Starch composition and molded body

Abstract

The present invention pertains to a starch composition comprising a starch and a vinyl alcohol-based polymer, wherein: the amylopectin proportion in the starch is at least 70%; the degree of saponification of the vinyl alcohol-based polymer is at most 96 mol%; and the proportion of the starch to the total mass of the starch and the vinyl alcohol-based polymer is 40-90 mass%, and the proportion of the vinyl alcohol-based polymer to the total mass of the starch and the vinyl alcohol-based polymer is 10-60 mass%.

Description

[Technical Field]

[0001] The present invention relates to a starch composition containing starch and a vinyl alcohol polymer, and a molded article made from the composition. [Background technology]

[0002] Molded articles containing vinyl alcohol polymers have been studied as water-soluble materials and are widely used. Starch has also attracted attention as a natural polymer that can be used as a raw material for biodegradable polymer materials, and its use has been studied.

[0003] Molded articles such as fibers and films obtained by spinning or film-forming a composition combining such a vinyl alcohol polymer and starch have been studied and reported. For example, Patent Document 1 describes a biodegradable fiber composed of a composition of starch and a polyvinyl alcohol polymer. Patent Document 2 describes a water-soluble fiber composed of a composition of an oxyalkylene group-containing polyvinyl alcohol resin and starch. Furthermore, Non-Patent Documents 1 and 2 describe water-insoluble starch-based biodegradable plastics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 3-249208 [Patent Document 2] Japanese Patent Application Publication No. 4-153309 [Non-patent literature]

[0005] [Non-Patent Document 1] Polymer Papers, Vol.50, No. 10, pp. 767-774 [Non-patent document 2] "Biodegradable Polymers and Plastics", The Royal Society of Chemistry, pp. 101-110 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional molded articles such as fibers and films made from compositions containing starch and vinyl alcohol-based polymers have not been highly water-soluble and highly biodegradable. For example, the biodegradable fiber made from starch and vinyl alcohol-based polymers described in Patent Document 1 does not focus on the water solubility of the fiber and cannot be said to be water-soluble. The water-soluble fiber described in Patent Document 2 does not focus on the biodegradability of the fiber and cannot be said to be biodegradable. The starch-based biodegradable plastics described in Non-Patent Documents 1 and 2 are water-insoluble. Therefore, although compositions combining starch and vinyl alcohol-based polymers have been investigated, there is still a demand for further improvement in both water solubility and biodegradability. Therefore, an object of the present invention is to provide a starch composition and molded article that combine high water solubility and biodegradability. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, the present invention includes the following preferred embodiments. [1] A starch composition comprising starch and a vinyl alcohol polymer, wherein the starch has an amylopectin ratio of 70% or more, the vinyl alcohol polymer has a degree of saponification of 96 mol% or less, and the proportion of the starch relative to the total mass of the starch and the vinyl alcohol polymer is 40 to 90% by mass, and the proportion of the vinyl alcohol polymer is 10 to 60% by mass. [2] The starch composition according to [1], which has a water dissolution temperature of 50°C or less. [3] The starch composition according to [1] or [2], further comprising a plasticizer. [4] The starch composition according to any one of [1] to [3], wherein the amount of structural units derived from a vinyl monomer containing an oxyalkylene group in the vinyl alcohol polymer is 1 mol % or less based on the amount of all structural units contained in the vinyl alcohol polymer. [5] The starch composition according to any one of [1] to [4], wherein the amount of structural units other than structural units derived from vinyl ester monomers, vinyl alcohol structural units, and vinyl acetal structural units in the vinyl alcohol polymer is 10 mass% or less based on the amount of all structural units contained in the vinyl alcohol polymer. [6] The starch composition according to any one of [1] to [5], which has a biodegradation rate of 50% or more in soil after 14 days. [7] A molded article made from the starch composition according to any one of [1] to [6]. [8] The molded article according to [7], which is a film, fiber, nonwoven fabric, woven fabric, braided cord, or tow. [Effects of the Invention]

[0008] According to the starch composition of the present invention, it is possible to provide a starch composition and a molded article having high water solubility and biodegradability. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0010] [Starch composition] The starch composition of the present invention is a starch composition containing starch and a vinyl alcohol-based polymer, wherein the starch has an amylopectin ratio of 70% or more, the vinyl alcohol-based polymer has a degree of saponification of 96 mol% or less, and the proportion of starch is 40 to 90% by mass and the proportion of vinyl alcohol-based polymer is 10 to 60% by mass relative to the total mass of the starch and the vinyl alcohol-based polymer. By using such a specific ratio of starch and vinyl alcohol-based polymer, the starch composition and molded articles are easily dissolved in water at relatively low temperatures, for example, below 50°C, resulting in high water solubility. Furthermore, the biodegradability of the composition as a whole and the biodegradability of the vinyl alcohol-based polymer contained in the composition can be improved. Furthermore, if the water solubility and biodegradability of the starch composition itself can be improved, the water solubility and biodegradability of molded articles made from the starch composition can also be improved.

