for example, a vinyl monomer is used. Specific examples of vinyl monomers include (meth) acrylic acid ester monomers, vinyl cyanide monomers, aromatic vinyl monomers, and the like. In particular, methyl methacrylate is suitably used as the (meth) acrylic acid ester monomer, and the graft ratio to the natural rubber latex is generally in the range of 10 to 60% by weight in terms of solid content.

In the present invention, the natural rubber latex can be used alone or in combination of two or more of the various natural rubber latexes.
The solid content concentration of the natural rubber latex is not particularly limited, but a preferable range is 40 to 60% by weight. If the solid content concentration is less than 40% by weight, the water content exceeds 60% by weight, making it difficult to remove the water in the composition. Further, when the solid content concentration exceeds 60% by weight, the latex concentration becomes high. For example, the aggregation of latex particles becomes remarkable at the time of mixing by a Henschel mixer, and it becomes difficult to maintain a uniform mixed state.

  The main components of the starch composition of the present invention are composed of starch and natural rubber latex, and the composition is constituted by adding 3 to 10 parts by weight of the natural rubber latex as a solid content to 100 parts by weight of starch. If the solid content concentration of the natural rubber latex is less than 3 parts by weight, the impact strength and cracking at the time of bending of the sheet are poor, and if it exceeds 10 parts by weight, the softening temperature decreases, the toughness or the tensile strength decreases. Therefore, the molded product is soft and has no waist, so that the coating for products is limited, which is not preferable.

  The starch composition having biodegradability of the present invention can be suitably used for various uses such as food and drink containers, various packaging materials such as sheets and films, cushioning materials, daily necessities, and agricultural products. In addition to the starch and natural rubber latex, various additives are selected according to various uses and required physical properties and functions, and are added singly or in combination of two or more without departing from the object of the present invention. You can also.

  Examples of the additive used include addition of a plasticizer because starch having a high molecular weight is used as a molding material. Specific examples of the plasticizer include sorbitol, mannitol, D-glucose, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, trimethylolpropane, and pentaerythritol. .

In the composition of the present invention, a hydrophilic polymer material such as polyvinyl alcohol, carboxymethyl cellulose, polyacrylic acid polymer, polyacrylamide or the like is added. By adding this hydrophilic polymer material, moisture contained in the natural rubber latex can be absorbed at the time of mixing with a Henschel mixer, and the dry-up can be greatly accelerated, which is effective for molding starch. In particular, polyvinyl alcohol (hereinafter referred to as “PVA”) is biodegradable and has a plasticizer function of starch. PVA is obtained by saponifying vinyl ester units. Examples of the vinyl compound monomer for forming the vinyl ester unit include vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl benzoate and the like. Among them, vinyl acetate is preferable from the viewpoint of obtaining PVA. PVA generally becomes less soluble in cold water due to crystallization due to hydrogen bonding between hydroxy groups as the degree of saponification increases (close to 100%). Also, when the degree of saponification is low (approximately less than 60%), it becomes difficult to dissolve in cold water due to an increase in hydrophobic groups.
Considering rapid dry-up with a Henschel mixer, a preferred PVA is a partially saponified PVA having a saponification range of approximately 80 to 90%.

In the starch composition of the present invention, it is preferable to add silica. By adding silica, adhesion between the natural rubber particle surfaces can be suppressed. When molding the starch composition, for example, when the moisture contained in the natural rubber latex is removed during mixing with the Henschel mixer used, the natural rubber particles tend to adhere to each other, and the natural rubber particle surface is tacked. Since the surfaces of the natural rubber particles are sticky, the natural rubber particles adhere to each other, and the natural rubber particles and the raw material starch are agglomerated or agglomerated. However, by adding silica as in the present invention, adhesion between the natural rubber particle surfaces can be suppressed.
As the silica to be used, wet method silica, dry method silica, synthetic silicate-based silica and the like can be used. The addition amount of silica depends on the addition amount of natural rubber latex, but as a rough guide, the ratio of solid content of natural rubber latex to silica is 10: 1.

