Environmentally friendly, stable colored mud and preparation method and application thereof

Abstract

The present invention relates to an environmentally friendly, stable colored mud and a preparation method and application thereof, and belongs to the technical field of gel materials. The colored mud includes the following raw materials in parts by weight: 30-40 parts of modified starch, 5-10 parts of vegetable gum, 10-20 parts of lithium magnesium silicate, 10-20 parts of stabilizer, 5-10 parts of cross-linking agent, 20-30 parts of citrate, 2-5 parts of polyol, and 0-5 parts of toner; wherein the stabilizer is a composition of glycerol, cellulose and casein; the cross-linking agent is N, N'-methylenebisacrylamide; the colored mud of the present invention does not add a cross-linking agent harmful to the human body, and the raw materials selected are all environmentally friendly and harmless to the human body. The colored mud of the present invention has good tensile properties, excellent stability, and improved playability. The environmentally friendly and stable colored mud is suitable as a children's toy.

Description

Technical Field

[0001] The invention relates to the technical field of gel materials, and in particular to an environmentally friendly and stable colored mud and a preparation method and application thereof. Background Art

[0002] As a kind of DIY toys for children, various modeling clay and gel toys have become increasingly popular in recent years. Due to their rich shapes and low prices, their development momentum cannot be underestimated. In recent years, there have been frequent reports of children being injured by such toys due to quality problems or improper use.

[0003] From the perspective of product technology, most of the raw materials for modeling clay and gel-based children's toys currently sold on the market use polymers, cross-linking agents, pigments and preservatives. In order to reduce costs, some manufacturers use low-priced raw materials with greater quality risks. These raw materials themselves are prone to precipitate toxic and harmful substances such as heavy metals into children's bodies during use, causing harm to children's health. For example, the raw material cross-linking agent must be used to increase the viscosity of this type of material. Children can stick to each other at will when playing with colored clay, which is convenient for making various shapes. The most commonly used cross-linking agents are borax and polyvinyl alcohol PVA. Although there are also boron-free cross-linking agents available, borax is very cheap but will bring excessive boron elements. Polyvinyl alcohol may precipitate formaldehyde during use, which has a greater impact on children. The preservatives used in modeling clay, such as formaldehyde, phenol, nitrosamines, etc., are used to delay the growth of microorganisms or the corruption caused by chemical changes, so that the shelf life can be extended. However, many preservatives are allergenic. If added in excess, they are likely to cause skin allergies, dermatitis and other injuries to young children. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an environmentally friendly, stable colored clay without adding harmful ingredients, and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides an environmentally friendly and stable colored mud, comprising the following raw materials in parts by weight:

[0007] 30-40 parts of modified starch, 5-10 parts of vegetable gum, 2-5 parts of lithium magnesium silicate, 10-20 parts of stabilizer, 5-10 parts of cross-linking agent, 20-30 parts of citrate, 2-5 parts of polyol, and 0-5 parts of color powder; wherein the stabilizer is a composition of glycerol, cellulose and casein; the cross-linking agent is N,N'-methylenebisacrylamide; the preparation method of the modified starch comprises the following steps: mixing citric acid and starch nanocrystals into a solution, drying, and then heating at 120-140°C for 2-8h to obtain a mixture, taking out, washing, drying, and grinding to obtain the modified starch.

[0008] The color mud of the present invention is improved in transparency by adding modified starch, and the modified starch is actually a derivative of starch-citric acid, because citric acid is dehydrated to generate an anhydride after being heated, and the anhydride and starch nanocrystals are used to obtain cross-linked starch by a dry reaction method. The cross-linking agent and citrate will further increase the cross-linking degree of the modified starch in the subsequent reaction, the water-based binding capacity will gradually decrease, the chemical stability will also be improved, and the color mud has good transparency. However, the reduced water-based binding capacity in the modified starch may affect the stability of the subsequent cross-linked gel network, so in order to improve the stability, the stabilizer and the plant gum are added, and the plant gum can improve the stability of the subsequent color mud.

[0009] In the present invention, a composition of glycerol, cellulose and casein is selected as a stabilizer, wherein glycerol can undergo a plasticizing reaction with gelatinized starch, and then the plasticized starch undergoes an esterification reaction with citrate, which can effectively improve the flexibility of the colored mud and make it more handy. In addition, citrate also has a certain antibacterial function. As the degree of crosslinking increases, the resistance of the modified cross-linked starch to gelatinization is enhanced. As the degree of crosslinking of the modified starch increases, the water-based binding capacity gradually decreases. The water solubility of the cross-linked starch derivative decreases, and the chemical stability increases accordingly. In addition, as the degree of crosslinking increases, its mechanical properties are also improved, and it has good transparency.

