A magnesium oxychloride cement doped with chitosan phosphate@nano-silica and a preparation method thereof

Abstract

The present invention belongs to the technical field of modification of magnesium oxychloride cement, and specifically relates to a magnesium oxychloride cement doped with chitosan phosphate@nano-silica and a preparation method thereof: Mix absolute ethanol, phosphoric acid, and triethyl phosphate in proportion, add phosphorus pentoxide and chitosan, after fully reacting, wash with absolute ethanol until neutral, and dry to obtain chitosan phosphate. Dissolve chitosan phosphate in an acetic acid solution, then put the surface-activated nano-silica into it, after fully reacting, wash with deionized water and dry to obtain chitosan phosphate@nano-silica. Mix magnesium chloride and water in proportion, add chitosan phosphate@nano-silica, and obtain a magnesium chloride mixed solution after fully stirring and ultrasonic treatment. Then, stir the light-burned magnesite and the magnesium chloride mixed solution evenly to form a magnesium oxychloride cement paste, inject it into a mold, and place it in the air for constant temperature and humidity curing to prepare a magnesium oxychloride cement with relatively high compressive strength and softening coefficient.

Description

Technical Field

[0001] The present invention belongs to the technical field of modification of magnesium oxychloride cement, and particularly relates to a magnesium oxychloride cement doped with chitosan phosphate@nano-silica and a preparation method thereof. Background Art

[0002] Magnesium oxychloride cement (MOC) is an air-hardening gel material prepared from active magnesium oxide powder and a magnesium chloride solution with a certain concentration. Compared with ordinary Portland cement, it has the advantages of high strength, fast setting speed, good heat preservation performance, light weight, simple curing conditions, good fire resistance, environmental friendliness, etc., and is mostly used in goods packaging, building materials, heat preservation materials, biological materials, etc. However, its water resistance is very poor. After the P5 phase (5Mg(OH)2·MgCl2·8H2O) that provides strength is soaked in water, the needle-like network structure changes into a loose-packed layered structure, and the compressive strength loss is more than 90%. At the same time, it also leads to the loss of other properties, greatly restricting its application range. Therefore, how to improve the water resistance of magnesium oxychloride cement has always been a hot research direction in this field.

[0003] Due to the low alkalinity and strong dopability of the magnesium oxychloride cement system, adding fillers is an economical and effective method. Fillers are mainly divided into inert fillers and active fillers.

[0004] Inert fillers include straw, glass fiber, etc. These fillers do not undergo chemical reactions in the magnesium oxychloride cement system and are only mixed together by the bonding action of magnesium oxychloride cement. And some inert fillers are difficult to be tightly combined with magnesium oxychloride cement because of the existence of an interface layer, which is more conducive to water infiltrating into the interior of magnesium oxychloride cement, causing the water resistance of magnesium oxychloride cement to deteriorate further.

[0005] Active fillers include fly ash, metakaolin, etc. The active substances in these fillers can undergo chemical reactions in the magnesium oxychloride cement system, interact with the cement matrix or generate new phases to improve the interface between the filler and the matrix. However, whether inert fillers or active fillers are selected, a large amount of incorporation will dilute the concentration of active magnesium oxide, slow down the hydration reaction rate, and cause the early compressive strength of magnesium oxychloride cement to decrease.

[0006] Inorganic nanoparticles have an extremely large specific surface area and strong reaction activity, and can be used as the nucleus of the hydration phase of cement-based materials. Only a small amount of addition can improve the material properties. However, the high specific surface area leads to the natural agglomeration characteristics of nanomaterials, and their dispersibility in the high-viscosity magnesium oxychloride cement system is very poor, resulting in stress concentration in the magnesium oxychloride cement system, reducing the compressive strength. At the same time, filling nanoparticles cannot significantly improve the water resistance of magnesium oxychloride cement. These are all problems that need to be solved urgently in the modification of magnesium oxychloride cement with nanoparticles. Summary of the Invention