  A filler may be added to the biodegradable starch composition of the present invention in order to adjust the mechanical strength and reduce the blending cost. Suitable fillers include calcium carbonate, talc, clay, mica and the like. Examples of the lubricant include glycerin ester, fatty acid, fatty acid metal salt, paraffin, and polyethylene wax. Furthermore, in order to improve the molding processability and physical properties, petroleum plastics such as polyethylene, polypropylene, polystyrene, polyamide, polyester, ethylene / vinyl acetate copolymer, alkylene / acrylate or methacrylate copolymer, Polymer materials such as methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, hydroxybutylmethylcellulose and other biodegradable resins such as polylactic acid, water, and the like can also be added. Colorants such as titanium oxide, carbon black, dyes, and pigments can be used as necessary. In order to improve the mechanical strength, natural fibers such as kenaf and hemp, synthetic fibers such as polyester and polyamide, and reinforcing materials such as various whiskers and glass fibers can be used.

Also, chemical foaming agents such as azodicarbonamide, p, p'-oxybisbenzenesulfonyl hydrazide, N, N'-dinitrosopentamethylenetetramine, carbon dioxide, nitrogen gas and butane are used to reduce weight and improve heat insulation. Hydrocarbon foaming agents such as pentane and propane, inorganic foaming agents such as sodium bicarbonate, and hollow bodies such as shirasu balloons, glass balloons and organic balloons can also be added.

  For the purpose of flame retardancy, bromine compound flame retardants such as pentabromodiphenyl, octabromodiphenyl ether, decabromodiphenyl ether, phosphate ester flame retardants such as triphenyl phosphate, antimony compounds such as antimony trioxide and antimony pentoxide Flame retardants, metal hydroxide flame retardants such as aluminum hydroxide and magnesium hydroxide can be added. In addition, additives such as an antioxidant, a crosslinking agent, and a compatibilizing agent can be appropriately added as necessary.

  For the production of the molded article of the present invention, a usual petroleum-based plastic molding technique can be applied. For example, starch, natural rubber latex and other additives are mixed in a mixer such as a Henschel mixer, tumbler mixer, barbary mixer, kneader mixer, etc. It is possible to employ a molding processing technique and a molding processing machine such as manufacturing of a sheet by using an inflation molding machine, manufacturing a film by an inflation molding machine, manufacturing a sheet by a calendar molding machine, and manufacturing a molded product by an injection molding machine.

Also, instead of kneading, mixing and forming the starch composition as a raw material as it is, after mixing with a mixer, producing pellets with a uniaxial or biaxial extruder, and using the pellets as master pellets It is also possible to carry out molding processing such as production of products by each molding processing machine and production of molded products by a vacuum pressure machine.
When manufacturing pellets, cutting of strands extruded from the strand die is considered to cause product defects (such as pinholes) because starch is hygroscopic when cut after cooling in a water bath. Hot cutting is preferred.

  When producing the molded product with the same composition of the biodegradable starch composition of the present invention, the molding temperature range employed is extrusion molding, T-die extrusion molding, injection molding, inflation molding, etc. In general, it is in the range of 160 to 220 ° C. When the molding temperature exceeds 220 ° C., burns and decomposition occur. In extreme cases, the color changes to brown or black, and the molding machine is damaged by seizure in the cylinder. Moreover, in the molding temperature range below 160 ° C., the starch composition is discharged in an unmelted state, which is not preferable. In a remarkable case, the shearing force between the cylinder and the screw is increased, which causes a trouble with an increase in pressure.

  Also, when the residence time in the cylinder is long, the starch composition is burnt and decomposed. Although depending on the molding temperature and the discharge speed, the residence time in the cylinder is preferably within 5 minutes at the maximum.