[0011] The starch composition of the present invention contains starch and a vinyl alcohol polymer, as described below, in which the proportion of starch relative to the total mass of the starch and the vinyl alcohol polymer is 40 to 90% by mass and the proportion of vinyl alcohol polymer is 10 to 60% by mass. If the proportion of starch relative to the total mass of the starch and the vinyl alcohol polymer is less than 40% by mass, in other words, if the proportion of vinyl alcohol polymer exceeds 60% by mass, the starch composition will not be sufficiently biodegradable. Furthermore, if the proportion of starch relative to the total mass of the starch and the vinyl alcohol polymer is more than 90% by mass, in other words, if the proportion of vinyl alcohol polymer is less than 10% by mass, it will be difficult to obtain a molded article composed of the starch composition.

[0012] The ratio of starch to the total mass of starch and vinyl alcohol-based polymer is preferably 44% by mass or more, more preferably 50% by mass or more, even more preferably more than 50% by mass, even more preferably 55% by mass or more, and extremely preferably 60% by mass or more, from the viewpoint of easily increasing the water solubility and biodegradability of the starch composition. In this case, for the same reasons, the ratio of vinyl alcohol-based polymer to the total mass of starch and vinyl alcohol-based polymer is preferably 66% by mass or less, more preferably 50% by mass or less, even more preferably less than 50% by mass, even more preferably 45% by mass or less, and extremely preferably 40% by mass or less. Furthermore, from the viewpoint of easily improving the moldability when producing a molded article from the starch composition and easily increasing the strength of the resulting molded article, the ratio of starch to the total mass of starch and vinyl alcohol-based polymer is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 78% by mass or less, and even more preferably 76% by mass or less. In this case, for the same reason, the proportion of the vinyl alcohol polymer to the total mass of the starch and the vinyl alcohol polymer is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 22% by mass or more, and still more preferably 24% by mass or more.

[0013] The ratio of starch or vinyl alcohol polymer to the total mass of starch and vinyl alcohol polymer may be calculated from the mixing ratio of each raw material when producing the starch composition, or may be calculated by separating and analyzing the starch composition constituting a molded product such as fiber by liquid chromatography or the like.

[0014] The total amount of starch and vinyl alcohol polymer contained in the starch composition of the present invention is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 85% by mass or more, and particularly preferably 90% by mass or more, based on the total amount of the starch composition of the present invention.

[0015] (starch) The starch composition of the present invention contains starch, and the amylopectin ratio of the starch is 70% or more. If the amylopectin ratio of the starch is less than 70%, the water solubility and biodegradability of the starch composition cannot be sufficiently improved. From the viewpoint of easily improving the water solubility and biodegradability of the starch composition, the amylopectin ratio of the starch is preferably 75% or more, more preferably 80% or more, even more preferably more than 80%, even more preferably 81% or more, and particularly preferably 82% or more. When extremely high water solubility of the starch composition is required, from the viewpoint of easily further improving the water solubility of the starch composition, the amylopectin ratio of the starch may be preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit of the amylopectin ratio may be 100% or less. The amylopectin ratio refers to the mass ratio of amylopectin when the total mass of amylose and amylopectin contained in the starch is taken as 100%. The amylopectin ratio can be measured by a colorimetric method using an iodine reactant or a quantitative method using concanavalin A as described in Carbohydrate Research, Vol. 180, 301-313 and Starch / Starke, Vol. 42, 302-305, etc.

[0016] The starch contained in the starch composition of the present invention is not particularly limited as long as it has an amylopectin ratio of 70% or more, and examples thereof include corn starch, potato starch, wheat starch, rice starch, tapioca starch, sweet potato starch, sago palm starch, soybean starch, arrowroot starch, bracken starch, lotus starch, cassava starch, waxy corn starch, high-amylose corn starch, commercially available amylose powders, and modified versions thereof. Modified starches include cationic starch, pregelatinized starch, oxidized starch, etherified starch, acetylated starch, modified amylose corn starch, esterified high-amylose corn starch, and hydrophobized waxy starch. The above examples do not necessarily mean that, for example, corn starch has an amylopectin ratio of 70% or more, but rather mean that, for example, commercially available corn starch having an amylopectin ratio of 70% or more can be used, or that starch adjusted to have an amylopectin ratio of 70% or more can be used. The starch composition of the present invention may contain one type of starch or two or more types of starch. When the starch composition of the present invention contains one type of starch, it is sufficient that the amylopectin ratio of the starch is 70% or more. When the starch composition of the present invention contains two or more types of starch, it is sufficient that the amylopectin ratio of the total starch contained in the starch composition is 70% or more. In this case, the amylopectin ratio of the total starch may be the weighted average of the amylopectin ratios of the two or more types of starches contained in the starch composition, or the amylopectin ratio measured for a mixture of two or more types of starch may be used. When the amylopectin ratio of the entire starch is calculated by weighted average, it can be determined from the amylopectin ratio of each starch by the following formula. Amylopectin ratio (%) of the whole starch = Σ(n a i×M a i) / 100 n a i: Amylopectin ratio of each starch (%) M a i: Percentage of each starch in total starch (wt%)