[0010] Lithium magnesium silicate, also known as hectorite, is a material with a special crystal structure and chemical composition. It can form a colorless, transparent, thixotropic gel when dispersed in water. Lithium magnesium silicate has the characteristics of high transparency, high viscosity and high thixotropy, and also has a nano-microcrystalline structure, so lithium magnesium silicate can form a highly transparent gel with cross-linked modified starch at a lower solid content. At the same time, lithium magnesium silicate is compounded with cellulose and casein. The three can effectively improve the tensile properties of the color mud, increase the playability of the color mud, and effectively improve the stability of the color mud.

[0011] Preferably, the mass ratio of citric acid to starch nanocrystals is 1:(0.9-1.5).

[0012] Preferably, the method for preparing starch nanocrystals comprises the following steps:

[0013] The starch is mixed with an acid solution to obtain a suspension, and then the suspension is washed to neutrality, and then freeze-dried to obtain the starch nanocrystal; wherein the mass ratio of the starch to the acid is 1:(300-310). The amorphous regions in the starch granules that are easily hydrolyzed are destroyed by inorganic means, leaving the crystalline regions that are difficult to hydrolyze. The starch nanocrystals obtained by this method have a high degree of crystallinity.

[0014] Preferably, the acid solution is a sulfuric acid solution.

[0015] Preferably, the stabilizer is a composition of glycerol, cellulose and casein in a mass ratio of 1:(0.5-2):(0.5-2).

[0016] Preferably, the polyol is at least one of 1,2-octanediol, monocaprylic glyceride, and 1,2-hexanediol. The above ingredients can destroy the cell membrane of microorganisms, and then interfere with the physiological environment of the cell membrane, thereby playing an antibacterial role. In addition, the above ingredients also have water retention and can maintain the "crystal mud" characteristics of the color mud.

[0017] Preferably, the plant gum is at least one of agar, pectin and carrageenan, which is used to improve the stability of the product and adjust the wettability of the product.

[0018] Preferably, the toner includes light yellow, phthalocyanine blue B, scarlet, carbon black, titanium dioxide and quartz sand.

[0019] Preferably, the modified starch is at least one of modified mung bean starch and modified pea starch. Mung bean starch and pea starch have high transparency and viscosity.

[0020] Preferably, the citrate is sodium citrate.

[0021] Preferably, the cellulose is wood fiber.

[0022] Preferably, the polyol is a mixture of 1,2-octanediol, monocaprylic glycerol, and 1,2-hexanediol in a mass ratio of 1:1:1. Compared with a single component, the polyol in this ratio has a better antiseptic and antibacterial effect and can effectively replace harmful preservatives.

[0023] In a second aspect, the present invention provides a method for preparing environmentally friendly and stable colored mud, comprising the following steps:

[0024] S1: firstly, the modified starch, stabilizer, lithium magnesium silicate and color powder are uniformly stirred, and then heated water is added and stirred to obtain a first mixture;

[0025] S2: heating the first mixture until the modified starch is completely gelatinized, then adding vegetable gum, cross-linking agent and part of citrate to obtain a blank, taking out part of the blank for cooling and testing, and if it is soft and non-sticky, it is qualified, no longer heating, adding polyol and the remaining citrate, stirring, to obtain the environmentally friendly and stable colored mud.

[0026] In the method for preparing the colored mud of the present invention, in S1, the modified starch is mixed with hot water and gelatinization is started, and the modified starch is plasticized with glycerol at the same time. In S2, the temperature is raised until the modified starch is completely gelatinized, and then the citrate undergoes an esterification reaction on the basis of the plasticized starch, and then undergoes a cross-linking reaction with a cross-linking agent to form a hydrogel with a network structure. The plant gum and lithium magnesium silicate can improve the tensile strength of the above-mentioned hydrogel, and the casein and cellulose in the stabilizer can further improve the stability of the colored mud, so as to obtain a highly transparent, environmentally friendly, stable colored mud with high playability and no harm to human health.

[0027] Preferably, in step (1), the temperature of the hot water is 60-80°C.

[0028] Preferably, in step (2), the heating temperature is 90-100°C.

