Composition suitable for resource recycling, and method for producing said composition

Abstract

Provided is a composition suitable for resource recycling, which can be easily produced while having high recyclability and a low environmental burden. Such a composition contains cellulose, an alcohol-soluble cellulose derivative, and a polyhydric alcohol as a liquid solvent, and contains no water or 10 parts by mass or less of water. The polyhydric alcohol is preferably a dihydric alcohol. In addition, a method for producing such a composition comprises: a mixing step for mixing cellulose, an alcohol-soluble cellulose derivative, and a polyhydric alcohol; and a gelling step for heating and pressurizing the mixture produced in the mixing step so as to gel the mixture.

Description

Composition Suitable for Resource Recycling and Method for Producing the Composition 【0001】 The present invention relates to a composition that can replace plastic, particularly a composition suitable for resource recycling and a method for producing the same. 【0002】 Conventionally, petroleum-derived plastics have been used for many products, and after use, they have been incinerated or recycled. However, not all of the plastic waste is properly incinerated or recycled, and since plastic does not decompose in nature, the environmental burden caused by microplastics and the like has become a problem. In addition, when plastic is incinerated, carbon dioxide is emitted, and there is also a theory that this carbon dioxide is the cause of global warming, and thus a reduction in carbon dioxide emissions is demanded. 【0003】 In response to these problems, bioplastics have been proposed in recent years. Bioplastics include biomass plastics and biodegradable plastics. The former is derived from organisms such as plants, and thus can contribute to reducing carbon dioxide emissions. In addition, the latter can be decomposed under certain conditions, and thus can contribute to suppressing the environmental burden. 【0004】 For example, Patent Document 1 discloses pellets in which vegetable fiber powder is bound with a water-soluble binder. This pellet has the merit of having a small environmental burden and being easy to recycle. 【0005】 Further, 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 small environmental burden. 【0006】 Japanese Patent Laid-Open No. 10-018200 International Publication WO2020 / 049995 Pamphlet 【0007】 As described above, in the compositions of Patent Documents 1 and 2, when water and water-soluble cellulose ether or the like are mixed, they become gel-like, making them difficult to handle. In addition, in the compositions of Patent Documents 1 and 2, the properties of the composition vary depending on the water content, so it is necessary to dry it to 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. 【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 contains no water, or contains 10 parts by weight or less of 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, when the composition is extruded, heating it above 100°C, the boiling point of water, causes the water to evaporate, 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 a temperature 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. 【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 a recycling standpoint, it is preferable to use cellulose obtained by disintegrating or otherwise removing crushed waste paper. However, it is also possible to use plant-derived materials such as cellulose derived from pulp or wood pulp, and in these cases as well, they are suitable for resource recycling, just as when crushed waste paper is used. If the particle size of the cellulose is too small, the entanglement between the fibers will decrease, which may reduce the strength of the molded body. On the other hand, if the particle size of the cellulose is too large, the absorption of plasticizer will be excessive, making it difficult to extrude the molded body during molding. The inventor of the present invention (hereinafter referred to as the inventor) has found through experiments that a particle size of cellulose of 1 mm or less is suitable, particularly 100 μm or less is preferred, and about 30 μm is more preferred. 【0021】 [Cellulose Derivatives] Cellulose derivatives are components that impart viscosity to a composition. Therefore, by using a cellulose derivative with high viscosity, the shape retention of the molded article can be improved. In this invention, as described later, a polyhydric alcohol is used as a solvent, so a cellulose derivative that is alcohol-soluble is used. As such a cellulose derivative, cellulose ethers such as methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, and carboxymethylcellulose can be used. 【0022】 In the composition of the present invention, it is believed that the composition gels (a pseudo-molten state) as the polyhydric alcohol penetrates into the cellulose molecular chain of the cellulose derivative. Through experiments, the inventors have found that the degree of penetration differs depending on the substituents (functional groups) of the cellulose derivative. Specifically, those that are bulky and have long-chain functional groups are preferred, and among those listed above, hydroxypropylmethylcellulose is preferred. 【0023】 [Polyhydric Alcohols] The composition according to the present invention is characterized by the use of a liquid polyhydric alcohol as a solvent instead of water. Since this polyhydric alcohol also acts as a plasticizer, the inventors considered suitable polyhydric alcohols from the standpoint of plasticizers as follows. 【0024】As the valency of polyhydric alcohols increases, the interactions within and between molecular chains (influence of hydrogen bonding forces) become stronger. When a composition containing such strongly interacting substances is molded at a temperature below a certain limit, the molded article becomes brittle. For example, if a composition using trihydric alcohols is molded at a temperature suitable for a composition using dihydric alcohols, the resulting molded article will be brittle. Therefore, a higher molding temperature is required for compositions using trihydric alcohols than for compositions using dihydric alcohols. On the other hand, since the present invention contains cellulose in the composition, if the molding temperature is raised above a certain temperature, the cellulose is prone to burning. Furthermore, it has been found that dihydric alcohols have higher compatibility with alcohol-soluble cellulose derivatives. From these viewpoints, it is preferable to use dihydric alcohols as polyhydric alcohols. 【0025】 Examples of dihydric alcohols that can be used include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, and tripropylene glycol. 【0026】 It has been found that if polyhydric alcohols (dihydric alcohols) volatilize quickly in natural environments, molded articles are more prone to deformation. Therefore, it is preferable to keep the vapor pressure of the polyhydric alcohol below 10 Pa at 20°C, and more preferably below approximately 1.5 Pa. On the other hand, if the vapor pressure of the polyhydric alcohol is too low, its affinity with the alcohol-soluble cellulose derivative decreases, making molding difficult. Therefore, it is desirable to use a polyhydric alcohol with a vapor pressure of approximately 1.5 Pa in combination with a polyhydric alcohol with an even lower vapor pressure. In this case, it is desirable that the former make up more than half of the total amount of 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 put into a mixer and mixed. Then, 20 to 40 parts by weight of liquid polyhydric alcohol are added and stirred and mixed (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 arise. 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 molding 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 described above 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. 【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. 【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. 【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, comprising an alcohol-soluble cellulose derivative and a polyhydric alcohol as a liquid solvent, and containing no water or 10 parts by weight or less of water.

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 has a vapor pressure of 10 Pa or less at a 20°C environment, and is a composition suitable for resource recycling according to any one of claims 1 to 3.

5. A method for producing a resource-recycling composition mainly composed of cellulose, comprising: 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.

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