A composition suitable for resource recycling and a method for manufacturing the same composition.

Abstract

The present invention provides a composition suitable for resource recycling that is easy to manufacture while possessing high recyclability and low environmental impact. Such a composition comprises cellulose, an alcohol-soluble cellulose derivative, and a polyhydric alcohol as a liquid solvent, and contains no water or 10 parts by weight or less of water. A dihydric alcohol is preferred as the polyhydric alcohol. Furthermore, a method for producing such a composition comprises a mixing step of mixing cellulose, an alcohol-soluble cellulose derivative, and a polyhydric alcohol, and a gelling step of heating and pressurizing the mixture produced in the mixing step to gel the mixture.

Description

Technical Field

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[0001] The present invention relates to a composition that can replace plastics, particularly a composition suitable for resource recycling and a method for producing the same.

Background Art

[0002] Conventionally, petroleum-derived plastics have been used in many products, and after use, they have been incinerated or recycled. However, not all plastic waste is properly incinerated or recycled, and since plastics do not decompose in nature, the environmental impact caused by microplastics and the like has become a problem. In addition, there is a theory that carbon dioxide is emitted when plastics are incinerated, and this carbon dioxide is the cause of global warming, so a reduction in carbon dioxide emissions is required.

[0003] In response to these problems, biodegradable plastics have been proposed in recent years. Biodegradable plastics include biomass plastics and biodegradable plastics. The former is derived from organisms such as plants, so it can contribute to reducing carbon dioxide emissions. In addition, the latter can contribute to suppressing the environmental impact because it decomposes under certain conditions.

[0004] For example, Patent Document 1 discloses pellets in which vegetable fiber powder is bound with a water-soluble binder. These pellets have the advantages of low environmental impact and easy recycling.

[0005] In addition, Patent Document 2 discloses a cellulose composition containing water-soluble cellulose ether, water-insoluble cellulose, and water. This cellulose composition also has biodegradability and a low environmental impact. <00​​​​​​​​​​​​ [Patent Document 2] International Open Brochure WO2020 / 049995 [Overview of the project] [Problems that the invention aims to solve]

[0007] As mentioned above, in the compositions described in Patent Documents 1 and 2, mixing water with water-soluble cellulose ether results in a gel-like substance, making it difficult to handle. Furthermore, in the compositions described in Patent Documents 1 and 2, the properties of the composition differ depending on the water content, so it is necessary to dry them to achieve an appropriate water content.

[0008] This invention has been made in view of the above problems, and its purpose is to provide a composition suitable for resource recycling that is easy to manufacture while having high recyclability and low environmental impact. [Means for solving the problem]

[0009] To solve the above problems, the cellulose-based composition suitable for resource recycling according to the present invention (hereinafter referred to as the "composition") comprises an alcohol-soluble cellulose derivative and a polyhydric alcohol as a liquid solvent, and does not contain water, or For an amount of cellulose ranging from 35 to 60 parts by weight 10 parts by weight or less and less than or equal to the amount of the polyhydric alcohol. It contains water.

[0010] As described in Patent Documents 1 and 2, various problems arise when a composition contains a large amount of water as a solvent. For example, if the composition is heated above 100°C, the boiling point of water, during extrusion molding, the water evaporates, making it difficult to maintain sufficient plasticity during molding. On the other hand, molding becomes difficult below 100°C. Furthermore, simply mixing water with a water-soluble cellulose derivative causes the composition (mixture) to gel, making it prone to clogging in the hopper of the extrusion molding machine, thus making it difficult to handle. In addition, it is necessary to dry the molded body so that its water content reaches a predetermined amount.

[0011] On the other hand, in the composition according to the present invention, since a polyhydric alcohol is used as a solvent instead of water, the polyhydric alcohol does not evaporate even when molded at temperatures of 100°C or higher (but below the boiling point of the polyhydric alcohol). Furthermore, the composition does not gel when simply mixed with an alcohol-soluble cellulose derivative and a polyhydric alcohol, making it easy to handle. Moreover, if the composition according to the present invention does not contain water, there is no need to dry the molded body. It has also been found that the hardness of the molded body can be adjusted by adjusting the amount of polyhydric alcohol mixed in.