[0029] In a third aspect, the present invention provides the use of environmentally friendly and stable colored clay in the preparation of children's toys.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The colored clay of the present invention does not contain borax, a cross-linking agent harmful to the human body, nor does it contain polyvinyl alcohol. (PVA)As a cross-linking agent, PVA is prevented from releasing formaldehyde during use, which is harmful to the human body. The raw materials of the color mud of the technical solution are all environmentally friendly and harmless to the human body. The finished color mud belongs to a non-Newtonian fluid, has soft and sticky characteristics, and is brightly colored and can be transformed into various shapes. The color mud of the present invention is improved by adding modified starch. The cross-linking agent and citrate will further increase the cross-linking degree of the modified starch in the subsequent reaction, the water-based binding ability will gradually decrease, the chemical stability will also be improved, and it has good transparency. In order to improve the stability, stabilizers and plant gums are supplemented, and plant gums can improve the stability of subsequent color muds. In the present invention, a composition of glycerol, cellulose and casein is selected as a stabilizer, wherein glycerol can undergo a plasticization reaction with gelatinized starch, and then the plasticized starch is esterified with citrate, which can effectively improve the flexibility of the color mud and make it more handy. In addition, citrate also has a certain antibacterial function. Lithium magnesium silicate has the characteristics of high transparency, high viscosity and high thixotropy, and also has a nano-microcrystalline structure, so lithium magnesium silicate can form a high-transparency gel with cross-linked modified starch at a low solid content. At the same time, lithium magnesium silicate is compounded with cellulose and casein, and the three can effectively improve the tensile properties of the color clay, and can also improve the stability of the color clay and increase the playability of the color clay.

[0032] (2) In the method for preparing the colored mud of the present invention, the modified starch is mixed with hot water in S1 and gelatinization begins, while the modified starch is plasticized with glycerol. In S2, the temperature is raised until the modified starch is completely gelatinized, and then citrate undergoes an esterification reaction on the basis of the plasticized starch, and then undergoes a cross-linking reaction with a cross-linking agent to form a hydrogel with a network structure. The plant gum and lithium magnesium silicate can improve the tensile strength of the above-mentioned hydrogel, and the casein and cellulose in the stabilizer can further improve the stability of the colored mud, thereby obtaining a highly transparent, environmentally friendly, stable colored mud with high playability and no harm to human health. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the product picture of Example 1. DETAILED DESCRIPTION

[0034] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0035] In the following examples, the raw materials used in the examples are as follows:

[0036] Pea starch: manufacturer is Guangzhou Huayu Biotechnology Co., Ltd.

[0037] Mung bean starch: the manufacturer is Beijing Haoliyu Industry and Trade Co., Ltd.

[0038] Corn starch: the manufacturer is Guangzhou Huayu Biotechnology Co., Ltd.

[0039] Agar: The manufacturer is Fujian Shishi Gaoxin Agar Food Co., Ltd.;

[0040] Pectin: The manufacturer is Xinjiang Fufeng Biotechnology Co., Ltd.;

[0041] Carrageenan: The manufacturer is Global Carrageenan Industrial Co., Ltd., Shishi City, Fujian Province;

[0042] Lithium magnesium silicate: The manufacturer is Jiangsu Bost Chemical Technology Co., Ltd.;

[0043] N, N′-methylenebisacrylamide: manufacturer is Jinan Jiayang Chemical Co., Ltd.;

[0044] Casein: The manufacturer is Gansu Hualing Dairy Co., Ltd.

[0045] Citric acid: manufacturer is Shandong Lemon Biochemical Co., Ltd.;

[0046] Sodium citrate: manufacturer is Wujiang Minghao Chemical Co., Ltd.;

[0047] Cellulose: Poplar wood powder cellulose, the manufacturer is Guangzhou Huayu Biotechnology Co., Ltd., the product specification is 200 mesh;

[0048] 1,2-Octanediol: The manufacturer is Shanghai Hongzhuang Chemical Technology Co., Ltd.;

[0049] Glyceryl monocaprylate: The manufacturer is Henan Honest Food Co., Ltd.;

[0050] 1,2-Hexanediol: The manufacturer is Jiangsu Bost Chemical Technology Co., Ltd.

[0051] Unless otherwise specified, other materials, reagents, etc. used in the examples can be obtained from commercial sources.

[0052] Example 1

[0053] An environmentally friendly and stable colored mud comprises the following raw materials in parts by weight:

[0054] 35 parts of modified starch, 7 parts of vegetable gum, 4 parts of lithium magnesium silicate, 14 parts of stabilizer, 6 parts of cross-linking agent, 26 parts of citrate, and 4 parts of polyol; wherein the stabilizer is a composition of glycerol, cellulose and casein in a mass ratio of 1:1:1; the cross-linking agent is N,N'-methylenebisacrylamide;

[0055] The preparation method of the modified starch comprises the following steps: mixing citric acid and starch nanocrystals into a solution, drying, and then heating at 130° C. for 6 hours to obtain a mixture, taking out, washing, drying, and grinding to obtain the modified starch.