[0017] (Vinyl alcohol polymer) The starch composition of the present invention further contains a vinyl alcohol-based polymer, and the saponification degree of the vinyl alcohol-based polymer is 96 mol% or less. If the saponification degree of the vinyl alcohol-based polymer exceeds 96 mol%, both the water solubility and biodegradability of the starch composition cannot be sufficiently increased. From the viewpoint of easily increasing the water solubility and biodegradability of the starch composition, the saponification degree of the vinyl alcohol-based polymer is preferably 94 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less. Furthermore, from the viewpoint of easily improving the moldability (e.g., spinnability, film-forming ability, etc.) when producing a molded article composed of the starch composition, the saponification degree of the vinyl alcohol-based polymer is preferably 80 mol% or more, more preferably 81 mol% or more, even more preferably 82 mol% or more, even more preferably 83 mol% or more, and particularly preferably 84 mol% or more. The saponification degree of the vinyl alcohol-based polymer can be measured in accordance with JIS K 6726.

[0018] The vinyl alcohol polymer contained in the starch composition of the present invention may be one type of vinyl alcohol polymer as described below, or two or more types may be used in combination. When the starch composition of the present invention contains one type of vinyl alcohol polymer, the degree of saponification of the vinyl alcohol polymer may be 96 mol% or less. When the starch composition of the present invention contains two or more types of vinyl alcohol polymers, the degree of saponification of the entire vinyl alcohol polymers contained in the starch composition of the present invention may be 96 mol% or less. In this case, the degree of saponification of the entire vinyl alcohol polymers can be calculated from the saponification degrees of each vinyl alcohol polymer using the following formula: Saponification degree (mol%) of the entire vinyl alcohol polymer = Σ(n b i×M b i) / 100 n b i: Degree of saponification of each vinyl alcohol polymer (mol%) M b i: Proportion (wt%) of each vinyl alcohol polymer in the total vinyl alcohol polymer

[0019] The average degree of polymerization (viscosity average degree of polymerization) of the vinyl alcohol polymer contained in the starch composition of the present invention is not particularly limited, but from the viewpoint of easily increasing both the water solubility and biodegradability of the starch composition, it is preferably 2,450 or less, more preferably 1,800 or less. Furthermore, from the viewpoint of easily improving the moldability of a molded article made from the starch composition and easily increasing the strength of the obtained molded article, the average degree of polymerization is preferably 500 or more, more preferably 700 or more, and even more preferably 1,000 or more. The average degree of polymerization can be measured in accordance with JIS K 6726, for example, by the method described in the Examples.

[0020] The vinyl alcohol polymer contained in the starch composition of the present invention is a saponified vinyl ester polymer obtained by polymerizing a vinyl ester monomer, such as vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate.

[0021] The vinyl ester polymer is preferably one obtained using one or more vinyl ester monomers as the monomer, more preferably one obtained using one vinyl ester monomer as the monomer, or may be a copolymer of one or more vinyl ester monomers with another monomer copolymerizable therewith.

[0022] Examples of other monomers copolymerizable with vinyl ester monomers include ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or its salts; acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, methacrylic acid, and the like. Methacrylic acid esters such as n-propyl acrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid or its salt, acrylamidopropyldimethylamine or its salt, and N-methylolacrylamide or its derivative. methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or a salt thereof, methacrylamidepropyldimethylamine or a salt thereof, N-methylolmethacrylamide or a derivative thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester, or acid anhydride thereof; itaconic acid or a salt, ester, or acid anhydride thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.The vinyl ester polymer may have structural units derived from one or more of these other monomers.

[0023] From the viewpoint of easily increasing the water solubility and biodegradability of the starch composition, the proportion of the structural units derived from the other monomers in the vinyl ester polymer is preferably 15 mol % or less, more preferably 5 mol % or less, even more preferably 3 mol % or less, still more preferably 2 mol % or less, particularly preferably 1 mol % or less, particularly more preferably 0.5 mol % or less, extremely preferably 0.2 mol % or less, and extremely more preferably 0 mol % based on the number of moles of all structural units constituting the vinyl ester polymer.

[0024] The vinyl alcohol polymer contained in the starch composition of the present invention is obtained by saponifying the vinyl ester polymer described above. The vinyl alcohol polymer used in the starch composition of the present invention may be a vinyl alcohol polymer having at least one functional group selected from the group consisting of a sulfonic acid group, a sulfonate group, a maleic acid group, an itaconic acid group, an acrylic acid group, and a methacrylic acid group, but from the viewpoint of facilitating enhanced biodegradability, it is preferably an unmodified vinyl alcohol polymer substantially free of such functional groups.

[0025] The amount of structural units derived from vinyl monomers containing an oxyalkylene group in the vinyl alcohol polymer contained in the starch composition of the present invention is not particularly limited, but from the viewpoint of moldability of the composition, it is preferably 1 mol % or less, more preferably 0.5 mol % or less, even more preferably 0.1 mol % or less, still more preferably less than 0.1 mol %, particularly preferably 0.05 mol % or less, and especially preferably 0.01 mol % or less, based on the amount of all structural units contained in the vinyl alcohol polymer. It is even more preferable that the vinyl alcohol polymer does not have structural units derived from vinyl monomers containing an oxyalkylene group.