[0012] While it is desirable that the composition according to the present invention does not contain water, water may be unintentionally included in the composition due to its presence in cellulose, or due to cellulose or cellulose derivatives absorbing water vapor from the air. Furthermore, there may be other reasons that necessitate the addition of water. When the composition contains water and the cellulose derivative is water-soluble, if the water can act as a solvent, the composition will approach a gelling state in its mixed state, which is undesirable. Therefore, it is preferable that the amount of water included is such that it cannot act as a solvent (10 parts by weight or less).

[0013] The composition according to the present invention is easily recyclable because its cellulose can be dissociated through the usual recycling process of waste paper. In other words, the composition according to the present invention can be recycled in the same way as ordinary waste paper and is compatible with the waste paper recycling flow. In particular, it is preferable to use paper shredder, pulp, wood pulp-derived cellulose, or a mixture thereof as the cellulose, as this makes it compatible with resource recycling.

[0014] The inventors of this invention have found through experiments that dihydric alcohols are preferable as polyhydric alcohols. They have also found that polyhydric alcohols with a vapor pressure of 10 Pa or less at 20°C are preferable.

[0015] As described above, simply mixing an alcohol-soluble cellulose derivative with a polyhydric alcohol does not result in a gelled composition; it remains in a highly fluid, moist powder state. In this state, it is easy to handle until it is fed into the hopper of an extrusion molding machine, but it cannot be extruded. The inventors of the present invention have discovered that applying a predetermined temperature and pressure to such a moist powder composition causes it to gel.

[0016] Therefore, the present invention also includes a method for producing a composition suitable for resource recycling, which mainly consists of cellulose. The method for producing such a composition comprises a mixing step of mixing cellulose, an alcohol-soluble cellulose derivative, and a polyhydric alcohol, and a gelling step of heating and pressurizing the mixture produced in the mixing step to gel the mixture.

[0017] The temperature at which the composition is added is preferably 100°C or higher. However, if this temperature exceeds the boiling point of the polyhydric alcohol, the polyhydric alcohol will evaporate, so it is preferable that the temperature be below the boiling point of the polyhydric alcohol. It is also necessary that the temperature does not cause burning of the cellulose. [Modes for carrying out the invention]

[0018] Embodiments of the composition according to the present invention are described below. The characteristic of the composition according to the present invention is that it contains cellulose, an alcohol-soluble cellulose derivative (cellulose ether), and a polyhydric alcohol as a liquid solvent, and does not contain petroleum-derived polymer compounds or water, or if it does contain water, it is only in small amounts.

[0019] The compositions of the present invention include both fluid substances in which multiple components are mixed together and molded articles obtained by solidifying and molding them. However, in the following description, to distinguish between them, the fluid substance (including gelled substances) will be referred to as the "composition," and the solidified and molded substance will be referred to as the "molded article."

[0020] 〔cellulose〕 From the perspective of recycling, it is preferable to use cellulose obtained by dissociating or the like from pulverized waste paper. However, naturally, plant-derived materials such as cellulose derived from pulp or wood pulp can be used, and even in these cases, it is suitable for resource circulation, similar to the case of using pulverized waste paper. If the particle size of cellulose is too small, the entanglement between fibers will decrease, and the strength of the molded body may decrease. On the other hand, if the particle size of cellulose is too large, the absorption of the plasticizer will be excessive, and extrusion during molding of the molded body will be difficult. The inventor of the present invention (hereinafter referred to as the inventor) has obtained the knowledge through experiments that the particle size of cellulose is preferably 1 mm or less, particularly preferably 100 μm or less, and more preferably about 30 μm.

[0021] 〔Cellulose derivative〕 The cellulose derivative is a component for imparting viscosity to the composition. Therefore, by using a cellulose derivative with high viscosity, the shape retention of the molded body can be enhanced. In the present invention, since a polyhydric alcohol is used as a solvent as described later, a cellulose derivative having alcohol solubility is used. As such a cellulose derivative, cellulose ethers such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, etc. can be used.

[0022] In the composition of the present invention, it is considered that the polyhydric alcohol penetrates into the cellulose molecular chain of the cellulose derivative, and the composition gels (pseudo-molten state). The inventor obtained the knowledge through experiments that the degree of penetration differs depending on the difference in the substituents (functional groups) of the cellulose derivative. Specifically, those having a bulky and long-chain functional group are preferable, and among the above-listed ones, hydroxypropyl methyl cellulose is preferable.

[0023] 〔Polyhydric alcohol〕 The composition according to the present invention is characterized in that a liquid polyhydric alcohol is used as a solvent instead of water. Since this polyhydric alcohol also acts as a plasticizer, the inventor examined suitable polyhydric alcohols from the viewpoint of plasticizers as follows.