  The purging operation after molding is important, and if there is a residue, foreign matters are mixed into subsequent molded products, causing defective products. In particular, injection molding requires caution. For example, starch may be unstable due to moisture content. This is because the starch-containing water in the cylinder becomes water vapor, and the screw is returned to the vapor pressure. As a result, the screw backs at the timing when the pressure is changed from the holding pressure, and in the case of remarkable, the set value may be exceeded and the measurement may become impossible. Accordingly, the starch composition is set to a high back pressure so that a constant amount can be supplied during measurement, and the screw rotation speed is set to be slow. Further, if the rotational speed is increased too much, it may cause burns or disassembly.

  Moreover, the sheet | seat extrusion-molded by the T-die extruder sets the temperature of a take-up roll to 60 degrees C or less, cools the sheet | seat shape | molded by predetermined thickness, and is taken up and wound up.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to a following example, unless the summary is exceeded.

  About the obtained biodegradable starch composition, in order to evaluate the physical properties of the biodegradable starch composition, a sheet of a test sample was molded by the following sample preparation method, and the sheet was molded according to the following measurement method The tensile strength, elongation rate, impact strength and flex cracking by Izod impact test were measured and evaluated. The measurement method was performed as follows.

Measuring method <impact strength>
Using a sample piece prepared according to the following sample preparation method, it was measured by a notched Izod impact test according to JIS K-7110.
<Tensile strength and elongation>
Using a sheet formed by a T-die extruder prepared according to the following sample preparation method, the sheet was measured in the M / D direction at a tensile speed of 50 mm / min according to JIS K-7127.
<Bending crack>
A sheet (thickness of about 0.5 mm) formed by a T-die extruder prepared according to the following sample preparation method is left in a standard room at room temperature of 23 ° C and humidity of 50% RH, and then bent by hand to 180 ° θ. The presence or absence of cracks in the sheet was observed.

The raw materials used and the sample preparation methods in the examples and comparative examples of the present invention are as follows.
For the raw materials used, in order to blend the biodegradable starch composition of the present invention,
Starch: Made by Nippon Corn Starch Co., Ltd., Amyloc No. 1A (Alphabized Corn Starch)
Natural rubber latex (1): Regex Corp. Regex N-60R (solid content 50% by weight, ammonia neutralized product)
Natural rubber latex (2): Regex Corp. Regex MG-10 (Methyl methacrylate 10 wt% grafted)
Silica: Leorosil QS-40 (dry silica) manufactured by Tokuyama Corporation
Glycerin: First grade reagent manufactured by Showa Chemical Co., Ltd. Lubricant: LICOWAX OP-PDR (Montanic acid ester) manufactured by Clariant Japan
Sorbitol: Showa Chemical Co., Ltd. reagent first grade Polyvinyl alcohol: Nippon Vinegar Polymer Co., Ltd. JP-18S
The raw materials were used. A starch composition was prepared from the raw materials described above according to the blending ratios in Table 1.

A test sample was prepared as follows using the starch composition having biodegradability of the present invention.
(1) Mixing The ingredients of the starch composition were mixed under a mixing condition of 500 rpm × 5 minutes using a 25 L Henschel mixer for mixing each raw material to be blended with the biodegradable starch composition of the present invention. In addition, L means a liter in a unit. The same applies below.
(2) Preparation of pellets The method for producing pellets of a starch composition having biodegradability according to the present invention is a method in which the starch composition prepared by the above mixing treatment is a single screw extruder with a vent port: screw; 50φ, L / D. = 28 was used to set the operating temperature of the heating zone of the single screw extruder to an operating temperature in the range of 175 to 195 ° C., extruded from the nozzle in a strand shape, and hot cut to give pellets of a predetermined size.
(3) Preparation of sheet A method for producing a sheet from the biodegradable starch composition of the present invention is obtained by using a T-die single screw extruder (manufactured by LAB TECH Engineering Co., Ltd. ): Die opening width: 300 mm, screw: 25φ, L / D = 30, rotation speed 88 rpm, each temperature set in the heating zone of the single screw extruder is set to an operating temperature within a range of 175 to 195 ° C. The sheet was extruded into a sheet shape, the temperature of the take-up roll was set to 55 ° C., and the sheet formed to a predetermined thickness of 0.7 mm was cooled, taken up and wound up.