[0026] As described above, the vinyl alcohol polymer contained in the starch composition of the present invention can be obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer. The polymer has structural units derived from the vinyl ester monomer and vinyl alcohol structural units, which are structural units obtained by saponifying the structural units derived from the vinyl ester monomer. In addition, the polymer may optionally also have vinyl acetal structural units obtained by acetalization of the vinyl alcohol structural units. The amount of structural units other than the above structural units (structural units derived from the vinyl ester monomer, vinyl alcohol structural units, and vinyl acetal structural units) in the vinyl alcohol polymer contained in the starch composition of the present invention is not particularly limited, but from the viewpoints of moldability and water solubility of the composition, it is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 1% by mass or less, based on the amount of all structural units contained in the vinyl alcohol polymer.

[0027] (plasticizer) The starch composition of the present invention may contain a plasticizer in addition to the starch and vinyl alcohol polymer described above, as long as the effects of the present invention are not impaired. The type and amount of plasticizer optionally contained in the starch composition of the present invention can be determined in consideration of the application and moldability of a molded article made from the composition. Examples of plasticizers include, but are not limited to, sugar alcohols and polyhydric alcohols. When the starch composition of the present invention contains a plasticizer, one type of plasticizer may be used, or two or more types of plasticizers may be used. When the starch composition of the present invention contains a plasticizer, the content of the plasticizer is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the starch, vinyl alcohol polymer, and plasticizer.

[0028] (Other ingredients) The starch composition of the present invention may contain other components in addition to the starch, vinyl alcohol polymer, and optional plasticizer, as long as the effects of the present invention are not impaired. Examples of optional other components include polymers other than the vinyl alcohol polymer and starch, crosslinking agents, antioxidants, stabilizers, lubricants, processing aids, antistatic agents, colorants, impact resistance aids, and foaming agents, among other additives. When the starch composition of the present invention contains the resin component or various additives, the content of these components is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the starch and vinyl alcohol polymer.

[0029] The biodegradation rate of the starch composition of the present invention in soil after 14 days is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. The biodegradation rate of the starch composition in soil after 14 days can be measured by adding 0.3 g of the starch composition to 150 g of soil and allowing it to stand for 14 days. The decomposition rate of the entire starch composition after 14 days can be measured by calculating the amount of oxygen consumed by microorganisms accompanying the biodegradation of the starch composition from the change in air pressure in the system. Here, the specific vinyl alcohol-based polymer contained in the starch composition is not easily biodegradable. However, according to the starch composition of the present invention, by containing the specific starch and the specific vinyl alcohol-based polymer in a specific mass ratio, it is believed that the biodegradability of the vinyl alcohol-based polymer can be synergistically enhanced, and as a result, the biodegradability of the starch composition as a whole can be enhanced. Therefore, the starch composition of the present invention has high soil biodegradability, even when focusing on the decomposition rate of the vinyl alcohol-based polymer, which is not easily biodegradable.

[0030] The dissolution temperature of the starch composition of the present invention in water is preferably not higher than 50° C., more preferably not higher than 45° C., and even more preferably not higher than 40° C. The dissolution temperature in water is the temperature at which the starch composition is completely dissolved when 0.1 g of the starch composition is added to 50 g of pure water at 0° C. and the water temperature is increased by 2.5° C. per minute while stirring at 500 rpm.

[0031] [Molded body] Using the starch composition of the present invention, a molded article having excellent water solubility and biodegradability can be obtained. The present invention also provides a molded article made from the starch composition of the present invention. The shape of the molded article made from the starch composition of the present invention is not particularly limited, and it can be molded into various forms, such as a film, fiber, nonwoven fabric, woven fabric, braid, tow, etc. The molded article is preferably a film or fiber. The method for producing a molded article using the starch composition of the present invention is not particularly limited, and a molded article can be produced by processing the starch composition of the present invention using various conventionally known production methods.

[0032] In a preferred embodiment of the present invention, when the molded article of the present invention is a fiber, for example, the following process can be carried out: (1) a spinning dope preparation step of obtaining a spinning dope containing starch, a vinyl alcohol polymer, a solvent, and, if necessary, a plasticizer and other components; (2) an undrawn fiber forming step of extruding the spinning dope into dry air to remove the solvent and form an undrawn fiber; and (3) A drawing step of drawing the undrawn fiber It can be produced by a production method including at least the steps of:

[0033] In the spinning dope preparation step (1), a spinning dope is prepared by mixing starch, a vinyl alcohol polymer, a solvent, and, if necessary, a plasticizer, etc. Examples of the solvent include water, dimethyl sulfoxide (DMSO), glycerin, ethylene glycol, and mixtures thereof. From the viewpoints of polymer solubility and ease of solvent removal, water is preferably used as the solvent. In a preferred embodiment, the spinning dope is prepared by dissolving starch, a vinyl alcohol polymer, a solvent, and, if necessary, a plasticizer in a batch-type dissolution tank and / or extruder. The temperature of the dissolution tank is preferably about 100 to 150°C.