[0056] Among them, the mass ratio of citric acid and starch nanocrystals is 1:1.

[0057] The method for preparing starch nanocrystals comprises the following steps:

[0058] Pea starch is mixed with a sulfuric acid solution to obtain a suspension, and then the suspension is washed to neutrality, and then freeze-dried to obtain pea starch nanocrystals; wherein the mass ratio of the pea starch to the sulfuric acid is 1:309. The acid solution is a sulfuric acid solution. The plant gum is agar. The citrate is sodium citrate. The cellulose is wood fiber. The polyol is a mixture of 1,2-octanediol, monocaprylic glyceride, and 1,2-hexanediol in a mass ratio of 1:1:1.

[0059] The method for preparing environmentally friendly and stable colored mud comprises the following steps:

[0060] S1: First, the modified starch, stabilizer, lithium magnesium silicate and color powder are uniformly stirred, and then 65°C hot water is added and stirred to obtain a first mixture;

[0061] S2: heat the first mixture to 95°C until the modified starch is completely gelatinized, then add vegetable gum, a cross-linking agent and 14 parts of sodium citrate to obtain a blank, take out part of the blank, cool it and test it. If it is soft and non-sticky, it is qualified, no longer heat it, add polyol and the remaining 12 parts of sodium citrate, stir, and obtain the environmentally friendly and stable colored mud.

[0062] Example 2

[0063] An environmentally friendly and stable colored mud comprises the following raw materials in parts by weight:

[0064] 30 parts of modified starch, 5 parts of vegetable gum, 2 parts of lithium magnesium silicate, 10 parts of stabilizer, 5 parts of cross-linking agent, 20 parts of citrate, 2 parts of polyol, 1 part of color powder; wherein the stabilizer is a composition of glycerol, cellulose and casein in a mass ratio of 1:0.5:0.5; the cross-linking agent is N,N'-methylenebisacrylamide;

[0065] The preparation method of the modified starch comprises the following steps: mixing citric acid and starch nanocrystals into a solution, drying, and then heating at 120° C. for 8 hours to obtain a mixture, taking out, washing, drying, and grinding to obtain the modified starch.

[0066] Among them, the mass ratio of citric acid and starch nanocrystals is 1:0.9.

[0067] The method for preparing starch nanocrystals comprises the following steps:

[0068] The mung bean starch and the sulfuric acid solution are mixed to obtain a suspension, and then the suspension is washed to neutrality, and then freeze-dried to obtain the mung bean starch nanocrystal; wherein the mass ratio of the mung bean starch to the sulfuric acid is 1:300. The acid solution is a sulfuric acid solution. The polyol is monocaprylic acid glyceride. The plant gum is pectin. The color powder is light yellow. The citrate is sodium citrate. The cellulose is wood fiber.

[0069] The method for preparing environmentally friendly and stable colored mud comprises the following steps:

[0070] S1: firstly, the modified starch, stabilizer, lithium magnesium silicate and color powder are uniformly mixed, and then hot water at 60° C. is added and stirred to obtain a first mixture;

[0071] S2: heat the first mixture to 90°C until the modified starch is completely gelatinized, then add vegetable gum, a cross-linking agent and 10 parts of sodium citrate to obtain a blank, take out part of the blank, cool it and test it. If it is soft and non-sticky, it is qualified, no longer heat it, add polyol and 10 parts of citrate, stir, and obtain the environmentally friendly and stable colored mud.

[0072] Example 3

[0073] An environmentally friendly and stable colored mud comprises the following raw materials in parts by weight:

[0074] 40 parts of modified starch, 10 parts of vegetable gum, 5 parts of lithium magnesium silicate, 20 parts of stabilizer, 10 parts of cross-linking agent, 30 parts of citrate, 5 parts of polyol, 5 parts of color powder; wherein the stabilizer is a composition of glycerol, cellulose and casein in a mass ratio of 1:2:2; the cross-linking agent is N,N'-methylenebisacrylamide;

[0075] The preparation method of the modified starch comprises the following steps: mixing citric acid and starch nanocrystals into a solution, drying, and then heating at 140° C. for 2 hours to obtain a mixture, taking out, washing, drying, and grinding to obtain the modified starch. The mass ratio of citric acid to starch nanocrystals is 1:1.5.

[0076] The method for preparing starch nanocrystals comprises the following steps:

[0077] Pea starch is mixed with a sulfuric acid solution to obtain a suspension, and then the suspension is washed to neutrality, and then freeze-dried to obtain pea starch nanocrystals; wherein the mass ratio of the starch to the sulfuric acid is 1:310. The polyol is 1,2-hexanediol. The plant gum is carrageenan. The color powder is titanium dioxide. The citrate is sodium citrate. The cellulose is wood fiber. The polyol is a mass ratio of monocaprylic glycerol.