  In the present invention, a sheet molded using a test sample obtained by molding a biodegradable starch composition prepared by adding natural rubber latex according to the blending ratio in Table 1 as in the above sample preparation method. The tensile strength, elongation rate, impact strength by Izod impact test and flex cracking are evaluated.

[Example 1]
Alpha starch corn starch (Nippon Corn Starch Co., Ltd., Amilok No. 1A) as starch, 100 parts by weight (the same applies hereinafter), natural rubber latex (1) (Regex Co., Ltd. Regitex N-60R solid content concentration 50 parts by weight (ammonia neutralized product) 3 parts by solid content, 6 parts glycerin (made by Showa Chemical Co., Ltd., reagent grade 1) as plasticizer, 5 parts sorbitol (made by Showa Chemical Co., Ltd., grade reagent) As a lubricant, 0.5 part of a montanic acid ester (Licowax OP-PDR, manufactured by Clariant Japan Co., Ltd.), polyvinyl alcohol (Nippon Acetate) is used to improve molding processability and physical properties and absorb moisture in natural rubber latex. -3 parts of Polymer Co., Ltd. (JP-18S) was blended and placed in a 25 L Henschel mixer, mixing conditions; 500 rpm x 5 minutes mixed. The obtained starch composition is supplied to a single screw extruder with a vent port: screw; 50φ, L / D = 28, and each set temperature of the heating zone of the single screw extruder is set to an operating temperature within a range of 180 to 200 ° C. It was set, extruded from a nozzle in a strand shape, and hot cut into pellets of a predetermined size.

The above pellets are supplied to a T-die single screw extruder (manufactured by LAB TECH Engineering Co., Ltd., with vent port): die opening width: 300 mm, and each set temperature of a heating zone of a rotation speed of 88 rpm and a single screw extruder is set to 175 to 195. Extruded into a sheet with the operating temperature set in the range of ℃, set the temperature of the take-up roll to 55 ℃, cooled the sheet formed to a predetermined thickness of 0.7mm, taken up and taken up It was.

About the manufactured sheet | seat etc., according to the said evaluation method, the tensile strength of the molded sheet | seat etc., elongation rate, the impact strength by an Izod impact test method, and a bending crack were measured. The physical properties of the obtained biodegradable starch composition were impact strength of 13.9 J / m ² , no bending cracking, and elongation of 245%. The results are shown in Table 1.

[Example 2]
In Example 2, the composition of the starch composition used in Example 1 was the same as in Table 1 except that natural rubber latex (1) was changed to 5 parts by solid content. A starch composition was obtained. From the obtained starch composition having biodegradability, pellets and sheets were formed in the same manner as in Example 1, and the obtained sheets and the like were measured for tensile strength, elongation by the same measurement method as in Example 1. The impact strength and bending cracking by the Izod impact test method were measured, and the physical properties of the biodegradable starch composition were evaluated. The results are shown in Table 1.

[Example 3]
In Example 3, a starch composition was obtained with the same composition as in Example 1 except that the natural rubber latex (2) was changed to 5 parts in terms of solid content. From the obtained starch composition having biodegradability, pellets and sheets were formed in the same manner as in Example 1, and the obtained sheets and the like were measured for tensile strength, elongation by the same measurement method as in Example 1. The impact strength and bending cracking by the Izod impact test method were measured, and the physical properties of the biodegradable starch composition were evaluated. The results are shown in Table 1.

[Example 4]
In Example 4, a starch composition was obtained with the same composition as in Example 1 except that the natural rubber latex (1) was changed to 10 parts in terms of solid content. From the obtained starch composition having biodegradability, pellets and sheets were formed in the same manner as in Example 1, and the obtained sheets and the like were measured for tensile strength, elongation by the same measurement method as in Example 1. The impact strength and bending cracking by the Izod impact test method were measured, and the physical properties of the biodegradable starch composition were evaluated. The results are shown in Table 1.