[0007] In view of the problems of poor water resistance of magnesium oxychloride cement in the prior art and the negative impacts on properties such as compressive strength after water resistance modification, the present invention provides a magnesium oxychloride cement doped with chitosan phosphate@nano-silica and a preparation method thereof: using the self-made nano-composite chitosan phosphate@nano-silica as a filler, by adopting hydrogen peroxide surface treatment to increase the dispersibility of nano-silica in the magnesium oxychloride cement system, which is beneficial to giving full play to the filling effect and high reactivity of nano-particles, increasing the compressive strength of magnesium oxychloride cement. At the same time, by using the chitosan phosphate loaded on the surface of nano-silica, the interface between the nano-silica filler and the magnesium oxychloride cement matrix is improved, and the water resistance of magnesium oxychloride cement is increased, so that the obtained magnesium oxychloride cement has both high compressive strength and high softening coefficient.

[0008] The main steps of the preparation method are as follows:

[0009] (1) Mix 20 mL of absolute ethanol, 5 mL of phosphoric acid, and 5 mL of triethyl phosphate evenly, then add 5 g of phosphorus pentoxide and 6 g of chitosan, heat in a water bath at 40 °C and stir. After reacting for 3 h, wash with absolute ethanol until neutral, dry to obtain chitosan phosphate, and dissolve 0.4 - 1.2 g of chitosan phosphate in 100 mL of 2% glacial acetic acid solution;

[0010] (2) Disperse 2 g of nano-silica evenly in 20 mL of 35% hydrogen peroxide solution, heat in a water bath at 35 °C and stir. After reacting for 24 h, dry to obtain surface-activated nano-silica, and then put it into the glacial acetic acid solution of chitosan phosphate obtained in step (1), heat in a water bath at 45 °C and stir. After fully reacting for 12 h, wash with deionized water and dry to obtain the nano-composite chitosan phosphate@nano-silica;

[0011] The mass ratio of surface-active nano-silica to chitosan phosphate is 1:0.2 - 0.6.

[0012] (3) Mix magnesium chloride and water evenly according to the molar ratio, then add the chitosan phosphate@nano-silica obtained in step (2), stir fully and ultrasonically to obtain a magnesium chloride mixed solution. Mix the magnesium chloride mixed solution with reactive magnesium oxide and water evenly according to the molar ratio to prepare a magnesium oxychloride cement paste, place it in the air, and maintain a constant temperature of 25 °C and a humidity of 60% for constant temperature and humidity curing.

[0013] Among them, the dosage of chitosan phosphate@nano-silica is 0.5 - 1.5% of the mass of reactive magnesium oxide, and the reactive magnesium oxide is derived from light-burned magnesite, with the content of reactive magnesium oxide ≥ 63%.

[0014] The molar ratio of reactive magnesium oxide, magnesium chloride, and water is 6.5:1:13.

[0015] Table 1 Chemical composition of light-burned magnesia

[0016]

[0017] The beneficial effects of the present invention are as follows: The incorporation of chitosan phosphate@nano-silica increases the compressive strength of magnesium oxychloride cement. The surface-loaded chitosan phosphate enables better combination of nano-silica and magnesium oxychloride cement matrix, improving the water resistance. Description of the Drawings

[0018] Figure 1 It is the infrared characterization results of chitosan and chitosan phosphate.

[0019] Figure 2 It is the infrared characterization results of nano-silica and chitosan phosphate@nano-silica.

[0020] Figure 3 It is the TEM characterization results. a is chitosan phosphate@nano-silica, b is unmodified nano-silica, and c is nano-silica treated with hydrogen peroxide. Detailed Embodiments

[0021] The present invention will be further described below in conjunction with embodiments, but not limited thereto.

[0022] Example 1

[0023] Mix 20 mL of absolute ethanol, 5 mL of phosphoric acid, and 5 mL of triethyl phosphate evenly, then add 5 g of phosphorus pentoxide and 6 g of chitosan. Heat and stir in a 40 °C water bath. After fully reacting for 3 h, wash with absolute ethanol until neutral, and dry to obtain chitosan phosphate. Dissolve 0.8 g of chitosan phosphate in 100 mL of 2% glacial acetic acid solution. Disperse 2 g of nano-silica evenly in 20 mL of 35% hydrogen peroxide solution. Heat and stir in a 35 °C water bath. After reacting for 24 h, dry to obtain surface-activated nano-silica, and then put it into the glacial acetic acid solution of chitosan phosphate. Heat and stir in a 45 °C water bath. After fully reacting for 12 h, wash with deionized water and dry to obtain the nanocomposite chitosan phosphate@nano-silica.