[0034] In the undrawn fiber formation step (2), an undrawn fiber is formed from the spinning dope obtained in step (1) by dry spinning. Examples of dry spinning include a method in which the spinning dope is extruded through a nozzle into heated dry air, and the solvent is evaporated to form a fiber. The dried fiber may be wound using a winding device or the like. The number of holes in the nozzle is not particularly limited, and may be, for example, 10 to 1,000. The temperature of the dry air is not particularly limited as long as it can remove the solvent, but is preferably 50 to 200°C, more preferably 60 to 150°C.

[0035] In the drawing step (3), the undrawn fiber obtained in step (2) is drawn. From the viewpoint of easily improving the mechanical properties of the fiber, the draw ratio is preferably 1.1 times or more, more preferably 3.0 times or more, even more preferably 3.5 times or more, even more preferably 4.0 times or more, particularly preferably 4.5 times or more, and especially preferably 5.0 times or more. The drawing temperature is preferably 100°C or more, more preferably 110°C or more, even more preferably 120°C or more, and preferably 200°C or less, more preferably 190°C or less, and even more preferably 180°C or less. The drawing time is preferably 5 seconds or more, more preferably 10 seconds or more, and preferably 60 seconds or less, more preferably 40 seconds or less. Drawing can be carried out by a conventional method, for example, in a hot air oven.

[0036] In another preferred embodiment of the present invention, when the molded article of the present invention is a film, the film can be formed by a film-forming method generally used for film formation, such as a casting method, a wet film-forming method, a dry film-forming method, an extrusion film-forming method, a melt film-forming method, a coating method, a casting method, an inflation film-forming method, etc. Among these, the molded article can be formed, for example, by the following steps: (1) a resin solution preparation step of obtaining a resin solution containing starch, a vinyl alcohol polymer, a solvent, and, if necessary, a plasticizer and other components; (2) a coating film forming step of applying the resin solution onto a substrate and removing the solvent to obtain a coating film; and (3) If necessary, a peeling step of peeling the coating film from the substrate. It can be produced by a production method including at least the steps of:

[0037] In the resin solution preparation step (1), a resin solution is prepared by mixing starch, a vinyl alcohol polymer, a solvent, and, if necessary, a plasticizer. The solvent may be any of those described above for the spinning dope preparation step (1). In a preferred embodiment, the resin solution is prepared by dissolving the starch, the vinyl alcohol polymer, the solvent, and, if necessary, a plasticizer in a batch-type dissolution tank and / or extruder. The temperature of the dissolution tank is preferably about 60 to 150°C.

[0038] In the coating film formation step (2), the resin solution is applied to a substrate, and the solvent is then removed to obtain a coating film. The casting surface can be any smooth, hard material, such as steel, aluminum, glass, or a polymer (e.g., polyolefin, polyethylene, polyamide, polyvinyl chloride, polycarbonate, polyhalocarbon, etc.). The evaporation rate of the aqueous solvent can be increased by heating the casting surface or by exposing the deposited solution to heated air or infrared light, for example. The casting surface can be flat, or can be prepared using a standard (drum-type) industrial film casting machine and then oven-dried. The heating temperature is not particularly limited as long as it is sufficient to remove the solvent, but is preferably 50 to 200°C, more preferably 60 to 150°C. Hot air or heating under vacuum conditions can be used to remove the solvent.

[0039] The peeling step (3) may be carried out as needed, and the dried film is peeled off from the substrate to obtain a film containing the starch composition of the present invention.

[0040] The molded article made from the starch composition of the present invention has high water solubility and is biodegradable in natural environments such as soil and water, and therefore can be used as a variety of molded articles. For example, when the molded article is a fiber, the fiber can also be used as a variety of fiber structures. For example, it can be processed into fiber structures such as cut fiber, filament, spun yarn, fabric (woven or knitted fabric, dry-laid nonwoven fabric, wet-laid nonwoven fabric), rope, and string-like material. When the molded article made from the starch composition of the present invention is a film, the film can also be used as a packaging material.

[0041] Furthermore, a molded article made from the starch composition of the present invention can be suitably used in the following applications, for example. air, oil and water filters; vacuum cleaner filters; furnace filters; face masks; coffee filters, tea or coffee bags; thermal and sound insulation; disposable hygiene products such as diapers, feminine pads, and incontinence articles; biodegradable textile fabrics for improving the absorbency and softness of clothing, such as microfiber or breathable fabrics; electrostatically charged structural webs for dust collection and removal; webs for stiff paper, such as reinforcing and wrapping paper, writing paper, newsprint, corrugated paperboard, and tissue paper, such as toilet paper, paper towels, napkins, and tissue paper; medical applications such as surgical drapes, wound dressings, bandages, or skin patches and self-dissolving sutures; dental applications such as dental floss and toothbrush bristles; agricultural applications such as greenhouses, tunnels, and weed control films; fishing applications such as fishing line, fishing tackle, bait, and fishing nets; and packaging applications such as plastic bags, packaging materials, food trays, and sachets.