[0024] As the valence of the polyhydric alcohol increases, the interaction within and between molecular chains (the influence of hydrogen bonding force) becomes larger. When a composition containing such a substance with a large interaction is molded at a temperature below a predetermined temperature, the molded body becomes brittle. For example, when a composition using a trivalent alcohol is molded at a temperature suitable for molding a composition using a divalent alcohol, a brittle molded body is obtained. Therefore, for a composition using a trivalent alcohol, it is necessary to increase the molding temperature higher than that of a composition using a divalent alcohol. On the other hand, since the composition of the present invention contains cellulose, when the molding temperature is increased to a certain temperature or higher, the cellulose is likely to be burned. Also, it has been found that the compatibility with an alcohol-soluble cellulose derivative is higher for divalent alcohols. From these viewpoints, it is preferable to use a divalent alcohol as the polyhydric alcohol.

[0025] As the divalent alcohol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, tripropylene glycol, etc. can be used.

[0026] When the evaporation rate of the polyhydric alcohol (divalent alcohol) in the natural environment is high, it has been found that the deformation of the molded body is likely to occur. Therefore, it is preferable that the vapor pressure of the polyhydric alcohol at 20°C environment is 10 Pa or less, and more preferably about 1.5 Pa or less. On the other hand, when the vapor pressure of the polyhydric alcohol is too low, the affinity with the alcohol-soluble cellulose derivative becomes low, and molding becomes difficult. Therefore, it is desirable to use in combination a polyhydric alcohol having a vapor pressure of about 1.5 Pa and a polyhydric alcohol having a lower vapor pressure than that. In this case, it is desirable that the former accounts for half or more of the total amount of the polyhydric alcohol.

[0027] 〔Manufacturing method〕 This section describes the process of manufacturing molded bodies (pellets) from each component of the composition. First, 35 to 60 parts by weight of cellulose and 15 to 30 parts by weight of an alcohol-soluble cellulose derivative are placed in a mixer and mixed. Then, 20 to 40 parts by weight of liquid polyhydric alcohol are added and stirred (mixing step). Note that if there is too much polyhydric alcohol, bleed-out will occur, so it is preferable that the amount of polyhydric alcohol be 30 parts by weight or less. At this point, the alcohol-soluble cellulose derivative dissolves in the polyhydric alcohol, but the composition has not gelled and is in a wet powder state. This powdered composition corresponds to the mixture in the present invention. At this time, the hardness of the molded body can be adjusted by changing the proportion of polyhydric alcohol. Note that cellulose does not dissolve in polyhydric alcohol. As described above, the ratio of the multiple components contained in the composition can be changed, but it is preferable to have the largest proportion of cellulose.

[0028] In Patent Documents 1 and 2, water is used as the solvent, so the composition gels simply by mixing the components. In this case, problems such as clogging of the hopper with the gelled composition occur, reducing productivity, and making it impossible to manufacture with a conventional extrusion molding machine occur. On the other hand, the composition according to the present invention does not gel simply by mixing the components, making it easier to handle during the manufacturing of the molded product.

[0029] Next, this moist powder composition (mixture) is placed in the hopper of an extrusion molding machine, and heat and pressure are applied inside (gelling process). In this embodiment, it is heated to about 100°C to 200°C and pressure of about 3 to 15 MPa is applied. Since this temperature is below the boiling point of polyhydric alcohols, the polyhydric alcohols do not evaporate. In this way, by heating and pressurizing the moist powder composition, the polyhydric alcohols enter the cellulose molecular chains of the alcohol-soluble cellulose derivative, causing the composition to enter a pseudo-molten state (gelling).

[0030] An extrusion machine produces pellets (an example of a molded body) by extruding a gelled composition. The extrusion temperature is preferably between 130°C and 210°C, and more preferably 180°C. The extrusion pressure is approximately 2 to 15 MPa. It is possible to lower the extrusion temperature to around 100°C, but the extrusion pressure needs to be increased as the temperature decreases.

[0031] As described in Patent Documents 1 and 2, when water is used as a solvent, there is a risk that the water will evaporate due to heating during extrusion molding. In this case, the plasticity of the composition will decrease, making extrusion difficult. On the other hand, the composition according to the present invention uses a polyhydric alcohol with a boiling point higher than the temperature during extrusion molding, so there is a low risk of the solvent evaporating during extrusion molding.