[Comparative Examples 1, 2, and 3]
The natural rubber latex (1) is 2 parts by solid content (Comparative Example 1), 15 parts (Comparative Example 2) and no natural rubber latex added (Comparative Example 3). In Comparative Example 3, no silica is added and PVA is 1 A starch composition was obtained with the same composition as in Example 1 except that the composition was changed to parts. The obtained starch composition was formed into pellets and sheets by the same method as in Example 1. Tensile strength, elongation and impact by Izod impact test method were measured for the obtained sheets and the like by the same measurement method as in Example 1. The strength and bending cracking were measured, and the physical properties of the starch composition were evaluated. The results are shown in Table 1.

As shown in Table 1, compared with the starch composition having poor impact strength, flex cracking and elongation as seen in Comparative Example 3 where no natural rubber latex is added, the present Examples 1 to 4 In the composition of the inventive starch composition having biodegradability, impact strength and flex cracking properties are remarkably improved. Even when the solid content of the natural rubber latex is as small as 3 parts by weight, the improvement in elasticity is accompanied by excellent impact strength and elongation, no bending cracking, and an improved effect is seen. Further, as seen in Example 4, when the solid content of the natural rubber latex is 10 parts by weight, the original tensile strength of starch is reduced, but the impact strength cannot be measured, indicating nondestructive (NB). This confirms the remarkable improvement in physical properties. And in the comparative example 1 with a small addition amount that deviates from the range of the addition amount of the natural rubber latex in the present invention, bending cracks occur and the effect of adding the natural rubber latex is not sufficiently exhibited. Moreover, in the comparative example 2 with much addition amount, tensile strength will fall remarkably, it will become a material without a waist as a molded object, and the utilization field of a molded object will be limited. Further, comparing Example 3 in which natural rubber latex was modified with vinyl monomer and Example 2 in which normal natural rubber latex was used, the elongation and impact strength were slightly reduced in rubber elasticity. Therefore, the tensile strength of the starch composition can be adjusted by graft-modifying the natural rubber latex with vinyl monomer, and the rubber properties of the starch composition can be adjusted by chemical modification, non-chemical modification or chemical modification of the natural rubber latex. By changing the degree of modification, the starch composition of the present invention can be employed as a molding material having physical properties according to the purpose of use.

  The starch composition having biodegradability of the present invention is improved in impact strength and bending cracking even with a small amount of natural rubber latex, and the effect of addition appears, so that the original biodegradability of starch, the characteristics of carbon neutral material It is possible to obtain a starch composition having biodegradability and having excellent physical properties without losing.

Claims (10)

  A starch composition having biodegradability, wherein natural rubber latex, which is an essential component, is added in an amount of 3.0 to 10.0 parts by weight based on 100 parts by weight of starch.   2. The starch composition having biodegradability according to claim 1, wherein the natural rubber latex is one to which a storage stabilizer is added.   The starch composition having biodegradability according to claim 2, wherein the natural rubber latex is obtained by adding ammonia as a storage stabilizer.   The starch composition having biodegradability according to claim 3, wherein the natural rubber latex is neutralized with ammonia.   The starch composition having biodegradability according to any one of claims 1 to 4, wherein the natural rubber latex is a field (sap) latex.   The starch composition having biodegradability according to any one of claims 1 to 4, wherein the natural rubber latex is chemically modified.   The starch composition having biodegradability according to any one of claims 1 to 6, wherein the natural rubber latex is physically concentrated by centrifugation.   The starch composition having biodegradability according to any one of claims 1 to 7, wherein the starch is raw starch.   The starch composition having biodegradability according to any one of claims 1 to 7, wherein the starch is a physically modified starch.   The starch composition having biodegradability according to any one of claims 1 to 7, wherein the starch is a chemically modified starch.