[0042] Molded articles made from the starch compositions of the present invention may also be loaded with odor absorbents, termite repellents, insecticides, rodenticides, etc. The resulting molded articles may be capable of absorbing water and oil and may be used for cleaning up water and oil spills or for controlled water retention and release in agricultural or horticultural applications.

[0043] The starch compositions of the present invention may also be incorporated into other materials such as sawdust, wood pulp, plastics, and concrete to form composites for use in building materials such as walls, support beams, press boards, drywall and backing, and ceiling tiles. They may also be incorporated into casts, splints, and other medical applications such as tongue depressors, and logs for decoration and / or burning in fireplaces. [Example]

[0044] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, % refers to mass unless otherwise specified. First, the measurement methods and evaluation methods are shown below.

[0045] <Degree of polymerization> The degree of polymerization of the vinyl alcohol polymer was calculated from the measured value of the intrinsic viscosity [η] of an aqueous solution at 30° C. according to JIS K 6726 using the following formula, where P is the average degree of polymerization of vinyl alcohol. logP=1.613·log([η]×104 / 8.29)

[0046] <Saponification Degree (mol%)> Measurement was carried out in accordance with JIS K 6726.

[0047] <Water-soluble> 0.1 g of the starch composition fibers obtained in the Examples and Comparative Examples, cut to approximately 2 mm, was added to 50 g of pure water at 0°C and stirred at 500 rpm for 5 minutes. After adding a few drops of iodine solution and confirming coloration, the water temperature was increased by approximately 2.5°C per minute while stirring. The temperature at which the composition became transparent was recorded as the dissolution temperature in water. Water solubility was evaluated from the measured dissolution temperature according to the following criteria. (Evaluation criteria for water solubility) ◎: Melting temperature is 40℃ or less ○: Melting temperature is over 40℃ and below 50℃ ×: Dissolution temperature exceeds 50°C

[0048] <Solubility in water at 60°C> 1 g of fiber obtained from the starch compositions obtained in the Examples and Comparative Examples was immersed in 100 g of water at 60°C without stirring, and after leaving it for 2 minutes, the solution was filtered and the weight of the remaining undissolved composition was measured to evaluate the solubility in water at 60°C.

[0049] <Soil biodegradability> 0.3 g of fiber obtained from the starch compositions obtained in the Examples and Comparative Examples was added to 150 g of moist soil, and the oxygen consumed by the microorganisms was measured by measuring the change in air pressure within the system to determine the degree of biodegradation. Biodegradation was evaluated using a pressure sensor-type BOD meter OxiTop (manufactured by WTW), and natural soil (paddy field soil) was used. Biodegradation was calculated from the actual oxygen consumption and theoretical oxygen consumption (ThOD) in the test system, with ThOD calculated from the composition formula of the test substance. The starch composition was introduced into soil under the above conditions, and the decomposition rate of the entire starch composition after 14 days, and the decomposition rates of the starch composition and vinyl alcohol polymer (hereinafter abbreviated as PVA) after 28 days were calculated from the oxygen consumed by microorganisms as the fibers biodegraded, based on the change in air pressure in the system. From the obtained decomposition rates, the overall decomposition rate on the 14th day was used to evaluate soil biodegradability according to the following criteria. The decomposition rate after 28 days was also measured in the same manner. (Evaluation criteria for soil biodegradability) ◎: Overall decomposition rate on the 14th day is 90% or more 〇: Overall decomposition rate on the 14th day is 70% or more but less than 90% △: Overall decomposition rate on the 14th day was 50% or more but less than 70% ×: The overall decomposition rate on the 14th day was less than 50% Of the starch and PVA contained in the starch composition, starch is easily biodegradable, while PVA is not. Therefore, soil biodegradability may be evaluated by focusing on the decomposition rate of the less biodegradable PVA, such as the decomposition rate of PVA on the 28th day. In this case, soil biodegradability may be evaluated, for example, according to the following criteria: (Evaluation criteria for soil biodegradability using PVA) ◎: PVA decomposition rate is 70% or more on the 28th day 〇: PVA decomposition rate on the 28th day is 48% or more but less than 70% △: PVA decomposition rate on the 28th day is 30% or more but less than 48% ×: Decomposition rate of PVA on the 28th day is less than 30%

[0050] <Fiber strength> According to JIS L 1013, pre-conditioned yarns were measured under conditions of a test length of 20 cm, an initial load of 0.25 cN / dtex, and a pulling speed of 50% / min, and the average value of n = 20 was used as the fiber strength. The fiber fineness (dtex) was determined by the mass method.

[0051] <Moldability (spinnability)> The moldability (spinnability) when producing fibers by the methods described in the following Examples and Comparative Examples was evaluated as ◯ if fibers could be molded without any problems, and × if fibers could not be molded.