[0078] The method for preparing environmentally friendly and stable colored mud comprises the following steps:

[0079] S1: firstly, the modified starch, stabilizer, lithium magnesium silicate and color powder are uniformly mixed, and then 80° C. hot water is added and stirred to obtain a first mixture;

[0080] S2: heat the first mixture to 100°C until the modified starch is completely gelatinized, then add vegetable gum, a cross-linking agent and 25 parts of citrate to obtain a blank, take out part of the blank, cool it and test it. If it is soft and non-sticky, it is qualified, no longer heat it, add polyol and the remaining 5 parts of citrate, stir, and obtain the environmentally friendly and stable colored mud.

[0081] Example 4

[0082] The difference between Example 4 and Example 1 is that the stabilizer in Example 4 is a composition of glycerol, cellulose and casein in a mass ratio of 1:0.4:0.4.

[0083] Example 5

[0084] The difference between Example 5 and Example 1 is that the stabilizer in Example 5 is a composition of glycerol, cellulose and casein in a mass ratio of 12.5:2.5.

[0085] Example 6

[0086] The difference between Example 6 and Example 1 is that the polyol in Example 6 replaces 1,2-octanediol with glycerol.

[0087] Example 7

[0088] The difference between Example 7 and Example 1 is that the polyol in Example 7 is a composition of 1,2-octanediol and 1,2-hexanediol in a mass ratio of 1:1.

[0089] Example 8

[0090] The difference between Example 8 and Example 1 is that the polyol in Example 8 is a composition of 1,2-octanediol and monocaprylic glycerol in a mass ratio of 1:1.

[0091] Example 9

[0092] The difference between Example 9 and Example 1 is that the modified starch in Example 9 is modified corn starch, that is, corn starch is used to make corn starch nanocrystals and then subjected to citric acid reaction to obtain the modified corn starch.

[0093] Comparative Example 1

[0094] The difference between Comparative Example 1 and Example 1 is that: Comparative Example 1 uses pea starch to replace modified starch.

[0095] Comparative Example 2

[0096] The difference between Comparative Example 2 and Example 1 is that: Comparative Example 2 uses pea starch directly mixed with citric acid for modification.

[0097] Comparative Example 3

[0098] The difference between Comparative Example 3 and Example 1 is that the cross-linking agent in Comparative Example 3 is polyvinyl alcohol.

[0099] Comparative Example 4

[0100] The difference between Comparative Example 4 and Example 1 is that the cross-linking agent in Comparative Example 4 is borax.

[0101] Comparative Example 5

[0102] The difference between Comparative Example 5 and Example 1 is that: Comparative Example 5 does not add lithium magnesium silicate.

[0103] Comparative Example 6

[0104] The difference between Comparative Example 6 and Example 1 is that: Comparative Example 6 does not add lithium magnesium silicate, but uses silicon dioxide instead.

[0105] Comparative Example 7

[0106] The difference between Comparative Example 7 and Example 1 is that no citrate is added in Comparative Example 7.

[0107] Comparative Example 8

[0108] The difference between Comparative Example 8 and Example 1 is that: Comparative Example 8 does not add citrate, but uses sodium chloride instead.

[0109] Comparative Example 9

[0110] The difference between Comparative Example 9 and Example 1 is that no polyol is added in Comparative Example 9.

[0111] Comparative Example 10

[0112] The difference between Comparative Example 10 and Example 1 is that no stabilizer is added in Comparative Example 10.

[0113] Comparative Example 11

[0114] The difference between Comparative Example 11 and Example 1 is that the stabilizer in Comparative Example 11 is a mixture of glycerol and cellulose in a mass ratio of 1:1.

[0115] Comparative Example 12

[0116] The difference between Comparative Example 12 and Example 1 is that the stabilizer in Comparative Example 12 is a mixture of glycerol and casein in a mass ratio of 1:1.

[0117] Comparative Example 13

[0118] The difference between Comparative Example 13 and Example 1 is that the stabilizer in Comparative Example 13 is a mixture of cellulose and casein in a mass ratio of 1:1.

[0119] Comparative Example 13

[0120] The difference between Comparative Example 13 and Example 1 is that the stabilizer in Comparative Example 13 is a mixture of cellulose and casein in a mass ratio of 1:1.

[0121] Comparative Example 14

[0122] The difference between Comparative Example 14 and Example 1 is that the method for preparing the colored mud in Comparative Example 14 is to directly mix all the raw materials and then add hot water just boiled at above 95°C to mix.