[0032] If the alcohol-soluble cellulose derivative is also water-soluble, a hot-cut or air-cooled extrusion machine should be used instead of a water-cooled one.

[0033] The pellets formed in this way can be used in the manufacture of plastic substitute products using injection molding machines, extrusion molding machines, blow molding machines, etc., just like conventional plastic pellets.

[0034] [Recycling process] Since the composition according to the present invention does not contain petroleum-derived resins, it can be easily recycled. Although a detailed explanation is omitted, the plastic substitute product is crushed and put into a pulper and stirred, similar to the recycling of ordinary waste paper. As a result, the cellulose is dissociated, and the cellulose can be used again as a paper material. [Examples]

[0035] In this example, cellulose is made from crushed paper. Furthermore, Metroze® 60SH-4000 (hydroxypropyl methylcellulose) from Shin-Etsu Chemical Co., Ltd. is used as the alcohol-soluble cellulose derivative, and dipropylene glycol, a dihydric alcohol, is used as the polyhydric alcohol. Note that Metroze is both alcohol-soluble and water-soluble.

[0036] The following shows the proportions of these ingredients in the example. In this example, in addition to the above-mentioned components, additives are added to prevent dripping and improve ease of feeding into the extrusion molding machine, but a detailed explanation is omitted. [Table 1] [Table 2] [Table 3]

[0037] Molded articles produced from compositions with the component ratios shown in these tables were confirmed to have acceptable product quality. These component ratios are merely examples of those found in compositions of acceptable product quality and can be modified as appropriate.

[0038] As described above, the composition according to the present invention does not contain water, making it easy to handle during manufacturing and eliminating the need to dry the molded article. Furthermore, the hardness of the molded article can be changed by altering the proportion of polyhydric alcohols. In addition, because it does not contain petroleum-derived polymer compounds, it has high recyclability and a low environmental impact. Moreover, because the composition according to the present invention has the above-mentioned properties, it can be molded using existing plastic injection molding machines and extrusion molding machines.

[0039] [Another embodiment] (1) In the embodiments described above, the composition did not contain water. However, there may be cases where it is impossible to avoid the inclusion of trace amounts of water, or where it is necessary to mix in a small amount of water for some reason. Therefore, the composition (mixed state before molding) may contain a small amount of water sufficient to achieve the objectives of the present invention. Note that if the cellulose derivative is water-soluble, the proportion of water will increase, and if water acts as a solvent, the composition will approach gelation in the mixed state, which is undesirable. Therefore, even if water is included, it is important that it is in a small amount so as not to act as a solvent. For this reason, even if water is included, it should naturally be less than or equal to the amount of polyhydric alcohol which is the solvent. Furthermore, the inventors have found that molding becomes difficult when the water content is about 10 parts by weight or more, so it is desirable that the proportion of water in the composition be 10 parts by weight or less.

[0040] (2) In the above embodiment, the composition before gelation was supplied to the extrusion molding machine when manufacturing the molded article, but the composition after gelation may also be supplied. [Industrial applicability]

[0041] The present invention can be used as a substitute for plastic. Furthermore, the composition according to the present invention is easily recyclable, and its raw materials can be crushed waste paper, pulp, cellulose derived from wood pulp, etc., so it can be easily incorporated into the paper resource recycling cycle (waste paper cycle flow) and is suitable for resource recycling.

Claims

1. A composition suitable for resource recycling, mainly composed of cellulose, Alcohol-soluble cellulose derivatives, It contains a polyhydric alcohol as a liquid solvent, A composition suitable for resource recycling that does not contain water, or contains 10 parts by weight or less of water and the amount of polyhydric alcohol or less, relative to 35 to 60 parts by weight of cellulose.

2. The resource recycling-friendly composition according to claim 1, wherein the cellulose is any of paper pulp, wood pulp-derived cellulose, or a mixture thereof.

3. The composition suitable for resource recycling according to claim 1, wherein the polyhydric alcohol is a dihydric alcohol.

4. The polyhydric alcohol is a composition suitable for resource recycling according to any one of claims 1 to 3, wherein its vapor pressure at a 20°C environment is 10 Pa or less.

5. A method for producing a composition suitable for resource recycling, mainly composed of cellulose, A mixing step of mixing the cellulose, an alcohol-soluble cellulose derivative, and a polyhydric alcohol, A method for producing a composition suitable for resource recycling, comprising a gelling step of heating and pressurizing the mixture produced by the mixing step to gel the mixture.

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