[0052] Example 1 Starch 1 (waxy corn starch) with a 100% amylopectin ratio, vinyl alcohol polymer 1 with a degree of polymerization of 1700 and a degree of saponification of 88 mol%, and sorbitol as a plasticizer were added to water in a mass ratio of 60:30:10 and stirred and dissolved at 140°C for 2 hours to obtain a spinning solution with a total concentration of vinyl alcohol polymer and starch of 55% by mass. This spinning solution was extruded into air at 120°C through a nozzle with 70 holes and a hole diameter of 0.1 mm, dried, and wound to obtain undrawn fibers. The resulting dried raw yarn was hot-drawn at 130°C at a hot draw ratio of 2.0 to produce fibers composed of the starch composition. The total draw ratio (hereinafter sometimes referred to as TD) of the resulting fiber was 2.0, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the above-mentioned method, and the decomposition rate of the entire starch composition after standing for 14 days was 72.6%, and the decomposition rate of the starch composition after standing for 28 days was 79.3%, and the decomposition rate of PVA was 48.3%. Therefore, the evaluation result of soil biodegradability was good, and the evaluation result of soil biodegradability by PVA was good.

[0053] <Example 2> Fibers composed of a starch composition were produced in the same manner as in Example 1, except that Starch 1 was replaced with Starch 2 (tapioca starch) having an amylopectin ratio of 83%, and the total concentration of the vinyl alcohol polymer and starch was 55% by mass. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0 times, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the method described above. After 14 days of storage, the overall decomposition rate of the starch composition was 74.1%, and after 28 days of storage, the decomposition rate of the starch composition was 79.6%, and the decomposition rate of the PVA was 49.1%. Therefore, the soil biodegradability evaluation result was rated as good, and the soil biodegradability evaluation result for PVA was rated as good.

[0054] Example 3 Fibers composed of a starch composition were produced in the same manner as in Example 1, except that Starch 3 (a blend of Starch 1 and Starch 4) with an amylopectin ratio of 70% was used instead of Starch 1. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0x, and the spinnability of the starch composition was good. The soil biodegradability of the obtained starch composition was measured according to the method described above. After leaving the sample for 14 days, the decomposition rate of the entire starch composition was approximately 70%, and after leaving the sample for 28 days, the decomposition rate of the starch composition was approximately 77%, and the decomposition rate of the PVA was approximately 40%. The soil biodegradability was evaluated as ◯, and the soil biodegradability of the PVA was evaluated as △. The predicted biodegradability values ​​described above were calculated from an approximation curve drawn from multiple separate measurement results for biodegradation rate and amylopectin ratio. The same applies to the predicted biodegradability values ​​in Comparative Example 2 below.

[0055] Example 4 Starch 1 having an amylopectin ratio of 100%, vinyl alcohol polymer 1 having a degree of polymerization of 1700 and a degree of saponification of 88 mol%, and sorbitol as a plasticizer were added to water in a mass ratio of 80:10:10 and stirred and dissolved at 140°C for 2 hours to obtain a spinning dope with a total concentration of vinyl alcohol polymer and starch of 65% by mass. Fibers composed of the starch composition were produced in the same manner as in Example 1, except for using this spinning dope. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 1.0, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the method described above. After 14 days, the overall decomposition rate of the starch composition was 102%, and after 28 days, the decomposition rate of the starch composition was 107.7%, and the decomposition rate of the PVA was 138.5%. Therefore, the soil biodegradability was evaluated as ⊚, and the soil biodegradability of the PVA was evaluated as ⊚.

[0056] <Example 5> Starch 1 having an amylopectin ratio of 100%, vinyl alcohol polymer 1 having a degree of polymerization of 1700 and a degree of saponification of 88 mol%, and sorbitol as a plasticizer were added to water in a mass ratio of 40:50:10 and stirred and dissolved at 140°C for 2 hours to obtain a spinning dope with a total concentration of vinyl alcohol polymer and starch of 50% by mass. Fibers composed of the starch composition were produced in the same manner as in Example 1, except for using this spinning dope. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0x, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the method described above. After 14 days, the overall decomposition rate of the starch composition was 55.4%, and after 28 days, the decomposition rate of the starch composition was 68.1%, and the decomposition rate of the PVA was 46.8%. Therefore, the soil biodegradability was evaluated as fair, and the soil biodegradability of the PVA was evaluated as fair.

[0057] Example 6 Fibers composed of a starch composition were produced in the same manner as in Example 1, except that vinyl alcohol polymer 2, having a degree of polymerization of 1700 and a degree of saponification of 96 mol%, was used instead of vinyl alcohol polymer 1. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0 times, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the method described above. After leaving the starch composition for 14 days, the decomposition rate of the entire starch composition was approximately 65%, and after leaving the starch composition for 28 days, the decomposition rate was approximately 75%, and the decomposition rate of the PVA was approximately 45%. The soil biodegradability evaluation result was considered to be Fair, and the soil biodegradability evaluation result for the PVA was considered to be Fair. The predicted biodegradability values ​​described above were calculated based on the finding that biodegradability decreases as the degree of saponification of the vinyl alcohol polymer increases. The same applies to the predicted biodegradability values ​​in Comparative Example 3 below.