[0123] Performance Testing

[0124] The colored mud samples of Examples 1 to 9 and Comparative Examples 1 to 14 were used as samples to carry out the following tests respectively:

[0125] 1. Transparency

[0126] The transparency of each sample was characterized by an ultraviolet spectrophotometer (Shanghai Tianmei, UV2310II). During the test, the sample was stretched to a strip with a thickness of 0.5 mm. The test wavelength range was 400nm-800nm ​​visible light range, the reference was air, and the transmittance at 550nm was recorded. It should be noted that no color powder was added to the samples used to test the transparency. The specific transmittance data is shown in Table 1.

[0127] Table 1 Transparency data of each group of samples

[0128]

[0129]

[0130] As shown in Table 1, the samples of Examples 1 to 8 all have good transparency before adding toner. The transparency of Example 1 is slightly better than that of Example 9, indicating that the transparency of mung bean starch and pea starch is higher than that of corn starch.

[0131] In Comparative Example 1, only pea starch was added without adding modified starch, and in Comparative Example 2, pea starch was directly mixed with citric acid for modification. Compared with Example 1, the transparency of both samples was significantly reduced. This is because the direct addition of pea starch reduces the subsequent cross-linking degree and chemical stability, resulting in reduced transparency. Pea starch needs to be first acid-hydrolyzed to form starch nanocrystals to obtain a higher crystallinity, which can make the product have better transparency. Therefore, the modified starch in Example 1 can significantly improve the cross-linking degree of subsequent products and have good transparency.

[0132] The transparency of Example 1 is slightly better than that of Comparative Examples 3 and 4, indicating that the crosslinking degree of N,N′-methylenebisacrylamide selected as the crosslinking agent in the present invention is comparable to that of borax and polyvinyl alcohol. The selection of the crosslinking agent can improve the network strength of the gel and also improve the transparency of the thixotropic gel.

[0133] The transparency of Comparative Examples 5 and 6 is also lower than that of the sample in Example 1. This is because lithium magnesium silicate has the characteristics of high transparency, high viscosity and high thixotropy, and also has a nano-microcrystalline structure, so lithium magnesium silicate can form a high-transparency gel with the cross-linked modified starch at a lower solid content.

[0134] Comparative Examples 7 and 8 did not add citrate, lacked the subsequent step of esterification reaction with the plasticized starch, and the formed gel network was weak, thus affecting the transparency of the product.

[0135] The transparency of the composition of Comparative Example 9 is not much different from that of Example 1, indicating that the addition of polyol has no significant effect on the transparency of the product.

[0136] Comparative Examples 10-13 verify that glycerol, cellulose and casein in the stabilizer have a synergistic effect. If any component is missing, the transparency of the product will be affected. Therefore, in Example 1, a composition of glycerol, cellulose and casein with a mass ratio of 1:1:1 is selected.

[0137] Comparative Example 14 is to directly mix the raw materials, which affects the dispersibility and cross-linking degree, thereby reducing the transparency. Therefore, Example 1 adopts a specific addition sequence to further improve the transparency of the product.

[0138] 2. Tensile properties

[0139] The tensile properties of the gel were tested using a small tensile and compression testing machine. Each group of gel was cut into 40mm×10mm, and the thickness was measured by a spiral micrometer. The distance between the clamps was set to 20mm, and the tensile speed was 100mm / min. The stress and strain of each group were recorded, and the stress and strain curves were drawn. The tensile strength, elongation, and compression modulus data were recorded according to the curves, as shown in Table 2.

[0140] 3. Stable performance

[0141] Each group of samples was placed in a test environment with a room temperature of 32±2°C and a relative humidity of 60-70% and an aging condition: a test environment with a temperature of 50±2°C and a relative humidity of 60-70% for one month, and then taken out and tested according to the above-mentioned tensile performance test method, as shown in Table 2 for details.

[0142] Table 2 Tensile properties data of each group under original, room temperature and aging conditions

[0143]

[0144]

[0145]

[0146] As shown in Table 2, the samples of Examples 1 to 3 have good plasticity and viscoelasticity. Moreover, after the sample of Example 1 was placed at room temperature for one month, the plasticity and viscoelasticity of the sample were not greatly affected, and after being placed under aging conditions for one month, the properties did not change significantly, indicating that the samples of Examples 1-3 have obvious stability.