[0024] Figure 1 It is the infrared characterization results of chitosan and chitosan phosphate, where the small and broad absorption peak at 3108 cm -1 is the N-H stretching vibration absorption peak, the peak at 2680 cm -1 is the C-H symmetric stretching vibration absorption peak, the peak at 1380 cm -1 is the C-N stretching vibration absorption peak, and the peak at 1130 cm -1The absorption peak at this position is the antisymmetric stretching vibration absorption peak of C-O-C (glycosidic bond). The above are the infrared characteristic absorption peaks of chitosan, which are all reflected in the infrared characterization results of chitosan phosphate. Compared with the infrared results of chitosan, new absorption peaks appear in chitosan phosphate. At 1630 cm -1 The absorption peak at this position is the stretching vibration absorption peak of P=O. At 1260 cm -1 The absorption peak at this position is the stretching vibration absorption peak of P-O-C. At 1093 cm -1 The absorption peak at this position is the stretching vibration absorption peak of N-P. At 850 cm -1 The absorption peak at this position is the stretching vibration absorption peak of P-O. The above results indicate that phosphate groups are successfully grafted onto chitosan.

[0025] Figure 2 are the infrared characterization results of nano-silica and chitosan phosphate@nano-silica. Among them, the absorption peak at 790 cm -1 is the symmetric stretching vibration absorption peak of Si-O. At 1100 cm -1 is the antisymmetric stretching vibration absorption peak of Si-O-Si. At 1630 cm -1 is the bending vibration absorption peak of Si-OH. These are the infrared characteristic absorption peaks of nano-silica, which are all reflected in chitosan phosphate@nano-silica. Compared with nano-silica, new peaks appear in chitosan phosphate@nano-silica. At 970 cm -1 is the stretching vibration absorption peak of C-O-Si, indicating that chitosan phosphate is successfully loaded on nano-silica.

[0026] Figure 3 are the TEM characterization results. a is chitosan phosphate@nano-silica, b is unmodified nano-silica, and c is nano-silica treated with hydrogen peroxide. It can be seen from a and c that the dispersion of nano-silica is better and it can maintain the morphology of spherical nanoparticles. It can be clearly seen from b that the unmodified nano-silica agglomerates and stacks seriously, forming larger clusters and losing the nanoscale.

[0027] Table 2 Zeta potential results

[0028]

[0029] (1) After mixing magnesium chloride and water evenly at a molar ratio of 1:13, chitosan phosphate@nano-silica is added to obtain a magnesium chloride mixed solution. Among them, the dosage of chitosan phosphate@nano-silica is 0.5% of the mass of active magnesium oxide.

[0030] (2) Mix the magnesium chloride mixed solution with reactive magnesium oxide and water at a molar ratio of reactive magnesium oxide, magnesium chloride, and water of 6.5:1:13 at room temperature, stir evenly to make a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain the temperature at 25°C and humidity at 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 122 MPa, and the softening coefficient is 0.67.

[0031] Example 2

[0032] The preparation of chitosan phosphate@nano-silica is the same as that in Example 1.

[0033] (1) Mix magnesium chloride and water evenly at a molar ratio of 1:13, and then add chitosan phosphate@nano-silica to obtain a magnesium chloride mixed solution. Among them, the dosage of chitosan phosphate@nano-silica is 1.0% of the mass of reactive magnesium oxide.

[0034] (2) Mix the magnesium chloride mixed solution with reactive magnesium oxide and water at a molar ratio of reactive magnesium oxide, magnesium chloride, and water of 6.5:1:13 at room temperature, stir evenly to make a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain the temperature at 25°C and humidity at 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 130 MPa, and the softening coefficient is 0.77.

[0035] Example 3

[0036] The preparation of chitosan phosphate@nano-silica is the same as that in Example 1.