[0058] Example 7 Starch 1 having an amylopectin ratio of 100% and vinyl alcohol polymer 1 having a degree of polymerization of 1700 and a degree of saponification of 88 mol% were added to water in a mass ratio of 90:10 and stirred and dissolved at 140°C for 2 hours to obtain a spinning dope with a total concentration of vinyl alcohol polymer and starch of 65% by mass. Fibers composed of the starch composition were produced in the same manner as in Example 1, except for using this spinning dope. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 1.0x, and the spinnability of the starch composition was not excellent but was at an acceptable level. The soil biodegradability of the obtained starch composition was measured according to the method described above. After leaving the starch composition for 14 days, the overall decomposition rate of the starch composition was approximately 100%, and after leaving the starch composition for 28 days, the decomposition rate of the PVA was approximately 100%. Therefore, the soil biodegradability was evaluated as ⊚, and the soil biodegradability of the PVA was evaluated as ⊚.

[0059] <Comparative Example 1> Fibers composed of a starch composition were produced in the same manner as in Example 1, except that Starch 1 was replaced with Starch 4 (modified amylose corn starch) having an amylopectin ratio of 30%. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0 times, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the method described above. After 14 days of storage, the decomposition rate of the entire starch composition was 57.8%, and after 28 days of storage, the decomposition rate of the starch composition was 68.7%, and the decomposition rate of the PVA was 21.8%. Therefore, the soil biodegradability was evaluated as Fair, and the soil biodegradability of PVA was evaluated as Bad.

[0060] <Comparative Example 2> Fibers composed of a starch composition were produced in the same manner as in Example 1, except that Starch 5 (a blend of Starch 1 and Starch 4) with an amylopectin ratio of 50% was used instead of Starch 1. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0 times, and the spinnability of the starch composition was good. The soil biodegradability of the obtained starch composition was measured according to the method described above. After leaving it for 14 days, the decomposition rate of the entire starch composition was about 65%, and after leaving it for 28 days, the decomposition rate of the starch composition was about 74%, and the decomposition rate of the PVA was about 32%. The soil biodegradability evaluation result was considered to be Fair, and the soil biodegradability evaluation result for PVA was considered to be Fair.

[0061] <Comparative Example 3> Fibers composed of a starch composition were produced in the same manner as in Example 1, except that vinyl alcohol polymer 3 having a degree of polymerization of 1700 and a degree of saponification of 98 mol% was used instead of vinyl alcohol polymer 1. The total draw ratio (hereinafter sometimes referred to as TD) of the obtained fiber was 2.0 times, and the spinnability of the starch composition was good. Furthermore, the soil biodegradability of the obtained starch composition was measured according to the method described above. After standing for 14 days, the decomposition rate of the entire starch composition was approximately 58%, and after standing for 28 days, the decomposition rate of the starch composition was approximately 65%, and the decomposition rate of the PVA was approximately 25%. Therefore, the soil biodegradability evaluation result is considered to be △, and the soil biodegradability evaluation result of the PVA is considered to be ×.

[0062] The water solubility and fiber strength of the starch compositions obtained in the Examples and Comparative Examples were evaluated according to the methods described above. The results are shown in Table 1. The solubility in 60°C water of the fibers obtained in Example 1 and Comparative Example 1 was also evaluated according to the methods described above. As a result, in Example 1, the residue obtained after filtration was 3%, indicating good solubility in 60°C water, whereas in Comparative Example 1, the residue obtained after filtration was 34%, confirming insufficient solubility in 60°C water. Note that the strength values ​​in parentheses in Table 1 are predicted values. The inventors have found that strength tends to increase when the PVA content in the starch composition is high, when the PVA saponification degree is high, and when the amylopectin ratio of the starch is high. The strength values ​​in parentheses in Table 1 are predicted values ​​derived from this tendency.

[0063] [Table 1]

Claims

1. A starch composition comprising starch and a vinyl alcohol-based polymer, wherein the starch has an amylopectin ratio of 70% or more, the vinyl alcohol-based polymer has a degree of saponification of 96 mol% or less, the proportion of the starch relative to the total mass of the starch and the vinyl alcohol-based polymer is 60 to 90 mass%, and the proportion of the vinyl alcohol-based polymer is 10 to 40 mass%, and the amount of structural units derived from a vinyl monomer containing an oxyalkylene group in the vinyl alcohol-based polymer is less than 0.1 mol% based on the amount of all structural units contained in the vinyl alcohol-based polymer.

2. 2. The starch composition according to claim 1, which has a dissolution temperature in water of 50°C or less.

3. 3. The starch composition of claim 1 or 2, further comprising a plasticizer.

4. 4. The starch composition according to claim 1, wherein the amount of structural units other than structural units derived from vinyl ester monomers, vinyl alcohol structural units, and vinyl acetal structural units in the vinyl alcohol polymer is 10 mass% or less based on the amount of all structural units contained in the vinyl alcohol polymer.

5. 5. The starch composition according to claim 1, which has a biodegradability of 50% or more in soil after 14 days.

6. A molded article made from the starch composition according to any one of claims 1 to 5.

7. The molded article according to claim 6, which is a film, a fiber, a nonwoven fabric, a woven fabric, a braid, or a tow.

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