[0147] The tensile strength and stability of Example 1 are better than those of Examples 4-5, and are also significantly better than those of Comparative Examples 10-13. This is because the cellulose and casein contents in Example 4 are relatively low, making it difficult to support the gel network, resulting in a soft feel of the product and reduced stability of the product. In Example 5, the cellulose and casein contents are relatively high, the supporting force is good, and the mechanical properties are improved, but its stability is reduced. Therefore, the stabilizer is limited in the present invention to a composition of glycerol, cellulose and casein with a mass ratio of 1: (0.5-2): (0.5-2). The feel and stability within the above range can be well guaranteed. In Comparative Example 10, no stabilizer is added, which affects the feel of the initial product, and the temperature resistance of the product is significantly reduced, indicating that the composition of glycerol, cellulose and casein in the present invention can stabilize the system. Although the stabilizers of Comparative Examples 11-13 have better performance than Comparative Example 10, due to the lack of a certain component in the stabilizer, the stability is significantly inferior to that of Example 1.

[0148] In Example 6, 1,2-octanediol in the polyol is replaced with glycerol, and in Examples 7-8, a certain component in the polyol is deleted respectively. In Comparative Example 9, no polyol is added. The tensile properties and stability of the products in Examples 6-8 are similar to those in Example 1, indicating that the type of polyol has little effect on the stability of the product. However, the stability of Comparative Example 9 without adding polyol is reduced, because the polyol mainly plays the role of thickener and moisturizer, and not adding polyol will affect the stability.

[0149] Example 9 uses modified corn starch to replace modified pea starch, and its stability is also similar to that of Example 1, but the modified pea starch has a slight promoting effect on the stability.

[0150] In Comparative Example 1, only pea starch was added without adding modified starch, and in Comparative Example 2, pea starch was directly mixed with citric acid for modification. Compared with Example 1, the tensile properties and product stability of both samples were significantly reduced. This is because the direct addition of pea starch reduces the subsequent cross-linking degree and chemical stability. Pea starch needs to be first acid-hydrolyzed to form starch nanocrystals to obtain a higher crystallinity, which can help improve the subsequent cross-linking degree. Therefore, the modified starch in Example 1 can significantly improve the cross-linking degree of subsequent products and has good transparency.

[0151] The tensile strength of Example 1 is slightly better than that of Comparative Examples 3 and 4, indicating that the crosslinking degree of N,N'-methylenebisacrylamide selected as the crosslinking agent in the present invention is comparable to that of borax and polyvinyl alcohol. The crosslinking agent of the present invention does not contain harmful components such as boron, and does not precipitate formaldehyde during use and preparation.

[0152] The tensile properties and stability of Comparative Examples 5 and 6 are also lower than those of the sample in Example 1, indicating that the combination of lithium magnesium silicate, cellulose and casein can synergistically effectively improve the tensile properties of the colored clay, increase the playability of the colored clay, and effectively improve the stability of the colored clay.

[0153] Comparative Examples 7 and 8 did not add citrate, and lacked the subsequent step of esterification reaction with the plasticized starch. The formed gel network was weak, so the tensile properties were poor and the stability was also reduced.

[0154] Comparative Examples 10-13 verify that glycerol, cellulose and casein in the stabilizer have a synergistic effect. If any component is missing, the stability of the system will be significantly reduced. Therefore, a composition of glycerol, cellulose and casein with a mass ratio of 1:1:1 is selected in Example 1. Glycerol can further plasticize the modified starch and increase the degree of cross-linking. Cellulose, as a reinforcing body, can improve the mechanical properties of the gel. Because cellulose and casein both contain a large number of hydroxyl groups or amino groups, they can form a strong force with lithium magnesium silicate through hydrogen bonds, thereby improving the stability of the system.

[0155] Comparative Example 14 is to directly mix the raw materials, which affects the dispersibility and degree of cross-linking, thereby reducing the stability of the system. Therefore, Example 1 adopts a specific order of adding materials. First, the modified starch is mixed with hot water to start gelatinization, and the modified starch is plasticized with glycerol at the same time. Then the temperature is raised to the modified starch for complete gelatinization, and then the citrate undergoes an esterification reaction on the basis of the plasticized starch, and then undergoes a cross-linking reaction with a cross-linking agent to form a hydrogel with a network structure. The plant gum and lithium magnesium silicate can increase the tensile strength of the above-mentioned hydrogel, and the casein and cellulose in the stabilizer can further improve the stability of the color mud, so as to obtain a highly transparent, environmentally friendly, stable color mud with high playability and no harm to human health.

[0156] 4. Antibacterial performance

[0157] The samples of Examples 1, 6-8 and Comparative Examples 7-9 were cut into 6 mm discs for standby use as carriers. The carrier immersion quantitative antibacterial test in the antibacterial and antibacterial effect evaluation method of "WS / T 650-2019" was used to detect the antibacterial rates of the above four groups of samples against Escherichia coli (ATCC8739NA), Staphylococcus aureus (ATCC6538), Candida albicans (ATCC10231) and Aspergillus niger (ATCC16404). Each test group was repeated three times and the average value was taken. The data are shown in Table 3.