[0037] (1) Mix magnesium chloride and water evenly at a molar ratio of 1:13, and then add chitosan phosphate@nano-silica to obtain a magnesium chloride mixed solution. Among them, the dosage of chitosan phosphate@nano-silica is 1.5% of the mass of reactive magnesium oxide.

[0038] (2) Mix the magnesium chloride mixed solution with reactive magnesium oxide and water at a molar ratio of reactive magnesium oxide, magnesium chloride, and water of 6.5:1:13, stir evenly to make a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain the temperature at 25°C and humidity at 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 126 MPa, and the softening coefficient is 0.72.

[0039] Example 4

[0040] Mix 20 mL of absolute ethanol, 5 mL of phosphoric acid, and 5 mL of triethyl phosphate evenly, then add 5 g of phosphorus pentoxide and 6 g of chitosan. Heat and stir in a 40 °C water bath. After reacting for 3 h, wash with absolute ethanol until neutral, dry to obtain chitosan phosphate. Dissolve 0.4 g of chitosan phosphate in 100 mL of a 2% glacial acetic acid solution. Disperse 2 g of nano-silica evenly in 20 mL of a 35% hydrogen peroxide solution. Heat and stir in a 35 °C water bath. After reacting for 24 h, dry to obtain surface-activated nano-silica, and then put it into the glacial acetic acid solution of chitosan phosphate. Heat and stir in a 45 °C water bath. After reacting for 12 h, wash with deionized water, dry to obtain the nanocomposite chitosan phosphate@nano-silica.

[0041] (1) Mix magnesium chloride and water in a molar ratio of 1:13 evenly, then add chitosan phosphate@nano-silica to obtain a magnesium chloride mixed solution. Among them, the dosage of chitosan phosphate@nano-silica is 1.0% of the mass of active magnesium oxide.

[0042] (2) Mix the magnesium chloride mixed solution with active magnesium oxide and water in a molar ratio of active magnesium oxide:magnesium chloride:water of 6.5:1:13 and stir evenly to make a magnesium oxychloride cement paste. Inject the magnesium oxychloride cement paste into a mold of 20 mm×20 mm×20 mm. Demold and cure after 1 day, keep the temperature at 25 °C and the humidity at 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 125 MPa, and the softening coefficient is 0.60.

[0043] Example 5

[0044] Mix 20 mL of absolute ethanol, 5 mL of phosphoric acid, and 5 mL of triethyl phosphate evenly, then add 5 g of phosphorus pentoxide and 1.2 g of chitosan. Heat and stir in a 40 °C water bath. After reacting for 3 h, wash with absolute ethanol until neutral, dry to obtain chitosan phosphate. Dissolve 1.2 g of chitosan phosphate in 100 mL of a 2% glacial acetic acid solution. Disperse 2 g of nano-silica evenly in 20 mL of a 35% hydrogen peroxide solution. Heat and stir in a 35 °C water bath. After reacting for 24 h, dry to obtain surface-activated nano-silica, and then put it into the glacial acetic acid solution of chitosan phosphate. Heat and stir in a 45 °C water bath. After reacting for 12 h, wash with deionized water, dry to obtain the nanocomposite chitosan phosphate@nano-silica.

[0045] (1) Mix magnesium chloride and water in a molar ratio of 1:13 evenly, then add chitosan phosphate@nano-silica to obtain a magnesium chloride mixed solution. Among them, the dosage of chitosan phosphate@nano-silica is 1.0% of the mass of active magnesium oxide.

[0046] (2) Mix the magnesium chloride mixed solution with reactive magnesium oxide and water in a molar ratio of reactive magnesium oxide : magnesium chloride : water of 6.5:1:13, stir evenly to form a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain a temperature of 25°C and a humidity of 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 123 MPa, and the softening coefficient is 0.64.

[0047] Comparative Example 1

[0048] (1) Mix magnesium chloride and water evenly in a molar ratio of 1:13 to obtain a solution.

[0049] (2) Mix reactive magnesium oxide, magnesium chloride and water in a molar ratio of 6.5:1:13, stir evenly to form a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain a temperature of 25°C and a humidity of 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 118 MPa, and the softening coefficient is 0.14.