[0158] Table 3 Antibacterial rate of samples in each group

[0159]

[0160] As shown in Table 3, Examples 1 and 6-8 all have obvious inhibitory effects on the above-mentioned harmful bacteria, proving that at least one of 1,2-octanediol, monocaprylic glyceryl, and 1,2-hexanediol has a good antiseptic and antibacterial effect. Among them, the polyol in Example 1 is a mixture of 1,2-octanediol, monocaprylic glyceryl, and 1,2-hexanediol in a mass ratio of 1:1:1, which can achieve the best effect.

[0161] In Comparative Example 9, no polyol is added, but there is still a certain inhibitory effect on harmful bacteria in the system. This is because excessive citrate is added to the raw materials. Citrate can inhibit the formation of bacterial biofilm, reduce the production of virulence factors protease and pyocyanin, and reduce the motility of bacteria. In Comparative Example 7, no citrate is added, and its antibacterial effect is reduced. In Comparative Example 8, citrate is replaced by sodium chloride, and its antibacterial performance is not significantly affected, but sodium chloride cannot react with the gel system to promote stability.

[0162] In summary, the color clay of the present invention does not add borax, a cross-linking agent that is harmful to the human body, nor does it add polyvinyl alcohol as a cross-linking agent, thereby preventing PVA from releasing formaldehyde during use and causing harm to the human body. The raw materials selected are all environmentally friendly and harmless to the human body. The color clay of the present invention has good tensile properties, excellent stability, and improved playability. The environmentally friendly and stable color clay is suitable as a children's toy.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An environmentally friendly and stable colored mud, characterized in that: The invention comprises the following raw materials in parts by weight: 30-40 parts of modified starch, 5-10 parts of vegetable gum, 10-20 parts of lithium magnesium silicate, 10-20 parts of stabilizer, 5-10 parts of cross-linking agent, 20-30 parts of citrate, 2-5 parts of polyol, 0-5 parts of color powder; wherein the stabilizer is a composition of glycerol, cellulose and casein in a mass ratio of 1: (0.5-2): (0.5-2); the cross-linking agent is N, N'-methylenebisacrylamide; the polyol is a mixture of 1,2-octanediol, monocaprylic acid glyceride and 1,2-hexanediol in a mass ratio of 1:1:1; the modified starch is at least one of modified mung bean starch and modified pea starch; The preparation method of the modified starch comprises the following steps: mixing citric acid and starch nanocrystals into a solution, drying, and then heating at 120-140° C. for 2-8 hours to obtain a mixture, taking out, washing, drying, and grinding to obtain the modified starch; The method for preparing environmentally friendly and stable colored mud comprises the following steps: S1: firstly, the modified starch, lithium magnesium silicate, stabilizer and color powder are uniformly stirred, and then heated water is added and stirred to obtain a first mixture; S2: heating the first mixture until the modified starch is completely gelatinized, then adding vegetable gum, cross-linking agent and part of citrate to obtain a blank, taking out part of the blank for cooling and testing, and if it is soft and non-sticky, it is qualified, no longer heating, adding polyol and the remaining citrate, stirring, to obtain the environmentally friendly and stable colored mud.

2. The environmentally friendly and stable colored clay as claimed in claim 1, characterized in that: The mass ratio of citric acid to starch nanocrystals is 1:(0.9~1.5).

3. The environmentally friendly and stable colored clay as claimed in claim 1 or 2, characterized in that: The method for preparing starch nanocrystals comprises the following steps: The starch is mixed with an acid solution to obtain a suspension, and then the suspension is washed to neutrality, and then freeze-dried to obtain the starch nanocrystals; wherein the mass ratio of the starch to the acid is 1: (300-310).

4. The environmentally friendly and stable colored clay as claimed in claim 1, characterized in that: The vegetable gum is at least one of agar, pectin and carrageenan; the color powder includes light yellow, phthalocyanine blue B, scarlet, carbon black and titanium dioxide; and the citrate is sodium citrate.

5. The environmentally friendly and stable colored clay as claimed in claim 1, characterized in that: In step (1) of the method for preparing the environmentally friendly and stable colored mud, the water temperature of the hot water is 60-80°C.

6. The environmentally friendly and stable colored clay as claimed in claim 1, characterized in that: In step (2) of the method for preparing the environmentally friendly and stable colored clay, the heating temperature is 90-100°C.

7. Use of the environmentally friendly and stable colored clay according to any one of claims 1 to 6 in the preparation of children's toys.

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