[0050] Comparative Example 2

[0051] The preparation of chitosan phosphate is the same as that in Example 1.

[0052] (1) After mixing magnesium chloride and water evenly in a molar ratio of 1:13, add chitosan phosphate to obtain a magnesium chloride mixed solution. Among them, the dosage of chitosan phosphate is 1.0% of the mass of reactive magnesium oxide.

[0053] (2) Mix the magnesium chloride mixed solution with reactive magnesium oxide and water in a molar ratio of reactive magnesium oxide : magnesium chloride : water of 6.5:1:13, stir evenly to form a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain a temperature of 25°C and a humidity of 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 120 MPa, and the softening coefficient is 0.65.

[0054] Comparative Example 3

[0055] (1) After mixing magnesium chloride and water evenly in a molar ratio of 1:13, add unmodified nano-silica to obtain a magnesium chloride mixed solution. Among them, the dosage of unmodified nano-silica is 1.0% of the mass of reactive magnesium oxide.

[0056] (2) Mix the magnesium chloride mixed solution with reactive magnesium oxide and water in a molar ratio of reactive magnesium oxide, magnesium chloride, and water of 6.5:1:13, stir evenly to make a magnesium oxychloride cement paste, inject the magnesium oxychloride cement paste into a mold of 20mm×20mm×20mm, demold and cure after 1 day, maintain the temperature at 25°C and the humidity at 60% in the air for constant temperature and humidity curing for 28 days, the compressive strength is 123MPa, and the softening coefficient is 0.36.

Claims

1. A magnesium oxychloride cement doped with chitosan phosphate @ nano-silica, characterized in that: The preparation method of the magnesium oxychloride cement is as follows: (1) Mix anhydrous ethanol, phosphoric acid, and triethyl phosphate evenly by volume ratio, then add phosphorus pentoxide and chitosan. After full reaction, wash with anhydrous ethanol until neutral, dry to obtain chitosan phosphate, and dissolve chitosan phosphate in glacial acetic acid solution; (2) Uniformly disperse nano-silica in hydrogen peroxide solution, dry after full reaction to obtain surface-activated nano-silica, and then put it into the glacial acetic acid solution of chitosan phosphate. After full reaction, wash with deionized water and dry to obtain the nano-composite chitosan phosphate@nano-silica; The mass ratio of surface-activated nano-silica to chitosan phosphate is 1:0.2 - 0.6; (3) Mix magnesium chloride and water evenly by molar ratio, then add chitosan phosphate@nano-silica obtained in step (2), stir well and sonicate to obtain a magnesium chloride mixed solution. Mix the magnesium chloride mixed solution, reactive magnesium oxide, and water evenly by molar ratio and stir to form a magnesium oxychloride cement paste, and cure it at a constant temperature and humidity in the air.

2. The magnesium oxychloride cement doped with chitosan phosphate @ nano-silica as claimed in claim 1, wherein In step (1), the volume ratio of anhydrous ethanol, phosphoric acid, and triethyl phosphate is 4:1:1, and the mass-volume ratio of phosphorus pentoxide, chitosan, and phosphoric acid is 5g:6g:5ml.

3. The magnesium oxychloride cement doped with chitosan phosphate@nano-silica as claimed in claim 1, wherein In step (1), the concentration of the glacial acetic acid solution is 2%, and the concentration of the glacial acetic acid solution of chitosan phosphate is 0.4 - 1.2%.

4. The magnesia-chloride cement doped with chitosan phosphate@nano-silica as claimed in claim 1, wherein: In step (3), the dosage of chitosan phosphate@nano-silica is 0.5 - 1.5% of the mass of reactive magnesium oxide.

5. The magnesium oxychloride cement doped with chitosan phosphate@nano-silica as claimed in claim 1, characterized in that: In step (3), the source of reactive magnesium oxide is light-burned magnesite, and the content of reactive magnesium oxide is ≥63%.

6. The magnesium oxychloride cement doped with chitosan phosphate@nano-silica as claimed in claim 1, characterized in that: The molar ratio of reactive magnesium oxide, magnesium chloride, and water is 6.5:1:13.

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